It is my way or the highway. All roads lead to road. I am back on the road. While you took the road, let's travel. I think we can agree that the concept and idea of a road is strongly instilled in us, and we all know what a road is. Well, a wide way leading from one place to another. Typically one with a specially prepared surface, which vehicles and bikes can use of course. It was not always the case that the surface was specially prepared, but with today's needs for fast mobility it has become ascension. We're using cars and motorbikes to transport people and lorries for goods. Have you checked how heavy a car is? And millions of cars pass over roads every day. That requires a material that can withstand all the stress for a long time. A material so common and mundane that we. Well, I at least didn't even think about it for the longest time. And reading up on asphalt was worth it to come briefly out of retirement to add this little episode to my list. My name is Johannes Vogel and you're listening to a post-conclusion episode of chemistry in everyday life. A podcast where I explain the chemistry that happens all around us in layman's terms. Chemistry is the study of the attributes and changes and substances can undergo. No matter if they're gas's liquids or solids. Believe me when I tell you that this happens everywhere around us at this very moment. So I'm obviously aware that I concluded my podcast due to time constraints with my job and family. And those constraints they're still there. But I received a really nice mail from one of my listeners recently. And I was kind of blown away by the request and suggestion for a topic. By the way, Carla is the listener's name. So Carla works in a company that manufactures and supplies asphalt or better bitumen for the construction of roads. And she was just curious what the chemistry behind it all is. She then explained what she's doing there. By the way, already showing that she knew quite a bit more than she let on. And asked if I could maybe make an episode about it. You guys have to understand that at various stages of my job. I had to drive a lot of highway kilometers across different European countries. And I was stuck in traffic jams due to construction sites a lot. Or I drove through them around midnight at what felt like snail speed. And each time when I'm stuck, apart from being annoyed, of course, I think about why roads for lack of a better term break. And what a road has to withstand on a daily basis. So to satisfy my own curiosity, I need to start reading. So what I want to say in my long winded way. I would like to say thank you to Carla for suggesting this topic. Asphalt and roads are a great subject of chemistry in everyday life. If there ever was one and that stayed in the back of my mind until the moment I had time to properly look into it. And write an episode. And so without any further ado, let's get cracking. I think it's best if we start talking a bit about the importance of asphalt. Actually, before we start, let's get wording out of the way. I'm going to talk about asphalt. And I will talk about something called bitumen. As far as I can see, the two words seem to be used interchangeably. So asphalt and bitumen meaning the same thing. But there's also something called asphalt concrete. That is different to asphalt and bitumen. But we'll get into that. Now, before we get into it, according to Wikipedia, apparently, we need globally 102 million tons of bitumen per year. 102 tons of that stuff each year. And like 85% of that is used in roads. That's only 90 million tons of bitumen in road works. Just for context, a BMW SUV weighs around 1.5 tons. So the weight of nearly 60 million BMW SUVs every year. Guys, that's a little bitumen. And for what? You know, a road is not all pure asphalt, right? Asphalt is a black, very viscous and sticky substance that is used to bind various types of rocks and crushed concrete and other similar stuff together. And function a bit like a glue, I guess. But the chemistry is simpler. That mixture of asphalt and rocks and stones and stuff is called an asphalt concrete, which is in the top layers of a road. Bitchman makes up about 5% of the entire asphalt concrete mix. As far as I could find out, there are actually three separate layers of varying bitumen content in a road. Each layer with a little less bitumen content, the further you go, below the road surface. And each layer has a slightly different function. Below that, there is a bitumen free layer that lets water drain away and below that, you go the ground. But that's all nice and well, but why? I mean, why do we bother? Well, when you think about it, a road has to withstand quite a lot of extreme circumstances, extreme weather, frost and hot summers, storms and, yeah, the list goes on. But also the sheer weight of cars and lorries driving over it is ridiculous. Absolutely ridiculous. And we, the drivers, of course, wanted to be quiet in the car in a smooth drive, not bumpy, you know. And then there's the fact that the tires should have traction. A minor thing, not. On loose dirt, car tires don't have a lot of grip. Oh, and it should not soak up water, you know, it shouldn't become soggy and stuff. Effectively, you need a material that is durable, rigid, but not too rigid, otherwise it cracks. But rigid enough and a little elastic, so it withstands the stress and strain of 24/7 driving on it. The surface cannot have any cracks, at the risk of having pockets of water that freezes to ice, which then expands and causes the cracks to grow. And at the same time, it needs to be resistant to sunlight. And of course, it has to keep these features of a large temperature range from down to maybe minus 10 minus 20 degrees Celsius in the cold regions, up to about 50 or 60 degrees Celsius in the equatorial regions. This is a huge temperature range, guys. Make no mistake about that. So why bitch, you man? Why do we choose this one? Well, it has the properties we need, and it is abundant. It occurs both naturally in various parts of the world, such as Alberta, Canada or Venezuela. But you can also obtain it from distilling crude oil. In crude oil, it is the fraction that is left at the bottom. So the stuff that boils at excessively high temperatures, which is at higher than 500 degrees Celsius. Wikipedia, my trusty source of freely editable information says 525 degrees Celsius. Let me see, which is 977 degrees Fahrenheit for my American friends. And their weird temperature system with numbers that make no sense to me. So as a reminder, in case of memory of my episode on that distillation is a bit hazy, distillations are processed by which you boil a mixture of liquid compounds. Depending on what temperature you're at, the more volatile compounds become a gas and rise to the top, where they can be collected by cooling them down to liquid form again in a side vent. While the not-so-volatile compounds stay at the bottom. And then the temperature is increased, and the difference so-called temperature fraction rises and is collected. So in a nutshell, it does the trick, and is readily available. It's as far as I know the most expensive part of the material is used in roads, but is still affordable. If you google for asphalt, there are a lot of hits as it is quite a big market to work in. I also wanted to know how much bitchum in you need per kilometer of road. But that seems to be one of those questions where it depends is the best answer, namely on weather and temperature. I found one thing, one source, the Sahara Business Group, on the website an estimate of about 2330 kilograms per cubic meter, that is a meter length width and depth, which can come down to about a kilometer of road apparently. That's according to their website, I cannot verify that. But now think about how many kilometers of road you have.
