2. Definitions
Selection of concrete proportions involves
a balance between economy and
requirements for placeability, strength,
durability, density, and appearance.
3. Placeability
Placeability is simply the traits that the wet
or plastic concrete has that allow it to be
placed and finished.
Placeability includes a mix that doesn't
segregate but that can be consolidated.
The ability to be pumped is another
consideration.
The classic way to measure placeability is
slump.
4. The purposes of design:
To achieve the stipulated minimum
strength and durability
To make the concrete in the most
economical manner
5. Methods of proportioning
Arbitrary proportion
Fineness modulus method
Maximum density method
Surface area method
Indian Road Congress, IRC 44 method
High strength concrete mix design
Mix design based on flexural strength
Road note No. 4 (grading curve method)
ACI Committee 211 methodACI Committee 211 method
DOE methodDOE method
Mix design for pumpable concrete
Indian standard recommended method IS 10262-82
6. Example
Design a concrete mix (using DOE
method) for a reinforced concrete work.
The concrete is to be designed for a mean
compressive strength of 45MPa at the age
28 days with 65mm slump. Maximum size
of aggregate is 20mm uncrushed
aggregate will be used. Sieve analysis
shows that 50% passes trough 600µm
sieve. Bulk specific gravity of aggregate is
found to be 2.65.
7. Step 1
find all the information from the question
Mean compressive strength
Type of cement used
Slump required
Max size of aggregates
Type of aggregates
Sieve analysis of fine aggregates
Bulk specific gravity of aggregates
Exposure / special conditions needed
Special materials used e.g.: fly ash.
8. Step 2
calculate the water/cement ratio. This is done in a rather
round about method, using table 1 and figure 1
Table 1 gives the approximate compressive strength of
concretes made with free w/c ratio of 0.50.
Using this table find out the 28 days strength for the
approximate type of cement and types of C.A (course
aggregate)
Mark a point on the “Y” axis in fig 1 equal to the
compressive strength read from table 1 which is at ratio
of 0.50. through this intersection point, draw parallel
dotted curve nearest to the intersection point. Using this
new curve, we read off the w/c ratio as against target
mean strength.
9. Step 3
Decide water content for the required
workability, expressed in terms of slump,
taking into consideration the size of
aggregate and its type from table 2.
10. Step 4
find the cement content knowing the w/c
ratio and water content.
Water content / (w/c ratio) = cement
content
11. Step 5
Find out the density of fresh concrete from
fig 2
The wet density : ________kg/m3
Next, find the weight of total aggregate
Next, find the percentage of fine
aggregate from fig 3 (b)
Lastly, find out the weight of fine and
course aggregates
12. Table 1: Approximate Compressive Strength Of Concrete Made with a
free water/cement ratio of 0.50. According to the 1988 British Method
Type of
cement
Type of
coarse
aggregate
Compressive strength at the age (cube) of days
( N/mm2
)
3 days 7 days 28 days 91 days
Ordinary
Portland
cement
(OPC) or
Sulphate
Resisting
Portland
(SRPC)
Uncrushed
Crushed
22
27
30
36
42
49
49
56
Rapid
Hardening
Portland
Uncrushed
Crushed
29
34
37
43
48
55
54
61
13. Table 2: Approximate Free Water Contents Required to Give Various
Levels of Workability According to 1988 British Method
Slump (mm)
V-B (s)
Very low
0 – 10
> 12
Low
10 – 30
6 - 12
Medium
30 – 60
3 - 6
High
60 – 180
0 - 3
1. Water content:
Maximum size of
aggregate (mm)
Type of aggregate
10 Uncrushed
Crushed
150
180
180
205
205
230
225
250
20 Uncrushed
Crushed
135
170
160
190
180
210
195
225
40 Uncrushed
Crushed
115
155
140
175
160
190
175
205
2. Reduction in water content when fly ash is used:
Percentage of fly ash in cementitious
material
Reduction in water content, kg/m3
10 5 5 5 10
20 10 10 10 15
30 15 15 20 20
40 20 20 25 25
50 25 25 30 30
14. Table 3: Requirements of BS 8110:Part I:1985 to Ensure Durability
Under Specified Exposure Conditions of Reinforced and Prestressed
Concrete Made With Normal Weight Aggregate.
Condition of
exposure
Nominal cover of concrete in mm
Mild
Moderate
Severe
Very severe
Extreme
25
-
-
-
-
20
35
-
-
-
20
30
40
50
-
20
25
30
40
60
20
20
25
30
50
Maximum
water/cement
itious
material
ratio
0.65 0.60 0.55 0.50 0.45
Minimum
content of
cementitious
material in
kg/m3
275 300 325 350 400
Minimum
grade MPa 30 35 40 45 50
15. Figure 1: Relation between compressive strength and free
water/cement ratio for use in the British mix design method.
