121 



utes, but must develop hard set in not less than 1 hour, 

 nor more than 10 hours. 



Tensile Strength. 



22. The minimum requirements for tensile strength for 

 briquettes 1 in. square in section shall be within the fol- 

 lowing limits, and shall show no retrogression in strength 

 within the periods specified:* 



Age. Neat Cement. Strength. 



24 hours in moist air 150-200 Ib. 



7 days (1 day in moist air, 6 days in water). .450-550 Ib. 

 28 days (1 day in moist air, 27 days in water). .550-650 Ib. 



One Part Cement, Three Parts Sand. 



7 days (1 day in moist air, 6 days in water). .150-200 Ib. 



28 days (1 day in moist air, 27 days in water). .200-300 Ib. 



Constancy of Volume. 



23. Pats of neat cement about 3 in. in diameter, % in. 

 thick at the center, and tapering to a thin edge, shall be 

 kept in moist air for a period of 24 hours. 



(a) A pat is then kept in air at normal temperature and 

 observed at intervals for at least 28 days. 



(b) Another pat is kept in water maintained as near 70 

 F. as practicable, and observed at intervals for at least 

 28 days. 



(c) A third pat is exposed in any convenient way in an 

 atmosphere of steam, above boiling water, in a loosely 

 closed vessel for five hours. 



24. These pats, to satisfactorily pass the requirements, 

 shall remain firm and hard and show no signs of distor- 

 tion, checking, cracking or disintegrating. 



Sulphuric Acid and Magnesia. 



2f>. The cement shall not contain more than 1.75% of 

 anhydrous sulphuric acid (SO 3), nor' more than 4% of 

 magnesia (MgO). 



ADDENDUM. 



ABSTRACT OF METHODS RECOMMENDED BV THE 



SPECIAL COMMITTEE ON UNIFORM TESTS OF 



CEMENT OF THE AMERICAN SOCIETY 



OF CIVIL ENGINEERS. 



Sampling. 

 1. Selection of Sample: The sample shall be a fair av- 



For example, the minimum requirement for the 24 hour 

 ne.it cement test should be some value within the limits of 

 150 and 200 Ib.. and so on for each period stated. 



