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Article

Influence of Self-Emulsifying Waterborne Epoxy Resin with Novel Hardeners on Pore Structure and Permeability of Cement-Based Materials

by
Feifei Wang
1,
Yunsheng Zhang
2,*,
Xiaoyun Song
3,*,
Lirong Liu
4,*,
Xianglin Sun
1 and
Peifeng Sun
5
1
College of Civil Engineering, Lanzhou University of Technology, Lanzhou 730050, China
2
School of Materials Science and Engineering, Southeast University, Nanjing 211189, China
3
Qingdao Institute of Marine Geology, China Geological Survey, Qingdao 266071, China
4
China Bluestar Chengrand (Chengdu)Testing Technology Co., Ltd., Chengdu 610041, China
5
Qingdao Zhonghui Qing Industrial Development Co., Ltd., Qingdao 266200, China
*
Authors to whom correspondence should be addressed.
Buildings 2025, 15(7), 997; https://doi.org/10.3390/buildings15070997
Submission received: 27 February 2025 / Revised: 16 March 2025 / Accepted: 19 March 2025 / Published: 21 March 2025
(This article belongs to the Special Issue Sustainable Approaches to Building Repair)
Browse Figures
Versions Notes

Abstract

With increasing service life, concrete durability gradually deteriorates, requiring urgent repair and reinforcement. Conventional cement-based repair materials exhibit disadvantages such as high brittleness, low tensile strength, poor adhesion, and insufficient durability, making them inadequate for high-quality structural repairs. Based on the molecular structure–activity relationship, this study developed a novel waterborne epoxy–cement-based composite repair material using self-synthesized waterborne epoxy resin (WEP). The mechanism by which WEP improves the performance of cement-based materials was elucidated. The results indicate that WEP significantly influenced the early formation of silicate crystals. Furthermore, the addition of WEP enhanced material flexibility and adhesion, achieving flexural strength of 12.9 MPa and direct tensile bond strength of 2.13 MPa at 28 days, representing increases of approximately 30% and 58%, respectively, compared to the control group. Stress–strain curve analysis revealed that the ultimate strain of WEP-modified cement mortar reached 0.024%. SEM analysis revealed that cured WEP formed a dense cross-linked network with cement hydration products. This microstructural modification refined the pore structure, effectively addressing the material’s brittleness, ductility, and durability limitations.

1. Introduction

Concrete, the primary material in land transportation infrastructure, experiences progressive deterioration in safety and durability over its service life, requiring urgent repair and reinforcement [1,2,3]. Infrastructure maintenance demands substantial financial resources: annual repair and reinforcement costs amount to $300 billion in the United States, while European nations dedicate more than half of their construction budgets to these critical activities [4]. The growing importance of concrete structure rehabilitation contrasts with the limitations of traditional cement-based repair materials. These conventional materials suffer from high brittleness, poor tensile strength, and weak bonding capabilities, compromising their reliability in high-performance structural repairs [5,6]. Consequently, the development of advanced repair materials that combine flexibility, superior adhesion, enhanced tensile strength, and extended durability has become a critical research priority [7].
The construction repair field has experienced significant advancement in recent decades, witnessing the emergence of diverse repair materials, including inorganic, organic, and organic–inorganic composites. Among them, the organic‒inorganic composite repair material is a composite material in which a certain amount of polymer is introduced when mixing cement-based materials, and the organic‒inorganic components combine with each other to form a dense structure. Compared to ordinary cement-based repair materials, organic‒inorganic composite repair materials have the advantages of good flexibility for enhanced crack resistance, strong bonding force for structural integrity, good durability against aggressive environments (particularly carbonation and freeze–thaw cycles), and dense structure for reduced water permeability, showing enormous potential in concrete repair applications [8,9,10,11].
Waterborne epoxy resin (WEP) has emerged as a highly effective polymer modifier for cement-based repair materials, optimizing their inherent high compressive strength and modulus while enhancing ductility and tensile performance [12,13]. As an innovative epoxy resin system, WEP utilizes water rather than organic solvents as the dispersion medium, providing superior water miscibility, flexibility, and mechanical strength [14,15,16]. From an environmental standpoint, this water-based approach significantly reduces volatile organic compound (VOC) emissions, minimizes toxicity concerns, and lowers fire hazards during application and curing processes compared to conventional solvent-based systems. From a life cycle perspective, the enhanced durability of WEP-modified repair materials will extend service life and reduce maintenance frequency, offsetting the environmental impact of polymer addition. Moreover, the lower cement content in polymer-modified systems contributes to reduced CO2 emissions associated with cement production. The incorporation of WEP into cement-based repair materials creates a synergistic composite system that leverages the strengths of both components while addressing their individual limitations [17,18]. Water consumption during cement hydration facilitates WEP cross-linking and curing processes. This mechanism enhances the system’s compressive strength and elastic modulus, effectively addressing WEP’s inherent rigidity limitations. The dried WEP forms an interpenetrating polymer network with cement hydration products, establishing a continuous phase that effectively fills material defects and voids. This microstructural modification significantly enhances the composite’s toughness, ductility, and durability [19,20]. Research by Guo et al. [3] showed that adding 5% WEP improved multiple mechanical properties of OPC mortar: interfacial flexural bond strength increased by 16.7%, direct interfacial shear strength increased by 29.8%, and interfacial tensile strength increased by 6.9%. Li et al. [21] demonstrated, through heat evolution and XRD experiments, that increased WEP dosage moderates cement hydration rates. A study by Zheng et al. [22] on WEP-modified HDHS cement-based materials revealed optimized pore structure with porosity reduced to 7.74%. However, currently, commercially available WEPs are not designed or produced for the modification of cementitious materials. The diversity of its molecular structure leads to discrete properties, which also results in a wide variation in the performance of WEP-modified cementitious repair materials on the market.
A systematic approach to molecular design and performance optimization is essential to address the limitations of commercial WEP formulations. This study presents a novel synthesis strategy for WEP that is specifically tailored to the cement hydration environment. A two-component system of a self-emulsifying curing agent (WEP-B) and epoxy resin (WEP-A) was developed, guided by molecular structure–activity relationships. A comprehensive evaluation of the self-synthesized WEP-modified cement-based repair materials included mechanical properties and durability testing across various dosage levels. Detailed analyses of pore structure characteristics and microstructural features revealed the underlying mechanisms of WEP-induced performance enhancement in cement-based repair materials.

2. Materials and Methods

2.1. Materials

This study utilized Type 42.5 ordinary silicate cement as the primary material. The cement had a specific surface area (fineness) of 360 m2/kg and a specific gravity of 3.15. A polycarboxylic acid superplasticizer (molecular weight: 12,000–20,000 g/mol; carboxyl group content: 18 ± 2%) with a 40% water reduction rate served as the water-reducing agent. All materials were sourced from Qingdao Kramer New Building Materials Co., Ltd. (Qingdao, China). Table 1 presents the chemical composition of the cement. Figure 1 shows the particle size distribution of the Type 42.5 ordinary silicate cement used in this study, displaying both differential and cumulative distributions. Table 2 summarizes the physical properties of the polycarboxylic acid superplasticizer. Natural river sand was used as the fine aggregate. The physical properties of the sand are summarized in Table 3. Figure 2 illustrates the particle size distribution of the river sand, showing the percentage passing through each standard sieve size.

