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It is well known that organic matter may affect the cementing process in soils, but what happens when cement is added to an organic soil? Both the organic matter content and the nature of this organic matter affect the properties of a treated soil. It appears that some organic compounds delay or even inhibit the hydration process of cement, while others do not affect the reaction at all. This paper presents some results of a laboratory study in which 13 different organic compounds were added separately to two different soils, and then treated with 10% cement. To assess the cementing process, undrained shear strength was measured on the different specimens, and some chemical analyses were performed on the pore liquid. The results indicate that the organic acids producing a pH lower than 9 in the pore solution strongly affect the development of cementing products and almost no strength gain was noted. Also, oils and hydrocarbons, which are insoluble in water, delay the cement hydration but do not affect the final strength. Finally, the pH value and the SO4 concentration in the pore solution are good indicators of the cementing effectiveness of the treated specimens.Key words: soil stabilization, organic compounds, undrained shear strength, cement, chemical analyses.

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Mineral carbonation of ultramafic rocks provides an environmentally safe and permanent solution for CO(2) sequestration. In order to assess the carbonation potential of ultramafic waste material produced by industrial processing, we designed a laboratory-scale method, using a modified eudiometer, to measure continuous CO(2) consumption in samples at atmospheric pressure and near ambient temperature. The eudiometer allows monitoring the CO(2) partial pressure during mineral carbonation reactions. The maximum amount of carbonation and the reaction rate of different samples were measured in a range of experimental conditions: humidity from dry to submerged, temperatures of 21 and 33 °C, and the proportion of CO(2) in the air from 4.4 to 33.6 mol %. The most reactive samples contained ca. 8 wt % CO(2) after carbonation. The modal proportion of brucite in the mining residue is the main parameter determining maximum storage capacity of CO(2). The reaction rate depends primarily on the proportion of CO(2) in the gas mixture and secondarily on parameters controlling the diffusion of CO(2) in the sample, such as relative saturation of water in pore space. Nesquehonite was the dominant carbonate for reactions at 21 °C, whereas dypingite was most common at 33 °C.

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