PHYSICAL AND CHEMICAL PROPERTIES. PARTS IV, V. 163 
Constancy of strength and volume.—Although hard burning is 
essential to the greatest efficiency in early strength, even some of 
the hardest-burned: Portland cements show considerable fluctua- 
tions in strength and volume after they have become thoroughly 
indurated, and there is no means of ascertaining beforehand how 
great this ultimate change may be. 
The extensive investigations made by a committee of the 
Society of German Portland Cement Manufacturers failed to 
establish any definite relationship between the durability of 
strength and any of the so-called accelerated tests for constancy 
in volume. Also, the 1-, 7-, and 28-day tests for strength fail 
to give definite information in this respect. That other methods 
based upon chemical composition or upon the strength of steamed 
or boiled mortars have proved equally as unsatisfactory is ap- 
parent from the differences in the requirements of the standard 
cement specifications of various countries intended to control 
this factor. The British specifications insist upon the Le Chate- 
lier test for constancy in volume and demand specified gains in 
tensile strength between 7- and 28-day periods; the American 
specifications only demand no retrogression in similar tests for 
strength and permit unsoundness jn the accelerated test; and 
the Germans rely almost entirely on the compressive strength of 
sand mortar cubes and use no accelerated tests. Our results in- 
dicate that the fluctuations in the strength of indurated cement 
were due largely to the same internal strains which developed 
abnormal changes in volume. 
Effects of free lime on the volume of indurated, hard-burned 
cement.—In most respects the results obtained by measuring 
the changes in volume of bars of neat and sand mortars verified 
the previous work and conclusions of E. D. Campbell and A. H. 
White,®** who were the first to measure the effects of hard-burned 
free lime and free magnesia on the volume constancy of Portland 
cement. 
Campbell and White found that bars of neat mortar of nonseasoned, 
hard-burned Portland cements which apparently contained no free lime 
seldom showed when immersed in water a linear expansion of more than 
0.040 per cent. Bars of similar cement kept in air contracted in volume 
and in a remarkably uniform manner. The smallest contraction noted at the 
end of four years was 0.300 per cent and the highest 0.392. 
In order to prepare a hard-burned cement containing free lime, these 
investigators added calcite, crushed and sized to pass a 12- and remain on 
a 20-mesh sieve, to a normal, raw mixture. In this way they manufactured 
a hard-burned cement which contained about 2.8 per cent of free lime, the 
* Journ. Am. Chem. Soc. (1906), 28, 1273. 
