Impact behavior and strain rate effects of artificial limestone by MICP

Abstract

Natural cemented calcareous sand and limestone are highly complex and not well understood in terms of the mechanical behavior due to the difficulty of obtaining undisturbed samples from far sea. This paper proposes an artificial method in a laboratory setting using microbial-induced carbonate precipitation (MICP) to simulate the natural process of cementation of limestone. The artificially cemented sand has a high degree of similarity with the natural weakly limestone in three aspects: (1) the mineral composition of the cemented material is also granular calcite and acicular aragonite; (2) the microstructure in interconnected open pore network can be gradually closed and contracted with cementation. The porosity reaches to approximately 9.2%; (3) both the stress-strain relationship and the unconfined strength closely resemble that of natural weakly limestone. Furthermore, both static and dynamic behaviors of artificial limestone were studied by quasi-static compression tests and Split Hopkinson Pressure Bar (SHPB) tests, finding that the unconfined strength of weakly artifical limestone exponentially increases with increasing strain rate. A rate-dependent bond strength was proposed and implemented in software to reveal the mechanism of strain rate effects. It is found that the loading velocity is too high to keep in sync with the initiation and propagation of cracks under impact loading. This delay-induced viscosity may restrict the movement of the surrounding balls, thus increasing resistance.