Construction Materials

The advancement of modern concretes, such as printable concrete, fluid concrete with adapted rheology, and ultra-high-performance concrete, has increased the importance of understanding structural build-up in cement-based materials. This process, which describes the time-dependent evolution of rheological properties, is a key factor to ensure the stability of concrete by influencing segregation, bleeding, formwork pressure, numerical modeling, and multi-layer casting. As a result, the structural build-up of cementitious materials has become a significant area of research in recent years. The structural build-up of cement based-materials results from both a reversible part (thixotropic behavior), driven by colloidal interactions, and an irreversible part, caused by cement hydration and the formation of C-S-H bridges. Various experimental techniques have been developed to investigate these processes, with various factors affecting the thixotropic behavior and overall structural build-up of cement suspensions. This review provides a comprehensive analysis of the current understanding of structural build-up in cement pastes. It covers measurement methods and key influencing factors, including the water-to-binder ratio (w/b), admixtures, temperature, and supplementary cementitious materials (SCMs). By consolidating the existing knowledge and identifying research gaps, this review aims to contribute to the development of sustainable, high-performance cement-based materials suitable for modern construction techniques. Full article

The construction industry generates approximately 45% of the world’s total waste, highlighting the need for sustainable solutions. This study investigates the incorporation of quartzite waste (QW) and fiberglass waste (FW) into the production of gypsum plasterboard to reduce its environmental impact while maintaining its structural performance. The optimum formulation (MQ-20) was determined by replacing 20% of the gypsum with QW, based on the observed free water loss and crystallization water. The physical, mechanical, and thermal properties of the reference and modified boards were evaluated. The results showed that the MQ-20 samples exhibited a 30% reduction in flexural strength compared to the reference, while still exceeding regulatory standards. In addition, the MQ-20 samples had a lower thermal conductivity (0.54 W/(m∙K)) than the reference (0.58 W/(m∙K)). Fire-resistance tests showed that the inclusion of QW and FW reduced the size and number of cracks, improving the structural stability of the plasterboard at high temperatures. This research demonstrates that the incorporation of industrial waste into plasterboard is a viable and environmentally friendly approach, providing both mechanical and thermal performance benefits. These findings provide a basis for future studies aimed at developing sustainable building materials with improved functional properties. Full article

Considering the urgent need for sustainable construction materials, this study investigates the mechanical and microstructural responses of novel hybrid geopolymer concrete blends incorporating Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBS), Cement (C) and Precipitated Silica (PS) as partial replacements for traditional cementitious materials. The motive lies in reducing CO₂ emissions associated with Ordinary Portland Cement (OPC). The main aim of the study was to optimise the proportions of industrial wastes for enhanced performance and sustainability. The geopolymer mixes were activated using a 10 M sodium hydroxide (NaOH)—Sodium Silicate (Na₂SiO₃) solution and cast into cubes (100 mm), cylinders (100 mm × 200 mm) and prism specimens for compressive, split tensile and flexural strength testing, respectively. Six combinations of mixes were studied: FA/C (50:50), GGBS/C (50:50), FA/C/PS (50:40:10), FA/GGBS/PS (50:40:10), GGBS/C (50:50) and GGBS/FA/PS (50:40:10). The results indicated that the blend with 50% FA, 40% GGBS and 10% PS exhibited higher strength. Mixes with GGBS and PS presented a l0 lower slump due to rapid setting and higher water demand, while GGBS-FA-cement mixes indicated better workability. GGBS/C exhibited a 24.6% rise in compressive strength for 7 days, whereas FA/C presented a 31.3% rise at 90 days. GGBS/FA mix indicated a 35.5% strength drop from 28 days to 90 days. SEM and EDS analyses showed that FA-rich mixes had porous microstructures, while GGBS-based mixes formed denser matrices with increased calcium content. Full article

