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Among natural light weight aggregates listed by the unit (pumice, diatomite, scoria, volcanic cinder, sawdust, rice husk), which one is the only natural aggregate used widely in light weight concrete production?
Answer & Solution
Correct answer: C.
1. The unit lists several natural light weight aggregates but notes most have only local availability.
2. Pumice is a light coloured volcanic glass with bulk density 500–900 kg/m³.
3. The unit states pumice is the only natural aggregate used widely, with use even traceable to Roman structures.
4. Pumice concrete does carry higher drying shrinkage and water absorption.
5. Diatomite, scoria and sawdust are limited to local or non-structural uses.
_Source: IGNOU Concrete Technology, Unit 11 "Special Concrete" (Light Weight, Aerated, No-Fines, High Density, Fibre Reinforced, Polymer Concrete)._
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