Search Results (17)

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

Rubberized concrete is a more environmentally friendly material than natural concrete as it helps to reduce rubber disposal issues and has superior impact resistance. Geopolymer concrete, on the other hand, is an economical concrete with higher mechanical properties than nominal concrete that uses fly ash and slag, among other industrial solid wastes, to lower carbon footprints. Rubberized geopolymer concrete (RuGPC) combines the advantages of both concrete types, and a thorough grasp of its dynamic compressive characteristics is necessary for its use in components linked to impact resistance. Despite the advantages of RuGPC, predicting its mechanical characteristics is sometimes difficult because of variations in binder type and combination. This research investigated the combined effect of ground granulated blast furnace slag (GGBFS) and fly ash (FA) on the workability, compressive strength, and stress–strain characteristics of RuGPC with rubber at 0%, 10%, and 20% fine aggregate replacement. Thereafter, energy absorption and ductile characteristics were evaluated through the concrete toughness and ductility index. Numerical models were proposed for the cube compressive strength, modulus of elasticity, and peak strain of RuGPC at different percentages of crumb rubber. It was found that RuGPC made with GGBFS/FA had similar stress–strain characteristics to FA- and MK-based RuGPC. At 20% of crumb rubber aggregate replacement, the workability, compressive strength, modulus of elasticity, and peak stress of RuGPC reduced by 8.33%, 34.67%, 43.42%, and 44.97%, while Poisson’s ratio, peak, and ultimate strain increased by 30.34%, 8.56%, and 55.84%, respectively. The concrete toughness and ductility index increased by 22.4% and 156.67%. The proposed model’s calculated results, with R² values of 0.9508, 0.9935, and 0.9762, show high consistency with the experimental data. RuGPC demonstrates high energy absorption capacity, making it a suitable construction material for structures requiring high-impact resistance. Full article

Lightweight concrete (LWC) has emerged as a transformative material in sustainable and high-performance construction, driven by innovations in engineered lightweight aggregates, supplementary cementitious materials (SCMs), fiber reinforcements, and geopolymer binders. These advancements have enabled LWC to achieve compressive strengths surpassing 100 MPa while reducing density by up to 30% compared to conventional concrete. Fiber incorporation enhances flexural strength and fracture toughness by 20–40%, concurrently mitigating brittleness and improving ductility. The synergistic interaction between SCMs and lightweight aggregates optimizes matrix densification and interfacial transition zones, curtailing shrinkage and bolstering durability against chemical and environmental aggressors. Integration of recycled and bio-based aggregates substantially diminishes the embodied carbon footprint by approximately 40%—aligning LWC with circular economy principles. Nanomaterials such as nano-silica and carbon nanotubes augment early-age strength development by 25% and refine microstructural integrity. Thermal performance is markedly enhanced through advanced lightweight fillers, including expanded polystyrene and aerogels, achieving up to a 50% reduction in thermal conductivity, thereby facilitating energy-efficient building envelopes. Although challenges persist in cost and workability, the convergence of hybrid fiber systems, optimized mix designs, and sophisticated multi-scale modeling is expanding the applicability of LWC across demanding structural, marine, and prefabricated contexts. In essence, LWC’s holistic development embodies a paradigm shift toward resilient, low-carbon infrastructure, cementing its role as a pivotal material in the evolution of next-generation sustainable construction. 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

