Project on Concrete Mix Design for various grades of Concrete
DESIGN MIX FOR M50 GRADE CONCRETE:
A-1 STIPULATIONS FOR PROPORTIONING
a) Grade designation : M50
b) Type of cement : PPC conforming to IS 1489 (Part 1)
c) Maximum nominal size of aggregate : 20 mm
d) Minimum cement content and
maximum water-cement ratio to be adopted and/or : Severe (for reinforced concrete)
Exposure conditions as per Table 3
and Table 5 of IS 456
e) Workability : 75 mm (slump)
f) Method of concrete placing : Chute (Non pumpable)
g) Degree of site control : Good
h) Type of aggregate : Crushed angular aggregate
j) Maximum cement content not including fly ash : 450 kg/m3
k) Chemical admixture type : Superplasticizer - normal
A-2 TEST DATA FOR MATERIALS
a) Cement used : PPC conforming to IS 1489 (Part 1)
b) Specific gravity of cement : 2.88
c) Chemical admixture : Superplasticizer conforming to IS 9103
d) Specific gravity of
1) Coarse aggregate [at saturated surface dry : 2.74
(SSD) Condtion]
2) Fine aggregate [at saturated surface dry : 2.65
(SSD) Condtion]
3) Chemical admixture : 1.145
e) Water absorption
1) Coarse aggregate : 0.5 percent
2) Fine aggregate : 1.0 percent
f) Moisture content of aggregate [As per IS 2386 (Part 3)]
1) Coarse aggregate : Nil
2) Fine aggregate : Nil
A-3 TARGET STRENGTH FOR MIX
PROPORTIONING
f’ck = fck+1.65 S
whichever is higher.
where
f’ck = target average compressive strength at
28 days,
fck = characteristic compressive strength at
28 days,
S = standard deviation, and
From Table 2, standard deviation, S = 5 N/mm2
From Table 1,
Therefore, target strength using both equations, that is,
a) f’ck = fck+1.65 S
= 50+1.65 × 5 = 58.25 N/mm2
The higher value is to be adopted. Therefore, target
strength will be 58.25N/mm2.
A-4 APPROXIMATE AIR CONTENT
From Table 3, the approximate amount of entrapped
air to be expected in normal (non-air-entrained)
concrete is 1.0 percent for 20 mm nominal maximum
size of aggregate.
A-5 SELECTION OF WATER-CEMENT RATIO
From Fig. 1, the free water-cement ratio required for
the target strength of 58.25 N/mm2
is 0.26 for OPC 43
grade curve. (For PPC, the strength corresponding to
OPC 43 grade curve is assumed for the trial). This is
lower than the maximum value of 0.45 prescribed for
‘severe’ exposure for reinforced concrete as per Table 5
of IS 456.
0.26< 0.45, hence O.K.
A-6 SELECTION OF WATER CONTENT
From Table 4, water content = 186 kg (for 50 mm
slump) for 20 mm aggregate.
Estimated water content for 75 mm slump
= 186 + ((3×186)/100)= 191.58 kg
As superplasticizer is used, the water content may be reduced. Based on trial data, the water content reduction of 23 percent is considered while using superplasticizer at the rate 1.0 percent by weight of cement.
Hence the water content
= 191.58 × 0.77
= 147.52 kg => 148 kg
A-7 CALCULATION OF CEMENT CONTENT
Water-cement ratio = 0.26
Cement content =148
0.26 = 569.23 kg/m3 => 570 kg/m3
From Table 5 of IS 456, minimum cement content for
‘severe’ exposure condition = 320 kg/m3
570 kg/m3 > 320 kg/m3, hence, O.K
A-8 PROPORTION OF VOLUME OF COARSE
AGGREGATE AND FINE AGGREGETE
CONTENT
From Table 5, the proportionate volume of coarse
aggregate corresponding to 20 mm size aggregate and fine
aggregate (Zone II) for water-cement ratio of 0.50 = 0.62.
In the present case water-cement ratio is 0.26.
Therefore, volume of coarse aggregate is required to
be increased to decrease the fine aggregate content. As
the water-cement ratio is lower by 0.25, the proportion
of volume of coarse, aggregate is increased by addition of 0.05, 5 times to the water cement ratio (at the rate of 0.01 for every ± 0.05 change in water-
cement ratio).
Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio
of 0.26 = 0.62 + 0.025= 0.645.
Volume of fine aggregate content = 1 – 0.645 = 0.355
A-9 MIX CALCULATIONS
The mix calculations per unit volume of concrete shall be as follows:
a) Total volume = 1 m3
b) Volume of entrapped air in wet concrete = 0.01 m3
c) Volume of cement = ((Mass of cement/Specific gravity of cement)× 1/1000
= ((570/2.88) × 1/1000) = 0.197 m3.
d) Volume of water
= ((Mass of water/Specific gravity of water) × 1/ 1000)
= ((148/1) ×1/100)
= 0.148 m3.
e)Volume of chemical admixture (superplasticizer) (@ 1.0 percentby mass of cementitious material)
=( Mass of chemical admixture / Specific gravity of admixture) × (1/ 1000)
= (4.12 /1.145) × (1/1000)
= 0.0036 m3
g) Volume of all in aggregate = [(a-b)-(c+d+e)]
= [(1-0.01) – (0.197 + 0.148 + 0.0036)]
= 0.641 m3
h) Mass of coarse aggregate = g × Volume of coarse aggregate × Specific gravity of coarse aggregate × 1 000
= 0.641 × 0.645 × 2.74 × 1000
= 1133 kg
j) Mass of fine aggregate
= g × volume of fine aggregate × Specific gravity of fine aggregate × 1 000
= 0.641 × 0.355 × 2.65 × 1000
= 604 kg
A-10 MIX PROPORTIONS FOR TRIAL
Cement = 570 kg/m3
Water =148 kg/m3
Fine aggregate (SSD) = 604 kg/m3
Coarse aggregate (SSD) = 1133 kg/m3
Chemical admixture = 4.12 kg/m3
Free water-cement ratio , = 0.26
Therefore all values are divided by the value of the cement,so that we get the design mix for M50 grade of concrete
=1:1.05:1.98 so the ratio is assumed by 1:1:2.
MIX DESIGN FOR M35 CONCRETE WITH FLY ASH.
B-1 STIPULATIONS FOR PROPORTIONING
a) Grade designation : M35
b) Type of cement : OPC 43 grade conforming to IS 269
c) Type of mineral admixture : Fly ash conforming to IS 3812 (Part1)
d) Maximum nominal size of aggregate : 20 mm
e) Minimum cement content and maximum
water-cement ratio to be adopted : Severe(for reinforced concrete)
and/or
Exposure conditions as per Table 3 and Table 5 of IS 456
f) Workability : 120 mm (slump)
g) Method of concrete placing : Pumping
h) Degree of supervision : Good
j) Type of aggregate : Crushed angular aggregate
k) Maximum cement content (OPC content) : As per IS 456
m) Chemical admixture type : Superplasticizer- normal
B-2 TEST DATA FOR MATERIALS
a) Cement used : OPC 43 grade conforming to IS 269
b) Specific gravity of cement : 3.15
c) Fly ash : Conforming to IS 3812 (Part 1)
d) Specific gravity of fly ash : 2.2
e) Chemical admixture : Superplasticizer conforming to IS 9103
f) Specific gravity of
1) Coarse aggregate (at SSD condition) : 2.74
2) Fine aggregate (at SSD condition) : 2.65
3) Chemical admixture : 1.145
g) Water absorption
1) Coarse aggregate : 0.5 percent
2) Fine aggregate : 1.0 percent
h) The coarse and fine aggregates are wet and their total moisture content is 2 percent and 5 percent
respectively. Therefore, the free moisture content in coarse and fine aggregate shall be as shown in (j)
below
j) Free (surface) moisture
1) Coarse aggregate : Free moisture = Total moisture content – Water absorption
= 2.0 – 0.5 = 1.5 percent
2) Fine aggregate : Free moisture = Total moisture content – Water absorption
= 5.0 – 1.0 = 4.0 percent
B-3 TARGET STRENGTH FOR MIX PROPORTIONING
f’ck = fck + 1.65 S
where
f’ck = target average compressive strength at
28 days,
fck = characteristic compressive strength at
28 days
S = standard deviation, and
From Table 2, standard deviation, S = 5 N/mm2
Therefore, target strength using both equations, that is,
a) f’ck =fck+1.65 S
= 35 + 1.65 × 5 = 43.25 N/mm2
The higher value is to be adopted. Therefore, target
strength will be 43.25 N/mm2
B-4 APPROXIMATE AIR CONTENT
From Table 3, the approximate amount of entrapped
air to be expected in normal (non-air-entrained)
concrete is 1.0 percent for 20 mm nominal maximum
size of aggregate.
