[Music] thank you hello everyone so welcome to nptel course on analysis and design of bituminous payments we met earlier in mechanical characterization of bituminous material the same a team of Faculty members who offered that course are offering this now the first thing the most important thing what are all the course references that is needed okay the first and foremost thing is payment analysis and design by Professor Huang this is a classic reference in those days at least when I was a graduate student we used to read from Yoder and with stack but the order and with stack was never revised and here also Professor Huang passed away a year back so but as of now this is the current and latest reference for this in addition to this what you really need to do is to get IRC 37 2008 this is the latest guideline ok for the design of ah payments ok so now you will be in curious to know that they have written it here as flexible payment and I have written it here as bituminous statement throughout this course we will be using only this terminology we will use only between us payment and concrete payment are not flexible payment or rigid payment of course this course is only about bitterness payment ah sometimes later we will also be offering something on concrete Pavement in a much more rigorous way but as of now we will be talking about bituminous payment and the terminology that will be used is only bituminous payment now the reasons will become obvious to you as we go along but I just want to give a hint the reason why one should stick to bituminous payment or concrete payment is basically related to the stress analysis procedure that is followed for bituminous payment we use what is really called this layered linear elastic theories for concrete pavement we use what is called demon elastic Foundation Winkler model Pastor neck model and all those things so now it is possible that you can model concrete payment using layered elastic theories it is also possible that you can model between a statement using the Winkler Foundation ok so there is nothing flexible or nothing rigid about it right now what are all the things that we are going to do here is we will first look into the various cross sections and how a payment fails then we will be talking about the overview of the design process and then we will talk about the stress analysis now you must be actually wondering as to why I first talk about failure and then talk about the design process and in fact many a time you will notice that and this holds Good not only for payment engineering but also for many civil engineering infrastructure what we do is always what we really call this proof checking ok so that means most of the time based on the past experience we have a very clear-cut idea of what should be the kind of layer thickness that should be provided so most of the time this comes more from the constructability aspect obviously when you are constructing a payment you are not going to tell your Highway engineer to construct 45.22 mm layer thickness that is not going to be possible the nominal maximum aggregate size the ability of the roller to compact the relation between the maximum aggregate size to the layer thickness all of these things play a critical role so what we first want to find out is these are the different cross sections and each cross section has a specific each layer in a cross section has a specific role to play so we will first understand intuitively what really are the failure conditions then we will try to compute the critical stresses and strains related to those failure criteria and for that we need to use a stress analysis procedure so that is the outline that I am going to take here now very simple ah cross section which is listed in Huang and more or less this is the standard cross section that is followed ah you should be little bit careful about the units that are used here this is an American textbook so most of these things are given in terms of inches even in some of the example problems that you will be working out from this textbook which will be shared with you the units will be mostly pounds inches but we will also be providing the conversion within the bracket so don't worry about it so if you go from the bottom you are talking about an actual subgrid then you talk about a compacted subgrid a sub base a base a binder and a surface now these two layers are bituminous in nature predominantly then these three layers are granular material and then you also have a prime coat between the base course and the binder course attack code between the binder course and the surface course it is not necessary that you need to provide a seal code but you can actually see that it is provided here right now this is the general cross section that you saw but if you take a look at the typical cross section that is provided in American roads ah which is most of the design procedures that follow Astro and what we call as mepdg mechanistic empirical payment design gate so you will see that there is a conventional flexible payment now this is we call it as phalt pavement or between us payment ok so what you are going to see is there is an actual subgrade that is a compacted subgrade Unbound sub base Unbound base and bituminous mixtures or asphalt concrete mixtures ok so this is something similar to the generic cross section that was presented to you earlier now there is something called as a deep strength payment okay Perpetual pavement and all those things so you will see that it is the same then actual subgrade the compacted subgrade is has a slightly more thickness this is the Unbound base and then what you are going to see here is the thickness of the asphalt concrete layers are substantial more or less it consists of the layer thickness of the Unbound base as well as the asphalt concrete ok so this is the Deep strength pavement in addition of course you have what is really called as a full depth payment and such kind of payment where propagated by asphalt Institute of United States so this is a non-profit organization which is basically promoting the asphalt related products so you will see that everything is asphalt so what you really see is a compacted subgrade then you have an asphalt base asphalt binder course asphalt surface course so obviously the cost of these constructions are going to be very very expensive some of these constructions are normally used in runways sometimes in heavy duty industrial flooring ok so that is the ah American design then you also have a different ah in inverted cross sections here so we will go from this side ok so there is an actual subgrid there is a compacted subgrade then you have a cement treated layer and an Unbound base and an asphalt concrete layer ok now why is this called as a inverted layer now the common tendency here is to see that as you go from as you go from the bottom