Essay About Lime Reactions And Formation Of Ettringite

Soil Stabilisation
Problems in lime and cement stabilized soilsSulphate attack leads to formation of ettringite which causes up-heaving in the stabilized soils due to volume change. Therefore, before the application of cement and lime stabilization techniques, the nature of sulphates present in the soils, soil–lime reactions, mechanisms involved in ettringite formation (delitritious reaction) and its related problems should be understood.. It is necessary to understand the various processes of sulphate attack causing the failures so that suitable protective measures could be taken in time. Ettringite formation has adverse effect on the engineering behaviour of lime and cement treated clays. Sulphate in soilsThe presence of sulphates in the ground or mixing water may affect the cation exchange, pozzolanic reactions of cement and lime treated soil systems. The above reactions depend on type and concentration of metal ions present, and availability of alumina and silica that can influence the engineering behavior of soil with time. Sulphates are present in the surface sediments, more so in regions of limited rainfall from sodium (thenardite, NaSO4 (10H2O), potassium (arcanite, K2SO4) and calcium (gypsum or selenite, CaSO4.2 (H2O) and magnesium, (MgSO4. (7H2O).Soil–lime-sulphate reactionsIt is important to know lime–soil reaction mechanisms. Lime–soil reactions can be classified into short term and long term reactions. Short term reactions include flocculation, lime migration, pH and cation exchange reactions and carbonation, and above reactions affect the physical properties of the soil system such as Atterberg limits and particle size distribution. The long term pozzolanic reactions include the formation of various new reaction products, which result in the growth of aggregates and affect the strength and compressibility of clays. The anions of sulphates combine with the available calcium and alumina, and form insoluble ettringite in the soil system. The formation of ettringite increases the porosity and simultaneously decreases the free moisture content during ettringite nucleation and its subsequent growth. A simplified geochemical reaction reported by Hunter (1988) for lime induced heave reactions can be summarized as follows:                                                Hydration of quicklime[pic 1]                            Ionization of calcium hydroxide; pH rises to 12:3[pic 2]                        [pic 3]                                                                        Formation of ettringite                                                                                                                Precautionary or remedial measuresThe preventive measures to be adopted to prevent ettringite formation in lime and cement stabilized clays are given below.