Page 11 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

to its action, and resulting in considerable doubt tensile strength required was 114 lbs. per sq. in.
at one time being raised as to the permanency of and two years later was raised to 142 lb. To-day the
such works. I would like to add here in parenthesis ultimate tensile stress is 325 lb. per sq. in. at seven
that the failures on investigation have been found days, as compared with 120 lb. in the first (1905)
to be due not to the quality of the cement, but British Standard Specification.
to other causes, and that no doubt need now be
entertained as to the permanency of such works AN INTERESTING POINT
if properly executed. Methods of testing both for One particularly interesting point to which I wish
strength and soundness, although crude compared to draw attention is that 5o years ago engineers
with our modern ideas, occupied much attention were in the habit of specifying the proportion of
and discussions on the subject, and questions aggregate to cement for mass work, such as in
regarding the mechanical properties naturally retaining walls, etc., at 6 to I, although certain
were prominent.
venturesome (sic) engineers were bold enough to
use as weak a proportion as 12 to I. How much have
STANDARDISATION OF CEMENT we advanced to-day in our specification of mass
The advent of the Engineering Standard work, with cement of practically three times the
Committee’s Specification and the introduction mechanical strength and much greater reliability
of the rotary kiln, ball and tube mills for grinding than could be obtained half a century ago ?
clinker, and steam treatment of the cement
marked a new era in production. On the one hand This brings me to a question of considerable
standardization simplified enormously the task of importance, and one which I venture to think
the manufacturer in reducing the great diversity of demands the careful consideration of all users
requirements of specifications issued by engineers of cement in mass work, including, besides dock
down to practically one unified system, and on the walls, breakwaters, and so forth, the enormously
other, the improvement in manufacture referred increasing requirements for main arterial ways,
to produced material which was more certain in its and other roads of less importance.
characteristics, and more reliable in its constitution.
The old requirement of spreading and turning
Apart from conservative prejudice there are
the cement before use on the site of the works
practical difficulties in mixing concrete with
became obsolete and the cement could be used
very small proportions of cement due to the
as delivered without fear. Greater reliance could
impossibility of ensuring thorough distribution of
be placed on cement manufacturers’ certificates
the cement throughout the aggregate. Portland
as the quality produced was one which remained
cement as produced to-day is undoubtedly a
practically unaltered even after the cement had lost
very fine material, and much too valuable to be
its original heat : I mean the heat due to , grinding.
squandered in the way it is. Should not this quality
be reserved for works where strength is the vital
It is difficult to compare the standard requirements factor, and some less expensive material and
of the current B. E. S. A. specification with the one with lower mechanical strength placed on
average quality of cement produced, say 25 the market to a standard specification (yet to be
and 50 years ago, but reference to the standard produced), but having just as reliable qualities, as
mechanical tests on 3 to 1 briquettes as set up the present standard specification for Portland
by the Germans in 1876 shows that the minimum cement requires, at considerably less cost per ton ?

12 The Indian Concrete Journal | November 2018