Experimental Study on the Mechanical Properties and Uniaxial Compressive Constitutive Relationship of Sea Sand Coral Concrete

The use of seawater, sea sand and coral to formulate concrete for marine engineering construction is an effective measure for rationally allocating resources and alleviating resource shortages. To promote the engineering application of marine concrete, it is necessary to study the mechanical properties and microstructure of marine concrete. In this study, sea sand coral concrete (SSCC) with strength grades of C20–C40 was prepared, and the compressive and flexural tests were conducted to observe the stress process and damage morphology of the specimens and to establish a constitutive model for SSCC under uniaxial compression. In addition, the microstructures of the SSCC hydration products and interfacial transition zone (ITZ) were observed via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the damage surface of the SSCC occurred directly through the coral aggregate, and the damage process was sudden and brief. Under uniaxial compression, the trend of the rising section of the stress-strain curve of SSCC with different strength grades are basically the same, but the shape of the descending section vary greatly, and the higher the strength grade is, the steeper the slope of the descending section. Quantitative relationships between compressive strength, elastic modulus, peak strain and peak stress and cube compressive strength were established. Based on the experimental results, a two-stage uniaxial compression constitutive model for SSCC was proposed, and the established constitutive model can effectively predict the stress-strain behavior of SSCC. In addition, the XRD patterns show that the early hydration rate of SSCC is faster than that of ordinary concrete (OC), which leads to a faster early strength development of SSCC. The SEM images show that the coral aggregate binds better to the cement matrix than the crushed gravel aggregate does and that the microstructure of the SSCC is denser than that of OC.