Researchers at the Department of Civil Engineering at Memorial University of Newfoundland has been studying the effect of rubber aggregate, especially crumb rubber as a partial replacement of fine aggregate, on structural behavior of reinforced concrete beams.
Twelve full-scale beams made with self-consolidating concrete and vibrated concrete mixtures were tested under flexural loading. The investigation included evaluations of the impact of crumb rubber on the flexural capacity, cracking behaviour, load-deflection response, concrete strain/stiffness, ductility, and toughness of the tested beams.
The beams’ mixtures were developed with variable percentages of crumb rubber (0% to 50%) using different binder content, addition of metakaolin, and/or utilizing air entrainment. The investigation also discussed the performance of some code-based equations in predicting the ultimate flexural capacity of the tested beams.
Based on the results obtained from the investigation, it can be concluded that as the percentage of crumb rubber increased from 0% to 50%, the first crack load, concrete’s stiffness and beams’ flexural stiffness generally decreased.
On the other hand, using up to 20% crumb rubber can improve the beam’s deformation capacity, ductility, and toughness with insignificant effects on the ultimate flexural load.
Further increase in the addition of crumb rubber (20% to 50%) appeared to limit the ability of beams to experience high deformation and absorb more energy, thus resulting in a reduction in the ductility and toughness of the tested beams.
Increasing the percentage of crumb rubber more than 20% appeared to affect the conservative estimation for the beams’ moment capacity based on the current ACI 318-08 and CSA-04 design codes. However, ACI 318-08 and CSA-04 can be used to obtain a conservative estimate of the ultimate moment capacity and also to provide adequate load factor against failure.
Researchers at Memorial University of Newfoundland believe that the results from this investigation will contribute to the enhancement of self-consolidating rubberized concrete performance and will be very useful in developing self-consolidating rubberized concrete with promising potential for structural applications.
The research can be found in a paper titled Performance of Full-Scale Self-Consolidating Rubberized Concrete Beams in Flexure, published by ACI Materials Journal.