1. You have the following chemical and physical data for two cements Cement GS (
ID: 1713565 • Letter: 1
Question
1. You have the following chemical and physical data for two cements Cement GS (96) GA(%) CAF (%) B. Fineness 28 49 19 380 370 12 10 Which cement (Type A or Type B) can be used in long term concrete strength? Explain 2. What is a flash set of Portland cement? State one reason for flash set. If flash set is encountered at the job site, what would you do? Explain why the Portland cement concrete can withstand the action of water without serious deterioration). 3. Explain both the usefulness and validity of the theoretical equations for predicting the potential compound composition of Portland cement from chemical analysis. 4. 5. Define the terms initial set and final set and discuss one method to determine them. 6. What is role of gypsum in the construction of Portland concrete? 7. What is the flash set?Explanation / Answer
FLASH SET OF PORTLAND CEMENT
Flash set -- a rapid development of rigidity in freshly mixed portland cement paste, mortar, or concrete.
Reason - If inadequate amounts of gypsum are added to the cement, flash set occurs.Further mixing can't dispel this rigidity, and a large amount of heat is produced in the process. Rapid development of rigidity can also be caused by false set. But in this case, little heat is generated. False set occurs because some of the gypsum dehydrates as a result of contacting hot clinker or high temperatures in the grinding mill. This creates plaster that rehydrates to form gypsum and stiffen the concrete.
Initial set & final set:
Initial setting time duration is required to delay the process of hydration or hardening. Final setting time is the time when the paste completely loses its plasticity. It is the time taken for the cement paste or cement concrete to harden sufficiently and attain the shape of the mould in which it is cast
Role of Gypsum:
This dual role of gypsum is discussed in the feature. Gypsum is the set retarder for ordinary portland cement (OPC). Without gypsum, ground clinker exhibits flash setting in a few minutes, due to the rapid hydration of calcium aluminates to form calcium aluminate hydrate (CAH)
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