Enhancing the fracture strength and ductility of concrete through the incorporation of various types of synthetic and natural fibers with varying textures and contents remains challenging. Natural fibers, being versatile and eco-friendly construction materials, can be an excellent alternative to synthetic fibers. However, studies on natural fiber-reinforced (especially through the incorporation of jute fibers) novel composites like geopolymer binders remain deficient. Thus, the effects of various lengths (15, 25 and 35 mm) and volume contents (0.10, 0.20, 0.30, 0.40, 0.50, 0.60, and 0.70%) of natural jute fibers on the mechanical performance of fiber-reinforced geopolymer concrete were studied. The results revealed that jute fiber reinforcement remarkably affected the workability, compressive strength, fracture strengths, water absorption and microstructure properties of the proposed geopolymer concretes. Increasing the fiber length and volume fractions in the geopolymer matrix lowered the slump values and workability and increased the compressive strength. The specimen prepared with a fiber length of 35 mm and volume fractions of 0.70% displayed the lowest slump value (28 mm) and highest compressive strength (31.5 MPa) at 28 days. In addition, the specimens made with fiber volume fractions of 0.10, 0.20, 0.30, and 0.40% showed a significant improvement in the splitting tensile and flexural strengths. However, increasing the volume of the jute fibers up to 0.50% led to a slight drop in the fracture strength of the geopolymers. The specimens prepared with a length of 25 mm and a volume of 0.40% achieved the highest enhancement of splitting tensile strength (18.7%) and flexural strength (29.1%) at 28 days. In short, sustainable geopolymer concrete with high fracture performance can be obtained by incorporating natural jute fibers, leading to practical applications in the construction sector. The proposed green concrete may enable a reduction in solid waste, thus promoting a more sustainable concrete industry. Full article

The strain-hardening geopolymer composite (SHGC) is a new type of fiber concrete with excellent ductility and environmental friendliness. However, the high cost of fibers greatly limits its widespread application. This paper proposes the use of untreated low-cost polyvinyl alcohol (PVA) fibers and polyethylene (PE) fibers to develop a low-cost, high-performance SHGC. Axial compression and axial tension tests were conducted on the SHGC with different PE fiber volume fractions (1%, 1.5%, and 2%) and different PVA fiber replacement ratios (0%, 25%, 50%, 75%, and 100%) to investigate the hybrid effects of fibers with different surface properties and to reveal the mechanism of fiber hybridization on the mechanical behavior of SHGCs. The results show that increasing the PE fiber volume fraction improves the compressive and tensile ductility of the SHGC while increasing the PVA fiber replacement rate impacts the strength indicators positively due to the good interface effect formed between its hydrophilic surface and the matrix. When the PVA fiber replacement ratio is 100%, the compressive strength (93.4 MPa) of the SHGC is the highest, with a 21.1% increase compared to the control group. However, the tensile strength shows a trend of first increasing and then decreasing with the increase in the PVA fiber replacement ratio, reaching the highest at a 25% replacement ratio, with a 12.5% increase compared to the control group. Furthermore, a comprehensive analysis of the economic and environmental performance of the SHGC indicates that a 25% PVA fiber replacement ratio results in the best overall economic benefits and relatively low actual costs, although the effect of fiber hybridization on carbon emission indicators is not significant. This paper provides new ideas and a theoretical basis for designing low-cost SHGCs. Full article

Low carbon and high performance have become key trends in the development of construction materials. Understanding the mechanism by which curing conditions affect the mechanical properties of high-ductility geopolymer concrete (HDGC) is of significant importance. This study investigated three sealing curing temperatures (room temperature, 45 °C, and 60 °C) and four curing durations (1 day, 3 days, 5 days, and 7 days), while considering two final curing ages (7 days and 28 days) to explore their effects on the axial tensile and compressive properties of HDGC. The results showed that both 45 °C and 60 °C could improve the brittle failure of HDGC under axial compressive loading. However, curing at 60 °C and for durations longer than 1 day in an oven would catalyze the formation of eight-faced zeolite crystals within the slag–fly ash geopolymer matrix, and it could weaken the matrix’s pore structure and subsequently affect the material’s later strength development. Nevertheless, oven heat curing enhanced the bridging effect between the fibers and the matrix, partially compensating for the reduction in the initial tensile strength of HDGC. This follows the pseudo-strain-hardening material’s saturation cracking criterion to enhance the strain-hardening behavior of HDGC and improve its tensile energy absorption capacity. A curing condition of 45 °C for 5 days is recommended to maximize the ductility of HDGC. This study provides important theoretical support for the design and promotion of green, low-carbon, high-ductility composite materials. Full article

