The pozzolanic reaction of fly ash in concrete with cement hydration product Ca(OH)2 produces:
Choose the correct answer
Free lime expansion
Additional C-S-H gel, which fills pore spaces, reduces permeability, and improves long-term strength
Ettringite
CO2 gas
Correct Answer
B. Additional C-S-H gel, which fills pore spaces, reduces permeability, and improves long-term strength
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Fly ash (IS 1489 Part 1: Class F, siliceous, from bituminous coal): SiO2 + Al2O3 + Fe2O3 > 70%. Reacts with Ca(OH)2 (from cement hydration) slowly to form C-S-H gel. Benefits: reduced permeability, lower heat of hydration, improved workability, better durability (sulphate resistance). Used up to 35% replacement of cement (IS 456).
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