Optimization of mix proportion of basic magnesium sulfate cement-based high-strength coral concrete

The diverse morphology of coarse coral aggregate and its complex pore structure cause uncertainty in the performance of coral aggregate concrete (CAC). Crushing coarse coral aggregates into fine aggregates may be an effective measure to achieve high performance CAC. This paper investigates the morphological parameters of single-size coral sand particles by numerical characterization and statistical analysis. The relationship between coral sand particle gradation and CAC performance is explored. Basic magnesium sulfate cement was used as the cementitious material, and compound-oriented coral sand (zone II medium sand) was used as the fine aggregate. Through a response surface method design, the flexural and compressive strengths of the synthesized basic magnesium sulfate cement-based high-strength CAC at 28 d achieve 13.1 and 79.1 MPa, respectively. The results show that the particles larger than 0.6 mm in the coral sand could enhance the flexural strength of CAC, while smaller (<0.6 mm) particles are more beneficial to the compressive strength. The particle gradation of group II1/2 is more likely to enable the coral sand to achieve a tightly packed state. After optimization by the response surface method, the critical proportioning parameters for achieving excellent mechanical properties of basic magnesium sulfate cement-based CAC are obtained: alpha-MgO:MgSO4 molar ratio of 8.3-9.5, cement ratio of 1.11-1.35 and admixture dose of 1.58-2.02%. Further, the recommended ratio is given in the 3D space under the ternary interaction. This method can provide a novel approach for designing and manufacturing high-performance CAC.