XI, A, 1 King: Pozzuolanic Properties of Meycauayan Tuff 31 



until they possess sufficient cohesion to stand handling, and 

 then store them for the remaining time in water. The results 

 thus obtained are supposed to indicate the behavior of the ma- 

 terial when used in construction. In practice, however, the 

 concrete is sometimes kept moist for a time by covering with 

 damp cloths and afterward sprinkling occasionally with water. 

 At other times, and this is the usual practice, the work is not 

 kept covered with wet cloth or earth, but is simply allowed 

 to dry under the influence of the sun and air currents. It is 

 rarely totally immersed in water. Laboratory tests should be 

 made as nearly as possible in conformity with construction prac- 

 tice. In order to note the effect of air storage equivalent to 

 ordinary construction practice on the tuff mixtures, one half of 

 the test specimens was stored in air, the other half was kept in 

 fresh water, up to the time of testing. The results obtained 

 on the specimens stored in air are altogether different from 

 those obtained on specimens kept in water, as shown in Table 

 VII and fig. 1. It would be interesting to conduct similar 

 experiments upon Portland cement mortars. Tensile and com- 

 pressive tests were made at the end of seven, twenty-eight, 

 sixty, and ninety days. The briquettes, both mortar and neat, 

 were broken in a standard Fairbanks testing machine. Com- 

 pression tests were made on a four-screw Olsen testing machine, 

 having a capacity of thirty thousand pounds. 



CONCERNING TEST SPECIMENS 



For the purpose of carrying out this investigation, a set of 

 30 cast-iron cylindrical compression molds having a diameter 

 of 3.568 inches (9.063 centimeters) and a height of 7.136 inches 

 (18.125 centimeters) were specially made. The diameter was 

 made 3.568 inches so that the area of the bearing faces would 

 be exactly 10 square inches (64.514 square centimeters) ; this 

 greatly facilitates the calculation of the strength per square inch 

 and is a very desirable feature when a considerable number of 

 determinations are made. The height was made twice the least 

 lateral diameter in order to secure the correct shearing angle 

 during rupture. 



Bauschinger" has shown that the following equation holds 

 true for sandstone and similar substances.^^ The equation show- 



" Johnson, J. B., The Materials of Construction. John Wiley & Sons, 

 New York (1912), 31. 



" In my opinion this equation is applicable to the tuff mixtures under 

 study; at least, a few comparative tests, using cubical and cylindrical speci- 