2.2. Preparation of WEP and WEP–Cement Repair Materials

2.2.1. Preparation of WEP

This study employed a self-emulsification method to prepare WEP [5], using bisphenol A-type epoxy resin (E-51) as part A (NEP-EP). Part B comprised two components: a self-emulsifying curing agent (hardener-S, LHD) and a modified Mannich curing agent (hardener-M, SBP), forming the self-emulsifying hardener WEP (NEP-HD). LHD enhances WEP’s water solubility following the “like dissolves like” principle, whereas SBP facilitates the cross-linking reaction between WEP-A and WEP-B. Detailed synthesis procedures are provided in the Supplementary Materials. Table 4 summarizes the basic properties of WEP-A and WEP-B, and Figure 3 depicts their molecular configurations.

2.2.2. Preparation of WEP–Cement Repair Materials

Initially, cement and sand were mixed and stirred for 1 min until a uniform dry mixture was obtained. Subsequently, half of the water was gradually incorporated and stirred for 3 min to produce the cement mortar. WEP-A and WEP-B were then weighed, combined in a container, and stirred for 30 s to prepare the WEP glue. The remaining water was added and mixed for 1 min to create the WEP emulsion. The WEP emulsion was then incorporated into the cement mortar and stirred for 3 min to produce the homogeneous WEP–cement mortar. The resulting mixture was poured into a mold and vibrated for 10 s. After 24 h, the specimens were demolded and cured at 25 °C and 98% relative humidity. The preparation process is shown in Figure 4. The sample mix proportions were designed based on the volume fraction method for 1 m3 of mortar. The polymer-to-cement ratio (P/C), water-to-cement ratio (W/C), cement-to-sand ratio (C/S), and superplasticizer dosage (as the percentage of cement weight (SP/%)) were determined through preliminary tests to achieve optimal workability and mechanical properties. Table 5 presents the detailed mixture proportions.

2.3. Fourier Transform Infrared Spectra (FTIR)

FTIR analysis was performed on hardened cement paste specimens after 28 days of hydration. The infrared wavelength range was 400–4000 c m − 1 , and the resolution was 0.1 c m − 1 .

2.4. Microstructure Characterization (SEM)

Fractured specimens of the hardened paste were oven-dried at 80 °C. Prior to SEM examination, specimens were sputter-coated with gold to ensure electrical conductivity.

2.5. Exothermic Analysis of Hydration

The hydration kinetics of cement pastes with different WEP contents were studied using isothermal calorimetry. Each 25 g sample was tested for 3 days at 20 ± 1 °C. The heat flow and cumulative heat were normalized by the weight of the paste.

2.6. Three-Dimensional Structure Analysis

To investigate the three-dimensional morphology and microstructure of cement paste, polymers, and pore networks, X-ray computed tomography (X-ray CT) analysis was performed on 28-day cured cement paste specimens (2 cm × 2 cm × 2 cm).

2.7. Mechanical Property

2.7.1. Compressive Strength

Prismatic mortar specimens measuring 4 cm × 4 cm × 16 cm were used. The testing procedure followed the standard DL/T 5126-2021 [23] requirements. Compressive strength tests were conducted at the ages of 7 days and 28 days after curing. Five specimens were tested for each mixing ratio at each age. The final results, accurate to 0.01 MPa, were calculated by averaging at least three valid measurements.

2.7.2. Flexural Strength

Prismatic mortar specimens measuring 4 cm × 4 cm × 16 cm were evaluated using a three-point bending test. The testing procedure followed standard DL/T 5126-2021 specifications. Flexural strength tests were performed at the ages of 7 days and 28 days after curing. For each mixing ratio, five specimens underwent flexural strength testing at each age. The final results, accurate to 0.01 MPa, were obtained by averaging at least three valid measurements.

2.7.3. Bonding Strength

The old base mortar used for the positive tensile bond strength test was a 7 cm × 7 cm × 2 cm sample, the size of the repair material poured on the base block was 4 cm × 4 cm × 1 cm, and the size of the bonding surface of the pulling head was a square of 4 cm × 4 cm. The test methods refer to the relevant requirements of the DL/T 5126-2021 standard.
The pressure oblique shear bond strength adopted 4 cm × 4 cm × 16 cm prismatic specimen with a miter shear angle of 30°. The test methods refer to the relevant requirements of the ASTM C882/C882M standard [24]. Both positive tensile bond strength and pressure oblique shear bond strength tests were conducted at the ages of 7 days and 28 days after curing.

2.7.4. Tensile Stress‒Strain Test

In this experimental setup, strain gauges were affixed to specimens to measure strain development during tensile loading. Strain values were recorded using a data acquisition system, while stress was determined from the load measurements of the universal testing machine. The tensile test specimens were prepared using figure-eight-shaped molds with dimensions of 78 mm × 22.5 mm × 22.2 mm. This methodology enabled the generation of tensile stress–strain curves for the water-based polymer-modified cement mortars at the age of 28 days.

2.8. Durability

2.8.1. Carbonation Resistance

The carbonation resistance test of concrete specimens was performed according to the GB/T 50082-2009 standard [25]. Cubic specimens (100 mm × 100 mm × 100 mm) were prepared with three replicates for each group during each carbonation period. The specimens were cured for 28 days prior to testing. The carbonation conditions were maintained at a carbon dioxide concentration of 20 ± 3%, relative humidity of 70 ± 5%, and temperature of 20 ± 2 °C.

2.8.2. Freeze–Thaw Resistance

The freeze–thaw resistance of mortar specimens was evaluated according to the DL/T 5126-2021 Test Procedure for Polymer-Modified Cement Mortar and JG/T 243 [26] Concrete Freeze–Thaw Test Equipment. For each group, three prismatic specimens with dimensions of 40 mm × 40 mm × 160 mm were prepared using triple-gang molds. The specimens were cured under standard conditions for 28 days prior to freeze–thaw testing.
The freeze–thaw cycles were conducted in a programmable environmental chamber (as shown in Figure 5). Each cycle consisted of freezing the specimens in water at −18 ± 2 °C for 2.5 h, followed by thawing in water at 20 ± 2 °C for 1.5 h. A total of 200 freeze–thaw cycles were performed. The specimens were placed in individual containers filled with water to ensure complete immersion during both the freezing and thawing phases. The mass and dynamic elastic modulus of the specimens were measured every 50 cycles to evaluate progressive deterioration.

