 Welcome to the session, High Strength Concrete, myself, Mr. Chetan G. Kunapure, assistant professor, Department of Civil Engineering, Valchin Institute of Technology, Sulapur. So, these are the loading outcomes at the end of this session. The student will be, will understand the concept of high strength concrete, classification of high strength concrete, and methods of making high strength concrete. Now, the concrete which is having compressive strength more than 55 Newton per mm square, that concrete is known as high strength concrete. The strength of, compressive strength of the concrete if it is less than 55, then it is termed as normal and standard grade concrete. And actually, the range of the compressive strength, if it is in between 55 to 100, then that concrete can be called as high strength concrete. Now, in case of this high strength concrete, the major first aspect is low water cement ratio or low water binder ratio. And the second aspect of this high strength concrete is minimum widths. Actually, widths are the sources from where the bond of the cement matrix and aggregate fails and the strength will reduce. So, widths and the strength of that bond between aggregate and cement matrix that is important. So, these two are very important aspect. Now, how we can assure the minimum widths in the concrete? So, minimum widths in the concrete that will make the concrete as a high strength concrete. So, proper particle packing will assure the high strength of the concrete. Now, let us see the schematic diagram. Now, these are aggregate particles. And the void between among all these aggregate particles, these are filled by matrix, cement and mortar. Now, let us see how these voids are filled and what will be the effect of these voids on the strength. Now, this aggregate particle, these four aggregate particles are in contact to each other. This is the enlarged diagram of this aggregate. Now, the macro filler of voids of these aggregates are nothing but the sand particles. And the micro fillers are nothing but the cement particles or cement paste which is in between the sand particles. So, this is entire structure, it may be micro level or at macro level, the structure of cement matrix and aggregates. So, whatever load or stresses are transferred from aggregate to aggregate that depends upon this void. And this void must be filled by sand particles and cement particles. Since macro level fillers are required, micro level fillers are also required. Now, let us see what is ideal high strength concrete. If that concrete in which the appropriate cement type is used in which low C3A, MGO, Freeline, low N, NA2O and K2O components are kept. If that type of cement is used, probably it must give us resistance to weathering and chemicals, resistance to wear and deterioration. It must give us high performance means high strength as well as other properties and it must be economic also. Then that concrete can be termed as ideal high strength concrete. Now, let us see the classification of high strength concrete. Generally, it is classified normal strength concrete and high strength concrete. Now, the compressive strength if it is in between 20 to 30, then that is called as normal strength concrete. And from 30 to 55, the concrete is called as standard grade concrete. This is given in IS 456. Now, high strength concrete is the concrete which is having the compressive strength more than 55. So, the boundary line between normal strength concrete and high strength concrete is 55 MPa. Internationally, the strength of concrete if it is more than 60 MPa, then that concrete is called as high strength concrete. Now, even one term is there ultra high strength concrete. If the strength of the concrete is more than 100 and 100 to 200 MPa, then that concrete is termed as ultra high strength concrete. Now, generally, these high strength concretes are used for high rise buildings and long span bridges. Now, let us see how the concept of high strength concrete arises. What is the cause behind that? In case of pre-stress concrete, the minimum grade of concrete required is M35. So, from the different conceptual point of view, this M35 grade of concrete is required. Now, whenever a pre-stress concrete is to be done, then minimum grade of concrete shall be M35. So, wherever when the pre-stress concrete technology started, then this has given the rise to the high strength concrete. Now, these are the some of the examples. Now, why do we need high strength concrete? What is the need of this high strength concrete? You just pause the video and write down the parameters why high strength concrete is required. These are the reasons. First is if we want early age strength for the concrete, we need this high strength concrete. Especially, this is in pavement because pavement are opened at the third day. So, at the third day, we need higher strength. So, for that purpose, high strength concrete is required. Next is by using high strength concrete, we can reduce the section sizes. The section sizes, especially column sizes, we can reduce so that we can get more carpet area in the building. So, in multi-storied buildings, the column section can be reduced. Next, in case of large span structures, especially long span bridges, high strength concrete is used to reduce the section sizes. Sometimes, if enhanced mechanical properties are required, means in hardened state, if compressor strength, higher compressor strength is required, flexural strength is required, higher modulus elastic is required, then we need this high strength concrete. For some applications also, special applications, especially dams, garages and parking floors, industrial floorings, high strength concrete is required. Now, let us see what are the methods of making high strength concrete. Now, some methods are listed here. Let us see one by one what are the methods. Now, first is seeding. Seeding means a fully hydrated cement, which is finally ground, is added into the fresh concrete mix. The mechanism of addition of this hydrated Portland cement to the fresh concrete is a little difficult. The seeding method is not a promising method to give the high strength concrete, but this is one of the method which is used for high strength concrete. Now, second is re-vibration. Now, concrete means this is a cement product. So, shrinkage cracks are appearing on the concrete surface, especially on the surfaces, micro hair cracks are appearing. These are plastic shrinkage cracks. These cracks may propagate in future also. The mixing water is added into the concrete which creates the capillary channels. Sometimes the water cement slurry is separating from the concrete matrix. In that case also, bleeding is the term which is used for that separation. At some spaces on the concrete surfaces, on concrete volumes, water may accumulate. And all these issues, these three issues will reduce the strength of concrete. Now, how we can rectify these issues? So, we can give the controlled re-vibration to the concrete which will reduce all these defects, will increase the strength. Now, next is use of admixtures. Nowadays, chemical admixtures are coming, model chemical admixtures are coming. In which water reducing agents are helping us to reduce the water cement ratio of the concrete. Now, next is high speed slurry mixing. Now, this involves the proper mixing of cement and water. This cement water paste that is added into the aggregate to produce the concrete. Means all the aggregate cement, water, sand is mixed at one time in conventional concrete. That is a little bit neglected here. Cement water paste which is added into the aggregate with the proper manner, which will increase the hydration process of that cement and which will give us the higher strength. Now, next is the concrete is the brittle material. So, the cracks in the concrete are forming and propagating also. Whatever may be the reason, it may be plastic shrinkage cracks or other cracks. So, formation and propagation of the crack that is definite in the concrete. And the main failure of the concrete is due to these cracks. So, how we can inhibit these cracks? If inhibition of the cracks will reduce failure of the concrete at those weak locations. So, which will increase the strength. Now, this can be done by using or by adding polythene or polystrene. And this is used as a substitute to the fine aggregate and it can be substituted up to 2-3%. So, this polythene and polystrene what this will do? This will arrest the cracks which are already formed and this will reduce or this will prevent the propagation of the cracks. Automatically, the strength of the concrete will increase. By this method, water concrete is welded that is of 105 mega Pascal. These are the references for the high strength concrete session. Thank you.