Project on Concrete Mix Design for various grades of Concrete

Answer

As per Indian Standard Codebook IS10262(2009) – Guidelines for Concrete Mix Proportioning.

A. Grade Designation - M35

B. Type of Cement - OPC 53

C. Type of Admixture - Fly ash

D . Maximum Nominal Size of Aggregate - 20mm

E. Minimum Cement Content 340kg - Table 5-IS456

F . Maximum Cement Content - 450kg As per code

G. Partial replacement of cement by Fly ash 30% as per requirement.

H. Maximum W/C ratio 0.45 - Table 5-IS456

I. Workability - 100mm

J Chemical Admixture PCS Type

• TARGET STRENGTH FOR MIX PROPORTIONS OF M35 GRADE CONCRETE

The strength of the concrete may deviate based on the quality of the material, method of mixing and construction practices. Hence target strength (Fck) should be higher than the required strength of the concrete (fck). The value of standard deviation(s) for different grades of concrete is given in Table 1 of IS456.

Fck = fck+1.65s “S” from Table1-IS10262

Fck = 35+1.65×5

Fck = 43.25 N/mm2

• SELECTION OF WATER-CEMENT RATIO

The maximum water-cement ratio for different grades of concrete is given in Table 5-IS456. You can reduce the water-cement ratio based on your requirements. The Water-cement ratio directly affects the strength of the concrete.

Maximum W/C ratio =0.45 Table 5-IS456

Adopted W/C ratio =0.45

• SELECTION OF WATER CONTENT

Maximum Water Content =186 L Table 2-IS1026

Above water-content is for 25 to 50mm slump, but we need 100mm slump for our concert as per specification. So we need to increase the water-content to get the required slump. Clause 4.2 of IS1026 suggests to increases 3% of water-content to get an extra 25mm slump. Hence we to increase water content by 6% to get an additional 50mm slump for our concrete.

Water-content for 100mm Slump =186+(0.06*186)

=197.16 L

Since we are using superplasticizers water-content can be reduced inorder to get strength in concrete. The amount of water-content to be reduced depends on the type of superplasticizer.

Percentage of Reduction in water content =20%

Water content requirement after SP =198 – (0.20*198)

=157.73

Adopted Water Content =160 L

• CALCULATION OF CEMENT AND FLY ASH CONTENT

Adopted Water Cement Ratio =0.45

Total Cementitious (Cement +Fly ash) requirement = Water Content / WaterCement ratio

=160/0.45

=355.55 kg

Since Fly ash is used the amount of Cementitious content (Cement+Fly ash) shall be increased to get good workability and strength. The percentage of cementitious content to be increased depends on the experience and research. Here we have increased the cementitious content by 10%.

Final Cementitious

Content (Cement+Fly ash) = 356*1.10

=391.6 kg

Minimum Cement Content required for ‘severe’ exposure =340kg Table 5-IS456

Adopted Cementious content =391.6 kg > 340kg

Fly ash content requirement = 391.6 * 0.30 30% replacement

= 117.48 ~ 118 kg

Cement Content requirement =Cementious content – Fly ash

=391.6-117.48

= 274.12

Calculation of Super Plasticiers @ 0.6 percent to the mass of cementitious content = = 391.6*(0.6/100) = 2.35 kg

• COARSE AND FINE AGGREGATE

Coarse Aggregate ratio = 0.62 Table3-IS10262

(For W/C =0.5)

Coarse Aggregate ratio for 0.45 w/c ratio = 0.63 (adding 0.01 for every decrease .05 and vice versa)

Final Fine Aggregate ratio = 0.37 (1-0.63) = 0.37

• MIX CALCULATIONS OF M35 GRADE CONCRETE

A. Volume of Concrete = 1 cu.m

B. Total Volume of Cement = Cement/(S.G*1000)

= 275/(3.15*1000)

= 0.087 cu.m

C. Total Volume of Fly ash = Flyash/(S.G*1000)

= 118/(2.5*1000)

= 0.041 cu.m

D. Volume of Water =Water /(S.G*1000)

= 160/(1*1000)

= 0.160 cu.m

E. Volume of Superplasticizers = Superplasticizers /(S.G*1000)

= 2.35/(1.12*1000)

= 0.002 cu.m

F. Total Aggregates requirement = A – (B+C+D+E)

=1 -(0.087 +0.041+0.160+0.002)

=0.71 cu.m

G. Coarse Aggregate (C.A) = F * C.A ratio * S.G * 1000

= 0.71*0.63 *2.74 *1000

= 1225.6 kg

I. Fine Aggregate (F.A) = F * F.A ratio * S.G * 1000

= 0.71*0.37*2.74 *1000

=719.8 kg

Cement Flyash Sand Aggregate Water and Superplasticizer needed for M35 grade concrete

MATERIALS QUANTITY

1. Cement 275 kg

2. Flyash 118 kg

3. Fine Aggregate 720 kg

4. Coarse Aggregate (20mm) 1226 kg

5. WATER 160 L

6. PCE based SuperPlasticizer 2 L

To find the design mix ratio divide the calculated value of all materials by the weight of cement. Therefore Mix Ratio of M35 Grade concrete by weight is Cement : Flyash: F.A : C.A : Water =

1: 0.4 : 2.6 : 4.46 : 0.58