Basics of Setting Time
When working with cement in any form, i.e. cement mortar, cement concrete etc. time is required for all process like mixing, transporting, placing, compacting and finishing. During this process cement mortar/ cement concrete must be in the plastic stage so that every process can be done easily. i.e. If It should not set and gain strength because after that it is difficult to work on it. While preparing and placing cement mortar/ cement concreting you have to complete all such processes in minimum of 30 minutes, after this time cement mortar/cement concrete starting to lose its plasticity which is called initial setting time of cement.
Once cement mortar/cement concrete is placed, it should completely lose its plasticity. So that external agencies may not harm it. This time should not be more than 10 hours (600 minutes) which called final setting time of cement.
The Initial setting time of cement is the time when the cement paste starts losing its plasticity and final setting time of cement is the time when the cement paste completely loses its plasticity. Setting time is essential that cement set neither too rapidly nor too slowly. For OPC, usually the value of initial setting time is 30 minutes and final setting time is 10 hours.
Use of Setting Time of Cement
- Initial setting time of cement is important, to know when the cement is starting to lose its plasticity. It is helpful in determining the time needed for the concreting process, i.e. transportation, placing and compaction of concrete.
- Final setting time of cement is important to know when the cement would be set. This testing of cement is helpful to determine safe removal time of side of form (not vertical support) or scaffolding of concrete.
Standard Guidelines to Determine Setting Time of Cement
- IS 4031 (Part 5)- 1988
- ASTM C 191
- BS EN 196-3:2005
Followings are the apparatus used in setting time test of cement paste:
01. Vicat Apparatus:
The Vicat apparatus shall consist of
- Vicat apparatus consists a frame has a movable rod with a platform at one end and the needle which can be attached at the other end.
I) Needle for determining the initial setting time – The needle shall have a diameter 1.13 ±05 mm, 50 ± 1 mm length and flat end.
II) Needle for determining the final setting time –The needle shall be of the same diameter as a needle for initial setting time, but length shall be 30 ±1, and connected with a brass covering hollowed out. Hollowed out provide to leave a circular cutting edge. The cutting edge is 5 ± 0.1 mm in diameter and 0.5 ± 0.1 mm in depth and 0.75 mm in diameter vent hole.
III) Plunger for determining the standard consistency – Plunger shall be of polished brass having a diameter of 10 ± 0.05 mm
- Graduated Scale: length of graduated scale is 40 mm and the smallest division is 1 mm
- Vicat Mould: Mould is having an Internal diameter of 70 ± 5 mm at the top and 80 ± 5 mm at the bottom and a height of 40 ± 0.2 mm.
02. Weighing Machine: At a load of 1000 g, the allowable variation shall be ± 1.0 g.
03. Stop Watch
04. Gauging Trowel
05. Measuring Cylinder
Procedure to Determine Setting Time of Cement
- Take 400 gm of cement for making a paste.
- The required quantity of water is 0.87 P, P = consistency of water. Water should be potable or distilled water. You can determine consistency from the standard consistency test of cement.
- Prepare a paste of weighed quantity of Cement and water.
- Maintain the time of gauging, gauging time is not less than 3 minutes and not more than 5 minutes. The gauging must be completed before any sign of setting occurs.
- Start a stop-watch at the instant when water is added to the cement. The gauging time is started to count from the time of adding water to the dry cement.
- The mould resting upon a non-porous plate, fill it with this paste
- After completely filling the mould, smoothen the surface of the paste, making it level with the top of the mould. The mould may be slightly shaken for remove the air.
- Place the mould under the rod bearing the needle. (needle for determining the initial setting time)
- Lower the needle slightly until it comes in contact with the surface of the test block and quickly release, allowing it to penetrate the test block.
- In the starting, the needle will completely penetrate the test block.
- Repeat this procedure until the needle fails to penetrate the block to the 5.0 ± 0.5 mm from the bottom of the mould.
- The period elapsing between the time when water is added to the cement and the time at which the needle fails to penetrate the test block to the 5.0 ± 0.5 mm from the bottom of the mould is called the initial setting time.
- To determine the final setting time the first needle is replaced by the (needle for determining the final setting time) needle with an annular attachment.
- When applying the needle gently to the surface of the mould, the needle makes an impression thereon.
- Cement called as final set while the attachment fails to make an impression on the surface of the test block.
- The period elapsing between the time when water is added to the cement and the time at which the needle fails to make an impression on the surface of the test block is called the final setting time.
Points to be Taken Care of
- Clean apparatus shall be used for the experiments.
- Temperature and Humidity- experiment shall be conducted at 27 ± 2°C temperatureand65 ± 5 percent of the relative humidity of the laboratory
- All the appliances shall be free from vibration during the test.
- Take care of the needle; it should keep straight during the experiment.
- If there are any scum forming on the surface of the test block, use the underside of the block for the determination.
- Initial Setting Time of Cement – Note down the time, when needle fails to penetrate 5 – 7 mm from the bottom of the test block. This time is denoted as an initial setting time of cement.
- Final Setting Time of Cement – Note down the time, when needle fails to make an impression on the surface of the test block. This time is denoted as a final setting time of cement.
- Acceptance criteria – Recommended result for various types of cement to their setting time gives by standard guidelines are as follows:
If your test value is not in a rage of the recommended result, there many reasons behind it, such that some chemical composition may have changed during production (manufacturing defect), fault in the testing apparatus, error in testing etc. In that case, you have to take care of the timing of work with it. If the initial setting time less than this value, all the process, i.e. mixing, transporting, placing complete within the time otherwise cement paste/concrete/mortar starts to getting set. If the final setting time is more than this value, you will have to retain scaffolding and the sides of the form, until the cement paste/concrete/mortar is completely rigid and will have to be careful to start the curing time.
Quantity Required to Determine Setting Time of Cement
- 500 gm (400 gm for mould + 100 gm supposed to wastage) cement is required to determine setting time of cement
- If due to any adverse factor, i.e. first experiment fails then that is necessary to make another sample, in that case, we need extra cement.
Cost to Determine Setting Time of Cement
- Cost of setting time test of cement is around Rs. 200 to 400. Cost generally depends on the various factors, i.e. area where test is conducted, the urgency of test results, numbers of the test, relation with client etc.
Frequency to Determine Setting Time of Cement
- Setting time test is conducted per every 50 MT cement used and also when the source, type and brand of cement is changed.
- Test frequency may be changed according to different standard guidelines.