Durability properties of cold recycling material using bitumen stabilisation incorporating reclaimed asphalt pavement

Despite many years of experience with the use of stabilized materials in road construction and comprehensive specifications based on this experience, a noticeable increase in problems related to road material stabilization is taking place in Southern Africa, resulting in serious cost increases and claims. The durability of mineral aggregates has been a subject of great concern for the performance of Hot Mix Asphalt (HMA), Cement Treated Base (CTB) and granular base layers and a number of durability tests have been developed and are in use. Unfortunately, because of the ubiquitous nature of aggregates considered suitable for Bitumen Stabilised Materials (BSMs) and their better performance, the durability of mineral aggregates for both virgin and recycled layers, cannot be overlooked. Durability is a time-dependent parameter or behaviour. Durability is achieved by resisting stresses and strains or withstanding destructive agents with which the materials come into contact. The destructive agents can include air, water, light, temperature, chemicals and traffic loading over a long period of time. The durability properties of BSMs are related to the intrinsic properties of the mineral aggregates, bitumen binder and mixture and climate conditions, namely moisture susceptibility, ageing behaviour, mineralogical composition and physico-chemical characteristics of the aggregates, and interaction between mastic (filler, binder, moisture content) and aggregates surface during adhesion. These mechanisms need to be investigated and reliably simulated using laboratory testing results. The identification of a relevant method that simulates field conditions and the development of a laboratory brushing device should be structured to suit the needs of the road construction industry. The project’s aim is to investigate the durability properties of selected BSM mixtures which include reclaimed asphalt pavement (RAP) with relatively high blending ratios of recycled graded crushed stone. In this study the RAP used in each mix design contains materials with relatively fresh binder. The proportions range from 100:0 to 0:100 of graded crushed stone: RAP. The tests used for assessing the durability of BSM-foam mixes in this research are the mechanical wet/dry test, the permeability test and the moisture induction simulation test (MIST). A portion of this study is dedicated to the mechanical characterisation of the BSM-foam mixtures and to the moisture damage simulation.