The previous article explained the basics of concrete as they relate to concrete floors on grade. It emphasized the need to take into account such properties as bleeding, shrinkage, hardening characteristics of concrete, and dimensions of slabs when designing floors. In using this article as a guide to specifying, the guidelines presented in the previous article should be kept in mind.
Probably the best method of specifying concrete floors on grade is to include the following paragraph: "Concrete work shall conform to all requirements of Specifications for Structural Concrete for Buildings,' ACI 301-72 (Revised 1975), except as modified by the supplemental requirements below." Concrete strength and type and grade of reinforcing steel must be specified as part of the supplemental requirements.
Other supplemental items that should be specified include: Location and detail of joints, class of floor, compressive strength of topping (Class 6 and 7 floors only), type of finish, materials for heavy duty toppings, dry-shake materials (if required), admixtures (air entraining, retarding, or accelerating, if required), surface tolerance, maximum aggregate size, and curing procedure and duration. ACI specifies the compressive strength and maximum slump based on the class of floor, as well as the minimum cement content per cubic yard of concrete depending on the maximum aggregate size. Because these items are included in ACI 301, they need not be included in the supplemental requirements unless the specifier chooses to use different values.