3. Results and Discussion

3.1. FTIR Analysis

FTIR spectroscopy identifies chemical bonds and functional groups through their characteristic absorption frequencies. This technique enables the analysis of cement hydration modification by waterborne polymers. Figure 6 presents FTIR spectra of WEP-modified cement pastes with varying P/C ratios at 28 days. The FTIR analysis revealed distinct effects of WEP on cement hydration products (CH and C-S-H). However, WEP did not alter the types of the hydration products formed. A sharp absorption band at ~3640 cm−1 corresponds to -OH stretching in C a ( O H ) 2 , while characteristic peaks between 3000 and 2700 cm−1 indicate asymmetric -OH bond stretching in the resin’s organic component. The epoxy groups (C-O-C) from WEP are evidenced by the absorption peak at ~910–920 cm−1, which decreases in intensity as the WEP reacts with cement hydration products. This indicates that the epoxy rings open during the curing process and form covalent bonds with Ca2+ ions and silicate phases. These Ca-O-C bonds (identified at ~1070–1090 cm−1) have binding energies of ~350–400 kJ/mol, significantly stronger than the hydrogen bonds (~20–40 kJ/mol) typically present in conventional cement matrices, contributing to enhanced mechanical properties at optimal WEP content.
The WEP’s amine groups (N-H) from the hardener component, visible at ~3300–3400 cm−1, also participate in the chemical reactions with cement hydration products. These amine groups form coordination complexes with Ca2+ ions from cement, creating Ca-N bonds (~250–300 kJ/mol) that further strengthen the interfacial transition zones. Additionally, the hydroxyl groups generated during epoxy ring-opening reactions form hydrogen bonds with the silicate chains in C-S-H gel, creating a more tightly integrated interpenetrating network structure. At optimal WEP incorporation (10%), these chemical bonds effectively integrate the polymer and cement phases, enhancing load transfer and crack resistance. However, at higher WEP contents, the excessive unreacted polymer molecules and oversaturation of chemical bonding sites lead to discontinuities in the matrix structure and weaken the overall performance.

3.2. SEM and EDS Analysis

Microstructural characterization of WEP-modified cement paste at varying P/C ratios was conducted at 7 and 28 days, as shown in Figure 7. The cement matrix microstructure exhibited progressive refinement with both increasing WEP content and extended curing duration. Control samples at 7 days revealed a relatively porous structure dominated by plate-like C a ( O H ) 2 crystals and gel-like C-S-H hydration products. The incorporation of 10% WEP promoted synergistic growth between needle-like AFT (ettringite) crystals and plate-like C a ( O H ) 2 , resulting in a more homogeneous distribution of hydration products. Samples containing 20% WEP demonstrated enhanced microstructural densification through the extensive formation and uniform distribution of plate-like C a ( O H ) 2 crystals. This refined crystal arrangement significantly improved the material’s mechanical strength and durability [27,28,29].
When the curing time reached 28 days, the C a ( O H ) 2 crystals in the control group became more intact, but the structure remained somewhat loose. In contrast, in the WEP-modified samples, particularly in the marked red box area, an advantageous interfacial transition zone was formed between the resin film and the cement hydration products. The identification of different phases in the microstructure, including the resin film, was confirmed through Energy Dispersive Spectroscopy (EDS) analysis. Figure 8 presents the EDS elemental mapping results of the control and WEP20 samples at 28 days. The WEP20 sample shows distinctive carbon-rich regions corresponding to the polymer resin, which are absent in the control sample. The quantitative elemental analysis (shown in the tables within Figure 8) further confirms this observation, with the WEP20 sample exhibiting a significantly higher carbon content (21.6%) than the control sample (12.3%). This higher carbon concentration is attributed to the organic polymer chains in the WEP. The distribution pattern of carbon-rich areas correlates precisely with the regions identified as resin in the SEM images (Figure 7). The resin effectively filled the pores between the hydration products [30,31,32,33]. When compared to similar polymer-modified cement systems reported by Pang et al. [7], the WEP20 specimens exhibit superior microstructural integration, with fewer microcracks and a more uniform distribution of hydration products. While previous studies showed distinct boundaries between polymer films and hydration products, the optimized WEP formulation creates a more continuous interpenetrating network with virtually seamless transitions between phases. This enhancement in the microstructure indicates that WEP not only optimized the matrix density through physical filling but also interacted with the hydration products owing to its unique chemical properties, forming a more stable composite system. As the WEP content increased from 10% to 20%, this modification effect became more pronounced, which yielded a denser and more homogeneous matrix structure.

3.3. Exothermic Analysis of Hydration

Figure 9 presents the hydration heat results of WEP-modified cement pastes with different P/C ratios. In the heat flow curves (Figure 9a), the control cement paste exhibited the highest heat flow peak (approximately 0.003 W/g) initially, which mainly corresponds to the rapid hydration stage of   C 3 S . With an increasing WEP content (from WEP5 to WEP20), the heat flow peak gradually decreased, and the peak appearance time was slightly delayed. This phenomenon is primarily attributed to the following mechanisms: First, the polymer film formed by the WEP emulsion on the surface of cement particles generates a physical barrier effect, reducing the direct contact probability between water molecules and cement particles. Second, the polymer particles in the WEP emulsion compete with cement particles for free water, decreasing the effective water content participating in the hydration reaction. Furthermore, the functional groups in WEP form complexes with calcium ions during the cement hydration process, altering the formation kinetics of hydration products [34].
From the cumulative heat curves (Figure 9b), during the 72 h hydration process, the control group generated the highest total heat (approximately 170 J/g), while the hydration heat gradually decreased with increasing WEP content. The total heat reduction was most significant in the WEP20 group, which was only approximately 150 J/g. This decreasing trend in hydration heat directly reflects the inhibitory effect of WEP on the cement hydration process, which is not only evident in the early hydration behavior but also continuously affects the later hydration process. In particular, the polymer film formed by WEP not only encapsulates the cement particles but also fills the voids between the hydration products [35,36]. This change in the microstructure affects the diffusion process of ions, thereby altering the kinetic characteristics of cement hydration.

3.4. X-CT and Pore Structure Analysis

Figure 10 presents the three-dimensional CT reconstruction images of WEP-modified cement pastes with different contents at 28 days. From Figure 10a, the cement phase (grey), resin phase (yellow), and their mixed phase display distinctly different spatial distribution characteristics in the WEP10 and WEP20 systems. In the WEP10 system, the cement phase displays a relatively continuous network structure, while the resin phase is more sporadically distributed within the cement matrix, indicating that at lower contents, WEP can effectively form an interpenetrating network structure with the cement matrix. In contrast, the resin phase in the WEP20 system is more densely and uniformly distributed. This difference reflects that higher resin contents significantly modify the microstructural characteristics of the composite material [37].
Further observation of the pore structure distribution in Figure 10b reveals that the WEP content has a significant impact on the pore characteristics of the material. The color coding clearly illustrates the distribution of pores of different sizes, with blue representing smaller pores and red to purple denoting larger pores. Quantitative analysis of pore parameters reveals significant differences between WEP10 and WEP20 systems. The WEP10 sample exhibits pores with more irregular shapes and higher tortuosity, with a lower average pore shape factor. In contrast, the WEP20 sample demonstrates more spherical pores with a higher average shape factor, indicating the polymer’s role in regulating pore geometry during formation.
The pore size distribution range in the WEP10 sample is 0.056–4.126 μm, displaying a more dispersed characteristic, with relatively more large-sized pores (red and purple regions). In contrast, in the WEP20 sample, the pore size range is reduced to 0.027–2.478 μm, with small-sized pores (blue regions) being predominant, indicating that a higher WEP content significantly modifies the pore structure characteristics of the material via a pore-filling mechanism. Pore connectivity analysis further supports these findings, with the WEP20 system showing a substantial reduction in pore connectivity compared to the WEP10 system. This reduced connectivity directly correlates with the enhanced impermeability observed in durability tests. This change in pore structure originates from the film-forming effect of the WEP emulsion during the cement hydration process and its interaction with cement hydration products. The pore-filling mechanism and film-forming behavior of WEP at high WEP incorporation result in a denser microstructure with decreased permeability pathways, which effectively hinders the ingress of aggressive agents such as CO2 and chloride ions, thereby enhancing the long-term durability of the material [38,39,40].

