Settime Time Time Monitoring of RCC through an Air-Coupled Ultrasound Technique

The construction of concrete pavements requires an understanding of the concrete properties in both fresh and hardened states. Fresh properties predict the consolidation ease and flow through reinforcing steel, while hardened properties determine responses to stress. Moreover, stresses in concrete pavements may be reduced by limiting the size of pavement concrete slabs through the saw-cutting procedure, which must be conducted at a specific time closely related to the set time — transition from a liquid into a solid state. Setting time is commonly determined through a penetration resistance test in the paste ­—or mortar— component of concrete. However, this technique is impractical for low-paste content concrete, like Roller-Compacted Concrete (RCC). However, air-coupled ultrasound monitoring has been proven successful in detecting setting time in conventional concrete. This study evaluates the air-couple ultrasound monitoring capabilities in detecting RCC setting time, for which no method currently can detect setting time in situ. A 50 kHz central frequency ultrasonic pulse and a set of microelectromechanical sensors are used to monitor the Leaky-Rayleigh (L-R) wave initiation in the RCC. Temperature sensors were embedded in the RCC specimens to track early-age temperature development. The results show that L-R wave initiation can be detected in RCC specimens and that there is a relationship between the amplitude of the L-R waves and the temperature in the RCC specimens. This method shows potential for implementation in RCC pavement construction, aiding decision-making for starting saw-cutting joints, performing finishing treatments, and ensuring bonding between different RCC pavement lifts.