钙源对微生物矿化胶结砂土材料均匀性的影响

Effect of calcium sources on uniformity of bio-cemented sand materials

微生物诱导碳酸钙沉积(MICP)技术可以改善砂土材料的力学性质,但MICP胶结砂土材料的均匀性问题是目前存在的重要问题,且严重影响了MICP技术的工程应用。进行小尺寸(直径3 cm、高度11 cm)和细长(直径5 cm、高度100 cm)砂柱试样的MICP一批次灌浆试验和溶液环境试验,探究氯化钙和乙酸钙两种钙源对MICP矿化反应过程和MICP胶结砂土材料均匀性的影响。MICP胶结砂土试样的碳酸钙含量和单轴抗压强度试验结果表明,与氯化钙作为钙源相比,乙酸钙作为钙源可以增加砂柱胶结长度,改善碳酸钙在灌浆方向的均匀性,减少MICP胶结砂土材料沿灌浆路径的强度差异;乙酸钙作为钙源可减缓MICP矿化反应过程,降低营养液中尿素的分解速率,进而提高营养液中未分解尿素和游离钙离子在MICP胶结砂土材料中的传输距离,有利于提高MICP胶结砂土材料的均匀性。

Microbially induced carbonate precipitation(MICP)technique is one of the promising methods that can improve the mechanical behaviors of the sand materials via the precipitated calcium carbonate crystals.However,the uniformity of bio-cemented sand materials is a vital problem and hinders the engineering applications of MICP technique.This study explores the effects of calcium chloride and calcium acetate on the MICP process and the uniformity of bio-cemented sand columns(3 cm in diameter and 11 cm in height,5 cm in diameter and 100 cm in height)treated one batch of MICP injection.The calcium carbonate content and unconfined compressive strength results of bio-cemented sand samples demonstrate that the calcium acetate can enhance the length of the cementation path,improve the calcium carbonate distribution along the grouting direction,and reduce the strength differences among the bio-cemented sand materials.Combining with the results of ammonium and calcium ion concentration in the solution environment,when the calcium acetate acts as the calcium source,the rate of MICP reaction is slower than that by calcium chloride,benefitting the transmission path of the undecomposed urea and the free calcium ions,thereby improving the uniformity of biocemented sand materials.