शैडोइंग अभ्यास: Introduction 2, Why "Portland" cement - वीडियो के साथ अंग्रेजी बोलना सीखें
पाठ बनाया जा रहा है...
1
Okay, so welcome back.
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In this second unit of this introductory module, I've called it Why Portland Cement?
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And what we're going to look at in this module is why the composition of cement is as it is.
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Why Portland cement?
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99.99% of cement made today is based on what we call Portland cement or more precisely Portland cement clinker.
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So clinker is these nodules you see in the picture here and that's the material that comes out of the cement kiln.
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And the name Portland, this is purely a marketing name,
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this was chosen by Joseph Aspin who was the person who patented the term Portland cement in 1824
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and what he wanted to do, he he wanted to highlight the appearance of his new material to Portland stone
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which was then regarded as the best building material in England.
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So don't worry about this word Portland, it's purely a marketing term.
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So the dominance of this type of cement is really not by chance.
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It's a direct consequence of the raw materials which we have available on earth.
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So here on the left, we see the composition of the Earth's crust.
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And it's really remarkable to see that we have just eight elements, that's to say oxygen, silicon, aluminium, iron, calcium, sodium, potassium, magnesium.
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These together make up more than 98% of the Earth's crust.
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This is quite remarkable, but those of you who may have done some astronomy
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will realise that it's a direct consequence of the formation of elements in stars.
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and it also means that this is not just the composition of the Earth
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but will be the similar composition for all the rocky planets we can imagine in the universe.
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What this means is that even elements we regard as quite common,
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like for example copper, are very very much less abundant than these eight rock forming elements,
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like for example silicon.
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And this relative abundance of 1 to 1000 will translate in terms of the availability and the cost of these materials.
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So having seen in the last module how the very large amount of cement is produced,
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clearly we can't think about making cement out of all the other elements that's in that remaining 2%.
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So now we can understand that the composition of the earth limits the practical chemistries we can have for cementitious materials.
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But looking on the bright side, it also means that we can explore all possible options.
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It means that there's no kind of breakthrough out there that we haven't discovered yet.
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And what we need to really know in a bit more detail is how cement works
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to understand how these different elements can be used.
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So this is what I've illustrated in the next few slides.
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So this schematic here really tries to explain this.
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When you mix grey cement powder with water, what you have is grains just floating about,
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and that is very convenient because it means you have a flowable material, you can cast into moulds, you can make into different shapes.
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And then we have a chemical process whereby these grey cement grains are dissolving
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and then the ions are reacting with the water to give us this new solid which are called the hydrates.
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So in this image here the red areas are the cement hydrates and these have a higher volume of solid
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and therefore it holds the cement grains together, creating a rigid solid.
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So let's go back and look at this composition of the earth.
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Most of those elements are associated with oxygen as oxides,
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and look at whether these different oxides can react to give us a cementitious material.
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Now if we take the two alkali oxides, sodium and potassium, the problem here is these produce very, very soluble salts.
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So maybe in your chemistry lessons you've used sodium hydroxide
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and you'll know that you can have very strong sodium hydroxide because a very high amount can go into solution without precipitating.
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So clearly this is no good for producing solid hydrates which hold the structure together.
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On the other hand, if we look at iron oxide and magnesium oxide, the problem here is that these oxides have fairly low mobility in alkaline solutions,
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which is the solutions we have in cementitious materials.
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So what we can see in this image here, this is just a piece of concrete taken from a normal concrete wall.
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And in this image we have some very bright areas.
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And these very bright areas are where all the iron oxide is located.
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And in fact, those bright areas are exactly the same as in the original cement grains.
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During that whole 30 years, that iron in the cement grains has just stayed in the same place.
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So it's not doing any harm, but basically it means it's not going out into solution,
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it's not precipitating new solids and therefore making very little contribution to the bonding and the development of strength.
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It's a similar story for magnesium.
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Here in this picture now, we see a blended cement.
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We're going to talk about that in a few modules time.
