EMINENTLY HYDRAULIC LIMES: GRAPPIER CEMENTS. 183 



and screened its weight averages about 43 Ibs. per cubic foot. Accord- 

 ing to Schoch,* the hydraulic limes average in specific gravity about 

 2.9 



Tensile and compressive strength. The results given in Table 77 

 are quoted by Schoch * as being fair averages for hydraulic-lime 

 mortars composed of one part lime and three parts sand; kept for 

 seventy-two hours after molding in a moist atmosphere and the remain- 

 der of the time under water. 



TABLE 77. 

 AVERAGE STRENGTH OF HYDRAULIC LIMES. (Scnocn.) 



These results may be compared with those given in Tables 78 and 79, 

 which are quoted by Beckwith as the averages of several series of experi- 

 ments carried on at Toulon and Marseilles on hydraulic-lime mortars 

 composed of about one part lime to two parts of sand. These mortars 

 were made into blocks and kept under salt water the entire time. 



TABLE 78. 

 TENSILE STRENGTH OF TEIL HYDRAULIC-LIME MORTAR. 



Ratio of compressive to tensile strength. When in use, limes and 

 cements are usually subjected to direct compressive stress only, tensile 

 strains being rarely applied in well-designed and well-built structures. 

 In testing, however, a test for tensile strength is much cheaper and 

 more readily applied than one for compressive strength. The result 

 is, that though limes and cements are almost entirely used in com- 



* Schoch, C. 

 p. 74. 



Die moderne Aufbereitung und Wertung der Mortel-Materialen, 



