Search Results (241)

The growing demand for eco-efficient construction materials has driven the development of low-clinker cement systems incorporating recycled mineral additives. Finely ground brick powder represents one of such materials with high pozzolanic potential. This article presents an experimental study on the effect of partially replacing slag cement CEM III and ordinary rapid-hardening cement CEM I with brick powder waste of different chemical compositions and fineness levels (63, 32, and 15 µm) on the physical and mechanical properties of blended cement mortars. Compressive and flexural strengths were determined at 2, 7, and 28 days, along with the strength activity index (SAI). Additionally, the setting times and standard consistency were investigated, with the latter showing a correlation with the workability of fresh mortars. Comprehensive microstructural analysis (TGA, SEM, EDX) confirmed the pozzolanic activity of the brick powder, which was manifested by the formation of C-S-H and C-A-S-H phases. The highest strength characteristics were achieved with a 15% replacement of cement by brick powder with a fineness of 32 μm and an increased SiO₂ content (63.06%). Comparative analysis with fly ash- and silica fume-modified mortars revealed that brick powder exhibits comparable performance, confirming its suitability as an active mineral additive. Full article

Artificial aggregates (AAs) are man-made construction materials, and their properties greatly depend on their manufacturing process (e.g., granulation and hardening) and the raw materials used. The conducted research aimed to determine the most advantageous composition of artificial aggregates prepared based on three wastes simultaneously: municipal waste incineration ash (MWIA), sediment from the bottom of a water reservoir (SBWR), recycled cement mortar (RCM)- which was the main waste. A production process of such aggregates was also developed, with the setting of the hardening temperature (20 °C, 200 °C, 400 °C). The X-ray diffractometry (XRD), differential thermal analysis (DTA), and thermogravimetry analysis (TGA) were used to characterize the waste. Then, the properties of cementitious composites prepared with artificial aggregate with the best strength parameters of 0–100% of the natural aggregate were determined. Carbon footprint calculations were performed for the production of artificial aggregate, depending on its composition and for cementitious composites. Full article

This paper investigates the printability and mechanical properties of 3D printed construction mortar (3DPCM) through the methods of vacuum dewatering and carbonation mixing, wherein flowability and extrudability serve as critical indicators of mortar printability. The results demonstrate that for mortar with a low water-to-binder ratio, both carbonation mixing and vacuum dewatering significantly reduce its rheological properties. Although a reduction in rheological performance is also observed in mortar with a high water-to-binder ratio by 7%, the effect is less pronounced. Furthermore, either carbonation mixing or vacuum dewatering effectively enhances printability, enabling highly flowable mortar to exhibit favorable printing performance while also markedly accelerating the hardening rate, thereby improving the shape retention of printed specimens. Additionally, the compressive strength can be enhanced by 4.1–4.6%. The printing process incorporating carbonation mixing or vacuum dewatering can enhance the interlayer bonding strength of mortar with high flowability; however, when both methods are applied simultaneously, the interlayer strength may decrease due to excessively rapid hardening. The final results indicate that vacuum dewatering and carbonation mixing can effectively improve the printability and buildability of more fluid mortar, providing feasibility for directly applying a wider range of mix proportions in printer-based manufacturing. Full article

Polymer modification is a widely employed technique for optimizing specific properties of mortars and concretes. This process entails the precise tailoring of the binder phase to the requirements of the given application. The polymer addition exerts a significant influence on both the fresh and hardened states of mortar or concrete. In this study, a systematic, stepwise experimental campaign was carried out to investigate the effects of three different polymer dispersions on the time-dependent properties of cement pastes, mortars, and concretes at different temperatures in the service temperature range. The experimental findings demonstrate that polymer modifications significantly influence the behavior of hardened cement-based materials. In general, the strength and deformation resistance decreased with increasing temperature, with this effect being more pronounced in polymer-modified materials. This is indicative of the intrinsic temperature-dependent behavior of the polymers. Temperatures of −20 °C induced specific alterations in the mechanical behavior, particularly evident in the flexural strength and in the early age stiffness development of the pastes, mortars, and concretes. This phenomenon is attributed to the freezing of pore water, which results in the stiffening of the binder structure. In summary, the findings offer significant insights into the structure–property relationships of polymer-modified cement-based materials in relation to temperature. Full article

