Mechanical properties and drying shrinkage of alkali-activated seawater coral aggregate concrete

Alkali-activated materials (AAMs) are identified as environmental-friendly substitutes for ordinary Portland cement (OPC) for lowing greenhouse-gas emissions and achieving efficient waste recycling. In this paper, well-durable AAMs were utilized to prepare the slag-based alkali-activated seawater coral aggregate concrete (AACAC) and three alkaline dosages (Na2O-to-binder ratios of 3, 4, and 6% by weight) were designed to determine their mechanical characteristics and drying shrinkage. The tested results indicated that the failure modes for all coral aggregate concrete (CAC) were characterized by the broken coral aggregates originated from their low strength and high brittleness. As the alkaline concentration increased, the compressive strength (f(cu)), splitting tensile strength (f(ts)), axial compressive strength (f(c)), elastic modulus (E-c), and interfacial bond strength (f(b)) between the new concrete and the old concrete, were gradually enhanced. Additionally, the (f(b)/f(ts)) ratio can be stabilized at about 0.70. Compared with the cement-based CAC, the AACAC achieved higher f(ts), E-c, and f(c) because of the improved interfacial microstructures between the aggregate and the paste matrix after using AAMs. Moreover, the utilization of coral aggregates can lower the drying shrinkage (approximately 14.7%) of conventional alkali-activated concrete (AAC) at the same alkaline content owing to the internal self-curing effect of porous aggregates.