Synergic impact of volcanic ash, carbide lime residue, and curing regime on the performance of geopolymer composites

This research explores the impact of different parameters on the properties of geopolymer (GP) composites incorporating volcanic ash (VA) and carbide lime residue (CLR). The Taguchi design of experiments was employed, considering five factors such as the binder content, curing temperature, activator solution-to-binder (AAS/B) ratio, sodium silicate-to-sodium hydroxide (SS/SH) ratio, and CLR replacement level, each at four distinct levels. A total of 16 GP mixtures were prepared and cured under either water or ambient conditions. The mixtures were evaluated based on workability, setting time, compressive strength, water absorption, bulk resistivity, and ultrasonic pulse velocity (UPV). Statistical analyses using the Taguchi method and ANOVA were employed to evaluate the impact of each parameter and to calculate the signal-to-noise (S/N) ratios. The optimal mix under water curing conditions consisted of 650 kg/m³ binder, a curing temperature of 50 °C, an AAS/B ratio of 0.60, an SS/SH ratio of 2, and 20 % CLR replacement of VA. This mixture reached a 28-day compressive strength of 21.1 MPa, a water absorption of 18.3 %, a bulk resistivity of 29.1 Ω·m, and an UPV of 3989 m/s. In contrast, the optimal mix for ambient curing included 600 kg/m³ binder, 100 °C curing temperature, an AAS/B ratio of 0.60, SS/SH ratio of 1.5, and 10 % CLR replacement of VA. Microstructure analysis of the optimum ambient- and water-cured mixes highlighted an amorphous morphology comprised mainly of calcium aluminosilicate hydrate gel along with calcium silicate hydrate in the latter.