The growing generation of solid waste, driven by urbanization and industrialization, represents one of today’s greatest environmental challenges. The construction industry can play a key role in this scenario by incorporating recycling and waste reuse practices. Glass, a fully recyclable material, is still largely disposed of in landfills. A promising alternative is the use of ground glass in cementitious materials, partially or completely replacing cement or aggregates. Thus, in this paper, the effect of partially replacing Portland cement with ground glass of different colors including green, blue, transparent, amber, and colorful (all colors used mixed) in proportions of 15 and 35% in mortars was evaluated. The ground glasses were characterized by laser granulometry and chemical analysis. The properties of the mortars were then evaluated in the fresh and hardened state (apparent specific gravity, mechanical strength, water absorption, and open porosity). Regarding workability, the highest improvement observed was 6.8% for the 35% colored glass series compared to the reference series. In terms of entrapped air, there was an increase of up to 18.8% in the 35% green glass series. At 28 days of hydration, the 15% colored glass series obtained a 33% increase in flexural strength compared to the REF series. In the microstructure, it was found that a 15% glass presence was sufficient to reduce the portlandite index from 16.04 to 13.53, while a 35% glass presence was sufficient to reduce it to 7.51% portlandite, equivalent to a 54% reduction, suggesting significant potential for the reaction of the finer glass fractions with portlandite. This study suggests that the use of glass waste in a cementitious matrix can provide an environmentally appropriate alternative for recycling this material, contributing to a sustainable application and increased recycling rates of glass waste. Full article

With the increasing application of manufactured sand, as one of the uncertain factors affecting the properties and performance of ready-mixed concrete proportioning with commonly used manufactured sand, residual flocculants in water-washed manufactured sand (WWMS) have received increased attention. Under certain prerequisites, a rapid detecting method for residual flocculants in WWMS was presented based on the pre-calibrated relationship between the Stormer viscosity of cement paste and the concentration of flocculants. Multi-dimensional and multi-factorial experiments were performed on cement paste, mortar and concrete orderly to explore the effects of flocculant content on the rheological (workability) and mechanical properties (compressive strength) of concrete. The results showed a good quantitative relationship between the Stormer viscosity and the flocculant content, and its mathematical formula depended on the type, molecular weight and content range of the flocculant. The residual flocculant contents in WWMS not only affected the workability of fresh concrete, but also the strength of hardened concrete to some extent. Full article

Three-dimensional concrete printing (3DCP) is rapidly emerging as a transformative construction technology, enabling formwork-free fabrication, geometric flexibility, and reduced labour. However, the lack of conventional reinforcement and the strict requirements for fresh and hardened properties present significant challenges. Fibre reinforcement and supplementary cementitious materials (SCMs), such as ground granulated blast furnace slag (GGBS), offer pathways to enhance printability while mitigating environmental impact. This study investigates the combined effect of natural cellulose microfibres and silica fume on the rheological, mechanical, and sustainability performance of 3D-printable mortars. Six mixes were prepared with 50% GGBS, 45% cement, and 5% silica fume, incorporating fibre dosages from 0% to 1%. Results showed that a 0.5% fibre dosage provided the most favourable balance. At this dosage, static yield stress increased to 9.35 Pa and thixotropy reached 8623 mPa·s, enhancing structuration for shape retention. Plastic viscosity remained stable at 4–5 Pa·s, ensuring adequate extrusion performance. Higher fibre dosages (≥0.75%) caused a significant increase in rheological resistance, with static yield stress reaching 208 Pa and thixotropy 135,342 mPa·s. This resulted in excessive structuration, fibre clustering, and poor extrudability. Compressive strength was achieved at 109.10 MPa (92% of silica fume-only mix) with 0.5% fibre. In comparison, flexural strength was 13.20 MPa at 0.5% fibre content and reduced gradually to 12.29 MPa at 1% fibre due to weak fibre–matrix bonding and porosity. Sustainability analysis confirmed that using 50% GGBS and 5% silica fume reduced embodied carbon compared to a 100% cement mix. This study also demonstrated that cellulose microfibres at 0.25–0.5% are optimal for balancing fresh properties, mechanical strength, and sustainability in 3D-printed mortars. Full article

