6. common lime is the product obtained by burning a pure, or nearly pure, carbonate of lime. On being treated with water it slakes rapidly, evolving much heat and increasing greatly in volume. It is now seldom used in engineering construction and will not be considered further.
7. Prof. M. Tetmajer has thus defined hydraulic limes: Hydraulic limes are the products obtained by the burning of argillaceous or siliceous limestones, which, when showered with water, slake completely or partially without sensibly increasing in volume. According to local circumstances, hydraulic limes may be placed on the market either in lumps, or hydrated and pulverized. The following table gives a classification of hydraulic limes according to M. E. Candlot 3 who states that the first class is seldom used for important work and that the fourth class is quite rare.
1 "Tests of Hydraulic Materials," by H. LeChatelier. Trans. Am. Inst. Mining Engrs., 1893.
2 "Masonry Construction," p. 48.
3 "Ciments et Chaux Hydrauliques," par E. Candlot.
Per Cent, of Clay in Limestone.
of Silica and Alumina in Finished Product.
Hydraulic Index, or Ratio of Silica and Alumina to Lime.
Approx. Time to Set, Days.
Feebly Hydraulic Lime Ordinary " " Real " " Eminently " "
5 to 8 8 to 15 15 to 19 19 to 22
9 to 14 14 to 24 24 to 30 30 to 33
.10 to .16 .16 to .31 .31 to .42 .42 to .60
16 to 30 10 to 15 5 to 9 2 to 4
Hydraulic limes should be burned slowly, and at such a temperature that sintering does not take place. The best hydraulic limes have a composition very similar to that of Portland cement. The comparatively low temperature at which they are burned permits them to slake on the addition of water. They gain strength much more slowly than cements.
Having considered the classification of hydraulic products as a whole, we may proceed to the discussion of Portland and natural cements, the hydraulic products which have by far the greatest importance here, and the only varieties which will be taken up in detail in the present work.