Normal mix and Designed mix concrete
Normal mix concrete
This is the common method of expressing the proportion of the materials in concrete a mix is in the form of parts of rations of cement, the fine and coarse aggregates with cement being taken as unity.
For example, 1:2:4 mix contains one part of cement, two part of fine aggregate a four parts of coarse aggregate. The amount of water, entrained air and admixtures, if any, are expressed separately.
The amount of entrained air in concrete is expressed as a percentage of the volume of concrete. The amount of admixtures are expressed relative to the weight of cement. Other forms of expressing the proportions are by ratio of cement to the sumo fine and coarse aggregates, i.e. aggregate-cement ratio and by cement factor or number of bags of cement per cubic meter of concrete. Normal mix concrete may be used for concrete of grade M20 of lower.
Proportions of Nominal mix concrete
| Grade of Concrete | Total Quantity Of Dry Aggregate per Bag of cement of 50 Kg (kg) |
Maximum water Content Per Bag of Cement of 50 Kg (liter) |
The proportion of fine Aggregate to Coarse Aggregate To Coarse Aggregate By Mass |
|---|---|---|---|
| M10 | 480 | 34 | Generally 1:2 with upper |
| M15 | 350 | 32 | Limit as 1:1.5 and lower |
| M20 | 250 | 30 | Limit as 1:2.5 |
Designed Mix Concrete
For high-performance concrete, the most rational approach of mix proportioning is to select proportion with specific materials, which possess more or less unique characteristics, Other factors like workability, durability, compaction equipment available, curing methods adopted, etc. also influence the choice of the mix.
The mix proportion so arrived at is called the designed mix concrete.