CE-106, Mix Design, Types of Cracks and Transportation of Concrete
CE-106, Mix Design, Types of Cracks and Transportation of Concrete
CE-106, Mix Design, Types of Cracks and Transportation of Concrete
However, a minimum cement content is required to ensure good
finishability, workability, and strength.
ACI Mix Design Procedure
7. Estimation of Coarse Aggregate Content
The percent of coarse aggregate to concrete for a given maximum size
and fineness modulus is given by Table 4.
The value from the table multiplied by the dry-rodded unit weight (the
oven-dry (OD) weight of coarse aggregate required per cubic foot of
concrete).
To convert from OD to saturated surface dry (SSD) weights, multiply by
[1 + absorption capacity (AC)].
ACI Mix Design Procedure
7. Estimation of Coarse Aggregate Content
The following graph can also be used for determining the required
volume of coarse aggregates.
ACI Mix Design Procedure
8. Estimation of Fine Aggregate Content
There are two standard methods to establish the fine aggregate content,
the mass method and the volume method. We will use the "volume"
method.
The volume of fine aggregates is found by subtracting the volume of
cement, water, air, and coarse aggregate from the total concrete
volume.
ACI Mix Design Procedure
9. Adjustment of Moisture Content
ACI Mix Design Procedure
10. Trial Batch
Using the proportions developed in the preceding steps, mix a trial
batch of concrete using only as much water as is needed to reach the
desired slump (but not exceeding the permissible w/c ratio).
The fresh concrete should be tested for slump, unit weight, yield, air
content, and its tendencies to segregate, bleed, and finishing
characteristics. Also, hardened samples should be tested for compressive
and flexural strength.
ACI Mix Design Example
Concrete is required for an exterior column located above
ground where substantial freezing and thawing may occur. The
28-day compressive strength should be 5,000 lb./in
2
. The
slump should be between 1 and 2 in. and the maximum
aggregate size should not exceed in.
The properties of the materials are as follows:
Cement : Type I, specific gravity = 3.15
Coarse Aggregate: Bulk specific gravity (SSD) = 2.70; absorption
capacity = 1%; dry-rodded unit weight = 100 lb./ft
3
; surface moisture
= 0%
Fine Aggregate: Bulk specific gravity (SSD) = 2.65; absorption
capacity = 1.3%; fineness modulus = 2.70; surface moisture = 3%
ACI Mix Design Example
1. Required material information
Already given
2. Choice of Slump
The slump is given ( 1 to 2 inches)
3. Maximum Aggregate Size
Given: inches
ACI Mix Design Example
4. Estimation of Mixing Water and Air Content
Since freezing and thawing is important, the concrete must be air-
entrained. From Table 2, the recommended air content is 6%; the water
requirement is 280 lb/yd
3
ACI Mix Design Example
5. Water Cement Ratio
Water/cement ratio. From Table3, the estimate for required w/c ratio to
give a 28-day strength of 5,000 psi.
ACI Mix Design Example
6. Calculation of Cement Content
Calculation of cement content. Based on steps 4 and 5, the required
cement content is:
wcigt o Ccmcnt =
280
lb
]t
3
,
0.40
= 7uu
Ib
]t
3 ,
7. Estimation of Coarse Aggregate Content
Using Table 4 for the fineness modulus of the fine aggregate of 2.70
ACI Mix Design Example
7. Estimation of Coarse Aggregates (Continued)
The coarse aggregates will occupy: 0.63 27 ft
3
/yd
3
= 17.01 ft
3
/yd
3
The OD weight of coarse aggregates: 17.01 ft
3
/yd
3
100 lb/ft
3
=
1,701 ft
3
/yd
3
8. Estimation of Fine Aggregates Content by the Absolute
Volume Method
Water: 280 lb/62.4 lb/ft
3
= 4.49 ft
3
Cement: 700 lb/(3.15 x 62.4 lb/ft
3
) = 3.56 ft
3
Coarse Aggregate: 1701 lb/(2.70 x 62.4 lb/ft
3
) = 10.10 ft
3
Air: 6% x 27ft
3
/yd
3
= 1.62 ft
3
Total 19.77 ft
3
ACI Mix Design Example
8. Estimation of Fine Aggregates Content by the Absolute
Volume Method (Continued)
Therefore, the fine aggregate must occupy a volume of:
= 27 ft
3
19.77 ft
3
= 7.23 ft
3
The oven dry (OD) weight of the fine aggregate is:
= 7.23 ft
3
2.65 62.4 lb/ft
3
= 1,196 lbs.
9. Adjustment for Moisture in Aggregates
Since the moisture level of the fine aggregate in our storage bins can
vary, we will apply a simple rule to adjust the water required.
Decrease the amount of water required by surface moisture content of the
weight of the fine aggregate.
Increase the amount of aggregate by the amount equal to the surface
moisture. (Refer to Concrete Technology, Neville, 2
nd
Edition)
ACI Mix Design Example
Estimated Batch Weights per yd3 (After adjustment of M.C.)
Water = 244 lb.
Cement = 700 lb.
Coarse aggregate = 1,718 lb.
Fine aggregate (wet) = 1,247 lb.
Total = 3,909 lb/yd
3
= 144.8 lb/ft
3
Questions and Discussion