Chapter 3 Concrete Construction

CHAPTER 3 CONCRETE CONSTRUCTION LEARNING OBJECTIVE: Recognize the different characteristics associated with concrete form design and concrete mix design; recognize the procedures in batching concrete and estimate concrete construction and labor. Identify the procedures and methods associated with precast and tilt-up construction. Concrete construction, once confined largely to paving and foundations, has been developed to the point where both large and small buildings are now constructed entirely of concrete with concrete joists (usually called floor or grade beams), concrete studs (usually called columns), concrete walls, concrete floors, and concrete roofs. This chapter explains some of the major factors concerning the design of concrete forms by means of specific examples. Information is also provided on the various methods by which you can select the proportions for quality concrete mixtures and adjust these mixtures to suit job requirements. We also cover types and uses of admixtures and slump testing procedures. We point out some of the types of equipment you are likely to encounter in concrete construction. A brief discussion is also included on precast construction and brick construction. But we must first discuss safety practices and procedures that should be considered the most important aspect of concrete construction work. CONCRETE SAFETY In concrete construction, as in all types of construction,a certain degree of danger is involved. To help you do your concrete work safely, we will discuss the various safety precautions concerning concrete. Form construction and concrete placement have peculiarities in each job; however, certain natural conditions will prevail in all situations. Wet concrete will always develop hydrostatic pressure and strain on the forms. Therefore, all stakes, braces, and other supporting members should be properly secured and inspected before placing the concrete. All formwork, shoring, and bracing should be designed, fabricated, erected, supported, braced, and maintained so that it will safely support all vertical and lateral loads that might be applied until loads can be supported by the structure. All nailing should be correctly placed and secured according to the plans and specifications. Careless nailing and exposed nails in formwork are a major cause of accidents. Adequate scaffolding should be built to permit crew members to stand clear of pouring areas. Rebar caps are a MUST for all exposed vertical rebar. Tools, particularly hammers, should be inspected frequently. GFCIs must be used with all power tools, and ensure the location of the GFCIs are close to your equipment. Supervisor(s) should check all forms before each pour. Stripped forms should be piled in advance of any movement or change of direction. During night operations, all equipment should be equipped with sufficient flood spotlights to make the perimeter of the operations clearly visible. The pouring bucket and the boom of the paver operating controls should have a synchronized warning device to function automatically with the motion of either the boom or the traveling bucket. Personnel may be subject to cement poisoning (lime); therefore, ensure they have their shirt sleeves rolled down and wear gloves and goggles when working with concrete. If concrete buckets and cranes are used in pouring, each bucket should be provided with a tag line or two, depending on the location. A crew member should never ride a free swinging concrete bucket during a pour. 3-1