WEBVTT - A Concrete Problem 0:00:04.400 --> 0:00:07.800 Welcome to tex Stuff, a production from my Heart Radio. 0:00:12.200 --> 0:00:15.400 Pay there and welcome to tech Stuff. I'm your host, 0:00:15.600 --> 0:00:19.040 Jonathan Strickland. I'm ad executive producer with I Heart Radio, 0:00:19.120 --> 0:00:23.880 and I love all things tech. And today's episode is 0:00:23.920 --> 0:00:28.120 going to focus on something that relates to climate change. 0:00:28.160 --> 0:00:30.319 You know, it was Earth Day not too long ago, 0:00:31.120 --> 0:00:34.360 and while I did not have an episode specifically for 0:00:34.479 --> 0:00:37.240 Earth Day, I thought it would be good to create 0:00:37.320 --> 0:00:42.159 something within that spirit. And recently I was perusing Scientific 0:00:42.240 --> 0:00:45.800 American like I do, and I saw an article by 0:00:45.880 --> 0:00:50.040 Benjamin star Ow titled X Prize Winners use c O 0:00:50.159 --> 0:00:53.920 two emissions to make concrete and We're gonna get to that, 0:00:54.280 --> 0:00:57.800 and Starrow made some excellent points. I highly recommend the article. 0:00:58.280 --> 0:01:00.319 But that article made me think, I should you an 0:01:00.320 --> 0:01:05.360 episode about concrete. We depend very heavily upon concrete. It 0:01:05.480 --> 0:01:10.480 is the most frequently used material around the world for 0:01:10.520 --> 0:01:13.920 the purposes of, you know, building stuff. It's the literal 0:01:14.080 --> 0:01:17.679 foundation for many of the structures we build. And the 0:01:17.720 --> 0:01:22.319 production and transportation of concrete represents a truly enormous source 0:01:22.400 --> 0:01:26.080 of carbon emissions, which of course are major contributors to 0:01:26.120 --> 0:01:29.080 climate change. And so I thought I would dedicate an 0:01:29.080 --> 0:01:33.000 episode to concrete. Now, you could argue it's not high 0:01:33.080 --> 0:01:36.280 tech stuff. Most of the time, concrete doesn't have you know, 0:01:36.760 --> 0:01:41.000 cool circuitry or artificial intelligence or anything like that, although 0:01:41.040 --> 0:01:43.480 we will talk about the technology that does use some 0:01:43.560 --> 0:01:47.560 of that stuff. However, concrete represents a technological advance, and 0:01:47.600 --> 0:01:50.440 there are some interesting technologies, like the ones that use 0:01:50.600 --> 0:01:54.280 CEO two to help actually make concrete, that we can 0:01:54.320 --> 0:01:58.360 talk about. But first let's talk about what concrete is. 0:01:59.120 --> 0:02:02.440 It is a material that is made up of aggregate, 0:02:02.920 --> 0:02:06.920 that is particulate material that ranges from medium grade down 0:02:06.960 --> 0:02:11.360 to course. So think of stuff like sand or gravel, 0:02:11.639 --> 0:02:16.919 or pebbles or crushed stone. These are loose, small, individual 0:02:16.960 --> 0:02:21.239 pieces of hard material. Now, obviously you can't just build 0:02:21.280 --> 0:02:23.840 with aggregate all by itself. You would end up with 0:02:23.919 --> 0:02:28.280 piles of particulate. You'd have sand dunes or or piles 0:02:28.280 --> 0:02:31.280 of gravel, which is not terribly useful. So another part 0:02:31.320 --> 0:02:35.840 of concrete is a binding agent. This is essentially a glue. 0:02:36.000 --> 0:02:39.280 It holds the particulate together and we go from having 0:02:39.280 --> 0:02:42.639 a pile of sand or gravel to concrete once we 0:02:42.840 --> 0:02:47.120 mix it with this binding agent, which gives that that 0:02:47.160 --> 0:02:50.519 material strength, and the result is something that's akin to 0:02:50.639 --> 0:02:54.320 an artificial stone, but it's one that when it's still 0:02:54.360 --> 0:02:57.840 in its viscous form, you can actually shape the stuff. 0:02:58.240 --> 0:03:01.400 Then it will harden and will hold that shape. So 0:03:01.480 --> 0:03:03.760 rather than having to look for a stone that's just 0:03:03.919 --> 0:03:07.080 the right shape, or having to employ a stonemason to 0:03:07.240 --> 0:03:10.800 cut an existing stone down to the correct shape, you 0:03:10.840 --> 0:03:14.239 could just, in theory, make one yourself out of concrete. 0:03:14.600 --> 0:03:18.440 Another important aspect of concrete is that it's chemically inert. 