Copyright Goodheart-Willcox Co., Inc. 378 Section 5 Concrete When planning concrete flatwork or creating unique shapes, check national, state, and local codes to ensure that concrete projects meet specific building codes. Consider these items when plan- ning concrete projects: • Intended use or uses • Type of finish on the surface of the concrete • Color to be added to the concrete • Weight that will be supported by the project Code Note Concrete Flatwork Thickness The International Building Code (IBC) states when concrete slabs are supported by the ground, it shall not be less than 3 1/2″ in thickness to ensure the slab has strength to adequately sup- port intended loads. Placing and Finishing Concrete Concrete is moved from a delivery truck to its final location by a variety of methods. Methods include chutes, push buggies, and buckets. The concrete can be handled by cranes or pumping through pipes. The method used should not restrict the consistency of the concrete. Consistency is governed by the placing conditions and the applica- tion. In other words, if conditions permit use of a stiff mix, the equipment should be designed to handle it. Preparation Subgrade should be properly prepared before the concrete arrives. Subgrade is the base on which the concrete is placed. Although a gravel subgrade is not required, it cushions the concrete slab when heavy loads are applied. A subgrade of gravel also helps remove moisture that has accumulated in the subgrade under the slab. Soil with excessive moisture expands when it freezes. The pressures created by freezing of the substrate raise sections of the slab, resulting in cracking. The subgrade must be compacted uniformly to reduce settling. Settling can cause cracking of the concrete slab when heavy loads are applied. If gravel is used as a base under the slab, the soil should be excavated to a uniform depth equal to the inches of gravel to be used as the base. Before receiving concrete, forms should be prepared, leveled, and adequately braced. See Figure 18-2. Subgrades should be smooth, compacted, and moist. Moistening the subgrade prevents rapid loss of water from the concrete when pavements, floors, and similar flatwork are being placed. This is especially important in hot weather. Any previously attached cement should be removed from forms. The forms should be tight in the seams and clean of dirt or other materials. Poorly constructed forms will sag, leak, and possibly fail. Forms should be constructed from materials that will furnish the desired texture to the finished concrete. Treating forms with oil or a release agent facili- tates their removal after the concrete has hardened. Wooden forms exposed to the sun for long periods of time should be thoroughly dampened with water to tighten the joints. Prior to placing concrete in forms, the forms should be brushed or sprayed with a release agent or oil. Reinforcing steel should be clean and free of loose rust and scale. All hardened mortar should be removed from the steel before placing the concrete. Portland Cement Association Figure 18-2. This worker is checking the subgrade for smoothness and proper height.