SPECIFICATIONS FOR PLAIN AND REINFORCED CONCRETE. 275 



39. Freezing Weather. Concrete shall not be mixed or deposited at a freezing temperature, 



i.il |>i(( u.niniis, approved by the enginn r, .m i.ik< -n to avoid the use of materials 

 i ,.vtic<l with ire crystals or containing frost ana to provide HUMUS to prevent the concrete from 



ing. 



Tin author has used the following specification for depositing concrete in freezing weather: 

 When the temperature of the air is below 40 F. during the time of mixing and placing concrete, the 

 water used in mixing concrete shall be heated to such a temperature that the temperature of the concrete 

 mixture shall not be less than 60 when it reaches its final position in the forms. Care shall be used 

 that the cement shall not be injured by boiling water. 



40. Rubble Concrete. Where the concrete is to be deposited in massive work, clean, large 

 stums, evenly distributed, thoroughly bedded and entirely surrounded by concrete, may Be 

 used, at the option of the engineer. 



1 1 . Forms. Forms shall be substantial and unyielding and built so that the concrete shall 

 conform to the designed dimensions and contours, and so constructed as to prevent the leakage 

 of mortar. 



42. The forms shall not be removed until authorized by the engineer. 



43. For all important work, the lumber used for face work shall be dressed to a uniform thick- 

 ness and width; shall be sound and free from loose knots and secured to the studding or uprights 

 in horizontal lines. 



44. For backings and other rough work undressed lumber may be used. 



45. Where corners of the masonry and other projections liable to injury occur, suitable mold- 

 ings shall be placed in the angles of the forms to round or bevel them off. 



46. Lumber once used in forms shall be cleaned before being used again. 



47. The reinforcement shall be carefully placed in accordance with the plans, and adequate 

 means shall be provided to hold it in its proper position until the concrete has been deposited 

 and compacted. 



DETAILS OF CONSTRUCTION. 



48. Splicing Reinforcement. Wherever it is necessary to splice the reinforcement otherwise 

 than as shown on the plans, the character of the splice shall be decided by the engineer on the 

 basis of the safe bond stress and the stress in the reinforcement at the point of splice. Splices 

 shall not be made at points of maximum stress. 



49. Joints in Concrete. Concrete structures, wherever possible, shall be cast at one opera- 

 tion, but when this is not possible, the resulting joint shall be formed where it will least impair 

 the strength and appearance of the structure. 



50. Girders and slabs shall not be constructed over freshly formed walls or columns without 

 permitting a period of at least four hours to elapse to provide for settlement or shrinkage in the 

 supports. Before resuming work, the tops of such walls or columns shall be cleaned of foreign 

 matter and laitance. 



51 A triangular-shaped groove shall be formed at the surface of the concrete at vertical 

 joints in walls and abutments. 



52 Surface Finish. Except where a special surface finish is required, a spade or special 

 tool shall always be worked between the concrete and the form to force back the coarse aggre- 

 gates and produce a mortar face. 



53. Top Surfaces. Top surfaces shall generally be " struck" with a straight edge or floated 

 after the coarse aggregates have been forced below the surface. 



54. Sidewalk Finish. Where a "sidewalk finish" is called for on the plans, it shall be made 

 by spreading a layer of I : 2 mortar at least } in. thick, troweling the same to a smooth surface. 

 This finishing coat shall be put on before the concrete has taken its initial set. 



