Influence of water-reducing admixtures on the mechanical performance of recycled concrete

The use of recycled aggregates from construction and demolition waste in concrete is not new. One of the main problems found in this application is the aggregates' high water absorption and, therefore, low workability. Incorporating water-reducing admixtures (plasticizers) can reduce the amount of water required, improving the compactness of concrete. This research aims at determining the suitability of using two types of water-reducing admixtures to improve the characteristics of concrete made with recycled aggregates. Three series of concrete with various replacement ratios (0%, 20%, 50% and 100%) of natural aggregate by coarse recycled concrete aggregate were manufactured for this study and used without admixtures, with a traditional plasticizer and a high-performance plasticizer. The basic properties of the aggregates were considered, and the workability and density of fresh concrete and key mechanical properties of hardened concrete, such as compressive strength, tensile strength, elastic modulus and abrasion resistance, were studied. The results obtained were encouraging to use plasticizers in concrete with recycled aggregates.