Factors affecting performance of sprayed seals in rural Victoria

Factors that significantly affect performance of in-service sprayed seals have been identified through developing comprehensive models using a multilevel analysis approach. Subjective condition data of surface distresses from five rural road networks in Victoria/Australia have been used. They include cracking, deformation, texture loss, stone loss and patching. Evaluations of individual distresses for representative segments are combined into a composite index called Surface Inspection Rating (SIR) which is used to trigger the need for resealing. Contributing factors considered include surface age, traffic volume, aggregate size, subgrade soil type, shoulder seal width, rainfall and temperature. For each network, statistically significant factors for each distress are identified and used in developing their SIR models. An overall SIR model has also been developed using condition data from all five networks. Predictions of this model have been compared with an existing model that has been developed using Markov Chains with surface age as the only predictor. The results show that both models have roughly similar deterioration rates of SIR up to 8 years of seal life, after which deterioration rate of the newly developed model becomes higher.