26-06-2013, 01:05 PM
Measurement of Rate of Absorption of Water by Hydraulic- Cement Concretes
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Scope
This test method is used to determine the rate of
absorption (sorptivity) of water by hydraulic cement concrete
by measuring the increase in the mass of a specimen resulting
from absorption of water as a function of time when only one
surface of the specimen is exposed to water. The specimen is
conditioned in an environment at a standard relative humidity
to induce a consistent moisture condition in the capillary pore
system. The exposed surface of the specimen is immersed in
water and water ingress of unsaturated concrete is dominated
by capillary suction during initial contact with water.
Significance and Use
The performance of concrete subjected to many aggressive
environments is a function, to a large extent, of the
penetrability of the pore system. In unsaturated concrete, the
rate of ingress of water or other liquids is largely controlled by
absorption due to capillary rise. This test method is based on
that developed by Hall3 who called the phenomenon “water
sorptivity.”
4The water absorption of a concrete surface depends on
many factors including: (a) concrete mixture proportions; (b)
the presence of chemical admixtures and supplementary cementitious
materials; © the composition and physical characteristics
of the cementitious component and of the aggregates;
(d) the entrained air content; (e) the type and duration of
curing; (f) the degree of hydration or age; (g) the presence of
microcracks; (h) the presence of surface treatments such as
sealers or form oil; and (i) placement method including
consolidation and finishing. Water absorption is also strongly
affected by the moisture condition of the concrete at the time of
testing.
Sample Conditioning
Place test specimens in the environmental chamber at a
temperature of 50 6 2°C and RH of 80 6 3 % for 3 days.
Alternatively, place test specimens in a dessicator inside an
oven at a temperature of 50 6 2°C for 3 days. If the dessicator
is used, control the relative humidity in the dessicator with a
saturated solution of potassium bromide (see 5.7), but do not
allow test specimens to contact the solution.
NOTE 3—To control the RH using the potassium bromide solution, the
solution should be placed in the bottom of the dessicator, to ensure the
largest surface of evaporation possible.