Search Results (237)

This study aims to enhance the performance of an innovative steel slag–ceramsite foam concrete (SSCFC) to advance sustainable green building materials. An eco-friendly composite construction material was developed by integrating industrial by-product steel slag (SS) with lightweight ceramsite. Employing a three-factor, three-level orthogonal experimental design at a fixed density of 800 kg/m³, 12 mix proportions (including a control group) were investigated with the variables of water-to-cement (W/C) ratio, steel slag replacement ratio, and ceramsite replacement ratio. The governing mechanisms of the W/C ratio, steel slag replacement level, and ceramsite replacement proportion on the SSCFC’s fluidity and compressive strength (CS) were elucidated. The synergistic application of range analysis and analysis of variance (ANOVA) quantified the significance of factors on target properties, and partial least squares regression (PLSR)-based prediction models were established. The test results indicated the following significance hierarchy: steel slag replacement > W/C ratio > ceramsite replacement for fluidity. In contrast, W/C ratio > ceramsite replacement > steel slag replacement governed the compressive strength. Verification showed R² values exceeding 65% for both fluidity and CS predictions versus experimental data, confirming model reliability. Multi-criteria optimization yielded optimal compressive performance and suitable fluidity at a W/C ratio of 0.4, 10% steel slag replacement, and 25% ceramsite replacement. Full article

Fly ash and slag are widely used as mineral admixtures to partially replace cement in low-carbon concrete. However, such composite concretes often exhibit a greater carbonation depth than plain Portland concrete with the same 28-day strength, increasing the risk of steel reinforcement corrosion. Previous mix design methods have overlooked this issue. This study proposes an optimized design method for fly ash–slag composite concrete, considering carbonation exposure classes and CO₂ concentrations. Four exposure classes are addressed—XC1 (completely dry or permanently wet environments such as indoor floors or submerged concrete), XC2 (wet but rarely dry, e.g., inside water tanks), XC3 (moderate humidity, e.g., sheltered outdoor environments), and XC4 (cyclic wet and dry, e.g., bridge decks and exterior walls exposed to rain). Two CO₂ levels—0.04% (ambient) and 0.05% (elevated)—were also considered. In Scenario 1 (no durability constraint), the optimized designs for all exposure classes were identical, with 60% slag and 75% total fly ash–slag replacement. In Scenario 2 (0.04% CO₂ with durability), the designs for XC1 and XC2 remained the same, but for XC3 and XC4, the carbonation depth became the controlling factor, requiring a higher binder content and leading to compressive strengths exceeding the target. In Scenario 3 (0.05% CO₂), despite the increased carbonation depth, the XC1 and XC2 designs were unchanged. However, XC3 and XC4 required further increases in binder content and actual strength to meet durability limits. Overall, compressive strength governs the design for XC1 and XC2, while carbonation durability is critical for XC3 and XC4. Increasing the water-to-binder ratio reduces strength, while higher-strength mixes emit more CO₂ per cubic meter, confirming the proposed method’s engineering validity. Full article

Ground granulated blast-furnace slag (GGBS), a waste product generated during steel production, can be added as a substitute for cement in concrete to mitigate the environmental impact of the cement and steel industries. However, the use of GGBS is limited because it decreases the early strength development of cement or concrete. This study evaluated the performance of incorporating synthesized C-S-H nanoparticles to enhance the compressive strength, early hydration, and microstructure of cement composite. The synthesized C-S-H nanoparticles were produced at standard atmospheric pressure and room temperature. Heat of hydration, X-ray diffraction, and thermogravimetric analyses were conducted to investigate the hydration and mechanical properties of the cement containing the C-S-H nanoparticles. Further, mercury intrusion porosimetry was conducted to examine the pore structures. The experimental finding demonstrated that adding C-S-H nanoparticles accelerated the early hydration progress in the cement composites, thereby increasing their initial compressive strength. Full article