3.5. Mechanical Property Results

3.5.1. Compressive Strength

Figure 11a presents the 7-day and 28-day compressive strength test results of WEP-modified cement mortar specimens with different P/C ratios. As the incorporation of WEP increases, the compressive strength of the specimens demonstrates a notable decline. The control group attained the maximum compressive strength of 60.3 MPa at 28 days, while the compressive strength was reduced to 38.7 MPa when WEP incorporation increased to 20%. This strength reduction is mainly due to the following reasons: First, the polymer particles in the WEP emulsion form a film-like structure on the surface of cement particles, hindering the extent of the cement hydration reaction. Second, the presence of polymers increases the deformation capacity of the material, rendering it more prone to localized deformation during compression. Furthermore, the high incorporation of WEP leads to an increase in internal defects within the material, thereby affecting its load-bearing capacity [41]. To address the challenge of compressive strength reduction at higher WEP contents, potential solutions include incorporating supplementary cementitious materials like silica fume to accelerate hydration, adding small amounts of hydration accelerators to counteract the WEP retarding effect, maintaining an optimal P/C ratio of approximately 0.1 for balanced performance, or developing modified WEP formulations with reduced hydration inhibition properties.

3.5.2. Flexural Strength

Figure 11b shows the 7-day and 28-day flexural strength test results of WEP-modified cement mortar specimens with different P/C ratios. The influence of WEP incorporation on the material demonstrates a trend of an initial increase succeeded by a subsequent decrease. When WEP incorporation is 10%, the 28-day flexural strength reaches a maximum value of 12.9 MPa, which represents an increment of approximately 30% in comparison to the control group’s 9.9 MPa. This reinforcing effect mainly originates from the following mechanisms: the network structure formed by polymers in the material enhances the ductility of the matrix, improving the deformation capacity of the material; simultaneously, the polymer film exhibits excellent crack-bridging ability, effectively preventing the propagation of microcracks [42,43]. However, when WEP incorporation increases further, the excessive polymer phase could result in a discontinuity in the material structure, deteriorating its flexural performance. This phenomenon occurs due to polymer particle agglomeration rather than uniform distribution, creating weak zones within the cement matrix. Excessive WEP significantly retards cement hydration, leading to insufficient formation of load-bearing hydration products. The difference in elastic moduli between polymer-rich regions and cement-rich regions becomes more pronounced, creating stress concentration points under loading. This microstructural discontinuity is evident in the SEM images, where the WEP20 sample at 28 days shows excessive polymer film formation (shown in the red boxes), which interrupts the continuity of the cement hydration network, creating potential weak zones that compromise flexural strength. The use of nano-dispersing agents improves WEP distribution within the cement matrix, while nano-reinforcement materials strengthen the interfacial transition zones between polymer and cement phases.

3.5.3. Bond Strength

Figure 11c presents the 7-day and 28-day positive tensile bond strength test results of WEP-modified cement mortar specimens with different P/C ratios. The introduction of WEP significantly enhances the interfacial bonding performance of the material. The optimal effect occurs at 10% WEP incorporation, with a positive tensile bond strength of 2.13 MPa at 28 days, which is an increase of approximately 58% in comparison to the control group. This reinforcing effect can be attributed to the following points: the active groups (such as epoxy and hydroxyl groups) in WEP can undergo chemical reactions with cement hydration products, forming stronger interfacial bonds; the presence of polymers enhances the microstructure of the interfacial transition zone, minimizing interfacial defects; and the toughness characteristics of polymers also contribute to enhancing the deformation coordination ability of the interface. However, when the incorporation of WEP increases further to 15% and 20%, the positive tensile bond strength demonstrates a decreasing trend, with the 28-day strength being reduced to 1.81 MPa and 1.63 MPa, respectively. This strength reduction is primarily attributed to the increased local structural inhomogeneity caused by the enrichment of excess polymers in the interfacial region, and excessive polymer films also affect the cement hydration process, impeding the development of matrix strength [44,45].
The pressure oblique shear bond strength (Figure 11d) also exhibits an initial increasing trend succeeded by a subsequent decrease with increasing WEP incorporation. At 10% WEP incorporation, the 28-day strength reaches a maximum value of 28.5 MPa, which is an increase of approximately 74% in comparison to the control group. This significant interfacial enhancement effect can be explained as follows: polymer modification enhances the shear deformation capacity of the material; the improvement in interfacial bonding strength enables the material to exhibit better integrity during the shearing process; and simultaneously, the formation of polymer network structure also enhances the stress transfer ability of the material. When WEP incorporation increases to 15% and 20%, the 28-day pressure oblique shear bond strength is reduced to 18.1 MPa and 16.3 MPa, respectively. The strength reduction is primarily ascribed to the increased discontinuity in the interfacial structure caused by excess polymers, as well as the excessive enrichment of polymers at the interface, thereby diminishing the overall shear resistance of the material [46].

3.5.4. Tensile Stress‒Strain Test

Figure 12 presents the 28-day tensile stress–strain curves of cement mortars with different levels of WEP incorporation. From the curve trends, it can be seen that the ultimate strain of the control group is approximately 0.008%. As WEP incorporation increases to 5%, 10%, 15%, and 20%, the corresponding ultimate strain values increase to approximately 0.011%, 0.014%, 0.018%, and 0.024%, demonstrating a significant improvement in the ductility of the material. The quantitative tensile properties extracted from these curves are summarized in Table 6, which clearly presents the tensile strength and ultimate strain values for each mixture. When WEP incorporation gradually increases from 5% to 15%, the peak stress of the mortar demonstrates an increasing trend, suggesting that the introduction of an appropriate amount of WEP can enhance the tensile strength of the material. The slope of the elastic portion of the stress–strain curves shows that with increasing WEP incorporation, the elastic modulus of the material gradually decreases. A lower elastic modulus enables the material to generate a more uniform strain distribution during the loading process, reducing stress concentration [47,48]. This reinforcing effect can be attributed to the synergistic mechanism between WEP and the cement matrix: At the physical level, the polymer film formed by the WEP emulsion during the cement hydration process can fill capillary pores and enhance the bonding strength of the interfacial transition zone, and simultaneously, the flexible chain segments of the polymer molecules endow the material with better deformation capacity. At the chemical level, the epoxy groups in WEP molecules undergo chemical reactions with cement hydration products, forming more stable chemical bonds, thereby improving the overall mechanical properties of the matrix. However, when WEP incorporation reaches 20%, the peak stress of the material decreases, suggesting that excessive WEP interferes with the normal hydration process of cement, causing strength loss. Interestingly, even under high incorporation conditions, the ultimate strain of the material still maintains an increasing trend, suggesting that WEP has a continuous positive effect on improving the toughness of cement-based materials.

