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Specific Surface Area of Geomaterials

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Video 1: Specific Surface Area
This is a typical MIP Mercury intrusion pycnometer.We have different types of port low pressure, port and high pressure port.More than anything these tests require a lot of patience.These are extremely expensive tests and setups.This is a helium gas pycnometer where you have containers in which you can heat thesample and you can keep them in the control system.You can allow their interaction the helium gas, you can find out what is the volume ofhelium that gets displaced and you can come to the bulk density and surface area.The balls that you are seeing over here are the standard materials which are used to calibratethe set up.This is a Blaine's Air Permeability Apparatus you must have used it; this is a U tube andin the U tube one part of the U tube is connected to pump air pump like the blood pressure machineand this is a sample holder.So, in a hole weight of the sample is compacted in the sample holder and this is attachedto the Blaine’s air permeability apparatus.And what you are seeing over here is the mercury column.So, initially the mercury is balanced.What you have to find out is that you have to find out how much time a material takesfor allowance of a certain amount of air through it and that is why we call this setup as Blaine'sAir Permeability.So truly speaking, the amount of air with passes easily or not easily is converted intospecific surface area.So, no need to remember all these equations and formula because they are all given theASTM course, they just try to understand what it is.So, if I create a sample at a given void ratio and ‘es’ is the void ratio of the specificmaterial which is being used as a standard material, ‘es’ is the standard material,which is normally cement PPC or OPC ‘t’ is the time which is taken by manometer todrop when the sample is used and Ts is that time which is the time taken by the standardsample to drop certain amount of air through it specific surface area of cement is known.Again the question now will you get it so, you can use different techniques to find itout.The void ratio of the sample can be often and void ratio of the cement is known andmano metric drop for the cement is known and enhance you can compute the surface area earlierpeople who are working in the field of cement and concrete technology they used to use thesedevices.But now, the question in your mind must be that where are geotechnical engineers aregoing to use this concepts, you must have got a hint that present day practice of environmentalgeomechanics is how finding material can be crushed.It defined material itself to imagine if I want to pulverize clays and if I want to createa nano size particles out of it.So, this is a very different scale of the particle size on which you are traversing.Because of the accurate advantages, the particle becomes extremely small in size, surface areaincreases, activity increases and so on.So, these things become an excellent environment filters, see if I can use them for cleaningup of different types of flue gases or the sludges.So, this is where the profession is heading to so, I might like to use this material inthe soils to decontaminate it.So, when you read the papers, you will find a lot of research is being done and this isthe need of the hour, when you go from micro to nanoscale.The as far as I know, like whatever understanding we have at the micro scale totally changesto at the nano scale that nano chemistry comes in.So for that, if we are granting it that fine, then we need to understand how we will haveit because the difference there will be difference in behavior at the micro scale and nano scaleis correct that right.So, your observation statement is absolutely correct.And this is a challenge people are facing.So bentonites you know most of the bentonites can be activated for extra sensitive environmentalprojects, if I have to stop the leakage of let us say radioactivity then I have to makematerial, so fine, so active that nothing passes out of the voids of the soils or forthat matter, even from the concrete also being used you come from a place very close to thatin an army does all these things or you should explore thermal resistance blast resistantand impact resistant structures, this is what now India is doing a lot of geotechnics isa lot.Another interesting device, you can check the thermal stability of the geomaterialsbecause most of the applications we have been talking about is you know materials comingin contact with elevated temperatures.So, how would you make refer refractories how would you make bricks how to make tileshow to make different types of you know what to call them as refractory materials.Have you ever seen a refractory materials in ovens?Normally, they create a layer of clay and which acts as a very good insulator.But without that layer, you cannot bake the chapattis or whatever tandoors.So that is a refractory material.So, when you go to the commercial level industrial level there, they cannot do clays only thenthey have to use the refectories, these refractories have to be tested for their thermal stability,particularly the minerals which are going to use for making these things.So, you will be surprised to know that geotechnics