The utilization of steel slag (SS) in construction materials represents an effective approach to improving its overall recycling efficiency. This study incorporates SS into a conventional ground granulated blast-furnace slag (GGBS)–fly ash (FA)-based binder system to develop a ternary system comprising SS, GGBS, and FA, and investigates how this system influences the static mechanical properties of ultra-high-performance geopolymer concrete (UHPGC). An axial point augmented simplex centroid design method was employed to systematically explore the influence and underlying mechanisms of different binder ratios on the workability, axial compressive strength, and flexural performance of UHPGC, and to determine the optimal compositional range. The results indicate that steel slag has a certain negative effect on the flowability of UHPGC paste; however, with an appropriate proportion of composite binder materials, the mixture can still exhibit satisfactory flowability. The compressive performance of UHPGC is primarily governed by the proportion of GGBS in the ternary binder system; an appropriate GGBS content can provide enhanced compressive strength and elastic modulus. UHPGC exhibits ductile behavior under flexural loading; however, replacing GGBS with SS significantly reduces its flexural strength and energy absorption capacity. The optimal static mechanical performance is achieved when the mass proportions of SS, GGBS, and FA are within the ranges of 9.3–13.8%, 66.2–70.7%, and 20.0–22.9%, respectively. This study provides a scientific approach for the valorization of SS through construction material applications and offers a theoretical and data-driven basis for the mix design of ultra-high-performance building materials derived from industrial solid wastes. Full article

This study systematically investigates the effect of steel fiber content on the fractal evolution characteristics of bending cracks in alkali-activated slag concrete (AASC) beams. A four-point bending test on simply supported beams, combined with digital image correlation (DIC) technology, was employed to quantitatively analyze the fractal dimension of crack propagation paths in AASC beams with steel fiber contents ranging from 0% to 1.4%, using the box-counting method. The relationship between fracture energy and fractal dimension was examined, along with the fractal control mechanisms of mid-span deflection, crack width, and the fractal evolution of fracture toughness parameters. The results revealed that as the steel fiber content increased, the crack fractal dimension decreased from 1.287 to 1.155, while the critical fracture energy of AASC beams increased by approximately 75%. Both mid-span deflection and maximum crack width were positively correlated with the crack fractal dimension, whereas the fractal dimension showed a negative correlation with critical cracking stress and fracture toughness and a positive correlation with the energy release rate. When the steel fiber content exceeded 1.2%, the performance gains began to diminish due to fiber agglomeration effects. Overall, the findings suggest that an optimal steel fiber content range of 1.0% to 1.2% provides the best crack control and mechanical performance, offering a theoretical basis for the design of AASC structures. Full article

This study investigates the thermal performance of 23 different mortar types, each containing different mixes, properties, and additives. A comprehensive literature review was conducted to collect experimental data on the thermal properties of these mortars, which were then used in a numerical analysis through thermal finite element modeling. The results showed that all mortar types contributed to reducing the internal temperature of structural steel and reinforced concrete elements, with performance primarily influenced by key factors such as the mortar’s thermal conductivity, specific heat capacity, thermal diffusivity, and coating thickness. In particular, the mortar with glass fiber reinforced polymer (GFRP) as a slag substitute and the mortar with expanded perlite replacing sand showed the highest thermal protection and achieved a temperature reduction on the order of 100%. In contrast, mortars containing 30% vermiculite or 15% light expanded polyvinyl chloride (PVC) as a sand substitute showed the lowest thermal performance. Full article

