The proper method for learning mix design for civil engineers

1. AMERICAN METHOD FOR MIX
DESIGNING

2. INTRODUCTION
 In 1991 the American concrete institute (ACI)
published guideline for normal, heavy weight
and mass concrete mix design.
 it describe by the ACI committee 211 is
presented.

3. BASIC CONSIDERATION
The following point must be considered while
designing the concrete mixes
Cost
Specification
Workability
Strength and durability

4. ACI 211
A properly proportioned concrete mix should
posses these qualities.
Acceptable workability of freshly mixed
concrete
Durability, strength and uniform appearance
of the hardened concrete
The concrete should be economical

5. DATA REQUIRED
1. Class of concrete to be designed.
2. Fine aggregate:
a) Specific gravity
b) Fineness modulus
3. Coarse aggregate:
a) Maximum size aggregate
b) Specific gravity
c) Unit weight

6. 4. From code specification:
a) Cement factor (minimum cement content )
b) w/c ratio
c) Air content
d) Nominal maximum size of aggregate.

7. STEPS FOR PROCEDURE
The standard ACI mix design procedure can be explained
in the following 9 steps.
1. Compressive strength.
2. w/c ratio
3. Air content selection.
4. Choice of slump.
5. Water content selection.
6. Cement content.
7. Coarse aggregate content.
8. Fine aggregate content.
9. Adjustment for aggregate moisture.

8. 1. Compressive strength (average compressive
strength) fcr the required target at 28 days for
mix design is determined by adding up an
empirical factor `K` to the design compressive
strength fc as per given equation:
fcr= =fc +k
2. The water cement ratio is relate with
strength and durability of concrete. Lower the
water cement ratio higher the durability of
concrete and is selected base on the target and
the type of concrete (air entrained or non air
entrained )

10. 3. Mainly attributes to the workability of the
concrete which depends upon ease of mixing,
placing, compaction and finishing.

11. 4. Air content as percentage of the concrete volume
is estimated depending upon the air entrained or non
entrained type of concrete exposures condition. Air
content for air entrained concrete are normally
specified but can also be determined by exposure
conditions based on table.
5. Water content is determined based on the NMSA,
type of concrete (air entrained or non air entrained ),
and specified slump. Then it is adjusted for the type
of aggregates.

13. 6. Cement content is calculated based
on the w/c ratio and the water
content.
 cement content =recommended
water content /recommended w/c
ratio
As according to the above table….

14. 7. Coarse aggregate content ACI recommends
the percentage (by unit volume).
 coarse aggregate based on nominal
maximum aggregate size.
 fine aggregate fineness modulus.

15. 8. Fine aggregate (fa) is calculating by
subtracting the absolute volume of the
known ingredients from unit volume of the
fresh concrete (1m^3) as following:
Fa=1-x
Where X= sum of all other ingredients( air,
water, cement and coarse aggregate) in cubic
meter.
Weight of FA=volume of FA x specific gravity of
FA.

16. 9. Finally water content is adjusted based on
the absorption and the current moisture content
of coarse and fine aggregates, in the account of
SSD condition of the aggregates. This is done
because moisture in aggregate affects the
aggregate weight and the amount of mixing
water.

17. CONCLUSION
Checked and adjusted by means of laboratory
trail and consisting of small batches.
Concrete Should be tested for slump
Workability
Air content
Should be tested for the strength at the
specified age.