Experimental Investigation of Mechanical, Durability, and Impact Properties of Crumb Rubber Modified Fly Ash Geopolymer Concrete

The high carbon dioxide emissions associated with Ordinary Portland Cement (OPC) production have intensified the need for sustainable alternatives in the construction industry. This study investigates the mechanical, durability, and impact performance of crumb rubber-modified fly ash-based geopolymer concrete (RGPC) as an eco-friendly material for structural applications. Crumb rubber was incorporated as a partial replacement for aggregate at proportions of 0%, 5%, 10%, 15%, 20%, 25%, and 50% by weight. Concrete specimens were prepared and cured under ambient conditions, and tested at 3, 7, 14, 28, and 56 days. The experimental tests included slump, compressive strength, impact resistance (drop-weight test), and durability under sulphuric acid exposure. The results indicate that workability increased with increasing crumb rubber content, with slump values rising from 15 mm for the control mix to 55 mm at 50% replacement. Compressive strength improved with curing age for all mixes; however, optimum performance was observed at 5–10% crumb rubber content. At 56 days, the 10% replacement achieved a compressive strength of 31.67 N/mm², comparable to the control (31.50 N/mm²), while higher replacement levels (≥20%) resulted in significant strength reductions of up to 39%. Impact resistance increased with curing age but decreased with increasing rubber content, although the 5% replacement exhibited relatively improved energy absorption at intermediate ages. Durability results showed that low crumb rubber content (5–10%) enhanced resistance to sulfuric acid attack, reducing strength loss compared to the control, whereas higher contents led to increased porosity and deterioration. In conclusion, the incorporation of crumb rubber in fly ash-based geopolymer concrete improves workability and can enhance durability and impact performance at low replacement levels. An optimum crumb rubber content of 5–10% is recommended to be used in the production of concrete.