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PRINCIPLES OF CONCRETE MIX DESIGN Presentation Transcript
1.PRINCIPLES OF CONCRETE MIX DESIGN
2.WORKABILITY OF CONCRETE
Workability(Slump,C.F,VB Time,Flow &
Slump Flow) is dependent on water
content of concrete.
For higher workability,water content is to be increased by about 3% for every additional
25 mm slump.
Otherwise, Plasticizers(up to 1%) or
Superplasticizers(up to 2%) can increase
the slump of concrete.
Workability(Slump,C.F,VB Time,Flow &
Slump Flow) is dependent on water
content of concrete.
For higher workability,water content is to be increased by about 3% for every additional
25 mm slump.
Otherwise, Plasticizers(up to 1%) or
Superplasticizers(up to 2%) can increase
the slump of concrete.
3.28-DAY COMPRESSIVE STRENGTH OF CONCRETE
4.1. 28 –Day compressive strength of concrete is dependent on W/C ratio or water/cementitious materials ratio of concrete.
Cementitious Materials(cement +Flyash) or
(cement+ g.g.b.s)or(cement+silica fume).
2. 28-Day compressive strength of concrete
is also dependent on the grade of cement
Cementitious Materials(cement +Flyash) or
(cement+ g.g.b.s)or(cement+silica fume).
2. 28-Day compressive strength of concrete
is also dependent on the grade of cement
5.TARGET 28-DAY COMPRESSIVE STRENGTH OF CONCRETE
The target 28-day compressive strength
of concrete is calculated based on standard
deviation value at the site of construction,&
this will depend on the degree of quality control
being exercized at the site.
For Good Q.C, S.D can be 3 or 4 N/mm2.
The W/C ratio or the W/cem.materials ratio
is chosen for the target 28-day compressive
strength of concrete.
The target 28-day compressive strength
of concrete is calculated based on standard
deviation value at the site of construction,&
this will depend on the degree of quality control
being exercized at the site.
For Good Q.C, S.D can be 3 or 4 N/mm2.
The W/C ratio or the W/cem.materials ratio
is chosen for the target 28-day compressive
strength of concrete.
6.WATER CONTENT OF CONCRETE
The water content of concrete(for a particular slump of concrete e.g 20mm or
50mm slump) will also depend on the
Max. size of aggregate & its type(angular or rounded).
Superplasticizers can reduce the water
content of concrete by 20% or more. A
few trials will be required to fix the % of
superplasticizer(% by wt. of cement) or
[% by wt. of (cement+flyash)],to provide the
desired workability of concrete.
7.Once the water content & the W/C ratio are decided, the cement content of concrete can be
calculated. Next the W/C ratio & the cement content of concrete are to be compared with the “min.cement content”& ‘max.W/C ratio’ specified for the site exposure condition.
The water content of concrete(for a particular slump of concrete e.g 20mm or
50mm slump) will also depend on the
Max. size of aggregate & its type(angular or rounded).
Superplasticizers can reduce the water
content of concrete by 20% or more. A
few trials will be required to fix the % of
superplasticizer(% by wt. of cement) or
[% by wt. of (cement+flyash)],to provide the
desired workability of concrete.
7.Once the water content & the W/C ratio are decided, the cement content of concrete can be
calculated. Next the W/C ratio & the cement content of concrete are to be compared with the “min.cement content”& ‘max.W/C ratio’ specified for the site exposure condition.
8.If flyash or g.g.b.s is used in concrete,
its proportion in the concrete mix can be decided based on it’s quality,quality of cement & the Project requirement.
its proportion in the concrete mix can be decided based on it’s quality,quality of cement & the Project requirement.
9.VOLUME OF COARSE AGGREGATE
This will depend on the Max. size of aggregate & the grading zone of the fine aggregate, for a fixed W/C ratio.
For every +/- 0.05 change in the W/C ratio, the Vol. of C.A is to be changed
by -/+0.01m3.
This will depend on the Max. size of aggregate & the grading zone of the fine aggregate, for a fixed W/C ratio.
For every +/- 0.05 change in the W/C ratio, the Vol. of C.A is to be changed
by -/+0.01m3.
10. Once C.A Vol. is decided, the Vol. of F.A
is automatically fixed.
Their mass are next calculated using absolute
Vol. method, using Sp.gr of each material.
These wt. of C.A and F.A are for saturated
surface dry aggregates. If dry aggregates
are used,the amount of mixing water should
be increased by an amoumt equal to the
moisture likely to be absorbed by the aggregates.
is automatically fixed.
Their mass are next calculated using absolute
Vol. method, using Sp.gr of each material.
These wt. of C.A and F.A are for saturated
surface dry aggregates. If dry aggregates
are used,the amount of mixing water should
be increased by an amoumt equal to the
moisture likely to be absorbed by the aggregates.
11.If wet aggregates are used,the necessary
reduction shall be made from the mixing water by an amount equal to the free
(surface) moisture available in the aggregates.
Necessary adjustments in the mass of aggregates are to be made, because
of dry or wet condition.
reduction shall be made from the mixing water by an amount equal to the free
(surface) moisture available in the aggregates.
Necessary adjustments in the mass of aggregates are to be made, because
of dry or wet condition.
12.The C.A of different size fractions should be combined in suitable proportions, so as to result in an overall grading conforming to Table 2 of IS 383,for 40,20,16 and 12.5 mm Max. size of aggregate.
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