Effect of Impurities in Water on Properties of Concrete

Effect of Impurities in Water on Properties of Concrete

The impurities in water used for the preparation of concrete may affect the properties of concrete in the following way:  

a) The strength & durability of concrete may be reduced due to the presence of impurities in the mixing water. Experiments show that water containing an excessive amount of dissolved salts reduces compressive strength by 10 to 30% of that obtained using potable water.  

b) The setting time of cement may be changed. Presence of Zinc chlorides retards the setting of concrete to such an extent that no strength test is possible at 2 and 3 days. On the other hands, the presence of calcium chloride accelerates setting and hardening.  

c) Presence of excessive chlorides cause dampness, surface efflorescence & increase the corrosion of reinforcing steel.  

d) Presence of algae in water reduces the bond between aggregate & comet paste & thus lowering the strength of concrete.  

e) Presence of sugar up to 0.15% by weight of cement retard the setting of cement and the early strength may be reduced. When the quantity of sugar increases to 0.2% by weight of cement, the setting is accelerated.  

f) Mineral oils not mixed with animal or vegetable oils have no adverse effect on the strength of concrete. But the presences of vegetable oils have a detrimental effect on the strength of concrete, particularly at later ages.

Common Impurities in Water  & their Permissible limits as per I.S Code

Name of Impurities	Permissible Limits
1.Organic matter	200 mg/lit
2.Inorganic matter	3000 mg/lit
3.Sulfates ( as SO2 )	400 mg/lit
4.Chlorides (as Cl) a) For plain concrete b) For R. C. C.	2000 mg/lit 500 mg/lit
5.Suspended matter	2000 mg/lit

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Role of Water and Quality of Mixing Water in Concrete