Cements – continued…..
This post is a continuation of our first coverage on Cements which was posted on Sep 7,’07.
Frequently Asked Questions on cements
(article is taken from ACC India Limited via The Hindu)
Can one save on the quantity of cement by using high-grade cement?
This is a misconception. Even if you were to use less cem
Can you judge the quality of cement from its colour?
ent, you would need to add the same quantity of water to prepare a concrete mix, let us say for one bag of cement. This would increase the water-cement ratio, as the cement quantity has been reduced. But it is common knowledge that when the water-cement ratio is increased, the resultant concrete tends to suffer from reduced strength and durability. This will certainly compromise the long-term strength of your construction.
Does high grade of cement ensure better results?
The grade of cement only indicates its compressive strength at 28 days. But cement continues to increase in strength beyond that period of time with not much of difference in the long-term strength.
You would not want your dream home to be tested after a mere 28 days. While almost all cements provide some basic initial strength, what you should look for is its long-term strength. It has been proved that blended or composite cements render higher strengths for a long duration.
Should we use cement that sets quickly?
Quick setting of the mix depends not only on the quality of cement but also on the quantity of water used in preparing the mix. If you consider that you are constructing your dream house after years of waiting and planning, you know you can easily afford to wait for the essential few additional hours needed for cement to set slowly and attain its strength.
Similarly, concrete also needs adequate time to set properly and attain its fullest strength. If your mason complains about the quality of cement saying `it sets slowly’, ask him to be patient. Wait a little while longer before you begin to worry. Setting is an essential property of cement. Slow setting of cement is healthy and does not necessarily mean that the cement cannot provide long-term strength.
The colour of the cement has absolutely no relationship or bearing on its quality. The colour of cement is determined by the colour and quantity of the raw materials that are used to manufacture it.
Cement reacts with water. So protect the cement bags from moisture. It is proper to store cement in a godown free from the vagaries of weather. Place the bags on a platform that is at least six inches above floor level. Stack the bags one over the other in a lot and do not lean them against any wall.
The number of bags in each stack should not be more than 15 bags. While taking out the bags for use, the norm of `first come first used’ should be followed. It is best to consume cement within two to three months of its manufacture.
In case you have any serious doubts about the quality of cement or if you feel the cement is not fit for use, you must of course consult the manufacturer. But here is a quick simple test you can do at the site yourself for reassurance.
Make a paste of a little cement with one-fourth the quantity of water and make little cubes or blocks of 50 x 50 x 20 mm size. Leave aside for a day.
Test the blocks to see how easily they break. If the cement is of a good quality, the blocks will be firm and will not crumble or break if you try to crush it with the pressure of your fingers.
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