72 STANDARD SPECIFICATIONS 



placed in the angles of the forms to round or bevel 

 them off. 



(e) Lumber once used in forms shall be cleaned before being 

 used again. 



(/) The forms must not be removed within 36 hours 

 after all the concrete in that section has been placed. 

 In freezing weather, they must remain until the con- 

 crete has had sufficient time to become thoroughly 

 hardened. 



(g) In dry but not freezing weather, the forms shall be drenched 

 with water before the concrete is placed against them. 



316. Depositing: 



(a) Each layer should be left somewhat rough to insure bond- 

 ing with the next layer above; and, if the concrete 

 has already set, it shall be thoroughly cleaned by scrub- 

 bing with coarse brushes and water before the next 

 layer is placed upon it. 



(6) Concrete shall be deposited in the molds in layers of such 

 thickness and position as shall be specified by the 

 Engineer in charge. Temporary planking shall be 

 placed at the ends of partial layers, so that none shall 

 run out to a thin edge. In general, excepting in arch 

 work, all concrete must be deposited in horizontal 

 layers of uniform thickness throughout. 



(c) The work shall be carried up in sections of convenient 



length and the sections shall be completed without 

 intermission. 



(d) In no case shall work on a section stop within 18 in. of 



the top. 



(e) Concrete shall be placed immediately after mixing, and 



any having an initial set shall be rejected. 



317. Expansion Joints: 



(a) In exposed work, expansion joints may be provided at 

 intervals of 30 to 100 ft., as the character of the struc- 

 ture may require. 



(6) A temporary vertical form or partition of plank shall be 

 set up, and the section behind shall be completed as 

 though it were the end of the structure. The partition 

 shall be removed when the next section is begun, and 

 the new concrete shall be placed against the old without 