B-5 SELECTION OF WATER CEMENT RATIO
From Fig. 1, the free water-cement ratio required for the target strength of 43.25 N/mm2 is 0.33 for OPC 43 grade curve. This is lower than the maximum value of 0.45 prescribed for ‘severe’ exposure for reinforced
concrete as per Table 5 of IS 456.
0.33 < 0.45, hence O.K
B-6 SELECTION OF WAT ER CONTENT
From Table 4, water content = 186 kg (for 50 mm slump) for 20 mm aggregate.
Estimated water content for 120 mm slump (increasing at the rate of 3 percent for every 25 mm slump)
= 186+( 8.2/100) × 186
= 201.25 kg
As superplasticizer is used, the water content may be
reduced.
Based on trial data, the water content reduction of
23 percent is considered while using superplasticizer
at the rate 1.0 percent by weight of cement.
Hence the arrived water content = 201.25 × 0.77
=154.96 kg ≈ 155 kg.
B-7 CALCULATION OF CEMENT CONTENT
Water-cement ratio = 0.36
Cement content =155/0.33
= 469.69 kg/m3 ≈ 470kg/m3
To proportion a mix containing fly ash the following
steps are suggested:
a) Decide the percentage fly ash to be used based
on project requirement and quality of fly ash.
b) In certain situations, increase in cementitious
material content may be warranted. The
decision on increase in cementitious material
content and its percentage may be based on
experience and trials.
NOTE — This illustrative example is with increase of 10 percent
cementitious material content.
Cementitious material content
= 470 × 1.10 = 517 kg/m3
Water content = 155 kg/m3
So, water-cementitious ratio= 155/517
=0.29
Fly ash @ 30 percent of total cementitious material content = 517 × 30 percent = 155.1 ≈ 155 kg/m3
Cement (OPC) = 517 – 155 = 362 kg/m3
From Table 5 of IS 456, minimum cementitious content
for ‘severe’ exposure condition = 320 kg/m3
517 kg/m3 > 320 kg/m3 , hence O.K.
B-8 PROPORTION OF VOLUME OF COARSE
AGGREGATE AND FINE AGGRAGETE
CONTENT
From Table 5, volume of coarse aggregate corresponding
to 20 mm size aggregate and fine aggregate (Zone II)
for water-cement ratio of 0.50 = 0.62.
In the present case water-cementitious ratio is 0.30.
Therefore, volume of coarse aggregate is required to
be increased to decrease the fine aggregate content. As
the water-cement ratio is lower by 0.2, the proportion
of volume of coarse aggregate is increased by 0.1
(at the rate of ± 0.01 for every ± 0.05 change in water cement ratio). Therefore, corrected proportion of
volume of coarse aggregate for the water-cementitious
ratio of 0.30 = 0.62 + 0.1 = 0.72.
For pumpable concrete these values may be reduced
by up to 10 percent. (see 5.5.2). Here, 10 percent
reduction is considered.
Therefore, volume of coarse aggregate = 0.72 × 0.9 = 0.648, say 0.65 m3.