The use of recycled burnt clay brick sand (RBS) and recycled concrete sand (RCS) in historical lime-based repair mortars can reduce the environmental impact caused by construction and demolition waste disposal. This study examined the use of fine recycled concrete and recycled brick aggregates for the production of historical repair mortars using hydraulic lime binder and the influence of the resulting mortars on the performance of historical buildings in reduced scale walls (stacks). Natural-river-sand mortar (NSM) was used as control. Results showed that the recycled-burnt-brick-sand mortar (RBSM) performed better in terms of strength compared to the recycled-concrete sand (RCSM) and the NSM mortars. At the age of 7 and 28 days, the flexural strength of the RBSM and the RCSM was 131% and 44%, respectively, and 300% and 68% above that of the control mortar. The 45-day flexural strength of the NSM and RCSM was similar whilst the RBSM mortar’s strength was 177% higher. The compressive strength followed similar trend. On the other hand, the strength and modulus of elasticity of the stacks were found to be largely influenced by the strength of the brick units. Full article

The construction sector significantly impacts the environment, driving the development of sustainable materials like plant-based concretes. These materials offer low embodied energy, effective thermal insulation, and natural hygroscopicity. However, one of the major difficulties is that the diversity of formulations complicates the performance assessment. Furthermore, few studies model their insulating capacity based on composition. This research employs mean-field homogenization techniques (Mori–Tanaka and double inclusion schemes) to predict thermal conductivity, integrating formulation, aggregate orientation due to implementation methods, and morphological characteristics at several scales. The models analyze key factors—aggregate type, aspect ratio, and orientation—improving insulation beyond experimental limitations. A multi-criteria approach further explores binder and aggregate proportions, hygric and mechanical properties, and raw material availability. One of the major results is that a preferred orientation increases thermal efficiency by 60 percent, a difficult factor to assess experimentally today. This study enables the optimized thermal performance of plant-based concretes before production, fostering innovative manufacturing approaches for eco-friendly construction. Full article

Asphalt emulsions are used in flexible pavement maintenance and rehabilitation treatments. Emulsion specifications for material characterization are based on testing methodology dating to the 1930s. Newer test methods, including particle size analysis (PSA) of binder droplets in emulsion, have been explored but not implemented into specifications. The objective of this study is to observe the particle size and performance of cationic slow-setting (CSS) emulsions and establish baseline particle size recommendations for cationic emulsions. Four physical property tests (residue, oversize particles, viscosity, and particle size) and two cold mix asphalt performance tests (indirect tensile strength (IDT) and direct shear test (DST)) were conducted on two emulsions (CSS-1 and CSS-1H) over a six-month period. The physical properties of both emulsions were acceptable, and median particle size of the CSS-1H was approximately 3 microns larger than the CSS-1. The IDT strength and DST shear strength of the CSS-1H were higher than of the CSS-1. Recommendations for particle size were proposed by defining maximum limits on median, d₁₀, d₉₀, and span. It is recommended that the maximum median (d₅₀) size of CSS emulsions is 6.0 microns. Future research is needed to standardize PSA procedures, assess recommendations for a wider range of emulsions, and evaluate applicability of minimum particle size limits. Full article

To address the issues of significant brittleness in self-compacting concrete (SCC), limited parameter ranges in existing steel fiber reinforcement studies, and incomplete performance evaluation systems, this study conducted mechanical performance tests on steel fiber-reinforced SCC (SFRSCC) with a wide range of volume fractions (1–3%) and multiple aspect ratios. A multi-indicator comprehensive evaluation model of compressive strength, flexural strength, and elastic modulus was established using an improved entropy-weighted TOPSIS method. Gray relational analysis was integrated to reveal nonlinear correlation patterns between fiber parameters (the volume fraction and aspect ratio) and mechanical responses. The experimental results demonstrated the following: (1) At a 3% fiber content, compressive and flexural strengths increased by 25.7% and 280%, respectively, compared to the control group; (2) the elastic modulus peaked at 2% fiber content, with excessive content (3%) causing an uneven fiber dispersion and diminishing performance gains; (3) short fibers (6 mm) achieved optimal compressive strength at 3% content and medium-length fibers (13 mm) significantly enhanced flexural strength, while long fibers (25 mm) maximized the elastic modulus at 2% content. The combined application of the improved entropy-weighted TOPSIS method and gray relational analysis identified that the high fiber content (3%) paired with medium-length fibers (13 mm) optimally balanced flexural strength and toughness, providing theoretical guidance for the application of SFRSCC in tensile- and crack-resistant engineering projects. Full article

