ABSTRACT
This study investigates the suitability of crushed coconut shell (CCS) and polyethylene terephthalate (PET) as partial replacement of coarse aggregate in concrete. The PET was crushed mechanically to sizes between 0-10mm while the CCS was crushed manually to sizes between 12.7-19.5mm. Various tests were carried out to ascertain the physical and engineering properties of the aggregates used in this study. Sieve analysis was carried out on all the various aggregates used in this study and it was observed that when combined it gives us an all in aggregate distribution which is ideal for concrete construction. Flakiness and elongation tests were also carried out and it was observed that CCS and PET have a flakiness index of 100% as compared to gravel with a flakiness index of 19.54%. PET had the highest elongation index of 67.35%, gravel with 29.48% and CCS in between with 28.24%. Specific gravity of all the aggregates used in this study was found out with PET, river sand, gravel and CCS having specific gravities of 1.32, 2.64, 2.70 and 1.38 respectively. Aggregate impact and crushing value tests were carried out on the aggregates with PET, gravel and CCS having AIV values of 0.3125%, 26.57% and 3.62% and ACV values of 2.29% and 28% for CCS and gravel respectively. This study was narrowed to 50% replacement of conventional coarse aggregate with varying percentages of CCS and PET from 0%, 10%, 20%, 30%, 40%, to 50%. Which led to 9 different mixes labelled A to I respectively. Slump test was carried out on the fresh concrete to ascertain its workability while compressive strength and water absorption tests were carried out on the various samples with different percentage replacement of CCS and PET. From the study it was observed that a mix percentage of 50% gravel, 20% CCS and 30% PET (sample F) and 50% gravel, 20% CCS and 30% PET (sample G) of gave us a compressive strength value of 18.4 N/mm2. Also it was observed that with increase in CCS content there was increase in compressive strength for up to 30% CCS and with decrease of percentage of PET from 50% to 20% there was increase in the compressive strength up to 18.4N/mm2. Also, Sample F has a lower water absorption capacity of 3.99 than G which has a water absorption capacity of 4.48 but both fall within the range specified for average absorption. It was can be concluded that samples F and G are viable and sustainable construction alternatives to conventional concrete and can be used in road drainage, gutter, slabs, kerbs, canal linings, blinding, low traffic road pavements, stone pitching, embankment, base for flexible pavements and minor concrete works in general.