Luyện nói tiếng Anh bằng Shadowing qua video: Introduction 2, Why "Portland" cement
Đang tạo bài học...
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.
📺 Cùng kênh
✨ Video gợi ý
C12
131 câu
Unit Conversion & Significant Figures: Crash Course Chemistry #2
Business EnglishUniversity StudentsWorking Adults
C11
218 câu
Introduction to Marketing: The Marketing Mix
Business EnglishUniversity StudentsWorking Adults
C12
102 câu
Chemical Manufacturing 101 - Texas
Business EnglishUniversity StudentsWorking Adults
C12
333 câu
Basic Introduction To Oil & Gas Well Perforating
Business EnglishUniversity StudentsWorking Adults
C11
99 câu
FIDIC Yellow Book 2017 Explained #construction #civilengineering #quantitysurveyor
Business EnglishUniversity StudentsWorking Adults
C129
26 câu
Docker in 100 Seconds
American AccentBusiness EnglishUniversity StudentsWorking Adults
B26
205 câu
Everything You Didn’t Know About Titanium Bikes
Business EnglishUniversity StudentsWorking Adults
C11
56 câu
MinuteCement - LC3
Business EnglishUniversity StudentsWorking Adults
C1677 câu
Inside PMBOK Guide 8: What Project Managers Must Know | Episode 542
Business EnglishUniversity StudentsWorking Adults
C12
32 câu
Day 1.2
Business EnglishUniversity StudentsWorking Adults
C11
92 câu
How Things Are Made | An Animated Introduction to Manufacturing Processes
Business EnglishUniversity StudentsWorking Adults
Từ vựng và ghi chú luyện nói cho bài học này
Bài luyện nói trình độ C1 này dựa trên video “Introduction 2, Why "Portland" cement”. Những từ được nhắc lại nhiều nhất trong bài: cement, Portland, material, composition, calcium. Video này có 139 câu và 2024 từ để luyện shadowing. Phần lời nói dài 14:22. Người nói giữ tốc độ đều, khoảng 141 từ mỗi phút, vừa sức để nói đuổi theo. Chỉ 80% số từ nằm trong 3.000 từ tiếng Anh thông dụng nhất, nên từ vựng khá khó.
Từ vựng quan trọng trong video
15 từ khó nhất trong video, kèm phiên âm và nghĩa:
| Từ | Phiên âm | Nghĩa |
|---|---|---|
| cement danh từ | /səˈmɛnt/ | xi măng |
| calcium danh từ | /ˈkælsi.əm/ | canxi |
| oxide danh từ | /ˈɑksaɪd/ | oxyt, oxit |
| magnesium danh từ | /ˌmæɡˈnizi.əm/ | magiê |
| silicon danh từ | /ˈsɪləˌkɑn/ | silic |
| sulfur danh từ | /ˈsʌl.fə/ | lưu huỳnh |
| aluminium danh từ | /ˌæl.(j)uˈmɪn.i.əm/ | nhôm |
| diagram danh từ | /ˈdaɪ.ə.ɡɹæm/ | giản đồ, biểu đồ |
| sodium danh từ | /ˈsəʊ.di.əm/ | natri, chất muối |
| module danh từ | /ˈmɑd͡ʒul/ | mô-đun, bộ phận rời |
| carbonate danh từ | /ˈkɑɹbəneɪt/ | cacbonat |
| hydrate danh từ | /haɪˈdɹeɪt/ | hydrat |
| mineral danh từ | /ˈmɪn.ə.ɹəl/ | khoáng sản, khoáng vật |
| consequence danh từ | /ˈkɑn.sɪ.kwəns/ | hậu quả |
| potassium danh từ | /pəˈtæsiəm/ | kali |
Cụm động từ bạn sẽ nghe
| Từ | Nghĩa |
|---|---|
| go back động từ | trở lại |
| take off động từ | bỏ |
Ngữ pháp trong video
Những cấu trúc người nói dùng nhiều nhất, kèm đúng cụm từ trong video:
| Cấu trúc | Trong video |
|---|---|
| Câu bị động be + quá khứ phân từ — nhấn vào việc xảy ra, không phải người làm | is based · was chosen · is produced |
| Thì hiện tại hoàn thành have/has + quá khứ phân từ — việc đã xảy ra nhưng còn liên quan đến hiện tại | I've called · haven't discovered · I've illustrated |
| Mệnh đề quan hệ who / which + mệnh đề — thêm thông tin về người hoặc vật | person who patented · solid which are · oxides, which are |
Phát âm cần chú ý
Người nói dùng 17 dạng rút gọn, ví dụ we're, I've, don't. Hãy nói theo dạng ngắn đúng như bạn nghe.
