Search Results (468)

This study investigated the effects of incorporating rice husk ash (RHA) as a partial replacement for cement on the properties of concrete. To determine the optimal replacement level, RHA was used to replace cement in varying proportions, ranging from 0% to 25% in 5% increments. The mix with 0% RHA served as the control. The properties evaluated included setting time, density, and compressive strength. The results revealed that blending RHA with cement increased the initial setting time. This was attributed to the lower calcium oxide (CaO₂) content of RHA, which slows early-age hydration reactions. Conversely, the final setting time was reduced due to the pozzolanic activity of RHA, which enhances later-stage reactions. Additionally, the inclusion of RHA resulted in a decrease in concrete density, owing to its lower specific gravity and bulk density compared to Portland cement. Despite this, RHA-modified specimens exhibited higher compressive strengths than the control specimens. This strength enhancement was linked to the formation of additional calcium–silicate–hydrate (C-S-H) gel due to the pozzolanic reaction between amorphous silica in RHA and calcium hydroxide (CaOH) from hydration reaction. The gel fills concrete voids at the microstructural level, producing a denser and more compact concrete matrix. Based on the balance between strength and durability, the optimal RHA replacement level was identified as 10%. Full article

Metakaolin (MK) obtained from calcined kaolinitic clay is a highly reactive pozzolanic ingredient for use as an emerging supplementary cementitious material (SCM) in modern sustainable binder productions. It provides elevated alumina to promote formations of Alumina Ferrite Monosulfate (AFm) and Calcium-Aluminium-Silicate-Hydrate (C-A-S-H) phases, enhancing the chloride binding capacity. However, due to inherent material uncertainty and lack of approach in quantifying hydration kinetics and chloride binding capacity across varied mixes, robustly assessing the chloride resistance of metakaolin-blended concrete remains challenging. In light of this, a machine learning-aided framework that encompasses physics-based material characterisation and ageing modelling is developed to bridge the knowledge gap. Through applying to laboratory experiments, the impacts of uncertainty on the phase assemblage of hydrated system and chloride penetration are quantified. Moreover, the novel Extended Support Vector Regression (XSVR) method is incorporated and verified against a crude Monte Carlo Simulation (MCS) to demonstrate the capability of achieving effective and efficient uncertainty-aware chloride resistance analyses. With the surrogate model established using XSVR, quality control of metakaolin towards durable design optimisation against chloride-laden environments is discussed. It is found that the fineness and purity of adopted metakaolin play important roles. Full article

The use of flawed excavated-mass aggregates produced from crushing and screening hydraulic engineering waste in concrete projects can reduce natural resource extraction, increase waste utilization rates, and minimize environmental pollution. However, the direct application of flawed excavated-mass aggregates is limited due to their high crushing index and water absorption rate. Therefore, this paper measures the multi-dimensional physical and mechanical properties of defective aggregates. A strengthening slurry is prepared by comprehensively modifying the crystallization strength and penetration path of sodium silicate solution using various chemical reagents. The strengthening mechanism of the slurry on flawed excavated-mass aggregates is analyzed using SEM and MIP tests. Concrete tests are designed to investigate the workability and mechanical properties of flawed excavated-mass aggregate concrete. The pore structure of the ITZ (Interfacial Transition Zone) in defective aggregate concrete is analyzed through BSE (Backscattered Electron) imaging to elucidate the strengthening mechanism of secondary crystallization reactions on the ITZ. The research findings can provide technical support for repairing aggregates with defects. Full article

Fly ash-based geopolymer concrete (FAGC) is a sustainable alternative to Portland cement concrete, offering significant reductions in carbon emissions while maintaining sufficient strength. This study proposes a three-stage framework for developing empirical formulae to accurately and interpretably predict FAGC compressive strength. In the first stage, predictive models were developed using linear regression (LR), deep neural network (DNN), and residual neural network (ResNet) approaches. Among these, the ResNet model achieved the highest predictive accuracy and effectively captured the complex nonlinear relationship between mix components, curing conditions, and compressive strength. In the second stage, global sensitivity analysis identified sodium silicate content, curing time, sodium hydroxide molarity, and water content as the most influential variables. Additionally, the interaction between fine aggregate content and curing temperature was found to have a substantial effect on strength development. In the final stage, an empirical formula was developed based on key variables and their interactions, providing a simple yet reliable tool for practical strength prediction with reduced computational requirements. The proposed framework is expected to bridge the gap between machine-learning prediction and applicability to support mix design optimisation and promote the wider adoption of sustainable geopolymer concrete in construction applications. Full article

