Floor surfaces highly resistant to abrasion and impact are required for many industrial and commercial uses. Such surfaces are usually built as two-course construction, with a base or structural slab topped by a wearing surface. The two courses may be cast integrally or with the heavy-duty surface applied as a separate topping.
In the first process, which is less costly, ordinary structural concrete is placed and screeded to nearly the full depth of the floor. The wearing surface concrete, made with special abrasion-resistant aggregate, emery, iron fillings, etc., then is mixed, spread to the desired depth, and troweled before final set of the concrete below.
The second method requires surface preparation of the base slab, by stiff brooming before final set to roughen the surface and thorough washing before the separate heavy-duty topping is cast. For the second method, the topping is a very dry (zeroslump) concrete, made with 3⁄8-in maximum-size special aggregate. This topping should be designed for a minimum strength, ƒ’c = 6000 psi. It must be tamped into ƒ’c place with powered tampers or rotary floats. (Note: If test cylinders are to be made from this topping, standard methods of consolidation will not produce a proper test;
tamping similar in effect to that applied to the floor itself is necessary.) One precaution vital to the separate topping method is that the temperatures of topping and base slab must be kept compatible.
(‘‘Guide for Concrete Floor and Slab Construction,’’ ACI 302.1R.)