Project on Concrete Mix Design for various grades of Concrete
PROJECT ON CONCRETE MIX DESIGN FOR VARIOUS GRADES OF CONCRETE
AIM
- To design a mix proportion for concrete of Grade M35 along with the addition of mineral admixture, Fly Ash.
- To calculate the concrete mix design proportion of Grade M50 without the addition of a mineral admixture.
INTRODUCTION
Concrete mix design involves a process of preparation in which a mix of ingredients creates the required strength and durability for the concrete structure. Because every ingredient in the mix consists of different properties, it’s not an easy task to create a great concrete mix. It is imperative that all ingredients be tested to determine their physical properties and the bearing capacity of the project location.
The ingredients to be tested: water, fine aggregate (sand), coarse aggregate, cement, chemicals.
The values of the physical properties obtained after testing will be used as the basis for all concrete mix design considerations.
The requirement of the assignment is to produce two individual concrete mix designs of M35 (with Fly Ash) and M50 grade concrete. A minimum of 35N/mm^2 and 50 N/mm^2 compressive strength of concrete is to be achieved at the 28-day. The guidelines for the process will be in accordance with the Indian Standard codal provisions of IS 10262:2009; IS 456:2000; IS 8112:1989; IS 383:2016. The initial data for the mix design is assumed by the designer in accordance with the codal provisions. The obtained mix proportion will be considered as a first trial value and may be subjected to revision upon compression test results. test.
PROCEDURE
PART 1: M35 GRADE CONCRETE MIX DESIGN WITH FLY ASH
I. Stipulations for proportioning
| a) | Grade | : M50 |
| b) | Type of Cement | : OPC Grade 43 conforming to IS 8112 |
| c) | maximum nominal size of aggregate | : 20 mm |
| d) | Minimum cement content | : 320 kg/m^3 (Table5, IS 456:2000) |
| e) | Maximum water-cement(w/c) ratio | : 0.45 (Table 5, IS 456:2000) |
| f) | Workability | : 100 mm (slump value for pumpable concrete) |
| g) | Exposure | : Severe |
| h) | Method of Placing | : Pumping |
| i) | Degree of supervision | : Good |
| j) | Type of aggregate | : Crushed angular aggregate |
| k) | Maximum cement content | : 450 kg/m^3 |
| l) | Chemical admixture type | : Superplasticizer |
| m) | Type of mineral admixture | : Fly Ash conforming to IS 3812 (Part1) |
II. Test data for materials
| a) | Cement used | : OPC 43 grade conforming to IS 8112:1989 |
| b) | Specific gravity of cement | : 3.15 |
| c) | Chemical admixture | : Superplasticizer |
| d) | Specific gravity of Coarse aggregate (CA) | : 2.74 |
| e) | Specific gravity of Fine aggregate (FA) | : 2.74 |
| f) | Water absorption of CA | : 0.5% |
| g) | Water absorption | : 1.0% |
| h) | Free surface moisture of CA and FA | : NIL |
| i) | Sieve Analysis of CA | : Table 2 of IS 383:2016 |
| j) | Sieve Analysis of FA | : Conforming to grading zone I of Table 4 of IS 383:2016 |
III. Target strength
f'ck = fck + 1.65 S
- f’ck = target average compressive strength at 28 days
- fck = characteristics compressive strength at 28 days, and
- s = standard deviation
From Table 1 of IS 10262:2009, Standard deviation, S= 5N/mm^2
Therefore, f'ck = 35 + (1.65x5) = 43.25 N/mm^2
IV. Selection of water content
From Table 5 of IS 456:2000,
for severe exposure, maximum w/c ratio =0.45
Based on experience, adopted w/c ratio =0.4
0.4<0.45, hence OK.
V. Selection of water content
From Table 2 of IS 10262:2009,
Maximum water content for 20mm aggregate = 186 liters for a slump value of 25mm to 50 mm.
For every 25 mm increase in slump value, an additional 3% increase in water content is taken.
hence, for a slump value of 100 mm, water content = 186 x 1.06 = 197 liters.
As superplasticizer is used, the water content can be reduced up to 20% and above. Based on trials, up to 29% water reduction can be taken.
hence the Water content = 197 x 0.71 = 140 liters.
VI. Calculation of cement content and Fy Ash Required
w/c ratio =0.4
Total Cementitious material (Cement + Fly AshCement) content = 140/0.4 = 350 kg/m^3
The percentage of Fly Ash needs to be decided based on the project requirement and quality of materials.
