Tensile strength measurement of the calcite bond between bio-cemented sand grains

An experimental protocol is proposed to investigate the tensile strength of a bio-cemented contact between two sand grains. Fourteen cemented contacts extracted from a bulk sample were observed using high resolution synchrotron X-ray tomography in order to compute with accuracy the contact surface areas between the active calcite crystals and the sand grains, as well as the orientation of the contact surface area. After the tensile test, SEM observations were performed in order to identify the failure mode. The obtained results show that the failure occurred at the interface between the calcite crystals and the sand grains, and can happen on both grains. According to these observations, the minimum contact surface area As has been computed from the 3D images, assuming that each active crystal is detached from the sand grain where its surface area is the smallest. The tensile strength of the biocemented bond deduced from these measurements is equal to 2.76 MPa on average. Finally, we show that in the bulk sample, only 26% of the total amount of calcite crystals are active and participate to the reinforcement of the granular medium.