STRENGTH CHARACTERISTICS OF LIME-FLYASH-SOIL-CEMENT MIXES UNDER DIFFERENT TEST CONDITIONS

Abstract

Nowadays fly ash is produced in large quantities as a waste product from several coal based thermal power stations in India. The annual production of fly ash in In0a ';s more than 38.4 million tonnes. Disposal of fly ash, apart from being health hazard, is a expensive operation. Speedy and afeective removal of fly ash has been recognized as a problem of national importance. It is an inert material in itself but tal,ins; advantage of its pozzolanic properties, fly ash can be util.zed to prepare as an alternative material for use in pavement tonstruction for expanding road network programme. The inveftigat,)rs all over the world have found that the fly ash can b? utilized in pavement construction and building constructioi suc:essfully and profitably. It would result in substantial s,ving in energy consumption and also economical in cost, thus helping to ease the twin problem of disposal and enviromental pollution. Lime is the cheapest material and is also available in large quantities in India. The term 'lime' is a general term which includes various chemical and physical forms of quick lime, hydrated lime and • hydraulic limes. Production of lime whether calcitic lime or dolomitic lime in India was about 63, 258 thousand tonnes per annum in 1988-1989. This material has been extensively used in buildings and roads, and is found to be a suitable material to iv treat properties of the soils also. P,nother material is cement, and is being used in Civil Engineering in a variety of mode of construction. In last two decades the use of this material has increased rapidly. Production of cement in India is more than 435 lakh tonnnes per anum at present. But cement is a costly material and its consumption in buildings is enormous and this material is not available for roads where it is required in abundance. Hence it is required to find a suitable alternative of cement. In fact the utilization. of lime, fl.y ash and cement to improve the stability of soil by soil-lime-fly ash or soil-cement mixes is well known. Design concept fcr soil-cement base course have been rationalized to some extelt but there is no fixed guidelines for the use of lime and fly ish in different types of soils under different environmental coiditions. In this study, investigation were carried out on pozz)lanic mixtures and soil employing lime, fly ash and cement with a view to determine optimum proportion of lime, fly ash and cement in different types of soils and to know the effect of different tests condition on strength characteristics of mixes. Fly ash was procured from Indraprastha Thermal Power Station, New Delhi. Lime used in this was of calcitic hydrated type of commercial quality, and ordinary portland cement available in the laboratory was used in this work. The experimental programme was carried out in four phases. In the first phase, properties of materials used for this study were determined. The second phase was to determine the proportioning of mixes comprising of soil, lime, flyash and cement. The study was carried out in 27 proportioning of mixes. The third phase was to determine the optimum moisture content and maximum dry density for each mixture. Based on the optimum moisture content and maximum dry denstiy, the unconfined compressive strength tests were conducted in the last phase of experimental programme. The unconfined compressive strength tests with different condition of curing time and temperature were conducted for different mixes and results were obtained. Fly ash in the mixture had negative effect on compressive streng h, but addition of lime or cement increased the strength of soil under different proportioning. Increase of lime or cement content increased the strength of soil with increase in curing time and temperature. As per IRC: 88-1984, 28 days strength of soil-lime-fly ash mix should be 7.5 kg/cm2 for its use as base course material in pavement construction. This strength, in the present study is obtained at lime fly ash cement proportioning of 3 : 15 : 6 when cured at 45°C in case of silty soil and of 9 : 15 : 6 (lime : fly ash : cement) at room temperature of 20°C in case of clayey and sandy soil.