Polyvinylpyrrolidone-Modified Construction Materials for Enhanced Durability and Environmental Resilience: A Critical Review

Abstract

Polymer modification is a well-established strategy for improving the performance and extending the service life of cementitious and other construction materials, with direct implications for environmental sustainability and infrastructure resilience. Among these polymers, polyvinylpyrrolidone (PVP), a non-ionic, water-soluble, and highly compatible polymer, has emerged as a uniquely versatile additive for mitigating degradation in aggressive environments. This review provides a critical and comprehensive synthesis of the state-of-the-art research on PVP’s roles in cement, mortar, concrete, and asphalt systems. The novelty of this work lies in its mechanistic integration and system-level interpretation, which consolidate fragmented knowledge across multiple domains—ranging from rheology and durability to nanotechnology and interfacial engineering—into a unified and coherent framework. Through cross-study comparison, this approach establishes a comprehensive understanding of PVP’s role in cementitious systems while outlining clear pathways for future research and practical implementation. This review provides the first integrated framework that connects PVP’s molecular structure, adsorption behavior, and ion-coordination mechanisms to its macroscopic influence on rheology, hydration, microstructure, and long-term durability. The review critically analyzes the underlying mechanisms, including physical pore-filling and crack-bridging, as well as chemical ion-coordination, which collectively govern PVP’s performance. Key quantitative findings are consolidated, showing that optimal PVP addition can reduce water absorption by over 35%, increase fracture toughness by ~47%, and, when used as an interfacial modifier, enhance the strain capacity of fiber-reinforced composites by over 100%. Reported benefits include improved workability, enhanced mechanical performance and toughness, superior durability under chemical and frost exposure, and the development of functional materials such as self-sensing concretes and photocatalytic coatings that support structural health monitoring and pollution mitigation. Overall, this review synthesizes current knowledge, consolidates experimental evidence in tabular form, and identifies future opportunities for leveraging PVP in the design of sustainable, low-impact, and environmentally resilient construction materials and infrastructures.

1. Introduction

Concrete is the backbone of modern civilization, shaping everything from residential buildings to massive transportation networks. As the most consumed manufactured material on the planet, its importance is unquestionable. Yet, despite its reputation for strength and durability, concrete suffers from several intrinsic weaknesses. Its low tensile strength, brittle nature, and porous microstructure make it vulnerable to chemical attack, freeze–thaw damage, and corrosion of embedded steel reinforcement [1,2]. These issues threaten the longevity and reliability of infrastructure worldwide, prompting ongoing efforts to develop more resilient cementitious materials.

One of the most effective strategies for addressing these limitations has been the incorporation of polymers into cement-based systems. Over the past several decades, polymer modification has evolved into a powerful tool for enhancing mechanical performance, improving durability, and tailoring material behavior. By introducing organic macromolecules into the cement matrix, researchers have achieved improvements in flexibility, adhesion, toughness, and resistance to water and chemical ingress [3,4]. These modifications are central to the development of high-performance and resilient infrastructure materials, a field that has seen continuous innovation over the past decades [5]. Among the many polymers investigated, polyvinylpyrrolidone (PVP) stands out for its exceptional versatility. Although widely used in fields such as medicine, biotechnology, and nanomaterials, PVP’s potential in cementitious systems has only recently begun to be fully appreciated. Its molecular structure, featuring a hydrophilic lactam ring with a polar carbonyl group and a hydrophobic vinyl backbone, enables it to interact with cement hydrates through a combination of hydrogen bonding, adsorption, and steric effects [1,6,7,8]. These interactions allow PVP to influence hydration kinetics, modify rheology, refine pore structure, and enhance interfacial bonding.

What makes PVP particularly compelling is its ability to contribute to emerging classes of advanced construction materials. In addition to improving traditional properties such as workability and durability, PVP has shown promise in enabling smart functionalities, including piezoresistive behavior for self-sensing concrete. Its compatibility with nanoparticles, carbon-based fillers, and bio-derived additives further expands its relevance in sustainable and multifunctional material systems. Despite these promising capabilities, research on PVP remains fragmented across multiple scientific domains. Studies focusing on rheology, hydration chemistry, mechanical performance, nanocomposites, and smart materials often operate independently, making it difficult to form a comprehensive understanding of PVP’s full impact.

In addition, recent advances in fracture mechanics and energy evolution analysis in geomaterials provide valuable methodological parallels for understanding crack initiation, propagation, and failure mechanisms in cementitious systems. Studies such as Wang et al. [9], which investigated the energy evolution and fractal characteristics of coal failure under dynamic loading, and Zhang et al. [10], which examined the evolution law of failure depth in large mining height working surfaces, highlight the importance of multiscale failure analysis and transport-driven degradation processes. Incorporating insights from these fields strengthens the motivation for reviewing PVP-modified materials, as similar mechanisms of crack evolution, energy dissipation, and structural degradation govern long-term durability in cement-based composites.

Despite the growing interest in polymer-modified cementitious systems, the role of PVP remains significantly underexplored compared with more established modifiers such as polycarboxylate ethers, styrene–butadiene latexes, and acrylic emulsions. Existing studies on PVP are scattered across unrelated research domains, including nanotechnology, biomedical materials, asphalt modification, and cement chemistry, resulting in a fragmented knowledge base with limited cross-comparison. This fragmentation has prevented the development of a unified mechanistic understanding of how PVP influences hydration, rheology, microstructure, and long-term durability. A consolidated review is therefore essential to integrate these isolated findings and clarify the multifunctional role of PVP across different material systems. Similar gaps have been noted in broader polymer-modified concrete research, where the lack of mechanistic synthesis has hindered the development of predictive frameworks for polymer–cement interactions [11].

Furthermore, the rapid evolution of advanced construction materials has created an urgent need to reassess polymer modifiers capable of enabling multifunctionality, sustainability, and enhanced durability. PVP is uniquely positioned within this landscape due to its amphiphilic structure, strong adsorption capacity, compatibility with nanomaterials, and ability to improve both mechanical performance and microstructural integrity at low dosages. Recent studies on multifunctional polymer–nanomaterial systems highlight the importance of modifiers that can simultaneously enhance dispersion, interfacial bonding, and durability [12]. However, no existing review provides a comprehensive synthesis of PVP’s mechanistic pathways, its cross-scale effects, or its potential contributions to next-generation cementitious composites. Expanding the introduction to highlight these gaps underscores the necessity of this review and situates it within the broader scientific effort to develop resilient, high-performance, and multifunctional construction materials.

This review aims to bridge that gap by synthesizing the diverse body of literature on PVP in cementitious materials. It examines the fundamental mechanisms governing PVP–cement interactions, evaluates its influence on fresh and hardened properties, and highlights its role in cutting-edge applications such as nanotechnology, fiber–matrix interface engineering and specialty cements. By integrating insights across scales, from molecular interactions to macrostructural performance, this review provides a holistic perspective on PVP’s current and future contributions to construction materials science.

Review Methodology

This critical review was prepared by conducting a systematic search of the scientific literature using major academic databases, including Scopus, Web of Science, and Google Scholar. The search strategy employed combinations of keywords such as “polyvinylpyrrolidone,” “PVP,” “polyvidone,” together with “cement,” “concrete,” “mortar,” “cementitious,” “durability,” “corrosion,” “nanomaterials,” and “asphalt”. The literature search covered the period 2005–2026, with particular emphasis on peer-reviewed articles published in the last two decades to ensure the inclusion of recent and relevant research. Studies were included if they reported clear experimental data on the effects of PVP on the physical, mechanical, or durability-related properties of cementitious or construction materials. Exclusion criteria comprised patents, conference abstracts lacking full datasets, and studies in which PVP was not a primary variable or focus. The selection process involved identification, screening, eligibility assessment, and final inclusion of relevant studies, which is summarized in a simplified PRISMA-style flow diagram (Figure 1). The selected literature was critically analyzed and synthesized according to underlying mechanisms and material properties, forming the structured narrative of this review. To ensure consistency between the conceptual schematics and the experimental evidence discussed in this review, all mechanistic illustrations were cross-checked against the referenced data. The pathways depicted, such as steric stabilization, ion coordination, film formation, and microstructural refinement, reflect trends repeatedly supported across multiple studies. No schematic element is presented without corresponding experimental justification.

2. PVP: A Profile of Its Key Properties

Before examining its influence on cementitious systems, it is essential to understand the fundamental characteristics of PVP. Also known as polyvidone, PVP is a synthetic, water-soluble polymer derived from the monomer N-vinylpyrrolidone. Its distinctive combination of chemical, physical, and rheological properties makes it an exceptionally versatile additive, distinguishing it from many other polymers used in material science. This versatility arises from its amphiphilic molecular structure, broad solubility profile, and strong affinity for both inorganic and organic surfaces.

2.1. Molecular Structure and Chemical Nature

The defining feature of PVP is its molecular architecture: a linear polyvinyl backbone bearing pendant pyrrolidone lactam rings. This structure imparts a pronounced amphiphilic character that governs its interactions with water, ions, and solid surfaces.

Hydrophilic component: The pyrrolidone ring contains a highly polar carbonyl group (C=O) and a nitrogen atom. The electron-rich carbonyl oxygen forms strong hydrogen bonds with water and other protic solvents, giving PVP its exceptional water solubility. Crucially, this carbonyl group also acts as a powerful coordination site for metallic cations such as Ca²⁺, Mg²⁺, and Al³⁺, which is the primary basis for its chemical interaction with cementitious systems [1,8]. This chelation ability can influence early hydration kinetics, ion mobility, and nucleation behavior.

Hydrophobic component: The polymer backbone consists of a nonpolar hydrocarbon chain (–CH₂–CH–), enabling PVP to associate with hydrophobic surfaces. This property is exploited when using PVP as a dispersant for nonpolar nanomaterials such as carbon nanotubes and graphene [7,13].

Additional chemical characteristics: PVP is non-ionic, meaning it carries no net electrical charge in solution. This is a major advantage in the high-ionic-strength environment of cement pore solutions, as it prevents undesirable electrostatic interactions that could lead to flocculation or precipitation. Furthermore, PVP is physiologically inert, non-toxic, and biocompatible, making it suitable for sensitive applications such as bone cements and ensuring it is an environmentally benign additive for general construction [6,14].

Commercial PVP is predominantly atactic, contributing to its amorphous nature and rapid solubility. The lactam ring can also participate in dipole–dipole interactions, enhancing adhesion to mineral surfaces such as C-S-H and Ca(OH)₂.

2.2. Physical and Solubility Characteristics

In its solid form, PVP is typically an amorphous, white to slightly yellowish, hygroscopic powder. Its typical physical appearance is shown in Figure 2. Its most commercially significant property is its exceptional solubility. Unlike many polymers that are soluble only in water or specific organic solvents, PVP dissolves readily in water and a wide range of polar organic solvents, including alcohols, amines, and certain chlorinated hydrocarbons. This versatility simplifies its incorporation into various material systems, whether water-based (e.g., concrete) or solvent-based (e.g., coatings and asphalt binders).

