Effect of polypropylene fibers and diatomite on mechanical properties of geopolymer mortar exposed to elevated temperatures

The aim of this study is to assess the effect of polypropylene fibers (PP) and diatomite aggregates (with replacement amount of 0%, 25%, and 40% of the river sand content) on the mechanical properties of slag-based geopolymer mortar (GPM) under the exposure of high temperatures up to 750 ⁰C. The workability, density, color change, mass loss, spalling resistance, mechanical properties (compressive strength, tensile stress-strain diagram, load-deflection response, failure mode) were evaluated before and after fire deterioration. The obtained results showed that the flow-table of slag-based geopolymer mortar reduced with the increasing diatomite aggregate content, also, the addition of 1% of PP fibers decreased the workability of GPM mixtures regardless of the aggregate type. The substitution of river sand with diatomite aggregates affected the mechanical properties of GPM samples at ambient temperatures negatively due to the high porosity and low bonding resistance of diatomite aggregate. However, the inclusion of PP fibers enhanced the tensile stress, strain capacity and flexural properties of all GPM specimens at room temperatures due to the ability of PP fibers to prevent crack's propagation which can enhance the bridging between geopolymer matrix and aggregates. After exposure the GPM samples to high temperatures, the results demonstrated that the sample contain diatomite aggregates had a higher thermal resistance and lower strength reduction than the samples that include 100% river sand aggregate.