 Welcome to the session Fiber Enforced Concrete FRC, myself, Mr. Chetanji Kunapre, Assistant Professor, Department of Civil Engineering, Palchen Institute of Technology, Solapur. Now, these are the learning outcomes. At the end of this session, students will be able to understand the features of fiber reinforced concrete and factors affecting properties of fiber reinforced concrete. Now, as we know the concrete is a mixture of basic ingredients, cement, sand, coarse aggregate and fiber reinforced concrete means some addition is made in that concrete. So, we can define this concrete as it is a mixture of cement mortar or cement concrete with discontinued discrete uniformly or orderly or randomly dispersed fibers. So, that is a fiber reinforced concrete. Now, what is the need of this type of concrete? Now, our plain concrete actually it possess very low tensile strength. So, low tensile strength means if any tensile stresses are occurring in the concrete probably that will be subjected to the cracks. Now, these cracks will widen and the reason for low tensile strength is the micro cracks and micro cracks and presence of micro cracks and their propagation will reduce the tensile strength. Now, how this tensile strength of concrete can be improved? One is the conventional method, conventional reinforcement or enforcing bars can be introduced in the concrete. So, that is our regular RCC and second is tensile strength can be improved by introducing the tendons into the concrete and that is pre-stressed concrete. But these are improvement techniques to improve the tensile strength of section not of the concrete. So, concrete will remain as it is which is brittle in nature. Now, before loading concrete is subjected to cracks, micro cracks. The reason is the drying shrinkage. Because of drying shrinkage there will be micro cracks and whenever these micro cracks are subjected to the loading these cracks will open up and start to propagate also. One more important thing is the initially the width of these micro cracks will be very small or with a few microns also. But the other two dimension depth and width of these cracks will be of higher magnitude. So, in case of structural cracks these are proceeding or they will proceed slowly. So, the crack is a major problem in our regular concrete. Now, we need some crack arrester in the which is the disadvantage of the plain cement concrete. So, addition of some fibres which are small, closely spaced, discontinuous and uniformly dispersed into the concrete will act as a crack arrester. So, functioning of crack arrester that is done by these fibres. So, continuous meshes, woven fibrics and long wires are not fibres. So, discrete fibres which are dispersed in the concrete these are called as fibres and that concrete is called as fibre reinforced concrete. Now, which properties of concrete will enhance by these fibres? We are talking about tensile strength, but what are the other properties which will enhance by fibres? You pause the video and think of that and write down the other properties which will enhance by these fibres. Now, following properties of concrete will enhance. First is the flexural strength, bending strength of the concrete. Second, impact resistance of the concrete. So, surface of the concrete must be very tough. Crack resistance of the concrete. So, cracks shall not propagate or will not propagate because of the fibres. Toughness of the concrete and more important property is ductility of concrete that will enhance. The concrete is brittle in nature. So, by addition of the fibre, if the ductility, the tactile property of the concrete will increase that is the better advantage. Now, there are various fibres and these different types of fibres can be used, but all that cannot be effective and economic also. But each fibre has got its own characteristics and limitation. So, let us see the fibres. Now, steel fibres, polypropylene fibres, nylon fibres, asbestos, coir, glass and carbon, these are the different fibres used in the concrete. Now, what is this fibre? Fibre is a small reinforcing material. The shape of the fibre may be circular, flat, with the straight end, with the different end with some texture or crimped surfaces. Now, this fibre can be described with the aspect ratio. Now, the aspect ratio of the fibre is the ratio of its length to its diameter. Now, typical aspect ratio of the fibre is ranging from 30 to 150. Generally, it is kept 120. Now, these are the steel fibres. You can observe the steel fibres and at the end, the ends are hooked and this will act as an anchorage into the concrete. So, round fibres and hooked fibres in both types of steel fibres are available. Diameter is 0.25 to 75 mm. Now, it improves the flexural impact and fatigue strength of the concrete. Now, application of the steel fibre is in the overall layers of the roads, airfield pavements, industrial floors and in some bridge decks also. Next is polypropylene fibre and nylon fibre. Now, this is polypropylene fibre. So, it has got very high tensile strength, but the modusofelasticity E is very low in case of polypropylene fibre. But because of the elongation, because it is modusofelasticity less, definitely there will be higher elongation and it will not contribute to the flexural strength. Now, next is asbestos. This is mineral fibre. Tensile strength is 560 to 980 Newton per mm square. So, it has got high flexural strength and cement paste. Now, next is coir fibre, jule fibre. So, this is a coconut tree. You can observe these fibres here and one is the cross section, non-jewel cross section of this fibre. So, coir fibre is in this form, which is a natural fibre that can be used in the concrete where that much tensile strength is not expected. Little bit improvement is expected by using the coir fibre. Next is glass fibres. This is a recent introduction into the fibre reinforced concrete. Tensile strength of glass fibre is 1020 to 4080 Newton per mm square. But glass fibre is affected by alkanine conditions. So, alkyl free or alkyl resistant fibres are important. So, that can be used in the concrete. So, one tread name is there that is Semphil, which is alkyl resistant glass fibre. Next is carbon fibre. Now, tensile strength of carbon fibre is 210 to 2850 Newton per mm square. These are used basically in cladding, panels and shells or type structure. So, their use is started yet. Now, the mass scale if it is used, definitely that will be one of the promising future. Now, these are the factors which affects the properties of the FRC. Because whenever some addition is made in the concrete, the properties may affect. Some property may enhance, some may reduce. Now, by observing and studying the factors which affects the property of the concrete, we can give the best solution. Now, FRC is actually mixture of fibres into the cement matrix. Cement matrix that is that which creates a better bond between cement paste and the aggregate. Now, first factor is the fibres may be orderly mannered or randomly distributed. This is the first factor. The proper distribution is there, definitely the properties of FRC will increase. Second thing important factor is transfer of stresses between matrix and the fibre. Whatever load of stresses are coming on the concrete, if all these stresses are effectively transferred from matrix to the fibre, then definitely your properties will enhance. Now, what are the factors, sub factors which will affect the transfer of stresses? First is type of fibre. Second, geometry of fibre whether it is a plain fibre, green fibre or hooked fibre. At the ends, what is the geometry that is also important. Third is fibre content. So, percentage of the fibre is important. So, fibre content is the third sub parameter. Fourth is orientation and distribution of the fibres. If it is distributed properly, if the fibre orientation is perpendicular to the crack, definitely that will arrest the crack more effectively. And next is size and shape of the aggregate. Fifth point which is important point because based on the size and shape, the cement matrix and its arrangement is dependent. And sixth is mixing and compaction technique of the concrete. So, how the bond will develop into cement matrix and fibre that depends upon this compaction. Now, next is for efficient trains transfer, this is important factor. For that, Young's modulus of matrix must be much lower than the Young's modulus of fibre. This is important factor. Next is the bond between fibre and the mix. Now, you can see this diagram. This beam which is a flexural member, so load is applied. Here, one crack is developed and this is the fibre mesh. So, this crack is arrested by the fibre. Now, how it is effective? So, the bond between fibre and mix that actually plays an important role in the stress transfers. How the stress is transferred to each other that is dependent upon interfacial bond. And last thing is the improvement in bond of the fibre and mix that depends upon the larger area of the contact. So, this larger area of the contact means the bond will increase by the area contact between fibre and matrix. And if it is improved, then the frictional resistance and the degree of gripping that will improve. And one more aspect is there, we can increase the bond by sodium hydroxide. These are the references for this fibre reinforced concrete session. Thank you.