Combined effect of hybrid PE-PBO fiber reinforcement on the mechanical properties of lightweight fly ash-slag-based engineered geopolymer composites at ambient temperature and after exposure to elevated temperatures

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.

Sustainable materials and technologies used in engineered cementitious composites (ECC) and engineered geopolymer composites (EGC) have gained significant attention from concrete researchers in recent decades, owing to their superior performance compared to traditional concrete. In this study, the performance of sustainable ECC and EGC made of metakaolin (MK) and magnetized water (MW) is evaluated and compared. This was carried out using 14 mixes (7 for ECC and 7 for EGC). The control ECC mix contained cement and ground granulated blast furnace slag (GGBFS) and the control EGC mix contained fly ash (FA) and GGBFS. In ECC, the cement and GGBFS were partially replaced by MK; and in EGC, the FA and GGBFS were replaced by MK. The replacement ratios were 20%, 40%, 60%, and 80% by volume. The tap water (TW) was completely replaced by MW in ECC and EGC mixes containing 0% and 20% MK. Fresh, mechanical, and durability properties were measured for both ECC and EGC such as; slump, compressive and flexural strength, water absorption, and sorptivity. The effect of different curing environments (tap water and seawater) on ECC/EGC compressive strength was also studies. Furthermore, microstructural analyses were performed on specific ECC and EGC mixtures. The microstructure analyses included scanning electronic microscope (SEM), energy dispersive X-ray (EDX), and mapping of the morphology surface. The fresh and mechanical properties indicated that EGC exhibited higher slump values (by up to 7.3 times) and higher compressive strengths (by up to 90%) than those of ECC, especially in the presence of MW. Seawater curing enhanced the EGC compressive strength by up to 16%. The durability results showed that absorption rates and sorptivity of EGC were relatively higher than those of the corresponding ECC. The SEM analysis showed that the concentration of gelatinous materials as CSH and ASG in the mixes using MW was higher than the similar mixes with made with TW, especially in the presence of MK. The EDX analysis and mapping showed that the ratio of Ca/Si was low in EGC compared to that in ECC.

Engineered geopolymer composite (EGC) is a high-performance material with enhanced mechanical and durability capabilities. Ground granulated blast furnace slag (GGBFS) and silica fume (SF) are common binder materials in producing EGC. However, due to the scarcity and high cost of these materials in some countries, sustainable alternatives are needed. This research focused on producing eco-friendly EGC made of cheaper and more common pozzolanic waste materials that are rich in aluminum and silicon. Rice husk ash (RHA), granite waste powder (GWP), and volcanic pumice powder (VPP) were used as partial substitutions (10–50%) of GGBFS in EGC. The effects of these wastes on workability, unit weight, compressive strength, tensile strength, flexural strength, water absorption, and porosity of EGC were examined. The residual compressive strength of the proposed EGC mixtures at high elevated temperatures (200, 400, and 600 °C) was also evaluated. Additionally, scanning electron microscope (SEM) was employed to analyze the EGC microstructure characteristics. The experimental results demonstrated that replacing GGBFS with RHA and GWP at high replacement ratios decreased EGC workability by up to 23.1% and 30.8%, respectively, while 50% VPP improved EGC workability by up to 38.5%. EGC mixtures made with 30% RHA, 20% GWP, or 10% VPP showed the optimal results in which they exhibited the highest compressive, tensile, and flexural strengths, as well as the highest residual compressive strength when exposed to high elevated temperatures. The water absorption and porosity increased by up to 106.1% and 75.1%, respectively, when using RHA; increased by up to 23.2% and 18.6%, respectively, when using GWP; and decreased by up to 24.7% and 22.6%, respectively, when using VPP in EGC.

Engineered Geopolymer Composites (EGC), also known as Strain-Hardening Geopolymer Composites (SHGC), are considered more environmentally friendly than their cement-based counterpart. This study for the first time presents EGC with an ultra-high compressive strength (i.e., over 150 MPa) and an ultra-high tensile ductility (i.e., over 9%) simultaneously. The blended use of fly ash (FA), ground granulated blast slag (GGBS), silica fume, alkali activator, and ultra-high-molecular-weight polyethylene fibers led to the successful development of “Ultra-high-strength & ductility EGC (UHSD-EGC)”. The UHSD-EGC were characterized with excellent multiple cracking and strain-hardening features. In addition, it was found that microstructures of FA-rich geopolymer matrix were looser than those with lower FA/GGBS ratios. The findings arising from this study provided a sound basis for developing EGC materials with ultra-high mechanical properties for sustainable and resilient infrastructure.KeywordsStrain-Hardening Geopolymer Composite (SHGC)Engineered Geopolymer Composites (EGC)Compressive strengthTensile ductilityMultiple cracking

Microstructure and residual strength properties of engineered geopolymer composites (EGC) subjected to high temperatures

A critical review of engineered geopolymer composite: A low-carbon ultra-high-performance concrete

Effect of slag on the mechanical properties and bond strength of fly ash-based engineered geopolymer composites

Self-healing performance of engineered geopolymer composites subjected to sodium sulphate

Feasibility study of engineered geopolymer composites based high-calcium fly ash and micromechanics analysis

Numerical approach for design of tunnel concrete lining considering effect of fiber reinforcements

