Effects of Grain Size and Treatment Methods on the Cementation of Bioimproved Calcareous Sand

Abstract

Calcareous sand, which is characterized by irregular morphologies and abundant intraparticle pores, poses difficulties for ocean construction. This study investigated the effects of microbially induced carbonate precipitation (MICP) treatment methods and grain size on the biocementation of calcareous sand. Calcareous sand specimens with a wide range of grain sizes were first treated by MICP with immersion and mix methods. Scanning electron microscopy analysis revealed the presence of air bubbles inside the specimens treated by the mix method, which hindered biocement production, further promoting the emergence of a gradual failure pattern and reducing the strength and stiffness of the sand specimens. A series of unconfined compressive strength tests indicated that the strength and stiffness of the calcareous sand specimens treated by the immersion method were considerably greater than those of the specimens treated by the mix method in the suitable grain size range. In addition, the immersion method was not suitable for sand specimens with a median grain size of <0.5 mm. By contrast, the mix method was suitable for sand specimens of various sizes. As with the immersion-treated specimens, the specimens treated by the mix method displayed better mechanical properties at the early treatment stages, although the mix method-treated specimens exhibited much lower increase rates of strength and stiffness; moreover, the mix method-treated specimens exhibited lower strength and stiffness after long-term treatment than the immersion-treated specimens.