Effect of Plant-Induced Calcite Precipitation on the Strength of Sand

A plant (jack bean) extract can function as a urease catalyst, similar to those of certain microorganisms such as Sporosarcina pasteurii, which can decompose urea into carbonate and ammonium ions. Carbonate ions decomposed from urea can combine with calcium ions to form calcium carbonate (usually calcite mineral). In this study, calcium chloride, calcium hydroxide, or calcium nitrate was added to urea solution with plant extract, and then mixed with Nakdong River sand to precipitate calcite within the sand-grain matrix. The mixed sand was compacted into a cylindrical specimen and cured for 3days at room temperature. A specimen without plant extract was prepared for comparison. A series of unconfined compression tests and analytical methods was carried out on sand treated with various amounts of urea and different calcium sources. With increasing amounts of urea, the unconfined compressive strength (UCS) of the sand treated with plant extract increased 10-fold up to 317kPa, compared to that of the sand without plant extract. Its strength was similar to that of 4% cemented sand with high-early strength portland cement. The strength of the specimen containing calcium chloride was higher than that with calcium hydroxide or calcium nitrate. (C) 2014 American Society of Civil Engineers.