3.6. Durability Performance Analysis

3.6.1. Carbonation Resistance

Figure 13 presents the carbonation performance test results of WEP-modified cement mortars at different ages. In Figure 13a, which shows the phenolphthalein indicator color test results, the purple region represents the uncarbonated area, while the colorless region represents the carbonated area. As WEP incorporation increases from 0% to 20%, the purple region gradually expands, suggesting that the carbonation depth gradually decreases. This qualitative observation result is highly consistent with the quantitative test data in Figure 13b: At the age of 56 days, the carbonation depth of the control group reaches approximately 9.5 mm, whereas when WEP incorporation is 5%, 10%, 15%, and 20%, the carbonation depth decreases to approximately 7 mm, 6 mm, 4 mm, and 3 mm, respectively, exhibiting a significant decreasing trend.
From the perspective of time evolution, the carbonation depth of each group of specimens increases with aging, but significant differences exist in the growth rate. The carbonation depths of the control group at 14 days, 28 days, and 56 days are approximately 6.5 mm, 8 mm, and 9.5 mm, respectively, with a relatively fast growth rate. However, when WEP incorporation reaches 20%, the carbonation depths at the corresponding ages are only approximately 0.8 mm, 1.2 mm, and 3 mm, with the carbonation progress being significantly slowed down. This inhibitory effect can be attributed to the dual action mechanism brought about by WEP modification: At the physical level, the dense polymer film formed by WEP in the cement matrix not only fills the capillary pores but also forms a protective layer on the pore wall surface, significantly reducing the permeability of the material, thus effectively hindering the penetration and diffusion of C O 2 . At the chemical level, the epoxy groups in WEP molecules form chemical bonds with cement hydration products. This cross-linked network structure, on the one hand, enhances the compactness of the matrix, and on the other hand, reduces the dissolution of C a ( O H ) 2 through chemical bonding, thereby inhibiting the carbonation reaction from the source [49,50].
When compared to alternative modification approaches, WEP demonstrates superior carbonation resistance over traditional methods such as limy fly ash or ultrafine fly ash addition. While fly ashes improve carbonation resistance primarily through pozzolanic reactions that depend on their fineness and substitution ratio, WEP provides more comprehensive protection through its dual mechanism. The continuous polymer film physically blocks CO2 penetration, while chemical interactions with hydration products create a more stable interfacial structure. Similarly, for resistance against aggressive environments, WEP creates a more effective impermeable barrier than what can be achieved through pozzolanic materials alone.

3.6.2. Freeze–Thaw Resistance

Figure 14 presents the freeze–thaw cycle performance test results of cement mortars with different levels of WEP incorporation. From the apparent morphology in Figure 14a, with an increase in freeze–thaw cycles, the surface of the control group specimens exhibits obvious spalling and damage, while the surface integrity of the WEP-modified specimens, especially in the high-incorporation group, is maintained relatively well [51]. This phenomenon is quantitatively verified by the mass change rate data in Figure 14b: after 200 freeze–thaw cycles, the mass loss rate of the control group reaches approximately 15%, while with an increase in WEP incorporation, mass loss significantly decreases. When WEP incorporation reaches 20%, the mass change rate is only around 4%. Interestingly, in the initial stage of freeze–thaw cycles (50 cycles), the WEP-modified specimens exhibit a slight increase in mass. This is mainly because during the freeze–thaw process, water gradually penetrates the internal pores under the repeated freeze–thaw action, and the network structure formed after polymer modification and the improved pore structure facilitate water storage. The dynamic elastic modulus change rate shown in Figure 14c further confirms the significant effect of WEP modification on improving the freeze–thaw resistance of cement mortar.
As shown in Table 7, specimens with a higher WEP content demonstrate significantly better retention of mechanical properties after freeze–thaw exposure. While the control group retained only 58% of its initial compressive strength and 51% of its initial flexural strength, the WEP20 specimens retained 85% and 87%, respectively. Interestingly, despite having lower initial compressive strength, the WEP15 and WEP20 specimens exhibited comparable or even higher residual compressive strength after 200 freeze–thaw cycles compared to specimens with lower WEP content. This enhanced freeze–thaw resistance can be attributed to the polymer network’s ability to absorb volumetric stresses during freezing and thawing, as well as its pore-refining effect, which reduces water penetration and subsequent damage.
After 200 cycles, the dynamic elastic modulus of the control group decreases by approximately 22%, whereas when WEP incorporation is 5%, 10%, 15%, and 20%, the reduction in dynamic elastic modulus decreases to approximately 14%, 10%, 4%, and 2%, respectively. This performance improvement can be attributed to the three-dimensional network structure formed by WEP in the cement matrix: the polymer film not only fills the capillary pores, thus reducing the water permeability of the material, but also absorbs the volumetric stress during the freeze–thaw process through its good elastic deformation ability, effectively alleviating the internal stress concentration. In addition, the chemical bonding formed between WEP molecules and cement hydration products improves the overall toughness of the material, enabling it to better adapt to the repeated stress caused by freeze–thaw cycles [52,53].

4. Summary and Conclusions

Based on molecular structure–activity relationships, a novel waterborne epoxy–cement-based composite repair material was developed and systematically investigated. The key findings are as follows:
(1)
The WEP forms a cross-linked network with cement hydration products, significantly refining pore structure, improving material toughness, and retarding cement hydration.
(2)
Optimal mechanical performance was achieved at 10% WEP incorporation, with a 28-day flexural strength of 12.9 MPa (30% increase over control) and a tensile strain capacity of 0.024% (compared to 0.008% for control), demonstrating substantially enhanced material flexibility.
(3)
The bond strength improvement (58% increase in tensile bond strength and 74% increase in shear bond strength at 10% WEP) results from the polymer’s high viscosity and chemical interaction between epoxy groups and cement hydration products. The covalent Ca-O-C bonds formed at the interface provide stronger connection points than physical adhesion alone, while coordination bonds between amine groups and calcium ions create chemical anchoring points that enhance structural integrity during loading.
(4)
WEP significantly enhanced durability, with the carbonation depth at 56 days reduced from 9.5 mm to 3 mm at 20% WEP incorporation and mass loss after 200 freeze–thaw cycles reduced from 15% to 4%.
From a practical applicability perspective, the WEP-modified repair material demonstrates favorable cost-effectiveness despite 15–20% higher initial costs compared to conventional cement-based materials. The extended service life significantly reduces life cycle costs. WEP synthesis employs readily available raw materials and conventional equipment, making industrial production feasible. With the optimal 10% WEP incorporation resulting in a balance between performance and economics and with application procedures being similar to traditional methods, without the requirement for specialized equipment, this material offers a practical and economically viable solution for concrete repair.
Future research should focus on optimizing the molecular structure for enhanced long-term durability in aggressive environments, investigating synergistic effects with supplementary cementitious materials, developing service life prediction models, and conducting field implementation studies to further validate the practical applications of these novel repair materials.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/buildings15070997/s1, Figure S1: The reaction equation of the intermediate product LHD-i prepared by E51 and M1000; Figure S2: The reaction equation of LHD-i and TETA end-capping to form LHD; Figure S3: The reaction equation for the synthesis of the intermediate segment SBP-i through the amine exchange reaction through thermal elimination; Figure S4: The reaction equation for the synthesis of SBP-ii by the catalytic addition reaction of E51 and PEG with boron trifluoride ether; Figure S5: The reaction equation of the central star-shaped molecule SBP-i grafted with the side chain SBP-ii to prepare SBP; Figure S6: The apparent photos of prepared part B of WEP after standing for 1 min (a) and 1 day (b); Table S1: The main chemicals used for preparing WEP; Table S2: Properties of WEP.

