Evaluation of the behavior of recycled aggregates in multiple cycles to manufacture concrete
Construction aggregates represent a high potential impact on the environment, and sources are increasingly scarce. The literature shows research on recycling rubble to produce new aggregates and their use in concrete, but there is not much evidence of the effect of multiple recycling cycles on this type of materials. In this research, the physical, chemical, and mechanical characteristics of recycled coarse aggregate subjected to several recycling cycles were studied. All the material that was used for recycling was from the same source (cast-in-place concrete) and the procedures were carried out according to the applicable INTE or ASTM standards. The methodology followed began with the characterization of the recycled coarse aggregate and was used in a mix design for concrete with a nominal resistance (f'c) of 210 Kg/cm2. Different proportions of recycled aggregate replacement were used: 30% Recycled – 70% Natural, 50% Recycled – 50% Natural and 100% Recycled. The following tests were carried out on the aggregate: granulometric analysis, specific gravity, mass density, abrasion, and alkali-aggregate reaction. A total of 140 test concrete specimens were made for all combinations in the 3 recycling cycles, failing them at 7, 14 and 28 days according to INTE C39:2022 (ASTM C39:2021). The investigation was able to conclude that there is technical feasibility for the use of rubble to obtain coarse aggregate in at least three recycling cycles, with some restrictions regarding the use of concrete due to the amount of fines, abrasion, and alkalinity reaction. . Particularly, it was also determined that further research is required regarding the effect of the alkali reaction on the quality and durability of concrete after the second recycling cycle, especially in such significant aggregate substitutions.
