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 United Kingdom since the 1930s for the building of single story and multistory dwellings, but had found little acceptance in North America. In recent years, however, due to increased awareness of the need for conservation of nonrenewable mineral resources, increased consideration is being given to the use of no-fines concrete in Canada and the United States. The compressive strength of no-fines concrete is considerably lower than that of conventional portland cement concrete and varies between 200 to 2000 psi (1.37 to 13.73 MN/square meters ). Young's modulus of elasticity is usually between 1.0 x 10,000,000 to 1.5 x 10,000,000 psi (0.7 x 100,000 to 1.2 x 100,000 MN/square meters) 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 42.0 percent. The shrinkage of no-fines concrete made with crushed limestone or river gravel, is of the order of 200 x 0.000001. This is about half for that of conventional concrete. Investigations at CANMET have indicated that no-fines concrete prisms with no air-entraining agent had poor resistance to freeze-thaw cycling; the corresponding 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, somewhat higher thermal insulating values, lower shrinkage, and lower unit weight. The major disadvantages are its low compressive, flexural, and bond strength, and higher permeability. The principal applications of no-fines concrete are for load-bearing cast-in-place external walls of single story and multistory housing, small retaining walls and as a dampproofing subbase material for concrete floors cast on grade. This type of concrete is also eminently suitable for construction in northern Canada because of its somewhat higher thermal insulating property and low cement content.