336 THF. IMI'KOVKMKXT OF RIVERS. 



9. Soundness. To test the soundness of the cement, at least two pats of neat 

 cement mixed for five minutes with 20 per cent of water by weight shall be made on 

 glass, each pat about 3 inches in diameter and J inch thick at the center, tapering 

 thence to a thin edge. The pats are to be kept under a wet cloth until finally set, when 

 one is to be placed in fresh water for twenty-eight days. The second pat will be 

 placed in water which will be raised to the boiling-point for six hours, then allowed to 

 cool. Neither should show (list. >rtkm or cracks. The boiling test may or may not reject, 

 at the option of the Engineer Officer in charge. 



xo. Time of Setting. The cement shall not acquire its initial set in less than forty-five 

 minutes and must have acquired its final set in ten hours. 



(The following paragraph will be substituted for the above in case a quick-setting 

 cement is desired: 



The cement shall not acquire its initial set in less than twenty nor more than 

 thirty minutes, and must have acquired its final set in not less than forty-five minutes 

 nor in more than two and one-half hours.) 



The pats made to test the soundness may be used in determining the time of set- 

 ting. The cement is considered to have acquired its initial set when the pat will bear, 

 without being appreciably indented, a wire -^ inch in diameter loaded to weigh } 

 pound. The final set has been acquired when the pat will bear, without being appre- 

 ciably indented, a wire ^ inch in diameter loaded to weigh i pound. 



11. Tensile Strength. Briquettes made of neat cement, after being kept in air 

 for twenty-four hours under a wet cloth, and the balance of the time in water, shall 

 develop tensile strength per square inch as follows: 



After seven days, 450 pounds; after twenty-eight days, 540 pounds. 



Briquettes made of i part cement and 3 parts standard sand, by weight, shall 

 develop tensile strength per square inch as follows: 



After seven days, 140 pounds; after twenty-eight days, 220 pounds. 



(In case quick-setting cement is desired, the following tensile strengths will be 

 substituted for the above: 



Neat briquettes: After seven days, 400 pounds; after twenty-eight days, 480 

 pounds. 



Briquettes of i part cement to 3 parts standard sand: After seven days, 120 

 pounds; after twenty -eight days, 180 pounds.) 



12. The highest result from each set of briquettes made at any one time is to be 

 considered the governing test. Any cement not showing an increase of strength in 

 the twenty-eight-day tests over the seven-day tests will be rejected. 



13. When making briquettes neat cement will be mixed with 20 per cent of water 

 by weight, and sand and cement with 12^ per cent of water by weight. After being 

 thoroughly mixed and worked for five minutes, the cement or mortar will be placed 

 in the briquette mold in four equal layers, and each layer rammed and compressed by 

 thirty blows of a soft brass or copper rammer J of an inch in diameter (or T V of an inch 