This study investigates the influence of steel fiber content (0~3% by volume) on the workability and mechanical properties of ultra-high-performance concrete (UHPC) incorporating slag or fly ash. Although UHPC exhibits excellent strength and durability, its brittleness and high cost hinder broader applications. Steel fibers are known to improve mechanical performance and toughness, but their interaction with mineral admixtures remains underexplored. Flowability, compressive strength, flexural behavior, impact resistance, and microstructure were evaluated. Results show that increasing fiber content significantly reduces workability, with fly ash-based mixes showing better flowability than slag-based ones. Mechanical properties improved with higher fiber volume, and an optimal content of 2% achieved the best balance between workability and strength. Impact testing and stress–strain analysis revealed that steel fibers enhance energy absorption and toughness under dynamic loading. SEM observations at 3 days indicated initial bonding between the fibers and matrix, with minor microcracks, suggesting further strength development over time. This work offers a fresh understanding of the combined influence of steel fibers and mineral admixtures in UHPC and supports their effective application in durable and cost-efficient high-performance concrete design. Full article

Geopolymer concrete (GPC) offers reduced carbon emissions and employs industrial by-products such as fly ash and ground granulated blast furnace slag (GGBFS). In this study, the synergistic augmentation of shear carrying capacity in steel-fiber-reinforced rubberized geopolymer concrete (FRGC) incorporating industrial by-products such as fly ash, GGBFS, and recycled rubber for sustainable construction is investigated. The reinforced rubberized geopolymer concrete (RFRGC) mixtures contained 20% rubber crumbs as a partial replacement for fine aggregate, uniform binder, and alkaline activator. The findings revealed that 1.25% steel fiber achieved optimal hardened properties (compressive strength, flexural, and split tensile strength), with 12 M sodium hydroxide and oven curing achieving maximum values. An increase in molarity improved geopolymerization, with denser matrices, while oven curing boosted polymerization, enhancing the bonding between the matrix and the fiber. The effect of steel fiber on the shear carrying capacity of RFRGC beams without stirrups is also discussed in this paper. An increased fiber content led to an increased shear carrying capacity, characterized by an improvement in first crack load and a delayed ultimate failure. These results contribute to sustainable concrete technologies for specifically designed FRGC systems that can balance structural toughness, providing viable alternatives to traditional concrete without compromising strength capacity. Full article

Engineered cementitious composites (ECCs), known for their superior ductility and strain-hardening behavior compared to conventional concrete, have been predominantly studied with polyvinyl alcohol (PVA) fibers. However, the potential economic and technical advantages of incorporating steel fibers into ECCs have been largely overlooked in the literature. This study investigates the mechanical performance of ECC reinforced with different types of steel fibers, including straight, twisted, hooked, and hybrid fibers of different lengths, as compared to PVA. The inclusion of various supplementary cementitious materials (SCMs) such as slag and fly ash with each type of steel fiber was also considered at a constant fiber volume fraction of 2%. The mechanical properties were assessed through compressive strength, splitting tensile strength, and four-point flexural tests along with calculations of toughness, ductility, and energy absorption capacity indices. This study compares the mechanical properties of different ECC compositions, revealing that ECCs with hybrid steel fibers (short and long) achieved more than twice the tensile strength, 12.7% higher toughness, and 36.4% greater energy absorption capacity compared to ECCs with PVA fibers, while exhibiting similar multiple micro-cracking behavior at failure. The findings highlight the importance of fiber type and distribution in enhancing an ECC’s mechanical properties, providing valuable insights for developing more cost-effective and resilient construction. Full article

To mitigate ecological damage from excessive natural aggregate extraction, this study developed an eco-friendly concrete using dune sand and steel slag as natural aggregates, enhanced with polyvinyl alcohol (PVA) fibers. Through orthogonal testing, the effects of the dune sand replacement ratio, steel slag replacement ratio, PVA fiber length, and PVA fiber content on concrete workability and mechanical properties were analyzed. The results show that slump exceeded 120 mm (meeting engineering requirements) in mixes except that with 40% dune sand, 60% steel slag, 18 mm PVA fiber length, and 0.4% PVA fiber content; 50% steel slag replacement significantly improved mechanical properties, yielding a 21.2% increase in 28 d compressive strength when replacement increased from 30% to 50%; 20% dune sand replacement for river sand is optimal; and while increased PVA content enhanced splitting tensile and flexural strengths, both its length and content should not exceed 9 mm and 0.3%, respectively. The concrete delivers acceptable performance while providing dual environmental benefits: reduced aggregate consumption pressure and achieved high-value-added dune sand–steel slag utilization. Full article

