Ecofriendly calcium phosphate and calcium bicarbonate biogrouts

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An important direction of construction biotechnology is production and application of the biogrouts to decrease the hydraulic conductivity of soil or fractured rocks. The most popular biogrout is a mixture of calcium chloride, urea, and either ureolytic bacteria or enzyme urease. A disadvantage of this biogrout is the release of a large quantity of toxic ammonia to air, as well as harmful ammonium and hydroxide ions to water. The aim of this study was evaluation of two new biogrouts that release less of harmful by-products to environment. First biogrout was a mixture of acidified hydroxyapatite solution from the bone powder with an addition of two times less urea that is used in conventional biogrout. Final pH was 7. Second biogrout was a solution of calcium bicarbonate produced from chalk powder and carbon dioxide with an addition of urea and acidotolerant ureolytic bacteria. This biogrout released to environment four times less ammonium and ammonia than conventional biogrout. Final pH was 8. Precipitation of about 2 g of calcium carbonate per kg of the cracked stone diminished the water seepage through the specimen by three orders of magnitude. Geotechnical or environmental engineering applications of these environmentally friendly biogrouts are limited by the consumption of a large volume of the grouting solution. It is due to low concentration of dissolved calcium, about 200-400 g m(-3) , in these liquid biogrouts. So, these biogrouts could be most effective for the sealing and strengthening of the materials with low porosity such as the fractured rocks or cracked concrete.

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