- Âm “sh” và “zh”: cementitious /ˌsɛmɛnˈtɪʃəs/, emission /ɪˈmɪʃ.ən/, dimension /daɪˈmɛn.ʃən/
- Từ dài — đặt trọng âm cho đúng: magnesium /ˌmæɡˈnizi.əm/, cementitious /ˌsɛmɛnˈtɪʃəs/, aluminium /ˌæl.(j)uˈmɪn.i.əm/, alumina /əˈl(j)uːmɪnə/, illuminate /ɪˈl(j)umɪneɪt/
Những âm người Việt thường gặp khó:
- Cụm phụ âm cuối — đọc đủ từng âm, đừng nuốt âm cuối: cement /səˈmɛnt/, consequence /ˈkɑn.sɪ.kwəns/, crust /kɹʌst/, dominance /ˈdɑmɪnəns/, blend /blɛnd/
- Âm /tʃ/, /dʒ/ và /ʒ/ — tiếng Việt không có, đừng đọc thành “ch” hay “gi”: module /ˈmɑd͡ʒul/, nodule /ˈnɑd͡ʒul/, marginal /ˈmɑː.d͡ʒɪ.nəl/, rigid /ˈɹɪd͡ʒ.ɪd/
- Âm /æ/ — mở miệng rộng hơn âm “e”: calcium /ˈkælsi.əm/, magnesium /ˌmæɡˈnizi.əm/, aluminium /ˌæl.(j)uˈmɪn.i.əm/, diagram /ˈdaɪ.ə.ɡɹæm/, potassium /pəˈtæsiəm/
Cách luyện với video này
- Nghe hết video một lần, chưa cần nói, và ghi lại những từ bạn chưa biết.
- Nói đuổi từng câu ở tốc độ bình thường, lặp lại mỗi câu đến khi nhịp của bạn khớp với người nói.
- Ghi âm giọng mình rồi so với bản gốc, chú ý các từ như cement, calcium, oxide.
Phương Pháp Shadowing Là Gì?
Shadowing là kỹ thuật học ngôn ngữ có cơ sở khoa học, ban đầu được phát triển cho chương trình đào tạo phiên dịch viên chuyên nghiệp và được phổ biến rộng rãi bởi nhà đa ngôn ngữ học Dr. Alexander Arguelles. Nguyên lý cốt lõi đơn giản nhưng cực kỳ hiệu quả: bạn nghe tiếng Anh của người bản xứ và lặp lại to ngay lập tức — như một "cái bóng" (shadow) đuổi theo người nói với độ trễ chỉ 1–2 giây. Khác với luyện ngữ pháp hay học từ vựng bị động, Shadowing buộc não bộ và cơ miệng phải đồng thời xử lý và tái tạo ngôn ngữ thực tế. Các nghiên cứu khoa học xác nhận phương pháp này cải thiện đáng kể phát âm, ngữ điệu, nhịp điệu, nối âm, kỹ năng nghe và độ lưu loát khi nói — đặc biệt hiệu quả cho người luyện IELTS Speaking và muốn giao tiếp tiếng Anh tự nhiên như người bản ngữ.