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And in this blended cement, the darker grains, such as in the center of the picture here,
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you see are now surrounded by a region of dark products.
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And these darker products are because all the magnesium that was in that slag grain is concentrated in that area.
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And same situation, this magnesium has not moved into the space between the grains.
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it's not really contributed to bridging the space between them.
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So this means we end up with just three oxides, which are really the most useful, and are the essential component for the Portland cement we have today.
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So this is really in no way a coincidence that we've ended up with this composition.
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Because if we now look at that ternary system between calcium oxide,
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silicon dioxide and alumina, we see the composition of Portland cement.
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And in fact, Portland cement, as we see it here, this is composed of calcium silicates.
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There's really only one other region in this diagram where we have minerals
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that will react with water in the way we previously saw and give us cementitious materials.
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And that's this region here, which is the region where we find calcium illuminate cement and calcium sulphur illuminate cement.
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Small amounts of sulphur is the sort of extra dimension which is not shown in this diagram here.
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So these other compositions, calcium aluminate,
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calcium sulphur aluminate, have a lot of advantage because they have less calcium in.
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You see, they're further away from that calcium oxide corner, means they have less calcium oxide,
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and therefore there's less CO2 produced chemically during the production of these phases.
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So that sounds very good, but the problem is that it's not so easy to make these
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because the raw materials we need are not so widely available.
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And we have to ask the question, what sources of minerals are there which contain much higher amounts of aluminium to silicon?
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Most minerals have about the same ratio of silicon to aluminium as in Portland cement, about two to one.
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To get a composition down here in this alumina rich part of the diagram, we have to go to materials like bauxite.
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Now bauxite is much more localized than the materials used for making Portland cement.
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It's estimated that only 10 countries contain about 90% of the reserves of bauxite.
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And of course bauxite is the first raw material for aluminium production.
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So the consequence of all this means that it's rather expensive
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and it means that you cannot produce calcium aluminate cement
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or calcium sulphur aluminate cement for the same cost as producing Portland cement.
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We can look at this effect of chemical CO2 and how it's related to composition in more detail on this slide here.
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So at the top we see the two calcium silicates which are present in Portland cement.
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These are known as tricalcium silicate or C3S, dicalcium silicate or C2S.
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And many people have proposed that what we should be doing is making Portland cement with more C2S as opposed to C3S.
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But the problem here is that the reduction in chemical CO2 is really very marginal.
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It's only around 10%.
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And that's more than offset by the much slower kinetics of C2S.
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So the strength development is much slower.
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And because the strength development is much slower, this would mean that in practical situations where people need a given strength at a given time,
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then they will use more cement.
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And that use of more cement will completely cancel out this 10% saving.
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So belight-rich clinkers really don't contribute at all to lowering CO2 emissions.
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Down here, we can see the figures for yellow mite.
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That's this complex phase called C4A3S bar.
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and as I said on the previous slide, this has a good reduction potential in terms of lower chemical CO2.
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But we have the problem of the cost of the raw materials.
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And finally on this slide I want to point out this line here
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because many people nowadays are proposing that we should use magnesium-based cements.
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There can be context in which this might be possible,
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not now, but if somebody can invent a way of producing magnesium-based cements from magnesium silicate rocks,
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it might be interesting.
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But what's happening at the minute, most people are using magnesium carbonate.
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And what you can see here very clearly is
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that the chemical CO2 emissions from a breakdown of magnesium carbonate
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are way higher than they are from the calcium silicate phases we have in Portland cement.
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So here we come back to that composition of the earth we've discussed in detail,
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and we compare it with the composition of a typical Portland cement.
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And you can see the elements present are similar.
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The big difference between the Portland cement and the composition of the earth is the dominance of this sector for calcium.
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And this is, as we explained in the last lecture, where the chemical CO2 is coming from.
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But from a practical point of view, it's very easy to make things with this composition because limestone, which is usually very pure calcium carbonate,
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is very widely distributed across the globe.
