In this paper, the effect of the original aggregate size of the recycled aggregate on the mechanical properties of the recycled aggregate concrete was evaluated. A series of concretes were produced in which natural aggregates, recycled aggregates, and original aggregates in recycled aggregates were matched for a single particle size distribution curve. The replacement levels of recycled aggregate were 25% and 50%, and equivalent mortar volume mix design was applied for recycled aggregate concrete. The results show that the mechanical strength of recycled aggregate concrete increases with increasing original aggregate size. This effect was observed to be greater in concrete using recycled aggregate with a high residual mortar content.

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The adhered mortar attached to recycled aggregate (RA) is one of the main causes of weakening the mechanical properties and durability performance of recycled aggregate concrete (RAC). Therefore, in order to improve the performance of RA and RAC, several methods have been proposed to remove the adhered mortar in RA. However, knowing the adhered mortar content is as important as removing it. This is because concrete mix designs considering the amount of adhered mortar have been proposed and better strength, durability and environmental benefits of these mix designs were reported compared to conventional RAC mix design. Therefore, in this study, the adhered mortar was removed by using two methods of ‘acid treatment’ and ‘chemical and mechanical stress treatment’ for three types of RA, and the test results obtained from each method were comparatively analyzed. The results showed that the adhered mortar contents determined by the two methods were different for the same aggregate, and neither allowed the complete removal of the adhered mortar from RA. It also showed that the test environment of the chemical-mechanical stress method can be harsh enough to damage the original aggregate in RA, and that the acid treatment can cause corrosion of RA depending on the type of aggregate.