Silica fume (micro silica) in concrete improves compressive strength because:
Choose the correct answer
It replaces cement in equal proportion
Its ultra-fine particles (0.1-0.2 micron) fill voids between cement particles (micro-filling) and react with Ca(OH)2 (pozzolanic), producing dense C-S-H, reducing porosity
It increases water-cement ratio
It reduces setting time dramatically
Correct Answer
B. Its ultra-fine particles (0.1-0.2 micron) fill voids between cement particles (micro-filling) and react with Ca(OH)2 (pozzolanic), producing dense C-S-H, reducing porosity
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Silica fume: SiO2 > 85%, extremely fine (200 x finer than cement). Benefits: high strength (up to 100+ MPa), low permeability, excellent durability. Added at 5-15% by mass of cement. Reduces Ca(OH)2 (leachable), eliminating weak zones at aggregate-paste interface. Requires superplasticizer to maintain workability.
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