Building Materials, Third Edition

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When aggregates are washed with water containing impurities, they get coated with layers of
silt, salts and organic matters. These reduce the bond between the aggregates and cement and
markedly affect the strength.

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Water fit for making concrete can be used for curing. Waters containing impurities and leading
to stains is objectionable. When concrete is subjected to prolonged wetting, even a very low
concentration of iron and organic matter may cause staining. Water containing more than 0.08
ppm of iron is not recommended for curing.

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1. What is the purpose of mixing water in concrete?


2. Enumerate the various impurities in water having deleterious effects on concrete.


3. How will you decide on satisfactory water for making concrete?


4. If water of unknown performance is to be used, explain how to determine its acceptability.


5. What are the effects of impurities, in the mixing water, may have on concrete?


6. Sea water can be used in concrete. Comment.


7. After what process would sewage water be usable?


8. What effect would the following impurities have if present in mixing water?
   (a) Algae (b) Oils (c) Suspended solids


9. Discuss the requirements of water for
   (a) Making concrete (b) Washing aggregates
   (c) Curing concrete.

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1. The effects of impurities in water are expressed in terms of
   (a) initial setting time (b) final setting time
   (c) compressive strength (d) soundness
   of Portland cement.


2. The difference in 7 days compressive strength of cubes and cylinders prepared with
   impure and pure waters should not differ by more than
   (a) 2% (b) 5% (c) 10% (d) 12%


3. The upper limit of suspended particles in water for the preparation of concrete is
   (a) 200 ppm (b) 2000 ppm
   (c) 5000 ppm (d) 10,000 ppm


4. Organic matter in water for making concrete should not be more than
   (a) 1000 ppm (b) 3000 ppm
   (c) 10000 ppm (d) 15,000 ppm


5. Consider the following statement in making concrete with sea water.
   
   
   1. Strength of concrete is reduced by about 10-20%
   
   
   2. Setting time accelerates