Development of a high-density geopolymer concrete for coastal protection applications

Abstract

With anticipated changes to the coastal wave climate due to climate change scenarios, coastal breakwaters are predicted to be exposed to greater wave energy and, thus, higher rates of damage. Breakwater armour unit design equations and most literature reveal that higher material density results in better stability to breakwater structures in such changed conditions. In this research, alkali-activated materials were studied extensively for their fresh properties and microstructure and a high-density geopolymer concrete mix with steel furnace slag (SFS) aggregate was developed and material properties were evaluated for on-site applications under ambient curing conditions. Moreover, the unique, sustainable high-density geopolymer concrete mix developed in the laboratory was upscaled for field applications in upgrading existing coastal breakwaters. The system is being tested at the Northern breakwater of NSW Ports’ Port Kembla harbour. The concrete uses steel furnace slag (SFS) aggregate in a blended fly ash-blast furnace slag binder (65/35 by mass proportions) proportioned to facilitate the elimination of delayed expansion of the aggregate. The concrete properties were measured, and microstructural analysis was undertaken. The geopolymer concrete developed offers higher bulk density to concrete on account of using SFS aggregates, with satisfactory workability and setting time. Most importantly, the fly ash- blast furnace slag blended binder used in this study leads to good strength gain in ambient curing and allows the diffusion of the free lime associated with the SFS aggregate into the geopolymer matrix to eliminate delayed hydration and expansion of the aggregate. The high-density allows the armour units to be smaller resulting in reduced armour mass requirements and material savings. This research provides a novel approach to both repairs of existing structures and construction of new structures with reductions to both cost and carbon footprint.