EFFECT OF TEMPERATURE AND SOLUTION pH ON CALCIUM CARBONATE PRECIPITATION AS BIO-BASED REPAIR MATERIAL IN CONCRETE

Abstract

In the present work, the effect of temperature and solution pH on calcium carbonate precipitation from bio-based repair materials is investigated. A microbial metabolic process precipitates calcium carbonate. Mixtures of bio-based materials typically comprise a microorganism, an organic carbon source, and a calcium source. When dry yeast is selected as the microorganism, carbon dioxide produced through the microbial metabolic process of consuming an organic carbon source, such as glucose, provides carbonate ions. The carbonate ions lead to reactions with the calcium ions present in the mixture, leading to the precipitation of calcium carbonate. Mixtures were tested at temperature conditions of 10, 20, and 30 ºC, and the pH of the solution was initially adjusted as 8.0 or 9.0, for up to 72 hours of elapsed time. In this research, temperature conditions of 20-30 °C is the optimum temperature range for increasing the precipitation of calcium carbonate. The results confirmed that the maturity index has a linear correlation with the decreasing rate of calcium ions. Large maturity indices mean that the decreasing rate of calcium ions is high. Maturity index was used as an indicator of the precipitation rate of calcium carbonate in the temperature range 10-30 ^oC; the datum temperature was 0 ^oC. The adequate concentration of the Tris buffer solution was found in the range 0.50-0.75 (mol/L), at an initial pH of 9.0, and 0.75-1.00 (mol/L), at an initial pH of 8.0. The rate of the initial reaction tended to be faster with the initial pH of 9.0.