Determination of the Slip-Up Time for Slip Form System Using Surface Wave Velocity

When applying the slip form system, the early setting time of concrete corresponds to the hardening time of early-age concrete indicating that cast-in-place concrete has developed sufficient strength to be safely stripped off the form. This hardening time is thus an important indicator for the determination of the slip-up velocity of the slip form system. Therefore, need is for a technique enabling to evaluate the early hardening time of concrete in order to secure the safety of the slip form system and the quality of the constructed concrete. Among the methods using ultrasonic waves, this paper applies the surface wave velocity to evaluate the degree of hardening of concrete so as to estimate the early setting time and decide the slip-up time of the slip form system. To that goal, penetration resistance test, compressive strength test and surface wave velocity measurement test are performed concurrently with respect to the mix materials and curing temperature of concrete. The test results are used to derive the relationship between the compressive strength and surface wave velocity according to the early hardening time of concrete. Continuous wavelet transform is applied for the measurement of the surface wave velocity. The validity of the application of the continuous wavelet transform is verified through numerical analysis. Finally, the surface wave velocity required for the slip-up of the slip form system is proposed and the applicability of the proposed surface wave velocity for the determination of the climbing time of the slip form system is verified by means of tests on a reduced-scale slip form system prototype.