LIME AND CEMENT INDUSTRIES 



703 



Ko. 



Per cent of 



plaster paris 



added 



1 



2 



Results of Candlot in 1891/ 



HORTAB 



N'eat cem. briq. 



1 cem. to 3 sand briq . . . 



.6 



1 



1.5 



2 



2.5 



3 



Days 0% lb 



7 485 



28 673 



7 223 



strength of sand briq. 1-3 lb, 

 persq. in. 

 8 days 7 days 28 days 



240 

 298 

 254 



174 



225 

 227 

 230 

 182 

 184 

 115 



SULFATE LIMB 



645 



738 

 252 



2^ 



533 



674 

 263 



160 



212 

 167 



285 

 305 

 320 

 381 

 290 

 295 

 235 



28 



333 377 377 



8< 



435 



790 

 185 

 367 



307 

 344 

 408 

 399 

 400 

 390 

 360 



4 



264 

 483 

 126 

 201 



Lewis considers tliese results remarkable as regards strength 

 and not explained. 



Cements liigb in alumina have a tendency to expand and to 

 blow or to clieck. Magnesia is also supposed to cause expansion 

 after a lapse of a considerable interval, while sulfates are looked 

 on as causes of disintegration of Portland cement when exposed 

 to sea water. Cements low in lime and without an excess of 

 alumina but high in silica are simply of low strength like under- 

 burned cements. If the alumina goes above S^, it is considered 

 high, if below 5^, it is considered very low. Mr Richardson 

 considers that over S^ of magnesia is an excessive and undesirable 

 quantity, and the proper limit for svilfuric acid is lifo. The fol- 

 lowing are the percentages of magnesia and sulfuric acid in Port- 

 land cements wdiich have been placed on American markets dur- 

 ing the past few years. 



* Ciments et chaux hydrauliques. Paris 1891. p. 254. 



