Non-Destructive Evaluation of Mortar with Ground Granulated Blast Furnace Slag Blended Cement Using Ultrasonic Pulse Velocity

Non-destructive evaluation using ultrasonic pulse velocity (V_p) testing has extensive applications in the concrete industry. With advances in construction technology, the use of ground granulated blast furnace slag (GGBFS) as a partial replacement to cement in a concrete mix is growing in popularity primarily because it reduces the initial capital cost of raw materials and the associated energy costs. This paper investigates the effect of the water-to-cement (w_c) ratio and the cement content replaced by GGBFS on the development with time of the ultimate compressive strength (fc') and the compression wave velocity (V_p) of mortar. The results showed that in the case of mortar with higher percentages of GGBFS replacement (where nucleation surfaces are more abundant), increasing w_c can increase fc' but cause a decrease in V_p. The posterior hydration process is highly dependent upon the water particles in the mixture after the first stage of hydration. After 7 days of curing, experimental results show that the fc' of slag blended cement mix design w_c ratio of 0.6 surpassed the fc' value of an Ordinary Portland cement. A regression model correlating the fc' and V_p of slag blended mortar is developed, which can be used to predict fc' at concrete ages ranging from 1 day to 28 days for mixes with GGBFS percentage replacement values ranging from 15% to 45%.