Molecular weight variability: The molecular weight of commercial PVP can be tailored over a very wide range, from a few thousand to over one million g/mol. This tunability allows precise control over its properties, particularly the viscosity of its solutions and its dominant function within the composite. The influence of PVP’s molecular weight on its performance in cementitious systems can be systematically summarized as follows:

• Low-molecular-weight PVP (e.g., <50,000 g/mol) primarily functions as a dispersant or secondary plasticizer. Its short polymer chains readily adsorb onto cement particle surfaces, providing steric stabilization that reduces interparticle friction and enhances fluidity (workability) without significantly increasing pore solution viscosity. However, because of their limited chain length, low-molecular-weight PVP is less capable of forming continuous polymer films or effective crack-bridging networks; consequently, its contribution to mechanical strength enhancement and long-term durability is relatively limited.
• High-molecular-weight PVP (e.g., 50,000 to 1,000,000 g/mol) functions as a balanced rheology modifier, thickener, and effective film-former. Its longer polymer chains moderately increase pore solution viscosity while still maintaining reasonable fluidity at appropriate dosages. These chains readily entangle and form continuous polymer networks within the pore structure, which are critical for pore filling and microstructural refinement, thereby enhancing durability. Simultaneously, this network enables effective crack bridging, leading to improved flexural strength and fracture toughness. As a result, this molecular weight range often provides an optimal balance between workability, mechanical performance, and long-term durability.
• Ultra-high-molecular-weight PVP (e.g., >1,000,000 g/mol) strongly increases pore solution viscosity due to extensive chain entanglement, which can significantly reduce fluidity and workability if not carefully controlled. However, it markedly enhances toughness, ductility, and crack resistance by forming highly entangled, continuous polymer networks that enable effective crack bridging and pore structure refinement, thereby reducing permeability and improving long-term durability. At excessive dosages, the pronounced viscosity increase may promote entrapped water and early-age porosity, potentially reducing compressive strength. In addition, the strong gel-forming capability of ultra-high-molecular-weight PVP contributes to shrinkage mitigation and internal curing by retaining water within the cementitious matrix.

Additional physical notes: PVP’s hygroscopic nature allows it to absorb significant moisture, which may influence drying behavior in cementitious systems. Its amorphous structure contributes to rapid dissolution and uniform film formation, while its ability to form hydration shells enhances colloidal stability and prevents particle agglomeration.

2.3. Solution Rheology and Film-Forming Ability

When dissolved in water, PVP acts as an effective viscosity modifier. The degree of thickening is directly related to polymer concentration and molecular weight. This rheological control is fundamental to its role as a workability-enhancing agent and set retarder in fresh cement paste [8,15].

Rheological behavior: PVP solutions typically exhibit Newtonian behavior at low concentrations but transition toward pseudoplastic (shear-thinning) behavior at higher concentrations. This shear-thinning effect improves pumpability and reduces energy requirements during mixing.

Film-forming properties: Upon evaporation of the solvent, PVP forms clear, transparent, and highly adhesive films. These films are hard and glossy yet retain elasticity, enabling them to bridge microcracks and fill pores within hardened cementitious matrices. This microcrack-bridging mechanism is a key contributor to the enhanced toughness and flexural strength observed in PVP-modified composites [1,16].

Additional functional notes: PVP films exhibit excellent optical clarity and high oxygen permeability, characteristics relevant to coatings and curing membranes. PVP also blends synergistically with polymers such as PVA, PEG, and acrylics, enabling tailored mechanical and rheological properties in hybrid cementitious systems.

2.4. Thermal Stability

PVP exhibits good thermal stability, making it suitable for applications involving moderate heat, such as the exothermic reaction of cement hydration or the hot-mixing process for asphalt. Thermogravimetric analysis (TGA) shows that adsorbed water is lost at around 100 °C, while significant thermal decomposition of the polymer backbone does not begin until well over 350–400 °C [8,13,17]. Differential scanning calorimetry (DSC) indicates a glass transition temperature (Tg) typically between 150 and 180 °C, depending on molecular weight and moisture content. This stability ensures that the polymer maintains its structural integrity and functional properties during the critical processing and curing stages of most building materials. At higher temperatures, PVP undergoes depolymerization and ring-opening reactions, forming a protective char layer that can provide limited thermal shielding in composite materials.

Table 1. Properties of PVP and their significance in construction applications.

Property	Description	Relevance to Construction and Building Materials
Molecular structure	Amphiphilic: Hydrophilic lactam ring and hydrophobic vinyl backbone. Non-ionic.	Interaction & Dispersion: Enables interaction with both inorganic (cement) and organic (asphalt, fibers) phases. Excellent as a dispersant for nanomaterials (carbon nanotubes, CNTs, graphene).
Solubility	High solubility in water and a wide range of polar organic solvents.	Ease of use: Can be easily and homogeneously incorporated into water-based systems like concrete and mortar mixes without special equipment.
Chemical reactivity	The carbonyl (C=O) group acts as a Lewis base, forming coordination complexes with metal ions (e.g., Ca2+, Al3+).	Bonding: Forms a strong chemical link between the polymer and the cement matrix, creating a robust organic–inorganic network that enhances strength.
Solution rheology	Acts as a viscosity modifier (thickener) in solution; viscosity is dependent on concentration and molecular weight.	Workability control: Functions as a plasticizer and set retarder, improving the flow of fresh concrete/mortar and extending the open time for placement.
Film-forming ability	Forms a continuous, adhesive, and flexible film upon solvent evaporation.	Microstructure & toughness: Fills and blocks capillary pores, reducing permeability and enhancing durability. Bridges microcracks, increasing flexural strength and fracture toughness.
Thermal stability	Stable up to high temperatures (decomposition > 350 °C).	Processing stability: Withstands the heat from cement hydration’s exothermic reaction and hot-mixing processes (e.g., asphalt) without degrading.
Biocompatibility & non-toxicity	Physiologically inert and environmentally safe.	Specialty applications: Essential for its use in biomedical materials like bone cements. Makes it a “green” and safe additive for general construction use.

summarizes the data reported in this section.

Table 2. Comparative performance of PVP vs. other polymer modifiers.

Property	PVP	PVA	PEG	Acrylics
Water solubility	Very high	Moderate	Very high	Low–moderate
Ion coordination	Strong (Ca2+, Al3+)	Weak	Moderate	None
Film-forming ability	Elastic, transparent	Brittle	Soft	Rigid
Rheology control	Strong shear-thinning	Newtonian	Shear-thinning	Variable
Crack bridging	Excellent	Moderate	Poor	Good
Environmental safety	High	Moderate	High	Variable

shows the comparative performance of PVP vs. other polymer modifiers.

3. Mechanism of PVP Interaction in Cementitious Systems

The remarkable influence of PVP on the behavior of cementitious materials arises not from a single dominant action but from a complex, multiscale, and synergistic interplay of chemical and physical mechanisms. These mechanisms operate simultaneously from the earliest stages of mixing through the long-term evolution of the hardened matrix. Collectively, they alter hydration kinetics, modify the development of the microstructure, and enhance the material’s mechanical performance and durability under environmental stresses.

3.1. Dominant Chemical Interaction: Ion Coordination and Network Formation

The primary chemical mechanism underlying PVP’s effectiveness is its strong ion–dipole coordination with metallic cations present in the cement pore solution. The pyrrolidone ring of the PVP monomer contains a highly polar, electron-rich carbonyl group (C=O), which acts as a potent Lewis base. This group readily forms stable coordination complexes with divalent (Ca²⁺) and trivalent (Al³⁺) cations released during the dissolution of cement phases such as tricalcium silicate (C₃S) and tricalcium aluminate (C₃A) [1]. This coordination mechanism produces several important consequences:

1. Adsorption onto hydrating surfaces: PVP macromolecules become chemically adsorbed onto the surfaces of unhydrated cement grains and, more critically, onto early hydration products such as C-S-H gel and Ca(OH)₂. Spectroscopic evidence confirms this interaction: Fourier-transform infrared (FTIR) analysis consistently shows a shift in the C=O absorption peak (e.g., from 1646 cm⁻¹ to 1652 cm⁻¹) when PVP is incorporated into cement, indicating a change in the chemical environment of the carbonyl group due to coordination [1,8].

2. Formation of an organic–inorganic hybrid network: This molecular-level adsorption results in the formation of a hybrid organic–inorganic network. The polymer chains act as flexible molecular bridges linking C-S-H particles, Ca(OH)₂ crystals, and other hydration products. X-ray diffraction (XRD) studies show subtle peak shifts and intensity changes in cementitious phases, demonstrating that PVP becomes partially integrated into the evolving microstructure rather than acting as an inert filler [1,8]. This hybrid network improves load transfer efficiency and enhances the cohesion of the matrix, contributing directly to mechanical strength development. Figure 3 shows a schematic representation of PVP molecular interactions in cementitious systems, showing coordination with Ca²⁺ and Al³⁺ ions, adsorption onto C-S-H and Ca(OH)₂ surfaces, and the formation of a hybrid organic–inorganic network.

3.2. Multifaceted Physical Mechanisms

In parallel with its chemical interactions, PVP exerts several important physical effects that influence both the rheology of fresh cement paste and the microstructure of the hardened material.

1. Steric hindrance and viscosity modification: In the fresh state, long PVP chains adsorb onto cement particle surfaces, creating a steric hindrance layer that prevents particle agglomeration and reduces interparticle friction. This steric stabilization produces a lubricating effect, improving workability and flow at optimal dosages [1,8]. Simultaneously, the adsorbed polymer layer slows the diffusion of water to cement grain surfaces, thereby retarding dissolution and hydration reactions. This mechanism explains the significant delay in setting times observed in PVP-modified systems [1,18].

2. Pore Refinement and matrix densification: As hydration progresses and free water is consumed, PVP becomes increasingly concentrated in the pore solution. Eventually, the polymer forms a continuous or semi-continuous hydrogel film that fills capillary pores. This pore-filling or pore-blocking mechanism leads to:

• Reduced total porosity;
• Refinement of pore size distribution;
• Decreased connectivity of capillary pores.

Scanning Electron Microscopy (SEM) images consistently show a denser, smoother, and more “glassy” microstructure in PVP-modified samples compared to plain cement [1]. This densification is a major contributor to improved durability, including reduced water absorption and enhanced resistance to chloride and sulfate ingress [1,2,19].

3. Film formation and crack bridging: In the hardened state, PVP forms a ductile polymer phase integrated within the cement matrix. When microcracks initiate under tensile or flexural loading, PVP chains or films spanning the crack can stretch and deform, acting as micro-reinforcing bridges. This crack-bridging mechanism:

• Absorbs fracture energy;
• Slows crack propagation;
• Increases the energy required for crack extension.

This is the primary reason for the observed improvements in flexural strength, fracture toughness, and overall ductility in PVP-modified composites [1,20].

It is important to note that the extent to which these mechanisms dominate is highly system-dependent. The strength of PVP–ion coordination, the degree of steric hindrance, and the continuity of the polymer film vary significantly with cement mineralogy, polymer chain length, and the ionic composition of the pore solution. Moreover, the literature shows inconsistencies in the relative contributions of chemical versus physical mechanisms, reflecting differences in experimental conditions, polymer purity, and measurement techniques. These uncertainties highlight the need for more standardized testing protocols when evaluating PVP–cement interactions.

3.3. Synergistic Effects

The chemical and physical mechanisms described above do not operate independently; rather, they exhibit strong synergistic interactions that amplify PVP’s overall impact.

• Chemical adsorption of PVP onto C-S-H surfaces anchors the polymer chains, enhancing the effectiveness of physical crack-bridging.
• Steric hindrance in the fresh state improves particle dispersion and packing, which complements the pore-filling effect during hardening.
• The hybrid organic–inorganic network formed through ion coordination provides a structural backbone that supports the densification and toughening mechanisms.

This synergy between molecular-level bonding and microstructural refinement is what makes PVP a uniquely powerful additive for producing high-performance cementitious materials. Figure 4 provides a conceptual overview of how these core mechanisms translate into the broad spectrum of performance enhancements discussed throughout this review.

Table 3. Overview of PVP’s chemical, physical, and synergistic mechanisms in cementitious systems.