0:03:18.919 --> 0:03:22.880 It is not reactive to stuff, so it's very stable. 0:03:23.120 --> 0:03:25.480 You don't have to worry about concrete getting wet and 0:03:25.480 --> 0:03:30.320 then going all droopy. Though with concrete, water does actually 0:03:30.400 --> 0:03:32.560 make a difference, but we'll get to that, because water 0:03:32.680 --> 0:03:36.040 is all part of the system. Now. Depending upon your 0:03:36.040 --> 0:03:39.320 point of view, you might argue that the binding agent 0:03:39.920 --> 0:03:43.520 for concrete has to be cement in order of you 0:03:43.640 --> 0:03:50.160 to consider the finished product actual concrete, otherwise it's something else. However, 0:03:50.240 --> 0:03:52.640 other people are a little more loosey goosey with a 0:03:53.000 --> 0:03:56.840 definitive terms, and they will use concrete to refer to 0:03:56.880 --> 0:04:01.160 materials that relied on other binding agents to hold together, particulate, 0:04:01.560 --> 0:04:04.120 or sometimes they might give a little ground, and and 0:04:04.160 --> 0:04:07.520 they'll call such stuff a sort of a predecessor to concrete. 0:04:07.960 --> 0:04:12.960 The discovery of cement probably dates back thousands of years 0:04:13.320 --> 0:04:17.839 when early people's observed something interesting with regard to their 0:04:17.920 --> 0:04:22.120 cooking fires. So people would dig a hole and into 0:04:22.160 --> 0:04:26.400 that hole they would, you know, build their their cooking fires. 0:04:27.000 --> 0:04:30.840 And those high temperatures from the fires would cause the 0:04:31.000 --> 0:04:33.719 edges of the hole to kind of dry and crack 0:04:33.839 --> 0:04:36.360 and sometimes even turn into a bit of a powder. 0:04:36.400 --> 0:04:39.440 And when it would rain, water mixing with that powder 0:04:39.640 --> 0:04:42.880 would sometimes become a sludge that would then harden into 0:04:42.960 --> 0:04:46.480 a stone like material. Now, one source I looked at 0:04:46.520 --> 0:04:50.320 for this episode was a paper titled Concrete History and 0:04:50.480 --> 0:04:54.960 Stories from World Scientific Now, according to that source, these 0:04:55.000 --> 0:04:59.279 ancient peoples used a protoconcrete to start construction on the 0:04:59.400 --> 0:05:02.599 famed hour of Babel, you know, the one that in 0:05:02.640 --> 0:05:08.239 the Bible was began construction and then God said, hey, guys, 0:05:08.680 --> 0:05:11.880 I don't dig how you're building up to the heavens, 0:05:11.920 --> 0:05:14.200 so I'm going to give you all different languages and 0:05:14.240 --> 0:05:17.120 scatter you so that you can't taught to each other anymore. 0:05:17.360 --> 0:05:20.680 But according to this paper, uh, what was happening was 0:05:20.720 --> 0:05:23.160 that the builders kind of ran out of raw material 0:05:23.240 --> 0:05:26.120 before they could finish construction, and then they just sort 0:05:26.160 --> 0:05:31.560 of abandoned the project. Now, several ancient civilizations used different 0:05:31.560 --> 0:05:35.599 aggregates and binding materials in an effort to create artificial stones. 0:05:36.160 --> 0:05:40.719 The Assyrians and the Babylonians used clay and bitumen. And 0:05:40.800 --> 0:05:43.920 you might not be familiar with bitumen um, And in fact, 0:05:43.960 --> 0:05:45.880 I don't even know if I'm pronouncing it correctly. I 0:05:45.880 --> 0:05:48.160 should have looked that up before this episode, but hey, 0:05:48.400 --> 0:05:52.480 let's wing it anyway. It's a petroleum based type of hydrocarbon, 0:05:52.680 --> 0:05:54.920 so it's a If you were to break down its 0:05:54.960 --> 0:05:58.039 chemical composition, you would say it's a compound of hydrogen 0:05:58.120 --> 0:06:02.000 and carbon, which is pretty common. In fact, that's the 0:06:02.080 --> 0:06:05.800 reason why a hydrogen based economy is harder than what 0:06:05.880 --> 0:06:09.520 it sounds like. Hydrogen is almost always bound to something else, 0:06:09.920 --> 0:06:15.040 and frequently it's carbon. Anyway, it's extremely viscous and it's 0:06:15.120 --> 0:06:18.120 really dense stuff, and it can be found in pitch 0:06:18.279 --> 0:06:22.320 lakes and oil sands out there in nature. So in 0:06:22.360 --> 0:06:25.360 some parts of the United States, it's referred to as asphalt. 