To perform its function satisfactorily as binder, paving bitumen must remain plastic. But when bitumen is exposed to weather in a thin film it loses quite a lot of its plasticity and becomes brittle. This happens because of certain chemical and physical changes. This phenomenon of natural deterioration is called weathering. Progressive weathering may ultimately result in the formation of fine cracks which go on widening with time. Engineer in charge should adopt suitable ways and means to minimize the effect of weathering. Rate of curing of the liquid bitumen (cut back) is affected by following factors:
- Evaporation rate of the solvent or volatility.
- Amount of solvent in the cut-back.
- Penetration of the bitumen used as base.
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