Improving the Quality of Recycled Fine Aggregate by Selective Removal of Brittle Defects

Crushed recycled aggregate contains particles with brittle defects such as cracks, pores, and voids. This study presents a method for improving the quality of recycled fine aggregate by selectively removing these defects. Fourteen recycled fine aggregates were manufactured by three types of processors including a jaw crusher, ball mill, and granulator. The influence of the recycled fine aggregate on the flowability and strength of the mortar was evaluated by multivariate analysis. The results showed that flowability was mainly affected by the filling fraction of the recycled fine aggregate and the content of components passing through a 0.075-mm sieve. Both the compressive and flexural strengths of the recycled mortars were unaffected by the filling fraction, but they were affected by the fraction of defects in the aggregate and its surface smoothness. In addition, the results clearly showed that polishing involved in ball mill or granulator processing is effective both for increasing the filling fraction of recycled fine aggregate and reducing the fraction of defects in the aggregate. Moreover, it was determined that the grain surface of grains was more irregular with the granulator than that with the ball mill, resulting in higher strength of the mortar subjected to the granulator. The fracture configuration resulting from flexural stress on the recycled fine aggregate in the mortar differed according to the type of aggregate. Furthermore, the calculated amounts of emitted CO2 and the compressive strength of the recycled mortar showed that the recycled fine aggregate should not be polished excessively.