Search Results (650)

This study presents the optimisation of an alkali-activated binder produced from ground granulated blast furnace slag (GGBFS) and potassium-rich sunflower husk ash (SHA), by varying SHA content, curing regime, and mixing procedure. Both materials are locally available in the Republic of Serbia. The influence of SHA content (15%, 25%, and 35% by mass of GGBFS) and curing conditions (ambient and 65 °C) on hydration products, workability, and compressive strength was examined. The water-to-binder ratio and GGBFS content were kept constant, and a one-part alkali activation approach was employed using untreated SHA. Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were performed on paste samples, after 2, 7 and 28 days of curing, while workability and compressive strength of mortars were measured after 7 and 28 days. Increasing SHA content enhanced the formation of C-S-H and C-A-S-H gels, resulting in a consistent rise in compressive strength, from 26.6 MPa to 36.2 MPa after 7 days and from 46.2 MPa to 55.1 MPa after 28 days of ambient curing. Workability was slightly reduced with increasing SHA content, resulting in flow diameters of 156.04 mm (15% SHA), 154.10 mm (25% SHA) and 152.76 mm (35% SHA). Curing at 65 °C accelerated early strength gain for 33% to 39% but produced lower 28-day strengths than ambient curing. Additionally, for the optimal mix, SHA was also pre-immersed in water for varying durations to assess its effect on workability, compressive strength, and potassium ion leaching. This pretreatment increased compressive strength by up to 14.7%, depending on immersion time, but reduced workability by up to 15.5%. The novelty of the research is reflected in attaining the highest 28-day compressive strength of 55 MPa (for 25% SHA by mass of GGBFS), under ambient curing, without SHA pretreatment or immersion, highlighting the potential for low-energy, sustainable binder systems using agricultural and industrial by-products. Full article

Iron-rich metallurgical slag is an underutilized precursor in alkali-activated materials (AAMs), despite its abundance and potential in sustainable construction and waste immobilization. This study evaluates a binary AAM system (Aachen GP), comprising 50 wt.% blast furnace slag (BFS) and 50 wt.% iron-rich slag (Fe₂O₃ ≈ 24.6 wt.%), against a BFS-only reference (Ref GP). Characterization included isothermal calorimetry, Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM–EDX), Brunauer–Emmett–Teller (BET) surface area, water permeability, porosity, and compressive strength. Aachen GP showed delayed setting (32.9 h), reduced cumulative heat (∼70 J/g), and lower bound water (4.6% at 28 days), indicating limited gel formation. Compared to Ref GP, it had higher porosity (38.4%), water permeability ($1.42\times {10}^{-10}$ m/s), and BET surface area (12.4 m²/g), but lower 28-day strength (14.4 MPa vs. 43 MPa). Structural analysis revealed unreacted crystalline phases and limited amorphous gel. While Aachen GP meets regulatory strength thresholds (≥8 MPa) for low- to intermediate-level wasteforms in Belgium and Germany, its elevated porosity may impact long-term containment. Further studies on radionuclide leaching and durability under thermal and radiation stress are recommended. Full article

Alkali-activated slag grouting materials exhibited excellent mechanical properties but still faced technical challenges such as insufficient fluidity and overly rapid setting. To enhance their workability, this study introduced fly ash as a modifying component, leveraging its morphological and activity effects to systematically investigate the composite influence on fluidity, setting time, and compressive strength. The mechanism was further elucidated through microstructural analysis of the mineral crystallization characteristics of polycondensation products. The results indicated that with increasing fly ash content, the fluidity of the grouting material continuously improved, and both the initial and final setting times were significantly prolonged, albeit at the expense of a gradual decline in compressive strength. At a 20% fly ash content, the fluidity spread increased to 292 mm, the initial and final setting times were extended to 70 min and 103 min, respectively, while the 1 d and 28 d compressive strengths reached 11.8 MPa and 48.1 MPa, achieving an optimal overall performance that met practical grouting requirements. Microscopic analysis revealed that fly ash enhanced the rheological properties and delayed the setting process through the “ball-bearing effect” and its low early-age reactivity. However, as the fly ash content rose, the active calcium content in the system continuously decreased, inhibiting the formation and development of key mineral crystals such as calcium silicate and calcium aluminosilicate, thereby leading to the reduction in compressive strength. Full article