Engineered geopolymer composites (EGCs) exhibit excellent tensile ductility and crack control ability, making them promising for concrete structure repair. However, their widespread use is limited by high costs of reinforcement fiber and a lack of an EGC–concrete interface bonding mechanism. This study investigated a hybrid PE/PVA fiber-reinforced EGC using domestically produced unoiled PVA fibers to replace commonly used PE fibers. The bond performance of the EGC–concrete interface was evaluated through direct tensile and slant shear tests, focusing on the effects of PE fiber content (1%, 2%, and 3%), fiber hybrid ratios (2.0:0.0, 1.5:0.5, 1.0:1.0, 0.5:1.5, and 0.0:2.0), concrete substrate strength (C30, C50, and C70), and the ratio of fly ash (FA) to ground granulated blast furnace slag (GGBS) (6:4, 7:3, and 8:2) on interface bond strength. Results showed that the EGCs’ compressive strength ranged from 77.1 to 108.9 MPa, with increased GGBS content significantly enhancing the compressive strength and elastic modulus. Most of the specimens exhibited strain-hardening behavior after initial cracking. Interface bonding tests revealed that a PE/PVA ratio of 1.0 increased tensile bond strength by 8.5% compared with using 2.0% PE fiber alone. Increasing the PE fiber content, PVA/PE ratio, GGBS content, and concrete substrate strength all improved the shear bond strength. This improvement was attributed to the flexible fibers’ ability to restrict thermo–hydro damage and deflect and blunt microcracks, enhancing the interface’s failure resistance. Cost analysis showed that replacing 50% of the PE fiber in EGC with unoiled PVA fiber reduced costs by 44.2% compared with PE fiber alone, offering the best cost–performance ratio. In summary, hybrid PE/PVA fiber EGC has promising prospects for improving economic efficiency while maintaining tensile ductility and crack-control ability. Future optimization of fiber ratios and interface design could further enhance its potential for concrete repair applications. Full article

Concrete-filled built-up cold-formed steel (CFS) columns offer enhanced load-carrying capacity, improved strength-to-weight ratios, and delayed buckling through providing internal resistance and stiffness due to the concrete infill. Integrating sustainable alternatives like self-compacting geopolymer concrete (SCGC) with low carbon emissions is increasingly favoured for addressing environmental concerns in construction. This review aims to explore the current knowledge regarding CFS built-up composite columns and the performance of SCGC within them. While research on geopolymer concrete-filled steel tubes (GPCFSTs) under various loads has demonstrated high strength and ductility, investigations into built-up sections remain limited. The literature suggests that geopolymer concrete’s superior compressive strength, fire resistance, and minimal shrinkage render it highly compatible with steel tubular columns, providing robust load-bearing capacity and gradual post-ultimate strength, attributed to the confinement effect of the outer steel tubes, thereby preventing brittle failure. Additionally, in built-up sections, connector penetration depth and spacing, particularly at the ends, enhances structural performance through composite action in CFS structures. Consequently, understanding the importance of using a sustainable and superior infill like SCGC, the cross-sectional efficiency of CFS sections, and optimal shear connections in built-up CFS columns is crucial. Moreover, there is a potential for developing environmentally sustainable built-up CFS composite columns using SCGC cured at ambient temperatures as infill. Full article

Ultra-high-performance geopolymer concrete (UHPGC) emerges as a sustainable and cost-effective alternative to Portland cement-based UHPC, offering similar mechanical properties while significantly reducing carbon footprint and energy consumption. Research on UHPGC components is extremely scarce. This study focuses on the flexural and crack behavior of UHPGC beams with different steel fiber contents and longitudinal reinforcement ratios. Five UHPGC beams were tested under four-point bending. The test results were evaluated in terms of the failure mode, load–deflection relationship, flexural capacity, ductility, average crack spacing, and short-term flexural stiffness. The results show that all the UHPGC beams failed due to crack localization. Increases in the reinforcement ratio and steel fiber content had favorable effects on the flexural capacity and flexural stiffness. When the reinforcement ratio increased from 1.18% to 2.32%, the flexural capacity and flexural stiffness increased by 60.5% and 12.3%, respectively. As the steel fiber content increased from 1.5% to 2.5%, the flexural capacity and flexural stiffness increased by 4.7% and 4.4%, respectively. Furthermore, the flexural capacity, flexural stiffness, and crack spacing of the UHPGC beams were evaluated using existing methods. The results indicate that the existing methods can effectively predict flexural capacity and flexural stiffness in UHPGC beams but overestimate crack spacing. This study will provide a reference for the structural design of UHPGC. Full article

