Optimization of Mechanical Properties and Embodied Energy of Polyvinyl Alcohol Fiber-Reinforced High-Strength Alkali-Activated Slag Mortars: Comparative Study

Abstract

The aim of this study is to investigate the physical, mechanical, sorptivity, and microstructural properties of high-strength alkali-activated slag (AAS) mixtures that were heat cured for 8 h. AAS mixtures were cured at room conditions, 50°C, and 75°C. Here, 0.25% and 0.50% polyvinyl alcohol (PVA) fiber (by volume) was used to prevent heat-cure cracks and increase flexural toughness. In addition, 200, 400, and 600 kg/m3 quartz aggregates were used instead of quartz powder in the mixtures. In this context, 36 different mixtures were produced for the experimental study. The physical, mechanical, and transport properties of AAS have been greatly improved by heat curing. As the quartz aggregate and PVA fiber content increased, the apparent porosity and water absorption of the mixtures increased also. Accordingly, the unit weights of the mixtures decreased relatively. The compressive strength of AAS varied between 43.5 and 102.5 MPa. In the case of heat-curing at 75°C, the compressive strength increased up to 1.8 times. The flexural strength of AAS was between 6.9 and 14.7 MPa. The PVA fibers prevented the brittle fracture observed in AAS. Whereas the PVA fiber ratio increases both compressive and flexural strength, the opposite situation was obtained for quartz aggregate. In addition, the PVA fibers reduced capillary water absorption. The embodied energy of AAS ranged from 4,998 to 5,768 MJ. The embodied energy of AAS was found to be relatively higher than that of conventional concrete. Withal, the scanning electron microscopes (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) analyses implied that the heat curing considerably improved the geopolymerization. As a result, more than 100 MPa compressive strength and approximately 15 MPa flexural strength can be obtained by using 0.25% PVA fiber in AAS mixtures cured at 75°C.