Rubber-Modified Self-Compacting Mortar Evaluating Setting Time and Strength Development

The influence of using crumb rubber (CR) obtained from the second scraping of used tires as fine aggregate in manufacturing self-compacting mortar (SCM) was investigated experimentally in this study. To explore this, natural fine aggregate in SCM mixes was partially replaced with CR at levels ranging from 5% to 25% by total fine aggregate volume. Two mix series, one with a total binder of 500 kg/m3 and the other with a 540 kg/m3 binder, were designed at water-to-binder ratios of 0.40 and 0.33. Ordinary Portland cement (80% by weight) and fly ash (20% by weight) were used to manufacture mortars. Twelve SCM mixes were cast and tested to evaluate their fresh-state properties, including setting times, flow diameter, and flow time. Moreover, the compressive strengths at 3, 7, 28, 56, and 90 days were determined for each mix to investigate their strength development. The test results indicated that the incorporation of CR adversely affected the fresh properties of the SCM mixes, and an increase in the CR replacement level systematically diminished their strength characteristics. Nevertheless, it was observed that it could be used in a controlled manner to achieve the desired properties.