Using almond shell biomass ash (ABA) as a potassium alkaline source and rice husk ash (RHA) as a soluble silica source to produce blast furnace slag (BFS)-based alkali-activated mortars offers a sustainable alternative to commercial activators. However, some thermal treatment is often needed to enhance ash dissolution, potentially increasing the CO₂ footprint. In this study, we evaluated how a low-CO₂-footprint thermal treatment for dissolving ABA, as well as RHA combined with ABA, affects the strength performance of binary (ABA/BFS) and ternary (RHA/ABA/BFS) alkali-activated mortars. This thermal treatment involved mixing the biomasses with hot water (85 °C) in a thermally insulated bottle (TIB). The binary alkali-activated mortar, cured for 7 days in a thermal bath at 65 °C, achieved 58.0 MPa in compressive strength, applying 1-h dissolution of ABA in a TIB. Additionally, the previous dissolution of RHA in conjunction with ABA for ternary alkali-activated mortar, cured also for 7 days in a thermal bath at 65 °C, resulted in mortars with a higher compressive strength, achieving 64.7 MPa. With the prior biomass dissolution method, the binary and ternary alkali-activated mortars cured at room temperature (20 °C) showed compressive strengths of 54.7 and 67.0 MPa after 28 curing days, respectively. Moreover, after 135 curing days, these mortars reached a compressive strength of 61.4 and 71.9 MPa, respectively. The BFS-alkali-activated binders with ABA and ABA plus RHA cut CO₂ emissions by 86.8% and 85.7% compared to the OPC-based binder, respectively. 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

Grouting materials can be used for reinforcement and water plugging of underground engineering in sandy strata. This study examines the mechanism of alkali-activated cementitious materials by selecting steel slag and ground slag to replace cement in double-liquid grouting materials. Various retarders were used to adjust the gel time, making it controllable for grouting materials. The results show that when the sodium silicate volume is in the range of 20–40%, the W/B is in the range of 0.7–1.0, and the steel-slag-to-ground-slag ratio (SS:SL) is 3:7, the macroscopic properties of the grouting material reach the optimal value, the microstructure is denser, and the hydration products are calcium hydroxide, calcium–silicate–hydrate (C-S-H) gel, and ettringite. When the cement content is 40%, the W/B is 0.8, the sodium silicate volume dosage is 30%, and the SS:SL ratio is 3:7, the 3 d compressive strength of the slurry reaches 14.57 MPa and the 28 d compressive strength reaches 21.14 MPa. To analyse the solidification effect of double-liquid grouting materials with mixed SS and SL on sandy soil, experiments were conducted to study the impacts of the soil moisture content, soil particle size distribution, and slurry quantity on the strength of consolidation. This study conducts an in-depth investigation into optimising the proportioning of industrial solid wastes and the multi-component synergistic mechanisms. This study provides a new method for the effective utilisation of industrial waste and a reference for the practical application of industrial waste as supplementary cementitious materials in the future. Full article

This study investigates the valorization of municipal solid waste incineration (MSWI) residues—specifically bottom ash with slag (BA + S) and fly ash (FA)—through alkaline activation in geopolymer and cementitious systems. The research demonstrates that alkali activation significantly improves mechanical properties, with compressive strengths up to 45.9 MPa for cement mortars and 33.2 MPa for geopolymers. A key innovation includes the quantification of hydrogen gas release during activation, with up to 72.5 dm³/kg H₂ from BA + S, offering insights into binder design and potential green hydrogen recovery. Environmental leachability assessments confirmed that activated BA + S immobilizes heavy metals effectively, although FA showed higher barium and lead leaching. Morphological analysis (SEM, granulometry) revealed microstructural changes enhancing reactivity. Additionally, a practical swelling test is proposed for early detection of expansion risk. The findings contribute to the development of sustainable, high-performance binders from waste, with implications for circular economy and energy valorization strategies. Full article

To address the challenges associated with Ordinary Portland Cement (OPC) in mine backfilling, including high costs, the large carbon footprint, and performance limitations, a novel cementitious powder (CP) based on alkali-activated slag is developed in this work. The mechanical performance and microstructural strengthening mechanism of this CP as a substitute for OPC in cemented copper tailing backfill (CTB) were systematically evaluated. The effects of key parameters, including the solid content (SC), tailing-to-cement ratio (TCR), and curing age (CA), were investigated using uniaxial compressive strength (UCS) tests and scanning electron microscopy (SEM) analysis. The results demonstrate that the novel binder exhibits superior performance. At a solid content of 73%, the CTB prepared with CP at a TCR of 10 or 12 achieved a compressive strength comparable to or exceeding that of the OPC-based counterpart with a TCR of 8. This represents a 33% reduction in binder dosage without sacrificing performance. The UCS of the CTB increased significantly with a decreasing TCR and an increasing CA, with the most rapid strength development observed during the early curing stages (≤7 days). The stress–strain behavior transitioned from plastic yielding to strain-softening with prolonged curing, and the macroscopic failure was predominantly governed by tensile cracking. Microstructural analysis revealed that the strength development of the CTB originates from the continuous formation of hydration products, such as calcium-silicate-hydrate (C-S-H) gel and ettringite. These products progressively fill pores and encapsulate tailing particles, creating a dense and interlocking skeletal structure. A lower TCR and a longer CA promote the formation of a more integrated and compact micro-network, thereby enhancing the macroscopic mechanical strength. This study confirms the viability of the slag-based binder as a sustainable alternative to OPC in mining backfill applications, providing a critical theoretical basis and technical support for the low-cost, eco-friendly utilization of mining solid waste. Full article

