Friday, March 4, 2011

Different Types of Shrinkage Of Concrete

1.Plastic Shrinkage: While the cement is in plastic condition shrinkage occurs during the period of hydration. It is believed that evaporation of water in air of water by aggregate or sub grade cause this shrinkage.

2.Drying Shrinkage: Withdrawal of water from concrete in saturated air cause drying shrinkage, The loss of water contained in hardened concrete does not cause shrinkage. The loss of water from gel pores cause drying shrinkage.

3.Carbonation shrinkage: Carbon-di-oxide(Co2) present in the atmosphere reacts with hydrated cement. As a result calcium hydroxide [Ca(OH)2] decomposes and forms calcium carbonate [CaCO3] and some other compounds of hydrated cement also decomposes.This reaction takes place even at low pressure of CO2 in atmosphere.This reaction is called carbonation. It accompanies with increase of weight and shrinkage of concrete. The shrinkage is due to the production of CaCo3 in the place of Ca(OH)2, where the volume of CaCO3 is less than the volume of of Ca(OH)2.

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