Usage potential and benefits of processed coconut shells in concrete as coarse aggregates

Abstract

As concrete consumes a lot of natural resources, sustainable growth is challenging. Around the world, 7.23 billion tonnes of concrete is produced annually, necessitating a significant quantity of aggregates to meet construction demands. Therefore, it is crucial to explore alternatives to coarse aggregates, which make up roughly 70–80% of the overall volume of the concrete. Additionally, waste management is a global concern that is exacerbated by up to 15% due to coconut shell trash. India ranked third in the world for coconut production in 2018, is particularly affected by this issue. This study investigates the usage of coconut shells in place of coarse aggregate. Owing to the high-water absorption of coconut shells, presoaked coconut shells were replaced as coarse aggregate with 5, 10, 15, 20, and 25% in M30 grade concrete. Slump, density, compressive strength, and microstructural characteristics were studied and evaluated. It is observed that, due to the presence of the plain surface on one side of the coconut shell, the workability of the concrete increased as the percentage of coconut shells increased. Because of the lower specific gravity of coconut shells, concrete produced by 15% replacement of coarse aggregates, reduced the density of the concrete by 7% when compared to the conventional concrete. The 28-day compressive strength of 15% coconut shell replaced concrete showed a 24% strength reduction compared to conventional concrete. C-S-H gel formation was evident from SEM analysis. It is important to note that the compressive strength of coconut shell aggregate concrete at 3, 7, 14, and 28 days, decreased rapidly beyond the 15% replacement of coarse aggregates. It has been found that concrete may be produced without impacting performance qualities when coconut shell aggregates are used in place of natural aggregates at an optimal replacement of 15%.