0:06:25.680 --> 0:06:28.520 Though the asphalt we used to pave roads is made 0:06:28.600 --> 0:06:31.520 up of other stuff in addition to a binder made 0:06:31.520 --> 0:06:36.520 from bitamin or a bitumin like substance. Meanwhile, the Egyptians 0:06:36.600 --> 0:06:40.839 and the Phoenicians were using gypsum and lime. Gypsum is 0:06:40.920 --> 0:06:45.520 made of calcium sulfate dihydrate, and it's a big ingredient 0:06:45.600 --> 0:06:51.279 and lots of stuff including drywall, chalk, fertilizer, and modern cement. 0:06:52.040 --> 0:06:55.440 Lime the material, not the fruit, so you don't you 0:06:55.440 --> 0:06:57.720 don't put this in a coconut and drink them both up. 0:06:58.040 --> 0:07:00.960 In this case, we're talking about an inorganic mineral made 0:07:00.960 --> 0:07:05.559 of calcium and various oxides. The Greeks also use lime, 0:07:06.040 --> 0:07:09.840 and they treated it in kilns to create burnt lime. 0:07:10.080 --> 0:07:14.800 Like kilns are an important element of creating cement. You 0:07:14.800 --> 0:07:18.640 couldn't just use this material as it was, you know, 0:07:18.880 --> 0:07:21.679 found in nature. You had to treat it to heat 0:07:21.800 --> 0:07:26.960 in order to have the chemical transition into what would 0:07:27.000 --> 0:07:31.240 become concrete or cement. Rather, we'll talk more about processing 0:07:31.320 --> 0:07:33.360 lime in a bit, because that does play a huge 0:07:33.480 --> 0:07:36.640 part in the production of cement. In fact, many early 0:07:36.720 --> 0:07:41.360 civilizations would use kilns similar to or in some cases 0:07:41.440 --> 0:07:44.960 exactly the same as the kilns that they would use 0:07:45.000 --> 0:07:48.760 to fire pottery. The kilns would reach the temperatures needed 0:07:48.800 --> 0:07:52.200 to quote unquote burn the lime, making it suitable to 0:07:52.280 --> 0:07:55.200 use as a binding agent. Most of these early forms 0:07:55.200 --> 0:07:59.160 of protoconcrete would cure in the air. They hardened upon 0:07:59.280 --> 0:08:02.880 exposure to the air, or, as spinn Thalo put it 0:08:02.920 --> 0:08:06.400 in an article in nineteen sixty seven, quote lime that 0:08:06.480 --> 0:08:10.320 needs air to achieve strength end quote. I like that phrasing. 0:08:11.080 --> 0:08:13.880 Then came the Romans. And while the Romans stole a 0:08:13.880 --> 0:08:17.440 ton of stuff from the Greeks, they also innovated quite 0:08:17.440 --> 0:08:19.680 a lot of stuff themselves, and one of those things 0:08:19.680 --> 0:08:22.320 they innovated was concrete. Now, the Greeks had been using 0:08:22.360 --> 0:08:25.600 concrete a little bit, but not anywhere to the extent 0:08:26.040 --> 0:08:29.840 that the Romans did. And the Romans discovered natural cements 0:08:29.880 --> 0:08:33.439 called Pozzolan's. Actually, I should say that Pezzolan's might have 0:08:33.480 --> 0:08:37.640 already been in use pre Roman times, but the Romans 0:08:37.640 --> 0:08:42.359 really went ham on the stuff. Mm hmm, ham and pozzolan. 0:08:42.920 --> 0:08:45.400 So what the heck is pozolan? Well, according to the 0:08:45.520 --> 0:08:51.080 American Concrete Institute, it is quote a solicitous and aluminous 0:08:51.120 --> 0:08:56.360 material that in itself possesses little or no simentitious value, 0:08:56.440 --> 0:08:59.920 but will in finally divided form, and in the present 0:09:00.040 --> 0:09:04.679 some moisture chemically react with calcium hydroxide at ordinary temperatures 0:09:04.720 --> 0:09:09.920 to form compounds having sementitious properties. End quote. That is 0:09:09.960 --> 0:09:13.880 a mouthful, but in plain English it means that it's 0:09:13.880 --> 0:09:16.640 a material that when ground up into a powder and 0:09:16.760 --> 0:09:21.440 mixed with water and material that contains calcium hydroxide, it 0:09:21.520 --> 0:09:26.080 becomes cement. Like that is, it can bind aggregate as 0:09:26.200 --> 0:09:30.280 cement and form concrete. Actually, I should point out in 0:09:30.320 --> 0:09:32.360 fact I Probace should have done this already. Cement and 0:09:32.400 --> 0:09:36.199 concrete are not the same thing. They are not synonymous. 0:09:36.200 --> 0:09:41.079 Cement is to concrete what flour is to a cake. Right. 