to the top the modulus value keeps increasing so if you call this as e one e two e three e four if I you are going to get C these kind of relation so the topmost is going to be the material having a higher modulus now what exactly is the modulus we will worry about it later but what you see here is this particular layer can actually have a modulus value slightly higher than this Unbound base and so that is why these sections are actually called as inverted sections you can and then this is an unfortunate terminology what is called a semi rigid or you can say a combination of concrete and bituminous pavement because bituminous pavement betweenness payment and then you can actually have what is really called as a Unbound sub base compacted subgrade but the most important thing that you see here is an asphalt treated base so it is not really a full bituminous mixtures except but you kind of try to use some amount of vitamin in it that vitamin could be in the same of a foam it could be in the form of an Emulsion now this is your cement treated base so instead of using an asphalt rated base that you see here you use a cement treated base here rest of the Cross sections are more or less the same so let us come to the IRC 37 2008 cross section and see what it says now there are many design aspects or also that are interest introduced here so let me just kind of give you a clue about what are this design aspects these words that you see here fatigue resistance layer vertical strain on the subgrade red resistance layer so all these things that are written in green color comes from the perspective of design so first let us take a look at the cross section the cross section is the same you have a subgrid it could be an Unbound or a treated granular base now this subgrade should be called as a what you can say as a compact and subgrid ok then you have a base here and then there are two bituminous layers ok so what we call in India as bituminous concrete and this could be called as dense vitamin as Macadam so there are going to be two grades here depending on the binder content used and the gradation that is used here now let us look into the design aspect what it says so first and foremost thing is there is a common perception that this vertical strain that you see here whatever that strain means if is limited there will not be any ah what you can say failure related to rotting we will see what are those rutting and fitting as we go along now in the same way if the strain at the bottom of the bituminous layer is limited you can actually see that there could be less probability for the bituminous payment to fail due to fatigue and this also can happen at the top so there is also tensile strain at the top tensile strain at the bottom of the bituminous layer so it is expected that you will construct these layers as rat resistance or fatigue resistance layers ok so this is the general cross section with the design aspects also integrated part of it there are many other cross sections that are given in IRC 37 you are advised to go on to take a look at it but I will just go talk about there is a cement rated sub base there is a cementrated base and because of this stiffness there is a necessity for something like a crack relief layer and then the bituminous layer rest of the things remain the same then in addition to that there is also one more cross section which we will be discussing as we go along it is about what is really called as cement rated sub base and this is the foam stabilized or so this is your reclaimed so if you constructed a bituminous payment and if it requires Rehabilitation what you could do is to do what is really called as the full depth reclamation and take all this material add it with the new material add a binder in the form of a foam or an Emulsion and lay it here and then on top of it you can have the regular bitterness layer ok so there are many ways in which one can construct such cross sections we will slightly go out and see what happens to the French cross section the French cross sections are empirical works very well so they do not give you much flexibility about what should be used so there is a Surface course there is a base course and this is called as a capping layer what is normally so it could be a drainage layer it could be anything so this is called as a capping layer and this capping layer is constructed on top of the nice upgrade and there are many design strategies that are followed see for instance you can have surface course of bituminous material base layer of bituminous material less than 15 centimeters and the most important thing is Unbound granular materials that can go as high as 50 centimeters and this is what is really called as a payment Foundation I have a reason for emphasizing all these things because at the end of the course what you are going to do is to take any of the existing IRC 37 cross sections use the distress functions apply the load compute the critical strain and substitute this critical strains in this distress functions and see whether ah design the equivalent standard axi load for which it has been designed whether it actually needs or not you are going to check it and sometimes you will be surprised so watch out for that right so the same thickness could be for low traffic I mean the same cross section design could be used for low traffic medium traffic as well as for high traffic as far as the French design is concerned there is also what is really called as a ah thick bituminous pavement now this thickness can go as high as 40 centimeters So within the Indian context you should be able to understand and appreciate it because if you add up the total bituminous layers in within the Indian context we normally do not exceed 15 or 16 centimeters whereas these people want you to provide something like 40 centimeters more than twice as much as normally that is produced and there are also some ah cross sections with hydraulic binders hydraulic binders is nothing but using cement as ah layer so you can call it as a cement rated sub base or cementrated base in addition to that the French people also have what is really called as a composite pavement so you can have a bituminous layer surface and base and then you can have a 40 centimeter thick cement reacted base OK and again you can have what is really called as the inverted Pavement in which you can have the material treated with hydraulic binder below which has a lot more stiffness and on top of it there is an Unbound granular material now there are some issues related to Computing the critical stresses and strain when you are using this kind of inverted payments OK ah it will become obvious as we go along because the stress analysis procedure that you follow basically assumes that even is greater than or equal to e to greater than or equal to e three and so on and so forth so sometimes when