In some cases, an increase in the cementitious material can be warranted. An increase in cementitious material content and its percentage may be based on experience and trial.
Assuming an increase of 10%,
Cementitious Material content= 350 x 1.1 = 385 kg/m^3
From table 5 of IS 456:2000, the Minimum cement content for severe exposure is 320 kg/m^3
350>320. Hence OK.
Water content= 140 kg/m^3
Water-Cement ratio = 140/385 = 0.364
Flyash is taken as 30% of total cementitious material content =385 x 0.3 = 115 kg/m^3
Cement content(OPC)= 385-115= 270 kg/m^3
Cement content saved while using Flyash = 350-270= 80 Kg/m^3
VII. Proportion of Volume of coarse aggregate and fine aggregate
From table 3 of IS 10262:2009, the Volume of coarse aggregate per unit volume of total aggregate corresponding to 20mm size aggregate and fine aggregate (Zone I) is 0.6.
In the present case, w/c ratio is 0.4.
Therefore, the volume of aggregate needs to be increased. As the w/c ratio is lower by 0.1, the proportion of the volume of CA is increased by 0.02.
Therefore, the corrected volume of CA for w/c ratio of 0.4 = 0.62
For pumpable concrete, the value will be reduced by 10%.
Therefore, Volume of Coarse Aggregate= 0.62x0.9= 0.56
Volume of Fine Aggregate= 1-0.56=0.44
VIII. Mix calculation
a) Volume of Concrete = 1 m^3
b) Volume of Cement = (mass of cement)/(Specific gravity of Cement) x (1/1000) = (270/3.15) x (1/1000) = 0.086 m^3
c) Volume of Flyash = (mass of flyash)/(Specific gravity of flyash) x (1/1000) = (115/2.2) x (1/1000) = 0.052 m^3
d) Volume of water = (mass of water)/(Specific gravity of water) x (1/1000) = (140/1) x (1/1000) = 0.14 m^3
e) Volume of chemical admixture = (mass of chemical admixture/Specific gravity of chemical admixture) x (1/1000)
= (7.0/1.145) x (1/1000) = 0.006 m^3 f) Volume of aggregate (F.A & C.A) = (a-(b+c+d+e) = (1-(0.086+0.052+0.14+0.006)) = 0.716 m^3
g) Mass of CA = e x Volume of CA x Specific gravity of CA x 1000 = 0.716 x 0.56 x 2.74 x 1000 = 1098 kg/m^3
h) Mass of FA = e x Volume of FA x Specific gravity of FA x 1000 = 0.716 x 0.44 x 2.74 x 1000 = 863 kg/m^3
IX) Mix Proportion
| Cement | : 270 kg/m^3 |
| Fly Ash | : 115 kg/m^3 |
| Water | : 140 kg/m^3 |
| FA | : 863 kg/m^3 |
| CA | : 1098 kg/m^3 |
| Chemical admixture | : 7 kg/m^3 |
| w/c ratio | : 0.364 |
| trial mix ratio | 1:2.24:2.85 |
X) The slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump on trial. The mix proportion shall be reworked for the actual water content and checked for durability requirements.
XI) Two or more trials having variation of 10% of w/c ratio of clause X shall be carried out and a graph between the three w/c ratio and corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trials. however, durability shall be met.
PART 2: M50 GRADE CONCRETE MIX DESIGN WITHOUT FLY ASH
I. Stipulations for proportioning
| a) | Grade | : M50 |
| b) | Type of Cement | : OPC Grade 43 conforming to IS 8112 |
| c) | maximum nominal size of aggregate | : 20 mm |
| d) | Minimum cement content | : 320 kg/m^3 (Table5, IS 456:2000) |
| e) | Maximum water-cement(w/c) ratio | : 0.45 (Table 5, IS 456:2000) |
| f) | Workability | : 100 mm (slump value for pumpable concrete) |
| g) | Exposure | : Severe |
| h) | Method of Placing | : Pumping |
| i) | Degree of supervision | : Good |
| j) | Type of aggregate | : Crushed angular aggregate |
| k) | Maximum cement content | : 450 kg/m^3 |
| l) | Chemical admixture type | : Superplasticizer |
II. Test data for materials
| a) | Cement used | : OPC 43 grade conforming to IS 8112:1989 |
| b) | Specific gravity of cement | : 3.15 |
| c) | Chemical admixture | : Superplasticizer |
| d) | Specific gravity of Coarse aggregate (CA) | : 2.74 |
| e) | Specific gravity of Fine aggregate (FA) | : 2.74 |
| f) | Water absorption of CA | : 0.5% |
| g) | Water absorption | : 1.0% |
| h) | Free surface moisture of CA and FA | : NIL |
| i) | Sieve Analysis of CA | : Table 2 of IS 383:2016 |
| j) | Sieve Analysis of FA | : Conforming to grading zone I of Table 4 of IS 383:2016 |
III. Target strength
f'ck = fck + 1.65 S
fck= characteristic compressive strength at 28 Days
f'ck= target average compressive strength at 28 Days
From Table 1 of IS 10262:2009, Standard deviation, S= 6.5 N/mm^2
Therefore, f'ck = 50 + (1.65x6.5) = 60.72 N/mm^2
IV. Selection of water content
From Table 5 of IS 456:2000,
for severe exprosure, maximum w/c ratio =0.45
Based on experience, adopted w/c ratio =0.4
0.4<0.45, hence OK.