The use of fiber-reinforced polymer (FRP) composites in retrofitting and strengthening reinforced concrete (RC) slabs has gained substantial attention due to their durability, high strength-to-weight ratio, and ease of application. The objective of this study was to theoretically investigate the flexural behavior of RC slabs strengthened with carbon fiber-reinforced polymer (CFRP) plates applied in different percentages and patterns using finite element methods (FEMs) in comparison with the experiment outcomes available in the literature using the ABAQUS software (version 2020). This study focused on understanding the influence of the CFRP configuration on the structural behavior, including the load-carrying capacity, flexural performance, crack patterns, and failure modes, under static loading on seventeen RC slabs of 1800 × 1800 mm and 150 mm thickness. A comprehensive program was adopted, where RC slabs were strengthened using CFRP plates with different coverage percentages (0.044, 0.088, 0.133, 0.178, and 0.223) and arrangements (unidirectional, cross-hatched, and grid patterns) to evaluate the slabs’ performance under realistic service conditions. After comparison, the results validate that the percentage and pattern of CFRP plates influence the performance of RC slabs. Higher CFRP plate percentages yielded greater strength enhancement, while optimized patterns guaranteed a uniform stress distribution and delayed crack initiation. This study hypothesizes that the flexural strength, stiffness, and failure behavior of RC slabs are significantly affected by the percentage and arrangement of CFRP strengthening, with certain configurations providing superior structural performance. The use of CFRP cross-hatched plates improved the load–deflection behavior, increasing the ultimate loads by 35% (452 kN) while reducing ultimate deflection, with the cross-hatched CFRP specimen showing the highest deflection among all the CFRP specimens. This study provides engineers and practitioners with valuable information on choosing appropriate strengthening plans for RC slabs using CFRP plates, leading to more cost-effective and ecologically friendly structural rehabilitation methods. Full article

This study examines the effects of steel fibers (SF) and carbon nanotubes (CNTs) on the performance of cementitious composites. Three types of mixes were analyzed: a reference mix (REF), a steel fiber-reinforced concrete (SFRC), and a hybrid mix containing both CNTs and SFs. The investigation included physicomechanical property evaluations, microstructural analysis, and ultrasonic pulse velocity (UPV) tests. Results indicate significant improvements in performance across the mixes, with the hybrid mix achieving the highest flexural and compressive strengths, highlighting a synergistic interaction between CNTs and SF to enhance load-bearing capacity. Additionally, the mixtures displayed reduced porosity and water absorption, signifying improved density and lower permeability. SEM analysis further confirmed a denser microstructure with enhanced crack-bridging capabilities due to the presence of CNTs and SF. UPV measurements supported these findings, demonstrating superior internal integrity and stiffness in the hybrid mix. These experimental results underscore the potential of hybrid reinforcement strategies for producing high-performance fiber concrete with enhanced durability, making it suitable for demanding construction applications. Full article

Concrete segregation can lead to variations in hardened concrete’s properties, such as strength and Young’s modulus, or permeability, resulting in changing volume ratios between aggregates and paste within a concrete element. One approach to mitigate this potential risk is to conduct a performance test to assess vibrated concrete’s segregation sensitivity. This paper outlines various methods to evaluate the segregation sensitivity of vibrated concrete, aiming to support adequate concrete casting. The focus is on practical feasibility while maintaining test accuracy. For hydraulic engineering in Germany, test procedures to evaluate segregation sensitivity on fresh and hardened concrete based on aggregate distribution are described in the “BAW-Code of practice MESB”. However, this method is very complex and, therefore, difficult to implement in practice. Another procedure for hardened concrete is based on concrete density. In this paper, both methods are compared to investigate if evaluating fresh concrete using a simple density criterion leads to a comparably significant differentiation of vibrated concrete with different segregation sensitivities. The primary emphasis lies in accurately classifying examined concretes in terms of their segregation sensitivity, evaluating the scatter of results, and assessing the practical applicability of these methods. The investigations demonstrate that a density-based method can yield reliable and comparable results to those obtained through the wash-out test according to “BAW-Code of practice MESB”. Additionally, a simpler and faster procedure is achievable with the density approach. Hence, density evaluation offers a practical alternative to the wash-out test. Full article