The risk of explosive spalling in high-strength cement-based materials during fire exposure poses a significant threat to structural integrity. To help mitigate this issue, this study explores the use of expanded polystyrene (EPS) beads as both a lightweight filler and a potential spalling-reduction agent in lightweight geopolymer and conventional cementitious mortars. Two EPS-containing mortars were developed: a lightweight alkali-activated slag (LWAS) mortar and a conventional lightweight Portland cement (LWPC) mortar, both incorporating EPS beads as a 50% volumetric replacement for sand. Specimens from both mortars were subjected to elevated temperatures of 200 °C, 400 °C, and 600 °C at a heating rate of 10 °C/min to simulate a rapid-fire scenario. Following thermal exposure, two cooling regimes were employed: gradual cooling within the furnace and rapid cooling by water immersion. Mechanical performance was evaluated through compressive, splitting tensile, and impact tests at room and elevated temperatures. Microstructural analysis was also conducted to examine internal changes and heat-induced damage. The results indicated that LWAS showed remarkable resistance to spalling, remaining intact up to 600 °C due to its nanoporous geopolymer structure, which allowed controlled steam release, while LWPC failed explosively at 550 °C despite EPS pores. At 400 °C, EPS beads enhanced thermal insulation in LWAS, lowering internal temperature by over 100 °C, but increased porosity led to faster strength loss. Both mortars gained strength at 200 °C from continued curing, yet LWAS retained strength better at high temperatures than LWPC. Microscopy revealed that EPS created beneficial fine cracks in the slag matrix but harmful voids in cement. Overall, LWAS composites offer excellent spalling resistance for fire-prone environments, though reinforcement is recommended to mitigate strength loss. Full article

To enhance the efficient utilization of industrial solid waste and support the low-carbon transition of cementitious materials, this study used steel slag, coal-fired slag, and desulfurization gypsum as the primary raw materials. A high-performance composite cementitious material system was developed based on the synergistic effects of physical activation (mechanical grinding) and chemical activation (alkali stimulation). This study systematically investigates the raw material characteristics, mix proportion optimization, mechanical behavior, and durability of composite cementitious materials through the integration of response surface optimization design and multi-scale analysis methods. The results indicate that the optimal mix proportions of the composite cementitious material are: 37.2% steel slag, 33.2% coal-fired slag, 9.6% desulfurized gypsum, 20% cement, 4% sodium silicate, and 0.1% superplasticizer. At this mix proportion, the measured 28-day average compressive strength of the composite cementitious material was 40.8 MPa, which closely matched the predicted value of 41.2 MPa from the response surface regression model, thereby confirming the model’s accuracy and applicability. The composite cementitious material demonstrated superior volume stability compared to ordinary cement under both water-curing and drying conditions. However, its freeze–thaw resistance and carbonation resistance were lower than those of cement. Therefore, considering these factors comprehensively, the composite cementitious material is recommended for application in road base and subbase layers. Full article

