Novel grout material comprised of calcium phosphate compounds: In vitro evaluation of crystal precipitation and strength reinforcement

Abstract

Calcium phosphate compounds (CPCs) have unique physicochemical properties. As grout material, they afford many advantages such as adequate physical strength, self-setting property, pH dependence of precipitation, non-toxicity, and recyclability. To apply CPCs to the permeability control and reinforcement of ground soil and rock, we explored suitable conditions for in vitro CPC precipitation, conducted unconfined compressive strength (UCS) tests of Toyoura sand test pieces cemented by CPC, and carried out observations and elemental analysis of precipitated CPC crystals.Two kinds of phosphate stock solution and two kinds of calcium stock solution were used to prepare the reaction mixtures, and CPC precipitation was detected in all reaction mixtures. The volume of CPC precipitation in the reaction mixture increased as the pH rose from strongly acidic to around neutral. The UCS of Toyoura sand test pieces cemented by 1.5 M diammonium phosphate and 0.75 M calcium acetate tended to increase with time, reaching a maximum of 63.5 kPa after 14 days of curing. Conversely, the UCS of test pieces cemented by using calcium nitrate was below 20 kPa and showed no significant increase in strength. CPC precipitation with calcium nitrate induced the formation of plate-like crystals, whereas that with calcium acetate induced whisker-like crystals.Elemental analysis of the cemented test pieces showed that the distributions of phosphorus and calcium were similar. The results indicate the practical feasibility of using novel CPC grouts as chemical grouts because of their self-setting property, and as biogrouts because of their crystal 3 structure and pH dependence of precipitation.

Effective Use of Plant-Derived Urease in the Field of Geoenvironmental/ Geotechnical Engineering

“…Unlike concrete, reexcavated muck that consists of soil, rock, and CPC grout is recyclable as an agricultural fertilizer. These advantages make it suitable for geotechnical applications [111]. In our study, UCS of more than 100 kPa was obtained by selecting superlative proportions of urea and urease enzyme with calcium acetate and dipotassium phosphate as calcium and phosphate stock solutions, respectively.…”

“…CPCs exist as phosphate rocks (mainly fluoroapatite) in the natural environment and as an important inorganic substance (mainly hydroxyapatite, HA) in living organisms [110]. Phosphate and calcium stock solutions can be made from fertilizers, and calcium and phosphate can also be extracted from the bones of livestock and the shells of marine animals, [111]. CPCs that precipitate after grout injection are non-toxic.…”

Improvement in the Unconfined Compressive Strength of Sand Test Pieces Cemented with Calcium Phosphate Compound by Addition of Calcium Carbonate Powders

“…12) When CPC-Chem was converted to CPC-Bio by the addition of microorganisms and an ammonia source, the UCS increased from 42.9 to 57.6 kPa. 13) Our aim was to achieve a UCS value of 100 kPa, which is needed to avoid ground liquefaction during earthquakes.…”

“…11) In recent years, a novel ground stabilizer developed to increase the number of options available among cementing mechanisms based on microorganisms. 12,13) Further, it is reported on a CPC chemical grout (CPC-Chem) that utilizes self-setting CPC mechanisms ( Fig. 1(a)), and on a CPC biogrout (CPC-Bio) whose solubility is dependent on its pH ( Fig.…”

Microbially-induced Carbonate Precipitation for Immobilization of Toxic Metals

“…It has also been used as a "bio-grout" for ground permeability control and reinforcement (Whiffin, Van Paassen, & Harkes, 2007;DeJong et al, 2010;Akiyama & Kawasaki, 2012), and the restoration of historical monuments (Tiano, Biagiotti, & Mastromei, 1999). Urease-producing organisms have also been proposed for novel applications in the bioremediation of toxic metals and radionuclides through the formation of insoluble metal-containing carbonates (Table 1).…”