Pengaruh penggunaan Sikacim dan cangkang kerang sebagai subtitusi Agregat halus terhadap sifat fisik beton

Seashell waste is one of the marine wastes that has the potential to pollute the environment if not utilized optimally. This study aims to utilize seashells as a partial substitution for fine aggregate (sand) in concrete mixtures with the addition of Sikacim admixture, and to investigate its effects on the physical and mechanical properties of concrete immersed in seawater. The tests were carried out on cylindrical specimens to measure compressive strength, porosity, and density at the ages of 7, 28, and 56 days, as well as on beam specimens for flexural strength at 28 days. The compressive strength test results showed that the seashell concrete with Sikacim addition (CK+S) experienced a significant increase from 17.13 MPa (7 days) to 39.81 MPa (56 days), which is higher than normal seawater concrete and seashell concrete without admixture (23 MPa). The 28-day flexural strength test indicated that CK+S achieved the highest value (8 MPa), followed by seashell concrete (CK AL) at 7 days (5.3 MPa), and normal seawater concrete (BN AL) at 7 days (4.29 MPa). The porosity test results showed that CK+S had the highest value at 28 days (6.52%), while BN AL at 7 days recorded the lowest (0.99%). The highest density was achieved by BN AL at 7 days (147.85), while CK+S had the lowest in the early stage. These findings indicate that CK+S excels in mechanical strength, whereas BN AL performs better in water resistance and density, allowing the mixture selection to be adjusted according to usage requirements.