0:09:41.160 --> 0:09:44.280 It's an ingredient, it's an important part, but it is 0:09:44.320 --> 0:09:47.920 not the same thing anyway. The source for the Romans 0:09:47.960 --> 0:09:51.679 was a puzzolonic ash, which in itself came from volcanic 0:09:51.760 --> 0:09:55.840 ash and pumice. So the Romans would collect this ash 0:09:55.880 --> 0:09:58.200 and they would use it with calcium hydroxide to create 0:09:58.200 --> 0:10:01.640 their cement. When did they start doing this, well, we're 0:10:01.679 --> 0:10:05.760 not really sure. It wouldn't have been any later than 0:10:05.880 --> 0:10:09.480 one fifty before Common era or B C. As there's 0:10:09.520 --> 0:10:12.400 evidence of concrete structures dating from around that time period, 0:10:12.800 --> 0:10:16.200 so it was definitely at least as late as that. 0:10:16.280 --> 0:10:19.320 It was probably earlier, much earlier. But there's just no 0:10:19.520 --> 0:10:23.679 Roman record that says, quote, it's to seventy four b C. 0:10:23.920 --> 0:10:26.960 And we just invented concrete. Also, why are our years 0:10:27.040 --> 0:10:31.240 counting down backward? Anyway? I'm off to the vomitorium end quote. 0:10:31.720 --> 0:10:34.880 And yeah, I made at least two dumb jokes based 0:10:34.880 --> 0:10:38.880 off inaccurate representations of ancient Rome's timekeeping in terminology, but 0:10:38.920 --> 0:10:43.200 I couldn't resist. Concrete would play an enormous part in 0:10:43.360 --> 0:10:46.960 the Roman architectural revolution. In fact, it was such a 0:10:46.960 --> 0:10:50.920 crucial component of that movement that we sometimes referred to 0:10:50.960 --> 0:10:54.880 it as the concrete Revolution. This marked a period in 0:10:55.000 --> 0:10:59.920 Roman history of huge architectural projects, including the famous Roman Pantheon, 0:11:00.040 --> 0:11:03.520 on which was has a dome made from concrete that, 0:11:03.640 --> 0:11:07.839 from its shape, supports itself with no need for additional 0:11:08.280 --> 0:11:11.480 columns or other supports apart from the walls, which kind 0:11:11.480 --> 0:11:16.040 of act like columns. The Romans could build enormous structures 0:11:16.040 --> 0:11:20.280 thanks to concrete, which could be poured and then cured. Well, 0:11:20.360 --> 0:11:23.840 it's the quote process of controlling the rate and extent 0:11:24.000 --> 0:11:28.160 of moisture loss from concrete during cement hydration end quote. 0:11:28.640 --> 0:11:34.199 That's the helpful definition from cement, Concrete and Aggregates Australia. 0:11:34.280 --> 0:11:37.800 So let's dive into that a little bit further. Hydration 0:11:38.000 --> 0:11:40.520 is the mixing of water with cement and aggregate that 0:11:40.559 --> 0:11:43.719 gets this whole binding process going. And I realized this 0:11:43.800 --> 0:11:46.160 is skipping over the modern method of producing cement, but 0:11:46.240 --> 0:11:48.800 we will get back to that a bit later. Right now, 0:11:49.040 --> 0:11:52.840 we're talking about Roman concrete, which uses a natural cement 0:11:52.960 --> 0:11:57.640 with fewer controls, and that meant consistency was a little variable. Okay, 0:11:57.679 --> 0:12:01.079 So you make the concrete by mixing together water, cement, 0:12:01.280 --> 0:12:04.960 and the aggregate, which forms a workable paste. You put 0:12:05.000 --> 0:12:07.079 this where you want it to go, such as in 0:12:07.120 --> 0:12:11.040 a form mold. So imagine that you've got like a 0:12:11.080 --> 0:12:14.079 wooden box that doesn't have a top and the sides 0:12:14.120 --> 0:12:17.000 and bottom are all removable, So you put it together. 0:12:17.240 --> 0:12:20.000 Then you pour the paste into that box so it 0:12:20.040 --> 0:12:22.520 takes on the shape of the box. Then you remove 0:12:22.640 --> 0:12:25.640 the wood once it's all done. But the once you're 0:12:25.679 --> 0:12:30.480 done bit is important. So the Roman concrete, like modern concrete, 0:12:30.480 --> 0:12:35.240 required hydration. That is, the cement needed moisture to harden further. 