Factors Affecting Properties Of Concrete

Factors Affecting Properties Of Concrete:

The factors which affect the properties of concrete (workability, bond strength, tensile strength, creep, shrinkage, bleeding, segregation, etc) are described below.

1. Water-cement Ratio:

Strength elasticity, durability, and impermeability of concrete are increased with the decrease in water-cement ratio, provided the concrete is workable. Shrinkage is increased with greater w/c ratio.

2. Cement Content:

With increases in cement content, w/c ratio decreased and consequently, strength, elasticity, durability, and permeability is increased. More cement improves workability but it also increases shrinkage which is undesirable.

3. Temperature:

The rate of setting and hardening of concrete is high at higher temperature. If the temperature of concrete falls below 0°C, free water in concrete turns into ice crystals and since ice has greater volume than the same quantity of water, the concrete is completely disrupted.

Such concrete on thawing will have no strength. If the temperature is more than the freezing temperature, cool concreting gives better ultimate strength, durability and less shrinkage.

4. Age Of Concrete:

The strength of concrete goes on increasing with age, though the rate of increase becomes very slow with the passage of time. The following table gives some ides of strength development with age:

Age                          Strength in percentage
      Ordinary cement Rapid hardening cement
7 days 35% 65%
28 days 60% 90%
3 months 85% 95%
1 year 100% 100%

5. Aggregate:

Size, shape, and grading of aggregates, control concrete properties to a large extent. Rounded aggregates give better workability than flaky and angular aggregates. Larger the size of the aggregate, greater will be the strength, provided concrete mix is workable. Property graded aggregates give better workability and strength.

6. Curing:

Curing is the process of keeping the setting concrete damp so that complete hydration of cement is brought about. Besides strength the curing affects following qualities:

a) It improves wear-resisting and weather resisting qualities.

b) It increases impermeability and durability.

c) It reduces shrinkage.

7. Frost:

The frost causes disintegration of concrete and as such strength, durability and impermeability are reduced. Resistance to frost action depends upon the structure of the pores in the concrete.

8. Entrained Air:

The entrained air in concrete is due to incomplete compaction. It has the effect of reducing the strength of concrete. With 1% of entrained air, the strength of concrete is reduced by 5%. It also increases permeability of concrete.

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