1156 posts
Quality control Question 23
It is known in all cement standards that the Initial Setting Time is 45 minutes minimum and the Final Setting Time is 10 hours maximum. Is there any definite time to be considered between end of initial setting and start offinal setting to ensure cement quality and workability.
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1156 posts
Re: Quality control
There is no definite interval between the initial and the final set of cement that denotes good or bad quality or workability. You must bear in mind that the test for setting time is conducted at a constant temperature in the laboratory. This is not the case when the cement is used in practice. In cold countries the setting time extends in practical applications and therefore a short setting time is best in these conditions. In hot countries (such as the Sudan) the setting time is shortened in practice and therefore a longer set in the laboratory conditions would be desirable.
1156 posts
Quality control Question 24
Please advise the chemical and physical properties of:
1. Oil well cement
2. Sulphate resistant cement
3. Slag cement
4. Fly ash cement
Can sulphate resistant cement be replaced with any of the other three cements mentioned above?
1156 posts
Re: Quality control
1. Oil well cement comes in different grades (API Grades A to J inclusive).They are designed to be slow setting and therefore have very low C3A contents and are coarsely ground. Some grades also contain added retarders. As they have low C3A content they are sulphate resisting and could be substituted for SR cement, however the setting time would be long.
2. Sulphate Resisting cement has a limit of four per cent on the C3A content to prevent attack by sulphates on the hydrated C3A.
3. Slag cement has up to 65 per cent granulated blast furnace slag added to the cement clinker and gypsum. The slag content undergoes the pozzolanic reaction and this enhances the impermeability and durability of concrete made from the cement. This makes the concrete resistant to sulphate attack and these cements can be substituted for SR cements.
4. Fly ash cement contains up to 35 per cent fly ash added to the cement clinker and gypsum. The fly ash undergoes the pozzolanic reaction and this enhances the impermeability and durability of concrete made from the cement. This makes the concrete resistant to sulphate attack and these cements can be substituted for SR cements.