Author Contributions

F.W.: Writing—review and editing, Visualization, Methodology, Investigation, Formal analysis, Data curation, and Conceptualization. Y.Z.: Writing—review and editing, Resources, Methodology, Funding acquisition, Formal analysis, and Conceptualization. X.S. (Xiaoyun Song): Writing—review and editing, Methodology, Funding acquisition, and Formal analysis. L.L.: Writing—review and editing, Project administration, Methodology, Investigation, and Conceptualization. X.S. (Xianglin Sun): Investigation, Data curation, and Conceptualization. P.S.: Investigation, Data curation, and Conceptualization. All authors have read and agreed to the published version of the manuscript.

Funding

The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (No. 52478260).

Data Availability Statement

The data presented in this study are contained within the article and Supplementary Materials.

Conflicts of Interest

Author Lirong Liu was employed by the company China Bluestar Chengrand (Chengdu)Testing Technology Co., Ltd. Author Peifeng Sun was employed by the company Qingdao Zhonghui Qing Industrial Development Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Zhang, X.L. Study on the Protective Performance of Concrete Coating Under the Action of Marine Environment. Master’s Thesis, Qingdao University of Technology, Qingdao, China, 2016. [Google Scholar]
  2. Jin, Z.; Li, M.; Pang, B.; Yang, L.; Chen, Y.; Wang, D. Internal superhydrophobic marine concrete: Interface modification based on slag microstructure regulation. J. Build. Eng. 2024, 86, 108769. [Google Scholar] [CrossRef]
  3. Guo, S.-Y.; Zhang, X.; Chen, J.-Z.; Mou, B.; Shang, H.-S.; Wang, P.; Zhang, L.; Ren, J. Mechanical and interface bonding properties of epoxy resin reinforced Portland cement repairing mortar. Constr. Build. Mater. 2020, 264, 120715. [Google Scholar] [CrossRef]
  4. U.S. Department of Transportation, Federal Highway Administration. Chapter 7—Capital Investment Scenarios—Highways. In Status of the Nation’s Highways, Bridges, and Transit Conditions and Performance Report, 23rd ed.; U.S. DOT: Washington, DC, USA, 2021. [Google Scholar]
  5. Pang, B.; Zhou, Z.; Hou, P.; Du, P.; Zhang, L.; Xu, H. Autogenous and engineered healing mechanisms of carbonated steel slag aggregate in concrete. Constr. Build. Mater. 2016, 107, 191–202. [Google Scholar] [CrossRef]
  6. Pang, B.; Zhou, Z.; Xu, H. Utilization of carbonated and granulated steel slag aggregate in concrete. Constr. Build. Mater. 2015, 84, 454–467. [Google Scholar] [CrossRef]
  7. Pang, B.; Yang, C.; Wang, P.; Tian, L.; Mei, B.; Song, X. Cement-based ductile rapid repair material modified with self-emulsifying waterborne epoxy. J. Build. Eng. 2023, 79, 107864. [Google Scholar] [CrossRef]
  8. Sun, C.; Liu, H.; Liu, L.; Zhao, P.; Huang, Y.; Lu, L. Effect of polymer to cement ratio on seawater corrosion resistance of polymer modified cementitious coatings. In Proceedings of the 2018 IEEE International Conference on Advanced Manufacturing (ICAM), Yunlin, China, 16–18 November 2018; pp. 451–454. [Google Scholar]
  9. Wang, R.; Xu, Y.D. Effect of curing temperature on the physical and mechanical properties of styrene butadienzene emulsionthioaluminate cement mortar. J. Chin. Ceram. Soc. 2017, 45, 227–234. [Google Scholar]
  10. Yang, Z.; Zhang, X.; Liu, X.; Guan, X.; Zhang, C.; Niu, Y. Flexible and stretchable polyurethane/waterglass grouting material. Constr. Build. Mater. 2018, 138, 240–246. [Google Scholar] [CrossRef]
  11. Fan, J.; Li, G.; Deng, S.; Deng, C.; Wang, Z.; Zhang, Z. Effect of Carbon Nanotube and Styrene-Acrylic Emulsion Additives on Microstructure and Mechanical Characteristics of Cement Paste. Materials 2020, 13, 2807. [Google Scholar] [CrossRef]
  12. Pang, B.; Zhang, Y.; Liu, G. Study on the effect of waterborne epoxy resins on the performance and microstructure of cement paste. Constr. Build. Mater. 2018, 167, 831–845. [Google Scholar] [CrossRef]
  13. Pang, B. Study on the Design, Preparation and Mechanism of Water-Based Epoxy-Concrete Composite Repair Materials. Ph.D. Thesis, Southeast University, Nanjing, China, 2021. [Google Scholar]
  14. Ying, G.-G.; Song, C.; Ren, J.; Guo, S.-Y.; Nie, R.; Zhang, L. Mechanical and durability-related performance of graphene/epoxy resin and epoxy resin enhanced OPC mortar. Constr. Build. Mater. 2021, 282, 122644. [Google Scholar] [CrossRef]
  15. Popvics, S.; Tamas, F. Investigation on Portland cement pastes and mortars modified by the addition of epoxy. Spec. Publ. 1978, 58, 357–366. [Google Scholar]
  16. Beeldens, A.; Van Gemert, D.; Schorn, H.; Ohama, Y.; Czarnecki, L. From microstructure to macrostructure: An integrated model of structure formation in polymer-modified concrete. Mater. Struct. 2005, 38, 601–607. [Google Scholar]
  17. Liu, J.; Farzadnia, N.; Shi, C. Effects of superabsorbent polymer on interfacial transition zone and mechanical properties of ultra-high performance concrete. Constr. Build. Mater. 2020, 231, 117142. [Google Scholar]
  18. Zhang, Z.; Zhang, H.; Lv, W.; Zhang, J.; Wang, N. Micro-structure characteristics of unsaturated polyester resin modified concrete under fatigue loads and hygrothermal environment. Constr. Build. Mater. 2021, 296, 123766. [Google Scholar]
  19. Wang, M.; Wang, R.; Yao, H.; Farhan, S.; Zheng, S.; Wang, Z.; Du, C.; Jiang, H. Research on the mechanism of polymer latex modified cement. Constr. Build. Mater. 2016, 111, 710–718. [Google Scholar]
  20. Betioli, A.; Filho, J.H.; Cincotto, M.; Gleize, P.; Pileggi, R. Chemical interaction between EVA and Portland cement hydration at early-age. Constr. Build. Mater. 2009, 23, 3332–3336. [Google Scholar]
  21. Li, P.; Jiang, Z.; An, X.; Maekawa, K.; Du, S. Time-dependent retardation effect of epoxy latexes on cement hydration: Experiments and multi-component hydration model. Constr. Build. Mater. 2022, 320, 126282. [Google Scholar] [CrossRef]
  22. Zheng, Z.; Li, Y.; He, S.; Ma, X.; Zhu, X.; Li, S. High density and high strength cement-based mortar by modification with epoxy resin emulsion. Constr. Build. Mater. 2019, 197, 319–330. [Google Scholar] [CrossRef]
  23. DL/T 5126-2021; Technical Specification for Polymer Modified Cement Mortar. China Electricity Council: Beijing, China, 2021.
  24. ASTM C882/C882M; Standard Test Method for Bond Strength of Epoxy-Resin Systems Used with Concrete By Slant Shear. ASTM International: West Conshohocken, PA, USA, 2020.
  25. GB/T 50082-2009; Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete. Ministry of Housing and Urban-Rural Development of the People’s Republic of China: Beijing, China, 2009.
