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The Structure of Concrete
•Three phases present in concrete:
(1) Aggregate particles
(2) Hydrated cement paste (hcp)
(3) Transition zone, which is the interfacial region between the
aggregates and the hcp.
•The amount, size, shape and distribution of these three
phases constitute the structure of concrete.
•Macrostructure - the structure visible to the human
eyes.
•Microstructure - the microscopically magnified portion
of a macrostructure.
•The structure of concrete is highly heterogeneous and
dynamic (i.e. changes with time).
Structure of the Aggregate Phase
•Aggregates in concrete are usually chemically stable.
Thus, the properties of concrete are influenced
primarily by the physical rather than the chemical
properties of the aggregate.
•The aggregate phase is predominantly responsible for
the unit weight, elastic modulus and thermal properties
of the concrete.
•Effects of the shape and texture of the coarse
aggregate:
–More angular and rougher texture gives better bonding with
the cement paste, but lower consistency in the fresh concrete.
•The aggregate phase is usually stronger than the other
two phases of concrete, and does not affect the strength
of the concrete, except in the case of weak aggregates.
Effects of flat and elongated aggregate -
tendency to trap bleed water.
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