Effects of Recycled Concrete Sand on the Physical, Mechanical Properties, and Hydration Heat of Mortar

The use of Recycled Concrete Aggregates (RCA) is one of the solutions to the problems of both the high demand for natural aggregates by the construction industry, as well as the decrease in landfill demolition debris overload. However, the production of concretes or mortars based on RCA with qualities similar to those made with Natural Aggregates (NA) poses challenges. The main objective of this experimental study is to determine the influence of replacing 20%, 40% and 60% of Natural Sand (NS) with Recycled Concrete Sand (RCS) with the combination of replacing cement with different mineral additions: 10% Silica Fume (SF), 10% Limestone Powder (LP), 20% natural Pozzolana (PZ) and 20% Ground Blast Furnace Slag (GBFS) on the mechanical and physical properties of a plastic mortar. The results obtained revealed that RCS, rich in attached mortar, exhibits low physical properties such as low density, rough grain shape and high water absorption. Regarding the mechanical behavior of the obtained mortar, the results show that the presence of RCS has a positive impact on the Compressive Strength (Sc) accompanied by an increase of the hydration heat (Q) compared to the reference mortar. Moreover, the use of mineral additions improved the mechanical strength of the mortar, especially SF, which was the most active addition, followed by PZ. An empirical equation is proposed to predict the hydration heat as a function of the compressive strength, taking into account the cement type and the age of the mortar (≤ 10 days).