360 BUILDING LAWS 



placed on any portion of the construction where the said 

 centers have been removed. 



"The concrete for all girders, beams, slabs, and columns, 

 shall be mixed in the proportions of 1 of cement, 2 of sa*nd or 

 fine gravel, and 4 of other aggregates, as before provided. 

 The concrete used in reinforced -concrete-steel construction 

 must be what is usually known as a wet mixture. When the con- 

 crete is placed in water it must be placed in a semidry state. 



"Only Portland cement shall be permitted in reinforced - 

 concrete constructed buildings. All cement shall be tested 

 in carload lots when so delivered or in quantities equal to 

 same, and report filed with the Bureau of Building Inspection 

 before using it in the work. Cement failing to meet the 

 requirements of the accelerated test will be rejected. 



"Soundness, Accelerated Test. Pats of neat cement will 

 be allowed to harden 24 hr. in moist air, and then be sub- 

 mitted to the accelerated test as follows: A pat is exposed 

 in any convenient way in an atmosphere of steam, above 

 boiling water, in a loosely closed vessel, for 3 hr., after 

 which, before the pat cools, it is placed in the boiling water 

 for 5 additional hr. 



"To pass the accelerated test satisfactorily, the pats shall 

 remain firm and hard, and show no signs of cracking, dis- 

 tortion, or disintegration. 



"Such cements, when tested, shall have a minimum tensile 

 strength as follows: Neat cement shall, after 1 da. in moist 

 air, develop a tensile strength of at least 150 Ib. per sq. in.; 

 and after 1 da. in air and 6 da. in water shall develop a tensile 

 strength of at least 500 Ib. per sq. in.; and after 1 da. in air 

 and 27 da. in water shall develop a tensile strength of at 

 least 600 Ib. per sq. in. Cement and sand tests composed of 

 1 part of cement and 3 parts of crushed quartz shall, after 

 1 da. in air and 6 da. in water, develop a tensile strength of 

 at least 175 Ib. per sq. in., and after 1 da. in air and 27 da. 

 in water shall develop a tensile strength of at least 240 Ib. 

 per sq. in. These and other tests as to fineness, set, etc., 

 made in accordance with the standard method prescribed by 

 the American Society of Civil Engineers, may, from time to 

 time, be required by the Bureau of Building Inspection. 



