Study on the Composition and Compressive Strength of Oyster Shell Concrete

Abstract

      This study aims to investigate the elemental compositions of oyster shell, particle morphology of oyster shell powder, and the compressive strength of concrete incorporating oyster shell powder as a partial replacement for Portland cement. The analysis included elemental composition using X-ray Fluorescence, as well as a comparative examination of particle surfaces among cement powder, non-burned oyster shell powder, and burned oyster shell powder, which was heated at 900°C for 5 hours. Concrete samples were prepared by replacing cement with oyster shell powder at 25% and 50% by weight, and compressive strength tests were conducted at 7, 14, and 28 days of curing age in accordance with BS 1881 standards. Elemental analysis revealed that oyster shells contain key elements similar to Portland cement, including calcium (Ca) 87.3%, silicon (Si) 5.7%, iron (Fe) 3.7%, and aluminum (Al) 1.0%. The calcium content in oyster shells was 8.4% higher than that found in cement. Surface analysis showed that after calcination, the crystalline structure of oyster shell powder transformed from calcium carbonate (CaCO₃) to calcium oxide (CaO), resulting in a particle morphology more closely resembling that found in cement, although a greater degree of interparticle voids remained. Compressive strength tests demonstrated that concrete incorporating burned oyster shell powder, Burned Oyster-shell Concrete (BOC) showed strength reductions of 14% and 65% at 25% and 50% replacement levels, respectively. In comparison, Non-burned Oyster-shell Concrete (NOC) resulted in greater reductions of 40% and 79%, respectively. These findings indicate that replacing Portland cement type I with burned oyster shell powder yields better compressive strength performance than using unburned powder. At 25% replacement, the compressive strength of BOC concrete remains within an acceptable range. The use of oyster shell powder as a partial cement replacement offers significant environmental benefits by utilizing industrial waste and reducing cement consumption.