you are going to have the modulus value of the bottom layer slightly more than what you see for the top layer you might have some interesting ah scenarios we will see ok so to compare all these cross sections what you will see is so there is a you can see South African cross section then there is a cross section from Netherland and this is a typical airport Amsterdam airport cross section so you see there is a 200 mm polymer modified asphalt 600 mm lean concrete base so this is what is available as far as the sheeple are put in Amsterdam 200 mm if you look into the Netherlands cross section again it depends on the country when you are going to have lot of water a lot of rain you are going to have some kind of porous structure that you constructed the surface wherein you allow the water to drain through and collect it through some of these drains so you can have 50 mm porous asphalt concrete 200 mm asphalt concrete and 300 mm of Unbound base but on the other hand if you look at the South African cross section you can have 50 mm bituminous layer 150 mm of Unbound layer and 150 mm of cement rated base so there are many combinations that are given and now this is where again Monty emphasized to you about what is really called as proof checking because most of this designs ah seems to have worked out already you will see that you will be asking a question so what is there to design because these guys have already worked out all the thicknesses now what you really need to find out is what is the constituent here what goes inside this material number one number two is how long this pavement will withstand so these are some of the issues that you will be able to answer now let us start talking about what really happens and these are all nice pictures that you have seen so there are going to be failures now these are the failures that are going to be the problem for you because this is where you are going to be seeing here so this is your traffic direction so you are going to see what is really called on this right hand side as low temperature cracking and what you see here is the fatigue cracking ok so this is the kind of cracking that can happen there are many types of cracking that can have most of this that form crack like a block ok so this could be due to your ah low temperature cracking there could be some of these cracks that could emanate from the bottom and come to the surface something called as a reflection cracking and you can have many many types of cracking so what I would always call as two types load induced and non load induced so that means if you are going to construct let us say a payment and you can think of it this way so this could be let us say 2.5 meters now what will be around sorry this could be 3.5 meters now normally what will be the width of the vehicle that you see here it will be roughly around 2.5 meter so there will be one location on either side where the layer is going to be subjected to repeated loading and this repeated loading will cost you all this what is really called as the map cracking are also called as alligator cracking ok now when you keep driving restricting yourself to the positioning your vehicle in the lane and when you are driving on top of it continuously there is one portion on either side of here where your truck is there the payment is going to be subjected to repeated load and because of this repeated load there is going to be an accumulation of strains that is going to be accumulation of damage and this is going to result in some kind of a cracks that basically come to the surface so this is ah the main issue as far as the cracking is concerned now the next thing that we want to really talk about is what is really called as the rating and you can actually see again all these things happen in the wheel path this is an extreme case of rotting ah you can actually see such pictures if you go to the Federal highways Administration site and in fact you can see so there is a lane here this Lane let us have 3.5 meters and you can actually see that this could be roughly 2.5 meters so typically you know when you are driving the driver will position his vehicle let us say half a meter from this Lane Edge and another half a meter from the lineage this has something to do what this what is really called as the vehicle wander so you are going to see that there is going to be considerable writing here now what will happen is if you take a look at the cross section you are going to see that there is a depression in the wheel path we will path depression so this is what you are going to call it as rutting and in fact if you recollect the IRC 37 cross section you will notice here that the topmost layer is designed to be a rut resistance layer but they also tell you that if you limit the vertical strain on the subgrade to some specific value we may not really have the expected rotting ok so that is a story that will slowly we will be able to unravel as we will go along because I just want in the first lecture give you a flavor of what you are going to do here then you can have bleeding which is due to poor Mix Design means using an inappropriate bitumen at a specific location so you using a VG 30 bit and bitumen where you should be using a vg30 vitamin or using ah more binder content than what is needed or not providing the enough aggregate gradation signs and all those things ok so this is more or less a general overview that I really wanted to talk about so what did we talk about we talk about the cross sections we talked about the failures and as far as the failures are concerned let me list everything so you can have rotting you can have fatigue damage you can have low temperature cracking you can have moisture induced damage but normally when we talk about the failure in bituminous pavement especially relating it to the cross section we will be focusing our attention on writing and fatigue and in the IRC 37 cross section we also saw that there was a direct resistance layer there was a also a fatigue resistance layer and you also saw that the critical strains related to this rut resistance and fatigue resistance were measured for rotting at the bottom of the pavement or on top of the subgrade and for fatigue at the bottom of the bituminous layer ok so these are some of the earlier assumptions that have been made these assumptions need not have to be true and you will be exploring it as we go along now let us understand what is really called as the design process now this needs to be discussed in detail and you will see that over the period of this course or three of my colleagues are going to cover different portion of it now let us Define this separately so this is the input that you are going to give this is the analysis that you are going to do and this is finally the strategy selection so what each of this basically means so let us assume that you know