Search Results (393)

Geopolymer mortars were produced from construction and demolition waste using a binary binder of recycled brick powder/recycled concrete powder (RBP/RCP = 70/30 wt%), activated with a hybrid alkaline solution (NaOH/Na₂SiO₃/KOH) and reinforced with sisal fibres at 0–2 wt%. Mechanical performance (compression and three-point bending) and microstructure–phase evolution (XRD, FTIR, SEM-EDS) were assessed after low-temperature curing. Sisal addition delivered a strength–toughness trade-off with a reproducible optimum at ~1.0–1.5 wt%; at 2.0 wt%, fibre clustering and connected porosity reduced the effective load-bearing section, penalising flexure more than compression. Microstructural evidence indicates coexistence and co-crosslinking of N-A-S-H and C-(A)-S-H gels—enabled by Ca from RCP—leading to matrix densification and improved fibre–matrix anchorage. Fractographic features (tortuous crack paths, bridging, and extensive pull-out at ~1.5 wt%) are consistent with an extended post-peak response and higher fracture work without compromising early-age strength. This study achieves the following: (i) it identifies a practical reinforcement window for sisal in RBP/RCP geopolymers, (ii) it links gel chemistry and interfacial phenomena to macroscopic behaviour, and (iii) it distils processing guidelines (gradual addition, workability control, gentle deaeration, and constant A/S) that support reproducibility. These outcomes provide a replicable, low-embodied-CO₂ route to fibre-reinforced geopolymer mortars derived from CDW for non-structural and semi-structural applications where flexural performance and post-peak behaviour are critical. Full article

This paper presents a microstructural, mineralogical, and mechanical study of low-carbon autoclaved concrete (AC), achieved by partially or fully replacing ordinary Portland cement (OPC) with ground-granulated blast furnace slag (BFS) and substituting lime with calcium carbide slag (CCS). Fourteen mixes were produced and evaluated in the green state and after autoclaving. Quantitative X-ray diffraction (XRD) using the Rietveld method, density, compressive strength, and life cycle assessment (LCA) were conducted. Results show that mixes containing BFS achieve green strengths equal to or higher than the OPC reference, ensuring integrity during autoclaving. Using BFS with an adequate calcium supply promotes the formation of pre-autoclave portlandite, which in turn favors tobermorite development and yields post-autoclave strengths comparable to the OPC reference. Partial lime replacement with CCS (50%) maintains mineralogy and strength, whereas excessive CCS may reduce available portlandite and lower strength. Life-cycle assessment indicates that raw material supply dominates emissions and that removing OPC cuts total CO₂ by 44% without compromising mechanical performance. These findings demonstrate the feasibility of OPC-lean/OPC-free, lime-optimized autoclaved concretes with substantially lower embodied impacts. Full article

Spent garnet (SG) wastes are generated in significant quantities by several industrial activities, including abrasive waterjet cutting (AWJ), abrasive blasting, and filtration and powdered media applications. These wastes represent a promising secondary raw material for the production of sustainable construction materials, particularly green mortars and concretes, through their partial replacement of natural sand in cementitious systems. Such applications are relevant to both hydraulically setting inorganic binders (cement-based materials) and alkali-activated cementitious materials (AACMs). The valorization of SG wastes offers multiple benefits, notably a dual environmental advantage: reducing the consumption of natural aggregates and diverting industrial waste from disposal by integrating it into a new life cycle as a value-added by-product. Additional potential advantages include reduced production costs and possible improvements in the overall performance of mortars and concretes. Despite these benefits, the use of SG as an aggregate replacement remains insufficiently explored, with existing studies providing only preliminary and fragmented evidence of its feasibility. This paper presents an overview of a comprehensive four-year research program investigating SG wastes derived from single-cycle AWJ processes and their incorporation into conventional mortars as partial fine aggregate replacement in cement-based construction composites. The validation stage of the performance assessment expands the range of SG sources by including new sampling from the original suppliers, enabling verification of the repeatability and reproducibility of earlier findings. A broad set of physical, mechanical, and durability properties—particularly resistance to freeze–thaw cycles—is evaluated to achieve a robust and comprehensive material characterization. These results are further correlated with chemical and microstructural analyses, providing critical insights to support the technological transfer of SG-based construction materials to industrial applications with reduced carbon footprint. Full article

