Mechanical performance and medium-term degradation of rubberised concrete

• Effect of tyre-rubber partial substitution to natural aggregate in concrete is investigated.
• Mechanical retrogradation, cracking and volumetric expansion occur in rubbercrete cured in moist environment after 60 days.
• Chemical and microstructural analysis of degradated rubbercrete show no anomaly.
• The most plausible hypothesis for degradation is that rubber swells in alkaline environment.
• Imperflux-based surface treatments of rubber can prevent degradation in rubbercrete.

This laboratory study deals with a comprehensive investigation of modified concrete specimens using rubber particles obtained from End of Life Tyres (ELT). Different types of mixes have been studied with different percentages of rubber particles used as a partial substitute for natural aggregates by using and comparing mixtures with various types of addition and surface treatment. Three types of rubber particles (ash rubber, crumb rubber and tyre chips) have been employed in the rubberised concrete mixtures replacing partially the natural aggregates. Test results shown that the rubberised concrete mix had some appealing characteristics such as a low mass density but worse compressive strength in line with previous studies. Among the most important findings, a decline in mechanical performance was observed in rubberised concrete specimens at an age of about 60 days. Moreover, cracking and delamination phenomena occurred on the test specimens cured under moist conditions which have never been described in the literature so far. The main innovation is in description of these results regarding time-dependent degradation of rubberised concrete and in a preliminary investigation about the causes of this phenomenon.