Estimation of the total and effective rubber contents of rubber-bitumens

Methods are described for estimating the total content of natural (unvulcanised) rubber in a rubber-bitumen and the effective rubber content; the latter is defined as the concentration of a standard rubber which would give a specific viscosity equivalent to that of the rubber in the test sample. The total rubber content is calculated from the iodine value of a solution, in carbon tetrachloride, of the acetone-insoluble fraction of the rubber-bitumen. The effective rubber content is determined by a measurement of the specific viscosity of a benzene solution of the acetone-insoluble fraction of the rubber-bitumen. The effective rubber content has been shown to be related to the elastic recovery of the binder. Both analytical techniques have been used to follow the effect of heating on rubber-bitumens and recommendations are given on the conditions of temperature and duration of heating in the preparation of rubberised binders for road use.