Use of grinded hardened cement pastes as mineral addition in mortars

Abstract Recycled Concrete Aggregates (RCA) are not enough used in the construction sector due to their high porosity and water absorption capacity. Fine particles which are composed of large amounts of attached hardened cement paste are even more difficult to valorize, while they could be used as mineral admixture in mortar or concrete. The objective of this work is to find a recovery track for this material as mineral addition. The use of a porous powder as mineral admixture in cementitious mortars raises the question of the effective water definition in such systems. Two powders are used, the first one is a grinded hardened cement paste (porous), and the second one is a limestone filler (non-porous). A comparison of the hydration degree, porosity, fresh, and hardened behaviors between cement pastes and mortars manufactured with the two powders is carried out. The results show that the porosity of the grinded hardened cement paste has an impact on the properties of cementitious materials. Depending on the studied properties (fresh or hardened properties), the substitution of cement by the porous powder could be done with, or without taking into account the water absorption. Taking into account the water absorption allows maintaining the fluidity of the mixture but decreases significantly the compressive strength for cement replacement percentages larger than 20%.