What is the quality of water for curing of concrete?

The water used for mixing and curing should be pure and free from harmful impurities of oils, salts, acids, salts etc or other harmful substances

Quality of Water for Concrete

The water used for mixing and curing of concrete should be pure and free from harmful impurities like oils, salts, acids, salts, sugars, organic substances or other harmful substances

Potable water means drinkable water is normally used for satisfactory for mixing concrete

How to check water quality is good for concrete?

If you have a doubt related to the development of strength by using water which is available for creating cement concrete will be found out by compressive strength and initial setting time tests

For the testing of compressive strength of concrete cube of 150 mm or 100 mm which depend on you and also the availability of equipment, at least three cube cast, cured for 28 days with the proposed water and tested as per the specification given in the IS CODE 516

The average of the comprehensive strength of three or more cube after 28 days curing should not be less than 90 per cent of the average strength of three similar concrete cubes which cast with same materials and cured with distilled water

The initial setting time of tested cement concrete block cast with the available or as per specification cement and the water which you want to be used shall not be less than 30 min tested as per the specification given in the IS CODE: 4031 part - 5

If you don’t know about which IS CODE required for which test Or which is code provided for which material Please watch below video

The PH value of proposed water should be less than 6
The permissible limits for solids in mixing water should be as given in below table

What is the quality of water for curing of concrete?
source IS CODE 456

The following guidelines should also be taken into consideration in respect of the quality of water

  1. For the neutralize the sample of 100 ml water by using phenolphthalein as an indicator, it should not require more than 5 ml of 0.02 normal NaOH. The details of the test are given in IS code: 3025 part 2
  2. For the normalize the sample of 100 ml water by using the mixed indicator, it should not require more than 52ml of 0.02 normal H2SO4. The details of the test are given in IS CODE: 3025 part 23

Effect of Impurities in water during curing of concrete

The impurities in water affect the properties of cement concrete in the following ways which are:

  • Carbonates and bicarbonates of sodium and potassium (alkali) affect the setting time of concrete. 
  • While sodium carbonate may result in quick setting, the bicarbonates may either accelerate or retard the setting alkali carbonates and bicarbonates should not exceed 1000 ppm 
  • slightly salty water contains chlorides and sulphates when chloride does not exceed 500 ppm and SO2 does not exceed 400 ppm the water is harmless
  • Weak water contains chlorides and sulfates, while chloride does not more than 500 ppm and SO2 does not more than 400 ppm
  • The seawater normally carries 3-4% of dissolved salts, about 75-80% of water is sodium chloride and 15% chloride and sulphate of magnesium. 
  • The salts present in seawater reduces the strength of concrete by 10 to 20% chlorides causes corrosion of reinforcing steel and efflorescence concrete
  • Salts of manganese, zinc, copper, tin and lead cause a marked reduction in strength of concrete
  • impurities in the Algae form may also be present in mixing water which is used for concrete or on the surface of aggregate particles. It combines and makes the bond with the cement and reduces the bond capacity between aggregate and cement paste. Algae present in water introduce a large quantity of air in the concrete thus lowering the strength of concrete
  • If the amount of sugar is less than 005 % by weight of water there is no adverse effect on the strength of concrete. Sugar content up to 0.15% by the weight of cement retard setting time. When the quantity of sugar exceeds 0.20% by weight of cement, 28-day compressive strength reduce
  • The vegetable oils have a detrimental effect on the strength of concrete at later ages. If the concentration of mineral oil is up to 2% by weight of cement a significant increase in strength has been noticed
  • Suspended particles of clay and silt are undesireble as they interfere with setting hardening and bond characteristics

Effect of seawater on cement concrete?

It is advisable to use clean water fil for drinking purposes for making cement concrete

However, at places where seawater is available in abundance and potable water is costly, seawater can be used for making plain concrete. The following kind of problem may create by using seawater for making cement concrete has to be studied from the following two aspects:

  1. Strength  of concrete 
  2. Corrosion of reinforcement

1. Strength of concrete

The seawater normally contains 3.5% of dissolved salts. About 78% of which is sodium chloride and 15% of magnesium chlorides tend to accelerate the setting of cement and to improve the strength of concrete in early stages

on the other hand, sulphates tend to retard the setting of cement and discourage the strength of concrete in the early stages. 

It is found that the net effect to these to contradictory actions is the fall in the strength of concrete to the tune of about 10 to 20%

Seawater tends to develop dampness and efflorescence. So that it can be adopted for concrete structures where the specification of finishing characteristics, not the first priority

2. Corrosion of reinforcement

It is found that seawater does not lead to corrosion of reinforcement by providing dense concrete and also by proving sufficient minimum cover to the reinforcement. 

The minimum cement content for concrete completely immersed in water (sever environment condition) should be 320 kg per m3 and minimum cover to reinforcement should be 75 mm

The IS code: 456 – 2000, prohibits the use of seawater for mixing and curing of reinforced concrete and prestressed concrete work. 

This types of specification permit the use of seawater for mixing and curing of plain cement concrete (PCC) under unavoidable situations

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