Interaction Type	Mechanism	Scale of Action	Evidence	Primary Consequence	References
Chemical	Ion-dipole coordination between PVP’s C=O group and Ca2+/Al3+ ions.	Molecular	FTIR (peak shifts), TGA (altered thermal decomposition).	Formation of a hybrid organic-inorganic network improved cohesion.	[1,8]
Physical	Steric hindrance and lubrication by polymer chains around cement grains.	Micro (particle level)	Rheology measurements (increased flow), set time analysis (retardation).	Enhanced workability and prolonged open time.	[8,15,18]
Physical	Pore-filling and pore-blocking with a continuous polymer/hydrogel phase.	Microstructural (pore level)	SEM (denser matrix), MIP (reduced porosity), and water absorption tests.	Significantly improved durability (lower permeability, chemical resistance).	[1,16,19]
Physical	Crack-bridging by ductile polymer chains across microcracks.	Micro/Meso (crack level)	Mechanical testing (increased flexural strength and toughness).	Enhanced ductility, fracture toughness, and resistance to crack propagation.	[1,20]

summarizes the data reported in this section.

3.4. Factors Governing the Variability of PVP Performance Across Studies

Although many studies report that PVP enhances workability, strength, and durability, the magnitude and direction of these effects vary widely across the literature. This variability arises from several interacting parameters that govern polymer–cement behavior, and understanding these factors is essential for critically interpreting conflicting results.

(1) Influence of dosage: Low PVP dosages (0.1–0.4%) typically improve dispersion and early strength, whereas moderate dosages (0.4–0.8%) increase viscosity and retard hydration. At higher dosages (>1.0%), excessive polymer accumulation can reduce compressive strength or even accelerate setting due to localized ion depletion. These non-linear trends explain why some studies report strength gains while others observe reductions at elevated polymer contents [21].

(2) Molecular weight dependence: Higher-molecular-weight PVP tends to form more continuous films and stronger polymer networks within the cementitious matrix, which enhances toughness and durability but often reduces flowability due to increased solution viscosity and chain entanglement. In contrast, lower-molecular-weight PVP primarily acts as a dispersant, improving particle dispersion with only a modest effect on viscosity. As a result, systems using different PVP molecular weights often report different ‘optimal’ dosages and performance windows, even when the nominal polymer content (by mass) is similar [22,23].

(3) Cement type and mineralogy: Cements with higher C₃A content exhibit stronger interactions with PVP due to enhanced Al³⁺ coordination, resulting in greater retardation. Blended cements (slag, fly ash, LC3) show milder retardation and more pronounced pore refinement. These mineralogical differences contribute to inconsistent setting time and strength results across studies [23].

(4) Water-to-cement ratio and curing regime: Higher w/c ratios dilute polymer concentration in the pore solution, reducing steric hindrance and delaying film formation. Elevated curing temperatures increase polymer mobility and accelerate hydration, altering the balance between retardation and strength gain. Variations in these parameters across studies contribute to divergent findings [24,25,26,27,28].

(5) Interaction with other admixtures: PVP may compete with polycarboxylate superplasticizers for adsorption sites, reducing SP efficiency in some systems while enhancing dispersion in others. This competition explains contradictory reports on slump retention and rheology [23].

(6) Test conditions and measurement protocols: Differences in mixing energy, curing humidity, specimen geometry, and testing standards (ASTM vs. EN) also contribute to variability. Many discrepancies in the literature arise from methodological differences rather than intrinsic material behavior.

A critical evaluation of the available literature indicates that the ‘optimal dosage’ values reported across different studies are not directly transferable between systems. Instead, these dosages are highly system-specific and depend on multiple interacting parameters, including cement mineralogy (especially C₃A content), water-to-cement ratio, curing temperature, polymer molecular weight, and the presence of other admixtures such as PCE-based superplasticizers. Because PVP’s mechanisms, steric dispersion, ion coordination, film formation, and pore-structure modification, do not scale linearly with mass fraction alone, a dosage that enhances performance in one mixture may produce negligible or even adverse effects in another. Consequently, reported ‘optimal dosages’ should be interpreted as mixture-dependent benchmarks rather than universal recommendations. Future studies should normalize dosage relative to polymer chain length, binder chemistry, and mixture design to enable meaningful cross-study comparison and avoid misleading generalizations.

4. Effect of PVP on Fresh Properties

The incorporation of PVP into cementitious systems exerts a pronounced influence on their fresh-state properties, primarily through modifications to rheology and hydration kinetics before hardening. These changes play a decisive role in determining the ease of mixing, placement, pumping, and finishing, as well as the time window available for construction operations. Understanding the fresh-property response of cementitious materials to PVP addition is therefore essential for optimizing their use in practical applications.

4.1. Workability and Flowability

At low to moderate dosages, PVP functions as an effective workability-enhancing admixture, exhibiting behavior comparable to that of conventional plasticizers. The improvement in flowability is largely attributed to the adsorption of PVP macromolecules onto the surfaces of cement particles. Once adsorbed, the polymer chains extend into the pore solution, creating steric repulsion between adjacent particles. This steric stabilization reduces particle agglomeration and interparticle friction, thereby facilitating relative particle movement under applied stress or self-weight. As a result, cement pastes containing optimal amounts of PVP display enhanced flowability and improved deformability, which are critical attributes for advanced applications such as self-compacting concrete (SCC) and oil well cementing systems, where high fluidity and stability are required to ensure uniform placement without mechanical vibration [8,15]. Experimental findings by Tapdiqov et al. [8] demonstrated that the addition of 0.6% PVP significantly increased the slump of cement paste, indicating a substantial enhancement in workability. However, the effect of PVP on workability is strongly dependent on dosage. At higher concentrations, the intrinsic viscosity of the dissolved polymer becomes increasingly dominant. The thickening of the pore solution counteracts the lubricating and dispersing effects of particle adsorption, leading to an overall increase in yield stress and plastic viscosity. Consequently, excessive PVP addition may result in reduced flowability and a stiffer mix, underscoring the importance of identifying an optimal dosage range for specific cement compositions and applications [8].

However, the improvement in workability is not universal. Several studies report reduced flowability at higher PVP dosages or when high-molecular-weight grades are used, indicating that the rheological response is sensitive to polymer concentration, chain length, and the initial w/c ratio. These system-specific dependencies explain why some researchers observe strong plasticizing effects while others report viscosity increases or stiffening. This variability underscores the need to interpret PVP’s influence on fresh properties within the context of mixture design and polymer characteristics.

4.2. Setting Time and Early Hydration Behavior

The influence of PVP on cement setting time represents one of its most significant yet complex effects. In general, PVP functions as a set-retarding agent, primarily due to the adsorption of its long polymer chains onto the surfaces of hydrating cement particles. This adsorbed polymer layer acts as a physical diffusion barrier, limiting water access to reactive mineral phases and thereby delaying their dissolution as well as the nucleation and growth of early hydration products [1,8]. This behavior is clearly evidenced in the work of Singh and Singh [1], who reported a systematic and pronounced increase in both initial and final setting times with increasing PVP content, up to 5%, in ordinary Portland cement systems. However, a critical review of the literature reveals that this effect is not universally monotonic and depends strongly on the cement system. In a notable contradiction, Tapdiqov et al. [8], investigating G-class oil well cement, observed that while PVP additions up to approximately 0.8% produced the expected retardation, further increases in polymer concentration resulted in a reduction in setting time, with values gradually approaching those of the polymer-free reference mixture. This discrepancy highlights a crucial point: the retarding influence of PVP is not a simple, universal law but a balance between competing mechanisms. The physical barrier effect (retardation) from polymer adsorption dominates at low dosages. However, at higher dosages, a chemically induced acceleration (via intense ion-polymer interactions) may become significant, particularly in cement chemistries with different C₃A content or fineness, such as those found in oil-well cements. Recent studies, however, suggest that the effect of PVP on setting time is not strictly monotonic and depends strongly on dosage and cement composition. Tapdiqov et al. [8], investigating G-class oil well cement, observed that while PVP additions up to approximately 0.8% produced the expected retardation, further increases in polymer concentration resulted in a reduction in setting time, with values gradually approaching those of the polymer-free reference mixture. This behavior was attributed to the emergence of a secondary acceleration mechanism at higher PVP concentrations. The authors proposed that a high density of polymer chains promotes extensive ion–polymer interactions, particularly with Ca²⁺ ions, which may locally alter ionic concentrations and facilitate the precipitation of certain hydration products, thereby offsetting the initial physical retardation effect. These findings highlight that the retarding influence of PVP cannot be assumed to scale linearly with dosage across all cement systems. Variations in cement mineralogy, fineness, and chemical environment, as well as interactions with other admixtures such as superplasticizers, can shift the balance between physical retardation and chemically induced acceleration. From a practical standpoint, this underscores the importance of identifying an optimal PVP dosage tailored to the specific cement system and performance requirements. Figure 5 shows a dosage–response curve showing the non-linear effects of PVP on slump and setting time in cementitious systems. Optimal performance is observed between 0.6 and 0.8% dosage, where workability peaks and retardation is most effective.

A schematic interpretation of the competing mechanisms governing PVP-induced setting behavior can be summarized as follows:

• Low PVP dosage: Polymer adsorption dominates, leading to steric stabilization, reduced interparticle friction, and the formation of a diffusion barrier around cement grains. Hydration kinetics are slowed, resulting in extended setting times.
• Intermediate PVP dosage: Retardation reaches a maximum as surface coverage increases and hydration inhibition becomes most effective.
• High PVP dosage: Polymer–ion interactions become increasingly significant. The high density of PVP chains promotes complexation with Ca²⁺ ions, locally modifying ionic concentrations and supersaturation conditions. This may facilitate the precipitation of certain hydration products, partially accelerating setting and offsetting the physical barrier effect.

The relative dominance of these mechanisms is highly sensitive to cement mineralogy, fineness, sulfate balance, and the presence of other chemical admixtures such as superplasticizers. Oil well cements, for example, may exhibit different ion availability and hydration pathways compared to ordinary Portland cement, leading to distinct PVP dosage–response relationships. From a practical perspective, these findings underscore that PVP-induced retardation cannot be assumed to increase linearly with dosage across all systems. Instead, an optimal PVP concentration exists for each cementitious formulation, at which the desired extension of setting time is achieved without triggering counterproductive acceleration or loss of early-age performance. Careful experimental calibration is therefore essential when incorporating PVP into cement-based materials for field applications.

Table 4. VP Dosage vs. fresh property metrics.

PVP Dosage (%)	Slump (mm)	Initial Setting Time (min)	Final Setting Time (min)	Flow Spread (%)	References
0.00	120	90	180	65	[1,8]
0.40	190	110	200	80	[1,8]
0.65	300	130	220	95	[8]
1.00	210	120	210	75	[1,8]

summarizes the effect of different concentrations of PVP on the fresh properties of the mixtures.

Table 5. Effect of PVP on the fresh properties of the mixtures.

Property	Effect of PVP Addition	Underlying Mechanism	References
Workability	Increased flowability at optimal dosages (typically <1%).	Lubricating effect and steric hindrance of adsorbed polymer chains.	[8,15]
Setting time	Generally, a retarder. It can show non-monotonic behavior (retardation peaks at an optimal dose) in specific systems.	Retardation: Adsorption of PVP on cement grains, creating a hydration barrier. Acceleration (at high doses): Potential acceleration via intense ion interaction and complexation.	[1,8]

summarizes the information reported in this section.

The contradictory trends reported in the literature—ranging from strong retardation to mild acceleration at high dosages—reflect the complex interplay between polymer adsorption, ion sequestration, and hydration kinetics. These inconsistencies indicate that PVP’s effect on setting time cannot be generalized and is strongly influenced by cement composition, polymer dosage, and curing temperature. As such, the setting time response should be considered system-specific rather than universally predictable.

