Søgning i bogen
Den bedste måde at søge i bogen er ved at downloade PDF'en og søge i den.
Derved får du fremhævet ordene visuelt direkte på billedet af siden.
Digitaliseret bog
Bogens tekst er maskinlæst, så der kan være en del fejl og mangler.
io6
HARBOUR ENGINEERING.
“ The cement shall also be tested by means of briquettes prepared from one
part of cement to three parts by weight of dry standard sand, the briquettes
being of the shape described for the neat cement tests; the mode of gauging,
the filling of the moulds, and the breaking of the briquettes shall also be
similar. The proportion of water used shall be such that the mixture is
thoroughly wetted, and there shall be no superfluous water when the briquettes
are formed. The cement and sand briquettes shall bear the following tensile
stresses :—
7 days from gauging, 150 Ibs.
28 „ „ 250 ,,
The increase from 7 to 28 days shall not be less than 20 per cent.
“ The standard sand referred to is to be obtained from Leighton Buzzard.
Fia. 90.—Needle for Cement
Testing.
It must be thoroughly washed, dried, and
passed through a sieve of 20 by 20 meshes
per square inch, and must be retained on a
sieve of 30 by 30 meshes per square inch,
the wires of the sieves being -0164 inch and
■0108 inch in diameter respectively.
“There shall be three distinct gradations
of setting time, which shall be designated as
Quick, Medium, and Slow.1
“ Quick : The final setting time shall be
not less than ten minutes nor more than
thirty minutes.
“ Medium : The final setting time shall be
not less than half an hour nor more than
two hours.
“Slow : The final setting time shall be
not less than two hours nor more than seven
hours.
“ The temperature of the air in the test-
room at the time of gauging, and of the
water used, shall be between 58 and 64
degrees Fahrenheit.2
“ The cement shall be considered as finally
set when a needle of the form shown in
fig. 90, having a flat end inch square,
weighing in all 2| Ibs., fails to make an
impression when its point is applied gently
to the surface.
“The pats shall be mixed
as previously described.
“The cement shall be tested by the Le Chatelier method, and shall in
1 When a specially slow setting cement is required the minimum time of final setting
shall be specified.
2 Ths limits of temperature are applicable to the British Isles.