A thorough understanding of the dispersion characteristics of graphene oxide (GO), its micro-pore enhancement mechanisms, and correlations with mechanical properties are crucial for advancing high-strength, durable green concrete. Introducing recycled concrete powder (RCP) can weaken the interfacial transition zone (ITZ) and inhibit hydration reactions, degrading the pore structure and affecting mechanical strength and durability. However, traditional methods struggle to accurately characterize and quantitatively analyze GO-modified pore structures due to their nanoscale size, microstructural diversity, and characterization technique limitations. To address these challenges, this study integrates deep learning-based backscattered electron image analysis with deep Taylor decomposition feature extraction. This innovative method systematically analyzes pore characteristic evolution and the correlation between porosity and mechanical strength. The results indicate that GO promotes Calcium Silicate Hydrate gel growth, refines pores, and reduces pore connectivity, decreasing the maximum pore size by 33.4–45.2%. Using a Convolutional Neural Network architecture, BSE images are efficiently processed and analyzed, achieving an average recognition accuracy of 94.3–96.9%. The optimized degree of GO coating on enhanced regions reaches 30.2%. Fitting porosity with mechanical strength and chloride ion permeability coefficients reveals that enhanced regions exhibit the highest correlation with mechanical strength and durability in regenerated cementitious materials, with R² values ranging from 0.79 to 0.99. The deep learning-assisted pore structure characterization method demonstrates high accuracy and efficiency, providing a critical theoretical basis and data support for performance optimization and engineering applications of recycled cementitious materials. This research expands the application of deep learning in building materials and offers new insights into the relationship between the microstructural and macroscopic properties of recycled cementitious materials. Full article

This study investigates the deterioration of the thermal and mechanical properties of geopolymer foam concrete (GFC) subjected to accelerated weathering through carbonation, salt fog, and UV radiation. GFC blocks were synthesized using metakaolin as the aluminosilicate precursor, activated with an alkaline solution consisting of 8 M NaOH and sodium silicate (Na₂SiO₃) at a NaOH/Na₂SiO₃ ratio of 0.51 wt.%. A 30% (v/v) H₂O₂ solution served as the foaming agent, and olive oil was used as the surfactant. Accelerated carbonation tests were conducted at 25 ± 3 °C and 40 ± 3 °C, under 60 ± 5% relative humidity and 5% CO₂, with carbonation depth, carbonation percentage, density, porosity, and thermal conductivity evaluated over a 7-day period. In parallel, specimens were exposed to salt fog and UV radiation for 12 weeks in accordance with ASTM B117-19 and ASTM G154-23, respectively. Compressive strength was monitored every week throughout the exposure period. Results show that carbonation temperature governs the type and kinetics of carbonate formation. The carbonation process, at 40 °C for 7 days, increased the density and reduced the porosity of GFC, resulting in a ~48% increase in thermal conductivity. Salt fog exposure led to severe mechanical degradation, with NaCl penetration reducing compressive strength by 69%. In contrast, UV radiation caused only minor deterioration, decreasing compressive strength by up to 7%, likely due to surface-level carbonation. Full article