4.3. Interaction with Other Admixtures and Practical Considerations

In practical concrete mix design, PVP would be used as part of a complex admixture system. Its interaction with other chemicals, particularly superplasticizers and air-entraining agents, is a critical consideration:

• Interaction with superplasticizers: Both PVP and polycarboxylate-based superplasticizers (PCEs) function via adsorption onto cement grains. This can lead to competitive adsorption, where one admixture may reduce the effectiveness of the other. Some studies suggest that the presence of a polymer like PVP may require an adjustment in the superplasticizer dosage to achieve the target workability. This interaction is complex and depends on the molecular architecture of both polymers.
• Impact on air entrainment: As a surfactant-like polymer, PVP can influence air content in the mix. While it is not a dedicated air-entraining agent, it can stabilize air bubbles, potentially increasing the air content. This could be beneficial for frost resistance but may require adjustments to the dosage of a primary air-entraining agent to avoid excessive air content, which would reduce compressive strength.
• Bleeding: By increasing the viscosity of the mix water, high-molecular-weight PVP can be highly effective at reducing bleeding and improving the overall stability of the fresh paste, which is particularly beneficial in SCC and grouting applications.

5. Effect of PVP on Hardened Microstructure

The incorporation of PVP into cementitious systems exerts a profound influence on the hardened microstructure, fundamentally altering the internal architecture of the composite. Rather than behaving as a simple additive, PVP participates in the formation of a hybrid organic–inorganic network whose micro- and nano-scale configuration governs the resulting mechanical, transport, and durability properties. The influence of PVP can be categorized into three dominant mechanisms: (1) pore structure refinement and matrix densification, (2) modification of hydration product morphology and polymer phase distribution, and (3) micro-level reinforcement and interfacial enhancement. Optional extended mechanisms, such as shrinkage mitigation and internal curing, may also be considered depending on the PVP dosage and molecular weight.

Table 6. Microstructural effects of PVP.

Mechanism	Observed Effect	Evidence	Performance Impact
Pore filling	Reduced porosity	MIP, SEM	Lower permeability
Crack bridging	Increased ductility	Flexural tests, SEM	Higher toughness
Ion coordination	Hybrid network formation	FTIR, XRD	Enhanced cohesion

summarizes the microstructure effects of PVP.

5.1. Primary Effect: Pore Structure Refinement and Matrix Densification

The most consistently reported microstructural transformation induced by PVP is the pronounced densification of the cement matrix, manifested by a reduction in total porosity and a refinement of the pore size distribution. This refinement is primarily attributed to a combined pore-filling and hydrogel formation mechanism. As cement hydration progresses and free water is consumed, PVP macromolecules, excluded from incorporation into the C-S-H crystal lattice due to their molecular size, become increasingly concentrated within the capillary pore network. Ultimately, these macromolecules form a continuous polymer film or interconnected hydrogel that physically occupies pore space that would otherwise remain void [1,16]. Direct evidence for this matrix densification is provided by complementary qualitative and quantitative analyses. SEM images consistently reveal a stark contrast between unmodified and PVP-modified cement pastes. The PVP-modified matrix exhibits a more compact, homogeneous, and glass-like morphology, in which large capillary voids characteristic of plain cement paste were replaced by a smoother and denser microstructure, confirming the polymer’s pore-filling action [1]. These microstructural observations are corroborated by transport property measurements. Water absorption tests conducted by Singh and Singh [1] demonstrated a reduction from 9.93% in plain mortar to 6.32% at an optimal PVP content of 3%, corresponding to a decrease exceeding 35%. This substantial reduction reflects a finer, less interconnected pore network and a pronounced suppression of capillary suction pathways, thereby significantly restricting fluid ingress.

A critical and often underemphasized aspect of this densification is the mitigation of interfacial transition zone (ITZ) weakness. The ITZ, which surrounds aggregate particles, is inherently more porous and mechanically inferior to the bulk cement paste. By improving the flowability of the fresh mix and reducing bleeding, PVP promotes more efficient packing of cement particles at the aggregate surface. Moreover, partial penetration of the polymer into the ITZ facilitates pore filling and enhances aggregate–paste adhesion, resulting in a strengthened interface and a more monolithic composite structure [15]. Collectively, the densification of the bulk matrix and the strengthening of the ITZ provide the fundamental physical basis for the enhanced durability performance of PVP-modified cementitious composites. By forming an effective barrier against the ingress of aggressive agents such as chlorides, sulfates, CO₂, and freeze–thaw water, pore structure refinement emerges as the primary mechanism underpinning improved resistance to corrosion, chemical attack, and environmental degradation.

This structural improvement at the ITZ is visually confirmed by SEM observations. In the plain water system, a distinct gap and a highly porous, weak ITZ are evident between the spherical particle and the surrounding hydrates, representing a typical failure point in composite cementitious materials [14]. In contrast, the incorporation of PVP fundamentally alters this interface. The gap disappears entirely, and the PVP-modified cement paste bonds tightly to the fly ash surface, forming a dense, continuous, and robust interfacial layer. The polymer functions as a molecular “glue,” significantly improving cohesion between the phases [14].

Despite the generally positive influence of PVP on flexural strength and toughness, the magnitude of improvement varies widely across studies. This variability is linked to differences in polymer molecular weight, film-forming ability, curing regime, and the degree of polymer dispersion within the matrix. In some cases, excessive polymer content may even reduce compressive strength due to increased entrapped water or delayed hydration. These limitations highlight the need for optimized dosage selection tailored to specific binder systems.

5.2. Influence on Hydration Products and Polymer Phase Distribution

Although PVP does not alter the fundamental chemical identity of cement hydration products, C-S-H, Ca(OH)₂, and ettringite remain the dominant phases; it exerts a pronounced influence on their morphology, crystallinity, and spatial organization within the hardened matrix. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses consistently reveal the characteristic signatures of these hydrates, accompanied by subtle peak shifts and changes in relative peak intensities. These features indicate physical integration and chemical interaction between the polymer and inorganic phases, rather than phase substitution or inhibition of cement hydration [1,8]. XRD analysis provides particularly compelling evidence of this interaction across both Portland cement and specialty cement systems. In Portland cement pastes modified with PVP, the principal diffraction peaks associated with C-S-H and hydrated lime are retained after prolonged hydration, yet their relative intensities are measurably altered. Singh and Singh [1] reported a marked reduction in the intensity of the portlandite peak in the presence of PVP, suggesting either suppressed Ca(OH)₂ crystallization or its partial consumption in secondary reactions facilitated by the polymer network. In addition, new, albeit minor, diffraction peaks, absent in the control sample, are detected in PVP-modified systems, providing evidence that PVP is not an inert filler but actively participates in, or modifies, the hydration process, potentially through the formation of low-concentration complex phases (e.g., calcium–polymer coordination structures) or through lattice distortion of existing hydrates.

Comparable behavior is observed in specialty calcium phosphate cement systems. Comparative XRD patterns of calcium phosphate cement with and without PVP exhibit remarkable consistency in the positions of the major diffraction peaks corresponding to β-tricalcium phosphate and calcium sulfate dihydrate [6]. The preservation of peak positions confirms that PVP does not induce the formation of new dominant crystalline phases nor disrupt the intrinsic crystal structures of the primary hydration products. Instead, variations in peak intensity and background features indicate that PVP integrates into the matrix in a manner that preserves the fundamental chemistry while modifying the microstructural arrangement. Taken together, these crystallographic observations indicate that PVP primarily resides within and interacts with the amorphous or poorly crystalline binding phase of the matrix, namely the C-S-H gel or its functional equivalent in calcium phosphate systems, rather than within well-defined crystalline domains. In this role, PVP modifies the “glue” of the microstructure rather than the “bricks,” influencing how hydration products are connected and packed without altering their chemical identity. Consequently, the polymer phase does not exist as discrete or isolated inclusions but forms an interpenetrating and co-continuous organic–inorganic network throughout the matrix, confirming the formation of a true composite material with a distinct crystallographic character. This integrated polymer network also affects hydration kinetics and long-term hydration degree. Studies employing PVP as a carrier for TEOS-derived nanofibers have reported increased chemically bound water content measured by thermogravimetric analysis (TGA), indicating that the hydrophilic polymer network retains moisture in the vicinity of unhydrated cement particles. Such localized water retention promotes more complete long-term hydration and contributes to the densification, improved cohesion, and refinement of the hardened cement microstructure [4].

5.3. Micro-Level Reinforcement and Interfacial Modification

Beyond its role as a pore-filling agent, PVP contributes to micro-scale reinforcement through its ductile and energy-dissipating behavior. This effect is particularly evident in improved toughness and flexural performance. Crack-bridging mechanisms dominate this reinforcement. When microcracks initiate within the brittle cement matrix, polymer chains and films spanning the crack path undergo elastic and plastic deformation. This deformation absorbs fracture energy and applies closing stresses across crack faces, effectively slowing or arresting crack propagation and increasing the energy required for failure [1,20]. The nanofibrous structures reported by Nguyen et al. [4], in which PVP serves as the carrier matrix, provide a compelling nanoscale visualization of this mechanism. The images clearly demonstrate the crack-bridging mechanism at the micro-level. The flexible, high-surface-area nanofibers are shown spanning across voids and cracks within the cement matrix, effectively “stitching” the inorganic phases together. This micro-reinforcement is a primary reason for the observed increases in fracture toughness and flexural strength in PVP-modified composites. PVP also serves as a powerful interfacial modifier due to its amphiphilic character and chemical functionality. When applied as a coating to hydrophobic synthetic fibers such as polyethylene, PVP transforms their surfaces from inert to hydrophilic, significantly enhancing fiber–matrix adhesion [20]. Similarly, when used as a dispersant for nanomaterials such as carbon nanotubes, PVP prevents agglomeration while acting as a compatibilizing interlayer that improves bonding with the surrounding C-S-H gel [7]. By eliminating weak interfaces and microstructural defects, PVP promotes a more continuous and mechanically robust composite.

Table 7. Overview of the effects of PVP on the hardened cementitious microstructure, including pore refinement, hydration product modification, and micro-level reinforcement.

Microstructural Feature	Effect of PVP Addition	Underlying Mechanism	Evidence/Measurement
Porosity & pore size	Significantly reduced total porosity; refined pore size distribution; denser ITZ.	Physical filling of pores and ITZ by the interspersed polymer phase; improved particle packing.	Water absorption tests, MIP analysis, and SEM.
Matrix morphology	Denser, more homogeneous, “glassier” appearance.	Interspersion of the polymer network throughout the C-S-H gel matrix.	SEM imaging.
Hydration products	No fundamental change in phase composition, but morphology is altered. May promote a higher degree of long-term hydration.	Polymer is integrated with, not a replacement for, C-S-H and CH. Retains water for continued hydration.	XRD, FTIR, TGA.
Reinforcement mechanism	Acts as a ductile reinforcement at the micro- and nano-scale, dissipating energy.	Crack-bridging by polymer chains/films; viscoelastic deformation of the polymer network.	Mechanical testing (flexural, fracture toughness, fatigue).
Interfacial modification	Acts as a compatibilizer/coupling agent for fibers and nanomaterials.	Improves the bond strength at the interface between the reinforcing phase and the cement matrix.	Single-fiber pull-out tests, SEM of fracture surfaces.

summarizes the data reported in this section.

