EXP NO: DATE:
HIGH STRENGTH CONCRETE
AIM
To prepare the mix design of high strength concrete and to test the properties of the prepared
concrete specimens such as compressive strength, flexural strength and split tensile strength
of the concrete specimens.
I. MIX DESIGN OF HIGH STRENGTH CONCRETE
1. DESIGN STIPULATIONS
Grade designation : M70
Type of cement : OPC 53 grade (IS 269)
Silica fume : Conforming to IS 15388
Maximum nominal size of aggregate : 20 mm
Exposure condition : Severe
Workability : 120 mm (slump)
Type of aggregate : Crushed angular aggregate
Maximum cement (OPC) content : 150 Kg/m3
Chemical admixture type : Superplasticizer
Specific gravity of cement : 3.15
Specific gravity of coarse aggregate in : 2.74
saturated surface dry (SSD) condition
Specific gravity of fine aggregate in : 2.65
saturated surface dry (SSD) condition
Specific gravity of fly ash : 2.20
Specific gravity of silica fume : 2.20
Specific gravity of chemical admixture : 1.08
2. TARGET STRENGTH FOR MIX PROPORTIONING
f’ck = fck + 1.65 S or
f’ck = fck + X; whichever is higher.
f’ck = fck + 1.65 S = 70 + (1.65× 6) = 79.9 N/mm2
f’ck = fck + X = 70 + 8 = 78 N/mm2
Target strength = 79.9 N/mm2
1
3. APPROXIMATE AIR CONTENT
Approximate amount of entrapped air to be expected in normal concrete is 0.5% for 20 mm
nominal maximum size of aggregate.
4. WATER CEMENT RATIO
For target strength of 79.9 N/mm2
Water - cementitious ratio = 0.3
0.3 ¿ 0.45 (maximum value)
Hence it is ok.
5. WATER CONTENT
For 20 mm aggregate water content = 186 Kg/m3 (50 mm slump)
For 120 mm slump
8.4
186 + ( × 186) = 201.62 ≈ 202 Kg/m3
100
When superplasticizers are used, water content is reduced by 20%.
Water content = 202 x 0.79 = 160.89 Kg/m3
6. CEMENT CONTENT
Water cement ratio = 0.23
Water content = 160.89 Kg/m3
160.89
Cement content = = 536.3 Kg/m3
0.3
Cementitious material content (10% increase) = 536.3 x 1.10 = 590 Kg/m3
Fly ash at 15% by weight of cementitious material = 590 x 15% = 88.5 Kg/m3
Silica fume at 5% by weight of revised cementitious material = 590 x 5% = 29.5 Kg/m 3
Cement content = 590 – 29.5 – 88.5 = 470 Kg/m3
160.89
Revised water cement ratio = = 0.272
5 90
2
Minimum cementitious material content 320 Kg/m3 ¿590 Kg/m3; hence it is ok.
7. PROPORTION OF VOLUME OF COARSE AGGREGATE AND FINE
AGGREGATE CONTENT
20 mm size aggregate, fine aggregate grading zone II
volume of coarse aggregate / volume of total aggregate = 0.66
water / cement = 0.272 ratio = 0.667
volume of fine aggregate = 1 – 0.667 = 0.34 per unit volume of total aggregate.
8. MIX CALCULATIONS
a. Total volume = 1 m3
b. Volume of entrapped air in wet = 0.005 m3
concrete
c. Volume of cement 4 70 1
= x = 0.1492 m3
3.15 1000
d. Volume of water 160.89 1
= x = 0.160 m3
1 1000
e. Volume of silica fume 2 9.5 1
= x = 0.0134 m3
2.2 1000
f. Volume of fly ash 8 8.5 1
= x = 0.04 m3
2.2 1000
g. Volume of chemical admixture at 5 90 X 0.5 % 1
= x = 0.00382 m3
1.08 1000
5% by mass of cementitious material
h. Volume of all in aggregate = [(a – b) – (c+d+e+f+g)] = 0.628 m3
i. Mass of coarse aggregate = h x volume of coarse aggregate x specific
gravity of coarse aggregate x 1000 =
0.628 x 0.66 x 2.74 x 1000 = 1135.675 ≈
1136 Kg
j. Mass of fine aggregate h x volume of fine aggregate x specific
gravity of fine aggregate x 1000 = 0.628 x
0.334 x 2.65 x 1000 = 565.82 Kg ≈ 566 Kg
3
9. MIX PROPORTION
i. Cement = 470 Kg/m3
ii. Fly ash = 88.5 Kg
iii. Silica fume = 29.5 Kg/m3
iv. Water = 160.89 Kg/m3
v. Fine aggregate = 566 Kg/m3
vi. Coarse aggregate = 1136 Kg/m3
vii. Chemical admixture = 4.13 Kg/m3
viii. Water cement ratio = 0272
10. VOLUME
2 cube = 0.15 x 0.15 x 0.15 x 2 = 6.75 x 10-3
1 beam = 0.1 x 0.1 x 0.5 = 5 x 10-3
Total volume = 11.75 x 10-3
cement = 6.624 Kg
Fly ash = 1.246 Kg
Silica = 0.4152 Kg
Water = 2.268 Kg
Fine aggregate = 8.3 Kg
Coarse aggregate 20 mm aggregate = 9.61 Kg
12 mm aggregate = 6.406 Kg
Chemical admixture = 58.2 g