has helped prevent tile industry.So some of my projects, which I did for different famous tile companies, quite educative.From there only I learned, you know, what materials to be used to create a sort of atile.So in this system, quick review for you.What we do is we do controlled heating of the sample in different environments.And this environment could be less oxygen or it could be nitrogen.So, normally the heating of the sample is done in 2 different types of environments.Which is one is you have free supply of oxygen.So that all the material which has to get oxygenated oxidized.So, second is in the nitrogen, so that nothing gets oxidized.And then what you observe over here is that there is a balance micro balance attachedto the sample where you can measure up to third decimal place of the milligrams alsoand you can plot a relationship like this.Which shows on y axis the weight loss percentage, and on the x axis is the temperature.So, let us first decipher the graph on y axis on the left-hand side and the temperatureon the x axis this is what is known as a thermal gravimetric analysis TGA.If you consider the first 2 parts of the graph this one and this one what it shows is asthe temperature increases, this side temperature increases x axis percentage weight loss increases,I want to see how much a material can get rid of the moisture which is adhering on itssurface number one.Number two what our chemical reactions which might be happening in the system and I heatit slowly.So, for that there is another equipment which is known as DTA differential thermal analysis,which is done.So, this is thermogravimetric analysis and differential thermal analysis.So, as the temperature increases and increase in temperature is controlled, that means,the rate of enhancement of temperature can be fixed by heating at certain temperature.So, depending upon the response which you get, I can define a reaction exothermic orendothermic reaction.So, there are a few soils or few minerals, when you heat them, they might become unstable,and they may start showing you exothermic reactions particularly when they come in contactwith water.So, when you are designing different types of systems of importance there you have todo all this test all right.So, just to remind you, what we do is we do these type of testing in dry air and in inertatmosphere like nitrogen.So, that we can compare the results and we can interpret the presence of different typeof wallet and materials in the geomaterials.So, suppose I want to differentiate between different types of coals.This is a very good method.See our subjects has become mostly consulting oriented like where you are to apply yourgrey matter in solving someone's problem.So, I am sure you must realize is becoming more of diagnostics or the problem diagnosticof a material application of a material for solving a situation or a problem.This is modern day geotechnical engineering is so, if you look at this trend, you know,this is what is known as differential scanning calorimetry is another interesting tool whichis used and when you talk about when you meet my students like Bhini and all these peoplewho are talking about the phase changes, which are occurring in the materials during youknow.How much it goes into system or how much it comes out of system multi-phase geomechanicswhen you talk about these type of studies become very important.Again, it shows the instability of the system.So, if you look at this graph for DSC analysis, differential scanning calorimetry, which isbeing used by chemical engineers quite a lot at a given temperature, how much heat flowoccurs in the material or outside the material?If I want to see this, you will observe that this material behaves very dubious you knowat a very small just extreme left to the center given temperature that behavior is differentand on the extreme right the behavior is different, it has too extreme peaks, these type of materialsI do not want in my team, is it not?They may be very dangerous, extremely moody materials.So, I have to observe this I have two ways to eliminate this type of method either Ido not select them or if I select them, then I have to make sure that these materials willalways remain exposed to a certain temperature range.Because they are also you will see that there is a thermal instability.So, lot of engineering has to be done with the material.That is what the science of technology of the clay minerals is simple example is a newuse different type of face packs on your face realized very freshness why?Because these are the minerals and you put them in water and when they are at hand onthe face they produce exothermic reaction or another way in the mineral produces exothermicreaction you will be very uncomfortable.So, the minerals which are used for most of the cosmetics are the ones which give youendothermic reactions.The cooler body most of the talc powders they are of that type so, this is how you can differentiatebetween the same thing is valid if I valid a barrier system inside the ground by usinga mineral and if water contaminant comes in contact with them in them and a lot of heatgets emitted what will happen?The whole soil might get crack thermally crack is not a good situation.So, compatibility of the material has to be checked before you use this material for anyapplication thermal compatibility.

