Rheological behavior at fresh state of structural recycled aggregate concrete

Abstract

At the end of their service life, concrete members can be demolished and reused as alternative constituents in the production of new concrete mixtures. This process leads to producing a sustainable construction material often referred to as Recycled Aggregates Concrete (RAC), in which ordinary aggregates are (partially or totally) replaced by Recycled Concrete Aggregates (RCAs). However, due to the intrinsic characteristics of RCAs (i.e., higher porosity in comparison with ordinary aggregates) the definition of reliable relationships, capable of predicting the relevant properties of RACs, is still considered an open issue. Moreover, in last years, the scientific community mainly focused on understanding the mechanical behavior of RAC at hardened state and only few studies addressed the properties at the fresh state. The present paper investigates the influence of RCAs on the resulting rheological behavior of RACs. In fact, the higher porosity of aggregates generally modifies the actual amount of free water, which controls the resulting workability, according to the well-known Lyse’s rule. Moreover, the initial moisture condition of aggregates is a further aspect to be duly taken into account. Therefore, this study is mainly intended at extending to RAC some conceptual tools, such as the aforementioned Lyse’s rule and the simplified Bingham model, whose application is well-established for ordinary concrete mixture. With this aim, several experimental tests were performed (i.e., slump and rheometer test) in order to investigate the effect of various aspects and parameters, such as the processing procedures of RCAs, the actual aggregate replacement ratio and the initial moisture condition of coarse recycled aggregates. Finally, it is worth highlighting that this work results from the SUPERCONCRETE Project (H2020-MSCA-RISE-2014 - n. 645704), funded by the European Union as part of the H2020 Programme.