Mechanical and durability properties of functionally graded crumb rubber concrete

Despite concrete's environmental drawbacks, it remains the most consumed human-made construction material worldwide. Incorporating crumb rubber from waste tyres as a substitute for natural fine aggregate offers an effective solution to mitigate the environmental challenges posed by tyre waste, whilst it also reduces the demand for natural fine aggregates. The functionally graded material concept may be applied to propose composite materials to address these problems, by using materials with different characteristics where they are needed within a structural component. The objective of this study is to evaluate the mechanical and durability properties of functionally graded crumb rubber concrete (FGCRC) specimens. Standard physical and mechanical tests were conducted according to ASTM C143/C143M – 20, ASTM C138/C138M − 24a, ASTM C39 – 21, and ASTM E119-22. Seven mixes with different percentages of rubber, ranging from 0 to 40%, were cast to analyse the potential of using FGCRC for sustainable structures. The specimens were cured in water and tested for fresh and hardened properties. The evaluated properties encompassed the slump test, fresh density, dry density, compressive strength, and fire resistance performance. The optimal replacement level of fine aggregate with rubber was found to be 20% by volume, which resulted in 10% reduction in compressive strength compared to the control sample. Additionally, concrete samples employing horizontal FGCRC layers resulted in 5% reduction in compressive strength compared to the control sample. Fire resistance testing demonstrated that FGCRC retained significant strength after exposure to elevated temperatures, highlighting its potential for fire-resistant applications. The findings indicate a promising potential for using FGCRC in structural applications.