When Water is mixed in cement it starts a chemical reaction. Then hydration process starts and makes a cement paste. This paste can be moulded in any shape until it hardens. Cement continues to react with water and slowly starts losing its plasticity and ultimately hardens. Time taken to harden the cement after mixing water into it is called as setting time of cement.
Initial setting Time: –
Time taken between Water mixed with cement to the time when Cement paste starts losing its plasticity. For ordinary portland cement, this time is 30 minutes.
Final Setting Time: –
Time taken between Water mixed with cement to the time when Cement paste completely lost its plasticity. For ordinary portland cement, this time is 600 minutes or 10 hours.
Significance: –
- Initial setting time helps to find the minimum time to place concrete in the desired location.
- Final setting time helps to find out time for deshuttering of formwork or stripping time of formwork.
- Concrete should not be disturbed after the Initial setting time of cement is reached.
- Concrete transportation, curing, placing time are dependent on the Setting time of the Cement.
Factors Affecting Setting Time: –
- The fineness of the cement. Finner cement starts hydration faster.
- Atmospheric temperature. Low Temperature slows down the hydration process and hot temperature speed it up.
- Humidity in weather directly impacts the setting time of cement.
- Chemical composition in sand and aggregates also impact the setting time of cement.
- Quality of water.
Apparatus Required in Cement Setting time Testing:-
Needle: – 1mm and 5mm needle to find out and Initial and Final setting time Respectively.
Vicat apparatus: – it consists of arrangement to hold the plunger and needle, which are made to fall freely.
StopWatch: – To calculate Time
Mould: – For cement Paste.
Weigh scale: – To measure sample weights.
Test Procedure: –
Initial Setting Time: –
- Check the weather of the lab:- Lab temperature should be around 27 degrees Celsius. Humidity should be around 65%.
- Take 400 grams of cement. Add water to it. Measure the quantity of water added.
- Mix cement and water properly for 3 – 5 minutes. Make a good paste. Add water 0.85P. Where P is % of water added to achieve consistency of cement.
- Note the time when water is added to the cement.
- Fill the Vicat Mould with Paste. Fill it to the edge. Smoothen the top surface of the paste.
- Remove air content in the mould with mild shakes.
- Immediately place the mould on the Vicat apparatus base. The base should be smooth.
- Lower the Plunger to a 1mm needle touch the top of the paste and remove it quickly.
- Let the Needle go deep in the cement paste.
- Note the reading of the depth by the needle.
- It should be 35 mm from the top. The means depth from the bottom should be 5 mm, as mould is of 40 mm depth.
- If the depth is more then try the next sample with less quantity of water. If the depth is less the try next sample with more water.
- Repeat these tests until the desired result is achieved.
- Note down the final time when the desired result is achieved.
- This Time is Initial Setting Time.
Final Setting time: –
- After the initial setting time procedure, Remove the 1 mm needle and attach 5 mm needle.
- Lower the Plunger to a 1mm needle touch the top of the paste and remove it quickly.
- If the needle doesn’t make a mark then Cement is set.
- If it deepens or makes a mark repeat the test until the result is achieved.
- Note down the final time when the desired result is achieved.
- This Time is Final Setting Time.
