Requirements of concrete mix design:
The requirements which form the basis of selection
and proportioning of mix ingredients are :
a ) The minimum compressive strength required from
structural consideration
b) The adequate
workability necessary for
full compaction with
the compacting equipment available.
c) Maximum water-cement ratio and/or maximum cement content
to give adequate durability for
the particular site conditions
d)
Maximum cement content
to avoid shrinkage
cracking due to
temperature cycle in
mass concrete.
Types of Mixes:
i.
Nominal Mixes
ii.
Standard mixes
iii.
Designed Mixes
Factors affecting the choice of mix
proportions
·
1) Compressive strength
·
2) Workability
·
3) Durability
·
4) Maximum nominal size of aggregate
·
5) Grading and type of aggregate
·
6) Quality Control
Factors to be considered for mix design
•
The grade designation giving the characteristic strength requirement of
concrete.
•
The type of
cement influences the
rate of development
of compressive strength
of concrete.
•
Maximum nominal size of aggregates to be used in concrete may be as
large as possible
within the limits prescribed by IS
456:2000.
•
The cement content is to be limited from shrinkage,cracking and creep.
•
The workability of concrete for satisfactory placing and compaction is
related to the size
and
shape of section,
quantity and spacing
of reinforcement and
technique used for transportation, placing and compaction.
