Differences between laboratory and in-situ conditions leading to bad estimation of the water absorption capacity of recycled concrete aggregates

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Poor estimation of the water absorption coefficient (WA) of recycled concrete aggregates (RCA) engenders inadequate effective water for the recycled aggregate concrete (RAC), leading to poor mechanical properties or poor workability. Pre-saturation of RCA before mixing could appear as a potential technical solution. However, pre-saturation before mixing is a complex task that is most generally not applied in RAC manufacturing. Therefore, better knowledge of in-situ RCA water absorption capacity is necessary. This paper focuses on the influence on the water absorption capacity of i) the initial moisture of RCA, and ii) their heterogeneity. For this purpose, 6.3/10 mm RCA were pre-wetted using different methods simulating long-term (LT) and short-term (ST) pre-moistened aggregates. It is shown that this pre-moistened history (LT or ST) leads to different levels of total water absorption for a same initial moisture level. The difference lies between 0 and 1%, depending on the initial moisture level. In addition, the heterogeneity of RCA was investigated by separating samples of RCA into classes of densities using a water jig. The WA is about 5% for heterogeneous 6.3/10 mm RCA, but for the homogenous specimens separated by density WA ranges from 2% to 9%.