Impact of Multiple Recycling on the Strength of Coarse Aggregate

Concrete structures are integral parts of modern civilization. Every year a huge amount of concrete waste is generated due to demolition of old concrete structures for replacing them with new high-rise buildings or other structures, which consequently, increasing the environmental loads. Recycling of demolished concrete is found to be an effective way for sustainable development which can also minimize the disposal problem associated with concrete waste. Recycling of demolished concrete to produce usable aggregate, therefore, has drawn attention of researchers in the field of concrete technology. However, most of the studies in this field are focused on 1st generation recycled aggregate. Effect of multiple recycling on the properties of aggregate is merely studied. In this study, the effect of multiple times recycling on aggregate strength is observed. Strength of aggregate is evaluated in laboratory by Aggregate Crushing Value (ACV) test and Aggregate Impact Value (AIV) test after each generation of recycling. The ACV and AIV values of 1st generation, 2nd generation and 3rd generation recycled aggregates are compared with the natural source aggregate. Strength degradation after each stage of recycling is recorded. In addition, the test results of 1st generation, 2nd generation and 3rd generation recycled aggregates are interpreted, investigated and compared with standard requirement to outline their corresponding applications. ACV value for natural aggregate is found to increase by 2.5% after 1st stage of recycling and it increased by 4.64% and 6.79% after 2nd and 3rd stage of recycling respectively. On the other hand, AIV value for natural aggregate is found to increase by 7.04% after 1st stage of recycling and it increased by 10.35% and 12.47% after 2nd and 3rd stage of recycling respectively. The study reveals that the strength of 1st generation recycled aggregates is quite similar to that of natural aggregate and can be used for concreting in general purposes. 2nd generation recycled aggregate cannot be used in the production of concrete in heavy duty floor but can successfully be used in concrete for wearing surface and 3rd generation recycled aggregates are too weak for road surfacing.