V. Selection of water content
From Table 2 of IS 10262:2009,
Maximum water content for 20mm aggregate = 186 liters for a slump value of 25mm to 50 mm.
For every 25 mm increase in slump value, an additional 3% increase in water content is taken.
hence, for a slump value of 100 mm, water content = 186 x 1.06 = 197 liters.
As superplasticizer is used, the water content can be reduced up to 20% and above. Based on trials, up to 29% water reduction can be taken.
hence the Water content = 197 x 0.71 = 140 liters.
VI. Calculation of cement content
w/c ratio =0.4
Cement content = 140/0.4 = 350 kg/m^3
From table 5 of IS 456:2000, the Minimum cement content for severe exposure is 320 kg/m^3
350>320. Hence OK.
VII. Proportion of Volume of coarse aggregate and fine aggregate
From table 3 of IS 10262:2009, the Volume of coarse aggregate per unit volume of total aggregate corresponding to 20mm size aggregate and fine aggregate (Zone I) is 0.6.
In the present case, w/c ratio is 0.4.
Therefore, the volume of aggregate needs to be increased. As the w/c ratio is lower by 0.1, the proportion of the volume of CA is increased by 0.02.
Therefore, the corrected volume of CA for w/c ratio of 0.4 = 0.62
For pumpable concrete, the value will be reduced by 10%.
Therefore, Volume of Coarse Aggregate= 0.62x0.9= 0.56
Volume of Fine Aggregate= 1-0.56=0.44
VIII. Mix calculation
a) Volume of Concrete = 1 m^3
b) Volume of Cement = (mass of cement)/(Specific gravity of Cement) x (1/1000) = (350/3.15) x (1/1000) = 0.111 m^3
c) Volume of water = (mass of water)/(Specific gravity of water) x (1/1000) = (140/1) x (1/1000) = 0.14 m^3
d) Volume of chemical admixture = (mass of chemical admixture/Specific gravity of chemical admixture) x (1/1000) = (7/1.145) x (1/1000) = 0.006 m^3
e) Volume of aggregate (F.A & C.A) = (a-(b+c+d) = (1-(0.111+0.14+0.006)) = 0.743 m^3
f) Mass of CA = e x Volume of CA x Specific gravity of CA x 1000 = 0.743 x 0.56 x 2.74 x 1000 = 1140 kg/m^3
g) Mass of FA = e x Volume of FA x Specific gravity of FA x 1000 = 0.743 x 0.44 x 2.74 x 1000 = 896 kg/m^3
IX) Mix Proportion
| Cement | : 350 kg/m^3 |
| Water | : 140 kg/m^3 |
| FA | : 896 kg/m^3 |
| CA | : 1190 kg/m^3 |
| Chemical admixture | : 7 kg/m^3 |
| w/c ratio | : 0.4 |
| tria; mix ratio | 1:2.56:3.26 |
X. The slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump on trial. The mix proportion shall be reworked for the actual water content and checked for durability requirements.
XI. Two or more trials having variation of 10% of w/c ratio of clause X shall be carried out and a graph between the three w/c ratio and corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trials. however, durability shall be met.
RESULT
- Mix Proportion by weight of M35 grade of concrete with fly ash is 1:2.24:2.85 and its water-cement ratio was found to be 0.364.
- Mix Proportion by weight of M50 grade of concrete without fly ash is 1:2.56:3.26 and its water-cement ratio was found to be 0.44.
These proportions are considered as an initial trial ratio for which laboratory tests are to be done and to be confirmed on the basis of the results obtained.
REFERENCES
- IS 10262:2009
- IS 456:2000
- IS 8112:1989
- IS 9103
- IS 383:2016