Bentonite is one of the SiO₂-rich pozzolanic clay types that has been enormously employed as a cost-effective and eco-friendly supplementary cementitious material in ordinary Portland cement (OPC) concrete. However, the use of bentonite in geopolymer concrete (GPC) has not been explored very widely. Further, the research available on the effect of utilizing treated bentonite in GPC is limited. The practical application of GPC is also very limited due to its significant shrinkage and high brittleness compared to OPC concrete. There are several studies available that have highlighted the use of polypropylene fibers (PPF) in improving the mechanical properties of GPC by reducing drying shrinkage and enhancing ductility. However, the effect of PPF on the durability properties of GPC needs to be addressed. Further, the effect of the combined integration of bentonite and PPF on the mechanical and durability properties of GPC has not been reported yet. The aim of this study is, therefore, to investigate the individual and combined effect of bentonite and PPF on the workability, mechanical properties, and durability of fly ash (FA)-based GPC. Bentonite replaced 10% of FA, and PPF was added at varying proportions (0.5%, 0.75%, and 1%) for raw and treated bentonite. Slump test was used to assess workability, while compressive, tensile, and flexural tests were utilized to evaluate the mechanical properties. Water absorption, acid attack, and abrasion resistance tests were used to evaluate durability. The results showed that bentonite and PPF significantly enhance mechanical properties, especially when combined with treated bentonite, with the highest improvement observed for mixtures with 1% PPF. The compressive strength was improved by an extent of 10% and 18% for raw bentonite-GPC and treated bentonite-GPC, respectively, compared to the control mix without bentonite. The durability test results revealed that water absorption of raw and treated bentonite-GPC mixtures at the age of 90 days was decreased by 16% and 21%, respectively, compared to the control mix (without bentonite). The mass loss of raw and treated bentonite-GPC mixtures in sulphuric acid solution was 5% and 10% lower, respectively, than the control mix (without bentonite). The mass loss of raw and treated bentonite-GPC mixtures in abrasion resistance tests was 6% and 12% lower, respectively, than the control mix (without bentonite). For durability performance, mixtures with 0.5% PPF perform the best, while higher PPF contents negatively impact the GPC durability. Full article

Engineered geopolymer composite (EGC) is becoming an uprising product in the civil industry as a substitute and solution for conventional geopolymer concrete (GPC) as GPC exhibits brittleness and has poor cracking resistance. In this paper, we explored high strength engineered geopolymer composite (EGC) made of polyvinyl alcohol (PVA) fibre and without coarse aggregate constituents characterised as high-performance geopolymer concrete. Varying alkaline solution to fly ash ratio (AL/FA) was investigated. Bond-slip behaviour and the mechanical properties, including compressive, tensile, and flexural strengths, were studied. PVA-EGC mix designs in this research was optimised using response surface methodology (RSM). Various parameters, including the amount of ground granulated blast slag (GGBS) and silica fume, were included in the parametric and optimisation study. Based on the RSM study, the use of quadratic studies found the responses to be well-fitted. Next, the optimised mix design was utilised for the casting of all the samples for the mechanical and bond-slip tests in this study. The main parameters of bonding behaviour include multiple embedment lengths (7 d, 10 d, 12 d and 15 d) and various sizes of rebar diameter used for pull-out tests. Moreover, the mechanical properties and bond behaviours of EGC were compared with those of conventional geopolymer concrete (GPC). The compressive strength of EGC and GPC at 28 days were designed to be similar for comparison purposes; however, EGC shows higher early compressive strength on day 1 compared to GPC. In addition, results indicate that EGC has superior mechanical properties and bond performance compared to GPC, where EGC is approximately 9 and 150% higher than GPC in terms of flexural and tensile strength, respectively. Pull-out tests showed that EGC samples exhibited higher ductility, as evidenced by the presence of multiple cracks before any exhibited failure in tension and flexure. Ductile failure modes, such as pull-out failure and pull-out splitting failure, are observed in EGC. In contrast, GPC specimens show brittle failure, such as splitting failure. Full article

