Challenge

Project on Concrete Mix Design for various grades of Concrete

RRishwan Khan J29 Jan 2023

Aim:-

To calculate the concrete mix design for M35 grae concrete with fly ash.

Procedure:-

Step 1:-

Stipulation for proportioning:-

Grade of designation:M35
Type of Cement : OPC 43 grade confirming to IS 8112
Typ of Mineral Admixtur: Fly ash confirming to IS 3812(Part- 1)
Maximum nominal size of aggregate : 20mm
Minimum Cement content: 320 kb/m^3(Table -s, Is 456 -2000, basd on exposure condition)
Maximum Water- cement ratio :0.45 (Table- 5 IS 456-2000, based on exposure condition)
Workability: 100mm slump value of pumpable concrete
Exposure condition : Severe (for reinforced concrete)
Method of concrete placing : Pumping
Degree of supervision : good
Type of aggregate: Crushed angular aggregate
Maximum cement content : 450 kg/m^3
Chemical admixture type : supeplasticizer

Step 2:-

Test Data for Materials:-

Cement used : OPC 43 grade confirming to IS 8112
Specific gavity of cement :3.15
Fly ash : Confirming to Is 3812 part 1
Specific garvity of Fly ash : 22
Chemical admixture: Super plastizicer conforming to IS 9103
Specific grvity of
1. coarse aggregate : 2.74,
2. Fine aggregate : 2.74
Water absorbtion :
1. Coarse aggregte: 0.5%
2. Fie aggregate :1%
Free suface moisture :
1. coarse aggreagte : nil
2. fine aggregate : nill
Seive analysis of aggragate

Step:3

To find Target mean strength for mix proportioning:-

Target mean strength , ft=fck + 1.65 s = 35+(1.65*5)=43.25 N/mm^2

Step 4 :

Selection of water cement ratio:-

Maximum water cement ratio = 0.45(for severe condition, from table 5 of IS 456-2000)
On experience water - cement ratio is = 0.4
0.4<0.45 hence ok

Step 5 :-

Calculation of water content :-

MAximum water conten for 20mm aggregate = 186 litres(Table 2 of IS 10262:2009)for 25mm to 50mm slump range
For 100 mm slump = 186+(6/100)*186 = 197 litres
As superplatizicers, is used the water content is reduced upto 30%
Based on trils water content reduction pf 29% is achieved with plastizizers
Hence, arrived water content = 197*0.71=140 litres

Step 6:-

Calculation of cement content :-

Water- cement ratio = 0.4

Cementatious material (Cement + flyash ) = 140/0.4 = 350 kg/m^3
In table 5 of IS 456- 2000, The cement content for severe exposure = 320 Kg/m^3
350 kg/m^3 > 320 Kg/m^3 Hence ok

To proportion the mix containing flyash the following steps are suggested:

The percentage of flyash need to be decided based on project requirement and quality of materials
In some cases increase in cementesious material can be warrned increase in cementesious material content and its percentage may be based on experience and trial
In this increase of 10% cementesious material content is considered
Cementatious material content = 350*1.1 = 385 Kg/m^3
Water content = 140 Kg/m^3
So water- cement ratio = 140/385 = 0.364
Fly ash at 30% total cementesious material content = 385*30% =115 Kg/m^3
Cement opc = 385-115 = 270Kg/m^3
Savings of cement while using fly ash = 350-270=80Kg/m^3
Fly ash being utilizex = 115Kg/m^3

Step 7:

Proportion of volume of coarse aggregate and fine aggregate content

From table 3 of Is 10262:2009, Volume of coarse aggregate corresponding to 2mm size of aggregate and fine aggregate (zone -1) for water- cement ratio = 0.6
Therefore the volume of coarse aggregate need to be increased to degrease the fine agggregate content
As the water - cement ratio is lowered by 0.1, the volume of coarse aggregate is increased by 0.02(at the rate of every +/- 0.01 for every +/- 0.05 change in water - cement ratio)
Hence the corrected value of coarse aggregate for the water- cement ratio = 0.64
(If coarse aggreagte is not of angular type, then also the volume of coarse aggregate may be required to be increased suitability, based o experience)
For pumpable concrete, theese are reduce by 10%
Volume of coarse aggregate = 0.64*0.9=0.576mm size of aggregate and fine aggregate (zone -1) for water- cement ratio = 0.6
volume of fine aggregate = 1-0.576 =0.424

Step 8:-

Mix calculations

volume of concrete=1m^3
volume of cement =(mass of cement/ Specific gravity of cement)*(1/1000)=(270/ 3.15)*(1/1000)=0.086m^3
volume of fly ash =(mass of fly ash/ Specific gravity of cement)*(1/1000)=(115/ 2.2)*(1/1000)=0.052m^3
volume of water =(mass of water/ Specific gravity of water)*(1/1000)=(140/1)*(1/1000)=0.140 m^3
volume of chemical admixture =(mass of admixture/ Specific gravity of admixture)*(1/1000)=(7.6/1.14)*(1/1000)=0.006m^3
volume of all in aggregate= (a-(b+c+d+e))= (0.086+0.052+0.140+0.006)=0.716 m^3
Mass of coarse aggregate= e * volume of coarse aggregate * specific gravity of coarse aggregate *1000 = 0.716*0.576*2.74*1000 = 1130kg/m^3
Mass of fine aggregate= e * volume of fine aggregate * specific gravity of fine aggregate *1000= 0.716*0.424*2.74*1000 = 831 Kg/m^3

Step 9:-

Mix Proportions

Cement = 270 Kg/m^3
Fly ash= 115 Kg/m^3
Water =140 Kg/m^3
Fine Aggregate = 831 Kg/m^3
Coarse aggregate = 1130 Kg/m^3
Chemical admixture = 7 kg/m^3
Water- cement ratio = 0.364Kg/m^3

Step 10:-

The slump shall be measured and the water content and dosages of amixtr shall be adjusted for achieving the required slump on trail. The mix proportion shall be reworked for the actual water content and checj-ked for durability requirements.
Two or more trails having variation of 10% of water- cement ratio in Clause 10(step 10) shall be carried out and a graph between three water- cement ratios and corresponding stregth shall be plotted to work out the mix proportions for the given target strength for free trails. However durability shall be met

Result : The mix design for M35 grade of concrete with fly as 1: 2.15:2.94