Effect of Waste Rubber Inclusion on the Microstructure and Mechanical Performance of Low-Density Foam Concrete

Foam concrete is a porous cement-based material that could accommodate a high-volume particle addition at the mid- to high-density range (0.8 to $1.6\mathrm{g}/{\mathrm{cm}}^3$). However, with low-density foam concrete (0.4 to $0.8\mathrm{g}/{\mathrm{cm}}^3$), conventional particle inclusion (e.g., sand) tends to degrade the cellular microstructure and mechanical performance. Therefore, to improve low-density foam concrete, the novel use of crumb rubber (the rubber particles recycled from waste tires) in foam concrete is studied, as its unique attributes can potentially allow for the retention of structure and improved performance in foam concrete. The influence of no inclusion, sand, and crumb rubber on the microstructure and mechanical performance in foam concrete with the density of cellularized cement paste as 0.40 and $0.60\mathrm{g}/{\mathrm{cm}}^3$ was studied. Computed tomography indicates that the inclusion of crumb rubber can mitigate the foam degradation concern associated with particle inclusion in low-density mixtures. A notable improvement was also observed in the mechanical properties of $0.40\mathrm{g}/{\mathrm{cm}}^3$ rubberized foam concrete mixtures—compressive strength, plateau strength, and impact resistance—when referenced to the sand inclusion counterpart.