This study assesses the strength of concrete incorporating coconut shells and polyethylene terephthalate (PET) as a partial replacement of coarse aggregates. The PET was manually cut into sizes smaller than 20 x 20 mm but greater than 10 x 10 mm, while the coconut shells cracked using a hammer into sizes passing sieve size of 25.4 mm.

This study was narrowed to 50% replacement of conventional coarse aggregate with varying percentages of coconut shells and PET from 0%, 10%, 20%, 25%, 30%, 40%, to 50%, leading to four (4) different mixes labeled a, A, B, and C respectively. A slump test was carried out on the fresh concrete mix to ensure its workability while density, compressive strength, and water absorption tests were carried out on the various samples with different percentage replacements of coconut shells and PET. The workability of concrete with CCS and PET ranges from 60-90 mm, observing that the inclusion of CCS and PET in concrete does not significantly improve or reduce the workability of concrete.

Furthermore, with the density ranging from 2,400 to 2,800 kg/m³, all samples can be used as normal-weight concrete. Then, a mix percentage of 50% gravel, 40% crushed coconut shells, and 10% PET (sample C) gave a compressive strength value of 6.01 MPa with an observation that the increase in the proportion of replacement of CCS and decrease in the proportion of PET escalates the compressive strength of concrete. Sample C also obtained a water absorption capacity of 6.52, indicating a more desirable durability characteristic.

It was concluded that sample C, in terms of workability, durability, and effectiveness, suitable for general is construction purposes although its compressive strength did not meet the standard of M15 (1:2:4) to reach 15 MPa. It can be used for plain cement concrete work such as leveling courses, bedding for footing, strip footing, and other minor concrete works in general.
Keywords: coarse aggregate, coconut shell, concrete, compressive strength, density, polyethylene terephthalate, water absorption, workability.

Research paper (Bachelor of Science in Civil Engineering - Structural Engineering)

Includes appendices and bibliographical references