Study of the influence of the substitution of natural aggregates by hardened cement aggregates in concrete and the exposure of concrete to a medium enriched with carbon dioxide

\nThe valorization of waste is an excellent way to protect the environment. This study focuses on waste consisting of cement that has hardened before use. The goal of this study is to determine the conditions under which these can be valorized in concrete. These wastes are used as aggregates, referred to as Hardened Cement Aggregates (HCA). First, the density, granulometry, and impact resistance of these aggregates were measured and compared to those of natural aggregates (NTA). The results showed that natural aggregates have a bulk density and specific gravity more than 25% higher than those of HCA. However, this trend reverses when considering mechanical strength. Specifically, the Los Angeles and micro-Deval abrasion coefficients of NA are 10% and 18% lower, respectively, indicating better mechanical resistance than HCA. This difference in performance is attributed to the higher porosity within the structure of HCA. When evaluating the concrete, it was observed that the poor physical and mechanical properties of HCA adversely affected the concrete produced with them (HCAC). Therefore, the subsequent phase of the research aimed to identify conditions that could optimize the properties of HCAC. Samples of HCAC were cured in two different environments: plain water (control) and CO2-enriched water (carbonated environment). The results demonstrated that curing in the carbonated environment significantly improved the mechanical properties of HCAC by over 20%. This increase allowed the concrete to reach a compressive strength of 28 megapascals, which matches the strength of concrete made with natural aggregates (NAC). Consequently, hardened cement aggregates can effectively replace natural aggregates in concrete when used in a carbonated environment.\n