INVESTIGATIONS ON MASTIC ASPHALT USING SOFT BITUMEN WITH RUBBER

Abstract

The use of new construction materials and innovative technology must be introduced due to the increase in all-round developmental activities in different parts of the country that the traffic intensity began to increase on the roads as well as the existing pavements which are s ec deterioration at a very fast rate. Thick rolled bituminous surfacing came into use on heavily trafi roads and these thick surfacing materials are not only costly and time consuming but also, someti fail to resist the stresses imposed by traffic due to tremendous increase in traffic intensity and axle loads. Critical locations such as roundabouts, bridge decks, intersections and bus stops are subjected to high stresses and need frequent maintenance. Besides polymer modified bituminous mixes, mastic asphalt is another recognized improved alternative for pavement surfacing specially for the above-mentioned critical sections. Mastic Asphalt Concrete (M.A.C.) is a mix of Coarse Aggregates (C.A.), Fine Aggregates (F.A.), Filler and Bitumen with or without modifier such as sulphur, rubber, polymer etc., which contains higher amount of filler and binder content as compared to conventional bituminous mixes. It . . . . . . . is potentially advantageous paving material due to high stability, durabilit resiliency and very low maintenance as;well as good riding quality. In the present investigation, an attempt has been made to develop new mastic asphalt mixes using rubber modifier as binder blended with soft grade of bitumen (80/100) for surfacing purposes at critical locations as mentioned above. Mastic asphalt mixes have been designed considering different percentages of tyre tread rubber content in wet process viz. 0%, 10% and 20% by weight of binder which are named as Mix I, Mix II and Mix III respectively. Various methods of testing besides Wilson Hardness test which is commonly used for design, have been evaluated and, the effect of three important variables including type of filler, temperature and rubber content on strength characten of mastic asphalt mixes are investigated. The first part of the dissertation consists of determination ;i3 . Wpb sisal ,properticis of 03iitituents, of thei rax)ea,tsuuhrasiC.A4,naturail 'saitdf aslEl.A.,) fillers of lime !, ,r.ii,;•sitple,pbwdegjandi,sionedliptolAitunienigntit,,b1140410 41,1144grAilWegilWitli)Ai.014401 of:Wickly used asphalt material ,testing, metlitods, Ile, grading( of, aggrega* s,.gnd1,physical,properti$sc,pI Narious ingredients, were consktered asF per IRC/MOSIT specifications and standards, Also,: a literature survey has been carried out on large number of important references from the published literature from India and abroad relates to the mastic asphalt. The specimens prepared with lime stone and stone dust for each type of mix (I, II & III) were subjected to various methods of testing like Marshall;" Hubbard field, Triaxial compression, Uniaxial compression, and Creep and Creep recovery, Skid resistance and Wilson hardness tests under different conditions in particular ease. It is found that the performance of mastic asphalt prepared with 80/100 grade bitumen is comparable with harder grades of bitumen and long period of cooking is not necessary as specified by IS/IRC. The mix can be prepared within one hour at the specified temperature (170 — 200 °C). It is also observed that when rubber-modified binder is used, there is further reduction in cooking time as well as improved stability at lower temperature: Rubberized mastic is more temperature susceptible and possesses better results at cold climatic condition (below about 40 °C). The rubber as a part of binder; increases the shearing resistance whereas cohesivity is decreased and 10% rubber modified binder may be considered as effective from economic point of view as well as improvement in performance. The softer grade of bitumen is cheaper and is easily available than harder grade and also, crumb rubber is a very cheap material, which brings down the cost of construction. The mastic asphalt with limestone is more plastic in nature and considered as more preferable filler than stone dust filler. But at the same time, stone dust may also be used for the same purpose, which is not included in IS/IRC specifications. The results of portable skid resistance for all the mixes showed enough skid resistance in both dry and wet conditions and hence don't require any surface treatment