Civil Engineering Reference
In-Depth Information
12.5
50
2.5
Non-air-entrained concrete
Specimens: 25 x 150-mm (1 x 6-in.)
mortar disks
Pressure: 140 kPa (20 psi)
Non-air-entrained concrete
Specimens: 100 x 200-mm (4 x 8-in.) cylinders
Water pressure: 20 MPa (3000 psi)
10.0
2.0
40
Curing:
7.5
1.5
1 day moist, 90 days
in air
7 days moist, 90
days in air
30
w/c ratio: 0.80
5.0
1.0
w/c ratio: 0.64
20
2.5
0.5
w/c ratio: 0.50
0.0
0.0
10
0
7
14
21
28
Period of moist curing and age at test, days
Fig. 1-20. Effect of water-cement ratio (w/c) and curing
duration on permeability of mortar. Note that leakage is
reduced as the water-cement ratio is decreased and the
curing period increased (
McMillan and Lyse 1929
and PCA
Major Series 227).
0
0.3
0.4
0.5
0.6
0.7
0.8
Water-cement ratio, by mass
Fig. 1-19. Relationship between hydraulic (water) perme-
ability, water-cement ratio, and initial curing on concrete
specimens (
Whiting 1989
).
4000
Air content
2%
4%
6%
and subjected to 20 MPa (3000 psi) of water pressure is
illustrated in Fig. 1-19. Although permeability values
would be different for other liquids and gases, the relation-
ship between water-cement ratio, curing period, and
permeability would be similar.
Test results obtained by subjecting 25-mm (1-in.) thick
non-air-entrained mortar disks to 140-kPa (20-psi) water
pressure are given in Fig. 1-20. In these tests, there was no
water leakage through mortar disks that had a water-
cement ratio of 0.50 by weight or less and were moist-cured
for seven days. Where leakage occurred, it was greater in
mortar disks made with high water-cement ratios. Also, for
each water-cement ratio, leakage was less as the length of
the moist-curing period increased. In disks with a water-
cement ratio of 0.80, the mortar still permitted leakage after
being moist-cured for one month. These results clearly
show that a low water-cement ratio and a reasonable
period of moist curing significantly reduce permeability.
Fig. 1-21 illustrates the effect of different water to ce-
ment ratios on concrete's resistance to chloride ion penetra-
tion as indicated by electrical conductance. The total charge
in coulombs was significantly reduced with a low water to
cement ratio. Also, the results showed that a lower charge
passed when the concrete contained a higher air content.
A low water-cement ratio also reduces segregation and
bleeding, further contributing to watertightness. Of course
watertight concrete must also be free from cracks, honey-
comb, or other large visible voids.
Occasionally, pervious concrete—no-fines concrete
that readily allows passage of water—is designed for
special applications. In these concretes, the fine aggregate is
3000
2000
1000
ASTM C 1202
0
0.2
0.3
0.4
0.5
Water to cement ratio
Fig. 1-21. Total charge at the end of the rapid chloride
permeability test as a function of water to cement ratio
(
Pinto and Hover 2001
).
greatly reduced or completely removed, producing a high
volume of air voids. Pervious concrete has been used in
tennis courts, pavements, parking lots, greenhouses, and
drainage structures. Pervious concrete has also been used
in buildings because of its thermal insulation properties.
Abrasion Resistance
Floors, pavements, and hydraulic structures are subjected
to abrasion; therefore, in these applications concrete must
have a high abrasion resistance. Test results indicate that
abrasion resistance is closely related to the compressive
strength of concrete. Strong concrete has more resistance to
