Shadowing Practice: Introduction 2, Why "Portland" cement - Learn English Speaking with Video
בחר מצב תרגול
כל מצב פותח חדר תרגול במסך מלא.
139 משפטים
אם המשפטים קצרים או ארוכים מדי, לחץ על ערוך כדי להתאים אותם.
1
Okay, so welcome back.
2
In this second unit of this introductory module, I've called it Why Portland Cement?
3
And what we're going to look at in this module is why the composition of cement is as it is.
4
Why Portland cement?
5
99.99% of cement made today is based on what we call Portland cement or more precisely Portland cement clinker.
6
So clinker is these nodules you see in the picture here and that's the material that comes out of the cement kiln.
7
And the name Portland, this is purely a marketing name,
8
this was chosen by Joseph Aspin who was the person who patented the term Portland cement in 1824
9
and what he wanted to do, he he wanted to highlight the appearance of his new material to Portland stone
10
which was then regarded as the best building material in England.
11
So don't worry about this word Portland, it's purely a marketing term.
12
So the dominance of this type of cement is really not by chance.
13
It's a direct consequence of the raw materials which we have available on earth.
14
So here on the left, we see the composition of the Earth's crust.
15
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.
16
These together make up more than 98% of the Earth's crust.
17
This is quite remarkable, but those of you who may have done some astronomy
18
will realise that it's a direct consequence of the formation of elements in stars.
19
and it also means that this is not just the composition of the Earth
20
but will be the similar composition for all the rocky planets we can imagine in the universe.
21
What this means is that even elements we regard as quite common,
22
like for example copper, are very very much less abundant than these eight rock forming elements,
23
like for example silicon.
24
And this relative abundance of 1 to 1000 will translate in terms of the availability and the cost of these materials.
25
So having seen in the last module how the very large amount of cement is produced,
26
clearly we can't think about making cement out of all the other elements that's in that remaining 2%.
27
So now we can understand that the composition of the earth limits the practical chemistries we can have for cementitious materials.
28
But looking on the bright side, it also means that we can explore all possible options.
29
It means that there's no kind of breakthrough out there that we haven't discovered yet.
30
And what we need to really know in a bit more detail is how cement works
31
to understand how these different elements can be used.
32
So this is what I've illustrated in the next few slides.
33
So this schematic here really tries to explain this.
34
When you mix grey cement powder with water, what you have is grains just floating about,
35
and that is very convenient because it means you have a flowable material, you can cast into moulds, you can make into different shapes.
36
And then we have a chemical process whereby these grey cement grains are dissolving
37
and then the ions are reacting with the water to give us this new solid which are called the hydrates.
38
So in this image here the red areas are the cement hydrates and these have a higher volume of solid
39
and therefore it holds the cement grains together, creating a rigid solid.
40
So let's go back and look at this composition of the earth.
41
Most of those elements are associated with oxygen as oxides,
42
and look at whether these different oxides can react to give us a cementitious material.
43
Now if we take the two alkali oxides, sodium and potassium, the problem here is these produce very, very soluble salts.
44
So maybe in your chemistry lessons you've used sodium hydroxide
45
and you'll know that you can have very strong sodium hydroxide because a very high amount can go into solution without precipitating.
46
So clearly this is no good for producing solid hydrates which hold the structure together.
47
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,
48
which is the solutions we have in cementitious materials.
49
So what we can see in this image here, this is just a piece of concrete taken from a normal concrete wall.
50
And in this image we have some very bright areas.
51
And these very bright areas are where all the iron oxide is located.
52
And in fact, those bright areas are exactly the same as in the original cement grains.
53
During that whole 30 years, that iron in the cement grains has just stayed in the same place.
54
So it's not doing any harm, but basically it means it's not going out into solution,
55
it's not precipitating new solids and therefore making very little contribution to the bonding and the development of strength.
56
It's a similar story for magnesium.
57
Here in this picture now, we see a blended cement.
58
We're going to talk about that in a few modules time.
59
And in this blended cement, the darker grains, such as in the center of the picture here,
60
you see are now surrounded by a region of dark products.
61
And these darker products are because all the magnesium that was in that slag grain is concentrated in that area.
62
And same situation, this magnesium has not moved into the space between the grains.
63
it's not really contributed to bridging the space between them.
