CONCRETE 



145 



impervious to water when set up. The jelly-like or quak- 

 ing mix should be used whenever it is possible, as it is more 

 uniform and gives the highest strength. The moderately 

 wet, although giving lower strength than the quaking, may 

 be necessary in some cases, but very wet or sloppy mixtures 

 should always be avoided, as they give a porous concrete 

 of low strength. 



PLACING AND CURING 



Forms. Form is a name given to the structure which 

 holds concrete in the required shape until it has hardened 



FOOTING 

 WITHOUT FOSMS 



At 1 / 1 ^-n V 



9»li6iM)/=ti^ileilte'*%p.^llteifs/i)feiJ/=')«-3-w)fc«//=*«»«Jr;//aJi'>^^ 



census* 



1 



Fig. 141. 



n u 



'J 'J 



S^OOTIA/G rVITSI rOISMJ 



Footing construction 



it 

 11 

 1 1 

 n 



D 



sufficiently to be self-supporting. Forms should be pre- 

 pared carefully to give the required shape to the finished 

 concrete. They must have sufficient strength and rigidity 

 to support the weight of the concrete. Concrete weighs 

 approximately 150 pounds per cubic foot and when in the 

 liquid state has a tendency to burst the forms. They should 

 always be water-tight, as the escape of any liquid causes 

 waste of materials, and water flowing out may wash a part 

 of the cement from the aggregate and thus make weak 

 places in the concrete. 



When forms for concrete work are placed underground, 

 the earth bank may be used for one side if it has sufficient 



