20S 



ANNALS NEW YORK ACADEMY OF SCIENCES 



may afterwards affect the metamorphism of cement. It has been pointed 

 out by Goldbeck (43) and by White (108) that the expansion or con- 

 traction of concrete depends upon whether the concrete remains wet or 

 dry, and that the strains caused by alternate wetting and drying of con- 

 crete may be a more fruitful cause of cracks than temperature changes. 

 The presence of an optimum quantity of water is necessary, however, 

 so that the proper reactions take place in the mass of setting cement, in 

 order that the strength may increase normally. 



QUALITY OF WATER AT FIRST ADDED 



Compressive strengths of neat cements gaged with various solutions. — 

 A normal Portland cement was mixed with the proper quantity of 

 water (21 per cent by weight) in which was dissolved, in the different 

 tests, varying concentrations of the salts indicated in the subjoined table. 

 The cement was worked for one minute, and the plastic mass was tamped 

 into glass cylinders approximately one inch in diameter, with the utmost 

 precaution to avoid all air bubbles and at the same time to subject all 

 specimens to the same pressure. 



Table 18 



Compressive Strengths of Neat Cement Mixed with Solutions of Various Salts 



(Age of specimens, 28 days. Average of two determinations) 



Mixes 



Pounds per 

 square inch 



Gain or loss, 

 per cent 



9. 



10. 

 11. 



12. 

 13. 

 14. 

 15. 

 16. 

 17. 

 18. 



Distilled water 



25% rock water 8 diluted with distilled water . . 



50% do. 



75% do. 



Rock water alone 



2% sodium chloride solution 



4% do. 



6% do. s 



8% do. 



10% do. 



Saturated solution of calcium sulphate (± 0.2% 



2 % solution of calcium chloride 



0.2% solution of magnesium sulphate 



0.2% solution of magnesium chloride 



Equal parts of 11 and 12 (CaS0 4 and CaCl 2 ) . . . 

 Equal parts of 13 and 14 (MgS0 4 and MgClj . . 

 Equal parts of 12 and 13 (CaCl 2 and MgS0 4 ). . . 

 Equal parts of 11 and 14 (CaS0 4 and MgCl 2 ). . . 



7330 

 6340 

 6495 

 6870 

 5605 

 6675 

 5815 

 5065 

 4215 

 5285 

 7025 

 6960 

 6680 

 5595 

 6565 

 7355 

 5810 

 6200 



-14 

 -11 



- 6 

 -23 



- 9 

 -21 

 -31 

 —43 

 -29 



- 4 



- 5 



- 9 

 -23 

 -10 

 +0.6 

 -21 

 -15 



s This water contained : CaO, 1177 parts per million. 

 MgO, 226 

 S0 3 , 408 

 CI, 4360 



