CHAPTER XX. 

 SPECIFICATIONS FOR NATURAL CEMENTS. 



SEVERAL sets of specifications for natural cements are reprinted 

 below, with a final comparative summary of their requirements on 

 different points. 



New York State Canals, 1896. 



Natural hydraulic cement must be of the best quality and of such 

 fineness that 90 per cent will pass through a sieve of 2500 meshes per 

 square inch and 80 per cent through a sieve of 10,000 meshes per square 

 inch. 



Briquettes made of equal parts of natural hydraulic cement and 

 crushed quartz, immersed in water as soon as they are sufficiently hard 

 to sustain a -g^inch wire weighted with 1 lb., must show a tensile 

 strength of 65 Ibs. per square inch at the expiration of seven days, 

 but briquettes showing less than such strength will be held until 

 twenty-eight days have elapsed, when, if they then show such strength 

 as to sustain as many pounds per square inch above 125 as the seven- 

 day test shows them to have fallen below 65 they will be deemed 

 to h^-ve passed this test. Briquettes made of neat cement must not 

 set so as to support a -j^-inch wire with a load of one quarter of a pound 

 in less than five minutes. Briquettes of neat cement must not show 

 checks or cracks when immersed in water for seven days after mixing. 



Rapid Transit Subway, New York City, 1900-1901. 



Fineness. 95 per cent shall pass a No. 50 sieve and 85 per cent 

 a No. 100 sieve. 



Tensile strength. At the end of seven days, one day in air, six 

 days in water, 125 Ibs., neat. At the end of twenty-eight days, one 

 day in air, twenty-seven days in water, 200 Ibs., neat. When mixed 

 1 to 1 with quartz sand: at the end of seven days, one day in air, six 

 days in water, 100 Ibs.; at the end of twenty-eight days, one day in 

 air, twenty-seven days in water, 150 Ibs. 



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