  26. JG/T 243; Technical Specification for Concrete Freeze-Thaw Test Equipment. Ministry of Housing and Urban-Rural Development of the People’s Republic of China: Beijing, China, 2009.
  27. Hou, D.; Yu, J.; Wang, P. Molecular dynamics modeling of the structure, dynamics, energetics and mechanical properties of cement-polymer nanocomposite. Compos. Part B Eng. 2019, 162, 433–444. [Google Scholar]
  28. Hua, W.D.; Jiang, H.Y.; Zhou, Z.X. Research on Nitric Acid Corrosion Resistance of Latex Modified Ordinary Portland Cement Mortar. Adv. Mater. Res. 2012, 485, 262–265. [Google Scholar] [CrossRef]
  29. Xu, A.; Zhang, J.L.; Zeng, L. Research status and prospects of polymeric grouting material. Concrete 2014, 10, 141–144. [Google Scholar]
  30. Ukrainczyk, N.; Rogina, A. Styrene–butadiene latex modified calcium aluminate cement mortar. Cem. Concr. Compos. 2013, 41, 16–23. [Google Scholar]
  31. Wong, W.G.; Fang, P.; Pan, J.K. Dynamic properties impact toughness and abrasiveness of polymer-modified pastes by using nondestructive tests. Cem. Concr. Res. 2003, 33, 1371–1374. [Google Scholar]
  32. Zhang, C.; Kong, X.; Yu, J.; Jansen, D.; Pakusch, J.; Wang, S. Correlation between the adsorption behavior of colloidal polymer particles and the yield stress of fresh cement pastes. Cem. Concr. Res. 2022, 152, 106668. [Google Scholar]
  33. Pang, B.; Zhou, Z.; Cheng, X.; Du, P.; Xu, H. ITZ properties of concrete with carbonated steel slag aggregate in salty freeze-thaw environment. Constr. Build. Mater. 2016, 114, 162–171. [Google Scholar]
  34. Kong, X.; Emmerling, S.; Pakusch, J.; Rueckel, M.; Nieberle, J. Retardation effect of styrene-acrylate copolymer latexes on cement hydration. Cem. Concr. Res. 2015, 75, 23–41. [Google Scholar]
  35. Taylor, H.F.W. Cement Chemistry, 2nd ed.; Thomas Telford Publishing: London, UK, 1997. [Google Scholar]
  36. Chen, B.; Qiao, G.; Hou, D.; Wang, M.; Li, Z. Cement-based material modified by in-situ polymerization: From experiments to molecular dynamics investigation. Compos. Part B Eng. 2020, 194, 108036. [Google Scholar] [CrossRef]
  37. Kim, J.H.; Robertson, R.E.; Naaman, A.E. Structure and properties of poly(vinyl alcohol)-modified mortar and concrete. Cem. Concr. Res. 1999, 29, 407–415. [Google Scholar] [CrossRef]
  38. Kim, J.H.; Robertson, R.E. Prevention of air void formation in polymer-modified cement mortar by pre-wetting. Cem. Concr. Res. 1997, 27, 171–176. [Google Scholar]
  39. Shi, C.; Zou, X.; Wang, P. Influences of ethylene-vinyl acetate and methylcellulose on the properties of calcium sulfoaluminate cement. Constr. Build. Mater. 2018, 193, 474–480. [Google Scholar] [CrossRef]
  40. Fang, X.; Chen, Z.; Jiao, Z.; Xiao, G.; Shao, L. Study on microstructure, rheology and thermal stability of cement epoxy asphalt mortar multiphase materials. Mag. Concr. Res. 2013, 65, 475–485. [Google Scholar] [CrossRef]
  41. Li, L.; Wang, R.; Lu, Q. Influence of polymer latex on the setting time, mechanical properties and durability of calcium sulfoaluminate cement mortar. Constr. Build. Mater. 2018, 169, 911–922. [Google Scholar] [CrossRef]
  42. Knapen, E.; Van Gemert, D. Polymer film formation in cement mortars modified with water-soluble polymers. Cem. Concr. Compos. 2015, 58, 23–28. [Google Scholar] [CrossRef]
  43. Gwon, S.; Jang, S.Y.; Shin, M. Microstructure evolution and strength development of ultra rapid hardening cement modified with redispersible polymer powder. Constr. Build. Mater. 2018, 192, 715–730. [Google Scholar] [CrossRef]
  44. Bi, J.X. Study on the Design, Preparation and Performance of Waterborne Polyurethane-Cement-Based Composite Repair Materials. Master’s Thesis, Southeast University, Nanjing, China, 2022. [Google Scholar]
  45. Albidah, A.; Abadel, A.; Alrshoudi, F.; Altheeb, A.; Abbas, H.; Al-Salloum, Y. Bond strength between concrete substrate and metakaolin geopolymer repair mortars at ambient and elevated temperatures. J. Mater. Res. Technol. 2020, 9, 10732–10745. [Google Scholar] [CrossRef]
  46. Sadrmomtazi, A.; Khoshkbijari, R.K. Determination and Prediction of Bonding Strength of Polymer Modified Concrete (PMC) as the Repair Overlay on the Conventional Concrete Substrate. KSCE J. Civ. Eng. 2019, 23, 1141–1149. [Google Scholar] [CrossRef]
  47. Wang, R.; Wang, P. Function of styrene-acrylic ester copolymer latex in cement mortar. Mater. Struct. 2009, 43, 443–451. [Google Scholar] [CrossRef]
  48. Shi, C.; Zou, X.; Yang, L.; Wang, P.; Niu, M. Influence of humidity on the mechanical properties of polymer-modified cement-based repair materials. Constr. Build. Mater. 2020, 261, 119928. [Google Scholar] [CrossRef]
  49. Li, H.; Ni, D.; Liang, G.; Guo, Y.; Dong, B. Mechanical performance and microstructure of cement paste/mortar modified by VAEC dispersible powder cured under different temperatures. Constr. Build. Mater. 2021, 278, 122446. [Google Scholar] [CrossRef]
  50. Pang, B.; Jia, Y.; Zhang, Y.; Ni, H.; Liu, G.; She, W.; Yang, L.; Qian, R. Effect of the combined treatment with inorganic and organic agents on the surface hardening and adhesion properties of cement-based materials. Mater. Des. 2019, 169, 107673. [Google Scholar] [CrossRef]
  51. Shaker, F.; El-Dieb, A.; Reda, M. Durability of Styrene-Butadiene latex modified concrete. Cem. Concr. Res. 1997, 27, 711–720. [Google Scholar] [CrossRef]
  52. Wang, M.; Wang, R.; Zheng, S.; Farhan, S.; Yao, H.; Jiang, H. Research on the chemical mechanism in the polyacrylate latex modified cement system. Cem. Concr. Res. 2015, 76, 62–69. [Google Scholar] [CrossRef]
  53. Shen, A.; Lin, S.; Guo, Y.; He, T.; Lyu, Z. Relationship between flexural strength and pore structure of pavement concrete under fatigue loads and Freeze-thaw interaction in seasonal frozen regions. Constr. Build. Mater. 2018, 174, 684–692. [Google Scholar] [CrossRef]
Buildings 15 00997 g001
Figure 1. Particle size distribution of the Type 42.5 ordinary silicate cement.
Figure 1. Particle size distribution of the Type 42.5 ordinary silicate cement.
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Figure 2. Particle size distribution of river sand showing the percentage passing through each sieve size.
Figure 2. Particle size distribution of river sand showing the percentage passing through each sieve size.
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Figure 3. Schematic diagram of the molecular configuration and chain link function of the final products, i.e., WEP-A and WEP-B.
Figure 3. Schematic diagram of the molecular configuration and chain link function of the final products, i.e., WEP-A and WEP-B.
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Buildings 15 00997 g004
Figure 4. Water-based epoxy-modified repair mortar mixing process.
