FEASIBILITY OF RAP FOR SUSTAINABLE ROLLER COMPACTED CONCRETE PAVEMENT

Abstract

Reclaimed asphalt pavement (RAP) being an inferior aggregate to natural aggregates is mostly recommended for lower layers of concrete pavements or in low-cost paving mixtures. In this regard, the use of RAP in roller-compacted concrete pavement (RCCP) mixes would cater the demands of sustainability. This thesis is a comprehensive laboratory investigation to determine the various sustainable ways of utilizing RAP in RCCP mixes. To provide a clear picture, two types of RAP: (i) Less aged RAP and (ii) Highly aged RAP, were utilized. The highly aged RAP had an oxidized asphalt layer which is brittle, and hence, termed as “stiff-RAP”. Meanwhile, the less aged RAP had an unoxidized asphalt layer, and hence, termed as “soft-RAP”. The RAP aggregates were directly utilized without any surface treatment being provided. The fractions in which the RAP was utilized were coarse, fine, and combined (coarse and fine both), respectively. All these RAP fractions were used in a proportion of 50 and 100% each, respectively. It was found that the use of stiff-RAP aggregates could increase the optimum moisture content (OMC) and water absorption characteristics due to the presence of water soaking dust contaminants in the RAP. Meanwhile, although the soft-RAP aggregates have a relatively lower water absorption than natural aggregates, higher OMC values could still be expected due to the considerable amount of agglomerated particles. But irrespective of the type of RAP utilized, the maximum dry density (MDD) reduces as the amount of RAP added increases. With reduction in the MDD, the strength of the RAP concrete also reduces as the RAP replacement level increases. Stiff-RAP mixes were found to show better strength properties than the soft-RAP mixes. But filling the missing gaps of the finer fraction of soft-RAP by natural fines could increase its suitability for RCCP mixes. In such scenario, fine RAP mixes could even outperform the coarse RAP mixes. But when the abrasion resistance is concerned, both the coarse RAP and fine RAP mixes provides better performance than the combined RAP mixes.