10 - Sprayed concrete

Abstract

This chapter provides an overview of sprayed concrete. Sprayed concrete is a mortar or concrete pneumatically projected at high velocity from a nozzle to produce a dense homogenous mass. Sprayed concrete normally incorporates admixtures and also include additions or fibers or a combination of these. There are two techniques used in spray concrete: wet process and dry process. In wet technique cement, aggregate, and water are batched and mixed together prior to being fed into a purpose-made machine and conveyed through a pipeline to a nozzle where the mixture is pneumatically and continuously projected into place. In dry process only the aggregate and cement are batched, mixed together and fed into a purpose made machine wherein the mixture is pressurized, metered into a compressed air stream and conveyed through hoses or pipes to a nozzle, where water is introduced as a very fine spray to wet the mixture, which is then projected continuously into place. Additions and fibres may also be in the mixture. In sprayed concrete, most types of cement are used, as in any concrete work, depending on the requirement of the finished product. Sprayed concrete is a versatile and economic method of concrete placement. Its potential application is almost limitless but it succeeds most notably where the use of rigid formwork is absent.