Engineering properties and SEM analysis of eco-friendly geopolymer mortar produced with crumb rubber

Abstract

In the present study, the influence of the crumb rubber utilization as fine aggregate on the engineering properties of fly ash-based geopolymer mortar was experimentally investigated. In this context, the natural sand used in the production of geopolymer mortars was substituted with the crumb rubber, which comes out in the course of applying the retreading process to the end-of-life tires, at the substitution levels of 10%, 20%, 30%, 40%, and 50% by volume of aggregate content. In this way, 6 different geopolymer mixtures, one of which was the control mixture, were designed and produced. Then, the effect of crumb rubber on the fresh-state properties like flowability and fresh unit weight and the hardened-state properties like dry unit weight, compressive and flexural strengths of geopolymer mortars were examined. Besides, the properties of crumb rubber such as grading, specific gravity, water absorption capacity, fineness modulus as well as surface texture and particle shapes were compared with that of the river sand. Moreover, the interfacial transition zone (ITZ) occurring between both natural sand and crumb rubber and geopolymer paste was viewed using the SEM images. The results obtained in the scope of this study showed that crumb rubber had no significant influence on the flowing capability of the geopolymer mortars; however, incorporation of crumb rubber and increasing its substitution level had important effects on the unit weight, strength characteristics and ITZ. Moreover, the photographic view of the mixtures revealed that the crumb rubber particles were well-distributed on the mortar cross-section, namely no bleeding and segregation problems were faced. As a consequence, the results obtained in the scope of this study showed that crumb rubber could be used in geopolymer mortar production, provided that it is at certain substitution levels.