Type of water required for fresh concrete

1. Concrete Technology 1

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WATER FOR CONCRETE
Quality of water is an important aspect of concrete making as it help to form strength giving silica-
gel. Distilled water which is suitable for drinking is best for concrete making. So the best way to check
whether the water is suitable or not is to make concrete cube with source water and similarly with
distilled water also. Now 14th day and 28th day compressive strength is taken and checked whether the
strength is 90% of that of the concrete cube made with distilled water or not.
DIFFERENT TYPE OF WATER IMPURITIES:-
1. Carbonate and bicarbonates :-
2. Chloride and sulphates :-
3. Salts of Mn, Sn, Zn, Cu, Pb :-
4. Silts and suspended particles :-

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DIFFERENT TYPE OF WATER IMPURITIES:-
1. Carbonate and bicarbonates :-
Carbonates and bi-carbonates of sodium and potassium effects the setting time, carbonates retards
the setting time while bi-carbonates accelerate or retard the setting. This also effects in concrete
strength. If it is used with concentration more than 1000ppm then test of setting time and 28days
strength should be carried out.
2. Chloride and sulphates :-
Blackish water contains chlorides and sulphides. If it does not exceeds 1000ppm and 3000ppm
respectively then the water is harmless.
3. Salts of Metals :-
Salt of Mn, Sn, Zn, Pb reduce the strength of the concrete. Salts like NaI, NaP, NaBr,NaSO3
reduces the initial strength to a extraordinarily high degree.
4. Silt and suspended particles:-
These undesirable particles interfere with the setting, hardening and bond characteristics.
Turbidity limit of 2000ppm is accepted.

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SALT WATER AS CONCRETE MAKING
Sea water contain salinity of about 3.5% of which 78% is sodium chloride and 15% are chlorides and
sulphates of magnesium. Sea water react with reactive aggregate, so salt water should be avoided if
aggregates are reactive in nature. This slightly accelerate the initial setting strength while reduces 28
days strength. Salt water may also lead to the corrosion of the reinforcement concrete. The salt water
which contain huge amount of chloride can cause efflorescence and persistence dampness and so it
should be used for plastering purpose if the appearance of the structure is important.
Some precautions:
• Low water-cement ratio should be maintained coupled with vibration.
• Clear cover of at-least 7.5 should be given.
• Should be avoided for prestressed concrete.
• Iron content more than 0.08ppm causes staining so should be avoided if appearance is important.

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Q.1 How to check whether a water is suitable or not?
Ans. Water is a very important factor for concrete as it helps to form silica-gel. Although pure distilled
water is best for concrete making but this not available in abundant. The best way to check whether a
water source is suitable or not is carrying out a test. Concrete cubes are made by using both source
water and distilled water and 28 days compressive strength is found out. If the strength is 90% of the
strength of that of the concrete cubes made with distilled water, than the distilled can be used for
concrete making purpose.
Q.2 Explain are the types of impurities that are found in water?
Ans. Impurities like carbonates and bi-carbonates effects the setting time of the concrete mix.
Carbonates retard the setting time, while bi-carbonates either accelerate or retard the setting time. This
also has effects on the concrete strength. If the water contains impurities more than 1000ppm than
28days test should be done.
Blackish water contains chloride and sulphides. These should not exceed 1000ppm and 3000ppm
respectively.
Salts of Mn, Sn, Pb, Zn reduces the strength to a great extend. Salts like NaI, NaP, NaBr and
NaSO3 reduces the initial strength of the concrete to a extraordinarily high degree.
The silt and suspended particle cause interfere with the setting, hardening and bond
characteristics. Turbidity limit of 1000ppm should not be exceeded.

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Q. 3 Is sea water is suitable for concrete, if not what are its effects?
Ans. Sea water contains salinity of about 3.5% out of which 78% is sodium chloride and 15% is chloride and
sulphate of magnesium. Salt water react with reactive aggerate as like that of alkalis of cement.so reactive
aggregate should not be used if the water id saline. Salt water may also cause corrosion to the
reinforcement concrete. Salt water slightly accelerate the initial setting but can cause reduction of about
10% of strength after 28days. The water containing huge amount of chloride can cause efflorescence and
persistence dampness so it should be avoided for plastering purpose.
Q.4 What are the precaution that should be taken for saline water?
Ans. Low cement-water ratio should be maintained coupled with vibration, clear cover of about 7.5cm
should be maintained, Iron content more than 0.08ppm should be avoided as they causes staining,

8. Do revise 8