Compressive stress-strain behavior of seawater coral aggregate concrete incorporating eco-efficient alkali-activated slag materials

Abstract

Appropriate utilization of wasted coral aggregates on reefs or islands that are far from the mainland would substantially reduce construction costs and shorten the construction period of offshore projects, but the application of coral aggregate concrete (CAC) in island construction is limited due to the low strength and poor anti-permeability resistance of the coral aggregates. In this paper, eco-friendly slag-based alkali-activated materials (AAMs) were considered as alternatives to ordinary Portland cement (OPC) to improve the weak characteristics of the coral aggregates. The whole stress-strain curves, axial compressive strength (fc), elastic modulus (Ec), and Poisson’s ratio (υc) of alkali-activated seawater coral aggregate concrete (AACAC) with different alkaline contents (Na2O-to-binder ratio of 3%, 4%, and 6% by mass) were investigated under uniaxial compression, and a scanning electron microscope (SEM) was employed to observe the interfacial microstructures between the paste matrix and the aggregates. The experimental results demonstrated that the failure patterns of CAC and AACAC under uniaxial compression were similar and were characterized by the coral aggregates being completely crushed. Additionally, the AACAC had a wider interfacial transition zone (ITZ), contained a higher Ec (approximately 9.9% improvement), and exhibited better ductility under the same concrete compressive strength (fcu) than the cement-based CAC. Finally, the constitutive relationship of stress-strain curves and an empirical model between Ec and fcu of AACAC were established based on the existing model.