Effect of saturation state of fine recycled concrete aggregates on the properties of mortars

Only a small fraction of concrete wastes is re-used as recycled concrete aggregates (RCA) in the manufacture of mortar and concrete. The fine recycled concrete aggregates (FRCA), essentially composed of mortar and hardened cement paste, possesses a large water demand which makes it harder to recycle into concrete and mortar compared to the coarse RCA. In order to optimize the use of FRCA into mortar, the saturation state of FRCA plays an important role on the properties of mortar.
In this paper, the influence of saturation state of FRCA (dried or saturated) on the properties of mortars of identical compositions was investigated. The results showed that the slump of mortars containing dried FRCA is always larger than that of mortars containing saturated FRCA. Indeed, in the case of dried FRCA, the theoretical amount of absorbed water is added at the begging of mixing leading to a temporary increase of the initial efficient W/C ratio and volume of paste, leading to a better workability before its absorption in to FRCA. Moreover, the compressive of mortars containing dried FRCA is always larger than that of mortar made with saturated FRCA, which is attributed to a thinner interfacial transition zone (ITZ) improving its mechanical properties.