PSI - Issue 70

Ravi Malik et al. / Procedia Structural Integrity 70 (2025) 682–689

684

concrete, geopolymer concrete has a compressive strength between 40 and 90 MPa. It also has a better tensile strength and less creep and drying shrinkage. According to long-term research, geopolymer concrete either maintains or gains strength over time; specimens that are ambient-cured do so more slowly than those that are heat-cured. The mechanical characteristics and hardening processes of fly ash-based geopolymer concrete (FA-Geopol Con.) were examined by (Ryu et al., 2013). Utilizing fly ash as a binder activated by sodium hydroxide (NaOH) and sodium silicate, the study investigates the development of compressive strength at different NaOH molarities (6M, 9M, and 12M) and mix ratios. SEM, EDS, XRD, and FT-IR investigations demonstrate that the improved geopolymerization of Si and Al components is responsible for the higher molarity (12M) yields of 47.5 MPa at 91 days. Dense reaction products with crystalline phases such as quartz and mullite and a change in Si-O-Si bonds that indicates polymerization are shown by microstructural studies. Because of the discontinuous pores, strength is resilient even when porosity grows with molarity. With a 7.8 – 8.2% ratio, the suggested tensile-to-compressive strength relationship (f_sp = 0.17(f_c)^0.3) is comparable to that of standard concrete and suggests suitability for precast goods that need to cure at 60°C. The study emphasizes the potential of FA-Geopol Con. as an environmentally benign building material, but more information is required for wider structural application. The early-age characteristics of low-calcium fly ash-based geopolymer concrete (GPC) cured at room temperature (23°C) are investigated by (Nath et al., 2015) with the goal of creating a cement-free, environmentally friendly substitute for Portland cement concrete that can be used in cast-in-situ applications. In contrast to earlier research that relied on heat curing (30 – 85°C), this study uses modest amounts of additives, such as calcium hydroxide (CH), ordinary Portland cement (OPC), and ground granulated blast furnace slag (GGBFS), to speed up setting and strength growth without the need for extra heat. Four different combinations with various additive (0 – 10%) and binder contents (450 – 730 kg/m³) were evaluated using Class F fly ash activated by a sodium hydroxide and sodium silicate solution (14M). According to the results, additives improved 1-day compressive strength (3.6 – 10.5 MPa) and greatly decreased setting times (e.g., from over 24 hours to 110 – 607 minutes). As binder concentration increased, 28-day strengths reached 26 – 58 MPa. At 550 – 650 kg/m³ binder content, workability is maximized. The study comes to the conclusion that GPC can be produced with sufficient early-age qualities for low to-moderate strength applications under ambient circumstances by combining low-calcium fly ash with GGBFS, OPC, or CH. This increases the practical value of GPC. (Khan et al., 2016) studied the use of low-calcium fly ash, cured at room temperature, to create high-strength geopolymer composites. The study investigates how calcium hydroxide (Ca(OH)₂), ultrafine fly ash (UFFA), and slag affect microstructure and compressive strength. A 12M NaOH and Na₂SiO₃ activator (ratio 2.5) was used to evaluate different binder formulations. The production of C -A-S-H and N A-S-H gels, which improve microstructure density, is responsible for the maximum 28-day compressive strengths (up to 108 MPa with equal parts) that were obtained by fly ash-slag blends. (Ramujee & Potharaju, 2017) has examined the mechanical behavior of fly ash-based geopolymer concrete. In comparison to comparable OPC control mixes, the study examines the compressive and split tensile strengths of GPC in low (G20), medium (G40), and high (G60) grades. OPC mixes were water-cured for 28 days, whereas GPC specimens, activated with sodium hydroxide and sodium silicate, were heat-cured for 24 hours at 60°C. The findings indicate that GPC has comparable split tensile strengths and compressive strengths between 30.4 to 71.4 MPa, which are marginally greater than OPC's 27.5 to 68.6 MPa. The empirical relation obtained from a regression analysis, substantially resembles the formula for OPC in ACI 318-99 and shows similar mechanical behavior. The study comes to the conclusion that GPC is a suitable engineered material for construction since it has OPC-like qualities, achieves target strength more quickly during heat curing. Using ground granulated blast furnace slag (GGBS) and fly ash as binders, (Xie et al., 2019) have examined the performance of geopolymeric recycled aggregate concrete (GRAC) that completely replaces Ordinary Portland Cement (OPC) with 100% recycled coarse aggregates. With the support of XRD and SEM analyses, the study investigates the effects of water-binder (W/B) ratios (0.3, 0.4, 0.5) and GGBS/fly ash ratios (25%, 50%, 75%) on fresh properties (slump, setting time) and hardened properties (compressive strength, stress-strain behavior, elastic modulus, Poisson's ratio, toughness, failure mode). The findings show a synergistic effect: GGBS increases mechanical strength while fly ash improves workability. With a 0.5 W/B ratio, the 50% GGBS/50% fly ash mix strikes the ideal balance, providing greater workability and compressive strength (51.4% higher than OPC concrete). Although high concentrations decrease ductility, GGBS content has a considerable impact on strength and stiffness. In comparison to OPC concrete, GRAC exhibits denser microstructures and better interfacial transition zones, establishing it as a high-performance, environmentally friendly substitute for civil engineering applications. The effects of superplasticizer dosages of 1%, 2%, and 3% on geopolymer concrete composites composed of fly ash and ground