6. Effect of PVP on Hardened Mechanical Properties

The microstructural densification and formation of a hybrid organic–inorganic network, as discussed previously, translate directly into substantial and measurable improvements in the hardened mechanical performance of PVP-modified cementitious materials. Importantly, the influence of PVP is not uniform across all mechanical properties. Its most pronounced effects are observed in properties governed by crack initiation and propagation, such as flexural strength, fracture toughness, and ductility, where it fundamentally alters the failure mechanism from a purely brittle, quasi-ceramic response to a more damage-tolerant, composite-like behavior. From a materials engineering perspective, PVP performs multiple synergistic roles within the cementitious matrix: (i) it acts as a pore-filling densification agent, (ii) it provides a flexible crack-bridging phase capable of dissipating fracture energy, and (iii) it functions as an interfacial modifier at hydration product boundaries and reinforcement surfaces. The relative contribution of each role depends strongly on polymer dosage, molecular weight, curing conditions, and the presence of additional reinforcements such as fibers or nanofillers. This dose-dependent behavior creates a critical design trade-off, which is conceptually illustrated in Figure 6. While durability-related properties linked to matrix densification often improve with increasing PVP content, mechanical properties governed by matrix rigidity, such as compressive strength, typically reach an optimal peak before declining at higher dosages. This occurs because an excessive volume of the softer polymer phase begins to compromise the overall stiffness of the composite. Understanding this trade-off is essential for optimizing PVP-modified systems for specific performance targets.

6.1. Compressive Strength: The Role of Densification

Compressive strength, the primary mechanical performance indicator for most structural concrete applications, is moderately but consistently enhanced by the incorporation of PVP when used within an optimal dosage range. This improvement is not due to intrinsic strengthening of the cement hydration products, but rather to polymer-induced microstructural densification. In conventional cementitious matrices, entrapped air voids and large capillary pores act as stress concentrators under compressive loading, serving as preferential sites for microcrack initiation and failure. By partially filling these voids and refining the pore size distribution, the interspersed PVP phase produces a denser, more homogeneous, and continuous load-bearing matrix. Consequently, compressive stresses are more uniformly distributed, increasing the load required to initiate catastrophic failure. However, the influence of PVP on compressive strength is strongly dose-dependent and distinctly non-monotonic, reflecting a critical design trade-off between beneficial pore refinement and the introduction of a mechanically weaker phase. Improvement phase (low dosages): At low to moderate PVP contents, the densification mechanism dominates, and a clear enhancement in compressive strength is consistently reported. Gürten et al. [2,3] observed that compressive strength increased with PVP addition, reaching a peak at approximately 1–3% by cement weight, with strength gains of up to 24% and 44% in different experimental programs. Similarly, Singh and Singh [1] reported a monotonic increase in compressive strength up to an optimal PVP content of about 3%, at which the strength exceeded that of the control mixture by approximately 8%. In addition to pore filling, these improvements were attributed to enhanced workability and reduced bleeding, which promoted better compaction and greater microstructural uniformity. Regression phase (high dosages): Beyond the optimal PVP content, typically in the range of 2–4% by cement weight, further increases in polymer dosage lead to a reduction in compressive strength [1,2,3]. Specimens with higher PVP contents (e.g., 5%) exhibit lower strength than those at the optimal dosage [2]. This regression occurs because PVP possesses significantly lower stiffness and compressive strength than the C-S-H gel. At elevated dosages, the polymer occupies a larger volume fraction of the matrix and may form continuous or semi-continuous compliant domains that deform preferentially under compressive loading. These regions act as mechanical weak points, promoting premature failure. Overall, while PVP can effectively enhance compressive strength through microstructural densification and stress redistribution, excessive polymer content compromises matrix rigidity. This behavior underscores the necessity of carefully optimizing the polymer-to-cement ratio to maximize strength gains while avoiding the detrimental effects of introducing an overly compliant polymer phase. It is critical to note that the reported magnitude of strength gain and the precise optimal dosage show considerable variation across the literature, ranging from a modest 8% [1] to a substantial 44% [3]. These inconsistencies are not contradictory but rather highlight the high sensitivity of PVP’s performance to specific system parameters. Factors such as the water-to-cement (w/c) ratio, cement fineness, and curing regime influence the initial porosity and hydration kinetics, thereby altering the effectiveness of PVP’s pore-filling mechanism. For instance, in lower w/c ratio mixtures where the initial pore network is already less connected, the beneficial densification effect of PVP may be less pronounced, while the negative impact of introducing a mechanically weaker polymer phase may emerge at lower dosages.

6.2. Flexural Strength: The Dominance of Crack-Bridging

In contrast to compressive strength, PVP exerts a far more pronounced and beneficial influence on flexural and tensile-related properties. Failure under these loading modes is governed primarily by the initiation and, more critically, the propagation of microcracks rather than bulk matrix crushing. Under such conditions, the role of PVP as a micro-reinforcing and energy-dissipating phase becomes dominant. The primary strengthening mechanism is crack-bridging. As microcracks initiate and attempt to propagate, ductile PVP chains and polymer films spanning across the crack faces are mobilized. These chains undergo stretching and viscoelastic deformation, absorbing a substantial portion of the fracture energy that would otherwise be concentrated at the crack tip. This process generates a closing traction across the crack faces, effectively retarding crack opening and requiring a higher applied load for further propagation. As a result, the relative increase in flexural strength is typically much greater than that observed in compression. For example, Singh and Singh [1] reported that at the same optimal PVP dosage of 3%, flexural strength increased from 8.67 MPa to 11.31 MPa, corresponding to an improvement of approximately 30%. This disproportionate enhancement demonstrates that PVP is particularly effective in mitigating tensile stress concentrations, shifting the mechanical response from abrupt brittle fracture toward a more gradual, damage-tolerant composite behavior. From a structural materials standpoint, this response aligns PVP-modified cementitious materials more closely with fiber-reinforced or polymer-impregnated composites, where toughness enhancement rather than strength alone governs performance [1].

6.3. Fracture Toughness and Ductility Enhancement

The crack-bridging and energy-dissipation mechanisms introduced by PVP incorporation directly lead to substantial improvements in fracture toughness $\left(K_{IC}\right)$ and overall ductility. Fracture toughness is a fundamental measure of a material’s resistance to unstable crack propagation, and its enhancement reflects greater damage tolerance and durability. These benefits arise from the viscoelastic deformation and stretching of PVP chains, which dissipate strain energy at the crack tip and make crack growth significantly more difficult. This toughening mechanism fundamentally alters the failure mode, producing a more gradual post-peak load–load–displacement response and reducing the likelihood of catastrophic fracture. The effect of PVP on fracture toughness is both significant and highly dose-dependent. A rise in $K_{IC}$ up to the optimal PVP content before declining at higher dosages. Quantitative results from [1] confirm this trend: fracture toughness increases from 1.03 MPa·m^1/2 in plain cement paste to a peak of 1.51 MPa·m^1/2 at 3% PVP, a remarkable 47% improvement. Beyond this optimum, excessive polymer content (e.g., 5%) weakens the matrix and reduces toughness. The enhanced toughness at the optimal dosage corresponds to a more ductile failure mode, allowing the material to undergo greater deformation before complete fracture. This toughening effect is further amplified in advanced composite systems. Nguyen et al. [4] demonstrated that incorporating TEOS/PVP nanofibers into cement paste produced a 66% increase in toughness due to nanoscale crack-bridging and enhanced energy dissipation, highlighting PVP’s ability to act as a carrier for additional reinforcing agents. Similarly, Men et al. [20] used PVP as a surface modifier for polyethylene (PE) fibers in engineered cementitious composites (ECC). The PVP coating improved fiber–matrix interfacial bonding, enabling more efficient stress transfer and sustained fiber bridging during crack opening. As a result, tensile strain capacity increased by 109%, and the failure mode transitioned to stable multiple cracking, a defining characteristic of highly ductile cementitious composites. Collectively, these findings show that PVP functions not only as a bulk matrix modifier but also as a powerful interfacial engineering agent capable of synergistically enhancing the performance of secondary reinforcements and unlocking significantly higher levels of toughness and ductility across diverse cementitious systems.

6.4. Hardness

The surface hardness of PVP-modified cementitious materials, typically evaluated using indentation techniques such as Vickers hardness testing, also exhibits a measurable improvement. Surface hardness is closely linked to near-surface porosity and microstructural integrity. The observed increase in hardness is a direct consequence of polymer-induced densification. A denser surface layer with reduced capillary porosity offers greater resistance to localized plastic deformation and microcracking under an indenter. Experimental results show that Vickers hardness reaches its maximum at approximately the same optimal PVP dosage (around 3%) as compressive strength [1]. At higher polymer contents, hardness tends to plateau or decline slightly, mirroring compressive strength trends and further confirming the existence of an optimal PVP content for balanced mechanical performance.

Table 8. Overview of the effects of PVP on hardened mechanical properties of cementitious materials.

Property	Effect of PVP Addition (at Optimal Dosages)	Underlying Mechanism & In-Depth Discussion	References
Compressive strength	Moderate increase (up to 44%). Non-monotonic, with an optimum around 3% PVP.	Primary: Microstructural densification and pore-filling, which reduces stress-concentrating voids. Limiting Factor: At high doses, the softer polymer phase becomes a weak link under compression.	[1,2,3]
Flexural & tensile strength	Significant increase (e.g., ~30%). More pronounced than compressive strength gains.	Primary: Crack-bridging by ductile polymer chains, which absorbs fracture energy and “stitches” microcracks. This directly counters the primary failure mode in flexure.	[1,20]
Fracture toughness & ductility	Substantial increase (e.g., ~47% in toughness; >100% in tensile strain in ECC).	Primary: Energy dissipation at the crack tip via polymer chain stretching and viscoelastic deformation. Synergistic: Acts as an interfacial coupling agent, improving fiber-matrix bond and unlocking ductility in composites.	[1,4,20]
Hardness	Increased, correlating with compressive strength trends.	Primary: Increased surface density due to the pore-filling effect, providing greater resistance to indentation.	[1]

summarizes the data reported in this section.

Table 9. PVP-induced durability mechanisms and supporting evidence.

Durability Mechanism	Observed Effect	Analytical/Experimental Evidence	Performance Impact	References
Transport property reduction	Lower sorptivity, reduced water absorption	Sorptivity tests, water uptake curves	Improved resistance to ingress	[1,2,3]
Chemical stability enhancement	Reduced leaching, stabilized hydrates	XRD, TGA, and ion leaching tests	Improved long-term chemical durability	[1]
Crack-related durability improvement	Reduced microcracking, enhanced toughness	Flexural tests, SEM crack morphology	Better resistance to crack propagation	[1,4,20]

summarizes the durability enhancement mechanisms of PVP in cementitious systems with corresponding experimental evidence.

To consolidate the findings discussed in the preceding sections,

Table 10. Overview of PVP’s Impact on Key Performance Indicators (KPIs) of Cementitious Materials.

Category	Performance Indicator	Optimal Dosage (wt%)	Direction of Change	Magnitude of Effect	Primary Controlling Factors & Mechanisms	References
Fresh properties	Workability/flowability	0.5–1.0%	↑ (Increase)	High	Mechanism: Steric hindrance and lubrication. Factors: PVP Molecular Weight, w/c ratio, cement fineness.	[8,15]
	Setting time	1.0–4.0%	↑ (Increase/Retardation)	High	Mechanism: Adsorption barrier on cement grains. Can be non-monotonic in some systems. Factors: Dosage, cement type (e.g., oil-well vs. OPC).	[1,8]
Mechanical properties	Compressive strength	1.0–4.0%	↑ (Increase, non-monotonic)	Moderate (~5–44% increase)	Mechanism: Pore-filling/densification vs. introduction of a weaker phase. Factors: Dosage is critical.	[1,2,3]
	Flexural strength	2.0–4.0%	↑↑ (Significant Increase)	High (~30% increase)	Mechanism: Crack-bridging by ductile polymer films. Factors: PVP Molecular Weight (longer chains are better).	[1,20]
	Fracture toughness/ductility	2.0–4.0%	↑↑ (Significant Increase)	Very high (~47% in paste; >100% in ECC)	Mechanism: Energy dissipation at the crack tip. Synergistic with fibers. Factors: Interfacial bond modification.	[1,4,20]
Durability properties	Permeability/water absorption	>2.0%	↓↓ (Significant Decrease)	Very high (>35% reduction)	Mechanism: Pore-filling and blocking of the capillary network. Factors: Dosage, curing conditions.	[1,2]
	Chloride & sulfate resistance	>2.0%	↑↑ (Significant Improvement)	High	Mechanism: Reduced permeability (transport inhibition). Factors: Matrix density is key.	[1,2,3]
	Freeze–thaw resistance	>2.0%	↑↑ (Significant Improvement)	High	Mechanism: Reduced water absorption and refined pore structure. Factors: Overall porosity.	[15]

provides a semi-quantitative “effect map” summarizing the impact of PVP on the key performance indicators (KPIs) of cementitious materials when used within typical dosage ranges. This table synthesizes the direction and approximate magnitude of the changes, highlighting the controlling factors and primary mechanisms for each property.

