Investigation on the rheology, self-shrinkage, pore structure, and fractal dimension of coral powder-cement slurry

Abstract

There is a significant amount of coral powder in coral aggregates, which has a negative impact on the operational performance, mechanical characteristics, and durability of coral reef sand concrete. The present study investigates the effect of coral powder with varying fineness and content on rheological and self-shrinkage properties using an Anton Paar MCR102 rotational rheometer and YC-BWS bellows self-shrinkage apparatus, respectively. The dynamic yield stress, rheological index, and plastic viscosity are obtained according to the Bingham model, Modified Bingham model, and Herschel-Bulkley model. The pore structures of coral powder-cement slurry are studied using a combination of MIP and SEM tests. Fractal theory is used to characterize the pore size distribution. The results demonstrate that the coral powder-cement slurry exhibits a shear thinning phenomenon. The Herschel-Bulkley model is successful in simulating the rheological behavior of cement slurry. The dynamic yield stress and plastic viscosity increase gradually as the fine coral powder content increases. With the increase in the coarse coral powder content, the dynamic yield stress decreases gradually while the plastic viscosity increases. The self-shrinking value of the coral powder-cement slurry increases rapidly within 1d but gradually stabilize with age. The self-shrinkage value increases with the increase in the coral powder admixture. The self-shrinkage value of the fine coral powder-cement slurry is less than that of the coarse coral powder-cement slurry. It is found that increase in the coral powder reduces the compressive strength of the cement paste, however, cement replacement with 10% coral powder is acceptable. Pore surface fractal dimension and capillary pore volume is able to effectively characterize pore size distribution and pore volume, respectively. Furthermore, the strength has a positive and negative linear relationship with the pore surface fractal dimension and capillary pore volume, respectively. The ratio of pore surface fractal dimension to capillary pore volume can be used as a parameter of the strength model. A linear relationship between the strength and the ratio of pore surface fractal dimension to capillary pore volume is proposed, and the model exhibits high accuracy.