Evaluation of the durability of concretes produced with recycled concrete aggregates using the two stage mixing approach

ABSTRACT

The recycling of the mineral fraction of civil construction residues is seen as a source potential of generation of aggregates. The Recycled Concrete Aggregates (RCA) are generally indicated for using in the production of new concretes. However, due to the old mortar adhered to RCA, these have smaller specific mass and higher porosity when compared to the natural aggregate. In the seek of improving the quality of RCA, various techniques have being developed, being one of the alternatives through of surface modification. This study objectified to verify the effect of the substitution of 20% of natural coarse aggregate by RCA and to perform the surface modification of the RCA through the two stage mixing approach. The replacement of aggregates was performed maintaining the particle size distribution of the natural coarse aggregate. The RCA treatment was performed in the pre-wetting period with contents of 25 and 100% of Portland cement. It were performed tests to evaluate the behavior of concretes in relation to mechanical properties and durability parameters. It was evident that the utilization of 20% of RCA in the production of a new concrete produces negative effects on the evaluated properties when compared to conventional concrete. The treatment in the RCA though the two stage mixing approach with 25% of Portland cement provided improvement in the concrete when compared to the normal mixing approach. On the other hand, the two stage mixing approach with 100% of Portland cement impaired the concrete behavior. It was concluded that the two stage mixing approach with 25% of Portland cement showed as a viable alternative to provide improvements in the RCA. Besides resulting in a concrete with good characteristics of mechanical properties and durability, it also enables the utilization of recycled aggregates and it does not generates additional cost in the process of concrete production.

Keywords
concrete; recycled concrete aggregates; two stage mixing approach; durability