Civil Engineering Reference
In-Depth Information
Plasticizer: Type 1, ASTM C 1017. Dosage of 30 g
per kg of cementing materials.
Shrinkage reducer: Dosage of 15 g per kg of cementing
materials.
Strength.
For a standard deviation of 2.0 MPa, the Â
must be the greater of
 = ˘ + 1.34
S
= 40 + 1.34(2) = 42.7
or
 = 0.9 ˘ + 2.33
S
= 36 + 2.33(2) = 40.7
therefore  = 42.7
Water to Cementing Materials Ratio.
Past field records
using these materials indicate that a water to cementing
materials ratio of 0.35 is required to provide a strength
level of 42.7 MPa.
For a deicer environment and to protect embedded
steel from corrosion, Table 9-1 requires a maximum water
to cementing materials ratio of 0.40 and a strength of at
least 35 MPa. For a severe sulfate environment, Table 9-2
requires a maximum water to cementing materials ratio of
0.40 and a strength of at least 35 MPa. Both the water to
cementing materials ratio requirements and strength
requirements are met and exceeded using the above deter-
mined 0.35 water to cementing materials ratio and 40 MPa
design strength.
Air Content.
For a severe exposure, Fig. 9-4 suggests a
target air content of 6% for 19-mm aggregate. Therefore,
design the mix for 5% to 8% and use 8% for batch propor-
tions. The trial batch air content must be within ±0.5 per-
centage points of the maximum allowable air content.
Slump.
Assume a slump of 50 mm without the plasticizer
and a maximum of 200 mm to 250 mm after the plasticizer
is added. Use 250 ± 20 mm for proportioning purposes.
Water Content.
Fig. 9-5 recommends that a 50-mm slump,
air-entrained concrete with 19-mm aggregate should have
a water content of about 168 kg/m
3
. Assume the retarding
water reducer and plasticizer will jointly reduce water
demand by 15% in this case, resulting in an estimated
water demand of 143 kg per cubic meter, while achieving
the 250-mm slump.
Cementing Materials Content.
The amount of cementing
materials is based on the maximum water-cementing
materials ratio and water content. Therefore, 143 kg of
water divided by a water-cementing materials ratio of 0.35
requires a cement content of 409 kg. Fly ash and slag will
be used to help control alkali-silica reactivity and control
temperature rise. Local use has shown that a fly ash
dosage of 15% and a slag dosage of 30% by mass of ce-
menting materials are adequate. Therefore, the suggested
cementing materials for one cubic meter of concrete are
as follows:
Cement:
These dosages meet the requirements of Table 9-8
(2.8% silica fume from the cement + 15% fly ash + 30% slag
= 47.8% which is less than the 50% maximum allowed).
Coarse-Aggregate Content.
The quantity of 19-mm
nominal maximum-size coarse aggregate can be estimated
from Fig. 9-3. The bulk volume of coarse aggregate rec-
ommended when using sand with a fineness modulus of
2.80 is 0.62. Since the coarse aggregate has a bulk density
of 1600 kg/m
3
, the ovendry mass of coarse aggregate for a
cubic meter of concrete is
1600 x 0.62 = 992 kg/m
3
Admixture Content.
For an 8% air content, the air-
entraining admixture manufacturer recommends a dosage
of 0.5 g per kg of cementing materials. The amount of air
entrainer is then
0.5 x 409 = 205 g = 0.205 kg
The retarding water reducer dosage rate is 3 g per kg of
cementing materials. This results in
3 x 409 = 1227 g or 1.227 kg of water reducer per cubic
meter of concrete.
The plasticizer dosage rate is 30 g per kg of cementing
materials. This results in
30 x 409 = 12,270 g or 12.270 kg of plasticizer per cubic
meter of concrete.
The shrinkage reducer dosage rate is 15 g per kg of
cementing materials. This results in
15 x 409 = 6135 g or 6.135 kg of shrinkage reducer per
cubic meter of concrete.
Fine-Aggregate Content.
At this point, the amounts of all
ingredients except the fine aggregate are known. The
volume of fine aggregate is determined by subtracting the
absolute volumes of all known ingredients from 1 cubic
meter. The absolute volumes of the ingredients is calcu-
lated by dividing the known mass of each by the product
of their relative density and the density of water. Assume a
relative density of 1.0 for the chemical admixtures. Assume
a density of water of 997.75 kg/m
3
as all materials in the
laboratory are maintained at a room temperature of 22°C
(Table 9-12). Volumetric computations are as follows:
Water (including
143
=
=
0.143 m
3
chemical
1.0 x 997.75
admixtures)
225
3.14 x 997.75
Cement
=
=
0.072 m
3
61
2.60 x 997.75
Fly ash
=
=
0.024 m
3
123
2.90 x 997.75
Slag
=
=
0.043 m
3
8.0
100
Air
=
=
0.080 m
3
55% of 409 = 225 kg
992
2.68 x 997.75
Coarse aggregate
=
=
0.371 m
3
Fly ash:
15% of 409 = 61 kg
Slag:
30% of 409 = 123 kg
Total
=
0.733 m
3
