Calcium sulphoaluminate cement is of interest chiefly because it
Answer: A
Its principal phase forms around 1,250 degrees rather than 1,450, and the raw mix contains less limestone, so both the fuel and the chemical emission fall. The limit on its use is the availability of the aluminous raw materials it requires.
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Assertion (A): Calcium sulphoaluminate cement is not simply a drop-in replacement for Portland cement despite its lower emissions.
Reason (R): It depends on bauxite or other aluminous materials that are far less abundant than limestone.
Answer: B
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the mechanism. Calcium sulphoaluminate cement emits substantially less carbon dioxide, but it needs an aluminous raw material, and bauxite is neither as abundant nor as widely distributed as limestone. The constraint is on raw material supply rather than on the chemistry, and it caps how far the cement can be adopted.
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State whether the following is true or false.
Every low-carbon cement can be adopted at the scale of Portland cement production.
Answer: C
Correct answer: False
Cement is made in billions of tonnes a year, so any substitute must have a raw material available at that scale and near the markets. Several low-carbon cements are excellent and limited to a fraction of that volume by supply - slag and fly ash by how much iron and coal are produced, sulphoaluminate cements by bauxite.
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Magnesium oxychloride cement, also called Sorel cement, is made by mixing magnesia with
Answer: D
The resulting binder is hard and takes a good polish, which made it popular for industrial flooring and for artificial stone. Its serious weakness is poor resistance to water, which restricts it to protected interior use.
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State whether the following is true or false.
Sorel cement is well suited to exterior work exposed to rain.
Answer: A
Correct answer: False
Sorel cement is a magnesium oxychloride, and its hydration products are soluble in water: exposed to rain it leaches and disintegrates, and the chlorides corrode any embedded steel. It is used indoors for industrial flooring, where its hardness and abrasion resistance are valuable and it stays dry.
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Magnesium phosphate cement is valued for repair work chiefly because it
Answer: B
Correct answer: gains high strength within an hour or two
Magnesium phosphate cement sets by an acid-base reaction rather than by hydration, and reaches usable strength in an hour. That suits a runway or road repair that must carry traffic the same day, and it is why the material is used despite costing several times what Portland cement does. The working time is minutes, not a day.
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Assertion (A): Magnesium phosphate cement is used for repairs despite costing several times as much as Portland cement.
Reason (R): The cost of closing a road or runway usually exceeds the cost of the material by a wide margin.
Answer: C
Both are true and the reason gives the economics: the decision is made on the total cost of the operation rather than on the price per tonne, and a rapid return to service dominates that calculation. Material cost is a small part of the total for such work.
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Geopolymer or alkali-activated binders are produced by
Answer: D
Fly ash, slag or calcined clay reacts with sodium silicate or hydroxide to form a binding network without any Portland clinker. Handling the caustic activator safely is one of the practical obstacles to wider adoption.
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State whether the following is true or false.
A geopolymer binder contains no Portland clinker.
Answer: A
The binding phase is formed by alkali activation of an aluminosilicate rather than by clinker hydration. This is what allows the very large emission saving claimed for such systems, since no limestone is calcined. The activator itself carries an emission burden that must be counted.
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Consider the following statements about alkali-activated binders.
1. They can be made from fly ash or ground slag.
2. The activator is typically a strong alkaline solution.
3. They require the same kiln and clinker as Portland cement.
Answer: B
The first two are correct. The third is precisely what they avoid, since dispensing with clinker altogether is the whole basis of their claimed environmental advantage. The saving comes from not calcining limestone at all.
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