 Hello, friends. Myself, Mr. Yusuke Kulkarni, Assistant Professor, Severeening Department, WIT Sholapur. I am here to discuss with you on requirements of good quality concrete. Learning outcomes of today's session. At the end of the session, students will be able to explain requirements of good quality concrete. Friends, you know a concrete is nothing but a composite material which is obtained from mixing of cement, sand, coarse aggregate, water and if required, add a mixture in definite proportions. So, these are the ingredients of concrete, cement, sand, coarse aggregate, water, etc. Now, let us see what are the requirements of good concrete. So, first requirement is use of good quality materials. This is very important. Cement which we are using, that must be of good quality, fresh one. We know cement should be used within three months from the date of manufacture. So, dates also must be checked. Then, good quality of sand, coarse aggregate and water also is equally important. They must be weighed carefully, measured carefully. Portable water should be used free from harmful organic substances, etc. Now, one more important thing is particle size distribution. So, sand and coarse aggregate these must be well graded, good shaped then clean without any impurities like soil, etc. Dust particles then the grading should be of good quality. The particle size distribution is nothing but distribution from largest permissible course to the smallest permissible fine of that particular aggregate. So, equal distribution should be there. Generally, 20 mm aggregates are used for RCC works. Aggregate should be hard, durable and properly graded. This is important thing. Proper mix design is equally important. Mix design of concrete must be done properly, referring relevant IS codes and should have all the ingredients in right proportions. This is very important. Workability of concrete. Workability of concrete is nothing but ease with which concrete can be mixed and placed. So, concrete must be workable enough so that the placement will be easy and also workability depends on amount of water in concrete. Amount of water should not be too much, otherwise strength will be affected. So, water amount is very important in concrete and workability and strength depends on amount of water or quantity of water which we are adding in this concrete. Too much fluidity will result in certain defects like whites will be there. So, that should be avoided. Proper mixing, handling and compaction is important. So, concrete should be mixed thoroughly so that it will be a homogeneous mix. Also handling of concrete should be proper. Otherwise there will be segregation of particles. Separation of particles from concrete mass should be avoided. Then concrete should be compacted properly. Then only it will be dense and compact. So, that is important. Proper and sufficient curing. One more important thing. Curing avoids loss of moisture at early stages of setting of concrete, remember. This is very important. Then only concrete will gain strength. So, the curing for minimum period, whatever is specified generally it is from 21 to 28 days for different concrete components. So, that must be done to its fullest extent and to the complete period that will ensure strength of concrete. Water cement ratio is very important aspect. It controls strength, durability and water tightness, remember. Water cement ratio should not be too much and should not be too low. Generally, range of water cement ratio should be between 0.4 to 0.55 depending upon the mixed design. So, water cement ratio affects quality of concrete a lot. So, it should be optimum. Now, good quality reinforcement. We know concrete is weak in tension. So, concrete members must be reinforced with good quality steel, so that they can take tensile forces effectively. Concrete will be equally strong in tension as it is strong in compression. Reinforcement may not be required for those members which are subjected to only compression like pedestals are there. Sufficient compression strength is also equally important. Concrete is graded or designated on basis of its compression strength, we know M20, M30 grades. So, M stands for mix and this 20 stands for characteristic strength of concrete in Newton per mm square. Now, for concrete of M20 grade what should be the strength after 28 days of curing? It should be 20 Newton per mm square minimum strength and so on. Durability of concrete is the extent to which the material is capable of resisting the deterioration caused by exposure to service conditions. And this particular durability of concrete depends upon strength of concrete. If strength is good durability will also be good and water tightness and weather resistance concrete will have good durability, remember. And concrete which is subjected to wear and tear like floor slabs are there, those must also be capable of resisting abrasion these particular concretes, right. And stronger the concrete it will be more durable, remember. Water tightness, concrete must be water tight, remember. There should not be too many pores in concrete. When will these pores more in concrete? If amount of water added is more than they required then there will be pores in concrete and this concrete will not be stronger one. Water tightness is equally important affected by water cement ratio. Now, friends let us pause a little here. Here are two questions for you. Number one, durability of concrete will be good if its blank space is there you have to fill this space it is good. Then second, prevention of loss of moisture from concrete during early stages of hardening is dash of concrete. So, I have to fill both these places by correct words. You know now, we have studied just now these things. Come on, write your answers. Okay, good, written the answers. What are the answers? Durability of concrete will be good if its strength is good, remember. And number two, prevention of loss of moisture from concrete during early stages of hardening is curing of concrete. Right? These are the correct answers. Now, few requirements, few more requirements. Concrete should be fire resistant. This is also one more requirement. Good quality concrete should be fire resistant. It should have minimum shrinkage one more important thing. If shrinkage is more, there will be more cracks in concrete. Okay, that should be avoided. And last but not the least, concrete should be economical. This is very important, right? So, these are the requirements of good quality concrete. These are the references for today's session. Thank you.