Concrete Mix Design

Concrete Mix Design

The design of concrete mix design involves the selection of relative proportions of various ingredients of concrete to meet the criteria of characteristic strength, workability, and durability in the hardened state. The common method of expressing the proportions of ingredients of a concrete mix is in the terms of parts or ratios of cement, fine and coarse aggregates. For e.g., a concrete mix of proportions 1:2:4 means that cement, fine and coarse aggregate are in the ratio 1:2:4, or the mix contains one part of cement, two parts of fine aggregate, and four parts of coarse aggregate. The proportions are either by volume or by mass. The water-cement ratio is usually expressed in mass.

Nominal Mix Concrete

Up to M20 grade of concrete, all mixes are nominal mix which means the relative proportions are fixed and no design is required.

Grade of concreteWt. of Fine Aggregate (FA) +
Wt of coarse Aggregate (CA)
for 50Kg of cement
FA:CAWt. of water (kg) per 50 kg of cement (w/c ratio)Ratio
M5800 (800/3+1600/3)60 (1.2)1:5.33:10.6
M7.5625 (625/3+1250/3)45 (0.91:4.16:8.33
M10480 (480/3 + 960/334 (0.68)1: 3.2: 6.4
M15330 (330/3 + 660/3)32 (0.64)1:2.2:4.4(1:2:4)approx
M20250 (250/2 + 500/3)30 (0.6)1:1.6:3.3(1:1.5:3)approx
FA:CA = Mostly 1:2 but can be in the range of 1:1.5 to 1:2.5

Design as per IS code

Calculate the mass of fine aggregate and coarse aggregate using the absolute volume principle.

 Absolute\: Volume\: = \frac{Weighi\: of\: material}{Specifc\: gravity\: of\: material\:*\: unit\: weight \:of\: water}

  \frac{M_c}{p_{w}<em>s_{c}}+\frac{M_{FA}}{p_{w}</em>s_{FA}}+\frac{M_{CA}}{p_{w}*s_{CA}}+V_{W}+V_{V}+V_{AD}=1m^3

Where   M_C, M_{FA}, M_{CA} are mass (kg/KN and 1KN=100kg) of cement, fine aggregate and coarse aggregate in one cubic meter of concrete.  S_c, S_{FA}, S_{CA} are specific gravity of cement, fine aggregate and coarse aggregate (Sc=ρc/ρw) and ρw density of water (1000kg/m3 or 10KN/m3)  V_W, V_V,V_{AD} are volumes of water, volume of void (air) normally 0.02 (2%) and volume of admixture is any.

  \rho _{mass}=\frac{Mass\: of \:solid}{Volume\: of\: solid}

  \rho _{bulk}=\frac{Mass\: of \:solid}{Volume\: of\: solid\:+\:Volume\: of \:void}

 \rho_{mass}=(1\:+\: void\: ratio)\rho_{bulk}

Fineness Modulus Method

Fineness modulus is obtained by adding the cumulative percentage of material retained on 11 IS sieves and divided by 100.

For example, Fine aggregate =1Kg and Coarse Aggregate =10Kg was taken for sieve analysis.

s-sieve
Number
Fine
aggregate
wt
retained.
Cumulative
Weight
Retained (kg)
%
Cumulative
Coarse
aggregate
weight
retained
Cumulative
Weight
Retained (kg)
%
Cumulative
150mm000
75mm000
40mm2.0 kg2.020
20mm3.0 kg5.050
10mm1.5 kg9.065
4.75mm2.5 kg1090
2.36mm0.15kg0.15151.10 kg10100
1.18mm0.20 kg0.353510100
600  \mu 0.25 kg0.606010100
300  \mu 0.15 kg0.757510100
150  \mu 0.25 kg1.010010100
 \Sigma 285 \Sigma 725

With a high aquaciment ratio, a lower fineness modulus value should be adopted and with a low aqueous ratio, a higher fineness modulus value should be adopted.

Fineness Modulus of fine aggregate =285/100=2.85
Fineness Modulus of Coarse aggregate =725/100=7.85

Ratio of the fine aggregate to mix aggregate (by volume )=  \frac{C-M}{C-f} *100

C= fineness module of coarse aggregate
F= fineness module of the fine aggregate
M= fineness module of mix aggregate
“F” lies between 2-3.5, “M” lies between 5-7, and “C” lies between 6-8.5

Maximum Density Method

Where:-
d = size of fine aggregate
D = maximum size of coarse aggregate
Pd = percentage by weight of particle size finer than “d” in the total mixture.

Concrete Mix Design
Concrete Mix Design

Also, Read————————– Limit State Method 0f Design | Reinforced Cement Concrete |

Subscribe ———————————- Civil Engineering

One thought on “Concrete Mix Design

Leave a Reply

Your email address will not be published. Required fields are marked *