This article covers the Mix design calculation of M35 Grade Concrete with Fly ash admixture and super plasticizer as per Indian Standard Codebook IS10262(2009) – Guidelines for Concrete Mix Proportioning.
I. STIPULATIONS FOR PROPORTIONING OF M35 GRADE CONCRETE
This section contains specifications for the materials and requirements for the concrete to be manufactured. The specific gravity of Fly ash is 2.1 to 3, while the specific gravity of GGBS is 2.85. Use the appropriate specific gravity value based on the type of admixture used.
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| 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 |
II. TEST DATA FOR MATERIALS
Materials must be tested to find its below physicals and chemical properties. Standard values are considered below.
| A | Cement Used | OPC 53 | Confirming to IS8112 |
| B | Specific Gravity of Cement | 3.15 | Test – IS: 2720 |
| C | Mineral Admixture | Fly ash | Confirming to IS12089 |
| D | Specific Gravity of Fly ash | 2.90 | |
| E | Chemical Admixture | @0.6% | IS9103 |
| F | Specific Gravity of | Test – IS 2386 | |
| Coarse Aggregate | 2.74 | ||
| Fine Aggregate | 2.74 | ||
| Admixture PCE based | 1.12 | ||
| G | Water Absorption | Test – IS 2386 | |
| Coarse aggregate | 0.5 % | ||
| Fine aggregate | 1 % | ||
| H | Sieve Analysis | Test – IS 2386 | |
| Coarse aggregate | Confirming to Table 2-IS383 | ||
| Fine aggregate | Zone II | Confirming to Table 4-IS383 |
III. TARGET STRENGTH FOR MIX PROPORTIONS OF M35 GRADE CONCRETE
The strength of concrete may vary depending on the quality of the material, the mixing method and the construction procedures. Therefore the target strength (Fck) must be greater than the required strength of the concrete (fck).
Table 1 of IS456 gives the standard deviation value (s) for different grade concretes.
| Fck | = fck+1.65s | “S” from Table1-IS10262 |
| Fck | = 35+1.65×5 | |
| Fck | = 43.25 N/mm2 |
IV. SELECTION OF WATER-CEMENT RATIO
The maximum water-cement ratios for different grades of concrete are given in Table 5-IS456. You can reduce the water-cement ratio based on your needs.
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 |
V. SELECTION OF WATER CONTENT
| Maximum Water Content | =186 L | Table 2-IS1026 |
The water content above is for a slump of 25 to 50 mm, but according to the specification our concrete requires a slump of 100 mm. Therefore, to get the desired slump, the water content must be increased. Clause 4.2 of IS1026 recommends increasing the water content by 3% to obtain an additional 25 mm slump. Therefore, to obtain a slump of 50 mm in addition to our concrete, the water content must be increased by 6%.
| Water-content for 100mm Slump | =186+(0.06*186) |
| =197.16 L |
As we use super plasticizers we can reduce the water content to gain strength in the concrete. The amount of water-content to be reduced depends on the type of super plasticizer.
| Percentage of Reduction in water content | =20% |
| Water content requirement after SP | =198 – (0.20*198) |
| =157.73 | |
| Adopted Water Content | =160 L |
VI. 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 flying ash is used, the amount of cementitious content (cement + fly ash) should be increased to get good performance and strength. The percentage of increasing cementitious content depends on 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
VII 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 |
VIII 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
| S.No. | 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
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