Setting describes the stiffening of the fresh cement paste. Onset of rigidity occurs. Then hardening begins, which indicates that a useful and measurable strength is developing. Setting and hardening result from the continuing reaction between the cementitious material and water.
- 1 What is hardening explain?
- 2 Who is responsible for setting & hardening of cement?
- 3 Why gypsum is used in hardening of cement?
- 4 What is final setting time?
What is setting for cement?
The setting is defined by ASTM C125 as ‘ the process, due to chemical reactions, occurring after the addition of mixing water, that results in a gradual development of rigidity of a cementitious mixture.’ In other words, it is the process a concrete mixture goes through, from being a liquid mixture to gaining certain
What is hardening explain?
From Wikipedia, the free encyclopedia Jump to navigation Jump to search Look up hardening or harden in Wiktionary, the free dictionary. Hardening is the process by which something becomes harder or is made harder. Hardening may refer to:
Hardening (metallurgy), a process used to increase the hardness of a metal Hardening (botany) or cold hardening, a process in which a plant undergoes physiological changes to mitigate damage from cold temperatures Hardening (computing), the process of securing a system against attack Target hardening, strengthening of the security of a building or installation to protect it from attack Sclerotization, a biochemical process forming cuticle in arthropods
Who is responsible for setting & hardening of cement?
Free 10 Questions 30 Marks 10 Mins The setting and hardening of cement after addition of water is due to hydration of some of the constituent compounds of cement such as Tricalcium aluminate, Tricalcium silicate, Dicalcium silicate, and Tetra calcium aluminoferrite.
These compounds are known as Bogue’s Compounds. Hydration of Bogues Compounds Tricalcium aluminate (C 3 A): Celite is the quickest one to react when the water is added to the cement. It is responsible for the flash setting. The increase of this content will help in the manufacture of Quick Setting Cement.
The heat of hydration is 865 J/Cal, Tricalcium silicate (C 3 S): This is also called as Alite, This is also responsible for the early strength of the concrete. The cement that has more C 3 S content is good for cold weather concreting. The heat of hydration is 500 J/Cal,
Dicalcium Silicate (C 2 S): This compound will undergo reaction slowly. It is responsible for the progressive strength of concrete. This is also called as Belite, The heat of hydration is 260 J/Cal. Tetra calcium Alumino ferrite (C 4 AF): This is called as Felite, The heat of hydration is 420 J/Cal, It has the poorest cementing value but it responsible for long term gain of strength of the cement.
Last updated on Sep 22, 2022 UPPSC AE Final Result Out on 1st December 2022. The candidates appeared for the interview from 17th October to 15th November 2022. A total of 266 candidates have been finally selected out of the total vacancies advertised. Also note that this is for the 2021 cycle.
Why gypsum is used in hardening of cement?
(2) The Mixing Amount of Gypsum – Gypsum is called the retarding agent of cement which is mainly used for regulating the setting time of cement and is an indispensable component. Without gypsum, cement clinker can condense immediately by mixing with water and release heat.
The major reason is that C 3 A in the clinker can dissolve in water quickly to generate a kind of calcium aluminate hydrate, a coagulant agent, which will destroy the normal use of cement, the retardation mechanism of gypsum is: when cement is hydrated, gypsum reacts with C 3 A quickly to generate calcium sulfoaluminate hydrate (ettringite) which deposits and forms a protection film on the cement particles to hinder the hydration of C 3 A and delay the setting time of cement.
If the content of gypsum is too little, the retardation affect will be unobvious. Too much gypsum will accelerate the setting of cement because gypsum can generate a coagulating agent itself. The appropriate amount of gypsum depends on the content of C 3 A in the cement and that of SO 3 in gypsum, and it also related to the fineness of cement and the content of SO 3 in clinker.
The amount of gypsum should account for 3% ~ 5% of the cement’s mass. If the content of gypsum exceeds the limit, it will lower the strength of cement and it can even lead to poor dimensional stability, which will cause the expanded destruction of cement paste. Thus, the national standard requires that the content of SO 3 should not be more than 3.5%.
Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9781845699550500049
What is the minimum curing period?
It is also recommended that the curing duration should not be less than 10 days for concrete exposed to dry and hot conditions and 14 days for concrete with mineral admixture.Q.
How strong is concrete after 4 days?
ALLOW PROPER TIME TO WATERCURE SLABS – After concrete is placed, the concrete increases in strength very quickly for a period of 3-7 days. Concrete which is moist cured for 7 days is about 50% stronger than uncured concrete. Water curing can be done after the slab pour by building dams with soil around the house and flooding the slab.
- The enclosed area is continually flooded with water.
- Ideally, the slab could be water cured for 7 days.
- Some builders on a tight schedule water cure for 3 days as this achieves approximately 80% of the benefit of water curing for 7 days.
- Consider planning your job to pour at the end of the week, build berms, then flood over the weekend.
You get the benefit of water curing without losing too much time in the schedule. Related Information:
What is final setting time?
1. objective – For convenience, initial setting time is regarded as the time elapsed between the moments that the water is added to the cement, to the time that the paste starts losing its plasticity. The final setting time is the time elapsed between the moment the water is added to the cement, and the time when the paste has completely lost its plasticity and has attained sufficient firmness to resist certain definite pressure.
What is standard setting time of cement?
Test Procedure : –
A cement paste is prepared by adding water 0.85P% by weight of cement. The time of mixing should not be less than 3 minutes and should not be more than 5 minutes. Now the paste is filled in the Vicat mould and the top is levelled off. The mould is now placed under the square needle with annular collar and is brought down touch the surface of the paste. Now the square needle with annular collar is suddenly released and allowed to make on impression on the cement paste by its own weight. The impression made by this square needle with annular collar is observed. The whole experiment is repeated with incremental time intervals until such a time when the square needle makes an impression on the paste while the annular collar fails to do so. The time elapsed between the moments when water is added to the cement to the time when the square needle makes an impression on the paste while the annular collar fails to do so is known as the Final Setting Time of the cement. The final setting time of cement should not be more than 600 minutes for Ordinary Portland Cement.
Also Read : Workability of Concrete & Factors Affecting It
What is cement setting rate?
Initial Setting Time of Cement – The time from the moment water is added to the cement to the moment when cement starts losing plasticity is called the initial setting time of cement. In other words, IST is the time when the stiffening starts in cement paste.
IST is the time until which the cement paste can be moulded into any desired shape without affecting its strength. In actual construction practice, time is required for concreting operations like mixing, transporting, placing, finishing, compacting, etc. The cement should remain in a plastic state until all these operations are completed.
There are certain points to be taken care of during these operations, you can read about these operations here- Steps in Concreting Process For ordinary Portland cement, IST is 30 min. hence, all the concreting steps need to be completed within 30 minutes, else the concrete will start losing plasticity and the full strength of concrete would not be achieved. Setting Time of Cement
What is the difference between setting and curing of concrete?
Concrete professionals often refer to two separate points in the concrete pouring process. The concrete is set to have set when it has stiffened to the point it supports some pressure without damage. A common example is walking on the slab without leaving footprints.