Table of Contents for cement quality checks at site-
- Check 1: Age of cement
- Check 2: Colour
- Check 3: Lumps
- Check 4: Temperature inside the bag
- Check 5: Texture
- Check 6: Float Test
- Check 7: Smell
- Check 8: Grade of Cement
- Check 9: Type of Cement
- Check 10: Strength Test
- How to store cement for better quality control?
- Final Words
Cement is an essential building material. It is manufactured by heating limestone, red clay, & bauxite at 1400 degrees centigrade in a rotary kiln. The high temperature melts the raw material and produces clinker. The clinker is ground with gypsum to make cement. The quality of cement is maintained by chemistry control, fineness, protection from moisture, proper packing and storage.
The Bureau of Indian Standard has published the guidelines for quality control of OPC & PPC in IS269:2015 and IS1489 (Part 1) respectively.
The present article enlists 10 checks to ensure the quality of cement at the site. The cement quality checks at site require no technical knowledge and are easy to perform.
Check 1: Age of Cement
The IS269:2015 recommends using the cement within three months of its production. With every passing day, the cement loses its ability to impart strength. The threshold for cement age has been decided as three months after which it may not be good enough for use.
You can check the date of manufacturing/packing on the cement bag for the cement age. The IS269 recommends cement manufacturers print “Best before 3 months from date manufacturing/packing”.
Check 2: Colour
The OPC, PPC, PSC etc. are grey. The colour of cement may slightly vary with batch and brand. However, the colour of cement in a bag should be uniform.
Different colour of cement for one bag shows the non-uniform burning of raw materials or the disproportion.
Check 3: Lumps
Moisture is the enemy of cement. The cement absorbs moisture from the atmosphere and starts setting. The setting of cement causes lumps.
Before buying a cement bag, it must be ensured it is free of lumps. Primary inspection for lumps can be done by pressing the cement bag from the outside. The lumps are harder and don’t get pressed.
Check 4: Temperature inside the bag
This check is another indicator of cement setting. Upon inserting the hand in a cement bag, it should feel cold. It represents the fact that cement has not absorbed the moisture and the setting hasn’t started.
The logic behind this check is that the water-cement reaction is exothermic. The heat is liberated when the water (or moisture) comes in contact with the cement.
Check 5: Texture
Take a small amount of cement into your hand and rub it. The texture of cement should be smooth. The logic behind the test is that the cement particles are very fine and hence offer no resistance when rubbed.
The cement adulterated with sand will feel rough as sand particles are relatively bigger.
Check 6: Float Test
The float test checks for the silt content in the cement. Throw a handful of cement into a bucket full of water. The cement should sink.
The floating particles indicate the presence of silt which is undesirable. The silt content prevents the bonding between cement and sand particles and hence lower strength is achieved.
Check 7: Smell
The cement having silt or clay smells like earth. The clay inhibits the bonding property of cement and hence it is undesirable.
Check 8: Grade of Cement
The OPC cement is available in five grades, namely 33, 43, 43S, 53 & 53S. IS269:2015 covers all five grades of cement. The 43S and 53S grade cement is used in sleeper manufacturing for railways and the ‘S’ represents ‘sleeper’.
The strength of cement increase with the increase in grade. The 53 grade OPC is stronger than the 43 grade. Similarly, the 43 grade is stronger than the 33 grade.
The grade of cement is essential to check in terms of the use of cement. The 33 grade is not generally used nowadays. The 43-grade OPC cement is used for masonry, plastering and other finishing works. For structural works, where strength is the major criteria for cement, 53-grade OPC is used.
PPC, PSC, white cement and all other types of cement don’t have any grade.
Check 9: Type of Cement
Cement is available in many forms. The performance of each type of cement is different from the other. For example, PPC shrinks more than OPC, low heat cement has lesser curing requirement than OPC, rapid-hardening cement attains strength faster than OPC, sulphate resisting resist is effective against sulphate attack and so on.
The approved design mix of concrete is compatible with a specific type of cement. If the type of cement is changed, the concrete may not give the desired performance. Hence, confirming the type of cement is a must before use.
Check 10: Strength Test
To perform the strength test of cement, prepare a beam with a mortar mix of 1:3 (1 part cement and 3 parts sand) and 0.85 times more water than required for standard consistency. The beam mould size is 200 mm x 25mm x 25 mm. The beam is cured for 7 days underwater.
After 7 days of curing, the beam is placed symmetrically on 150 mm apart supports. A load of 340 N (approx. 34kg) is applied at the beam centre.
A beam made of good quality cement should not fail or develop cracks.
How to store cement for better quality control?
Control of cement quality starts with storage. The cement bags should be stored under a shed and a platform should be provided at the bottom. The water should not enter inside the shed.
The bags should be properly stacked one over another having a maximum height of 10 bags. The new stock shouldn’t block the old stock. The bags first brought in should be consumed first.
The quality check of the cement at the site is one of the pieces in the big picture of overall quality management. The above mentioned 10 checks are site checks and give an indication of the current status of cement and are of basic nature. These checks are not wholesome. Hence, lab checks should also be performed in conjugation with these to ensure the overall quality.
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These Must-Do Concrete Tests will ensure your concrete quality too.