Evaluating Self Healing Capability of Bituminous Mastics

The self-healing capability of bituminous materials has been known for many years. Researches were mostly focused on the self healing behaviour during load repetitions. The tests are either time consuming and/or complex. In this paper, a simple self healing test procedure is presented combining the fracture-healing-re-fracture test (FHR) with morphological observations. A fast displacement speed loading was applied first to produce a flat open crack with a crack width of 100–200 μm. Then the specimen was placed in a silicone rubber mould to heal. Various healing periods, temperatures and material modifications were applied. Fluorescence microscopy was used to observe the morphological change during the healing periods. After healing, the specimen was re-fractured under the same condition as the original fracture test. The experimental results indicate that the self healing capability, which was quantified by the re-fracture strength, increases with increasing healing time and increasing healing temperature. A strength recovery master curve at any healing temperature can be obtained through a time-temperature superposition principle. When comparing the strength recovery master curve with the morphological healing observation from fluorescence microscopy, the healing process observed in this paper is believed to be a viscosity driven process, consisting of two steps namely crack closure and strength gain. A Styrene-Butadiene-Styrene polymer modified bituminous mastic shows lower healing capability than a standard 70/100 penetration grade bituminous mastic. The test procedure proposed in this paper is proven to be simple and effective for evaluating and comparing the self healing capability of bituminous materials.