## Factors affecting the choice of mix proportions

__Factors affecting the choice of mix proportions__

- Compressive strength
- Workability
- Durability
- Maximum nominal size of aggregate
- Fineness Modulus and zone of aggregate
- Quality Control

**Significance of Max. w/c Ratio & Min. Cement Content**

Water Cement Ratio

- Strength Criteria
- Durability Criteria

- Durability decreases with increase in w/c ratio
- Higher is the aggressiveness of the environment lower should be the w/c ratio
- Strength of paste increases with cement content and decreases with air and water content

Studies show that, Capillary porous start to be connected when w/c is higher than 0.40, When w/c is higher than 0.70, all capillary porous are connected

Hence, The maximum value for w/c ratio is 0.70. Concrete exposed to a very aggressive environment the w/c should be lower that 0.40

**Advantages of low water-cement ratio:**

- Finer microstructure
- Low chloride ion diffusion
- Corrosion resistance
- Low susceptibility to carbonation, electrochemical attack

**Statistical Quality Control of Concrete**

- Results in variation of strength from batch to batch and also within the batch
- It impossible to have a large number of destructive tests for evaluating the strength of the end products
- The aim of quality control is to limit the variability as much as practicable
- By devising a proper sampling plan it is possible to ensure a certain quality at a specified risk
- Extent of variation of strength can be ascertained by relating the individual strength to the mean strength and determining the variation from the mean with the help of the properties of the normal distribution curve