Reducing the large amounts of carbon dioxide emitted during cement processing is crucial to control the adverse effects of greenhouse gases. This study provides a promising alternative technology to reduce such carbon dioxide emissions and investigate physical and mechanical characteristics of alkali-activated materials with rice husk ash (RHA). To this end, compressive strength, drying shrinkage, and water penetration resistance of mortar made with RHA, blast furnace slag (BFS), and alkaline activator (sodium carbonate, NC) are investigated. Two RHA particle sizes of 45 and 150 µm types are used, thereby varying the RHA replacement ratio of 0, 7.5, 15.0 wt.%. Based on adiabatic hydration temperature, Archimedes porosity, pH, ignition loss, scanning electron microscopy, and energy-dispersive X-ray spectroscopy and X-ray diffraction results of paste, the effect of RHA on mechanical characteristics is examined. Experimental investigation reveals that compressive strengths of mortar sample made with the RHA replacement ratio of 15 wt.% to BFS were recorded between 48 and 51 MPa. When the RHA replacement ratio of 15 wt.% 150 µm was used, the length change was 1147 × 10⁻⁶ and the moisture penetration depth was less than 11 mm. Notably, water penetration resistance significantly improves with increasing RHA content; however, at high replacement ratios, the particle-size effect is not prominent. Furthermore, increasing the RHA replacement ratio decreases the porosity but increases the ignition loss and produces C-S-H gel. Full article

Recent global strategies highlight the urgency of addressing greenhouse gas (GHG) emissions, particularly CO₂ from energy-intensive industries such as cement production. Studies show that the cement industry contributes around 8% of the global CO₂ emissions, emphasizing the need for innovative and structural mitigation strategies. While advancements in carbon capture technologies, LC3 cement, alternative raw materials, and renewable energy integration are critical for achieving the net zero emissions (NZEs) goal, the challenge lies in having a structured and comprehensive approach for systematically categorizing, prioritizing, and assessing various CO₂ improvement measures within cement plants. To address this gap, this study introduces a structured assessment model designed to evaluate and rate proposed CO₂ improvement measures based on their alignment with the global NZE targets and plant-specific milestones, providing an overall cement plant performance score. The assessment tool developed in this study provides a quantitative scoring system for assessing the implementation level and impact of various CO₂ improvement measures within cement plants. The framework integrates the cleaner production concept and the 5Cs approach to the decarbonization of the cement industry, offering a systematic yet flexible method for cement industry decarbonization. To validate the assessment tool, two cement plants with different production scales and located at different geographical locations were analyzed. Plant A achieved an overall performance score of 3.315, while plant B scored 3.68. The assessment identified a potential CO₂ reduction of 20–30% through targeted improvements, highlighting that even well-established cement plants have opportunities for emissions reduction and efficiency enhancement. This study advances existing assessment methodologies by providing an adaptable, data-driven, systematic, and scalable tool that enhances decision-making, strategic modifications, and resource allocation for achieving NZE targets. Additionally, this assessment tool bridges the gap between global targets and plant-level implementation, ensuring effective transition towards sustainability in the cement industry. Full article

Faced with environmental challenges posed by traditional building materials and the management of agricultural waste, this study uses dwarf hulls, an abundant waste product in West Africa, as a natural stabilizer for earth bricks. Three mixtures were studied: soil + water (reference), soil + néré husk decoction, and soil + decoction with weekly sprinkling. The results show a significant improvement in compressive strength with the decoction. At 28 days, it increases from 0.967 MPa (reference) to 1.251 MPa with decoction and 1.360 MPa with sprinkling. At 90 days, these values reach 1.060 MPa, 1.39 MPa, and 1.502 MPa, respectively, confirming the beneficial effect of tannins and humidification. On the other hand, the tensile strength decreased from 0.10 MPa for the reference mixture to 0.08 MPa and 0.08 MPa with decoction and sprinkling. This study highlights the potential of using néré husk as a durable stabilizer. However, further research is needed, particularly on the addition of plant fibers, to improve tensile strength. Full article

