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:red_flag:WATER USED IN CONCRETE MIX, Honeycombs-in-Concrete-629x420 -…
:red_flag:WATER USED IN CONCRETE MIX
Water is important ingredient for concrete- To
cause hydration
The function of water in concrete mix:
To dampen the aggregate from absorbing additional water.
To make the mix workable and easy to placed
To lubricate the mixture of gravel, sand and cement for placing
Enable the chemical reaction that caused setting and hardening
If the water is:
a) Not enough
-For hydration thus
cement too dry
and
difficult to place
b) Too much
-Cement weakened,
less strength
and durability
i.
More void
as the water evaporates, less density .
ii. Will form a chalk powder layer on the surface of concrete mix. Thus prevent proper bonding of the next layer of concrete and creates a plane of weakness
iii. Cement grout leak out from work-carry away cement leaving sand and agg-cause '
Honeycomb
' in concrete
Properties of water
i. Free from oil
ii. Free from acid, alkalis, or other organic impurities
iii. pH value not less than 6
iv. Free from iron, vegetable matter or other substance
v. salt water is not recommended because of present of harmful salt
Salt in sea water
-containing 3.5% dissolved salt (78% of sodium chloride, 15% chloride and magnesium sulphate)
-Suitable for use as mixing water for unreinforcement concrete
-Concrete mix with sea water have higher early strength but in later ages may be lower
-Seawater is not suitable for concrete work because it can cause corrosion of reinforcement
-Salt reduce the ultimate strength of concrete usually 10-20% in strength of concrete at 28 days.
Industrial water
-The industrial waste water containing acids or alkalis
-A typical sewage contain roughly 400 ppm (part per million) (0.04%) of organic matter. After treatment reduced to 20 ppm (0.002%) or less
Silt or suspended particles
About 2000 ppm (0.2%) of suspended clay or fine rock particles in mixing water
-Algae can cause :
a) reduction in strength of concrete by :
i. Combine with cement to reduce bond
ii. Cause a large amount of air to be entrained
b) Weakness of bond between aggregate and cement paste
c) Large quantities of air entrained in the concrete, thus lowering the strength of the concrete
Suitability of water
-Suitability of water for making concrete can be categorized into :
a) Treated water
b) Water from natural sources.
-Common types of testing water for concrete are:-
a) Initial Setting Time Test
b) Compressive Strength Test