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And it means that you can make these porthens cements out of limestone.
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The other elements are generally coming from something like clay, but you can make this almost everywhere in the world.
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And therefore, transportation of the final product is minimized.
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So the other important aspect is the pattern of reaction of the Portland cement.
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And this is shown in this diagram here, which plots the heat evolution, which is a signature of the rate of reaction.
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And what we can see is at the beginning of the reaction, we have a burst of reaction,
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and then we have this period here where the reaction remains slow for several hours.
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From a practical point of view this is extremely important as it gives us time to mix the cement
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and transport it to the building site.
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And then after about three hours the reaction takes off again.
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Now this pattern of reaction means that really it's very very simple to use cementitious materials.
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Here we see a picture from India where people are making concrete under really quite rustic conditions.
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But nevertheless, because it's such a robust chemical reaction, it still works, it still gives very good quality building materials.
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Really, what we're going to see is that for these reasons I've explained to you here,
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cements based on Portland clinker will be the most important materials for the foreseeable future.
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They can be made from widely available raw materials, there's an incredible economy of scale, leading to very low cost,
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and they're very easy to use even by unskilled workers.
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Given the composition of the earth, this composition, Portland cement clinker, really is the best option.
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But in the next lecture, what we're going to see, how by replacing part of this Portland cement, we can lower environmental impact.
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So, thank you very much.
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इस पाठ की शब्दावली और बोलने के सुझाव
यह C1 स्तर का स्पीकिंग पाठ वीडियो “Introduction 2, Why "Portland" cement” पर आधारित है। सबसे ज़्यादा दोहराए गए शब्द ये हैं: cement, Portland, material, composition, calcium। इस वीडियो में शैडोइंग के लिए 139 वाक्य और 2024 शब्द हैं। बोला गया हिस्सा 14:22 लंबा है। वक्ता लगभग 141 शब्द प्रति मिनट की स्थिर गति से बोलता है, जो शैडोइंग के लिए आरामदायक है। केवल 80% शब्द अंग्रेज़ी के 3,000 सबसे आम शब्दों में से हैं, इसलिए शब्दावली कठिन है।
