Tens. str. i^sq 

 in. section 



7 days 28days 



154 



173 



148 



227 



180 



205 



105 



84 



698 KEW YOEK STATE MUSEUM 



4 Magnesia possesses strong hydraulic properties wlien ignited 

 alone but has none when heated with silica, alumina and clay, 

 and probably plays no part in the formation of cement. It will 

 not replace lime in mixtures, the composition of which should 

 be calculated' on the basis of lime only, without regard to the 

 magnesia present. 



Using the formula previously given they made up and tested 

 cements as shown below. -^ 



R. Cato 



Silicates CaO Si02 A1203 Pat. test Hot test 



Silicate 95 8) o ^^ 70 ^.q ok 01 o Set hard, sound, Sound, off glass, 



Aluminate 4.2 f '^'^^ ^^-^^ ^^'^^ ^ on glass hard 



Silicate 91.6 | ot? 71 q 04 1 a Set hard, sound, Sound, off glass, 



Aluminate .4 f '^'^^ '^-^ ^^'^ * on glass hard 



Silicate *'5.3( o on <7c\ kk oo ak t Set hard, sound, 



Aluminate 14.7 f ^•'^^ '^'^^ '^'^•^^ ^ off glass Sound on g ass 



Silicate 74.8 j „ .^ aq qi 10 «q 10 Set quick, sound, Sound, od g ass, 



Aluminate 25.2 j ^-^^ ^^'"^^ ^^'^^ ^^ off glass hard 



The actual composition of some leading cements on the market 



is given below. 



Calcium silicates 



R.Cato 

 Formula SiA CaO Si02 Pat. test. Hot test 



2 Ca SiO 1.85 65.1134.89 Set hard, hard 7 days, hard 6 weeks Sound, on glass, hard 

 Si^CaOl Si02 2,33 TO 30 Set soft, fairly hard 7 days,hard 6 w-eks 



3 CaO SiO-i 2.8 73.63 26 82 Set soft, fairly hard days, hard 6 weeks " 

 SJ^CaO S1O2 3.27 7u.£6 23.44 Cracked soft 1 day, hard 6 weeks " 



Dr Michaelis considers that in good Portland cement the 

 ratio of the total silicates to the lime should be about as one 

 to two, and that the variation from this ratio should only be 

 within narrow limits. Cements rich in lime set more slowly, but 

 harden better than those poor in lime. Cements rich in silica 

 generally set slower than those rich in alumina but the former 

 harden very energetically in the beginning and are better for 

 use under salt water. According to I)r Michaelis^ the celebrated 

 German Portland cement manufactured at Stettin in Germany 

 has a silica percentage of nearly 25 with 5.7^ of alumina and 

 2.5/^ of ferric oxid. 



A material like the limestone of Teil is for instance admirably 

 suited for the manufacture of Portland cement to be used in 



' Cem. and eng. news. 1897. v. 3, no. 6, p. 85. 



^ Schoch. Die moderne aufbereitung und wertung der mortel materialien. 

 p. 85. 



