Civil Engineering Reference
In-Depth Information
Table 3-7. Frost and Deicer-Scaling Resistance of Fly Ash Concrete
Results at 300 cycles
Frost resistance in water,
Deicer scaling resistance,
Fly ash mixtures*
ASTM C 666 Method A (AASHTO T 161)
ASTM C 672**
Class of
Expansion,
Mass loss,
Durability
Water
Curing
Identification
fly ash
%
%
factor
cure
compound
A
C
0.010
1.8
105
3
2
B
F
0.001
1.2
107
2
2
C
F
0.005
1.0
104
3
3
D
F
0.006
1.3
98
3
3
E
F
0.003
4.8
99
3
2
F
C
0.004
1.8
99
2
2
G
C
0.008
1.0
102
2
2
H
F
0.006
1.2
104
3
2
I
C
0.004
1.7
99
3
2
J
F
0.004
1.0
100
3
2
Average of:
Class C
0.006
1.6
101
3
2
Class F
0.004
1.8
102
3
2
Control mixture
0.002
2.5
101
2
2
* Concrete mixtures had a cementitious materials content of 307 kg/m
3
(517
lbs/yd
3
), a water to cementitious materials ratio of 0.40 to 0.45, a target air
content of 5% to 7%, and a slump of 75 mm to 100 mm (3 in. to 4 in.). Fly
ash dosage was 25% by mass of cementitious material.
Gebler and Klieger 1986a
.
** Scale rating (see at right)
0 = No scaling
1 = Slight scaling
2 = Slight to moderate scaling
3 = Moderate scaling
4 = Moderate to severe scaling
5 = Severe scaling
(2718)
(564 lb/yd
3
) of cementitious material and a maximum
water to cementitious materials ratio of 0.45 is recom-
mended. A satisfactory air-void system is also critical.
The importance of using a low water-cement ratio for
scale resistance is demonstrated in Fig. 3-19. The effect of
high fly ash dosages and low cementing material contents
is demonstrated in Fig. 3-20. The performance of scale-
resistant concretes containing fly ash at a dosage of 25% of
cementing material by mass is presented in Table 3-7. The
table demonstrates that well designed, placed and cured
concretes with and without fly ash can be equally resistant
to deicer scaling.
The ACI 318 building code states that the maximum
dosage of fly ash, slag, and silica fume should be 25%, 50%,
and 10% by mass of cementing materials, respectively for
deicer exposures. Total supplementary cementing materi-
als should not exceed 50% of the cementitious material.
Dosages less than or higher than these limits have been
shown to be durable in some cases and not in others.
Different materials respond differently in different envi-
ronments. The selection of materials and dosages should
be based on local experience and the durability should be
demonstrated by field or laboratory performance.
5
ASTM C 672
4
3
2
Drying Shrinkage and Creep
1
Moist cure
0
When used in low to moderate amounts, the effect of fly
ash, ground granulated blast-furnace slag, calcined clay,
calcined shale, and silica fume on the drying shrinkage and
creep of concrete is generally small and of little practical
significance. Some studies indicate that silica fume may
reduce creep (
Burg and Ost 1994
).
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
Water to portland cement ratio
Fig. 3-19. Relationship between deicer-scaling resistance
and water to portland cement ratio for several air-entrained
concretes with and without fly ash. A scale rating of 0 is no
scaling and 5 is severe scaling (
Whiting 1989
).
