Evaluating the use of recycled rubble as a partial substitute for coarse aggregate in new concrete mixes.

Abstract

Currently Uganda is suffering from litter from construction and demolition wastes due to the limited capacity of landfills available. This study aimed at adding value to the useless litter(rubble) to a useful one. The researcher carried out an evaluation of the use of recycled rubble in new concrete mixes where the concrete cubes with rubble aggregates and natural aggregates through the controls both fresh and hardened were put under test.

This study was descriptive in nature and followed an empirical approach that relied on direct observation and experimentation in acquisition of new knowledge. The research was quantitative in nature and involved experimental setup. Laboratory tests of slump test and compressive test focused on physical properties of workability and compressive strength respectively.

The tests showed that the workability of fresh recycled concrete is lower than that of the natural concrete subjected under similar conditions, an average slump of 52.7mm of recycled concrete (rubble) against 77.5mm of natural concrete. Rubble aggregates can be substituted with natural ones for purposes of making concrete however, rubble should not be used on a large scale as this study showed that increase in the rubble aggregates leads to a decrease in compressive test (mix design). This is due to the shield by the mortar on the rubble aggregates that interdicts the effectiveness of the new mortar paste aggregate bond.

Further research on flexural strength and bond strength between recycled concrete and steel and chemical tests are recommended.