Relationship between ultrasonic pulse velocity and uniaxial compressive strength for cemented paste backfill with alkali-activated slag

This study mainly investigates the effects of binder content, water to binder (w/b) ratio, activator dosage, and sodium silicate to sodium hydroxide (SS/SH) ratio on uniaxial compressive strength (UCS) and ultrasonic pulse velocity (UPV) of cemented paste backfill (CPB) containing AAS (AAS-CPB). Experimental results show that both UPV and UCS of AAS-CPB increases linearly with increasing binder content or decreasing w/b ratio. At low levels, an increase in the activator dosage yields higher UCS and UPV, while negative effects are found with excessively high activator dosage. The SS/SH ratio has a major influence on both UCS and UPV, depending on the curing time. It is also found that, irrespective of the mixture properties, the UPV profiles are similar in character to the corresponding UCS profiles. UPV is less sensitive to the variation in the mixture properties and curing time than UCS. AAS-CPB experiences a rapid increase in both UCS and UPV up to 28 days, followed by a slight increase. A strong exponential relationship is obtained between UCS and UPV for all mixtures. The main findings of this study show that ultrasonic test technique can be successfully used in most mines for estimating the compressive strengths of AAS-CPB samples.