Since the number of existing steel-reinforced concrete buildings affected by carbonation-induced corrosion is steadily increasing, there is a high demand for durable repair methods. Chemical re-alkalization (CRA) represents one such approach, relying on the transport of alkaline pore solution from a repair mortar into carbonated concrete. With the introduction of clinker-reduced binder systems such as hybrid alkali-activated binders (HAABs), their suitability for CRA and governing material parameters require further clarification. In this study, material-related chemical and structural influences on CRA were investigated using an adapted form of Fick’s second law of diffusion, incorporating a time-dependent attenuation factor, β(t). The CRA progression was evaluated over 28 days, distinguishing between an initial suction phase and a subsequent diffusion phase. The results show that a high initial alkalinity of the mortar pore solution (pH > 14) significantly enhances re-alkalization during the suction phase, reflected by suction factors a > 1. In contrast, progression during the diffusion phase is primarily governed by the potassium concentration gradient at the mortar–concrete interface, while structural parameters such as capillary porosity show no systematic correlation with the deceleration factor b (−0.46 ≤ b ≤ −0.26). The findings indicate that, within the investigated range, mortar pore solution chemistry has a stronger influence on CRA than structural properties, providing guidance for the targeted design of alkaline repair mortars. Full article

Coral aggregate concrete (CAC) serves as a critical material for sustainable development in marine engineering, effectively addressing the shortage of aggregate resources in the construction of offshore islands and reefs. In this paper, the aggregate characteristics, static and dynamic mechanical properties and modification technology of CAC are systematically reviewed. Research indicates that the coral aggregates (CAs), due to its high porosity (approximately 50%), low bulk density (900–1100 kg/m³), and rough, porous surface, results in relatively low static compressive strength (20–40 MPa), insufficient elastic modulus, and significant brittleness in CAC. However, its dynamic performance shows the opposite advantage. Under impact loads, the energy absorption capacity is enhanced by 32.6–140.3%, compared to ordinary concrete (OC) due to the energy dissipation mechanism of pore platic deformation. Through the modification techniques, such as aggregate pre-treatment (acid washing/coating), incorporation of auxiliary cementitious materials (silica fume increases strength by 16.4%), fibre reinforcement (carbon fibres enhance flexural strength by 33.3%), and replacement with novel cementitious materials (magnesium sulphate cement improves chloride ion binding capacity by 90.7%), the mechanical properties and durability of CAC can be significantly optimised. This paper highlights gaps in current research regarding the high strain rate (>200 s⁻¹) dynamic response, multi-factor coupled durability in marine environments, and the engineering application of alkali-activated materials, providing theoretical basis for future research directions. Full article

To address the energy and environmental challenges, this study targets the need for ultra-low energy buildings in China’s hot summer-cold winter region (HSCW) by developing high-performance alkali-activated foam concrete (AAFC) insulation material. Initially, a target performance indicator system was established. Subsequently, a mix proportion design method based on the volume method was proposed, and preliminary mix proportions were designed and tested to achieve the target performance. Accordingly, eight factors, including alkali equivalent and SiO₂ aerogel content, were selected for further optimization. A systematic optimization of performance was then conducted using an L₃₂(4⁸) orthogonal experimental design. Range analysis and analysis of variance indicated that foam content significantly affected all target properties. The water-to-binder ratio notably influenced mechanical performance and dry density. Alkali equivalent and activator modulus directly regulated the reaction process. Notably, the incorporation of 2.5 wt% SiO₂ aerogel reduced the thermal conductivity to 0.1107 W/(m·K), highlighting its significant role in improving thermal insulation and effectively resolving the common trade-off between insulation and mechanical properties in FC. Furthermore, the waterproofing agent played a critical role in reducing water absorption and enhancing frost resistance. Finally, the optimal mix proportion was determined through matrix analysis, with all material properties meeting the expected targets. Test results confirmed that the optimized FC achieved a dry density of 576.34 kg/m³, compressive and flexural strengths of 5.83 MPa and 1.41 MPa, respectively, a drying shrinkage rate of only 0.614 mm/m, a mass water absorption of 3.87%, and strength and mass loss rates below 10.5% and 1.8% after freeze–thaw cycles. Therefore, this material presents a novel solution for the envelope structures of low-energy buildings. Full article

