A pavement designer wants to design a flooring structure that is reliable and cost effective. Various materials have been used for the construction of pavements in order to economize the design. The depletion of the natural resources of building materials and the problem of disposal of industrial wastes also require the use of alternative materials in the construction of pavements. The subsoil is sometimes stabilized or replaced with a stronger soil material to improve its strength. This stabilization is also adequate when the available surface is made up of weak soil. Increasing the strength of the subfloors can lead to economy in the structural thickness of the pavement. The good quality of the aggregates implies a significant cost of transportation in places where it is not available. Alternatively, it may be possible to use marginal aggregates available locally in cemented form. Some examples of cementing materials, which can be mixed with the marginal aggregates to develop a bound underlying layer / base layer (Austroads 2004, French Manual 1997, Theyse et al., 1996), are cement, lime, Coal, pozzolanic materials, etc. The stiffness of said layer may be higher than the conventional non-bonded granular layer, thus reducing the overall stress level to the pavement structure (R-90 2009). In addition, such bonded material can further contribute to the fatigue life of the pavement structure. These factors are expected to contribute some economics to pavement design (Little et al., 2000, Thoøgersen 2004, Thompson 1986).
The fly ash is the waste material, which is obtained after burning coal in the thermal plants. It can be used as a stabilizer for the soil due to its pozzolanic effect or to an inherent hardening property under favourable conditions of moisture and compaction. The objective of this project is to study the effect of fly ash in an expansive soil for the design of flexible pavements and to reduce the amount of lime in fly ash from lime by the effective use of fly ash. A percentage of fly ash without additives was used to reduce the cost of construction and this is a good method for disposal. Initially the properties of the soil indices were studied by determining the liquid limit, plastic limit, shrinkage limit, grain size analysis and specific gravity tests. CBR, OMC and swelling index tests confirmed that the soil had taken clay which is very expansive in nature. Unconfined compression strength tests and soaked RBC tests were conducted for various fly ash ratios and optimal contents were obtained and soil resistance was found to be improved. If locally available soil is good in nature, pavement construction becomes easier and cheaper. But if the soil is weak in nature instead of going for an alternative, it costs higher the available soil can be modified by adding this type of stabilizer which involves low cost.