Basic magnesium sulfate cement (BMSC) exhibits rapid setting, early strength development, high ultimate strength, and good durability, making it a promising construction material for the extreme environments of Mars. Following the principle of in situ resource utilization (ISRU), this study employs the Martian regolith simulant NUAA-1M, developed by Nanjing University of Aeronautics and Astronautics, as both a mineral admixture and aggregate to prepare Martian basic magnesium sulfate cement (M-BMSC) and Martian basic magnesium sulfate cement concrete (M-BMSCC). The effects of NUAA-1M fines on the setting time, compressive strength, hydration heat evolution, hydration products, microstructure, and pore structure of M-BMSC were systematically investigated. Moreover, the fundamental physical and mechanical properties of M-BMSCC incorporating NUAA-1M as an aggregate were evaluated, and an empirical correlation model was established between its compressive strength (f_cu), flexural strength (f_t), and splitting tensile strength (f_sp). Results indicate that with increasing NUAA-1M fines content, the setting time of M-BMSC was prolonged, while its compressive strength initially increased and then decreased. The incorporation of NUAA-1M fines modified the hydration process and phase assemblage of M-BMSC, promoting the formation of magnesium (alumino)silicate hydrate (M-(A)-S-H) gels and refining the pore structure. Hydration monitoring within 24 h confirmed the rapid hydration characteristics of M-BMSC, demonstrating its suitability for Martian conditions. M-BMSCC exhibited excellent early- and high-strength performance, achieving a 28-day compressive strength of 59.2 MPa at a binder-to-aggregate ratio of 2:1, corresponding to a total NUAA-1M content of 84.75% in the mixture. This work provides a novel ISRU-based material strategy for the construction of Martian bases and infrastructure. Full article

This study systematically investigates the key parameters governing the mechanical performance of fly ash-based geopolymer across paste, mortar, and concrete scales. Comprehensive mechanical testing, combined with SEM and MIP analyses, elucidated the relationships between activator composition, pore structure, and strength development. A key innovation is the development of a cross-scale quantitative framework linking mortar strength to concrete compressive strength, enabling preliminary predictive capability across material scales. Grey relational analysis identified curing temperature as the most influential factor, followed by SiO₂/Na₂O and H₂O/Na₂O ratios. Thermal curing accelerates strength development and temperatures of 70~80 °C markedly enhance reaction rates. Both compressive and flexural/splitting tensile strengths increase and then decrease with NaOH concentration or sodium silicate modulus, with optimal performance at 24~26% NaOH and SiO₂/Na₂O ratio of 1.2~1.4, while increasing H₂O/Na₂O reduces strength nearly linearly, constrained by workability. Concrete compressive strength rises with coarse aggregate content up to 60~70% before declining. SEM and MIP confirm that optimal activator formulations produce a dense, homogeneous gel matrix with lower porosity and fewer unreacted particles. Strong square-root correlations between compressive and tensile-related strengths were observed across all material systems. Overall, this work establishes a quantitative foundation for geopolymer mix design and provides actionable guidance for developing high-performance, low-carbon geopolymer concrete. Full article

Semi-Flexible Pavement (SFP) combines the flexibility of asphalt concrete and the rigidity of cement concrete to provide excellent high-temperature rutting resistance in the summer. However, its application is often limited by the fluidity and mechanical properties of cement-based grouting materials. This study systematically optimized the mix ratios of three types of grouting materials (cement-based, mineral-modified, and polymer-enhanced) using response surface methodology combined with orthogonal tests. The effects of water–binder ratio (W/B), sand–binder ratio (S/B), mineral admixtures and polymer additives on the key properties of grouting materials were systematically studied. By using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), the evolution of the mixture microstructure and the mechanism of performance change were also analyzed. The test results show that the optimal mix ratio of the cement-based grouting material is W/B = 0.46 and S/B = 0.15; the optimal mix ratio of the mineral grouting material is to replace part of the cement with fly ash (9%), silica fume (6%) and microspheres (3%). Microscopic tests show that fly ash effectively inhibits bleeding; silica fume and fly ash promote the formation of calcium silicate hydrate (C-S-H) gel; microspheres optimize the rheology of the slurry; and the synergistic effect of silica fume and microspheres reduces the internal pores of the grouting material, achieving high fluidity, low bleeding rate and excellent mechanical properties of the grouting material. The polymer-reinforced grouting material is an enhanced slurry formed by adding high-performance water reducer (0.8%), rubber powder (2%) and coupling agent (0.9%) to the optimal mineral grouting material. The combined effect of rubber powder and coupling agent significantly improves the adhesive property between the grouting material and the asphalt interface, making it more suitable for the road performance of SFP in low-temperature environments. Full article