This study prepares solid-waste-based alkali-activated material (AAM) concrete using ground granulated blast furnace slag (GGBFS), fly ash (FA), steel slag (SS), and desulfurized gypsum (DG) as primary raw materials, with Na₂SiO₃ as the activator. Taking the GGBFS content (X₁), Na₂SiO₃ content (X₂), and water-to-binder ratio (X₃) as independent variables and the 3-day, 7-day, and 28-day compressive strengths and slump as response values, it investigates the influence of each factor and their interactions, constructs a response surface prediction model, screens for the optimal mix proportion with comprehensive performance, and explores the microstructural characterization and strength formation mechanism of the AAM concrete via SEM and EDS. The results indicate the following: (1) compared with binary and ternary mixtures, the use of the quaternary solid waste mixture not only enhances strength and optimizes the microstructure but also increases the utilization rate of low-quality solid wastes; (2) the regression coefficients (R²) of the response surface models are all greater than 0.98, exhibiting good goodness of fit and rationality. Experimental validation confirms that each model shows excellent predictive capability; (3) AAM concrete exhibits comprehensively superior mechanical properties to ordinary cement, with leading early- and late-stage compressive strengths and splitting strengths, albeit with a slightly lower slump; (4) the performance synergy is prominent. Combined with microscopic analysis (highly polymerized C-S-H gels and a dense structure), the superiority of its macroscopic mechanical properties stems from the optimization of the microstructure, reflecting the intrinsic correlation of the “microscopic densification-macroscopic high strength. Full article

To clarify the effect of sand ratio on the freeze–thaw performance of full solid waste geopolymer concrete (FSWGC) and establish a constitutive model for its post-freeze–thaw mechanical behavior, FSWGC was prepared via alkali activation—using fly ash, slag, silica fume as cementitious materials, and cold-bonded geopolymer lightweight aggregates (CBGLAs) and recycled sand as aggregates. With sand ratios (0.45, 0.55, 0.65) as the core variable, rapid freeze–thaw tests were conducted to measure mass loss, relative dynamic elastic modulus, mechanical properties, and axial compressive stress–strain characteristics of FSWGC. Results show that higher sand ratios significantly aggravate freeze–thaw damage: after 100 cycles, the 0.65 sand ratio specimen has a mass loss rate of 4.61% and a relative dynamic elastic modulus retaining only 34.4% of its initial value, with accelerated strength degradation. This is due to yjr weakened wrapping of recycled sand by cementitious materials, forming a weak interfacial transition zone. The modified Guo constitutive model for FSWGC, and the further established model considering freeze–thaw cycles, accurately describe the stress–strain curve of FSWGC before and after freeze–thaw. This study provides theoretical and experimental support for FSWGC mix optimization, durability design, and mechanical response calculation in cold regions. Full article

With the growing demand for sustainable and high-performance construction materials, alkali-activated materials (AAM) have attracted significant interest as eco-friendly al-ternatives to cement-based systems. Nevertheless, the tensile ductility and AAM–concrete interfacial bonding of polyethylene fiber-reinforced AAM remain insufficiently understood, and systematic knowledge on how activator modulus governs these multi-scale properties is still limited. This study aims to clarify how activator modulus (Ms = 0, 0.5, 0.8, 1.1, 1.4) influences the mechanical, interfacial, and microstructural behavior of an engineered AAM reinforced with polyethylene fibers. The effects are investigated through uniaxial tensile tests, single-fiber pull-out experiments, bond tests with concrete, and microstructural analyses (SEM, XRD, CT). Results show that an activator modulus of 1.1 yields the best overall performance, achieving a 28-day tensile strength of 3.77 MPa and ultimate tensile strain of 3.68%, representing increases of 231% and 64.6% compared with a modulus of 0. Microstructural observations confirmed that the optimized modulus promotes extensive gel formation, improves fiber–matrix interfacial bonding, and enhances strain-hardening with multiple microcracks. Interfacial tests further demonstrated that Ms strongly affects bond performance between AAM and concrete, with 1.0–1.1 providing balanced adhesion and matrix ductility, while excessive activation (Ms = 1.4) caused interfacial defects and bond deterioration. These findings deepen the understanding of the micromechanical role of activator modulus and provide guidance for the mix design of durable, high-ductility AAM suitable for sustainable infrastructure. Full article

