A COMPARATIVE LABORATORY STUDY ON PERMEABILITY OF SUB BASE MATERIALS USING CHEMICAL ADDITIVES AND FIBERS

Abstract

Granular Sub-Base (GSB) is an intermediate layer provided between subgrade and base course. One of its roles is drainage. Of course. it's an integral part of the pavements. This being layer placed just on top of' subgrade and just beneath unbound base course, its role is to serve as drainage layer as well as load bearing layer. 1-lence. GSI3 layer plays a vital role to provide strength and support to the overlying pavement. Traditionally, aggregates for sub-base application were composed of sand, gravel, quarry stone, crushed rock and natural mineral materials that provided necessary strength and durability. But use of these traditional materials in (;SI3 layer construction is not possible in all time, especially in hill roads where hauling distance is considerable, as a result of which it would be uneconomical. Hence, in the present study, an attempt has been made to Litilize locally available materials found during hill roads excavation in Chamoli district. The main purpose of this study is to investigate the elTect of permeability on GSI3. In this study, three different types of aggregates collected from different sources and chemical additives such as flyash, lime, and fibres were used. GSB mixes were prepared by mixing three difibrent types of aggregates with different percentages of flyash (i.e. 22 %. 25 %. 2 %), lime (i.e. 2 %. 3 %, 4 %, 5%), and fibres (i.e. 0.5%, 1.0%,1 .5%.2.0%). Initially, physical propeIies of these materials were ascertained to judge its suitability for the job. Secondly, these materials were proportioned to meet the desired gradation limits as specified in MoRl&I I. Ihirdly: performance related tests like MDD & OMC. soaked CBR and permeability were performed in the laboratory with or without chemical additives like lime, flyash and fibre. Inclusion of lime improves engineering properties of GSB mixture considerably. Incorporation of fibre enhanced the reinforcing effect of the matrix and as a result of which there was a significant improvement on tensile strength of the mixture. Also, the permeability characteristics of' the GSI3 mixes are improved by the addition of polypropylene fibre. On the basis of the resi Its. it was found that polypropylene fibre is the best sub base material as it has good strength and is more permeable compared to chemical additives such as lime and flyash