64
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.
65
So this is really in no way a coincidence that we've ended up with this composition.
66
Because if we now look at that ternary system between calcium oxide,
67
silicon dioxide and alumina, we see the composition of Portland cement.
68
And in fact, Portland cement, as we see it here, this is composed of calcium silicates.
69
There's really only one other region in this diagram where we have minerals
70
that will react with water in the way we previously saw and give us cementitious materials.
71
And that's this region here, which is the region where we find calcium illuminate cement and calcium sulphur illuminate cement.
72
Small amounts of sulphur is the sort of extra dimension which is not shown in this diagram here.
73
So these other compositions, calcium aluminate,
74
calcium sulphur aluminate, have a lot of advantage because they have less calcium in.
75
You see, they're further away from that calcium oxide corner, means they have less calcium oxide,
76
and therefore there's less CO2 produced chemically during the production of these phases.
77
So that sounds very good, but the problem is that it's not so easy to make these
78
because the raw materials we need are not so widely available.
79
And we have to ask the question, what sources of minerals are there which contain much higher amounts of aluminium to silicon?
80
Most minerals have about the same ratio of silicon to aluminium as in Portland cement, about two to one.
81
To get a composition down here in this alumina rich part of the diagram, we have to go to materials like bauxite.
82
Now bauxite is much more localized than the materials used for making Portland cement.
83
It's estimated that only 10 countries contain about 90% of the reserves of bauxite.
84
And of course bauxite is the first raw material for aluminium production.
85
So the consequence of all this means that it's rather expensive
86
and it means that you cannot produce calcium aluminate cement
87
or calcium sulphur aluminate cement for the same cost as producing Portland cement.
88
We can look at this effect of chemical CO2 and how it's related to composition in more detail on this slide here.
89
So at the top we see the two calcium silicates which are present in Portland cement.
90
These are known as tricalcium silicate or C3S, dicalcium silicate or C2S.
91
And many people have proposed that what we should be doing is making Portland cement with more C2S as opposed to C3S.
92
But the problem here is that the reduction in chemical CO2 is really very marginal.
93
It's only around 10%.
94
And that's more than offset by the much slower kinetics of C2S.
95
So the strength development is much slower.
96
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,
97
then they will use more cement.
98
And that use of more cement will completely cancel out this 10% saving.
99
So belight-rich clinkers really don't contribute at all to lowering CO2 emissions.
100
Down here, we can see the figures for yellow mite.
101
That's this complex phase called C4A3S bar.
102
and as I said on the previous slide, this has a good reduction potential in terms of lower chemical CO2.
103
But we have the problem of the cost of the raw materials.
104
And finally on this slide I want to point out this line here
105
because many people nowadays are proposing that we should use magnesium-based cements.
106
There can be context in which this might be possible,
107
not now, but if somebody can invent a way of producing magnesium-based cements from magnesium silicate rocks,
108
it might be interesting.
109
But what's happening at the minute, most people are using magnesium carbonate.
110
And what you can see here very clearly is
111
that the chemical CO2 emissions from a breakdown of magnesium carbonate
112
are way higher than they are from the calcium silicate phases we have in Portland cement.
113
So here we come back to that composition of the earth we've discussed in detail,
114
and we compare it with the composition of a typical Portland cement.
115
And you can see the elements present are similar.
116
The big difference between the Portland cement and the composition of the earth is the dominance of this sector for calcium.
117
And this is, as we explained in the last lecture, where the chemical CO2 is coming from.
118
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,
119
is very widely distributed across the globe.
120
And it means that you can make these porthens cements out of limestone.
121
The other elements are generally coming from something like clay, but you can make this almost everywhere in the world.
122
And therefore, transportation of the final product is minimized.
123
So the other important aspect is the pattern of reaction of the Portland cement.
124
And this is shown in this diagram here, which plots the heat evolution, which is a signature of the rate of reaction.
125
And what we can see is at the beginning of the reaction, we have a burst of reaction,
126
and then we have this period here where the reaction remains slow for several hours.
127
From a practical point of view this is extremely important as it gives us time to mix the cement
128
and transport it to the building site.
129
And then after about three hours the reaction takes off again.
130
Now this pattern of reaction means that really it's very very simple to use cementitious materials.
