AbstractImprovement in the mechanical properties of soil by lime (Ca(OH)2) results from the formation and development of cementitious phases. The newly formed phases interlock and bond the soil particles together increasing the strength of the soil and improving its durability. In the present work the engineering properties including plasticity, density, compressive strength, porosity, permeability and frost heave resistance were investigated for cylindrical specimens of a Devonian Red-Marl containing various amounts of lime (2-14 wt%), cured for up to 24 weeks at different temperatures (25, 50 and 75°C) and in different environments (sealed, unsealed, air, nitrogen and carbon dioxide).
Mineralogical analysis of Red-Marl as well as montmorillonite, kaolinite and illite and also the reaction products of these materials with lime (10-20wt%) were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy with energy dispersive analysis (TEM/EDAX) and thermogravimetric analysis (TG). The Red-Marl was found to consist of illite/glauconite, quartz and feldspar with minor amounts of chlorite and haematite.
It was observed that curing temperature has a dramatic effect on the reaction between soil and lime and on the engineering properties of the cured soil-lime samples. At normal curing temperatures the plasticity index decreases markedly and the strength increases only marginally with increasing lime content and curing time. At elevated temperatures, the strength sharply increases in a moist environment whereas lack of sufficient moisture virtually stops any further reaction. It was observed that carbonation of lime does not contribute to any great extent to the increase in strength and should be minimized. The addition of a small amount of NaCl in conjunction with lime may accelerate the reaction slightly. It was observed that the nature of clay soil alters by adding lime and the cured materials show a greater durability with a significant improvement in properties such as pore structure, permeability, volume stability and frost resistance.
The analyses of the newly formed cementitious material shows it to consist of almost amorphous gel forming foil-like membranes and fine filaments which interconnect the soil particles. Morphological development and microstructural analyses of the gel suggest that it is formed as a result of the progressive breakdown of the original clay particles by reaction with lime.
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