The performance trends observed in PVP-modified systems align with broader findings reported for other polymer-modified and nanomodified cementitious composites. For example, studies incorporating nano-graphite platelets have shown that nanoscale additives can significantly refine pore structure and enhance mechanical performance through crack-bridging and matrix densification mechanisms, which parallels the microstructural refinement observed in PVP-modified systems [29]. Similarly, research on macro-synthetic fiber (MSF) reinforcement in conventional and e-waste aggregate concretes demonstrates that polymer-based additives can improve toughness, post-cracking behavior, and durability by enhancing fiber–matrix interactions [30]. These comparisons highlight that PVP’s multifunctional role, combining dispersion, interfacial modification, and microstructural densification, is consistent with the mechanisms reported in other advanced composite systems. However, unlike nanomaterials or MSF, PVP achieves these improvements at significantly lower dosages and without introducing additional solid phases, underscoring its efficiency as a molecular-scale modifier. This contextualization situates PVP within the broader landscape of composite enhancement strategies and reinforces the relevance of its mechanistic contributions.

7. Effect of PVP on Durability

The long-term performance and service life of cement-based materials are governed primarily by their durability, that is, their ability to withstand physical, chemical, and environmental degradation over time. The incorporation of PVP has been shown to exert a broad and predominantly positive influence on nearly all key durability indicators of cementitious systems. This improvement stems from PVP’s ability to directly address one of the fundamental weaknesses of conventional cement-based materials: their inherently porous and interconnected microstructure. By refining pore size distribution, blocking capillary pathways, and forming a hybrid organic–inorganic network within the cement matrix, PVP substantially reduces permeability and transport kinetics. As a result, PVP-modified cementitious materials exhibit enhanced resistance to aggressive agents, delayed degradation processes, and improved retention of mechanical integrity under severe environmental exposure. In effect, PVP acts as a first-line, microstructure-level defense mechanism against the most common deterioration pathways. From a durability design standpoint, PVP primarily extends the initiation phase of degradation (e.g., chloride ingress, sulfate attack, freeze–thaw damage), thereby increasing the predicted service life of concrete structures without requiring significant changes to mix design or construction practice.

7.1. Resistance to Chemical Attack and Ion Ingress

Most chemical degradation mechanisms in concrete are controlled by the ingress of aggressive aqueous species into the pore network, where they interact with cement hydration products. The durability enhancement imparted by PVP arises from a dual protective mechanism: (i) physical restriction of ion transport and (ii) chemical shielding of reactive phases.

7.1.1. Physical Barrier and Transport Inhibition

The primary durability benefit of PVP originates from its ability to refine and partially block capillary pores, resulting in a more tortuous and less interconnected transport network. This significantly reduces permeability and slows the diffusion of aggressive ions such as chlorides (Cl⁻), sulfates (SO₄²⁻), and hydrogen ions (H⁺).

• Chloride resistance: Chloride ingress is the dominant cause of steel reinforcement corrosion in reinforced concrete. Gürten et al. [2] demonstrated via electrochemical measurements that PVP-modified concrete exhibited markedly improved resistance to chloride-induced corrosion. The reduced permeability delayed chloride arrival at the steel surface, effectively prolonging the corrosion initiation period.
• Sulfate and acid resistance: Sulfate ions react with calcium aluminate phases to form expansive products such as ettringite, inducing internal stresses and cracking, while acidic solutions directly dissolve alkaline hydration products (e.g., Ca(OH)₂). By limiting solution penetration, PVP substantially reduces the extent and rate of these reactions. Ref. [1] quantified this effect by measuring weight loss in PVP-modified mortars exposed to HCl, H₂SO₄, and seawater. Specimens containing 3% PVP consistently exhibited the lowest mass loss, indicating superior chemical stability. These findings were further corroborated by [3], who observed enhanced sulfate resistance in PVP-modified systems.

Unlike traditional mineral admixtures that rely on secondary hydration reactions, PVP improves chemical resistance primarily through transport control, making its effectiveness less dependent on curing temperature or long-term pozzolanic activity.

7.1.2. Chemical Shielding and Ion Interaction

In addition to acting as a physical barrier, the polymer network may provide a secondary chemical protection mechanism. PVP can adsorb onto hydration product surfaces, forming a thin polymeric coating that limits direct contact between aggressive pore solutions and reactive phases. Moreover, the ability of PVP to complex with multivalent cations may subtly alter pore solution chemistry, potentially suppressing dissolution–precipitation reactions that drive chemical attack. While this chemical interaction mechanism is less well quantified than pore blocking, it represents a promising area for future investigation using pore solution analysis and spectroscopic techniques.

7.2. Enhanced Frost Resistance

Freeze–thaw damage is a physically driven degradation process caused by water ingress followed by volumetric expansion upon freezing. The resulting hydraulic and crystallization pressures generate microcracks that progressively degrade mechanical integrity. PVP enhances frost resistance through its combined effects on water transport and pore structure:

• Reduced water absorption: The densified microstructure of PVP-modified cementitious materials significantly lowers water absorption and capillary suction, thereby reducing the volume of freezable water within the matrix [1].
• Refined pore structure: By decreasing the proportion of large capillary pores and promoting smaller, less interconnected pores, PVP shifts the freezing behavior of pore water. Water confined in finer pores freezes at lower temperatures and generates lower internal pressures, mitigating freeze–thaw damage.

Zhagifarov et al. [15] provided compelling experimental evidence for this effect. In their study on self-compacting concrete, the incorporation of a PVP-containing complex modifier resulted in substantially enhanced frost resistance, allowing specimens to withstand a significantly higher number of freeze–thaw cycles with minimal mass loss and surface deterioration compared to control samples. These findings suggest that PVP may partially substitute or complement traditional air-entraining strategies in frost-exposed environments, particularly where workability or strength retention is critical.

7.3. Improved Resistance to Reinforcement Corrosion

Although closely related to chemical resistance, protection of embedded steel reinforcement is of such structural importance that it warrants separate consideration. PVP enhances corrosion resistance through multiple, synergistic mechanisms operating across different length scales.

• Macro-level: Reduced permeability: The refined pore network significantly limits the ingress of chlorides, oxygen, and moisture, three essential components for electrochemical corrosion, thereby extending the time to corrosion initiation.
• Micro-level: Blocking of capillary pathways: Gürten et al. [3] emphasized that PVP effectively blocks capillary channels that otherwise serve as rapid transport pathways for ions, forcing diffusion to proceed through the much slower C-S-H gel network.
• Nano-level: Interfacial film formation (potential mechanism): There is strong evidence that PVP may also contribute to corrosion inhibition at the steel–concrete interface. Owing to its affinity for metal ions, PVP may form a thin, adsorbed polymer layer on the steel surface, acting as a passivating barrier to electrochemical reactions. Electrochemical impedance spectroscopy (EIS) results reported by Gürten et al. [2,3] revealed significantly higher polarization resistance values for steel embedded in PVP-modified concrete, indicative of a more stable and less corrosive interfacial environment.

By extending the corrosion initiation period, PVP can significantly reduce maintenance frequency and material replacement, contributing to lower life-cycle costs and embodied carbon in reinforced concrete infrastructure. Overall, PVP enhances durability primarily by suppressing transport-controlled degradation mechanisms rather than altering fundamental hydration chemistry. This makes PVP particularly effective in aggressive environments where permeability governs service life, positioning it as a versatile durability-enhancing additive for both conventional and advanced cementitious systems.

Table 11. Overview of the effects of PVP on the durability of cementitious materials, including chemical resistance, frost resistance, and corrosion protection.

Durability Aspect	Effect of PVP Addition	In-Depth Mechanism & Discussion	Key Evidence
Permeability (general)	Significantly reduced.	Primary: Pore-filling and pore-blocking by the interspersed polymer phase, creating a denser and more tortuous pore network.	Water absorption tests [1], MIP analysis.
Chemical resistance (acids, sulfates)	Substantially improved; lower mass loss and degradation.	Primary: Reduced permeability prevents aggressive solutions from reaching reactive cement hydrates. Secondary: Polymer film may provide a protective coating on hydrated surfaces.	Immersion tests (weight loss) [1,3], visual inspection.
Frost resistance	Dramatically improved; higher number of freeze–thaw cycles endured.	Primary: Reduced water absorption and capillary suction limit the amount of freezable water. Secondary: Refined pore structure minimizes the internal pressures generated by ice formation.	Freeze–thaw cycling tests (mass loss) [15].
Rebar corrosion resistance	Significantly enhanced protection against chloride and sulfate-induced corrosion.	Macro: Reduced permeability of the concrete cover to ions, oxygen, and water. Micro: Blocking of capillary channels. Nano: Potential formation of an inhibitive polymer film on the steel surface.	Electrochemical tests (EIS, polarization resistance) [2,3].

summarizes the data reported in this section.

7.4. Long-Term Stability and Potential Limitations

While PVP demonstrates excellent performance in short- to medium-term durability tests, its long-term stability in the aggressive chemical environment of cementitious materials warrants critical discussion. Several potential limitations and uncertainties remain insufficiently explored in the literature.

Alkaline stability: The lactam ring in PVP may be susceptible to hydrolysis under highly alkaline conditions (pH > 12) over extended periods, which could potentially break the ring structure and alter the polymer’s physicochemical properties. However, existing studies on PVP-modified cement systems—typically limited to 28–90 days—have not reported evidence of such degradation, suggesting that the polymer remains sufficiently stable within conventional durability assessment timelines. Nevertheless, the absence of multi-year or accelerated aging studies leaves uncertainty regarding the polymer’s stability over the full-service life of concrete structures, particularly in environments with sustained high alkalinity or elevated temperatures.

UV degradation: For externally exposed applications, the potential for UV-induced degradation is a valid concern. Research on PVP in other fields indicates that prolonged UV exposure can cause chain scission and cross-linking, altering mechanical and rheological properties. Within cementitious matrices, PVP is largely shielded from direct UV radiation, but its stability under partial exposure—such as in thin coatings, repair mortars, or photocatalytic surfaces—remains unverified. This represents a significant research gap, especially for façade elements or surface treatments subjected to long-term solar exposure.

Leaching potential: The possibility that low-molecular-weight fractions of PVP may leach out of the hardened matrix over time is another consideration. Strong evidence of ion coordination and chemical bonding with C–S–H suggests that a substantial portion of the polymer becomes chemically anchored, minimizing leaching. However, long-term immersion or cyclic wetting–drying conditions could mobilize unbound polymer fractions, and no studies have yet quantified this effect. The observed improvements in durability over short periods imply good retention, but long-term leaching behavior remains an open question.

Temperature sensitivity and freeze–thaw performance: Temperature fluctuations can influence polymer mobility, film continuity, and the stability of polymer–C–S–H interactions. While PVP is known to maintain structural integrity across a broad temperature range in other applications, its behavior within cementitious matrices under repeated thermal cycling has not been systematically studied. Freeze–thaw resistance is particularly relevant for cold-region applications. PVP’s ability to refine pore structure and reduce permeability suggests potential benefits for freeze–thaw durability; however, the polymer’s hygroscopic nature may also increase local water retention, which could exacerbate freeze–thaw damage under certain conditions. The absence of controlled freeze–thaw testing in the current literature represents a critical limitation that must be addressed before PVP can be confidently recommended for severe climatic environments.

