Reduction in the depth of carbonation was observed up to 12.5%
of crumb rubber. This can be attributed to the improved pore structure
at reduced water–cement ratios. Miguel and Jorge [28] had
mentioned that, when the tyre aggregates were replaced for the
coarse aggregates in concrete, the carbonation depth had
increased. In our case, the depth of carbonation had decreased up
to 10% crumb rubber substitution This could be because of the reason
that the fine aggregates and the replaced crumb rubber were
almost the same size (Zone II) and these closely packed rubber particles
along with the natural aggregates in the concrete may prevent
the entry of carbon dioxide gas into the concrete. The
rubber powder might have provided a filler effect in the concrete
to reduce the depth of carbonation. Increase in the depth of carbonation
beyond 10% crumb rubber would be due to the lack of
internal packing in the concrete specimens.