'High-Alumina Cement' (HAC) is no longer used in structural applications because:
Choose the correct answer
It takes too long to set (>72 hours)
'Conversion' in warm/humid conditions reduces strength by 30–50% — concrete becomes weaker than ordinary concrete over time
Its colour is unsuitable for buildings
It is too expensive for any use
Correct Answer
B. 'Conversion' in warm/humid conditions reduces strength by 30–50% — concrete becomes weaker than ordinary concrete over time
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HAC (Aluminous cement): initial strength very high (30 MPa in 24 hours). Problem: 'conversion' — at high temperature and humidity, tricalcium aluminate hydrates (hexagonal) convert to cubic forms → 30–50% strength loss + increased porosity. Catastrophic collapses in UK (1970s roof failures). Now restricted to refractory lining, seawater (sulfate resistant), not structural use.
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