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In today scenario, lack of stable ground for development of infrastructures is very common. In view of this, construction of buildings on unsuitable ground is unavoidable and making a suitable ground before constructions is real challenging issue for Geotechnical Engineers. To overcome the difficulties experienced with problematic soil in geotechnical applications on one side and safe disposal of solid wastes on the other side, an attempt is made in this investigation to explore the possibilities of utilizing solid wastes to improve the engineering behavior of problematic soil. In this, solid waste namely Rice Husk Ash for stabilization is selected to study the effects of same on the index and engineering characteristics of problematic soil.

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The rice husk ash is mixed with soil in various proportions like 5%, 10%, 20%, 30%, 40%, 50% and 80%. For instance, fly ash is solid waste from thermal power plant which is used for various civil engineering applications like manufacturing of cement and bricks and other geotechnical construction works. Here the type of solid waste namely RICE HUSK ASH (RHA) is selected to study the effects of the index and engineering characteristics of problematic soil. In order to utilize the rice husk ash for the improvement of problematic clay a detailed program are formulated and index, compaction, shear strength and CBR tests are conducted on problematic clay and alluvial soil with increasing % of solid wastes.

Rice husk ash reactivity

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The properties of RHA depend greatly on whether the husks have undergone complete destructive combustion or have only been partially burnt. Houston classified RHA into high-carbon char (black), low-carbon (grey) ash and carbon-free (pink or white) ash. Colour changes are associated with the completeness of the combustion process as well as structural transformation of the silica in the ash. Studies have shown that pink ash consists essentially of tridymite and cristobalite, the high-temperature crystalline forms of silica. There is little if any quartz, the low-temperature crystalline form of silica. At low combustion temperatures considerable amorphous silica remains, giving black and grey ash. Also, white colour is an indication of complete oxidation of the carbon in the ash. The characteristic of the ash depends on temperature, burning time, cooling time and burning type. The type of ash suitable for pozzolanic activity is amorphous rather than crystallized.

Effect on compaction characteristics of soil:

It has been observed that when the admixture of lime RHA has been added to the soil, the maximum dry density decreases and the optimum moisture content increases irrespective of the ratio of lime to RHA in the admixture. The reduction in maximum dry density is due to the presence of RHA, which is a lightweight material with specific gravity of 2.06. The increase in optimum moisture content is due to the additional water required for the hydration of lime as well as to assist flocculation of the clay clods. Additional water might be absorbed by the fine RHA particles present. It should be noted that the reduction in maximum dry density need not imply that there is a corresponding reduction in strength attainable as the strength is primarily due to the pozzolanic reactivity which occurs after a considerable curing time.

Effect of RHA on Index properties:

Understanding of plasticity soils of fine grains soils are playing vital role not only for soil classification and also they are very much useful to predict engineering property like Shear strength, permeability and compressibility and also swell ability of clay through empirical relationship. The liquid limit and plastic limit are governed by both physical and physicochemical mechanisms. In montmorillonide mineral enriched clays, the plasticity behavior is governed by physio-chemical mechanism and whereas for kaolinite mineral enriched clays, it the physical force governing the same. Further in the presence of coarser fraction the plasticity characteristic of clay are significantly influenced and the operating mechanism may be physical are physiochemical, which essentially depends on the percentage of coarser fractions in clays.

Effect of Rice Husk Ash on Liquid Limit:

Liquid limit is referred as generalized state parameter which has been given greater attention compared to plastic limit. The liquid limit is largely influenced by type and amount of clay content, and also it shows that ion concentration ionic valency also largely influences the liquid limit of clay soil. The variation of liquid limit soil with increasing percentage of RHA. It has been seen that at any percentage the liquid limit continuously decreases for RHA. Liquid limit reduces from 57% to 30.5% for soil +80% RHA for alluvial soil and reduces from 60% to 26.5% for soil +80% RHA for clay soil.


Rice husk ash in combination with lime can be used for soil stabilization.The plasticity index of the soil is significantly reduced by the addition of the admixture of lime and RHA. This is more pronounced when a longer curing time is allowed. The maximum dry density is decreased and the optimum moisture content is increased when the soil is treated with the admixture of lime and RHA.The unconfined compressive strength of the soil is increased when the soil is treated with the admixture of lime and RHA. There is an optimum quantity of admixture at which the unconfined compressive strength is maximum. It has been found that the unconfined compressive strength value is maximum when the quantity of admixture added to the soil is 10% of the total weight. As the curing time is increased, the strength of the treated soil is increased.

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