0:12:35.840 --> 0:12:39.880 Once dried out, concrete is set, and generally speaking, the 0:12:39.920 --> 0:12:43.400 faster it dries out, the weaker it is. Don't get 0:12:43.440 --> 0:12:46.240 me wrong, it's still strong stuff and it can withstand 0:12:46.360 --> 0:12:51.079 incredible compressive forces, that is, forces that push down on it, 0:12:51.320 --> 0:12:53.880 you know, in an attempt to compress it. But it 0:12:53.920 --> 0:12:56.480 can also be a little brittle, and if the concrete 0:12:56.520 --> 0:13:01.280 remains wet, the reactions within cement will tenue and sometimes 0:13:01.280 --> 0:13:04.720 for years if it remains moist before drying out. It's 0:13:04.760 --> 0:13:07.719 this process of hardening that is called curing. It's not 0:13:08.280 --> 0:13:10.800 the drying out part, it's the hardening part that's that's 0:13:10.840 --> 0:13:14.080 kind of the the end process is dried out. It's 0:13:14.120 --> 0:13:16.640 the keeping it wet in order to get the hardness 0:13:16.640 --> 0:13:20.040 and strength you want. That's important. Um and in fact 0:13:20.080 --> 0:13:24.720 concrete part of that mass is made up of water. Chemically, 0:13:24.800 --> 0:13:29.080 what's going on is calcium silicates are undergoing an exothermic reaction. 0:13:29.080 --> 0:13:34.120 As they interact with water, they release hydroxide ions, calcium ions, 0:13:34.160 --> 0:13:37.400 and heat. The bit about releasing heat is what makes 0:13:37.440 --> 0:13:42.960 this an exothermic reaction. Eventually, calcium and hydroxide ions saturate 0:13:43.040 --> 0:13:47.840 the system and they begin to form calcium hydroxide crystals. Meanwhile, 0:13:47.920 --> 0:13:52.760 calcium silicate hydrate forms. The crystalline structures provide seed points 0:13:52.800 --> 0:13:55.240 for further ions to kind of glom onto, and the 0:13:55.280 --> 0:13:57.920 process can grow from there. But it does need water 0:13:58.040 --> 0:14:01.920 to continue this reaction, and as those crystals form, the 0:14:02.160 --> 0:14:06.480 concrete gets harder and stronger. Controlling this reaction falls to 0:14:06.559 --> 0:14:09.280 the rate at which water molecules can diffuse through the 0:14:09.280 --> 0:14:14.080 calcium silicate coating. As the reaction progresses, that coding gets 0:14:14.120 --> 0:14:17.000 thicker and it gets more difficult for water to make 0:14:17.080 --> 0:14:20.280 its way through, which in turn means the reaction begins 0:14:20.280 --> 0:14:23.480 to slow down. Hydration will continue as long as water 0:14:23.560 --> 0:14:25.720 can get into the system and as long as there 0:14:25.720 --> 0:14:30.480 remains unhydrated compounds within the paste. This process can go 0:14:30.520 --> 0:14:34.920 on for days or weeks, or months or even years. 0:14:35.080 --> 0:14:38.280 I'll be there for you when the rain starts to fall. 0:14:39.000 --> 0:14:42.320 As long as water can permeate an access unhydrated cement, 0:14:42.800 --> 0:14:47.440 the process will continue. Also, while the reactions release heat, 0:14:47.840 --> 0:14:51.640 this process itself goes through an interesting revolution. Early on 0:14:51.800 --> 0:14:55.440 in the hydration process, the reactive mixture will release a 0:14:55.480 --> 0:14:57.880 good amount of heat, the temperature will will go up 0:14:57.920 --> 0:15:01.360 several degrees, but after the first now fifteen minutes to 0:15:01.360 --> 0:15:04.440 half an hour of the reaction, that temperature starts to drop. 0:15:05.160 --> 0:15:07.360 Then a few hours in the amount of heat it 0:15:07.400 --> 0:15:10.880 releases will begin to climb again, and over several hours 0:15:10.880 --> 0:15:14.120 it will peak, and once you get like twenty hours in, 0:15:14.880 --> 0:15:18.600 it will then begin to slowly drop the temperature again, 0:15:18.840 --> 0:15:22.000 very slowly ramping down. And what's happening is that the 0:15:22.120 --> 0:15:26.360 rate of the reactions themselves changes as things initiate and 0:15:26.400 --> 0:15:29.040 then water it continues to react with the cement mixture. 0:15:29.400 --> 0:15:31.800 Then it gradually becomes more difficult for water to make 0:15:31.800 --> 0:15:35.600 its way to unhydrated elements of the cement, so the 0:15:35.600 --> 0:15:39.920 curing process can be done without having to heat anything 0:15:39.960 --> 0:15:43.680 else up, and in fact it itself heats up. As 0:15:43.720 --> 0:15:46.000 we'll learn a bit later, that's kind of the opposite 0:15:46.000 --> 0:15:49.800 of the actual modern process of making cement. So concrete 0:15:49.880 --> 0:15:54.480 formation is exothermic, but the production of cement turns out 0:15:54.480 --> 0:15:58.720 to be endo thermic. I'll explain more later on this episode. 