## IRC Method Of Concrete Mix Design

About IRC 44-1976

- Primarily implemented in the design of Concrete Rigid Pavements on Road Construction.
- Flexural strength is more often specified than compressive strength in the design of concrete mixes for pavement construction.

**Basic Differences from IS method**

Strength Criteria–

Checking of Flexural strength have more priority than Compressive strength as the rigid pavement has negligible thickness compared to its length and width.

Aggregate Used–

The type of aggregate can have a predominant effect, crushed rock aggregate resulting in concrete with higher flexural strength than uncrushed (gravel) aggregates for comparable mixes.

Type of Cement Used:

IRC: 15-2002 specified that for concrete roads OPC should be used(Recommended).

Workability Criteria:

- 30mm slump at pour, the concrete will be transported from central batching plant through transit mixer, at a distance of 20km during high temperature season(Concreting never done if temperature is >40 and <5 degree Celsius).
- If Plasticizers used as 5 -10% reduction in water content.
- If Super plasticizers used as 20 -30% reduction in w.c.

Selection of Water Cement Ratio:

Finding target flexural strength of cement from the equation S’=S+K.S. Then find the w/c ratio from fig.1 curve D in IS:456-2000

Or otherwise use

Curve A and B – For OPC 33 Grade

Curve C and D – For OPC 43 Grade

**Steps In IRC Method**

Steps in IRC Method:

- All other steps are same as we follow in IS 10262-2009
- Repeat all the step at least 2 times, by changing the w/c ratio by 10%.
- Draw the graph with w/c ratio vs flexural strength.
- Then find the w/c ratio corresponding to the target flexural strength and find all other quantities of Ingredients.