Demonstrating the Worth of Recycled Aggregates - A Case Study from Qatar

Abstract

Recycled aggregates are widely used in unbound applications in many countries. However, in some areas the materials available may not meet all the requirements of the local specifications. This is the case in Qatar, where large quantities of excavation waste are available. The excavation waste described in this paper is a weak limestone and did not meet the requirements for sand equivalent and liquid limit/plasticity index in the Qatar construction specifications. It did meet requirements for mechanical properties, durability and grading. A trial road was constructed to demonstrate the suitability of the recycled aggregates as unbound subbase. The road consisted of three sections: (1) recycled aggregates made from excavation waste; (2) recycled aggregates made from clean crushed concrete; and (3) excavation waste mixed with 20% dune sand. Two layers of subbase were placed in each section, and the stiffness was measured with a lightweight deflectometer on top of each layer. The compacted trial sections gave satisfactory stiffness but did not achieve 100% of the laboratory dry density, as required by the Qatar construction specifications. A trafficking trial was carried out on the top layer of subbase, and the resulting rut depths were measured. In each section, the measured rut depths were less than 10 mm, compared to a limiting value of 30 mm, and the trafficked surface of the subbase showed no signs of damage. An asphalt layer was then placed and the road has been subjected to repeated load coming from heavy trucks for over one year and is showing no signs of deterioration. The site trial demonstrated the suitability of the locally available materials, thus contributing to sustainable construction. ASCE.