How to Prevent Hairline Cracks in Concrete Surface?
Hairline cracks are categorized as cracks in concrete that has width lesser than 0.003 inches or 0.08 mm. Hairline cracks are rarely a great concern. It can only be controlled and its tough to eliminate. It can be minimized some important construction practices.
Causes of Hairline Cracks in Concrete Surface
Only if you know the causes of hairline cracks, you will be able to prevent it. The main reason behind hairline cracks are plastic shrinkage in concrete. This is a attack procedure happening in concrete during the plastic state of concrete, i.e. before the hardening state.
Plastic shrinkage of concrete happens when there is rapid depletion of moisture from the concrete surface, without staying there to support adequate hydration of concrete. This depletion of moisture is caused due to temperature of air, concrete, the relative humidity and the wind velocity of the region. These factors results in high evaporation both during cold and hot weather. Other reasons are:
1. The addition of chemical admixture - Its type and dose
2. Screeding and finishing operations
3. Alkali-Aggregate Reactions
4. Poor workmanship and quality construction
5. Bleeding of Concrete
6. Water loss from concrete either due to absorption of aggregates, or formwork or subgrade.
7. Insufficient Curing Period
Prevention of Hairline Cracks in Concrete
1. Curing process must be started as soon as the finishing has completed without any delay
2. The air above the surface can be saturated by using fog nozzles.
3. Before pouring the concrete, the subgrade and the formwork must be dampen. Remove excess water.
4. If the temperature is not favorable, a evaporation retardant can be used.
5. The wind velocity can be reduced by using wind breakers
6. Between the finishing operations, keep it mind to cover the surface with a plastic sheet.
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