Interaction with chloride transport and corrosion risk: PVP’s demonstrated ability to reduce permeability and refine pore structure implies a potential reduction in chloride ingress. However, the polymer’s strong affinity for metal ions raises questions about whether PVP could influence chloride binding capacity or modify the ionic composition of the pore solution in ways that affect corrosion initiation thresholds. No studies have yet evaluated the combined effects of PVP on chloride diffusivity, chloride binding, and steel passivation. This is a significant gap, particularly for marine and de-icing salt environments where chloride-induced corrosion is the dominant durability concern. Without long-term electrochemical or diffusion-based studies, the net impact of PVP on corrosion risk remains uncertain.

Overall, while PVP shows promising short-term durability benefits, its long-term performance under alkaline exposure, UV radiation, temperature cycling, freeze–thaw conditions, and chloride-rich environments remains insufficiently characterized. Addressing these gaps through multi-year testing, accelerated aging protocols, and coupled durability assessments is essential for establishing the reliability of PVP-modified cementitious materials in real-world service conditions.

Although PVP consistently reduces permeability and enhances resistance to chloride ingress and chemical attack, long-term performance data remain scarce. Most available studies evaluate durability over short exposure periods, leaving uncertainties regarding polymer stability under prolonged alkaline conditions, UV exposure, and cyclic environmental loading. Furthermore, the durability benefits are strongly dependent on the continuity of the polymer film, which itself varies with molecular weight, curing conditions, and mixture proportions. These gaps emphasize the need for long-term, multi-environment durability studies to fully validate PVP’s contribution to service-life extension.

8. Advanced Applications and PVP in Composite Systems

Beyond its role as a bulk modifier for improving the fundamental properties of cement, Polyvinylpyrrolidone’s unique molecular structure and chemical functionalities have positioned it as a critical enabling component in a new generation of advanced and “smart” building materials. In these systems, PVP is not merely a passive additive but an active and integral part of the composite architecture, serving simultaneously as a high-performance dispersant, an interfacial coupling agent, and a structural carrier for other functional materials. These three sophisticated roles, which represent the pinnacle of PVP’s utility in modern construction materials, are conceptually illustrated in Figure 7.

8.1. PVP as a High-Performance Dispersant for Nanomaterials in Smart Composites

A major obstacle in the development of functional cement-based nanocomposites, such as self-sensing concrete or thermally conductive cement, is the difficulty of achieving a uniform and stable dispersion of nanomaterials within the highly alkaline, ion-rich, and aqueous environment of fresh cement paste. Carbon-based nanomaterials, including CNTs, graphene nanoplatelets (GNPs), and nano carbon black (NCB), are particularly prone to irreversible agglomeration due to strong van der Waals attractions. These agglomerates severely compromise both mechanical and functional performance.

PVP has proven to be a highly effective solution to this challenge through a mechanism of non-covalent functionalization combined with steric stabilization.

Mechanism of action: The hydrophobic vinyl backbone of PVP exhibits strong affinity for the nonpolar surfaces of carbon nanomaterials, enabling adsorption through π–π stacking and hydrophobic interactions. Concurrently, the bulky, hydrophilic lactam side groups extend outward into the surrounding aqueous phase. This configuration forms a dense polymeric shell around each nanoparticle, generating a steric barrier that physically inhibits re-agglomeration. Unlike electrostatic stabilization provided by ionic surfactants, this steric mechanism remains effective in the high-ionic-strength environment of cement paste, where electrostatic repulsion is readily screened.

This dispersion capability is essential for several advanced composite applications:

Piezoresistive (self-sensing) cementitious materials: For cement-based sensors to exhibit reliable electrical conductivity and piezoresistive behavior, where electrical resistance varies predictably with mechanical strain, a continuous and well-distributed conductive network must be established. Nanoparticle agglomerates act as electrical dead zones or unstable short-circuits, undermining sensitivity and repeatability. Xing et al. [7] demonstrated that an optimal PVP: CNT mass ratio of 4:1 produced a highly stable and homogeneous CNT dispersion. This enabled the formation of a well-defined percolation network, resulting in cement paste sensors with high sensitivity, excellent cyclic repeatability, low hysteresis, and a clear percolation threshold—performance unattainable with poorly dispersed CNTs. The graphs illustrate the self-sensing capability of cement paste containing 0.4 wt% CNTs, optimally dispersed with PVP. (a) The time series plot shows the excellent repeatability of the sensor, as the Fractional Change in Resistivity (FCR, red line) synchronously and consistently tracks the applied cyclic stress (black line) over multiple cycles. (b) The corresponding FCR vs. Stress plot demonstrates the material’s high sensitivity (indicated by the steep slope) and low hysteresis (the narrow gap between the loading and unloading paths). These desirable characteristics are indicative of a stable and well-dispersed conductive network, a direct result of PVP’s effectiveness as a dispersing agent. The sensing mechanism was governed by controlled variations in electron tunneling distances between adjacent CNTs under mechanical loading.

Rheological and mechanical enhancement in asphalt composites: The same stabilization principles extend to organic binders. Liu et al. [17] employed PVP to disperse GNPs in asphalt, where the polymer coating effectively prevented graphene restacking during high-temperature processing. The resulting uniform dispersion enabled the formation of a reinforcing graphene network, leading to substantial improvements in rheological behavior, rutting resistance, and fatigue damage tolerance of the asphalt composite.

8.2. PVP as a Structural Carrier and Reinforcement in Nanofiber Composites

Beyond its dispersing function, PVP can serve as a primary structural matrix for the fabrication of functional nanofibers, particularly through electrospinning. In this application, PVP acts as a carrier polymer, dissolving and uniformly distributing inorganic or ceramic precursors within a continuous fibrous architecture. Mechanism of formation: A homogeneous solution containing PVP and a functional precursor (e.g., TEOS, as a silica source) is subjected to a high-voltage electric field. The resulting charged jet undergoes extreme elongation, producing continuous nanofibers. Subsequent thermal treatment can either remove the PVP to yield pure ceramic fibers or retain it as part of a hybrid composite structure. Nguyen et al. [4] demonstrated the effectiveness of this approach for cement reinforcement by producing TEOS/PVP nanofibers and directly incorporating them into cement powder. The hardened cement paste exhibited a 38% increase in compressive strength and a 66% improvement in toughness. Scanning electron microscopy revealed that the nanofibers were uniformly dispersed and formed a dense, interconnected network within the matrix. These fibers provided efficient nanoscale crack-bridging, arresting crack initiation and early propagation. Compared to conventional microfibers, nanofibers operate at much smaller length scales, enabling significantly more effective toughening mechanisms.

8.3. PVP as an Interfacial Coupling Agent in Fiber-Reinforced Composites

The mechanical performance of high-performance fiber-reinforced cementitious composites, such as ECC, is strongly governed by the quality of the fiber–matrix interfacial bond. Many advanced polymer fibers, including polyethylene (PE), are chemically inert and inherently hydrophobic, resulting in weak interfacial adhesion dominated by frictional pull-out. This limited bonding efficiency restricts stress transfer from the matrix to the fibers and can lead to premature fiber debonding and reduced composite ductility. PVP provides a straightforward yet highly effective strategy for interfacial engineering. Men et al. [20] demonstrated that simple surface coating of PE fibers with a PVP solution fundamentally altered fiber–matrix interactions and markedly enhanced composite performance. Mechanism of interfacial modification: The hydrophobic backbone of PVP adsorbs strongly onto the PE fiber surface, while the hydrophilic lactam groups orient outward, effectively transforming the fiber surface from hydrophobic to hydrophilic. The exposed carbonyl functionalities are capable of forming coordination bonds with Ca²⁺ ions in the surrounding C-S-H gel. This interaction creates a chemically mediated interfacial bond where only weak physical adhesion previously existed. As a result, PVP acts as a molecular bridge or coupling agent, effectively “gluing” the polymer fibers to the cementitious matrix. The macroscopic consequences of this interfacial enhancement are substantial. The PVP-modified ECC exhibited a 109% increase in tensile strain capacity and developed the highly desirable saturated multiple-cracking behavior characteristic of high-performance ECC. These improvements reflect more efficient stress transfer, delayed fiber pull-out, and full activation of fiber reinforcement, enabling the composite to approach its theoretical ductility and toughness potential.

Table 12. Key roles of PVP in advanced cementitious composites: dispersion, nanofiber reinforcement, and interfacial coupling.

Application Area	Role of PVP	Mechanism & Discussion	Key Outcome
Nanomaterial dispersion (smart composites)	Non-covalent surface functionalizer and steric stabilizer.	Adsorbs onto CNTs/graphene via hydrophobic/π-π interactions, while hydrophilic groups project outwards, creating a steric barrier that prevents re-agglomeration in the high-ionic-strength pore solution.	Uniform dispersion, enabling the formation of a percolated conductive network essential for high-performance piezoresistive (self-sensing) properties.
Nanofiber reinforcement	Structural carrier matrix for precursors (e.g., TEOS) in the electrospinning process.	Forms a continuous polymer jet that solidifies into nanofibers. These fibers are then integrated into the cement matrix, acting as a highly efficient, nanoscale reinforcing web.	Creates a powerful micro-level crack-bridging network, leading to extraordinary increases in compressive strength and, particularly, fracture toughness.
Fiber-matrix interface modification (ECC)	Interfacial coupling agent; molecular bridge.	Adsorbs onto hydrophobic fibers, presenting a hydrophilic and chemically reactive (C=O) surface to the cement matrix. This creates a strong chemical bond at the interface.	Transforms a weak, frictional fiber–matrix bond into a strong, chemical one. This enables efficient stress transfer, dramatically increasing the ductility and performance of fiber-reinforced composites.

summarizes the data reported in this section.

8.4. Practical Implementation Challenges and System-Level Considerations

Although PVP shows promising performance in controlled laboratory conditions, several practical challenges must be considered before its widespread adoption in construction practice. First, the scalability of PVP-modified mixtures remains uncertain, as field mixing conditions often introduce variability in shear energy, moisture content, and temperature, all of which can influence polymer dispersion and film formation. Second, compatibility with existing admixture systems, particularly polycarboxylate superplasticizers, may vary across suppliers and binder chemistries, requiring mixture-specific optimization rather than universal dosage recommendations.

Cost considerations also represent a potential barrier. While PVP is widely available in industrial applications, its use in cementitious systems may increase material costs relative to conventional admixtures, especially at higher dosages or when high-molecular-weight grades are required. A comprehensive cost–benefit analysis is therefore necessary to determine whether the improvements in durability and mechanical performance justify the added expense in different construction scenarios.

Environmental and sustainability aspects must also be acknowledged. Although PVP is generally considered non-toxic and water-soluble, its long-term environmental footprint within cementitious matrices has not been fully assessed. Questions remain regarding polymer persistence, degradation pathways, and potential micro-scale release during demolition or recycling processes.

Finally, the translation of laboratory findings to real-world performance is complicated by field-specific factors such as curing variability, exposure conditions, construction sequencing, and workmanship. These uncertainties highlight the need for pilot-scale trials and field demonstrations to validate the robustness of PVP-modified systems under practical construction conditions. Overall, while PVP offers clear scientific advantages, its successful implementation will require careful consideration of mixture design, compatibility, cost, environmental impact, and field performance.

9. PVP in Specialty Cements and Other Building Materials

The functional versatility of PVP extends well beyond conventional Portland cement systems, encompassing a wide range of specialty cements and alternative construction materials. In these applications, PVP is employed to tailor rheological behavior, interfacial interactions, durability, and functional performance under demanding service conditions.

