Evaluation of the sensitivity of different indices to the moisture resistance of bituminous mixes modified by hydrated lime and other modifiers

Abstract

The beneficial effect of hydrated lime added as filler to bituminous mixes in improving the moisture damage resistance of mixes has been known for a long time. However, the effect of binder modification using hydrated lime is less explored. Similarly, very little information is available on the influence of hydrated lime on the moisture resistance of bituminous mixes under critical conditions of high temperature and slow rate of loading. Extensive experimental investigations were conducted in the present study to quantify the relative beneficial effect of addition of hydrated lime in dry and wet methods on the moisture resistance of bituminous mixes. In the dry method, 1.5% and 2% lime (by weight of dry aggregate) was added as filler whereas in the wet method, VG30 and VG40 bitumen were modified using 20% and 30% lime (by weight of virgin binder). The moisture damage resistance of these mixes was evaluated by conducting different tests such as indirect tensile strength, dynamic modulus and dynamic creep tests to assess the sensitivity of different mix parameters in estimating the moisture resistance and to measure the influence of moisture damage on the mechanical properties and rutting performance. The performance of the conventional and lime-modified mixes was also compared with that of polymer and crumb rubber-modified bituminous mixes since lime-modified mixes have been evaluated in this study as possible alternatives to PMB and CRMB mixes, which are popularly used for roads with high traffic volumes. Lime-modified mixes were found to have the best moisture resistance compared to unmodified mixes and PMB- and CRMB-modified mixes. Evaluation of moisture damage in terms of dynamic modulus and dynamic creep tests was found to be significantly more sensitive to moisture damage compared to tensile strength ratio. The beneficial effect of lime has been observed to be significantly more under more severe conditions of high temperature and slow rate of loading compared to lower temperature and high frequency conditions.