USEFUL DATA 



the structure in which pouring is taking place shall be maintained at a temperature 

 well above the freezing point. Aggregates and water used shall not be heated to more 

 than 70 degrees. The use of salt to lower the freezing point shall not be permitted. 



Placin^T Concrete Under Water. Concrete may be placed only in still water, 

 with the use of a tremie properly designed and operated. Concrete shall be mixed with 

 more water than is ordinarily permissible so that it will flow readily through the tremie. 

 Coarse aggregate used in concrete thus placed shall not be more than one inch in 

 diameter. 



In case the flow of concrete is interrupted, or in case it is necessary to provide a 

 construction joint, care shall be taken to remove all laitance before proceeding with 

 the work. 



Protection of Exposed Surfaces. The surfaces of concrete exposed to prema- 

 ture drying shall be covered and kept wet for a period of at least seven days after 

 pouring. 



REMOVAL OF FORMS 



Forms shall not be removed from the concrete until it is sufficiently hard to permit 

 of this being done with safety. 



In weather of a temperature above 60 degrees, the minimum time after pouring for 

 the removal of forms shall be as follows: 



Wall forms and forms for the sides of beams 2 days 



Column forms and forms under slabs of span less than 4 feet . 4 days 



Slabs of span between supported girders or shoring between 4 and 



10 feet 6 days 



Supports or shoring shall be maintained under horizontal members a minimum time 

 after pouring in accordance with the following table: 



Beams, Girders and Flat Slabs in ordinary building construction . 3 weeks 

 Spans over 30 feet At least 1 month 



Under all floors upon which building materials are being placed during construc- 

 tion, the supports or posts shall be left at least two weeks longer than specified in the 

 above schedules. 



In weather of a temperature below 60 degrees, the forms and supports shall be left 

 in place a longer period, depending upon the weather encountered. 



Especial care shall be taken in the removal of forms from any concrete that may 

 have become frozen. Where it is likely that the concrete might have frozen, it may be 

 tested by placing a piece of the concrete in warm water or upon a stove, after which, 

 if the concrete is properly set, it shall not show any deterioration due to such treatment. 

 A similar test may be made directly upon the structure by submitting it to the flame 

 of a blow torch, which treatment will not produce any melting, if the concrete is 

 properly set. If the concrete has frozen, the forms shall not be removed from it until 

 it has had sufficient time to thoroughly thaw and set in warm weather. 



193 



