97
OF ENGINEERING FORMULÆ.
Portland Cement.
Conclusions derived from Mr. Grant's Experiments.
1. Portland cement improves by age, if kept
from moisture.
2. The longer it is in setting the stronger it
will be.
3. At the end of a year, 1 of cement to 1 sand
is about f ths the strength of neat cement; 1 to 2
about i strength ; 1 to 8 about |rd; 1 to 4, |th ;
1 to 5 about ith.
4. The cleaner and sharper the sand the greater
the strength.
5. Strong cement is heavy ; blue grey, slow-set-
ting. Quick-setting cement has generally too much
clay in its composition—is brownish and weak.
6. The less water used in mixing up the cement
the better.
7. Bricks, stones, &c., used with cement should
be well soaked.
8. Cement setting under still water will be
stronger than if kept dry.
9. Blocks of brickwork or concrete should be
kept in water until required for use.
10. Salt-water is as good as fresh for mixing
cement.
11. Bricks of neat Portland cement are equal
to Blue bricks, Bramley-Fall stone, or Yorkshire
landings (in a few months).
12. Bricks of 1 cement to 4 or 5 of sand are
equal to picked stock bricks.
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