इस वीडियो की मुख्य शब्दावली
वीडियो के 15 सबसे कठिन शब्द, उच्चारण और अर्थ के साथ:
| शब्द | उच्चारण | अर्थ |
|---|---|---|
| cement संज्ञा | /səˈmɛnt/ | सीमेंट |
| calcium संज्ञा | /ˈkælsi.əm/ | चूर्णातु |
| oxide संज्ञा | /ˈɑksaɪd/ | जारेय, ऑक्साइड |
| magnesium संज्ञा | /ˌmæɡˈnizi.əm/ | भ्राजातु, मैग्नीसियम |
| silicon संज्ञा | /ˈsɪləˌkɑn/ | सैकता |
| sulfur संज्ञा | /ˈsʌl.fə/ | गन्धक |
| aluminium संज्ञा | /ˌæl.(j)uˈmɪn.i.əm/ | एल्युमिनियम, स्फटयातु |
| diagram संज्ञा | /ˈdaɪ.ə.ɡɹæm/ | आलेख, मापचित्र |
| sodium संज्ञा | /ˈsəʊ.di.əm/ | क्षारातु, सोडियम |
| module संज्ञा | /ˈmɑd͡ʒul/ | मॉड्यूल |
| hydrate संज्ञा | /haɪˈdɹeɪt/ | जलीय |
| mineral संज्ञा | /ˈmɪn.ə.ɹəl/ | खनिज |
| consequence संज्ञा | /ˈkɑn.sɪ.kwəns/ | परिणाम, नतीजा |
| hydroxide संज्ञा | /haɪˈdɹɒks.aɪd/ | उदजारेय |
| potassium संज्ञा | /pəˈtæsiəm/ | दहातु, पोटैशियम |
वीडियो में आने वाली फ़्रेज़ल वर्ब
| शब्द | अर्थ |
|---|---|
| take off क्रिया | उतारना |
इस वीडियो का व्याकरण
वक्ता जिन संरचनाओं का सबसे अधिक प्रयोग करता है, वीडियो के असली शब्दों के साथ:
| संरचना | वीडियो में |
|---|---|
| Passive voice be + past participle — ज़ोर इस पर कि क्या होता है, न कि कौन करता है | is based · was chosen · is produced |
| Present perfect have/has + past participle — बीता हुआ काम जिसका असर अभी भी है | I've called · haven't discovered · I've illustrated |
| Relative clauses who / which + उपवाक्य — व्यक्ति या वस्तु के बारे में अतिरिक्त जानकारी | person who patented · solid which are · oxides, which are |
ध्यान देने योग्य उच्चारण
वक्ता 17 बार संक्षिप्त रूपों का प्रयोग करता है, जैसे we're, I've, don't। इन्हें वैसे ही छोटा बोलें जैसा आप सुनते हैं।
- “sh” और “zh” की ध्वनियाँ: cementitious /ˌsɛmɛnˈtɪʃəs/, emission /ɪˈmɪʃ.ən/, dimension /daɪˈmɛn.ʃən/
- लंबे शब्द — बलाघात सही रखें: magnesium /ˌmæɡˈnizi.əm/, cementitious /ˌsɛmɛnˈtɪʃəs/, aluminium /ˌæl.(j)uˈmɪn.i.əm/, alumina /əˈl(j)uːmɪnə/, illuminate /ɪˈl(j)umɪneɪt/
हिंदी भाषियों के लिए मुश्किल ध्वनियाँ:
- /v/ और /w/ का फ़र्क़ — /v/ में ऊपर के दाँत निचले होंठ को छूते हैं, /w/ में होंठ गोल होते हैं: consequence /ˈkɑn.sɪ.kwəns/, dissolve /dɪˈzɑlv/, invent /ɪnˈvɛnt/, whereby /wɛə(ɹ)ˈbaɪ/
- /z/ — इसे “ज” (/dʒ/) न बनाएँ: magnesium /ˌmæɡˈnizi.əm/, compose /kəmˈpəʊz/, dissolve /dɪˈzɑlv/, localize /ˈloʊkəlaɪz/, minimize /ˈmɪn.ɪˌmaɪz/
- /æ/ — “ऐ” से ज़्यादा खुला: calcium /ˈkælsi.əm/, magnesium /ˌmæɡˈnizi.əm/, aluminium /ˌæl.(j)uˈmɪn.i.əm/, diagram /ˈdaɪ.ə.ɡɹæm/, potassium /pəˈtæsiəm/
इस वीडियो से अभ्यास कैसे करें
- पहले बिना बोले पूरा वीडियो एक बार सुनें और जो शब्द नहीं आते उन्हें लिख लें।
- सामान्य गति पर एक-एक वाक्य की शैडोइंग करें और हर वाक्य तब तक दोहराएँ जब तक आपकी लय वक्ता से न मिल जाए।
- अपनी आवाज़ रिकॉर्ड करें और मूल से तुलना करें, ख़ासकर cement, calcium, oxide जैसे शब्दों पर ध्यान दें।
शैडोइंग तकनीक क्या है?
शैडोइंग (Shadowing) एक विज्ञान-समर्थित भाषा सीखने की तकनीक है जो मूल रूप से पेशेवर दुभाषिया प्रशिक्षण के लिए विकसित की गई थी। विधि सरल लेकिन शक्तिशाली है: आप मूल अंग्रेज़ी ऑडियो सुनते हैं और तुरंत इसे ज़ोर से दोहराते हैं — जैसे वक्ता की छाया 1-2 सेकंड की देरी से। शोध से पता चलता है कि यह उच्चारण सटीकता, स्वर, लय, जुड़ी हुई ध्वनियाँ, सुनने की समझ और बोलने की प्रवाहशीलता में काफ़ी सुधार करता है।