Integrating local, bio-sourced materials, such as earth and agricultural waste like dwarf hulls, is a sustainable solution to the challenges of climate change and increasing urbanization. The use of bio-based materials such as néré husk (Parkia biglobosa) in the manufacture of compressed earth bricks is a sustainable alternative for improving their thermal performance. This study assesses the impact of adding hulls in different forms (fine powder < 0.08 mm, aggregates from 2 mm to 5 mm, and aqueous maceration) on the thermal conductivity and effusivity of bricks. The tests were carried out using the asymmetric hot plane method, applying a constant heat flux and measuring the temperature variation via a thermocouple. Three samples of each formulation were analyzed to ensure the reliability of the results. The results show that the addition of fine powdered husk reduces the thermal conductivity of the bricks to 0.404 W/m.K and their effusivity to 922.2 W/(Km²) s¹/², compared with 0.557 W/m.K and 1000.32 W/(Km²) s¹/² for the control bricks. The addition of coarser aggregates (2 mm–5 mm) gives intermediate values (0.467 W/m.K and 907.99 W/(Km²) s¹/²). Aqueous maceration, on the other hand, results in an increase in thermal conductivity to 0.614 W/m.K. These results confirm that the shape and method of incorporation of the husk influence the thermal performance of the bricks, with fine powder offering the best thermal insulation. This approach highlights the potential of bio-based materials for eco-responsible construction. Full article

The use of reclaimed asphalt pavement (RAP) in asphalt mixtures has increased due to its economic and environmental benefits. However, RAP integration can negatively impact the durability and performance of asphalt binders, particularly at low temperatures. This study evaluates the effects of RAP modification on the $\Delta T_C$ parameter, a key indicator of binder brittleness and resistance to non-load-related cracking, focusing on PG XX-34 and PG XX-28 grades commonly used in Kansas. Laboratory testing was conducted on virgin and RAP binders subjected to Rolling Thin-Film Oven (RTFO) and Pressure Aging Vessel (PAV) aging. Blended binders were prepared with RAP replacement levels of 15%, 25%, and 40%. The critical temperatures $T_{C,m}$, $T_{C,S}$, and $\Delta T_C$ values were calculated using data from Bending Beam Rheometer (BBR) testing. The results showed that increasing RAP content generally led to more negative $\Delta T_C$ values, indicating reduced relaxation capacity and higher susceptibility to thermal cracking. RAP source variability also affected performance, with some sources causing more severe deterioration than others. These findings highlight the limitations of conventional linear blending assumptions and underscore the need for improved RAP characterization in binder selection. The study recommends limiting RAP replacement to 25% unless the RAP source demonstrates favorable properties, incorporating $\Delta T_C$ thresholds (−2.5 °C and −5.0 °C) into binder specifications, and further investigating RAP–virgin binder interactions to enhance long-term pavement performance. The findings support the potential adoption of $\Delta T_C$ as a specification criterion for binder evaluation, helping agencies like the Kansas Department of Transportation (KDOT) balance binder durability and RAP use. Full article

The usage of geopolymer-based materials (GPBMs) in concrete structures has been broadly promoted by the current construction sector. GPBMs have an outstanding influence on enhancing concrete mechanical properties. Geopolymers (GPs) also have a potential impact on reducing the carbon dioxide emissions emitted by the current cement production procedure. Therefore, this paper aims to evaluate the impact of some variables that affect green and mechanical properties of fly ash-based geopolymer concretes (FA–GPCs), i.e., different silica fume (SF) contents, alkaline activator solution (AAS) percentages, sodium silicate-to-sodium hydroxide (SS/SH) ratios, sodium hydroxide (NaOH) molarity, and additional water. A slump test was used to evaluate the concrete workability to assess the green properties of the designed fly ash-geopolymer concrete mixes (FA–GPCMs). The 14- and 28-day compressive strengths were used to evaluate the concrete’s mechanical properties. Results indicate that the workability of prepared FA–GPCMs reduced with improving SF content (5% to 30%), SS/SH ratio (1% to 3%), and NaOH molarity (10 M to 16 M), while reducing alkaline activator percentages to 35% resulted in a decrease in the FA–GPCMs’ workability. Also, increasing SF replacement percentages from 5% to 15% in FA–GPCMs resulted in significant 14- and 28-day FA–GP compressive strength enhancements compared to FA–GPCM produced with 0% SF, while SF contents of 20%, 25%, and 30% led to a decline in the 14- and 28-day FA–GPC compressive strength compared to that of G1–SF15%. Full article

