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The reduction in weight is accompanied by a considerable decrease in
strength. Another type of light weight concrete is made by “entraining” air
bubbles in the mix to which a substance has been added to keep the bubbles
stable during setting.
1. Answer the following questions:
1. How is concrete made? 2. What takes place when water is added to the
cement? 3. Does the whole mixture set and harden when hydration takes place?
4. A solid mass is formed, right? 5. Do you know what is termed “aggregate”?
6. Is sand known as “fine aggregate”? 7. And what is meant by “coarse
aggregate”? 8. Can concrete be made on a building site and poured into position
as a wet mix? 9. Are you able to explain what is meant by “in-situ” concrete?
2. Read the following and then describe the behavior of concrete:
1. Curing. Concrete becomes hard by the chemical combination of cement and
water, during which process it is necessary to prevent as far as possible
evaporation of the water from the surface of the concrete; this is called
“curing”, and is accomplished by covering the concrete, as soon as it can be
done without damaging the surface, with damp cloths, wet straw, wet sand, etc.,
kept wet by sprinkling, or by immersing in water.
2. Hardening. The strength of concrete under favorable curing conditions
increases with age. Hardening is very rapid in the early stages, but continues
more slowly for an indefinite period amounting to years.
3. Insert the needed words and groups of words:
Portland cement is a … product. It is made of …, … or … . They are … and …
with water to form a paste. The mixture is then … in a kiln. The clinker is
ground to … .
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