Quantitative assessment of the saturation degree of model fine recycled concrete aggregates immersed in a filler or cement paste

We study water transfer between different model fine recycled concrete aggregates and fresh filler or cement paste in which they are immersed. Our aim is to introduce a spread based experimental protocol for studying the time evolution of water content in initially dry aggregates when mixed with such pastes. The procedure developed hereby is tested on three model Cement Paste Sands (CPS) prepared with different water-to-cement ratios leading to very different porosities and pore structures. The results show that water content in the CPS reaches a maximum no later than 6 min after first contact with limestone filler or cement paste then remains fairly constant afterwards. The saturation degree, i.e. ratio of the water content in the CPS to their water absorption, increases with the porosity of the CPS and remains less than one whatever the paste. The corresponding reduction of water absorption capacity in a cement paste should be taken into account during mix design of a recycled concrete.