131
Here we see a picture from India where people are making concrete under really quite rustic conditions.
132
But nevertheless, because it's such a robust chemical reaction, it still works, it still gives very good quality building materials.
133
Really, what we're going to see is that for these reasons I've explained to you here,
134
cements based on Portland clinker will be the most important materials for the foreseeable future.
135
They can be made from widely available raw materials, there's an incredible economy of scale, leading to very low cost,
136
and they're very easy to use even by unskilled workers.
137
Given the composition of the earth, this composition, Portland cement clinker, really is the best option.
138
But in the next lecture, what we're going to see, how by replacing part of this Portland cement, we can lower environmental impact.
139
So, thank you very much.
הורד אפליקציה
כל מה שאתה צריך כדי לדבר בשטף
הגיית AIציון לכל משפט
תרגול IPAשלוט בכל צליל
אוצר מיליםבנה את מאגר המילים שלך
משחק אוצר מיליםלמד תוך כדי משחק
אותו ערוץ
FOR YOU
המלץ על סרטון
C11
218 משפטים
Introduction to Marketing: The Marketing Mix
Business EnglishUniversity StudentsWorking Adults
C1677 משפטים
Inside PMBOK Guide 8: What Project Managers Must Know | Episode 542
Business EnglishUniversity StudentsWorking Adults
C12
106 משפטים
What is Engineering?: Crash Course Engineering #1
Business EnglishUniversity StudentsWorking Adults
C12
68 משפטים
What Is Basic Oxygen Furnace - Understanding the basic oxygen process.
Business EnglishUniversity StudentsWorking Adults
C11
43 משפטים
What is an Organization? - the Nature of Organizations
Business EnglishUniversity StudentsWorking Adults
C12
133 משפטים
Carbon Fiber - The Material Of The Future?
Business EnglishUniversity StudentsWorking Adults
C11
689 משפטים
Natural Stone 101: Everything You Need to Know About Designing with the Oldest Building Material
Business EnglishUniversity StudentsWorking Adults
C12
234 משפטים
Cursed Units 2: Curseder Units
Business EnglishUniversity StudentsWorking Adults
C16
114 משפטים
Introduction to Contract Law
Business EnglishUniversity StudentsWorking Adults
C130
26 משפטים
Docker in 100 Seconds
American AccentBusiness EnglishUniversity StudentsWorking Adults
C16
261 משפטים
The Human Element
Business EnglishDaily ConversationUniversity Students
Vocabulary and speaking notes for this lesson
This C1 speaking lesson is built on the video “Introduction 2, Why "Portland" cement”. The speaker keeps coming back to these words: cement, Portland, material, composition, calcium. This video has 139 sentences and 2024 words to shadow. The speech runs for 14:22. The speaker talks at a steady 141 words per minute, a comfortable pace for shadowing. Only 80% of the words are among the 3,000 most common in English, so the vocabulary is demanding.
Key vocabulary in this video
The 15 most advanced words in the video, with pronunciation and meaning:
| Word | Pronunciation | Meaning |
|---|---|---|
| cement noun | /səˈmɛnt/ | A powdered substance produced by firing (calcining) calcium carbonate (limestone) and clay that develops strong cohesive properties when mixed with water. The… |
| calcium noun | /ˈkælsi.əm/ | The chemical element (symbol Ca) with atomic number 20: a soft, silvery-white alkaline earth metal which occurs naturally as carbonate in limestone and as… |
| oxide noun | /ˈɑksaɪd/ | A binary chemical compound of oxygen with another chemical element. |
| magnesium noun | /ˌmæɡˈnizi.əm/ | The chemical element with an atomic number of 12. It is a light, easily flammable, silvery-white alkaline earth metal. |
| silicate noun | /ˈsɪlɪkət/ | Any salt of silica or of one of the silicic acids; any mineral composed of silicates. |
