Jiale Zhang

Calcareous sand is widely used in marine and island reef engineering; however, its low strength and severe particle breakage are further exacerbated under dynamic loading, making the dynamic performance of reinforced calcareous sand critical to engineering safety. Nevertheless, research on the dynamic characteristics of EICP/MICP-reinforced calcareous sand remains very limited. The dynamic performance was evaluated using Split Hopkinson Pressure Bar (SHPB) tests, and the results were compared with UCS data to examine the effects of particle gradation and fiber content on both dynamic and static behaviors. The results show that dynamic strength increases with calcium carbonate content (CCC) and impact pressure. Under the same CCC, the dynamic strength is consistently higher than the static strength, with a maximum difference of up to 2.5 MPa. Fiber incorporation significantly enhances structural integrity, and SEM analysis reveals that this improvement stems from effective bonding between fibers and cementitious materials. Based on the static and dynamic test results, the optimal mix ratio for EICP-reinforced calcareous sand is determined as 50% coarse sand content and 0.4% fiber content by mass, which provides theoretical support and design parameters for sustainable green reinforcement of calcareous sand foundations in marine and island reef engineering.

Ecological concrete designed by empirical method does not consider the mesoscopic influence of aggregates, resulting in problems such as low strength, excessive porosity, and poor stability with different gradations, which severely restricts the development and application of ecological concrete. To achieve the refined design of ecological concrete, a mesoscopic specific surface area design method based on statistical analysis is proposed. First, the meso-aggregate model with sub-millimeter precision was established using a high-precision 3D scanner, and CloudCompare was used to calculate the specific surface area of the mesoscopic aggregate model, laying the foundation for the statistical analysis of specific surface area. Second, statistical analysis methods verified that the mean specific surface area of 20 aggregates from a single random sampling reliably estimates the mean of the overall aggregate population. Third, the optimal water–cement ratio was calculated considering the water absorption characteristics and the mortar-wrapping capacity of aggregates; standard cubic specimens were prepared using this optimal water–cement ratio, with aggregates evenly coated with mortar and no obvious mortar settlement. Fourth, the cubic compressive strength of specimens naturally cured for 7 days was tested; experimental results showed that the cubic compressive strength of specimens formed by this project’s design method increased by more than 30% compared to the empirical design method. The results indicate that using the average volume-specific surface area of 20 aggregates to assess the overall average volume-specific surface area of aggregates is both reliable and relatively efficient. Based on the reliable estimation of the overall average volume-specific surface area of aggregates derived from this method, measurements were taken of the thickness of water films adsorbed on dry aggregates and the thickness of mortar coatings on surface-dry aggregates. Further, the optimal water–cement ratio for eco-concrete was deduced, and a comprehensive set of feasible refined methods for eco-concrete mix proportion design was proposed. In contrast to the empirical method, concrete designed via the subject’s methodology exhibits a marked enhancement in compressive strength while retaining favorable pore characteristics—rendering it well-suited for deployment in the slope protection of reservoirs and ponds and thereby facilitating the realization of ecological slope protection functionality.