Performance Evaluation of Cold Mix with Use of Modifiers

Hot Mix Asphalt (HMA) is used predominantly as a paving mix from many decades in road construction. In India almost 90 percent road network is occupied by bituminous pavements only. Certain limitations associated with HMA use are like emission of green house gases from hot mix plant, shut down of plants during rainy season, problems in maintaining the paving temperature when hauling distances are more etc. Cold mix asphalt consists of unheated aggregate with emulsion or cutback as binder. Cold mix also offers advantages like; reduction in emissions, low fuel consumption, can be used in rainy seasons etc. The main difference between cold mix and HMA is that aggregates and emulsion or cutbacks are mixed at ambient temperature (10?C-30?C) in case of cold mix and aggregates and binder are mixed at high temperature (138?C-160?C) in case of HMA. In the emulsion based cold mix technology, the addition of pre-wetting water to the aggregate, thereafter addition of emulsion to it, production of the mix, laying and compaction, all processes are done at the room temperature (23?C to 25?C). In addition to this, field trials have proved that cold mix can be easily produced by using hot mix plant and laid in using similar techniques. They also found the performance of cold mixes in an acceptable level as cracks formed in cold mix bitumen pavement repaired themselves over time & because of this flexibility of cold mix surface it could last longer on low volume roads than hot mix. Cold mix can be used mainly for base course and sometimes for binder or wearing course. Bitumen is used largely for the construction of flexible pavements with Cold Mix technology. However, pavements may undergo one or several of the most common distresses i.e. rutting (permanent deformation under heavy vehicles loading) and fatigue cracking (cracks due to repetitive application of loads) at high in-service temperatures, and thermal cracking (cracks due to the lack of flexibility) at low in-service temperatures. To overcome these distresses, the performance of standard cold-mix bitumen may be improved by using modified bituminous emulsions, that is, by modifying bitumen properties before emulsification. Thus, cold-mix bitumen has been traditionally modified by addition of a large list of different types of substances called as ?modifiers?. Bitumen modification for paving applications is mostly carried out by means of polymers, both virgin (polyethylene, EVA, SBS, SBR, etc.) and waste (plastics from agriculture, crumb tyre rubber, etc.)