Alkali-activated binders (AAB) are a suitable and sustainable alternative to ordinary Portland cement (OPC), with reductions in natural resource usage and environmental emissions in regions where the necessary industrial residues are available. Despite its potential, the lack of mix design methods still limits its applications. This paper proposes a systematic parametric validation for AAB mix design applied to pastes and concretes, valorizing steel slag as precursors. The composed binders are based on coal fly ash (FA) and Basic Oxygen Furnace (BOF) steel slag. These precursors were activated with sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH) alkaline solutions. A parametric investigation was performed on the mix design parameters, sweeping the (i) alkali content from 6% to 10%, (ii) silica modulus (SiO₂/Na₂O) from 0.75 to 1.75, and (iii) ash-to-slag ratios in the proportions of 75:25 and 50:50, using parametric intervals retrieved from the literature. These variations were analyzed using response surface methodology (RSM) to develop a mechanical model of the compressive strength of the hardened paste. Flowability, yield stress, and setting time were evaluated. Statistical analyses, ANOVA and the Duncan test, validated the model and identified interactions between variables. The concrete formulation design was based on aggregates packing analysis with different paste contents (from 32% up to 38.4%), aiming at self-compacting concrete (SCC) with slump flow class 1 (SF1). The influence of the curing condition was evaluated, varying with ambient and thermal conditions, at 25 °C and 65 °C, respectively, for the initial 24 h. The results showed that lower silica modulus (0.75) achieved the highest compressive strength at 80.1 MPa (28 d) for pastes compressive strength, densifying the composite matrix. The concrete application of the binder achieved SF1 fluidity, with 575 mm spread, 64.1 MPa of compressive strength, and 26.2 GPa of Young’s modulus in thermal cure conditions. These findings demonstrate the potential for developing sustainable high-performance materials based on parametric design of AAB formulations and mix design. Full article

The utilization of steam-cured steel slag fine aggregate concrete (SC) faces challenges in accurately predicting its stress–strain relationship. The mechanical properties of steam-cured SC and its stress–strain relationship have been systematically investigated through combined tests and machine learning (ML) approaches. The results showed that steam curing at 50 °C greatly increased the peak stress and ductility of SC. Specimens, the steel slag fine aggregate (SA) content of which was 40% by volume, and which were subjected to steam curing at 50 °C, exhibited superior mechanical and deformation properties. The prediction performance of three ML models—random forest (RF), backpropagation neural network (BPNN), and support vector regression (SVR)—was compared based on the test data. The analysis results revealed that the RF model achieved optimal performance (R² = 1.00), whereas the SVR model underperformed overall. Through the transfer validation method, it was found that the BPNN model, after parameter optimization, demonstrated a superior generalization ability in cross-mix-proportion predictions. It exhibited satisfactory prediction stability for steam-cured SC with an untrained mix proportion. In contrast, the RF model tended to overestimate peak stress. The theoretical reference for realizing the comprehensive utilization of steel slag in precast concrete components has been provided. Full article

This study investigates the long-term corrosion behavior of reinforced concrete (RC) under accelerated chloride exposure for about 1600 days, using electrochemical methods like galvanostatic pulse (GP) testing. Two concrete mixes (T1 and T2), incorporating distinct supplementary cementitious materials (SCMs), were evaluated to determine their performance in aggressive environments. Specimens with varying reservoir lengths were exposed to a 10% NaCl solution (by weight), with electromigration applied to accelerate chloride transport. Electrochemical assessments, including measurements of rebar potential, concrete solution resistance, concrete polarization resistance, corrosion current, and mass loss, were conducted to monitor the degradation of embedded steel. The findings revealed that smaller reservoirs (2.5 cm) significantly restricted chloride and moisture penetration, reducing corrosion, while larger reservoirs (10 cm) resulted in greater exposure and higher corrosion activity. Additionally, T1 mixes (partial cement replacement with 20% fly ash and 50% slag) showed higher corrosion currents and mass loss, whereas T2 mixes (partial cement replacement with 20% fly ash and 8% silica fume) demonstrated enhanced matrix densification, reduced permeability, and superior durability. These results underscore the importance of mix design and exposure conditions in mitigating corrosion, providing critical insights for improving the longevity of RC structures in aggressive environments. Full article