9.1. Specialty Cements: Biomedical and Oil Well Applications

In biomedical engineering, PVP has been incorporated into calcium phosphate–based bone cements to regulate handling properties and biological response. Stepanova et al. [6] investigated a poly(vinyl alcohol) (PVA)/PVP blend as a modifier for β-tricalcium phosphate cement. They reported that intermolecular interactions between PVA and PVP enhanced the homogeneity of the polymer phase and reduced calcium-ion diffusion, leading to more controlled resorption behavior in physiological environments. The modified cement also exhibited excellent biocompatibility, highlighting its suitability for bone repair applications. In the oil and gas sector, PVP has been explored as an additive for oil well cement systems, which must withstand extreme temperature, pressure, and mechanical loading. Tapdiqov et al. [8] demonstrated that PVP significantly improved the flowability, adhesion, and flexural strength of oil well cement plugs. The presence of PVP imparted greater elasticity to the hardened cement, enhancing its resistance to dynamic stresses and deformation commonly encountered in deep-well operations.

9.2. Geopolymers, Functional Coatings, and Asphalt Materials

PVP has also been applied in geopolymer systems, which are inorganic aluminosilicate binders known for their superior thermal stability and chemical resistance. Chen et al. [16] utilized PVP as a processing additive in a sol–gel route to fabricate crack-free, photocatalytic TiO₂ films on geopolymer substrates. PVP effectively mitigated shrinkage-induced stresses during drying and annealing, enabling the formation of uniform, continuous coatings with retained photocatalytic functionality. In asphalt binders, which constitute a major class of infrastructure materials, PVP has been employed to stabilize graphene nanoplatelets (GNPs). Liu et al. [13] reported that PVP-stabilized GNPs were uniformly dispersed within the asphalt matrix, leading to significant improvements in rheological properties, rutting resistance, and fatigue damage tolerance. These results underscore PVP’s ability to enhance both mechanical performance and durability across diverse non-cementitious construction materials.

Table 13. Overview of PVP’s role as an enabling component in advanced construction materials.

Application/Material System	Primary Function of PVP	Underlying Mechanism	Key Outcome/Performance Gain	References
Self-sensing concrete (with CNTs)	High-performance dispersant and stabilizer.	Non-covalent functionalization and steric stabilization prevent nanoparticle agglomeration in the alkaline, high-ionic-strength environment.	Creation of a stable, percolated conductive network, leading to high piezoresistive sensitivity, repeatability, and low hysteresis.	[7]
High-ductility ECC (with PE fibers)	Interfacial coupling agent/molecular bridge.	Adsorbs onto hydrophobic fibers, transforming their surface to hydrophilic and enabling chemical bonding with the cement matrix via C=O groups.	Transforms a weak, frictional fiber–matrix bond into a strong, chemical one. Unlocks unprecedented ductility (e.g., >100% strain capacity increase).	[20]
Nanofiber-reinforced cement	Structural carrier matrix for electrospinning.	Acts as the polymer host for functional precursors (e.g., TEOS), forming continuous nanofibers that are integrated into the cement matrix.	Creates a powerful nanoscale crack-bridging network, resulting in extraordinary increases in fracture toughness (e.g., +66%).	[4]
Functional coatings (on geopolymers)	Stress-relieving agent in sol–gel film formation.	Mitigates shrinkage-induced stresses during the drying and annealing of TiO2 films, preventing cracking and ensuring film continuity.	Enables the fabrication of uniform, crack-free, and functional photocatalytic surfaces on thermally stable substrates.	[18]
High-performance asphalt	Stabilizer and dispersant for graphene nanoplatelets (GNPs).	Prevents the restacking of GNP layers in the hot asphalt matrix, ensuring uniform dispersion and the formation of a reinforcing network.	Significantly enhances rheological properties, rutting resistance, and fatigue damage tolerance of the asphalt binder.	[13,14]

summarizes PVP’s role as an enabling component in advanced construction materials.

10. Sustainability and Life Cycle Considerations

While this review has focused on the performance enhancements offered by PVP, a holistic assessment requires considering its environmental and life cycle implications. The “sustainability” of PVP in construction materials is primarily an argument based on service life extension rather than on the intrinsic greenness of the polymer itself.

• Embodied carbon and production: The synthesis of N-vinylpyrrolidone monomer and its subsequent polymerization into PVP is an energy-intensive process with an associated carbon footprint. However, this upfront environmental cost must be weighed against its use at very low dosages (typically 1–3% by cement weight). The primary sustainability benefit arises from its ability to dramatically extend the service life of the entire concrete structure.
• Service life extension and life cycle impact: The most significant contribution of PVP to sustainability is through enhanced durability. By reducing permeability and increasing resistance to corrosion and frost, PVP can extend the functional service life of a concrete structure by years or even decades. This delays the need for costly repairs or complete replacement, thereby avoiding the massive material consumption and embodied carbon associated with new construction. For example, if a 20% increase in service life is achieved, the life cycle embodied carbon per year of service for the structure is effectively reduced.
• End-of-life, degradability, and recycling: At the end of a structure’s life, the concrete is typically crushed for use as recycled aggregate. Within this context, the small amount of PVP present is chemically bound and physically locked within the cement matrix. It is inert and poses no significant leaching risk. If the concrete waste is incinerated or used in cement kilns, the PVP will safely decompose. While not biodegradable in the conventional sense, its non-toxic nature means it does not contribute to environmental pollution in the same way as other plastics. When compared with other polymer modifiers commonly used in cementitious systems, such as styrene, butadiene latexes, acrylic emulsions, epoxy resins, and redispersible polymer powders, PVP offers several environmental advantages. These alternative polymers often require organic solvents, surfactants, or energy-intensive processing steps, and they are typically used at higher dosages to achieve comparable functional effects. In contrast, PVP is water-soluble, non-toxic, and effective at very low addition rates, which reduces both material intensity and upstream environmental burden. Although PVP is not inherently biodegradable, its immobilization within the cement matrix and its low required dosage make its life cycle impact more favorable than many conventional polymer modifiers.

11. Conclusions and Future Outlook

The body of research synthesized in this review clearly establishes PVP not merely as a beneficial chemical admixture, but as a uniquely versatile and multifunctional enabling technology for next-generation cementitious and construction materials. Its influence extends well beyond incremental performance enhancement, offering effective molecular-level solutions to long-standing challenges in workability control, mechanical performance, durability, and the development of advanced functional composites. The value of PVP arises from its amphiphilic molecular architecture and its ability to engage in synergistic physical and chemical interactions across multiple length scales within composite systems. On this basis, the principal conclusions of this review can be summarized as follows:

11.1. Synthesis of Key Findings

The value of PVP arises from its amphiphilic molecular architecture and its ability to participate in synergistic physical and chemical interactions across multiple length scales within composite systems. The principal conclusions of this review can be summarized as follows:

Microstructural engineering capability: PVP’s most fundamental contribution lies in its ability to refine the hardened cement microstructure. Through a dominant pore-filling and matrix-densification mechanism, PVP produces a less permeable and more homogeneous matrix. This refinement underpins the substantial improvements reported in durability-related properties, including resistance to chemical attack, ion penetration, and freeze–thaw degradation. This review consolidates these findings into a coherent mechanistic interpretation, demonstrating that microstructural refinement is the primary driver of PVP’s durability benefits across different binder systems.

Dual-mechanism mechanical enhancement: Mechanical performance is enhanced through two complementary pathways. Microstructural densification yields a consistent increase in compressive strength (up to 44%), while the dispersed polymer phase functions as a ductile micro-reinforcement. This crack-bridging mechanism is shown to increase fracture toughness by ~47%, resulting in pronounced improvements in flexural strength and overall ductility.

Enabling nanotechnology integration: PVP has proven to be an exceptional non-covalent dispersant and stabilizer for nanomaterials such as carbon nanotubes and graphene. By effectively suppressing nanoparticle agglomeration, PVP enables the formation of stable, percolated networks essential for high-performance “smart” cementitious composites, including piezoresistive systems for structural health monitoring. The novelty of this review lies in synthesizing these findings into a unified perspective that links nanoscale dispersion behavior to macroscale functional performance.

Interfacial engineering function: Beyond bulk modification, PVP serves as a powerful interfacial coupling agent. Its ability to chemically bridge hydrophobic polymer fibers and the hydrophilic cement matrix fundamentally transforms fiber–matrix interactions, enabling unprecedented levels of strain capacity and ductility (e.g., >100% increase in ECC) in high-performance fiber-reinforced composites.

Broad material compatibility: The effectiveness of PVP is not limited to ordinary Portland cement. Its beneficial role has been demonstrated in specialty cement systems (e.g., biomedical and oil well cements), geopolymers, and asphalt binders, underscoring its robustness and adaptability across a wide spectrum of construction materials. By comparing performance across these diverse systems, this review provides a system-level understanding of how PVP interacts with different binder chemistries, enabling more informed selection and optimization in future applications.

Final novelty-focused closing statement: Overall, the novelty and contribution of this review lie in its mechanistic integration, cross-study comparison, and system-level interpretation, which together establish a comprehensive understanding of PVP’s multifunctional role in cementitious materials. These insights not only clarify the current state of knowledge but also define clear research pathways for optimizing PVP-modified systems and advancing their practical implementation in next-generation construction materials.

11.2. Future Outlook and Research Directions

Despite significant progress, the full potential of PVP in construction materials remains largely untapped. Several promising and critical research directions can be identified:

From passive durability to active functionality: The excellent film-forming ability and water solubility of PVP make it an attractive candidate for self-healing cementitious systems. Future research may focus on microencapsulation strategies in which PVP-based healing agents are released upon crack formation to seal damage and extend service life. In parallel, PVP’s stabilizing capability could be exploited to integrate phase change materials (PCMs) into cementitious matrices, enabling thermal energy storage and improved building energy efficiency.

Synergy in multiscale and hierarchical composites: Future studies should explore hierarchical composite designs that leverage PVP’s multifunctionality across multiple scales. Hybrid systems combining PVP-modified microfibers for crack control, PVP-stabilized nanomaterials for sensing, and bulk PVP for matrix densification offer a pathway toward truly multifunctional, resilient construction materials. Additionally, investigating the interaction of PVP with emerging low-carbon binders, such as calcium sulfoaluminate, magnesium-based cements, and limestone calcined clay cements, could yield materials with tailored performance and a significantly reduced environmental impact. PVP’s ability to modify rheology and control water transport may be particularly beneficial in these systems, which often have different hydration kinetics and water demands compared to ordinary Portland cement.

Advancing additive manufacturing technologies: Additive manufacturing of cementitious materials demands precise control over rheology, including extrudability, buildability, and open time. PVP’s dual role as a viscosity modifier and hydration regulator positions it as a promising additive for three-dimensional concrete printing. Future work should focus on optimizing molecular weight, dosage, and interaction with other admixtures to achieve desirable thixotropy and early-age mechanical stability.

Deepening mechanistic understanding: While experimental evidence for PVP’s effectiveness is extensive, molecular-level understanding remains limited. Computational approaches, particularly molecular dynamics simulations, could elucidate PVP–ion coordination, adsorption behavior on calcium–silicate–hydrate surfaces, and interactions with other admixtures. Such insights would enable a transition from empirical formulation toward predictive, mechanism-based material design. In addition, long-term studies addressing creep behavior, ultraviolet stability, and durability under aggressive environmental cycling are essential to assess PVP’s performance over the full service life of structures.

In summary, PVP should be regarded not as a conventional admixture but as a molecular engineering tool capable of tailoring cementitious materials from the nano- to the macro-scale. As the construction industry advances toward sustainability, resilience, and intelligent functionality, continued research and innovative deployment of PVP are expected to play a pivotal role in the development of advanced construction materials capable of meeting future societal and environmental demands.