Understanding Polymer Modified Binders in Asphalt

Polymer modified binders:

First, understanding the basics of polymers. Polymers are very large molecules formed by combining many smaller molecules together chemically. The starting molecules of polymers is called monomer which on combination forms random co-polymers. Co-polymers like SBR are widely used as a modifier in asphalt mix. They are very widely used for preventive pavement maintenance technique in cold weather like in chip seals, slurry seal, cold recycled mix and micro-cracking.

There are basically two types of polymer used as a modifier, namely Plastomer and Elastomer. Plastomers polymers like ethylene vinyl acetate (EVA) have high rate of strength gain but shows brittle behaviour at low temperature. Elastomers like SBR and NR shows a very elastic behaviour, stretches to around ten times and quickly return to original shape upon release of stress. The process of modifying asphalt differs in both plastomers and elastomers. Plastomers forms a tough and rigid network while elastomers forms an elastic framework.

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Its advantage over other polymer modifier is its availability in emulsion which can be easily used when diluted with water. It also do not have any flammable solvents. PVA modified emulsion have shown increased compressive strength over neat mix in cold mix

Tests done for Polymer Modified Binders: Elastic Recovery Test: this test is widely used in the states of US and some other countries also. The test measures the degree of recovery upon release of stress. The test uses a ductilometer that elongates the asphalt specimen at constant rate. After some time, the specimen is cut and allowed to rest. The distance between the ends of the cut specimen is now measured. The elastic recovery is calculated as:

% recovery = (initial elongation-observed elongation after rejoining sample)/(initial