STRENGTH CHARACTERISTICS OF BITUMINOUS MIXES USING MODIFIED BINDERS

Abstract

The demand of bitumen has increased tremendously in recent years due to rapid urbanisation. In India, the annual consumption of bitumen in 1990 was 1.6 million tonnes. The target of Lucknow Road Development plan (1981-2000) is of 2.6 million kilometer road network. For construction of new roads and maintenance of existing roads, bitumen demand would be 4.4 million tonnes by the end of the year 2001. Requirement of bitumen in the country is met only by imported crude. Traditional bituminous binders present various limitations to cope with the excessive overloading and increasingly severe climatic conditions, which lead to important stress related problems, premature failure of bituminous surfacing. So, it is necessary to improve desirable properties of the bitumen by modifying it by different type of modifiers. The modifiers used in the present study are sulphur, crumb rubber (CR) obtained from discarded tyres and styrene-butadiene-styrene copolymer (SBS). Blends were prepared with different contents of these modifiers and test for penetration, ductility, softening point, Marshall stability and tensile strength were conducted. The results have shown that while penetration and ductility value decreases with content of the modifier, the softening point increases showing suitability of the binder in high temperature regions. The Marshall stability and indirect tensile strength also increased by the use of modifiers, 8% SBS added to bitumen, increases the Marshall stability 1.6 times, indirect tensile strength 1.5 times. The blends of CR and sulphur as well as SBS and sulphur had remarkable improvement in stability and tensile strength of bituminous mixes. These modified blends are suitable as overlay materials on surfaces which are badly cracked. They can also be successfully used as a renewal courses as a part of maintenance work and in pavements subjected to high traffic loads. The modified binders will certainly increase the initial cost of road construction but it will prove to be economical if life cycle cost is taken into consideration such as increased life span, less maintenance etc. (