ABSTRACT
This work aimed at evaluating the influence of the use of recycled concrete aggregates on the mechanical performance of precast concrete. Recycled concrete was obtained as scraps of the precasting process itself and characterized by physical properties quite close to those of ordinary aggregates, due to the high strength class of the original concrete, which was in the range 50—55 MPa. Several substitution percentages were tried, between 5% and 30% by weight of the total amount of aggregate used for preparing concrete, in order to establish the maximum replacement percentage that could allow the same concrete strength class to be maintained. For this purpose, several concrete mixtures were prepared using rejected concretes coming from different precasting plants. Concrete performance was evaluated after 1, 7 and 28 days of wet curing, in terms of compressive strength. The results obtained showed that the quality of the old concrete influences the maximum substitution percentage that can be tolerated. When the Original strength class is 55 MPa, the substitution can be carried out at a percentage of up to 30%. In addition, the drying shrinkage of two concrete mixtures prepared with 70% of one of these recycled concrete fractions was monitored for 100 days of curing at a relative humidity of 65% and a temperature of 15°C. The results obtained were encouraging, particularly when a shrinkage-reducing admixture was added to the concrete mixture in addition to a water-reducing admixture.
