Project on Concrete Mix Design for various grades of Concrete
Concrete mix design for M35 grade with fly ash
Aim: To calculate design ratio of concrete mix M35 grade given cement type OPC 53, concrete volume of 1 cubic metre, nominal aggregate size of 20 mm, workability of 100 mm in accordance with the codes: IS 456:2000, IS10262, IS1026 , IS12089
Introduction to concrete mix design
Concrete mix design is the process of selecting ingredients for a given mixture and determining their proportions, in order to get desired properties like workability, strength, durability and corrosion resistance.
Concrete mix design is a highly systematic and sequential process. Every step has to be carried with precision and in compliance with the codes.
|
|
|
|
|
|
The first step is determining the required workability of slump value of concrete. Slump value refers to the subsidence of a mould of concrete after removing the slump cone. A higher slump value indicates higher subsidence. Such concrete is nicely placed and compacted. We assume a slump value of 100mm for concrete mix design.
The next step in concrete mix design is to determine aggregate size. By increasing the aggregate size required cement is reduced. But it may affect workability. A balance is sought between economy and workability.
Next the designer has to decide the required volume of water for concrete mix design. After this one has to determine the required water cement ratio.
With the value of water content and water cement ratio the designer can calculate cement content. Finally the designer calculates fine and coarse aggregate.
|
Grade designation |
M35 |
|
Cement type |
OPC53 |
|
Admixture used |
Fly ash |
|
Maximum nominal aggregate size |
20 mm |
|
Minimum cement |
340 kg( from Table IS456:2000) |
|
Maximum cement |
450 kg |
|
Percentage replacement of cement with fly ash |
30% |
|
Workability |
100 mm |
Significance of Fly ash
Fly ash is known for having cement like properties. Fly ash is an effluent which creates storage problems on site. But due to its cement like attributes it can be useful input to construction industry. Cement addition brings down cement requirement for concrete making thus improving overall economy. The addition of fly ash reduces cement volume by 30%.
Test data for materials
Materials should be tested in laboratory for verification of their properties. Material quality is checked with reference to code book standards.
|
Specific gravity of cement |
3.15 |
|
Mineral admixture |
Fly ash |
Calculation of Target compressive strength
Fck = fck + 1.65s
where fck = compressive strength
s= standard deviation
For M35 grade concrete s.d.= 5 ( Table 1 IS10262)
= 35 + 1.65(5)= 43.25 N/mm2
Selection of water cement ratio
Maximum w/c ratio comes out as 0.45
Maximum water content for aggregate nominal maximum size 20mm=186(Table 2 of IS1026)
Water content for 100 mm slump value= 186+ (0.06*186)= 197.16 litre
Total cementitious ratio= water content/water cement ratio
= 186/0.45= 413.3
Since Fly ash is used cement amount is raised by 1.1%.
Cement required= 413.3*1.1= 454.63 kg
Fly ash content required= 454.63*0.30= 136.38 kg
Cement content = 454.63- 136.38= 318.25 kg
Coarse and fine aggregate
Coarse aggregate ratio= 0.62 (for w/c ratio of 0.5)
Fine aggregate ratio= 0.37
The value of fine aggregate could be determined using the formula
1000(1-a0) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +(Fa / Sp. Gr.* Pf )}
Fa= Fine Aggregate Content
Pf= Sand Content as percentage of total Aggregates
= 0.36
a0 = Percentage air content in concrete (As per IS :10262 for 20 mm nominal size of
aggregates air content is 2 %) = 0.02
1000(1-.02)= 318.25/3.15+ 197.16+ (Fa/2.62*0.36)
980= 101.03 + 197.16 + (Fa/2.62*0.36)
980-(101.03 + 197.16) = Fa/2.62*0.36
681.81= Fa/2.62*0.36
Fa= 643 kg
The value of coarse aggregate could be determined using the formula
1000(1-a0) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +Ca/ Sp. Gr.* Pc)}
where Pf= Sand Content as percentage of total Aggregates
Hence, 1000(1-0.02) = {(318.25 /3.15) + 197.16 + Ca / (2.67 x 0.64)}
980 = 298.19+ Ca / (2.67 x 0.64)
Ca /(2.67 x 0.64) = 681.81
Ca = 681.81 * 2.67* 0.64 = 1165 kg
Mix calculations of M35 grade concrete
|
Cement Volume |
1 cubic metre |
|
Total volume of cement |
318.25/(3.15*1000) = 0.1031 cubic m |
|
Total volume of fly ash |
136.38/(3.15*1000)= 0.043 cubic m |
|
Volume of water |
197.16/1000= 0.197 |
|
Coarse aggregate |
1165 kg |
|
Fine aggregate |
643 kg |
Calculation of concrete mix design for M50
Aim: To calculate concrete mix design for OPC53 of grade M50 with normal aggregate size of 20 mm and slump value of 50-75 mm in accordance with IS10262 and IS456.
|
Grade designation |
M50 |
|
Cement type |
OPC53 grade corresponding to IS8112 |
|
Maximum nominal aggregate size |
20 mm |
|
Maximum water cement ratio |
0.35 |
|
Workability (slump value) |
50-75 |
|
Maximum cement |
450 kg/m3 |
Concrete mix design formula is a highly systematic engineering process. The mix design is in compliance with desirable concrete properties like workability and durability.
Steps
|
|
|
|
|
|
Test data
Specific gravity of cement= 3.15
Target strength for mix proportioning
Fck = fck + 1.65s
where fck = compressive strength
s= standard deviation
For M50 grade concrete s.d.= 5 ( Table 1 IS10262)
=50 + 1.65(5)= 58.25 N/mm2
Selection of water cement ratio
According to IS456:2000 w/c ratio is taken as 0.35.
Selection of water content
From Table 2 of IS456 maximum water content comes out to be 186 litres.
Estimated water content for desired slump value= 186+(6/100)*186= 197 litres
Calculation of cement content= Water/(w/c ratio)
= 197/0.35= 563 kg
Proportion of volume of coarse and fine aggregate. Using table 3 of IS10262 volume of coarse aggregate is 0.63, while the ratio of fine aggregate is 0.37.
The value of fine aggregate could be determined using the formula
1000(1-a0) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +(Fa / Sp. Gr.* Pf )}
1000(1-0.20)= 563/3.15 + 197+ Fa /(2.62* 0.36)
980= 178.8 + 197 + Fa /(2.62* 0.36)
604.2 = Fa /(2.62* 0.36)
Fa= 569.9 kg
The value of coarse aggregate could be determined using the formula
1000(1-a0) = {(Cement Content / Sp. Gr. Of Cement) + Water Content +Ca/ Sp. Gr.* Pc)}
where Pf= Sand Content as percentage of total Aggregates
Hence, 1000(1-0.02) = {(563 /3.15) + 197 + Ca / (2.67 x 0.64)}
980 =178.8 + 197 + Ca / (2.67 x 0.64)
Ca /(2.67 x 0.64) = 604.2
Ca = 604.2 * 2.67* 0.64 = 1032.4 kg
|
Cement Volume |
1 cubic metre |
|
Volume of water |
197 litre |
|
Water cement ratio |
0.35 |
|
Cement content |
563 kg |
|
Coarse aggregate |
1165 kg |
|
Fine aggregate |
643 kg |