Q) How to improve the quality of concrete
Concrete is the required proportion of cement, aggregate
(sand or gravel), water and admixtures. We want to improve the quality of
concrete by:
o
Use
High grade of Cement:
High-grade cement gives higher
surface area and more surface of cement particle available for hydration.
o
Use
Mineral Admixtures:
Use mineral admixtures like GGBS.
Triple hydration occurs; it helps to increase the strength of concrete.
o
Water-Cement
Ratio:
Use the lower W/C ratio, gives higher
strength. If the reduction of water not possible due to workability, use superplasticizers,
which reduces the amount of water.
o
Curing:
Ensure the curing, because concrete
hydrated for a minimum of 7 days. Curing essential for optimum strength gain and
durability. It’s necessary for maintaining the required moisture content and
temperature.
o
Vibration/
Compaction:
Concrete strength depends on
compaction. Vibration helps to remove the air entrapped in the concrete pour. This
is done after the concrete pour. Improper compaction leads to presences of air
voids in concrete which reduce strength. It is observed that 5% void, decreases
concrete strength by 30%.
o
Ratio:
Ensure correct ratios of cement,
sand, aggregate, and water. Extra cement gives extra strength but it causes to
crack. Extra cement & water causes heavier segregation
o
Steel:
Ensure the correct steel in the correct
position. It is essential. It’s not essential occurs failure.
o
Mixing
Time:
Concrete strength increase with the increase in mixing time up to 2 minutes, beyond that time there is no increase
in strength.
o
Type
& Size of Aggregate:
Spherical or rounded aggregate
provides more compaction than irregular shape. Well graded aggregate gives more
strength. The maximum size of aggregate, it’s surface area is small, lower w/c
ratio & gives more strength. But the smaller surface area leads to gel bond,
which causes less strength. Aggregate in concrete is weak, concrete also weak.
Weak rocks like chalk are unsuitable
for aggregate use.
o
Proper grading of aggregate
o
Maintain curing temperature between 10
to 30 degree Celsius
o
More density gives more strength. Use
aggregate with specific gravity between 2.8 to3
o
Aggregate- cement ratio should be high,
but not too high to avoid improper bonding
o
Sand will be free from clay
o
Vibration time required for a compact,
dense & non-bleeding mass
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