The effects of rice straw ash (RSA) and microsilica (MS) on durability properties (water absorption and chloride ion penetration) of M40 grade Pavement Quality Concrete (PQC) were studied. Ten concrete samples were prepared by partially substituting cement with RSA and MS in various proportions. A significant reduction was observed in the water absorption and chloride ion penetration in concrete samples with an increase in the curing age as well as with an increase in the proportion of MS and RSA. The maximum reduction in water absorption and chloride ion penetration was observed in R2M3 (10% RSA and 7.5% MS) as compared to control concrete (R0). The analytical relationships were developed between the above-mentioned parameters and curing age of concrete. A linear equation was established between the initial and secondary rate of water absorption of concrete and also between the chloride ion penetration of concrete at 10–20 mm and 25–35 mm depth. Both these equations were applicable to all the concrete samples of this study. Predictive charts were generated between the above-mentioned parameters and days of curing in water. © 2019 The Authors