........... is added to make white concrete.
Try it first: pick an option, then read the explanation.
Correct answer: B. Metakaolin
⬛ Making White Concrete
Metakaolin is a highly reactive pozzolanic material produced by calcining (heating) kaolin clay at 650–850°C. When used with white cement, it reacts with calcium hydroxide produced during hydration to form additional cementitious compounds. Importantly, metakaolin is white in colour, so it does not discolour the concrete.
Other supplementary cementitious materials like fly ash are grey or beige and would spoil the whiteness. Pigments can add any colour but are not specifically needed for white concrete. Rice husk ash is grey-black and unsuitable.
Metakaolin — option B.
Key takeaway
Metakaolin is both white and highly reactive — the right choice for white concrete alongside white Portland cement.