Backfilling Shaft Surround Using Recycled Concrete Waste Material

Abstract

The massive development in the State of Qatar to fulfil the Qatar National 2030 Vision requires efforts to direct the construction sector towards reducing economic, social and environmental impacts through the application of more sustainable construction techniques. The Public Works Authority, Qatar (Ashghal) has acknowledged that using available domestic sources to produce quality aggregate by recycling pavements, construction and demolition waste, and industry by-products is beneficial when natural sources are getting depleted. One of the projects exploring the possibility of utilizing the recycled concrete waste as surround backfill material is Contract C853/1 named the Wakrah-Wukair Drainage Network Branches (WWDNB). This is an ongoing mega drainage project associated with the construction of 67 number of shafts and approximately 17 km of sewer pipes at a maximum depth of 48m below ground level. The proposed material would be replacing the conventionally used materials such as graded limestone, gabbro aggregate and foamed concrete. This paper assesses the feasibility of utilizing recycled concrete aggregate (RCA) for backfilling of permanent shafts whilst satisfying the requirements of the Qatar Construction Specifications (QCS). A number of laboratory tests were therefore conducted, and the proposed material was found to be of acceptable quality. Additionally, mock-up tests are scheduled to confirm the field attributes before implementation on site for shafts in non-traffic areas. Using RCA as shaft backfill is more beneficial from a sustainability perspective as it will decrease the carbon footprint by 70% when compared with using traditional backfill materials. The goal of the study is to introduce an industry-wide application which is both sustainable and economical.