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1950-51 Theatre Catalog, 9th Edition, Page 129 (109)

1950-51 Theatre Catalog, 9th Edition
1950-51 Theatre Catalog
1950-51 Theatre Catalog, 9th Edition, Page 129
Page 129

1950-51 Theatre Catalog, 9th Edition, Page 129

Halting Segregation in Forms-It is just as important to prevent segregation in the forms as it is when transporting the concrete from the mixer to the forms. It is good practice to deposit concrete in the forms where it is to be used rather than to place it at a few points and drag it or cause it to fiow where needed. Depositing the concrete uniformly around the forms prevents segregation and honeycombing.

With thoroughly mixed concrete delivered at proper consistency and without segregation, placing of concrete is made easy; but even in this case further care is required to see that the material fiows properly into the corners and angles of forms and, in reinforced work, around the reinforcement.

Placing by Vibration-Vibration has many advantages as a means for placing concrete. The modern high-frequency concrete vibrators make it possible to place mixtures economically, which are impracticable to place by hand methods. For example, concrete of a stiff consistency can be readily placed by vibration in forms containing closely spaced reinforcements, which with hand-placing would require a medium consistency.

Concrete of a better quality can be made with the same amount of cement because less mixing water is required for the stiff mixes. 0n the other hand, concrete of the same quality is produced more economically because more aggregate can be used. Vibration not only permits the use of stiffer mixes but also permits using a smaller proportion of sand to coarse aggregate, both reducing the amount of mixing water.

For concrete mixes having consistencies that can be readily placed by the usual hand methods, there is generally little advantage in vibration, as segregation may occur. Only when using mixes which are stiffer and harsher than required for hand-placing will the full benefits of vibration be realized. With vibration more rapid placing is often possible, and the concrete also can be placed into locations where it is impracticable to spade or rod by hand methods. Earlier finishing of surfaces and removal of the forms at shorter periods are other advantages which are sometimes obtained.


Reinforcement is the term used to describe the steel bars or small or large mesh metal reinforcement placed in cone crete to increase its tensile strength. Concrete is a material which is very strong in compression*that is, very strong in bearing loads that are placed directly upon it, but it requires steel bars or other metal reinforcement in some structures to increase its power to resist stresses or forces that tend to bend or pull it apart such as the heavy foot trafiic in a theatre.

On most work done by concrete contractors, sizes, location, and spacing of reinforcement usually are determined in advance by experienced engineers, blueprints showing details of construction being furnished. Where it is necessary for the contractor to determine the sizes and spacing of reinforcement, it is recommended that he consult an engineer experienced in reinforced concrete design.


Specifications * Most specifications require that reinforcement shall be free from rust, scale, or other coatings that will reduce the bond between the concrete and the steel. It is necessary to clean bars or metal reinforcement which do not meet this requirement. Bending or straightening reinforcement in a manner that will injure the material is to be guarded against. Heating of reinforcement likewise is not permitted. No. 18 annealed wire usually is used to tie reinforcement together where lapping and intersections occur.

Construction DetailseGeneral specifications require that reinforcement shall be accurately placed and secured, and shall be supported by concrete or metal chairs or spacers or metal hangers. Ordinarily, reinforcement is placed after all form work is built.

In general, it is recommended that all reinforcement be protected by at least a 34-inch covering of concrete. A thicker covering is generally required in that part of the structure exposed to the weather or to the ground. In placing concrete, it is desirable to work the material around and under all reinforcement and embedded fixtures, working the concrete with suitable tools.

Where conditions make spading difficult, or where reinforcement is closely spaced, batches of mortar containing the same proportion of cement to sand used in the concrete are first deposited in such locations. Then filling with the specified mix is carried on in such a manner that the concrete is plastic and flows readily, with light tamping, around the reinforcement. Tapping the form with a rubber or wood mallet or any similar practical method may be used to make the concrete settle around and under reinforcement.


Since the top surfaces, or finishes, of concrete floors take the actual wear and grind, they deserve all the attention possible during construction. If they are properly laid out, concrete fioors will resist extremely severe conditions indefinately and ndustingfethat most troublesome of floor diseases*will be avoided. Due to the thinness of a fioor finish and the nature of its service, it is particularly important that certain basic principles be followed in its construction, since, for example, a different manipulation or working of the concrete into place is used in making a floor finish than in the structural base slab.

Fundamental Requirements

Concrete can be made to have a wide range of qualities. Thus, the strength, resistance to wear, watertightness and other characteristics may be varied by changes in the materials or the proportions of the ingredients used and by differences in the manipulation of the concrete.

The quality of the materials affects the quality of the concrete. Portland cement

XLLUSTRATED HERE ARE: 1. rougheninq base with a stiff wire broom to insure bond: 2. screedinq concrete to proper level with stool-edged screed: 3. a mechanical float ovens out the finish: i. this may also be done with a long hand float,- 5. short floats may also be used to oven out the surface with lrowolinq following.
1950-51 Theatre Catalog, 9th Edition, Page 129