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 concrete||Wt. of Fine Aggregate (FA) +|
Wt of coarse Aggregate (CA)
for 50Kg of cement
|FA:CA||Wt. of water (kg) per 50 kg of cement (w/c ratio)||Ratio|
|M5||800 (800/3+1600/3)||–||60 (1.2)||1:5.33:10.6|
|M7.5||625 (625/3+1250/3)||–||45 (0.9||1:4.16:8.33|
|M10||480 (480/3 + 960/3||–||34 (0.68)||1: 3.2: 6.4|
|M15||330 (330/3 + 660/3)||–||32 (0.64)||1:2.2:4.4(1:2:4)approx|
|M20||250 (250/2 + 500/3)||–||30 (0.6)||1:1.6:3.3(1:1.5:3)approx|
Design as per IS code
Calculate the mass of fine aggregate and coarse aggregate using the absolute volume principle.
Where are mass (kg/KN and 1KN=100kg) of cement, fine aggregate and coarse aggregate in one cubic meter of concrete. are specific gravity of cement, fine aggregate and coarse aggregate (Sc=ρc/ρw) and ρw density of water (1000kg/m3 or 10KN/m3) are volumes of water, volume of void (air) normally 0.02 (2%) and volume of admixture is any.
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.
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 )= *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
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
Also, Read————————– Limit State Method 0f Design | Reinforced Cement Concrete |
Subscribe ———————————- Civil Engineering