6505-4 - The Structure of Concrete Three phases present in...

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1 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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2 Structure of Hydrated Cement Paste Anhydrous Portland cement - angular particles in the size range 1 to 50 μ m. Calcium silicate hydrate (C 3 S 2 H 3 or C-S-H) Recall the chemical reactions: 2C 3 S + 6H C 3 S 2 H 3 + 3CH 2C 2 S + 4H C 3 S 2 H 3 + CH C-S-H makes up 50 to 60% of the solids in a completely hydrated cement paste. C-S-H appear as very small fibrous crystals which fill the space formerly occupied by water and the dissolved cement particles. Calcium hydroxide Constitutes 20 to 25% of the volume of solids in the hydrated paste. Large prismatic crystals. Little contribution to strength of concrete.
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This note was uploaded on 05/26/2011 for the course CGN 6505 taught by Professor Mang during the Spring '11 term at University of Florida.

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6505-4 - The Structure of Concrete Three phases present in...

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