Durability assessment of industrial by-product and marine resource-based ultra-high-performance concrete

The increasing demand for concrete and the associated environmental impacts such as depletion of natural resources (e.g., fresh water, river sand, and coarse aggregates) have prompted the development of seawater and sea-sand concrete (SWSSC). On the other hand, incorporating industrial by-products in concrete as supplementary cementitious materials (SCMs) can offset the cement carbon footprint. Utilizing seawater, sea sand, and industrial wastes in ultra-high-performance concrete (UHPC) fabrication can lead to a sustainable as well as durable construction material, especially suited for marine infrastructure development. This experimental work investigates the durability properties of ultra-high-performance seawater and sea-sand concrete (UHP-SWSSC) with partial substitution of cement by ground granulated blast furnace slag and silica fume as SCMs. Five mixes were developed with varying proportions of SCMs as cement replacement (0% as control mix, 25% and 50% by mass) and water-to-binder ratio (0.15, 0.2 and 0.25). In addition to mechanical behaviour through standard axial compression tests on cube specimens, several durability indicators such as water absorption, sorptivity, the permeability of chloride ions, and volume of permeable voids were measured over time. Results reveal that the incorporation of SCMs in UHP-SWSSC although improves the mechanical properties marginally, significantly enhances the durability performance. In comparison to the control mix, 53%, 75%, and 95% reductions in the volume of permeable voids, rate of water absorption and non-steady state chloride migration coefficient were observed in a 50% SCM replaced mix, respectively. Addition of ground slag and silica fume induced a relatively compact matrix through refinement of the microstructure, which made the resulting concrete nearly impermeable to ion movements. An optimum water-to-binder ratio of 0.2 was established, below which neither the strength nor the durability characteristics improved further.