Compressive strength of fly ash-based geopolymer concrete with crumb rubber partially replacing sand

• Rubber replacement plays a key role in strength reduction of geopolymer concrete.
• Appropriate rubber amount may be replaced without significant strength reduction.
• The fly ash type and Na2SiO3/NaOH also leads to the strength reduction.
• The regression models are used to identify critical parameters and interactions.

This study presents the feasibility of geopolymer concrete to which crumb rubber from recycled tires has been added. Geopolymer concrete utilizes industrial by-products like fly ash. Therefore, the use of rubberized geopolymer as a binder in concrete production not only reduces the emission of carbon dioxide, because of the elimination of cement, but also utilizes an industrial disposal of recycled tires to produce a sustainable construction material. In this research, fly ash, an alkaline liquid mix of sodium hydroxide and sodium silicate, and crumb rubber were used as the basic constituents of the geopolymer. Various factors that influence the compressive strength were studied, such as molarity of sodium hydroxide, size of aggregates, amount of rubber, and types of fly ash. An appropriate amount of rubber may be replaced with an equal volume of fine aggregates in rubberized geopolymer concrete. The analysis of variance (ANOVA) indicates that fine aggregates can be replaced with an equal volume of crumb rubber, up to 5% in three types of fly ash-based geopolymer concrete at the 95% confidence level. The regression model indicates that the correlation between rubber replacement and other parameters are not statistically significant.