This study presents a rigorous experimental and numerical investigation of the synergistic effect of metakaolin (MK) and waste glass (WG) on the structural performance of reinforced concrete (RC) beams without stirrups. A two-phase methodology was adopted: (i) optimization of MK and WG replacement levels through concrete-equivalent mortar mixtures and (ii) evaluation of the fresh and hardened properties of concrete, including compressive and tensile strengths, elastic modulus, sorptivity, and beam shear capacity. Five beam groups incorporating up to 30% MK, 15% WG, and 1% steel fiber were tested under four-point bending. The results demonstrated that MK enhanced compressive strength (up to 22%), WG improved workability but reduced ductility, and the combined system achieved a 13% increase in shear strength relative to the control. Steel fibers further restored ductility, increasing the ductility index from 1.338 for WG-only beams to 2.489. Finite Element Modeling (FEM) using ABAQUS with the Concrete Damage Plasticity (CDP) model reproduced experimental (EXP) load–deflection responses, peak loads, and crack evolution with high fidelity. This confirmed the predictive capability of the numerical framework. By integrating material-level optimization, structural-scale testing, and validated FEM simulations, this study provides robust evidence that MK–WG concrete, especially when fiber-reinforced, delivers mechanical, durability, and structural performance improvements. These findings establish a reliable pathway for incorporating sustainable cementitious blends into design-oriented applications, with direct implications for the advancement of performance-based structural codes. Full article

Three-dimensional concrete printing (3DCP) is an emerging technology that improves design flexibility and material efficiency in construction. However, widespread adoption of 3DCP requires overcoming key material challenges. These include controlling rheology for pumpability and buildability and achieving sufficient mechanical strength. This paper provides a comprehensive review of the application of nanoclays (NCs) as a key admixture to address these challenges. The effects of three primary NCs (attapulgite (ATT), bentonite (BEN), and sepiolite (SEP)) on the fresh- and hardened-state properties of printable mortars are systematically analyzed. This review summarize findings on how NCs enhanced thixotropy, yield stress, and cohesion, which are critical for shape retention and the successful printing of multilayered structures. Quantitative analysis reveals that optimized dosages of NCs can increase compressive strength by up to 34% and flexural strength by up to 20%. For enhancing rheology and printability, a dosage of approximately 0.5% by binder weight is often suggested for ATT and SEP. In contrast, BEN can be used at higher replacement levels (up to 20%) to also function as a supplementary cementitious material (SCM), though this significantly impacts workability. This review consolidates the current knowledge to provide a clear framework for selecting appropriate NCs and dosages to develop high-performance, reliable, and sustainable materials for 3DCP applications. Full article

The replacement of natural aggregates with recycled aggregates in concrete production has gained attention as a sustainable approach for valorizing construction and demolition waste (CDW). Although regulatory frameworks in this area remain underdeveloped, extensive research has demonstrated that acceptable mechanical and durability properties can be achieved. However, the elevated water absorption associated with recycled materials—mainly due to residual attached mortar and increased porosity—continues to pose a challenge. When used without prior treatment, these particles absorb part of the mixing water intended for cement hydration, potentially compromising both fresh and hardened concrete performance. This study explores the use of graphene oxide (GO) nanocoating as a surface modification strategy to mitigate water absorption. Absorption test were performed to evaluate the effectiveness of the treatment, followed by the preparation of multiple concrete mixes incorporating varying substitution rates of natural aggregate with untreated and GO-treated recycled material. The mixtures were assessed for workability and compressive strength. Results indicate that GO nanocoating substantially reduces water (up to 30%) uptake and improves the overall performance of concrete containing recycled constituents, increasing its compressive strength by up to 32%, highlighting its potential as a viable pretreatment for sustainable concrete production. Full article

Electrochemical treatment by means of direct current (DC) is usually used as a measure for steel rebar corrosion protection, e.g., cathodic protection (CP), electrochemical chloride extraction (ECE), and re-alkalization (RA). However, the passage of an electrical charge through the pore system of concrete or mortar, coupled with the migration of ions, concentration changes, and resulting phase changes, may alter its chloride penetration resistance and, subsequently, the time until rebar corrosion activation. Porosity changes in hardened Portland cement mortar were studied by means of mercury intrusion porosimetry (MIP) and electrochemical impedance spectroscopy (EIS), and alterations in the mortar surface phase composition were observed by means of X-ray diffraction (XRD). In order to innovatively investigate the impact of DC treatment on the properties of the mortar–electrolyte interface, the cathode-facing mortar surface and the anode-facing mortar surface were analyzed separately. The corrosion of steel coupons embedded in DC-treated hardened mortar was monitored by means of the free corrosion potential (E_oc) and polarization resistance (R_p). The results showed that the DC treatment affected the surface porosity of the hardened Portland cement mortar at the nanoscale. Up to two-thirds of the small pores (0.001–0.01 µm) were replaced by medium-sized pores (0.01–0.06 µm), which may be significant for chloride ingress. Although the porosity and phase composition alterations were confirmed using other techniques (EIS and XRD), corrosion tests revealed that they did not significantly affect the time until the corrosion activation of the steel coupons in the mortar. Full article