0:15:59.400 --> 0:16:02.320 Now we've got some more to say about the process 0:16:02.600 --> 0:16:06.160 of concrete forming, and we'll talk a lot more about 0:16:06.200 --> 0:16:08.880 cement in just a moment. But first let's take a 0:16:08.960 --> 0:16:19.880 quick break. Now. I mentioned that if concrete dries out quickly, 0:16:20.200 --> 0:16:23.840 it won't be as strong as concrete that was hydrated properly. 0:16:24.000 --> 0:16:26.080 But let's get a bit more detailed with that, because 0:16:26.120 --> 0:16:29.080 it's not as simple as just you know, drenching wet 0:16:29.160 --> 0:16:31.720 cement mix as you wait for it to cure. The 0:16:31.760 --> 0:16:35.120 amount of water you add makes a difference. The ratio 0:16:35.240 --> 0:16:38.600 of water to cement is important. A low water to 0:16:38.640 --> 0:16:41.080 cement ratio means you're gonna end up with concrete that's 0:16:41.200 --> 0:16:44.280 very strong, but it's also very difficult to work. So, 0:16:44.280 --> 0:16:47.720 in other words, the paste will be extremely viscous and 0:16:47.760 --> 0:16:50.280 you might end up with shapes you totally didn't intend 0:16:50.320 --> 0:16:52.320 and now you're stuck with them unless you, you know, 0:16:52.400 --> 0:16:56.680 grab some heavy duty tools. High water to cement ratio 0:16:56.760 --> 0:16:59.480 means you're gonna have a paste that's really workable, but 0:16:59.600 --> 0:17:01.880 the over all strength of the concrete will be low. 0:17:02.400 --> 0:17:05.959 So it's not just how long the cement is kept moist, 0:17:06.320 --> 0:17:08.720 but how much water you use to do it. In 0:17:08.760 --> 0:17:11.240 our modern era, there are other things we can add 0:17:11.280 --> 0:17:14.560 to cement and aggregate to improve stuff like workability, and 0:17:14.600 --> 0:17:17.840 plasticity and strength. But let's get back to the Romans, 0:17:17.920 --> 0:17:19.880 because we've got to get back to them, because they're 0:17:19.920 --> 0:17:24.560 always Roman around. It's a dad joke. The Romans learned 0:17:24.600 --> 0:17:28.760 about the hydration process and produced a lot of concrete, 0:17:28.760 --> 0:17:32.000 at least for the time anyway, They relied on the 0:17:32.080 --> 0:17:36.040 natural cement features of volcanic ash. Many of those structures 0:17:36.080 --> 0:17:39.560 exist in whole or in part today, which is really 0:17:39.600 --> 0:17:42.399 just a testament to the strength and durability of concrete. 0:17:42.960 --> 0:17:45.720 But there was a pretty long span of time between 0:17:45.760 --> 0:17:48.880 the fall of the Roman Empire and the widespread use 0:17:48.920 --> 0:17:52.679 of concrete and other civilizations outside of some uses in 0:17:52.760 --> 0:17:56.159 building in churches and cathedrals, And it may be that 0:17:56.240 --> 0:17:59.679 the knowledge of producing concrete was largely kept in religious 0:17:59.720 --> 0:18:03.120 scents as far back as the earliest examples of the stuff, 0:18:03.520 --> 0:18:06.240 which gave the edge to the clerical folks out there 0:18:06.240 --> 0:18:09.679 over everybody else. So the Roman Empire trips on a 0:18:09.680 --> 0:18:14.000 bananappeal and falls and Europe plunges into the Dark Ages 0:18:14.720 --> 0:18:16.959 kind of. I mean, the history of the Dark Ages 0:18:17.040 --> 0:18:20.680 is actually really complicated, but for our purposes, the secrets 0:18:20.720 --> 0:18:24.280 to cement and concrete are largely lost until the fifteenth 0:18:24.280 --> 0:18:28.720 century when the rediscovery of an old manuscript written by 0:18:28.920 --> 0:18:34.359 Marcus vitruvious Polio, usually just called Vitruvius, rekindled interest. Now, 0:18:34.400 --> 0:18:37.520 Vitruvius was an architect and engineer way back in the 0:18:37.640 --> 0:18:41.760 first century b c. He wrote a long manuscript about 0:18:41.800 --> 0:18:45.439 the principles of architecture, and it included a section on 0:18:45.520 --> 0:18:50.119 the production of Roman concrete. So as the Renaissance began 0:18:50.200 --> 0:18:54.000 to bloom in Europe, there was a new interest in concrete. 