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Question
Write a note on Deccay of Concrete.
Solution
The cement concrete although mechanically strong, but due to the presence of free lime it become susceptible to the attack of acidic water. Alkaline water do not have marked effect on concrete strength. Also lime is more soluble in soft water than hard water and hence deterioration of concrete in contact with soft water is more. Presence of sulphates cause maximum damage because it reacts with tricalcium aluminate to form sulpha aluminates which occupies more volume and hence undergo expansion making the cement structure weak.
PROTECTION OF CONCRETE
• By giving a coating of bituminous material. This prevents direct contact between concrete and water. This is a very inexpensive method.
• By coating the surface with silicon fluoride in a soluble form together with oxides of Zn, Mg or AI. the precipitate of calcium fluoride so-formed in the capillaries prevents dissolution of lime.
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RELATED QUESTIONS
Calculate the quantity of the pure lime and soda required for softening of 1,00,000 litres of water containing the following impurities in ppm. The purity of lime is 70% and soda is BS% Ca(HCO3) = 30.2 , Mg(HCO3) = 20.8 ,CaCI2 = 28.1 ,MgCl2 = 8.78, CaSO4 = 35, MgSO4 = 6.7 .
Calculate the amount of lime (85% pure) and soda (95% pure) required to soften one million litre of water which contains CaCO3 = 12. 5ppml MgCO3 = 8.4ppml
CaCl2 = 22.2ppml , MgCl2 = 9.5ppml C02 = 33ppml HCI = Z3ppml organic matter= 16.Bppm
Calculate the amount of lime {80 %purity) and soda {90% purity) required for softening of 50,000 of hard water whose chemical analysis results are given below. Ca(HCO3 ) = 40.5 mg/L, Mg( HCO3)2 = 73.0 mg/L, MgSO4 = 60.0 mg/L, CaSO4 = 34.0 mg/L, CaCl2 = 27.5 mg/L and NaCI = 20.0 mg/L.
A sample of water contains following impurities :
Mg(HCO3)2 =73 mg/lit , MgSO4 = 120 mg/lit , CaCl2 = 222 mg/lit and Ca(NO3)2 = 164 mg/lit . The purity of lime is 74% and soda is 90% . Calculate the quantity of lime and soda needed for softening of 50,000 litres of water .
