MICP-Treated Coral Aggregate and Its Application in Marine Concrete.

In marine engineering applications, substituting conventional crushed stone coarse aggregates with coral aggregates offers dual advantages: reduced terrestrial quarrying operations and minimized construction material transportation costs. However, the inherent characteristics of coral aggregates-low bulk density, high porosity, and elevated water absorption capacity-adversely influence concrete workability and mechanical performance. To address these limitations, this investigation employed microbial-induced carbonate precipitation (MICP) for aggregate modification. The experimental design systematically evaluated the impacts of substrate concentration (1 mol/L) and mineralization period (14 days) on three critical parameters, mass gain percentage, water absorption reduction, and apparent density enhancement, across distinct particle size fractions (4.75-9.5 mm, 9.5-20 mm) and density classifications. Subsequent application trials assessed the performance of MICP-treated aggregates in marine concrete formulations. Results indicated that under a substrate concentration of 1 mol/L and mineralization period of 14 days, lightweight coral aggregates and coral aggregates within the 4.75-9.5 mm size fraction exhibited favorable modification effects. Specifically, their mass gain rates reached 11.75% and 11.22%, respectively, while their water absorption rates decreased by 32.22% and 34.75%, respectively. Apparent density increased from initial values of 1764 kg/m and 1930 kg/m to 2050 kg/m and 2207 kg/m. Concrete mixtures incorporating modified aggregates exhibited enhanced workability and strength improvement at all curing ages. The 28-day compressive strengths reached 62.1 MPa (11.69% increment), 46.2 MPa (6.94% increment), and 60.1 MPa (14.91% increment) for the 4.75-9.5 mm, 9.5-20 mm, and continuous grading groups, respectively, compared to untreated counterparts.