Copyright Goodheart-Willcox Co., Inc. Chapter 18 Concrete Flatwork and Formed Shapes 379 Placing Concrete When concrete is being placed, it should be as near as possible to its intended location. Concrete should not be placed in large quantities in one area, be allowed to run, or be worked over a long distance in the form. Segregation (separation) of ingredients can occur in areas where the grade slopes. The concrete can pool or bunch up from the force of concrete running down the truck chute. Generally, concrete should be placed in hori- zontal layers having uniform thickness. If the form is deep, the concrete should be compacted or vibrated after each layer is placed. See Figure 18-3. Layers or lifts are usually 6″ to 12″ thick in rein- forced concrete and up to 18″ thick for nonrein- forced applications. Concrete should not be allowed to drop freely more than 3′ or 4′. Drop chutes of rubber or metal can be used when placing concrete in thin vertical sections. On large projects, concrete can be moved by means of a concrete pump truck that pushes the concrete through a hose attached to a boom. The use of a pump truck aids in moving concrete to isolated areas where other means can be almost impossible. See Figure 18-4. A hose can be worked down into the wall forms to reduce the distance the concrete drops or can be moved around with a boom to deliver concrete to the forms around the structure. Use of a boom truck allows much faster placing of concrete compared to using wheelbar- rows or other devices. Slab Construction Steps involved in placing and finishing concrete for slab construction include the following: 1. Determine size and location of the slab. 2. Excavate area to the appropriate depth and slope include the area of the forms. 3. Construct forms for the concrete slab. 4. Place reinforcement if required or needed. 5. Determine the amount of concrete and type order for delivery. 6. Place concrete inside forms. 7. Level concrete in the forms (screed). 8. Wait if bleed water appears, then wait until it evaporates. 9. Edge the concrete slab. 10. Joint the concrete slab. 11. Float the concrete slab. 12. Trowel the surface of the concrete. 13. Texture the surface if required or needed. 14. Cure concrete as soon as the fi nishing operation is completed. Dmitry Kalinovsky/Shutterstock.com Figure 18-3. A concrete worker is using a vibrating machine to compact freshly placed concrete. Note that the worker is wearing appropriate PPE—protective clothing and gloves, safety shoes, safety glasses, and a hard hat. John Cooke/iStock/Thinkstock Figure 18-4. Concrete pump truck being used to pump concrete to a house footing in a new residential subdivision.