VISUAL INSPECTION AND MECHANICAL TESTING OF FLY ASHBASED FIBROUS GEOPOLYMER COMPOSITES UNDER FREEZE-THAW CYCLES

Abstract

Geopolymer is a binder that can be considered as an alternative to Portland cement. The utilization of geopolymer concrete as an alternative to the Portland cement-based concrete adds sustainability to the environment by reducing the energy consumption and greenhouse gas emission associated with cement production. Fiber reinforcement is a popular practice known to improve performance of construction materials. In this thesis, an experimental study was conducted to evaluate freeze-thaw behaviour of fiber reinforced geopolymer composites. To build up an extensive experimental program, four different fiber types, namely, basalt fiber (BF), steel fiber (SF), and glass fiber (GF) with two different lengths and three fiber volume fractions of 0.4, 0.8, and 1.2% were utilized for geopolymer composite production. To monitor freeze-thaw resistance, 100, 200, and 300 cycles were applied as per ASTM C666. In the current study, the solid binding component of geopolymer composite was the fly ash with a fixed dosage of 550 kg/m3 while the alkaline activators were Na2SiO3 and NaOH solutions. A constant alkaline activator-to-binding material (solid binding component) ratio of 0.5 was assigned. In total, 13 different fly ash-based geopolymer mixtures were designed. Based on the results of the experimental program it was found out that the workability of the fresh geopolymer composites was adversely affected by the fiber addition. A continuous increase in both compressive and flexural strengths was achieved when the volume fraction of the BF and SF type fibers were increased. Another critical finding is that utilization the fiber decreased the damage of the freeze-thaw cycles. Therefore, it was proved that the use of fiber can be an effective way to increase the durability of the geopolymer composites against the freeze-thaw cycle. Based on the visual inspection of the specimens throughout the whole exposure period, it was found out that the geopolymer specimens maintained their integrity with varying levels of mass loss even after being subjected to the 300 freeze-thaw cycles.