Cationic Catalysis of Lime Treated Soft Soils Greeshma Nizy Eujine*, Chandrakaran S** and Sankar N*** *Research Scholar, Department of Civil Engineering, National Institute of Technology Calicut, Kerala – 673601, India. Email- nizy_123@yahoo.com ** ***Professor, Department of Civil Engineering, National Institute of Technology Calicut, Kerala– 673601, India Abstract: Stabilization of soils is an effective method for improvement of soil properties and the pavement system performance. A study was conducted to examine the stabilizing effects of an enzyme and lime on improving the suitability of a natural soft clay as a subgrade material. The tests were carried out by introducing the additives into the soil in two different stages. The enzyme and lime were first mixed individually- Soil Lime mixtures and Soil Enzyme mixtures and later concurrently- Soil Enzymatic Lime mixtures. The initial part of the study determined the variation of index properties of the three soil combination. Laboratory tests were performed with different percentages of the additives on the soil and the modification of Atterberg Limits, Grain Sizes Distribution and Free Swell Index in the soil mixtures was studied week after week for a month. From the result of the plasticity indexes obtained, satisfactory values were noted and the respective dosages were chosen as the optimum. The latter part of the study examined the optimum dosages of enzyme, lime and enzymatic-lime that produced maximum strength improvement on the treated soil. The strength criteria were investigated by conducting unconfined compressive tests on 3.8mm diameter cylindrical specimens of samples cured with the dosages at and near the optimum combinations. The effect of density and moisture content was predominant in all cases and this enabled to identify the maximum dry density (MDD) and optimum moisture content (OMC) for the mixes. It was found that enzymatic- lime stabilized soils gave speedy stabilization as compared to enzyme stabilized and lime stabilized soils. The paper discusses the results obtained throughout the study. Under standard conditions, satisfactory reasons are found stating that Enzymatic Lime is a possible economical and innovative methodology for soil stabilization. Keywords: Ground Improvement, Enzyme, Lime Stabilization, Soft Soil. Introduction In situ soil stabilization is commonly brought about by compaction, rearrangement of soil particles, addition of chemical reactants, or thermal process. Among these techniques, hydrated lime has proved to be a cost effective, easy to apply, favored method of soft soil improvement for most engineers. Rooted in the success of lime stabilized soils, various additives have been suggested to be incorporated with soil and with soil-lime and tried over the last few decades. Numerous research works are and have been done to understand the behavior of soil-lime mixtures in the presence of other salts/chemicals. But the effect of various inorganic additives such as calcium chloride and calcium sulphate with lime on the behavior of clay is yet to be studied in detail. Based on this idea, it was decided to integrate an enzyme into soils along with hydrated lime. The enzyme used in the work is an enzyme soil stabilizer produced in the United States by Nature Plus, Inc. A number of case studies have been reported [1] stating that enzyme by itself improves soil properties while no literature has been found on enzymatic lime soil stabilization. It is to be assumed in the work that like soils subjected to other modes of treatment, any improvements in the engineering behavior of enzymatic lime treated soil systems will mainly be attributed to the aggregation effects [2]The scope of the paper includes observation of the changes in Atterberg Limits of lime and enzyme treated soil systems and the unconfined compressive strength improvement of soil samples subjected to such treatments. Mechanism of stabilization As mentioned, the paper describes the use and effect of chemical agents lime and enzyme on the index properties of stabilized soils. The utilization of lime in soil modification is not a novel technology. It is a traditional means in a variety of construction applications since the time of Romans and has never entirely disappeared. When used in soil, lime modification describes an increase in strength brought by cation exchange capacity rather than cementing effect brought by pozzolanic reaction [3]. It alters the clay surface mineralogy, producing a reduction in plasticity and moisture holding capacity, and an improvement in soil stability. But the disadvantages of lime stabilization include lime carbonation and sulfate salt reactions which may lead to disintegration of bonds on aging. To account for the negative impacts, a number of salts and chemicals have been added with lime to soil and tested. Among these already tried and proved agents include cement, flyash, rice husk etc. It was hence decided to mix an enzyme with lime for the purpose of soil stabilization and to study its effects on soil properties. Enzymes are organic molecules that catalyze very specific chemical reactions if conditions are conducive to the