Steel slag aggregate (SSA), as a high-performance and sustainable material, has demonstrated significant potential in enhancing the mechanical properties of concrete and improving the bond behavior between reinforcement and the concrete matrix, thereby contributing to the seismic resilience of steel slag concrete columns (SSCCs). Nevertheless, the underlying mechanism through which SSA influences the seismic performance of SSCCs remains insufficiently understood, and current analytical models fail to accurately capture the effects of bond strength on structural behavior. In this study, a comprehensive experimental program comprising central pull-out tests and quasi-static cyclic loading tests was conducted to investigate the influence of SSA on bond strength and the seismic response of SSCCs. Key seismic performance indicators, including the hysteresis curve, equivalent viscous damping ratio, and ductility coefficient, were evaluated. The role of bond strength in governing energy dissipation and ductility characteristics was elucidated in detail. The results indicate that bond strength significantly affects the seismic performance of SSCC components. At an SSA replacement ratio of 40%, the specimens show optimal performance: energy dissipation capacity increases by 11.3%, bond–slip deformation in the plastic hinge region decreases by 10%, and flexural deformation capacity improves by 9% compared to the control group. However, when the SSA replacement exceeds 60%, the performance metrics are similar to those of ordinary concrete, showing no significant advantages. Based on the experimental findings, a modified bond–slip constitutive model for the steel slag concrete–reinforcement interface is proposed. Furthermore, a finite element model incorporating bond–slip effects is developed, and its numerical predictions exhibit strong agreement with the experimental results, effectively capturing the lateral load-carrying capacity and stiffness degradation behavior of SSCCs. Full article

Geopolymer recycled aggregate concrete (GRAC) is an eco-friendly material utilizing industrial byproducts (slag, fly ash) and substituting natural aggregates with recycled aggregates (RA). Incorporating steel-polypropylene hybrid fibers into GRAC to produce hybrid-fiber-reinforced geopolymer recycled aggregate concrete (HFRGRAC) can bridge cracks across multi-scales and multi-levels to synergistically improve its mechanical properties. This paper aims to investigate the mechanical properties of HFRGRAC with the parameters of steel fiber (SF) volume fraction (0%, 0.5%, 1%, 1.5%) and aspect ratio (40, 60, 80), polypropylene fiber (PF) volume fraction (0%, 0.05%, 0.1%, 0.15%), and RA substitution rate (0%, 25%, 50%, 75%, 100%) considered. Twenty groups of HFRGRAC specimens were designed and fabricated to evaluate the compressive splitting tensile strengths and flexural behavior emphasizing failure pattern, load–deflection curve, and toughness. The results indicated that adding SF enhances the specimen ductility, mechanical strength, and flexural toughness, with improvements proportional to SF content and aspect ratio. In contrast, a higher percentage of RA substitution increased fine cracks and reduced mechanical performance. Moreover, the inclusion of PF causes cracks to exhibit a jagged profile while slightly improving the concrete strength. The significant synergistic effect of SF and PF on mechanical properties of GRAC is observed, with SF playing a dominant role due to its high elasticity and crack-bridging capacity. However, the hydrophilic nature of SF combined with the hydrophobic property of PF weakens the bonding of the fiber–matrix interface, which degrades the concrete mechanical properties to some extent. Full article