Dynamic behaviour of manufactured sand shotcrete at early age

Abstract

Manufactured sand has become progressively the primary source of sand for construction in China, and the manufactured sand shotcrete at an early age is vulnerable to the blast loading in rock tunnels. In this regard, this paper mainly presents the dynamic behaviours of manufactured sand shotcrete that has not been extensively studied. The results indicate that the quasi-static uniaxial strength and elastic modulus of the shotcretes increase exponentially with the curing ages, and both of them follow the same trend: increase quickly before the curing age of 7 d, and then slow down after the age of 7 d. The dynamic increase factor (DIF), dynamic elastic modulus and failure pattern of manufactured sand shotcretes are sensitive to both strain rate and curing age. The DIF increases linearly with increase of the strain rate at the same curing age, ans decreases exponentially with increasing curing age under the same impact velocity. The dynamic modulus increases linearly with increasing strain rate at the same curing age. For the same curing age, the fragments size decreases with increasing impact velocity. The incident energy, reflected energy, transmitted energy and absorption energy present an obvious strain rate dependency, all increasing linearly with increasing strain rate. With the curing age increasing, the reflected energy ratio decreases, while the transmitted energy ratio and absorbed energy ratio increase. In the meantime, the energy ratio varies more obviously before the curing age of 7 d. The energy absorption capacity of shotcrete specimens improves with the curing age increasing. A theoretical constitutive model of the manufactured sand shotcrete is presented, and the theoretical results agree well with the experimental curves.