The low flexural strength and high brittleness of cement-based materials greatly compromise their safety, durability, and service life. In situ polymerization is a promising strategy for enhancing the toughness of cement-based materials. However, the underlying mechanisms responsible for this mechanical improvement remain insufficiently understood. This study introduces acrylamide (AM) monomer into a cement matrix, where in situ polymerization forms a strong polymer–cement network, demonstrably enhancing mechanical performance. The factors influencing this mechanical enhancement were investigated across multiple scales using techniques including nanoindentation, crack width measurement, solid-state silicon nuclear magnetic resonance (²⁹Si NMR), thermogravimetric analysis (TGA), and so on. This research confirms that in situ polymerization influences silicate chain length (from 3.405 to 3.714) and pore structure at the nanoscale, modifies the morphology of hydration products, enhances the hardness of the interfacial transition zone (0.025 ± 0.002 to 0.055 ± 0.004 GPa) at the microscale, and reveals that at monomer concentrations below 1 wt%, both the compressive and flexural strengths of the cement-based material are improved, with 28d compressive and flexural strength increasing by 23.86% and 26.58%, respectively. Conversely, higher monomer dosages lead to a simultaneous reduction in both compressive and flexural strengths. Consequently, through tracking the hydration process on the mechanical properties of cement-based materials across multiple scales, this study provides deeper insights into the in situ polymerization system and offers an effective strategy for the design and preparation of high-performance concrete. Full article

To address the issues of insufficient protection and poor durability in concrete during service, this study developed a novel polymer–silicate composite gel system by combining silane with fluorocarbon resin emulsion and applied it to mortar specimens. The chloride ion resistance enhancement of mortar provided by the novel gel system was evaluated using the RCM method and natural chloride ion penetration tests, with SEM images employed to analyze its anti-permeation mechanism. Results indicate that the chloride ion migration coefficient of the novel composite gel system is 4.91 × 10⁻¹² m²/s, representing a 63.97% reduction compared to the single fluorocarbon gel system. Within the 0–5 mm depth range, free chloride ion contents at 14, 28, and 56 days decreased by 55.35%, 50.10%, and 43.64%, respectively, demonstrating excellent resistance to chloride penetration. Acid and alkali resistance tests demonstrated that the system retained the inherent corrosion resistance of the fluorocarbon component. Carbonation tests demonstrated that the system exhibited a slight decrease in carbonation resistance compared with the pure fluorocarbon gel system, while still maintaining a satisfactory performance level. Overall, the polymer-silicate composite gel system significantly enhanced the mortar’s resistance to chloride ion penetration. Full article

The increasing generation of construction and demolition waste (CDW) and the overexploitation of natural aggregates (NA) have necessitated sustainable solutions for recycled aggregate concrete (RAC). This study proposes an innovative inorganic–organic combined modification method using water glass (WG) and sodium methyl silicate (SMS) to enhance the performance of recycled coarse aggregate (RCA) and RAC. A comprehensive experimental program was conducted, including crushing value tests, capillary water absorption, compressive and splitting tensile strength analysis, nanoindentation and Fourier transform infrared spectroscopy (FTIR). The results demonstrated that the combined treatment of 40% WG and 10% SMS significantly improved the RCA properties, reducing water absorption by up to 46.47% and increasing the compressive strength of the RAC by 34.8%. Through mechanistic analysis, it was found that after treatment with SMS solution, a hydrophobic film formed on the surface of the RCA, thereby preventing the transmission of moisture. The interface transition zone between the RCA and the new cement mortar was enhanced, consequently improving the mechanical properties of the RAC. This study contributes to improving the properties of recycled aggregate and recycled aggregate concrete, and to the understanding of the mechanism of combined modification. Full article

