No-fines concrete - its properties and applications

Abstract

No-fines concrete consists solely of normal portland cement, water and coarse aggregate. It has been used in Europe and the U.K. since the 1930's for the building of single- and multi-storey dwellings, but had found little acceptance in North America. In recent years, however, due to increased awareness of the need for conservation of non-renewable mineral resources, increased consideration is being given to the use of no-fines concrete in Canada and the U.S.A. The compressive strength of no-fines concrete is considerably lower of conventional portland cement concrete and generally varies than that between 200-2000 psi (1.4-13.7 MN/m2). Young's modulus of elasticity is usually between 1.0 x 106 to 1.5 x 106 psi (0.7 x 10 4 to 1.2 x 10 4 MN/m2) depending on the strength level of the concrete. The ratio of modulus of rupture to compressive strength expressed as a percentage varies between 10.8 and 31.0 per cent. The shrinkage of no-fines concrete made with crushed limestone or river gravel is of the order of. 200 x 10-6. This is about half that of conventional concrete. Investigations at the Mines Branch have indicated that no-fines concrete prisms with no air-entraining agent had poor resistance to freeze-thaw cycling. The prisms incorporating an air-entraining agent were able to withstand up to 274 freeze-thaw cycles compared with 56 for prisms without an air-entraining agent. The principal advantages claimed for no-fines concrete are economy in materials, higher thermal insulating values, lower shrinkage and lower unit weight. The major disadvantages are its low compressive, flexural, and bond strengths and higher permeability. The principal applications of no-fines concrete are for load-bearing, cast-in-place external walls of single- and multi-storey housing, small retaining walls and as a damp-proofing sub-base material for concrete floors cast on grade. This type of concrete is also eminently suitable for construction in northern Canada because of its higher thermal insulating property and low cement content.