0:18:54.200 --> 0:18:58.520 In fact, Giovanni Giocondo used Roman concrete to build a 0:18:58.560 --> 0:19:01.480 part of the bridge called the Pont the Notre Dame 0:19:01.640 --> 0:19:05.720 in Paris in fourteen nine, which, as I understand it 0:19:05.760 --> 0:19:08.480 is widely thought of as the first example of the 0:19:08.520 --> 0:19:12.399 modern use of concrete, and it was also necessary. The 0:19:12.600 --> 0:19:16.159 Pont Notre Dame sometimes gets called the most ancient of 0:19:16.240 --> 0:19:19.840 bridges in Paris, but this is largely a matter of 0:19:19.920 --> 0:19:24.520 point of view, because it hasn't always been the same bridge. 0:19:24.960 --> 0:19:28.320 The Pont Neuf is the oldest bridge that remains in 0:19:28.359 --> 0:19:31.800 its original form in Paris, but there has been a 0:19:31.840 --> 0:19:35.920 bridge at the location of Polt Notre Dame. The longest. However, 0:19:36.280 --> 0:19:40.600 that Pont Notre Dame Bridge has gone through multiple collapses 0:19:40.680 --> 0:19:44.200 and demolitions and otherwise has been destroyed numerous times, only 0:19:44.240 --> 0:19:47.480 to have been rebuilt. So this is a real ship 0:19:47.520 --> 0:19:50.760 of theseus kind of thing we've got going on here anyway. 0:19:51.119 --> 0:19:54.600 Giacondo used a recipe of Roman concrete as part of 0:19:54.600 --> 0:19:57.720 the rebuilding process after the bridge suffered a collapse in 0:19:57.760 --> 0:20:01.840 fourteen ninety nine when the way of houses on the 0:20:01.840 --> 0:20:04.680 bridge proved to be too much for the old structure. 0:20:05.359 --> 0:20:09.040 This version of the bridge, the concrete one, stood largely 0:20:09.119 --> 0:20:12.919 unaltered until eighteen fifty three, So that was back in 0:20:12.960 --> 0:20:16.760 four but widespread use really wouldn't kick into high gear 0:20:16.800 --> 0:20:20.480 for a few more centuries. In seventeen seventy four, an 0:20:20.560 --> 0:20:24.080 English engineer by the name John Smeaton learned that by 0:20:24.160 --> 0:20:27.800 using quicklime as an ingredient for making cement, he could 0:20:27.880 --> 0:20:32.280 make better, harder cement, and later in seventeen ninety three 0:20:32.560 --> 0:20:38.240 he discovered something else which brings us to calcination. Calcination 0:20:38.680 --> 0:20:41.720 is the process of heating up a solid to a 0:20:42.000 --> 0:20:44.960 very high temperature, and the purposes to burn off any 0:20:45.119 --> 0:20:49.000 volatile substances within that solid mass so that you're left 0:20:49.000 --> 0:20:52.960 with a more pure lump of whatever it was you 0:20:53.119 --> 0:20:57.480 started off with. Smeaton discovered that calcinating limestone that had 0:20:57.640 --> 0:21:01.960 clay content in it would produce hydraulic lime. As the 0:21:02.040 --> 0:21:06.520 name implies, this produces a lime that hardens underwater. Three 0:21:06.600 --> 0:21:10.640 years later, an Englishman named James Parker patented a hydraulic 0:21:10.760 --> 0:21:16.080 cement produced by calcinating limestone that contained clay. Engineers began 0:21:16.359 --> 0:21:21.679 building lime kilns, essentially ovens dedicated to calcinating limestone. So 0:21:22.600 --> 0:21:27.040 they were trying to recreate the effect that those ancient 0:21:27.119 --> 0:21:32.359 peoples saw around their their fires, their food fires, years 0:21:32.359 --> 0:21:36.119 and years and years centuries earlier. Now let's skip ahead 0:21:36.160 --> 0:21:40.720 to eighteen twenty four. A builder named Joseph Asten found 0:21:40.760 --> 0:21:43.359 that by grinding up chalk and putting it in a 0:21:43.440 --> 0:21:47.800 kiln with clay produced an even stronger type of cement. 0:21:48.600 --> 0:21:52.160 This is the type of cement we call Portland cement. 0:21:52.600 --> 0:21:56.320 It's named after the Isle of Portland in the English Channel. 0:21:56.760 --> 0:22:00.520 It's where a type of limestone called Portland stone comes from, 0:22:00.600 --> 0:22:03.399 and that stone played a huge part in British architecture. 