In the United States, approximately 10 billion gallons of mixing water is required annually to produce close to 400 million cubic yards of concrete. In response to the declining supply of freshwater in some locations and with the goal of decreasing the environmental footprint of the concrete industry, there is current interest in either full or partial replacement of fresh water with seawater in concrete mixtures. Research indicates that the early-age strength of seawater concrete is typically higher than that of normal concrete, but that the long-term strength is affected less.

This study investigates the early-age properties of seawater concrete by measuring its ultrasonic pulse velocity. This nondestructive test method is commonly used to assess the quality of concrete, and its value correlates well with the compressive strength. Neat cement paste specimens were prepared at several water–cement ratios using either fresh water or salt water at various salinities (36, 24, and 12 g/L). The highest salinity of 36 g/L was chosen because it is the approximate salinity of the ocean, while 24 and 12 g/L represent either brackish water or seawater that has been mixed with freshwater. The ultrasonic pulse velocity of the specimens was measured at various points in time until 28 days. Additionally, the compressive strength was measured at both 7 and 28 days. By comparing the evolution of the ultrasonic pulse velocity and the compressive strength between the various mixtures, the effect of seawater on the early-age properties of seawater concrete can be better understood.