Technical Questions

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What does a pozzolan do in the concrete?

Q. What does a pozzolan do in the concrete?

 

A. As the definition implies, a pozzolan combines with calcium hydroxide in the concrete to form calcium silicate hydrate, similar to that produced by hydration of portland cement. This adds to the strength, impermeability, and sulfate resistance, and reduces expansion from the alkali-silica reaction that might otherwise take place. Use of pozzolans may increase or decrease water demand depending on the particle shape, surface texture, and fineness. Fly ash usually decreases water demand. Most of the other pozzolans increase the water demand. Pozzolans reduce bleeding because of fineness; reduce the maximum rise in temperature when used in large amounts (more than 15% by mass of cementitious material) because of the slower rate of chemical reactions; which reduce the rise in temperature.

 

References: SP-1(02); E3-13 ; SP-221; ACI CT-18; ACI 232.1R-12; ACI 232.2R-03; ACI 234R-06; Supplementary Cementing Materials in Concrete; ASTM C618; ASTM C1240

Topics in Concrete: Pozzolan; Cementitious Material; Materials; Concrete Fundamentals

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