Performance enhancement of rubberised-alkali-activated-concrete utilising ultra-fine slag and fly ash

Abstract

This paper investigates the strength and durability properties of low calcium fly ash based rubberised alkali-activated concrete (RAAC) with a replacement of natural fine aggregate (NFA) with crumb rubber (CR) at different percentages. RAAC was prepared using a mix of Sodium silicate (Na2SiO3) and 8 M Sodium hydroxide (NaOH). The prepared specimens were cured at ambient room temperature and an elevated temperature of 60°C. The properties of RAAC, including density, slump, air content, compressive and flexural strengths, and elastic modulus were examined. The durability characteristics like carbonation depth, water penetration, and electrical resistivity were also investigated. The experiments indicated that slump, density, and strengths declined with increasing CR%. In addition, RAAC also displayed a higher water absorption and carbonation depth than conventional alkali-activated concrete (AAC) and was more prone to chemical, water, and chloride attacks. However, the higher electrical resistivity (ER) of RAAC indicated a higher compressive strength. The heat curing further enhanced the strength of RAAC and marginally improved its durability. Finally, the findings are supported with microstructural investigations. The heat-cured specimens possessed a comparatively denser microstructure compared to ambient-cured specimens. It is concluded that the discarded tyres can be used in RAAC production for structural applications, hence providing a sustainable solution for waste utilisation.

Keywords

• Rubberised alkali-activated concrete (RAAC)
• Crumb rubber (CR)
• Strength
• Durability
• Carbonation
• Water absorption