Composite geopolymer concrete (CGPC), is receiving growing attention in the construction sector for its sustainable nature, environmental benefits, and its valuable role in promoting efficient waste utilization. The strategic incorporation of reinforcing fibers into geopolymer concrete (GPC) matrices is critical for enhancing mechanical performance and meeting the durability requirements of high-performance construction applications. Although substantial research has focused on strength enhancement of fiber-reinforced geopolymer concrete (FGPC) individually, it has neglected practical considerations such as energy use for curing and life-cycle assessments. Thus, this study investigates the cost-effective aspects of FGPC cured under different regimes. Different cementitious binders were incorporated, i.e., fly ash (FA) and ground granulated blast-furnace slag (GGBS), in addition to alkaline activators (a combination of sodium hydroxide and sodium silicate), hooked-end steel fibers (HESFs), basalt fibers (BFs), and polypropylene fibers (PPFs), as well as aggregates (gravel and sand). The effect of different geopolymer-based materials, reinforcing fibers, and different curing regimes on the mechanical, durability, and economic performance were analyzed. Results showed that the applied thermal curing regimes (oven curing or steam curing) had a considerable impact on durability performance, compressive strength, and flexural strength development, especially for GPC mixes involving high FA content. Cost analysis outcomes suggested that the most affordable option is GPCM1 (100% FA without fibers), but it demonstrates low strength under ambient curing conditions; RGCM4 (100% GGBS and 0.75% HESF) provided the best strength and durability option but at higher material cost; RGCM7 (50% FA, 50% GGBS, and 0.75% HSF) exhibited a balanced choice since it offer satisfied strength and durability performance with moderate cost compared to other options. Full article

Silica fume (SF) is extensively utilized for enhancing concrete properties. This study examines the impact of SF dosage on concrete frost resistance. Specimens were produced by replacing cement with SF at 5%, 10%, 20%, and 30% ratios. Mechanical testing and microscopic characterization measured variations in mass loss, relative dynamic elastic modulus, flexural strength, hydration products, and pore structure. Digital image correlation tracked failure development during flexural tests. Results indicated that SF-modified concrete showed lower mass loss, better elastic modulus retention, and improved flexural strength maintenance compared to plain concrete after identical freeze–thaw (F-T) cycles. Additionally, SF-modified concrete demonstrated reduced crack widths and slower crack expansion during bending. The 10% SF mixture, after 300 cycles, achieved optimal results characterized by 2.83% mass loss, 88.1% relative dynamic modulus, and only a 17% flexural strength reduction. Microscopic studies confirm that SF addition increases calcium silicate hydrate formation, decreases calcium hydroxide levels, and refines pore structure with higher density. These modifications enhance frost resistance. A service-life prediction model using gray model approach methodology projected that 10% SF concrete would last 2.01 times longer than unmodified concrete under F-T exposure. Full article

This study investigates the bond strength of fifteen cement-based adhesive mortars used for expanded polystyrene (EPS) in External Thermal Insulation Composite Systems (ETICS). Field surveys and contractor interviews (170 questionnaires) found that adhesive layer thicknesses in real applications typically range from 15–20 mm and frequently exceed 20 mm, in contrast to the smaller values most often recommended by guidelines and technical instructions. Laboratory testing was conducted using two approaches: the standardized pull-off procedure according to EAD 040083-00-0404 (EAD and EAD′ variants) and an in-house pull-off procedure designed to reflect practical conditions of substrate type (concrete slab, silicate block), substrate orientation (horizontal, vertical), and adhesive layer thickness (10 and 20 mm). The results showed that adhesive bond strength is strongly influenced by adhesive layer thickness, substrate type, and substrate orientation. Increasing thickness from 10 mm to 20 mm on concrete substrates typically reduced bond strength by about 65–75%, while vertical orientation lowered adhesion to about half of that obtained in horizontal placement. Silicate substrates exhibited generally lower bond strength but higher variability, occasionally with ratios above unity due to their greater porosity. In some configurations, detachment occurred already during specimen preparation, underlining the variability of performance. The combined effect of increased thickness and vertical orientation on concrete substrates reduced adhesion by about 85% compared to the 10 mm horizontal baseline, highlighting the severity of unfavorable application conditions, whereas on silicate blocks, the effect was weaker but accompanied by large variability. The findings indicate that adhesive layer thickness has a stronger impact on bond strength than orientation and that substrate properties play an important role. The study provides a comparative perspective on current and alternative testing approaches, revealing significant differences in the results. The author’s testing method makes it possible to account for, in laboratory conditions, primarily the geometric shape and orientation of samples that are close to the actual form of adhesive mortar application in real insulation installations. This allows for the assessment of the properties of mortars and substrates that were not exposed under the conditions of current testing methods. The above provides a basis for further discussion on the inclusion of realistic application conditions in the evaluation of adhesive mortars used for bonding thermal insulation in ETICS, and for the validation assessment of an additional testing method, which is currently of an experimental nature. Full article