| cementitious adjective | /ˌsɛmɛnˈtɪʃəs/ | Resembling or having some properties of cement; containing cement. |
| clinker noun | /ˈklɪŋkɚ/ | A very hard brick used for paving customarily made in the Netherlands. |
| silicon noun | /ˈsɪləˌkɑn/ | A nonmetallic element (symbol Si) with an atomic number of 14 and atomic weight of 28.0855. |
| aluminate noun | A compound, containing aluminium and oxygen with more electropositive elements, that is a salt of the hypothetical aluminic acid | |
| bauxite noun | /ˈbɔːksaɪt/ | The principal ore of aluminium; a clay-like mineral, being a mixture of hydrated oxides and hydroxides. |
| sulfur noun | /ˈsʌl.fə/ | A chemical element with atomic number 16, having a bright yellow color and characteristic smell, used commercially in a variety of products such as… |
| aluminium noun | /ˌæl.(j)uˈmɪn.i.əm/ | A light, silvery metal extracted from bauxite, and a chemical element (symbol Al) with an atomic number of 13. |
| diagram noun | /ˈdaɪ.ə.ɡɹæm/ | A plan, drawing, sketch or outline to show the function or operation of something, or to show the relationships between the parts of a whole. |
| sodium noun | /ˈsəʊ.di.əm/ | The chemical element (symbol Na) with an atomic number of 11 and atomic weight of 22.990. It is a soft, waxy, silvery, reactive alkali metal that is never… |
| module noun | /ˈmɑd͡ʒul/ | A self-contained component of a system, often interchangeable, which has a well-defined interface to the other components. |
Phrasal verbs you will hear
| Word | Pronunciation | Meaning |
|---|---|---|
| go back verb | To return to a place or state after having been there at a previous time. | |
| make up verb | /ˌmeɪk ˈʌp/ | To constitute, to compose. |
| point out verb | To identify among a group of similar subjects, or in a scene where the subject might not be readily seen or noticed, with a gesture of the body. | |
| take off verb | To remove. |
דקדוק בסרטון הזה
המבנים שהדובר משתמש בהם הכי הרבה, עם המילים המדויקות מהסרטון:
| מבנה | בסרטון |
|---|---|
| הווה מושלם (Present perfect) have/has + past participle — פעולה שקרתה בעבר ועדיין יש לה חשיבות או השפעה עכשיו | I've called · haven't discovered · I've illustrated |
| סביל (Passive voice) be + past participle — הדגש הוא על מה שקורה, לא על מי שעושה את הפעולה | is based · was chosen · was then regarded |
| משפטי זיקה (Relative clauses) who / which + clause — מידע נוסף על אדם או דבר | person who patented · solid which are · oxides, which are |
Pronunciation to watch
The speaker uses 17 contractions and reduced forms, such as we're, I've, don't. Say them the short way, as you hear them.
- The “sh” and “zh” sounds: cementitious /ˌsɛmɛnˈtɪʃəs/, emission /ɪˈmɪʃ.ən/, dimension /daɪˈmɛn.ʃən/
- Long words — get the stress right: magnesium /ˌmæɡˈnizi.əm/, cementitious /ˌsɛmɛnˈtɪʃəs/, aluminium /ˌæl.(j)uˈmɪn.i.əm/, alumina /əˈl(j)uːmɪnə/, illuminate /ɪˈl(j)umɪneɪt/
How to practise with this video
- Listen to the whole video once without speaking and note the words you do not know.
- Shadow it sentence by sentence at normal speed, repeating each one until your rhythm matches the speaker.
- Record yourself and compare with the original, paying attention to words like cement, calcium, oxide.
מהי טכניקת השאדואינג?
שאדואינג היא טכניקת למידת שפה מבוססת מדע שפותחה במקור להכשרת מתורגמנים מקצועיים ופופולרית על ידי הפוליגלוט ד"ר אלכסנדר ארגואלס. השיטה פשוטה אך עוצמתית: אתה מקשיב לאודיו באנגלית ילידית וחוזר עליו בקול רם מיד — כמו צל העוקב אחרי הדובר עם עיכוב של 1–2 שניות בלבד. בניגוד להאזנה פסיבית או תרגילי דקדוק, שאדואינג מכריח את המוח והשרירים בפה לעבד ולשחזר דפוסי דיבור אמיתיים בו זמנית. מחקרים מראים שזה משפר משמעותית את דיוק ההגייה, האינטונציה, הקצב, הדיבור המחובר, הבנת השמיעה ושטף הדיבור — מה שהופך אותו לאחת השיטות היעילות ביותר להכנה לIELTS Speaking ולתקשורת באנגלית בעולם האמיתי.