Nowadays, 3D printing has revolutionized the construction and building industry, enabling researchers to push the boundaries of creating structural components with this innovative technique. A key factor for the success of this approach lies in selecting the optimal mix design, which must possess suitable properties for printing while ensuring strong performance once hardened. However, achieving this optimal mix is complex due to limited knowledge regarding the necessary fresh-state properties, the characteristics and proportions of the constituents, the influence of printing parameters on these properties, and the various challenges encountered during and post printing. This paper aims to address these aspects by offering a comprehensive review of the steps researchers have taken to develop an optimized 3D printable mix. Full article

Recycling construction and demolition (C&D) waste into recycled aggregate (RA) and recycled aggregate concrete (RAC) is conducive to natural resource conservation and industry decarbonization, which have been attracting much attention from the community. This paper aims to present a synthesis of recent scientific insights on RA and RAC by conducting a systematic review of the latest advances in their properties, test techniques, modeling, modification and improvement, as well as applications. Over 100 papers published in the past three years were examined, extracting enlightening information and recommendations for engineering. The review shows that consistent conclusions have been drawn about the physical properties in that RA can reduce the workability and the setting time of fresh RAC and increase the porosity of hardened RAC. Its impact on drying and autogenous shrinkage is governed by its size and the strength of the parent concrete. RA generally acts negatively on the durability and mechanical properties of concrete, but such effects remain controversial as many opposite observations have been reported. Apart from the commonly used multiscale test techniques, real-time monitoring also plays an important role in the investigation of deformation and fracture processes. Analytical models for RAC were usually modified from the existing models for NAC or established through regression analysis, while for numerical models, the distribution of attached mortar should be considered to improve their accuracy. Machine learning models are effective in predicting RAC properties. Modification of RA can be implemented by either removing or strengthening the attached mortar, while the modification of RAC is mainly achieved by improving its microstructure. Current exploration of RAC applications mainly focuses on the optimization of concrete design and mix procedures, structural components, as well as multifunctional construction materials, revealing the room for its further exploitation in the industry. Full article

This study developed a vinyl acetate-ethylene rapid repair mortar (VAE-RRM) by using a binary blended cementitious system (ordinary Portland cement and sulfoaluminate cement) and vinyl acetate-ethylene (VAE) redispersible polymer powder. The effects of the polymer-to-cement ratio (P/C: 0~2.0%) on setting time, mechanical properties, interfacial bonding, and microstructure were systematically investigated. The results reveal that VAE delayed cement hydration via physical encapsulation and chemical chelation, extending the initial setting time to 182 min at P/C = 2.0%. At the optimal P/C = 0.9%, a synergistic organic–inorganic network enhanced flexural strength (14.62 MPa at 28 d, 34.0% increase) and interfacial bonding (2.74 MPa after interface treatment), though compressive strength decreased to 65.7 MPa due to hydration inhibition. Excessive VAE (P/C ≥ 1.5%) suppressed AFt/C-S-H growth, increasing harmful pores (>1 μm) and degrading performance. Microstructural analysis via scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) demonstrates that VAE films bridged hydration products, filled interfacial transition zones (ITZ), and refined pore structures, reducing the most probable pore size from 62.8 nm (reference) to 23.5 nm. VAE-RRM 3 (P/C = 0.9%) exhibited rapid hardening (initial setting time: 75 min), high substrate recovery (83.3%), and low porosity (<10%), offering an efficient solution for urban infrastructure repair. This work elucidates the dual mechanisms of pore refinement and interface reinforcement driven by VAE, providing theoretical guidance for designing high-performance repair materials. Full article

In the frame of an extended research program dealing with wood shavings and wood sawdust utilization in mortar, thermal conductivity and thermal behavior under various temperatures of mortars containing wood shavings and sawdust as a replacement for a part of the conventional aggregates were studied. Mixes with 0, 30, 50 and 70% replacement of conventional fine limestone aggregates with wood shavings were made. Also, mixes with 0, 10 and 20% replacement of aggregates with wood sawdust were made. The density of fresh concrete and the thermal conductivity of hardened concrete were determined. Thermal conductivity was determined with the guarded hot plate method according to standard ΕΝ 12667:2001. Specimens were also submitted to 100, 200, 300, 400, 500 and 600 °C. Flexural and compressive strength were determined 24 h after thermal strain. Results showed that thermal conductivity decreased when volume replacement increased, both for the use of wood shavings and sawdust, thus improving the thermal properties of mortar. Flexural and compressive strength exponentially decrease as exposure temperature increases. Full article