0:22:03.520 --> 0:22:07.760 Fact it still does. More people made contributions towards the 0:22:07.880 --> 0:22:11.679 understanding and production of cement. But the next innovation I 0:22:11.720 --> 0:22:15.920 want to talk about came courtesy of Frederick Ransom. Ransom 0:22:15.960 --> 0:22:19.840 wanted to find a way to consistently make the best cement, 0:22:19.920 --> 0:22:23.280 which required a new type of kiln. So the old 0:22:23.320 --> 0:22:28.320 cement kilns were essentially vertically aligned ovens. So think of 0:22:28.359 --> 0:22:31.600 like a chimney. You would load this stuff up with 0:22:31.720 --> 0:22:35.080 limestone and clay, You would have fuel at the bottom. 0:22:35.280 --> 0:22:39.280 You get the kiln up to a certain temperature, and 0:22:39.359 --> 0:22:42.119 you would kind of mix everything together, and in between 0:22:42.160 --> 0:22:44.399 loads you might even allow the oven to go cool, 0:22:44.480 --> 0:22:47.879 which represented a pretty darn big waste of energy because 0:22:48.400 --> 0:22:50.680 it takes a lot of fuel to get kilns up 0:22:50.720 --> 0:22:53.720 to temperature, and once you get it up there, it 0:22:53.760 --> 0:22:55.640 takes less fuel for you to just keep it there 0:22:55.640 --> 0:22:57.639 than it would if you let it go cold and 0:22:57.680 --> 0:23:00.359 had to start it up again. And by high to pachures, 0:23:00.400 --> 0:23:04.359 we're talking up around four dred degrees celsius and hotter. 0:23:04.960 --> 0:23:07.439 The result of this process is that the limestone and 0:23:07.440 --> 0:23:11.880 the clay partially melt together into nodules that are called clinker. 0:23:12.480 --> 0:23:16.439 The clinker, once cooled, can be crushed into a powder 0:23:16.600 --> 0:23:20.520 mixed with gypsum, and then you've got your cement. A 0:23:20.560 --> 0:23:22.880 lot of stuff actually happens in this process, but I'm 0:23:22.880 --> 0:23:25.400 going to explain more in just a moment, so stick 0:23:25.440 --> 0:23:28.560 with me. Ransom figured out that one way you can 0:23:28.640 --> 0:23:32.200 make a better kiln is to go from this vertically aligned, 0:23:32.800 --> 0:23:37.160 you know, smokestack style kiln to a tilted one, one 0:23:37.200 --> 0:23:40.440 that was almost closer to horizontal than vertical, but still 0:23:40.480 --> 0:23:44.240 on an incline. So the raised end, the part that's 0:23:44.320 --> 0:23:47.760 higher up, would be where you would feed limestone and 0:23:47.800 --> 0:23:51.360 clay into the kiln. On the opposite end, the lower end, 0:23:51.680 --> 0:23:54.600 you would have an opening at the base where clinker 0:23:54.640 --> 0:23:56.720 could pass through, and that's also where you would have 0:23:56.760 --> 0:24:00.000 your heat source that would get the raw materials up 0:24:00.040 --> 0:24:03.880 to the right melting point, and the whole thing would rotate, 0:24:04.240 --> 0:24:07.960 shifting material around and causing it to gradually move down 0:24:08.000 --> 0:24:11.280 the length of the kiln. It was a rotating kiln, 0:24:11.800 --> 0:24:14.159 so you would feed in your mix of limestone and 0:24:14.200 --> 0:24:16.639 clay at the top and at that end of the kiln, 0:24:16.720 --> 0:24:19.679 far from the heat source, you would have the relatively 0:24:19.760 --> 0:24:25.560 chilly temperatures of between seventy two degrees celsius. At this temperature, 0:24:25.640 --> 0:24:29.640 any water content in the feed would evaporate off. This 0:24:29.720 --> 0:24:32.640 is also the end where any gas is given off 0:24:32.640 --> 0:24:36.040 by the process would escape. The raw material would then 0:24:36.080 --> 0:24:39.600 sift down further into the kiln as the kiln rotated, 0:24:39.760 --> 0:24:43.119 and it would start to reach hotter segments. So once 0:24:43.160 --> 0:24:47.080 the material reached between four hundred to six hundred degrees celsius, 0:24:47.520 --> 0:24:52.040 the clay would start to decompose into oxides like silicon 0:24:52.160 --> 0:24:57.000 dioxide and aluminum oxide, and the limestone would decompose into 0:24:57.119 --> 0:25:02.720 calcium carbonate, magnesium oxide, and some carbon dioxide. So some 0:25:02.800 --> 0:25:06.560 of that carbon dioxide would then expel out the end 0:25:06.720 --> 0:25:10.520 of the kiln, but we would continue our journey down 0:25:10.600 --> 0:25:13.760