Video 2: An Overview of Chemical Characterization
So, now, let me start the chemical characterization of geomaterials.How do you analyze the thermal properties of different particles in the field.How would you react to different philosophically only concrete technologies talk about heatof hydration, to lisping we should also be talking about innovation?Because chemically cement and soils are saying if you look at the composition, the compositionis same only thing is the presence of certain chemicals is more in cement as compared tothe soils.So, when these type of questions come in mind that suppose if I had to evaluate 2 to 3 materialsand if I have chalk out a strategy that whatever materials should be utilized and this is wherewe talk about the chemical characterization.This is an intricate subject.So, earlier we talked about XRD if you remember X ray diffraction, now I am talking aboutX ray fluorescence XRF.So, XRF technique gives you the chemical composition of the material, it could be elemental analysis.And the percentage oxides which are present in the material XRF we call it this is theunit which is used for finding out the chemical composition of geomaterials, rocks, scienceand science, different type of admixtures.So, man-made geomaterials that will be in advantage of geomechanics we utilize extensivelyICP what is known as inductively coupled plasma you must have studies in your 10+2 physics,sorry chemistry, I am sure.So, what ICP units are, they are used for determining the level of contamination ofchemicals present in the solution of any geometry there.So, you take geomaterial, dissolve it in water make a solution, let the chemicals or heavymetals which are present in the system leach out in the solution and then you analyze thesolution to get the concentration of heavy metals which are present in.so, there are 2 versions of this testing 1 is only ICP where you just do qualitativeanalysis.What are the heavy metals present there is something known as MS Mass Spectroscopy.So, mass spectroscopy also tells you the quantity is qualitative quantitative analysis pH isa very important factor as far as the chemical characterization is concerned, and I am sureall of you must have used electrodes which I will show you subsequently to determinethe pH of the soil.In present day environmental geomechanics, we use gas chromatography you must have comeacross this term GC-MS in environmental sciences course, I am sure you must use this.So, when the soils are contaminated with you know, organic contaminants, different typesof gases or contaminants, which are organic in nature, hydrocarbons, oil contaminatedsoils, different type of organic contaminants contaminated soils and so on.In present day industrial application, this type is very important so, we get a lot ofprojects from the industries, where they have to comply with environmental impact analysisEIA.So, for conducting, these are the tools and then you are to do a very comprehensive analysis,comprehensive analysis to show that the soils are not containing any contaminants and henceenvironmental impact of the process the industry is following is alright.Otherwise, you can submit a report to the agencies which are responsible for monitoringthe environment and they may serve a notice to close it down.This is becoming a very interesting profession and very interesting.We use some time NMR also nuclear magnetic resonance, it must have studied physics course.This also tells you the type of bonds which are present between the soils and contaminantsand the type of contaminants which you have, that can be obtained with the help of NMR.There is something known as FTIR spectroscopy, this is Fourier transform infrared spectroscopyFTIR.So, these gadgets are very advanced gadgets and they are utilized mostly to establishthe bonding which is occurring between the geomaterials and the contaminants alright.So these are very sensitive issues when you talk about the environment and norms, we canestablish with the help of these gadgets.One of the tests which is done to establish the chemical characterization or the potentialof this geo materials, whether they are chemically active or not, would be cation exchange capacityCEC.I will be talking about this.This is a simple test.And it tells you quite with accuracy, what is the potential of a geomaterial to interactwith the environment, how reactive it would be, how active would be knowledge or solutionanalysis, how the pore solution can be extracted from the soil.And this is what I enjoyed writing an analogy between, you know, blood sampling from humanbody that you can take out the pore solution and the way you analyze blood to diagnosethe disease and remediation of the disease.Similar things we can do here once you have the solution of the soils and the geomaterials,you know, what is why the soils are healing, and how to treat them, how to diagnose andhow to do that rectification of the disease.These subjects are becoming very advanced and lot of gadgets and many efforts are beingmade to standardize all these things.