This study investigates the potential of producing zero-clinker, alkali-activated binders and concrete entirely from industrial by-products—ladle furnace slag (LFS), coal ash (CA), and cement kiln dust (CKD). The incorporation of CKD enhanced the workability and compressive strength properties of the alkali-activated mixtures, with the highest mechanical properties at 20% CKD addition. XRD, FTIR, and SEM analyses confirmed the formation of hydrocalumite, indicating improved hydration and microstructural densification. Mortar and concrete produced using the eco-cement reached 28-day strengths of 34.5 MPa and 32.6 MPa, corresponding to concrete class C20/25. These findings demonstrate the feasibility of manufacturing 100% waste-based construction materials suitable for sustainable, non-reinforced applications. Full article

Against the backdrop of China’s Western Development Strategy, numerous infrastructure projects are being constructed in desert regions. Utilizing local aeolian sand (AS) as a raw material for concrete production offers significant cost-saving potential but is hindered by challenges such as limited applicability and inadequate mechanical strength of the resulting concrete. To address these limitations, aeolian sand was ground into aeolian sand powder (ASP) and subjected to treatment with single alkali activators (NaOH, Na₂SiO₃) and a composite alkali activator (NaOH + Na₂SiO₃). The treated and untreated ASP was then used to replace 50% of cement by mass for the preparation of aeolian sand powder–aeolian sand concrete (ASPC). Mechanical performance tests and advanced characterization techniques (SEM, TG-DSC, XRD, FTIR, nanoindentation, and NMR) were employed to investigate the effects of different activators on the mechanical properties of ASPC and elucidate the underlying enhancement mechanisms. The results demonstrated that the composite activator outperformed its single-activator counterparts: ASPC-4-6 (incorporating 4% NaOH and 6% Na₂SiO₃) exhibited 16.3–23.1% higher compressive strength and 12.1–17.6% higher splitting tensile strength across all curing ages compared to plain ASPC. Under the influence of OH⁻ from the composite activator, ASP showed more pronounced reductions in potassium feldspar, montmorillonite, and SiO₂ content, accompanied by the formation of C-S-H gel—replacing the amorphous, water-absorbent N-A-S-H generated by single activators. The presence of highly polymerized hydration products and more stable potassium A-type zeolites in ASPC-4-6 led to a reduction in macropore volume, optimization of pore structure, and refinement of the aggregate–mortar inter-facial transition zone. These micro-structural improvements collectively contributed to the significant enhancement of mechanical properties. This study provides novel insights into the large-scale and multi-dimensional utilization of aeolian sand in concrete. Full article

Basic oxygen furnace slag (BOFS) is one of the major by-products of the steelmaking industry. Its limited utilization as a construction material is primarily attributed to its chemical properties, which hinder its stability and hydraulic activity due to its high free lime (f-CaO) content. This paper explores the performance of supplementary cementitious material (SCM) synthesized with ground granulated blast furnace slag (GGBFS), freshly produced BOFS (f-BOFS), and stockpiled BOFS (s-BOFS). A total of 10 mixtures with ordinary Portland cement (OPC) replacement percentages were assessed, maintaining a total replacement of 50% OPC, incorporating 15%, 25%, and 35% of each material by weight. The laboratory experimental program encompassed material characterization, fresh and hardened properties, pozzolanic activity, and durability assessment, with comparative studies conducted for each evaluation item. Test results indicate that f- or s-BOFS, when used with GGBFS, can be a viable alternative SCM with the potential for hydraulic activities and pozzolanic reaction. The newly synthesized SCMs demonstrated improved strength development in mortar mixtures. The mixture containing [15% f-BOFS + 35% GGBFS] achieved a 28-day compressive strength of 20.6 MPa, while the [25% BOFS + 25% GGBFS] blend reached a compressive strength of 19.7 MPa. These mixtures meet Grade 80 criteria as per ASTM C989/C989M Standard Specification for Slag Cement for Use in Concrete and Mortars. A performance-based ranking system was developed by integrating results from flowability, air content, strength activity index, drying shrinkage, alkali–silica reaction, and sulfate attack. The novelty of this work lies in assessing BOFS–GGBFS blends as SCMs using this multi-criteria approach to identify the most sustainable and technically viable mixtures. Moreover, the study highlights the influence of storage-induced weathering by directly comparing the reactivity and performance of f- and s-BOFSs in ternary blends, providing new insights into optimizing the utilization of slag. Notably, regardless of f- and s-BOFSs, proportions of [15% BOFS + 35% GGBFS] demonstrated superior strength development and achieved an excellent overall ranking. These findings confirm the potential of such slag blends as suitable SCMs for mortar and concrete applications, thereby advancing the sustainability and efficiency of cementitious materials. Full article

