PHYSICAL AND CHEMICAL PROPERTIES. PARTS IV, V. 188 
(d) Adequate reasons are given for the beneficial results obtained by 
Bamber’s method of grinding the clinker in the presence of a 
limited amount of live steam. It is suggested that even greater 
efficiency might be obtained by dropping the red-hot clinker 
into water as soon as it leaves the rotary kiln. 
PART IV. THE STRENGTH OF PORTLAND CEMENT. 
(12) Observations obtained from testing the strength of Port- 
land cement : 
(a) High testing rotary cements would meet with universal approval 
and the problem of cement testing and standardization would 
be greatly simplified were it not for their characteristic drop 
in tensile strength. 
(6) The failure to establish a more definite relationship between the 
tensile and compressive strengths can be attributed partly to 
the fact that the large cubes or cylinders usually used for 
testing the strength under compression are less apt to show 
the peculiarities of cement than the small briquettes used for 
tension test. 
(c) Results obtained by crushing small specimens show the up and 
down values common to tension test curves, but even when all 
specimens are practically the same size, the values do not 
always go up and down coincidently. 
(d) Tension tests are as useful as determinations of compressive 
strengths, and a retrogression in the value of either occurs 
only when due to the development of undesirable, contending 
influences. 
(e) The characteristic fluctuations in strength could not be attributed 
to the different rates of hardening of the different constituents 
of the cement and to a deterioration of the sulphates and 
aluminates. 
(f) The development and the maintenance of the early strength does 
not depend upon the early gain in strength, upon a narrow 
limitation of the percentage of calcium oxide, the value of the 
silica-alumina ratio, the hydraulic modulus, nor upon any other 
available chemical information. 
(g) In most instances it was found possible to change the natural 
effect of any of these factors by altering the degree of burning, 
the fineness of either the raw material or the finished product, 
and by seasoning the cement or the clinker.in a different man- 
ner or to a different extent. 
(h) No reliance can be placed on rules which are deduced simply 
from analyses or percentage of gain. 
(13) The physical and chemical properties of free and com- 
bined calcium oxides and their influence on the development of 
the strength of calcareous cements. 
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