10 
BULLETIX 532, U. S. DEPARTMENT OF AGRICULTURE. 
GRAVEL CONCRETE WITH HYDRATED LIME, STORED IN AIR. 
Curve 557 on figure 8 shows the contraction of a 1:2:4 gravel concrete 
specimen in which 15 per cent of hydrated lime was substituted for cement. 
This specimen was cured indoors and allowed to dry out immediately after 
molding. Here again, as in the case of the ordi- 
nary concrete specimens, we have a progressive 
contraction, the maximum amount being about 
0.00045 inch. This is somewhat less than in the 
specimen untreated with hydrated lime. As but 
one specimen was measured, no claim can be 
made that the hydrated lime aided in decreasing 
the contraction. 
TAR-COATED SPECIMEN. 
It is reasonable to expect that any application 
of more or less waterproof material to the sur- 
face of the concrete will greatly retard the ab- 
sorption of moisture, or. if the concrete be 
already wet, will prevent it from drying out 
rapidly. In order to determine the effect of 
such a coating on the change in length of con- 
crete, a mixture of 1:2:4 concrete, having a 
crushed gneiss aggregate, was prepared, and 
measurements were started two days after 
pouring. It was then immersed in water and 
the measurements continued. At the - end of 13 
days the specimen was removed from water and, 
after surface drying for one day, a hot applica- 
tion of vertical retort tar was made. Note that 
after 13 days' expansion continued slightly, al- 
though the specimen had been removed from 
the water and coated with tar, while at the end 
of about 30 days this expansion ceased and a 
slight contraction began. However, the speci- 
men was still somewhat expanded up to the 
end of 150 days, after which it contracted very 
slowly. The tar coating evidently served to re- 
tain the moisture in the concrete for a con- 
siderable length of time and thus kept it ex- 
panded. 
REINFORCED CONCRETE SPECIMENS. 
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Four specimens were made up of 1 : 2 : 4 gravel 
concrete containing 0.61 per cent, 1.2 per cent, 
and 1.8 per cent of steel. These specimens were 
allowed to dry out in the air of the laboratory, 
and measurements were taken at frequent in- 
tervals. The plain gravel specimens showed a 
maximum contraction of only 0.035 per cent at 
the ago of months, as compared with 0.06 per 
cenl I'm- the crushed gneiss specimens previously reported. This difference in 
contraction is not due necessarily to the different aggregates. The specimens 
containing 0.61 and 1.2 per cent steel showed a contraction of only 0.02 per cent, 
N0i±vwaod3O nKin 
