Factors Affecting the Shrinkage of Concrete
- Relative humidity
- Water cement ratio
- Size of specimen
- Humidity (Drying Condition)
- Hardness of Aggregates
- Moisture Movement in Concrete
- Type of Coarse Aggregates
- Shape of Aggregates
Other factors that affect the magnitude of shrinkage include mix proportions, material properties, curing methods, environmental conditions, and geometry of the specimen. Water content has been found to affect the magnitude and rate of drying shrinkage in concrete. Other factors include elastic properties of the aggregate used in the concrete mix; in general, aggregate with a high elastic modulus will produce low shrinkage concrete. Aggregates that contain clay minerals will affect shrinkage behavior as well.
Temperature: An important factor that influences the water requirement of concrete and thus its shrinkage is the temperature of fresh concrete. Concreting done in mild winter have a much less cracking tendency than the concreting done in hot summer months.
Relative humidity: If the concrete specimen is kept in 100% relative humidity for any length of time, there will not be any shrinkage instead of slight swelling.
Time: Shrinkage decreases rapidly with time
- It is observed that 14 – 34% of 20years shrinkage
- 66 – 85% of 20 years shrinkage, occurs in one year
Water cement ratio: The water-cement Ratio also Influences the magnitude of shrinkage.
- It plays a major role in shrinkage properties its size, modulus of elasticity influence the magnitude of drying shrinkage.
- Harder aggregates influence a higher magnitude of shrinkage
- Softer aggregates influence a lower magnitude of shrinkage.
The ratio of shrinkage b/w paste and aggregates is
SC = Sp (1 – a)n
‘n’ varies b/w 1.2 – 1.7