The effect of coconut shell charcoal on the compressive strength and density of a lightweight concrete mixture with fly ash

Suitable materials still need to be made available in coastal areas, particularly for using a fine aggregate in buildings due to the high salt chloride and sulfur content. This study substitutes coconut shell charcoal for fine aggregate with a mixture of fly ash, intending to lower the specific gravity of the concrete to make it lighter than regular concrete. The test specimens are a 15cm×30cm cylinder. The material testing of crushed stone as coarse aggregate and sand as fine aggregate was prepared according to the Indonesian Standard of Testing (SNI 7656-2012). The experimental purpose is to make light concrete mixtures with coconut shell charcoal to decrease the substantial weight of concrete. The testing procedure was divided into two stages. First, determining the compressive strength of regular concrete follows by using 10%, 12.5%, 15%, 17.5%, and 20% coconut shell charcoal as a cement mixture with 10% fly replacement. The compressive strength of regular concrete at 28 days reaches 20.04 MPa. Meanwhile, the compressive strengths of coconut shell charcoal concrete are 16.49 MPa, 15, 39 MPa, 14.57 MPa, 13.28 MPa, and 11.48 MPa, respectively, using 10%, 12.5%, 15%, 17.5%, and 20% coconut shell charcoal mixing. Thus, concrete density decreased by 1.62%, 2.60%, 3.60%, 5.22%, and 7.23% compared to regular concrete. The highest compressive strength was obtained for 10% coconut shell charcoal-mixed concrete. Instead, the lowest density was obtained with a 20% mixture. As a result of using coconut shell charcoal, the density of the concrete is reduced, making it lighter than standard concrete.