Effect of Waste Tire Aggregate on Thermal and Strength Characteristics of Fly Ash–Based Geopolymer Composites Produced at Various Binder Contents

Abstract

The main objective of the current study is the recycle of end-of-life tires as fine aggregate in the production of fly ash–based geopolymer composites. Moreover, it aimed to improve some adverse characteristics caused by the recycled fine aggregate named crumb rubber of such composites by changing the binder content of the composite mixture. In this regard, four crumb rubber replacement levels of 10%, 20%, 30%, and 40% were designated in the production of rubberized geopolymer composites. The main mixtures were designed at a binder content of 600 kg/m3. Herein, it should be stated that in the current study, the term binder content was considered a total of precursor (aluminosilicate-rich raw material) and alkaline activator. According to the performance of the geopolymer composites, the binder content was increased to first 700 kg/m3 and then 800 kg/m3. Thereby, twelve crumb rubber incorporated and three plain fly ash–based geopolymer composites were designed and produced in this study. The performance of these composites was evaluated in terms of fresh and hardened state properties. As fresh state properties, the flowability and fresh unit weight were tested while as hardened state properties, dry unit weight, compressive and splitting tensile strength, total and capillary absorption capacities, and thermal conductivity were tested. The results revealed that replacing river sand with crumb rubber remarkably influenced the characteristics of geopolymer composites. The flowability, unit weights, strength performance, and thermal conductivity of geopolymer composites decreased whereas the absorption capacity increased. Increasing binder content became a remedy for some characteristics of composites. As a consequence, it can be stated that this waste material can be used in the production of such composites but in a controlled manner.