Comparative study on the effect of fiber type and content on the fire resistance of alkali-activated slag composites

Abstract

Alkali-activated slag (AAS) binder has been recognized as a suitable material for construction applications owing to its low carbon footprint and good mechanical and durability performance. As a promising alternative to the conventional Portland cement binder, it is important to maximize the performance of AAS composites under normal and harsh environmental conditions such as exposure to fire. The use of fibers in a brittle matrix is a well-known approach to enhance the mechanical strength and cracking behavior under thermal loading. In this study, polypropylene fiber (PPF), glass fiber (GF), and basalt fiber (BF) are used at volume fractions of 0.5%, 1%, and 1.5% in AAS mortar mixes. First, the workability, compressive strength, and flexural strength of mixes were evaluated at ambient temperature. Then, the mortar mixes were exposed to elevated temperatures of 200, 400, 600, and 800 °C, and the residual flexural and compressive strengths and the mass loss as well were determined. Furthermore, the changes in the matrix after heat treatment were investigated utilizing scanning electron microscopy (SEM) analysis. Based on the test results, the fiber type and dosage did not have a considerable influence on the mass loss of mixes, and in general, fiber-reinforced mixes showed a higher mass loss due to the melting of fibers. The optimum PPF, GF, and BF content based on the compressive strength measured at the ambient and elevated temperatures was found equal to 0.5%, 0.5%, and 1%, respectively. Whereas, the optimum percentages to achieve the highest flexural strength were equal to 0.5%, 1%, and 1%, respectively. It was found that the GF-reinforced mix containing 0.5% and 1% GF exhibited 33% and 160% higher residual compressive and flexural strengths at 800 °C, respectively, compared to that of the control mix.