BackgroundDue to growing global concerns regarding the management of construction waste, this study investigates the feasibility of creating engineered geopolymer composites by replacing traditional industrial by-products (slag) with construction waste, specifically recycled brick waste powder.ResultsPolyvinyl alcohol fibers were incorporated into the engineered geopolymer composite mixtures. The substitution of slag with recycled brick waste powder was carried out at varying percentages: 0, 20, 40, 60, 80, and 100%, resulting in six different engineered geopolymer composite mixtures. The study evaluated the flexural strength, sorptivity, water absorption, and abrasion resistance of the engineered geopolymer composites, and also, microstructural characterization was conducted using scanning electron microscopy. The findings demonstrated that incorporating recycled brick waste powder into the engineered geopolymer composite mixes resulted in a decrease in flexural strength by 35.59% and a notable increase in midspan deflection by 339% when slag was replaced. Concurrently, there was a significant rise in water absorption and sorptivity by approximately 304 and 214%, respectively, when slag was entirely substituted with recycled brick waste powder. Conversely, abrasion resistance decreased, with the inclusion of recycled brick waste powder resulting in an 84% increase in volume change. The scanning electron microscopy (SEM) analysis showed active geopolymerization of recycled brick waste powder within the engineered geopolymer composite mixtures.ConclusionsThe results of this investigation demonstrate that it is feasible to produce engineered geopolymer composites using recycled brick waste powder instead of slag. The greater ductility and increased midspan deflection point to areas that require further optimization, even in spite of the observed decreases in flexural strength and abrasion resistance. The SEM examination reveals an active geopolymerization, highlighting the potential of recycled brick waste powder to produce environmentally friendly and sustainable construction materials. These results offer a good starting point for further studies that try to maximize the durability and performance of these composites.

This paper presents a high-tensile-strength engineered geopolymer composite (EGC) reinforced by polyethylene (PE) fibers. The influences of fiber dosage (1.5%, 1.75%, and 2.0%) and length (6, 12, and 18 mm) on the mechanical properties and strain-hardening performance of EGCs were examined. The results indicated that increasing either fiber dosage or length decreases the flowability of EGC due to the skeleton formed by fibers. The increase of fiber dosage from 1.5% to 2.0% enhanced the fiber bridging effect in the EGCs with 12-mm PE fibers and subsequently enhanced their compressive and tensile strengths by 9.0% and 12.7%, respectively. Differently, the increase of 18-mm fiber dosage from 1.5% to 2.0% introduced more voids inside the EGCs, which decreased their compressive and tensile strengths by 3.8% and 3.6%, respectively. Fiber clusters were more likely to occur in EGC with a higher dosage of longer fibers, which reduced its tensile strength. A higher fiber dosage improved both tensile strain capacity and crack control capacity of EGC. On the other hand, increasing the fiber length from 6 to 18 mm increased the tensile strength by 42.0%, strain capacity by 148.0%, and crack control ability of EGC by enhancing the fiber-bridging effect, although it was detrimental to the compressive strength of the EGCs with 18-mm fibers due to the magnified air-entrapping effect. In addition, a prediction model modified based on the test results can accurately predict the tensile strength of PE fiber–reinforced EGCs. The environmental assessment indicated that the developed EGCs exhibit dramatically lower environmental impacts than the conventional engineered cementitious composite.

Experimental research on the flexural properties and pore structure characteristics of engineered geopolymer composites prepared by calcined natural clay

Recycled tyre steel (RTS) fibre is favoured as a replacement for industrial steel fibre to reduce the environmental impact and material cost of fibre reinforced cementitious composites as well as a potential substitute for the commonly used polyvinyl alcohol (PVA) fibre to develop sustainable engineered geopolymer composites (EGC). This paper systematically examines the effect of hybrid PVA and RTS fibre dosage on the engineering properties of fly ash-slag based EGC, with special focus on uniaxial tensile behaviour and dynamic compressive and splitting tensile behaviour. Results indicate that combining RTS fibres with PVA fibres can effectively improve the drying shrinkage resistance of EGC. All studied EGC mixes exhibit expected strain-hardening and multiple cracking behaviour under uniaxial tension and about 5% enhancement in tensile strength is captured for EGC when 0.25% PVA fibre is replaced with RTS fibre. The incorporation of RTS fibres can improve the quasi-static compressive strength of EGC up to 31%, as compared to EGC with 2.0% PVA fibre. Replacing 0.25 to 0.5% PVA fibre with RTS fibre is beneficial to the dynamic mechanical properties of EGC, where up to 20% improvement in dynamic splitting tensile strength is found for EGC.

Engineered geopolymer composites (EGC) featuring extraordinary tensile ductility are a potential alternative to engineered cementitious composite. In this study, the local bonding properties of steel bars in EGC were investigated. Monotonic loading tests of the 120 specimens were performed using the pullout test method. The study examined the ultimate tensile strain of EGC, diameter and anchorage length of the steel bar on bond performance. The results showed that the EGC, with an ultimate tensile strain of 4.57%, had the highest peak bond strength. By comparing the test results of rebar to ordinary concrete bond performance provided in several previous literature, it was demonstrated that EGC has superior bond performance with rebar compared to ordinary concrete. Based on this, suggestions were provided for the design of rebar anchorage length in EGC. Finally, a mathematical model suitable for determining the bond–slip curve between EGC and steel bars is proposed.