Geopolymer materials possess several outstanding advantages, including the wide availability of raw materials, an energy-saving and environmentally friendly production process, and excellent engineering technical performance. They are regarded as a new type of green building material that can achieve high-value-added resource utilization of industrial solid waste. They are one of the current research hotspots in the field of materials. Fly ash and slag, the most common industrial wastes in China, have been discharged in large quantities, significantly impacting the country’s ecological environment. Based on this, this paper primarily investigates the mechanical properties and strength formation mechanism of geopolymer paste to develop geopolymer materials with enhanced mechanical properties. This research uses metakaolin as the silicate raw material and uses sodium silicate mixed with NaOH as the alkali activator to prepare geopolymer paste. By adding fly ash and slag, the mechanical properties of the geopolymer paste are improved. The effects of the alkali activator modulus, Na₂O equivalent, and content of fly ash and slag on the setting time and strength of geopolymer paste are studied. XRD, FTIR, and SEM are employed to characterize the phase, molecular structure, and microscopic morphology of geopolymer paste, as well as to analyze the microstructure and reaction mechanism of these materials. The results show that the setting time of the geopolymer increases with the increase in modulus and shortens with the increase in Na₂O equivalent. Fly ash and slag, respectively, act as retarders and early strength promoters. The ratio of n(SiO₂)/n(A1₂O₃) (that is, the modulus of the alkali activator) of the geopolymer is an important factor affecting its strength. The metakaolin and fly ash–slag–metakaolin exhibit the best mechanical properties when their molar ratios are 2.97 and 3.26, respectively. Through microscopic characterization using XRD, FTIR, and SEM, it is observed that fly ash–slag–metakaolin exhibits the most complete polymerization reaction, generates the most amorphous silicate aluminosilicate gel, and displays the best inter-gel bonding effect, resulting in the best mechanical properties. 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 widespread use of recycled fine aggregate (RFA) is hindered by its porous and weak adhered mortar. In this study, a nano-SiO₂–sodium silicate mixed solution (NMS) was used to soak and strengthen the adhered mortar. Alkali-activated slag was adopted as the cementitious material, and the resulting treated waste liquid (RNMS) was recycled as a sodium silicate source for the alkali activator. The effects of modified RFA (MRFA) incorporation and RNMS use on the performance, economic, and environmental benefits of alkali-activated slag recycled fine aggregate mortar (AASRM) were evaluated. Compared with the control group, mortars using only MRFA showed significantly improved performance, with a 28-day compressive strength increase of 57.6% (reaching 38.3 MPa) and enhanced workability. The capillary water absorption and 90-day drying shrinkage rates decreased by 49.5% and 40.2%, respectively. Microstructural analysis revealed that NMS treatment promoted the formation of additional C-(N)-A-S-H gel, thereby densifying the surface of the RFA and strengthening the interfacial transition zone (ITZ). More importantly, using RNMS as the alkali activator source maintained the excellent performance of the AASRM mortar, with the compressive strength reaching 95.6% of that prepared with a fresh alkali activator, while effectively reducing material costs and embodied carbon. This study not only successfully applies MRFA in alkali-activated mortar systems but also provides an effective approach for the in situ recycling of treated waste liquid. Full article

It is known that geopolymer mortar exhibits high compressive strength but relatively low flexural strength, high brittleness, and poor toughness. Engineering practices for cement-based materials have demonstrated that incorporating fibers can effectively prevent the expansion of existing cracks and the formation of new ones in the materials. Adding polypropylene fibers to geopolymer mortar can, on the one hand, improve the crack resistance of the mortar, and on the other hand, enhance the impact resistance of the geopolymer mortar. In this paper, slag, metakaolin, and fly ash are utilized as silico-aluminous raw materials, standard sand is employed as aggregate, and a mixture of water glass and NaOH in a specific proportion is used as the alkali activator to prepare geopolymer mortar. Polypropylene fibers are incorporated to improve its mechanical properties. The effects of fiber length and mixing method on the mechanical properties of geopolymer mortar are studied to determine the optimal fiber length and mixing method. The mechanism of the mechanical properties of fiber-reinforced geopolymer mortar is analyzed by combining SEM. The research results indicate that the geopolymer mortar with 15 mm single-doped fibers exhibits the best flexural strength and toughness. In contrast, the geopolymer mortar with 12 mm single-doped fibers demonstrates the best compressive strength. The geopolymer with 9 mm and 18 mm hybrid-doped fibers has the best mechanical properties and is superior to the geopolymer mortar with single-doped fibers. Full article

In response to escalating environmental concerns, the construction industry is under growing pressure to adopt sustainable practices. As a major consumer of natural resources and a significant emitter of greenhouse gases, it paradoxically holds the potential to become a leader in green transformation. This study investigates the development of innovative, fire-resistant, and alkali-activated hybrid binder foams incorporating recycled materials: fly ash, coal slag, and ground brick waste, as sustainable alternatives to traditional building materials. The fire resistance performance at a technical scale and the thermal behavior of fiber-reinforced, alkali-activated hybrid binder foams synthesized from recycled aluminosilicate precursors were determined. The properties of unreinforced composite were compared with the composites reinforced with merino wool, basalt fibers, polypropylene fibers, and coconut fiber. Small-scale fire-resistance tests revealed that merino wool-reinforced composites exhibited the best thermal insulation performance, maintaining structural integrity, that is, retaining shape and continuity without delamination or collapse for 83 min under fire exposure. Analyses combining chemical characterization (X-ray fluorescence) with microstructural methods (computed tomography and colorimetry) confirmed that fire performance is strongly influenced not only by fiber type but also by pore distribution, phase composition, and oxide migration under thermal loading. These findings demonstrate the potential of fiber-reinforced foamed, alkali-activated hybrid binder as eco-efficient, printable materials for fire-safe and thermally demanding construction applications. Full article