170 AXXALS FEW YORK ACADEMY OF SCIENCES 



tive and coagulative properties of these materials unquestionably do not 

 compare with the coagulative powers of the complex colloid which 

 Michaelis postulates (64, 65). If, therefore, the hydration of cement 

 does not proceed in a properly regulated manner, it is conceivable that it 

 may become a hydrolysis, with deleterious effects. 



If the mixed cement is allowed to freeze, the setting will not take 

 place, but on thawing out the mass, setting is resumed. Obviously the 

 transition of the water to the solid phase hinders solution and diffusion, 

 and upon resuming the liquid form, water promotes these processes as 

 before. A slow setting has, however, been observed in frozen mixes (94), 

 and it is quite possible that the phenomenon of regelation may account 

 for this. 



Smoke gases have been found to have a disintegrating effect upon 

 cement setting at a temperature lower than 7 C. ; this is attributed to 

 the formation at these temperatures of a hyd rated calcium carbonate, 

 having the formula OaCOo,5H 2 by the action of the carbon dioxide of 

 the smoke gases upon the lime of the cement. At slightly higher tem- 

 peratures this hydrate is transformed to pulverulent calcium carbonate, 

 with consequent disintegration of the structure of which it forms a part 

 (107). 



The effects of moderate variations in the temperature of the mixing- 

 water upon ultimate strength are practically of no great moment : even 

 mixes that have been frozen and afterwards allowed to resume their set 

 are not materially affected in their ultimate strength, if the set has not 

 proceeded too far at the time of freezing (11 ). More than one repetition 

 of the freezing process upon the same mix, however, will be quite de- 

 structive to the final hardening. 



If the hardening be considered a process of crystallization, repeated 

 freezing may be assumed to destroy the strength by the formation, 

 through rapid temperature changes, of relatively small and non-adhesive 

 crystals of the calcium hydroxide during the critical foundation period 

 of growth of the crystalline structure, so impeding and misdirecting 

 consequent interlocking that a weak structure results. 



If, on the other hand, the colloidal theory is adhered to, it is only 

 necessary to point out that the colloidal cell walls about the cement 

 grains may be ruptured by the expansion of the contained water in freez- 

 ing. This would result in discontinuity of the internal structure, and if 

 sufficiently widespread, as would be the case in repeated 'freezings, would 

 alone account for weakness. 



Studies have been made of the ultimate resistance obtained from frozen 

 mortars by varying the amount of gaging water, with the view of estab- 