you are going to construct a bituminous payment now this construction could be a brand new payment or it could be widening and strengthening existing two lane road into your four lane road or a six Lane Road it could be anything now first and foremost thing is what is that you want to really ask and please understand this design process ah not only necessary to be followed for payment engineering but for any civil engineering structure for that matter so here the load that is coming here is your traffic ok so that is the most important thing so when we are talking about traffic we are talking in terms of two things what is really called as the volume count what is called as the axial load so when I say axi load what are the different types of axial combinations that you are going to see and how each of this truck having a different combination of axles what is the total number that you are going to talk about so that comes under the load or traffic the next thing is where is the road going to be constructed what is the load carrying capacity of the existing soil so what we really call as the foundation now this is where I want to keep making the distinction as we go along so when you are going to construct your bituminous payment ah depending on the country you live ah someone will say that you know go find out the CBR value of the subgrade if it is going to be for bituminous payment if it is going to be for concrete pavement they will tell you go find out the modulus of subgrade reaction the soil is the same the road that you are going to construct has only some changes in the Constitution the layers type of materials that you use but since the stress analysis procedure demands modulus of subgrade reaction for concrete you will be measuring the the same for the subgrade material but for the same subgrade material if you are going to construct a bituminous pigment you are going to find out some c b or some resilient modulus or something like that ok so the most important thing is what is the foundation you can say the load carrying capacity and this is where you will also be able to relate that ah what is called as a compacted subgrid so many of the design charts that are given in IRC 37 talk about the thickness to be provided on top of a subgrade having 10 percent CBR now what will really happen if your actual CBR of the road is three percent so that means you are going to constructed a compacted subgrid such that it will have around 10 percent or 15 percent CBR simple the third and the most important thing is climate OK climate plays a critical role more so in the within the context of India because what will really happen in India is whatever the cross section that you are going to use in the northern part of the India may not necessarily work out in the southern part of the India or the Eastern or the western part of the India because it has something to do with the maximum payment temperature minimum payment temperature presence of the water table and so forth so on and this depending on the temperature the material properties especially the betweenness properties also will change which means the load carrying capacity will change which means the damage accumulation also will be at a different rate at a different month time period in a year climate plays a critical role and then the material properties are you going to use unmodified vitamin modified vitamin are you going to use stabilized base stabilized sub base crack relief layer what are its properties and everything so this are the various inputs that you need to have so that means before you start designing your payment you need to have these four things in your hand the traffic the foundation the climate and the material properties so after having found out all these things we go to the Next Step which is the analysis and now this is what I said there is a trial design strategy that you need okay what is the trial design so that means we already have a clear cut idea of what should be the thickness of each of this layer okay so it could be a bituminous concrete layer 40 mm y40 mm because your nominal maximum aggregate says may be 13.2 and typically three times the nominal maximum aggregate size is what you are going to use for your layer thickness so 40 mm more or less comes there so you take the trial design and then there is something called as the payment analysis model what exactly are this analysis model so that means given any payment cross section how do you compute the critical stresses and strain at a different spatial locations so this is what is really called as payment analysis models then after that what do you do is you come to the distress prediction models ok so we will be explaining as we go along so that means for this payment cross section that you have taken as a trial with the material properties that are giving given as input and using a computational mechanics procedure that you are going to follow what will be the critical stresses and strains and how this critical stresses and strains can be related to the expected life of the pavement OK in terms of running in terms of fatigue so this comes under the distress prediction model and then finally what we do is we do the dimension accumulation and when you do the damage accumulation you basically are checking against your estimates that you made in your traffic with the trial design that you have taken so let us assume ah I do not want to ah use the load equivalency Factor here because it has not had been introduced let us assume that I am designing a road for 1000 trucks just giving a simple example so this is the ah traffic part that comes in and I take a trial design strategy and after doing all the calculations I realized that oh this can withstand 1200 trucks so what you really do is use immediately say yes but let us say you find out that oh this cross section can actually take only 900 trucks then what you do is you modify the strategy so that means you probably increase the thickness r you increase the modulus value of the constituent layer by using let us say polymer modified vitamin or anything like that and then you come to the next stage so this is a iterative process as can be seen and then you come to the next option so one is comes from the constructability issue another comes from the life cycle cost analysis and I will also talk in terms of little bit in terms of reliability so using all these factors you do what is really called as the strategy selection right now what I am going to do is to introduce some basic Design Concepts and straight away get into the payment analysis models that is what I am going to do OK and within this context there are some road tests that have been actually ah carried out over a period of time at many places in the world and that is something that we will discuss in the next lecture thank you very much [Music]