Mechanical behavior of fiber reinforced slag-based geopolymer mortars incorporating artificial lightweight aggregate exposed to elevated temperatures

Abstract

The present research investigates the effects of artificial lightweight aggregate (ALWA) and polyvinyl alcohol (PVA) fiber utilization on the mechanical performance of slag-based lightweight geopolymer mortar (LGPM) specimens cured at ambient temperature. Also, the influence of elevated temperature (250 °C and 500 °C) on the resulting performance of LGPM samples was studied. For the production of LGPM specimens, 60% and 80% ALWA were utilized as a partial replacement of river sand. The slag-based LGPM samples were activated by a mixture of sodium silicate and 12 M sodium hydroxide solutions. The fresh and hardened state properties of LGPM specimens with and without fibers were assessed by workability, density, compressive strength, uniaxial tensile strength, and flexural strength tests. Also, the micro-scale variations were evaluated by scanning electron microscopy (SEM). The findings revealed that the incorporation of ALWA reduced the workability, density, and compressive strength of the LGPM, and the reductions in all these properties were more with 1% PVA inclusions. Meanwhile, inclusions of 1% PVA fibers significantly enhanced the uniaxial tensile and flexural behaviors of LGPM. After exposure to 250 °C, all mechanical strengths were improved due to the further geopolymerization, while mechanical strength reductions were observed at 500 °C due to the vapor impact and difference in thermal expansion. The uniaxial tensile strength of fiber-reinforced LGPM samples was improved from 1.47 MPa to 2.16 MPa at 250 °C, while uniaxial tensile strength reduced at 500 °C, and the samples exhibited a brittle failure mode due to the melting of PVA fibers. The results pointed out that tensile and flexural properties of LGPM significantly enhanced with ALWA and 1% PVA fiber utilization.