Water Absorption by Capillarity, Physical and Mechanical Properties of Concrete Containing Recycled Concrete Aggregate with Partial Cement Replacement by Metakaolin

An alternative way to mitigate the impact generated by the Construction and Demolition Waste (CDW) on the environment is recycling this material in order to utilize it as Recycled Concrete Aggregates (RCA) in concrete. Studies carried out demonstrated that while using a scientific mix-design, it is possible to have a Recycled Aggregate Concrete (RAC) with mechanical properties similar the ones in conventional concrete. However, the durability of the recycled concrete is still a matter that should be explored further. The use of Supplementary Cementitious Materials (SCMs), such as metakaolin, has been shown to be efficient when partially replacing cement. It has the ability to improve the packaging of concrete by decreasing the volume of the pores of the material and, consequently, reducing the water absorption capacity of RAC, since RCA presents greater water absorption compared to natural aggregates. Therefore, the aim of this study is to evaluate the durability and mechanical behavior of RAC with 60 MPa of compressive strength by totally replacing the natural coarse aggregate by RCA. Also, part of the cement was replaced by metakaolin. The coarse aggregate considered in this research has 19 mm as nominal maximum size. Total absorption, capillarity absorption, compressive strength test and tensile strength test were carried out for all mixtures. The research results showed that the use of metakaolin offset the increase in capillary absorption in recycled concrete caused by the use of RCA, reaching a value close to concrete with only natural aggregate and without metakaolin for this durability parameter.