Foamed concrete, a lightweight material with excellent thermal insulation and low density, is increasingly popular in construction. This study uses the discrete element method (DEM) to simulate the compressive behavior of foamed concrete, analyzing the effects of particle radius, porosity, and void distribution. The results highlight the important role of geometric and material parameters. Smaller particle radii improve packing density and strength, while a uniform void distribution maximizes compressive strength by minimizing stress concentration. This information provides a basis for optimizing the design of foamed concrete for better mechanical performance and wider applications in sustainable construction. Full article

Plastic Concrete is a low-strength ($f_{cm,28\mathrm{d}}$ ≤ 1.0 MPa), low-stiffness impervious concrete used for cut-off walls in earthen dams worldwide. These properties are achieved through a very high w/c ratio (w/c ≥ 3.0) and water-binding additions (e.g., bentonite). To date, the effect of mix design, especially w/c ratio, as well as bentonite content and type, on the long-term time development of the microstructural properties and corresponding compressive strength of Plastic Concrete has yet to be systematically studied. Furthermore, in the literature, mercury intrusion porosimetry (MIP) and X-ray diffractometry (XRD) have yet to be applied systematically to Plastic Concrete for this purpose. The present study closes this gap. Ten Plastic Concrete mixes with two bentonite–cement ratios, three types of sodium bentonite and two swelling times were produced. MIP and XRD measurements and compressive strength tests were performed at sample ages of 7 d, 28 d, 56 d, 91 d and four years. The results show that both MIP and XRD can be successfully used; however, meticulous sample preparation and data analysis must be considered. The porosimetry results show a bi-modal pore size distribution, with two age-dependent peaks at approximately 10,000–20,000 nm and 100–700 nm. The results also exhibit a clear pore refinement over time, with coarse porosity dropping from 26% to 15% over four years. In addition, the fine porosity peak is significantly refined over time and positively correlates with the significant increase in compressive strength. The XRD results show no unexpected crystalline phases over the same period. Overall, this study links MIP and corresponding compressive strength data specifically for Plastic Concrete for the first time, confirming the key role that the mix design of Plastic Concrete plays in defining its long-term microstructural and mechanical properties and ensuring more realistic cut-off wall design in the future. In addition, the experimental boundaries for MIP testing on Plastic Concrete are set out for the first time, enabling future research in this field. Full article

This study investigates the influence of ballast and sub-ballast thicknesses on the structural behavior of a heavy-haul railway platform by using finite element modeling with SysTrain software (v. 1.84) A parametric analysis was conducted to assess how variations in layer thickness affect key performance parameters, including total deflection, bending moments in the rails, and vertical stresses within the railway track. The results indicate that reducing ballast thickness increases deflection and vertical stresses, while excessive thickness elevates system stiffness, reducing its ability to dissipate stresses. This condition can intensify the transmission of dynamic loads to track components, accelerating rail and sleeper wear and requiring more frequent corrective interventions, thereby increasing maintenance costs. Deflections remained within the 6.35 mm limit established by AREMA, except for one case (6.85 mm), where an excessive ballast thickness (160 cm) combined with low material stiffness resulted in non-compliance. Vertical stresses in the substructure ranged from 106.9 kPa to 155.9 kPa, staying within admissible limits. Additionally, the study highlights the significant role of material properties, particularly the resilient modulus, in the overall track performance. The findings enhance the understanding of how ballast and sub-ballast geometry affect railway structural behavior, demonstrating how numerical modeling with SysTrain can support decision-making in track design and maintenance strategies. Full article