Effects of Crushing and Grinding on the Porosity of Hardened Cement Paste

The objective of this paper was to study the impact of crushing and grinding on the porosity of hardened cement paste, which is responsible for the high values of recycled concrete aggregate (RCA) water absorption. Hardened cement pastes with three different water to cement ratios have been crushed in one to three steps with a jaw crusher to produce aggregate larger than 2 mm and ground with a disc crusher in order to produce particles lower than 150 µm. Water absorption tests and mercury intrusion porosimetry (MIP) were performed for the different resulting sizes. It was observed that the crushing procedure did not significantly affect the porosity of the aggregate. However, MIP performed on the powders showed differences in the pore size distribution compared with the monolith. This can better be attributed to a modification of the surface roughness of the particles than to a modification of their porosity. In all cases, the water absorption rate was the highest during the first 1 min after soaking in water. It was also observed that the morphology of the particles changed from a step of crushing to another.

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