Figure 4. Water-based epoxy-modified repair mortar mixing process.
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Figure 5. Programmable environmental chamber used for freeze–thaw testing.
Figure 5. Programmable environmental chamber used for freeze–thaw testing.
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Figure 6. FTIR spectra of WEP-modified cement paste samples with different P/C ratios at 28 days of curing.
Figure 6. FTIR spectra of WEP-modified cement paste samples with different P/C ratios at 28 days of curing.
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Figure 7. SEM micrographs of cement paste modified with different WEP contents at 7 and 28 days of curing.
Figure 7. SEM micrographs of cement paste modified with different WEP contents at 7 and 28 days of curing.
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Buildings 15 00997 g008
Figure 8. EDS elemental mapping results of control and WEP20 samples at 28 days.
Figure 8. EDS elemental mapping results of control and WEP20 samples at 28 days.
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Figure 9. Hydration heat results of WEP–cement paste with different P/C ratios: (a) heat flow and (b) total heat.
Figure 9. Hydration heat results of WEP–cement paste with different P/C ratios: (a) heat flow and (b) total heat.
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Figure 10. CT reconstruction images of WEP–cement paste with different P/C ratios after 28 days of hardening: (a) distribution of cement phase, resin phase, and mixture phase and (b) distribution of pore structure.
Figure 10. CT reconstruction images of WEP–cement paste with different P/C ratios after 28 days of hardening: (a) distribution of cement phase, resin phase, and mixture phase and (b) distribution of pore structure.
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Figure 11. Mechanical properties of WEP-modified cement mortar with different P/C ratios: (a) compressive strength; (b) flexural strength; (c) positive tensile bond strength; and (d) pressure oblique shear bond strength.
Figure 11. Mechanical properties of WEP-modified cement mortar with different P/C ratios: (a) compressive strength; (b) flexural strength; (c) positive tensile bond strength; and (d) pressure oblique shear bond strength.
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Figure 12. Tensile stress–strain curves of cement mortars with different WEP contents at 28 days.
Figure 12. Tensile stress–strain curves of cement mortars with different WEP contents at 28 days.
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Figure 13. Carbonation performance of cement mortars with different WEP contents: (a) phenolphthalein test results at different ages and (b) carbonation depth development.
Figure 13. Carbonation performance of cement mortars with different WEP contents: (a) phenolphthalein test results at different ages and (b) carbonation depth development.
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Figure 14. Freeze–thaw resistance of cement mortars with different WEP contents: (a) appearance after different freeze–thaw cycles; (b) mass change rate; and (c) dynamic modulus change rate.
Figure 14. Freeze–thaw resistance of cement mortars with different WEP contents: (a) appearance after different freeze–thaw cycles; (b) mass change rate; and (c) dynamic modulus change rate.
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Table 1. Chemical composition of the cement (% wt.).
Table 1. Chemical composition of the cement (% wt.).
CaOSiO2Al2O3Fe2O3MgO K 2 O Na2O S O 3 LOI
49.2726.3610.624.493.241.270.532.013.71
Table 2. Physical properties of the polycarboxylic acid superplasticizer.
Table 2. Physical properties of the polycarboxylic acid superplasticizer.
PropertyAppearanceSolid ContentBulk DensitypH Value (20% Solution)Chloride Ion Content
ValueWhite powder≥99%0.40–0.60 g/cm37–90.02–0.25%
Table 3. Physical properties of the natural river sand.
Table 3. Physical properties of the natural river sand.
PropertyBulk Density (kg/m3)Apparent Density (kg/m3)Void Ratio (%)Fineness ModulusGrading Zone
Value14502660432.69Zone II
Table 4. Properties of polymers and hardeners.
Table 4. Properties of polymers and hardeners.
Polymer TypeExteriorSolid Content (%)Viscosity (mPa·s)pH ValueDensity (g/cm3)
WEP-AMilky liquid5011057.81.1~1.0
WEP-BPale yellow liquid509009.41.0
Table 5. Water-based epoxy–cement mortar mixture.
Table 5. Water-based epoxy–cement mortar mixture.
Mark Polymer-to-Cement Ratio (P/C)Water-to-Cement Ratio (W/C)Cement-to-Sand Ratio (C/S)Superplasticizer Dosage (SP/%)
WEP000.310.50.05
WEP50.050.310.50.05
WEP100.10.310.50.05
WEP150.150.310.50.05
WEP200.20.310.50.05
Table 6. Tensile properties of cement mortars with different WEP contents at 28 days.
Table 6. Tensile properties of cement mortars with different WEP contents at 28 days.
Mixture Tensile Strength (MPa)Ultimate Strain (%)
Control3.70.008
WEP54.00.011
WEP104.20.014
WEP154.50.018
WEP203.20.024
Table 7. Residual mechanical properties after 200 freeze–thaw cycles.
Table 7. Residual mechanical properties after 200 freeze–thaw cycles.
Mixture Initial Compressive Strength (MPa)Residual Compressive Strength (MPa)Retention Rate (%)Initial Flexural Strength (MPa)Residual Flexural Strength (MPa)Retention Rate (%)
WEP060.335.0589.95.051
WEP548.330.46310.76.662
WEP1045.232.57212.910.178
WEP1542.634.18010.18.180
WEP2038.732.9859.28.087
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Wang, F.; Zhang, Y.; Song, X.; Liu, L.; Sun, X.; Sun, P. Influence of Self-Emulsifying Waterborne Epoxy Resin with Novel Hardeners on Pore Structure and Permeability of Cement-Based Materials. Buildings 2025, 15, 997. https://doi.org/10.3390/buildings15070997

AMA Style

Wang F, Zhang Y, Song X, Liu L, Sun X, Sun P. Influence of Self-Emulsifying Waterborne Epoxy Resin with Novel Hardeners on Pore Structure and Permeability of Cement-Based Materials. Buildings. 2025; 15(7):997. https://doi.org/10.3390/buildings15070997

Chicago/Turabian Style

Wang, Feifei, Yunsheng Zhang, Xiaoyun Song, Lirong Liu, Xianglin Sun, and Peifeng Sun. 2025. "Influence of Self-Emulsifying Waterborne Epoxy Resin with Novel Hardeners on Pore Structure and Permeability of Cement-Based Materials" Buildings 15, no. 7: 997. https://doi.org/10.3390/buildings15070997

APA Style

Wang, F., Zhang, Y., Song, X., Liu, L., Sun, X., & Sun, P. (2025). Influence of Self-Emulsifying Waterborne Epoxy Resin with Novel Hardeners on Pore Structure and Permeability of Cement-Based Materials. Buildings, 15(7), 997. https://doi.org/10.3390/buildings15070997

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