What is the purpose of adding gypsum in cement?

Gypsum is a mineral and is hydrated calcium sulfate in chemical form. Gypsum plays a very important role in controlling the rate of hardening of the cement. During the cement manufacturing process, upon the cooling of clinker, a small amount of gypsum is introduced during the final grinding process.

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Some concrete specification requires the testing of compressive strength for both 7 days and 28 days. Why?

7-day compressive strength test results are usually not used for acceptance purpose but for information only. Instead, 28-day compressive strength test results are commonly adopted for acceptance purpose.

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What is the main purpose of chamfers in concrete structures?

Some would suggest aesthetics as the answer of the question. Others may consider safety on the contrary because chamfered edge is less liable to damage to the concrete structure and any objects hitting on it. However, the main reason of the provision of chamfer is to make formworks easier to pull out after concreting operation.

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Why is liquid nitrogen added to fresh concrete sometimes instead of ice block/chilled water?

Traditionally, chilled water and ice have been employed to reduce the temperature of concrete mix in hot weather condition. Chilled water has a limitation in its cooling potential. For instance, even if all mixing water has been converted into chilled water, the temperature reduction achieved in concrete mix is only about 2.7oC.

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M-35 Mix Designs as per IS-10262-2009

Raj Mohammad Khan

Following table shows the M-35 Mix Designs as per IS-10262-2009, hope this helps all civil engineers here
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