spaces enclosed by previously constructedFORMS. These forms are usually removed oncethe plastic concrete hardens into the shapeoutlined by the forms.Forms for concrete structures must be tight,rigid, and strong. If the forms are NOT tight, lossof water and paste may cause sand streaking aswell as weakness to the concrete. The forms mustbe strong enough to resist the high pressureexerted by the concrete.Form MaterialsUndisturbed soil or clay, if sufficiently rigidand excavated to proper dimensions, maybe usedas EARTH FORMS. Design, specifications, andconstruction methods, however, dictate what kindof form materials are to be used on certainstructures. Wood, plywood, steel, fiber glass, andother approved materials are commonly used asform materials. Forms for concrete pavement andcurves should be metal; surfaces exposed to viewin the finished structure and those requiringspecial finishes should be wood, plywood, orother approved material.Figure 7-28.-Form for concrete column.Foundation FormsFoundation forms may include forms or partsof forms for column footings, pier footings, andwall footings. Whenever possible, the earth shouldbe excavated and the hole used to contain thefoundation of footing forms. In most cases,FOOTINGS are cast directly against the earth,and only the sides are molded in forms. In somecases where there is a firm natural earth surfacethat is capable of supporting and molding theconcrete, parts of forms are often omitted.Figure 7-26 shows a typical large footing form.Figures 7-27 and 7-28 show typical footing formsfor a concrete pier and a concrete column,respectively.Wall FormsWall forms are made up of five basic parts.They are as follows: (1) sheathing, to shape andretain the concrete until it sets; (2) studs, to forma framework and support the sheathing; (3) wales,to keep the form aligned and support the studs;(4) braces, to hold the forms erect under lateralpressure; and (5) ties and spreaders or tie-spreaderunits, to hold the sides of the forms at thecorrect spacing (fig. 7-29).Wall forms may be built in place or pre-fabricated, depending on the shape and thedesirability for reuse.Wall forms are usually reinforced againstdisplacement by the use of TIES. Two types ofFigure 7-29.-Parts of a typical wall form.7-19
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