Initial and final Setting time of cement & its test procedure, hi guys in this article we know about initial setting time and final setting time of cement, its test procedure explanation significance and result with the help of Vicat appartus.
As we know when cement is mixed with water, there is new bond formed between major component of cement like calcium to form hydrated molecules, this process is known as hydrolysis of cement or hydration. Now cement major component begin to hydrates and makes cement paste. Fresh ready mix cement have plasticity property and This paste can be moulded into any desired shape due to its plasticity.
Within this time period cement continues to react with water and slowly cement starts losing its plasticity and set harden. This complete cycle is called Setting time of cement.
The time to which cement can be moulded in any desired shape without losing it strength is called Initial setting time of cement,or The time at which cement starts hardens and completely loses its plasticity is called Initial setting time of cement,or The time available for mixing the cement and placing it in position is an Initial setting time of cement. If delayed further, cement loses its strength. For Ordinary Portland Cement, The initial Setting Time is 30 minutes.
The time at which cement completely loses its plasticity and became hard is a final setting time of cement,or The time taken by cement to gain its entire strength is a Final setting time of cement,or For Ordinary Portland Cement, The Final Setting Time is 600 minutes (10hrs).
Initial and final setting time of cement,its test procedure,result & significance
Setting time of cement define as the time required for stiffening of cement paste to a defined consistency. Indirectly related to the initial chemical reaction of cement with water to form aluminum-silicate compound.
Setting time of cement is two types: 1) initial setting time of cement and 2) Final setting time of cement.
What is initial and final setting time of cement? Division on setting time of cement is based on Initial setting time of cement and Final setting time of cement. Generally Initial setting is the time elapsed between the moment water is added to the cement to the time at which paste starts losing its plasticity. Final setting time of cement is the time elapsed between the moment the water is added to the cement to the time at which paste has completely lost its plasticity and attained sufficient firmness to resist certain definite pressure.
Initial setting time of cement is caused due to start of rate of hydration and initial loses its plasticity, when water is added to cement mix, there is a new chemical reaction between water molecules and cement component, to form new bond and product as hydrates of aluminum-silicate compound known as hydration of cement. During this it starts to looses plasticity.
Final setting time of cement is caused due to completely stoppage of of rate of hydration and plasticity, when water is added to cement mix, there is a new chemical reaction between water molecules and cement component, to form new bond and product as hydrates of aluminum-silicate compound known as hydration of cement, it can moulded in desire construction work or placed,After 10 an hours its completely lost its plasticity and stop hydration of cement, this is final setting time.
For OPC (Ordinary Portland Cement), The initial Setting time is 30 minutes and final setting time is 10 hrs (600minute).
The major factors affecting the setting time of cement are cement composition, water-cementitious material ratio (w/cm), environmental conditions like temperature & humidity,and admixtures like Accelerator and Retarder. When cement hydrates faster, the time of setting is reduced. Increases in the w/cm result in increased time of setting.
To modify the cement used in concrete properties i.e to shorten the time of setting or to delay the setting time of cement. Admixtures are used and they are as follows:
Accelerators: accelerator is used to shorten the time of setting or increase the rate of hardening or strength development for example calcium chloride. Retarder: it is used to delay the setting time of cement for example soluble zinc salts gypsum ,sugar, carbohydrate derivatives & lignosulphates.
Environmental factors temperature and humidity greatly affect the setting time of cement. Rate of hydration of cement is increase in hot weather condition (reducing setting time) and its reduced in cold climatic condition (increase setting time), where as high humidity reduce the rate of hydration (increase setting time) and low humidity increased the rate of hydration of cement ( reduce setting time).
Significance of Initial and final setting time of cement:- When we add water to cement mix, its start hydration and new chemical bond is formed between molecules of cement and water, mixing cement with water, it takes time to place the cement paste in position, initial setting time possess a primary role in strength & it is mandated that cement paste or concrete is placed in position before it crosses initial setting time. i.e.,30mins. And it shouldn’t be disturbed until it completes Final setting time i.e., 600mins for Ordinary Portland Cement (OPC).
Initial and final setting time of cement Test procedure
According to as per IS code IS: 4031 (Part 5) – 1988. Initial and final setting time of cement test is done using VICAT apparatus conforming to IS: 5513 – 1976.
Vicat Appartus: Initial & Final setting time of cement test is done by with the help of Vicat appartus. Vicat apparatus consist of Weighing balance of 1000g with accuracy 1g, Measuring cylinder of 200ml, VICAT apparatus, VICAT Mould, Glass plate, the plunger of 10mm dia and Hand Trowel and stop watch.
Initial and Final Setting time of Cement test Procedure:-
1) Initial time setting test
● Take 300g of cement and place it in a bowl or tray. Now add water of Start the stopwatch at the moment water is added to the cement to make cement paste of consistency 0.85P, Where P is the Standard consistency of cement is considered.
● Now fill the cement mix in Vicat mould. If any excessive paste remained on Vicat mould is taken off by using a trowel.
● Then, placed the VICAT mould on non porous plate (Glass plate) and square needle 1×1 mm is attached to the moving rod of Vicat appartus, see that the plunger should touch the surface of VICAT mould gently.
● Release the Plunger and allow it to penetrate into the test mould.
● Note down the penetration of the plunger from the bottom of mould indicated on the scale. Repeat the same experiment at different positions on the mould until the plunger should stop penetrating 5 to 7mm from the bottom of the mould, it shows that test is completed.
The time period elapsed between the moment water is added to the cement and the time, the needle fails to penetrate the mould of 5mm to 7 mm when measured from the bottom of the mould, is the initial setting time of cement.
2) final setting time test
● the cement paste is prepared by adding water and it is filled in Vicat mould
● the needle with annular collar is attached to inplace of square needle
● the needle is gently released the time at which the needle make an impression on test block specimen and the coller fails to do so is noted. It is about 10 an hours, this give final setting time of cement.
Final setting time is that time period between the time water is added to cement and the time at which 1 mm needle makes an impression on the paste in the mould but 5 mm attachment does not make any impression.
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