Glass is a substance that is present in most houses since glass-based items are made and consumed in relatively high quantities. This has led to the buildup of glass in concerning quantities all over the world, which is a problem for the environment. It is well known that glass has several advantageous physiochemical features that qualify it as an appropriate material for use in the construction industry as an aggregate. The features include being non-biodegradable, resistant to chemical assault, having low water absorption, having high hydraulic conductivity, having temperature-dependent ductility, having alterable particle gradation, and having a wide availability in a variety of forms and chemical compositions. Because of these qualities, glass has been used in various investigations and field tests conducted in civil engineering to evaluate its effectiveness as an engineering aggregate and to develop environmentally friendly management strategies for waste glass. These studies and research have utilized glass in various forms, such as fine recycled glass, medium recycled glass, coarse recycled glass, powdered glass, and glass-based geopolymers. This study focuses on research studies that present results on physicochemical, mechanical, and durability characteristics. These studies and research contain samples of pure glass or glass as replacement percentages in materials (0–100%), including but not limited to unbound granular materials (such as recycled concrete aggregates and crushed rock). In light of the information assembled in this review article, it is legitimate to claim that glass has strong promise as a material in various civil applications. Full article

The construction industry is increasingly focused on sustainability, with a particular emphasis on reducing the environmental impact of cement production. One approach to this problem is to use recycled materials and explore eco-friendly raw materials, such as alumino-silicate by-products like fly ash, which can be used as raw materials for geopolymer concrete. To enhance the ductility, failure mode, and toughness of the geopolymer, researchers have added crumb rubber processed from scrap tires as partial replacement to fine aggregate of the geopolymer. Therefore, this study aims to develop rubberized geopolymer concrete (RGC) by partially replacing the fine aggregate with crumb rubber (CR). To optimize the mechanical properties of RGC, response surface methodology (RSM) has been used to develop 13 mixes with different levels and proportions of CR (10–30% partial replacement of fine aggregate by volume) and sodium hydroxide molarity (10–14 M) as input variables. The results showed that the strength properties increased as the molarity of NaOH increased, while the opposite trend was observed with CR. The maximum values for compressive strength, flexural strength, and uniaxial tensile strength were found to be 25 MPa, 3.1 MPa, and 0.41 MPa, respectively. Response surface models of the mechanical strengths, which were validated using ANOVA with high R² values of 72–99%, have been developed. It has been found that using 10% CR with 14 M sodium hydroxide resulting in the best mechanical properties for RGC, which was validated with experimental tests. The result of the multi-objective optimization indicated that the optimum addition level for NaOH is 14 M, and the fine aggregate replacement level with CR is 10% in order to achieve a rubberized geopolymer suitable for structural applications. Full article

Concrete infrastructure repair remains a formidable challenge. The application of engineering geopolymer composites (EGCs) as a repair material in the field of rapid structural repair can ensure the safety of structural facilities and prolong their service life. However, the interfacial bonding performance of existing concrete with EGCs is still unclear. The purpose of this paper is to explore a kind of EGC with good mechanical properties, and to evaluate the bonding performance of EGCs with existing concrete using a tensile bonding test and single shear bonding test. At the same time, X-ray diffraction (XRD) and Scanning electron microscopy (SEM) were adopted to study the microstructure. The results showed that the bond strength increased with the increase in interface roughness. For polyvinyl alcohol (PVA)-fiber-reinforced EGCs, the bond strength increased with the increase in FA content (0–40%). However, with the change of FA content (20–60%), the bond strength of polyethylene (PE) fiber-reinforced EGCs have little change. The bond strength of PVA-fiber-reinforced EGCs increased with the increase in water–binder ratio (0.30–0.34), while that of PE-fiber-reinforced EGCs decreased. The bond–slip model of EGCs with existing concrete was established based on the test results. XRD studies showed that when the FA content was 20–40%, the content of C-S-H gels was high and the reaction was sufficient. SEM studies showed that when the FA content was 20%, the PE fiber–matrix bonding was weakened to a certain extent, so the ductility of EGC was improved. Besides, with the increase in the water–binder ratio (0.30–0.34), the reaction products of the PE-fiber-reinforced EGC matrix gradually decreased. Full article