Volume of fine aggregate content = 1 – 0.65 = 0.35 m3
B-9 MIX CALCULATIONS
The mix calculations per unit volume of concrete shall
be as follows:
a) Total volume = 1 m3
b) Volume of entrapped air
in wet concrete = 0.01 m3
c) Volume of cement
= (Mass of cement /Specificgravity of cement )×( 1/1000)
= ( 362/3.15 )×(1/1000)
= 0.114 m3
d) Volume of fly ash = (Mass of fly ash /Specificgravity of fly ash) × (1/1 000)
= (155/2.2)×(1/1000)
= 0.070 m3
e) Volume of water =( Mass of water /Specific gravity of water) × (1/1 000 )
= (155/1)×(1/1000)
= 0.155 m3
f) Volume of chemical admixture (superplasticizer) (@ 1.0 percent by mass of cementitious material)
= (Mass of chemical admixture /Specific gravity of admixture )×(1/1 000)
= (5.17/1.145)×(1/1000)
= 0.004 m3
g) Volume of all in aggregate
= [(a-b)-(c+d+e+f)}]
= (1-0.01)-(0.114 + 0.070+ 0.155+0.004)
= 0.647 m3
h) Mass of coarse aggregate = g × volume of coarse aggregate × Specific gravity of coarse aggregate × 1 000
= 0.647 × 0.65 × 2.74 × 1000
= 1152.3 kg ≈ 1153 kg
j) Mass of fine aggregate = g × Volume of fine aggregate × Specific gravity of fine aggregate × 1 000
= 0.647 × 0.35 × 2.65 × 1000
= 600.01 ≈ 600 kg
B-10 MIX PROPORTIONS
Cement = 362 kg/m3
Fly ash = 155 kg/m3
Water (Net mixing) = 155 kg/m3
Fine aggregate (SSD) = 600 kg/m3
Coarse aggregate (SSD) = 1153 kg/m3
Chemical admixture = 5.17 kg/m3
Free water-cementitious materials ratio = 0.29
NOTE — Aggregates shall be used in saturated surface dry condition. If otherwise, when computing the requirement of mixing water, allowance shall be made for the free (surface) moisture contributed by the fine and coarse aggregates. On the other hand, if the aggregates are dry, the amount of mixing water shall be increased by an amount equal to the moisture likely to be absorbed by the aggregates. Necessary adjustments are also required to be made in mass of aggregates. The surface water and percent water absorption of aggregates shall be determined according to IS 2386 (Part 3).
B-11 ADJUSTMENT ON WATER, FINE AGGREGATE AND COARSE AGGREGATE (IF THE COARSE AND FINE AGGREGATE IS IN WET CONDITION)
a) Fine aggregate (Wet)Mass of wet fine aggregate= mass of fine aggregate in SSD condition ×[1 + Free (surface) moisture /100]
= 600 × (1+4/100)
= 624 kg/m3
b) Coarse aggregate (Wet)
Mass of wet coarse aggregate = mass of coarse aggregate in SSD condition×[1 + Free (surface) moisture /100= 1153 × (1+1.5/100)
= 1170.2 kg/m3 ≈ 1170 kg/m3
The coarse and fine aggregates, being wet, contribute water to the mix to the extent of free moisture over SSD condition. The quantity of this water is required to be subtracted from the calculated water content.
1) Water content contributed by wet coarseaggregate= Mass of wet coarse aggregate – mass of SSD condition coarse aggregate
= 1170 – 1153 = 17 kg
2) Water content contributed by wet fine aggregate = Mass of wet fine aggregate – mass of SSD condition fine aggregate
= 624 – 600 = 24 kg
The requirement for added water becomes :
= 155 - 16 - 29
= 110 kg/m3
B-12 MIX PROPORTIONS AFTER ADUSTMENT
FOR WET AGGREGATES
Cement = 362 kg/m3
Fly ash = 155 kg/m3
Water (to be added) = 110 kg/m3
Fine aggregate (Wet) = 624 kg/m3
Coarse aggregate (Wet) = 1170 kg/m3
Chemical admixture = 4.74 kg/m3
Free water-cementitious materials ratio = 0.33
B-13 mass of coarse aggregate shall be divided into two fractions of 20 – 10 mm and 10 – 4.75 mm, in a suitable ratio, to satisfy the overall grading requirements for 20 mm max size aggregate as per Table 7 of IS 383. In this example, the ratio works out to be 60:40 as shown under B-2 (k).
B-14 The slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump based on trial, if required. The mix proportions shall be reworked for the actual water content and checked for durability requirements.
B-15 Two more trials having variation of ± 10 percent of water-cementitious materials ratio in B-10 shall be carried out and a graph between these water cementitious materials ratios and their corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trials. However, durability requirement shall be met.