When it comes to civil construction or engineering, one of the motley construction materials that come to mind instantly is probably concrete, apart from reinforcement steel, cement, bricks etc. That’s because, it is such a widely used element virtually in any construction project in any part of the world. Here, few points about concrete, useful primarily from construction angle have been mentioned. While some of these points are oriented towards Indian projects and find mentions of Indian Standard (IS) codes, the same could also be useful for any other project as concrete is an universal phenomenon and most aspects of it are strikingly similar irrespective of location.
* Reinforced cement concrete (RCC) grades to be used in mild, moderate, severe, very severe & extreme environmental exposure conditions are M20, M25, M30, M35 & M40 respectively, at the minimum as per IS codes. That means, the grade of concrete should not be less than M30 in a location where the concrete structure would be subjected to environmental exposure of “severe” category as described by relevant codes, even if the structure can be designed with M25 grade. This is important primarily from durability point of view.
* Similarly, Plain cement concrete (PCC) grades to be used in moderate, severe, very severe & extreme environmental exposure conditions are M15, M20, M20 & M25 respectively, at the minimum.
* Concrete in sea water or in sea exposed environment should be of minimum M20 grade for PCC & M30 for RCC. Additionally, use of Portland Pozzolana Cement or Portland Slag Cement is recommended for such concrete.
* Special measures are mentioned in various codes for concrete pouring in extreme temperature conditions. Indian codes regard concrete pouring at ambient temperature above 40¤C as hot weather concreting & below 5¤C as cold weather concreting & prescribes special measures in IS 7861, Part-I & II respectively.
* Analysis of fresh concrete can be done by Buoyancy method & that of hardened concrete by Chemical analysis method. The relevant IS code is IS 1199.
* Testing of hardened concrete can be performed by several methods. The widely used ones are: a) Core test – IS 516. b) Load test (for flexural members). c) Non Destructive Tests or NDTs which are Ultrasonic Pulse Velocity test (IS 13311, Part-I), Rebound/Smidt hammer test (IS 13311, Part-II), Probe Penetration test, Pullout & Maturity test.
* Tensile strength of concrete is tested by primarily two tests: a) Flexural test – IS 516 b) Split Cylinder test – IS 5816.
* IS codes suggest that for prestressed concrete not lower than M30 grade of concrete should be used.
Contd. in Part-II….