P ACINI, METAMORPHI8M OF PORTLAND CEMENT 211 



The general conclusion that may be drawn from these values is that 

 the effect of electrolytes in the mixing water, when the cement is after- 

 wards subject to immersion in water, is to increase the strength at the 

 early periods (7 and 28 days), but later to depress it (15). In general, 

 the more concentrated solutions give a greater depression of strength. 

 The early increase in strength is probably due, in the presence of an 

 optimum quantity of water, to additional cementing or void-filling ma- 

 terial precipitated in the pores of the mortar by reaction between the 

 added electrolytes and the solutions resulting from the action of water 

 upon cement. This deposited material may, in its later history, revert 

 to a soluble form and be washed away, leaving abnormal voids, or else 

 in its growth may disrupt the cells it occupies, in either case reducing 

 the strength. 



Effect of gaging grout with rock ivaters. In grouting deep tunnels, 

 the question has arisen as to the advisability of using the rock w r ater at 

 hand when fresh water was inaccessible. The water available in the 

 instance in hand was an effluent from a shale bearing a small proportion 

 of pyrites, and when it issued from the rock face it contained a quantity 

 of dissolved hydrogen sulphide. As none of the water was immediately 

 available for a laboratory test, an artificial mixture was made up, in 

 which the quantities of dissolved salts and hydrogen sulphide occurring 

 in the natural water was purposely exaggerated, to obtain accelerated 

 effects. 



TABLE 20 

 Analysis of the Artificial!!/ Mineralized Water 



Parts per million 



H,S '. 891 



CaO 1764 



MgO 1461 



SO 3 1948 



Cl 2920 



A grout was made up according to specifications, using a normal Port- 

 land cement, and Cow Bay sand with 100 per cent passing 10 sieve, 75 

 per cent passing 40 sieve; in the proportions 1: iy 2 with 35 per cent of 

 liquid. The wet mix was poured into glass cylinders, kept 24 hours in 

 air until set had developed and immersed in water. 



Four sets of three specimens each were made, the first set mixed with 

 35 per cent of distilled water; the second, 35 per cent of the water above 

 mentioned; the third, 35 per cent of a 10 per cent dilution of this water, 

 and the fourth, 35 per cent of a 1 per cent dilution. 



Xo discrepancy was observed in the setting time, as all the specimens 



