XI, A, 1 King: Pozzuolanic Properties of Meycauayan Tuff 25 



due to the presence of water of hydration, which, as it were, 

 predisposes the material to chemical activity when mixed with 

 hydrated lime and tempered with water. The Meycauayan tuff 

 contains only 4.34 per cent of water of hydration, which is con- 

 sidered low for this class of material. The German Society for 

 the Testing of Technical Material, in October, 1909, adopted new 

 norms for the testing of tuffs and specified a minimum content 

 of 7 per cent of water of hydration. Water undoubtedly has 

 had a great deal to do in determining the chemical and physical 

 properties of tuffs, but just to what extent is a question which 

 has as yet not been completely solved. Tetmajer ^^ has shown 

 that blast-furnace slags, analogous in every way to natural slag 

 such as is investigated in this paper, when allowed to cool in 

 the ordinary way into a solid mass and then crushed to powder, 

 with the addition of lime, exhibit no hydraulic properties to speak 

 of, whereas by suddenly cooling the melted vitreous slag in water 

 a product is obtained that possesses very pronounced hydraulic 

 properties when mixed with lime. In fact, some tuffs that 

 have been deprived of their water of hydration by heating to 

 700° C. no longer show hydraulic properties. This led Tetmajer 

 to make the statement that the efficacy of tuffs and trasses as 

 cementing material could be judged accordincr to the loss on 

 ignition. 



F. Tannhaeuser ^^ is of altogether a different mind concerning 

 the cause of the hydraulicity of trasses. He maintains that the 

 pozzuolanic properties of trass from the Brohl and Nette Valleys 

 depend upon the content of sodalite minerals which are found in 

 the groundmass. Tannhaeuser has shown that the alkalies of the 

 sodalite minerals are replaced by the calcium of the hydrated 

 lime with the formation of difficultly soluble silicates and that 

 a precipitation of chemically active silicic acid does not occur 

 at this time. Furthermore he concludes from his investigation 

 that the water content has nothing to do with the hydraulic 

 activity of the tuff. 



Pozzuolanas or tuffs possessing marked hydraulic properties 

 vary widely in their chemical and mineralogical compositions. 

 They are not fixed chemical compounds having a constant com- 



" Vol. 7, 95, cited by Johnston in the Materials of Construction. John 

 Wiley & Sons, New York (1912), 95. 



" Ein Beitrag zur Petrographie des Trasses und zur Erklarung seines 

 hydraulischen Wirkungsweise. Bautechnische Gesteinuntersuchung, Mitt. 

 a. d. Min.-Geol. Inst. d. k. Tech. Hochschule (1911), 2, 34-44. Abstracted 

 in Tonind.-Zeitg. (1912), 36, 739. 



