Comparison of the Effects of Hydrated Lime on the Moisture-Induced Damage of Stone Mastic Asphalt (SMA) Mixtures

Abstract

Moisture-induced damage is one of the most prominent distresses affecting pavement structures worldwide. As a consequence, various strategies for mitigating this phenomenon have been proposed, including the use of additives to improve bitumen-aggregate bonding, engineered to mitigate/counteract the moisture damage effects. Among these, the reported benefits of various lime forms, such as hydrated lime (HL), have propelled its use (mainly in the United States from the early 70s) as widely reported in scientific literature. However, very few studies have been conducted in the United Kingdom with locally available materials, specifications and testing methods suitable for that purpose. Therefore, this study investigates the effects of HL on the moisture damage resistance of stone mastic asphalt (SMA) mixtures designed, produced and tested under local UK conditions. A set of asphalt slabs with a target 4.0% air voids content and two bitumen contents (5.6 and 6.2%) using granite aggregates were manufactured using a roller ‘slab’ compactor consisting of control mixtures (0% HL) and those with 1, 2 and 3% HL by weight of total mixture. Characterisation of the mixtures was done via the saturated ageing tensile stiffness (SATS) test to account for both the effects of ageing and moisture damage. The SATS test results showed a positive effect of the addition of HL on the moisture damage resistance, however increasing HL contents only produced marginal additional improvements. The influence of the reduction in bitumen content was negligible. Furthermore, the results indicated an optimum dosage of 1% HL for enhanced moisture damage resistance.