Civil Engineering Reference
In-Depth Information
The gradation of the fine aggregates is defined by the fineness modulus.
The desirable fineness modulus depends on the coarse aggregate size and
the quantity of cement paste. A low fineness modulus is desired for mixes
with low cement content to promote workability.
Once the fineness modulus of the fine aggregate and the maximum
size of the coarse aggregate are determined, the volume of coarse aggregate
per unit volume of concrete is determined using Table 7.5. For example,
if the fineness modulus of the fine aggregate is 2.60 and the maximum ag-
gregate size is 25 mm (1 in.), the coarse aggregate will have a volume of
of concrete. Table 7.5 is based on the unit weight of ag-
gregates in a dry-rodded condition (ASTM C29). The values given are
based on experience in producing an average degree of workability. The
volume of coarse aggregate can be increased by 10% when less workabil-
ity is required, such as in pavement construction. The volume of coarse
aggregate should be reduced by 10% to increase workability, for example
to allow placement by pumping.
0.69 m
3
/m
3
yd
3
/yd
3
1
2
4. Air Entrainment Requirements
Next, the need for air entrainment is evaluat-
ed. Air entrainment is required whenever concrete is exposed to freeze-thaw
conditions and deicing salts. Air entrainment is also used for workability in
some situations. The amount of air required varies based on exposure conditions
T ABLE 7.5
Bulk Volume of Coarse Aggregate per Unit Volume
of Concrete*
Nominal Maximum
Bulk Volume of Dry-Rodded Coarse Aggregate
Size of Aggregate,
Per Unit Volume of Concrete for Different
mm (in.)
Fineness Moduli of Fine Aggregate**
Fineness Modulus
2.40
2.60
2.80
3.00
9.5 (3/8)
0.50
0.48
0.46
0.44
1
2
12.5
1
2
0.59
0.57
0.55
0.53
3
4
19
1
2
0.66
0.64
0.62
0.60
25 (1)
0.71
0.69
0.67
0.65
1
1
37.5
1
2
0.75
0.73
0.71
0.69
2
50 (2)
0.78
0.76
0.74
0.72
75 (3)
0.82
0.80
0.78
0.76
150 (6)
0.87
0.85
0.83
0.81
*American Concrete Institute (ACI 211.1).
**Bulk volumes are based on aggregates in a dry-rodded condition as described
in ASTM C29 (AASHTO T19).
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