Bounding recycled aggregate pavement mixtures using hydraulic binders and cold bitumen emulsion.

With the current emphasis on sustainable development, recycling in the construction industry including highway planning, design, construction and maintenance has become a default option. Traditionally, recycled aggregate has been employed as filling or capping materials. However, the need to replace virgin materials in higher grade applications and reduce landfill has stimulated the need to enhance their performance. The requirements of using low energy and low environmental impact binders such as bituminous emulsion and industrial by-products as hydraulic binders whilst maintaining a long shelf life presented a further challenge.The primary aim of this research was to investigate methods by which a mixture of recycled aggregate composed of road planings, concrete demolitions and bricks with proprietary bitumen emulsion as binder could be enhanced to comply with the prevailing specifications and performance requirements for pavement materials, by using novel combinations of bituminous emulsions and latent hydraulic binders.The preliminary investigation focussed upon the establishment of an appropriate method of compaction of bitumen emulsion recycled aggregate mixtures to ensure results were consistent and representative of field performance. The main investigation evaluated the environmental conditions including freeze-thaw, low and high humidities and varying temperatures upon the behaviour and performance of loose pre-compacted and compacted recycled product using a range of novel latent hydraulic binders and bituminous emulsion combinations. Test methods included Indirect Tensile Stiffness Modulus test, Repeated Load Axial test, Indirect Tensile Fatigue test, Compressive Strength test and a novel modification of the Indirect Tensile Strength test was proposed and developed for enhance assessment of performance.The key findings were that whilst bitumen emulsion mixtures could perform adequately, the addition of a latent hydraulic binder enhanced the mixture's performance in terms of mechanical properties and withstanding extreme conditions exemplified by freeze-thaw and high humidity, whilst maintaining shelf life. However, it was deduced that the performance could be heavily influenced by the condition, consistency and composition of the recycled aggregate. It is recommended that further work should focus on rigorously investigating the influence of recycled components on mixture properties to optimise their performance for given applications, and extended to include tar bound material.