The construction industry’s growth is causing a surge in CO₂ emissions, driven by increased demand for concrete and other building materials. There is a growing demand for more sustainable building materials, including alkali-activated materials. This study investigates the impact of varying ratios of Na₂SiO₃ and NaOH on the mechanical properties and microstructure of metakaolin (MKW) and ceramic brick waste (CBW) based geopolymer binder. Geopolymer binder precursors were made of three main CBW/MKW ratios: 100/0%wt. (C100), 50/50%wt. (C50M50), and 0/100%wt. (M100). Alkaline activator solutions had three different Na₂SiO₃/NaOH ratios: 0.5, 1.0, and 2.0. The investigation into the geopolymer binder mechanical properties was conducted using a range of analytical methods, including compressive strength, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The findings of the study indicate that the Na₂SiO₃/NaOH ratio alone is inadequate for evaluating geopolymer mechanical properties when different AS/P ratios are employed, given its influence on other parameters, such as the W/S ratio and the total Na₂O content. CBW-based geopolymer binders demonstrate limited capacity to attain substantial compressive strengths because they contain high amounts of unreacted CBW particles, as shown by XRD analysis. The incorporation of MKW precursor resulted in enhanced reactivity and intensified geopolymerization reaction. After the evaluation of all essential ratios, the most favorable Na₂SiO₃/NaOH ratio is 1.0. This determination was based on the highest strengths observed in designs that contained ≥50% of MKW precursor, attributed to predominance of goosecreekite and N-A-S-H gels, as evidenced by XRD and FT-IR analysis. Full article

This study presents a comprehensive strategy for mitigating drying shrinkage of alkali-activated slag mortar (AASM) with the high-dosage incorporation of waste concrete powder (WCP). Response surface methodology (RSM) coupled with microstructural analysis is used to investigate the synergistic effects of WCP particle size (R), activator modulus (AM), activator content (AC), and water to solid ratio (W/S) on shrinkage behavior and matrix development. The optimized mix—WCP-R = 33.6 µm, AM = 1.23, AC = 6.03%. and W/S = 0.49—exhibits a 120-day drying shrinkage of only 1450.1 µε, significantly lower than that of conventional AASM. Microstructural observations reveal that coarser WCP particles act predominantly as fillers, enhancing stability, whereas finer particles promote gel formation but increase shrinkage. A high AM (1.6) refines the pore structure by reducing large pores (>0.05 µm), while a low W/S (0.46) decreases total porosity to 7.67%, collectively restricting moisture transport. The coexistence of C-(A)-S-H gel and hydrotalcite improves matrix integrity. Notably, this optimized HWAASM achieves a substantially reduced carbon footprint of 180 kg CO₂-eq/t, underscoring its significant environmental advantage. The findings advance the understanding of shrinkage mechanisms in high-WCP-AASM and offer an eco-friendly route for valorizing construction waste and developing low-carbon building materials. Full article

The construction industry is among the most resource-intensive sectors, generating nearly 40% of global CO₂ emissions and over two billion tonnes of construction and demolition waste (CDW) annually. This study investigates the sustainable reuse of CDW in developing binder-free alkali-activated paste (AAP) using sodium hydroxide (NaOH) as an activator. Eleven formulations were prepared by varying the brick-to-total waste ratio (BW/TW: 0–1), NaOH concentrations (0–10%), and curing durations (7, 28, and 60 days). The mixes were evaluated for unconfined compressive strength (UCS), shear modulus (G_o), durability (wet–dry and freeze–thaw cycles), and microstructural evolution. Results showed significant improvements in mechanical and durability properties with increased NaOH content, BW/TW ratios up to 0.9, and longer curing times. The optimal mix (10% NaOH, BW/TW = 0.9, 60 days of curing) achieved a UCS of 28.7 MPa and a G_o of 30 GPa, while exhibiting minimal mass loss (<2% freeze–thaw; <3% wet–dry). Microstructural analyses revealed densified matrices and enhanced gel formation. A dimensional analysis using the Buckingham π theorem yielded a scalable predictive model that correlates material composition, alkaline activation, and curing with mechanical performance. The study underscores the feasibility of transforming CDW into durable, high-performance AAPs for sustainable infrastructure development. Full article