The applicability of C&D waste material in South Africa road construction.

Abstract

In contrast to developed countries, South Africa is starting to adopt the practice of using recycled rubble from civil engineering demolition works in road construction. This change is due to environmental considerations, but somewhat unique nature of the South African road construction techniques requires a careful classification of these alternative materials and a rigorous study. In this study the possibility of reclaiming the Construction and Demolition (C&D) waste produced in the Durban Metropolitan Area was investigated. A lack of policies for the reuse of waste produced by the civil industry caused the storage of large quantities of C&D waste in the metropolitan landfill sites. In order to decrease this volume the rubble can be reused as construction material for road works. Without alteration in collection process, the C&D waste should be kept sorted according to its nature in landfill site to keep its characteristics as homogeneous as possible. Moreover, specific tests performed in this thesis confirmed the viable construction properties of this material such as non-plasticity and bearing capacity that conform to the South African construction standard. The suitability of the C&D materials in civil works is further demonstrated by the analysis of the rubble generated by the deconstruction of the Natal Command, an ex-military area, in Durban. The demolition of the study area has followed a rigorous procedure of deconstruction. This approach allowed the principal components of the waste (Concrete and Masonry) to be kept separated. Laboratory tests accurately assessed the geotechnical properties of concrete, masonry and of a blend of them which were previously identified as suitable aggregates for unbound road base or sub-base layers. These materials are considered as A1a in AASHTO classification and as G4 in COLTO classification. In addition to the standard test of characterisation, the risk of polluting the environment was assessed. An instrumented embankment was built in accordance with South African road compaction standards using blend material. This enabled the verification of the behaviour of C&D material in real-word working conditions. The instrumentation recorded the stresses, strains and moisture at three depths of the embankment during the passage of trucks at different predetermined speeds. The results of the monitoring were analysed and correlated to the results coming from the full performance material characterization carried out in laboratory. This study will thus enhance knowledge of the behaviour of C&D material and also provide a useful tool to the designer in the planning stages as well as information for contractors involved in C&D road construction application.