Water absorption in rubber-cement composites: 3D structure investigation by X-ray computed-tomography

Cement composites containing recycled rubber add the advantage of a hydrophobic character to the typical benefits of a lightweight aggregate, and contribute to giving value to a relevant secondary raw material all over the world. In this work, we have tested these innovative construction composite materials in terms of water uptake by capillary rise, important cause of deterioration of masonries and building heritage at large. Moreover, we have investigated the potential of the X-ray-computed tomography in order to clarify the role played by rubber grains in affecting the air void system [dimension range: 10 µm−1 mm] of these porous materials, i.e. porosity, size distribution and localization of the pores within the cementitious matrix. This technique has been used also to gain information about the solid itself, i.e. on cement-rubber area distribution, as this parameter affects specifically the “bulk” surface energy (hence contact angle) of the composite. Results indicate that rubber-cement composites have higher porosity over the whole explored range, and more sensitively in the smallest detectable range [10 µm–100 µm]. Their lower permeation to water is ascribed to the assessed increase of the composite bulk water contact angle, and formally consistent with a lower mean radius of the pores.