Using china clay waste in sprayed concrete Available to Purchase

The extraction of china clay produces large quantities of waste material including coarse sand, waste rock, overburden and micaceous residue. The current annual rate of waste generation in the UK is approximately 20 Mt. In the UK china clay extraction is concentrated in the south-west of England and the total volume of stockpiled waste in this relatively small area is estimated at 500 Mt. Current utilisation for this waste assecondary aggregate is restricted to a limited number of uses in local markets, which are now saturated. In order to increase usage levels and reduce the landfill burden, new and alternative uses for this waste material are required. This paper describes a study undertaken to evaluate the potential of using waste china clay sand as an aggregate for dry-mix sprayed concrete applications, primarily as a concrete repair material. In addition, the project explored the possible enhancement of some of the properties by using mica and metakaolin, which are also by-products of china clay production. The evaluation was undertaken by characterising the physical properties of the waste sand, developing a variety of concrete mix designs and conducting site trials to assess performance. The programme also examined the effect of additions (silica fume and metakaolin), admixtures (accelerators and superplasticisers) and polypropylene fibres. The project was able to identify the best mix design as a result of the trials and grade the mixes in terms of performance for spraying ability, compressive strength and durability. The results of the study show that the use of china clay sand aggregate for dry-mix sprayed concrete is effective and the natural sand grading of this aggregate is suited very well to this application. Also, the use of metakaolin as an addition to a sprayed concrete mix provides enhanced durability characteristics to the mix at the same time as improving its spraying performance.