have in your region and that should give you a fairly good idea of how much asphalt concrete you have around your area alone. But when I say it does the trick, what do you actually mean by that? To explain that, we must delve a bit into something called material science, which is a discipline that sits quite squarely between chemistry, physics, and engineering. Since a science that develops and investigates materials for a very specific job, the making often involves polymer chemistry and engineering, while the testing is physics and engineering. So first off, let's look at what I said about bitumen being a liquid. I think viscous liquid. That doesn't sound very useful for a road, does it? I mean the emphasis here is on viscous. As I said, it acts more like a glue, as it is a solid half the time, which means that asphalt concrete at ambient temperatures is a tough and hard solid, with all the rocks and gravel and so on giving structural integrity and strength, while the bitumen is holding it all together like glue would do. And in doing so, giving the road some flexibility, so that there are no cracks of the first side of a lorry driving over it's speed. In addition, bitumen as a liquid also fills all the cracks between the stones and the sand and the gravel, and because it stems from petrol, it doesn't mix with water. Hence, the top layer does not allow water to go inside of the road, unless there are cracks. Just imagine you had a pocket of water in a road and then the water freezes to ice. Ice is less dense than water, which means larger volume, and that can increase the cracking size and break the road. So watertight surfaces are a good thing, another plus for bitumen. The last thing that now needs to be taken into consideration is as silly as this may sound, driving comfort. Let me briefly explain that. Have you ever driven over a cobblestone road? If you have, you may remember that even at very low speeds inside your car, your brain just rattles so loudly in your skull, you can't hear yourself think. Never mind another person in the car. And forget about your cup of coffee in the cup holder, that liquid won't stay in. Now imagine you're driving at the allowed speeds of your highway. No, you're not driving at the highway top speeds. That is because the surface is not smooth. Asphalt concrete is spread onto the surface at high temperatures, around 160 to 180 degrees celsius. I looked that up, that's 320 to 356 degrees Fahrenheit, which makes it malleable and reasonably easy to flatten it out. So that our surface is smooth. I assume with those big rollers that you see when driving past the construction site. It has to be said here that there are asphalt concrete types now that are also possible to be applied at different temperatures in order to make it more versatile. So we now have a composite material in asphalt concrete that is strong, has tensile strength. That means it does not crack easily and is waterproof while when put on the ground can be flattened out quite nicely. Great. Well actually I haven't told you the entire story yet. Bitcheman has the right properties but they're not good enough in many cases. In the hot equator region standard bitcheman can be a bit soft, with the surface being consistently exposed to the very hot sun. And in the frozen and cold north, well when it becomes brittle in the frigid air and prone to cracking under consistent exposure to stress. In addition, roads are out in the open and typically frequently exposed to the sun. Some more and some less of course. I mentioned in other episodes as well. The sun's energy that is delivered to earth through radiation has quite an effect and it causes the exposed bitcheman on the surface to lose some of its plasticity and flexibility as it ages. Believe it or not, the sun's radiation can actually chemically alter the materials. These are so called photochemical reactions which is another source of damage to the road. So that is obviously not good and it means there is a need to modify the bitch. As I said also called an asphalt concrete binder. What we're observing is a well-known concept in polymer chemistry. You see while we all know about the melting point and the boiling point of a substance, for example ice melts to liquid water above zero degrees Celsius. And it boils at atmospheric pressure at a hundred degrees Celsius. To my fire and high brigade, I'm sure you guys have an inkling what temperatures I'm referring to. I don't know them off the top of my head. So we all know about melting and boiling points. A morphous polymers and similar materials have another important temperature point. A morphous here is the opposite of crystalline which refers to the way the polymer arranges itself on a molecular level. That is crystalline means highly ordered while a morphous is is unordered. A bit of a mess and no logical arrangement observable. By the way, for those who have not listened to previous episodes of mine, where I explained what polymers are, polymers are on a molecular level these long, long chains of ever repeating same structures called fittingly repeating units or monomers. Often tens of thousands of units per chain. Polymers are a versatile and often easily and cheaply made materials as a solution to a problem. Examples are bulletproof cavlar, rubber entires, biodegradable plastic bags, all examples of synthetic polymers. While for example DNA, chitine, cellulose and proteins are examples of nature's polymers out there. Anyway, small detour. Let's get back to that other temperature point. There's a temperature for each and every of these amorphous polymers below which the material is brittle, rigid and unyielding, which means it breaks rather than bends. And above this temperature the same material is more like a rubber, more flexible, bendy and squishy. This temperature is called the glass transition temperature because the material transitions from a brittle glass to a more soft rubber like material. Of course, each material is different and there's a spectrum of other physical features. But knowing the glass transition temperature is really important. Imagine you have a rubber band whose glass transition temperature is at 50 degrees Celsius rather than below room temperature. It's kind of useless having something that is supposed to be bendy and squishy but is actually rigid at the temperature you want to use it at. Coming back to Bichiman, the asphalt concrete binder, you guessed it. In cold winters the temperature can go below Bichiman's glass transition temperature and the material that was able to give slightly when a lorry with heavy load drives over it, it is now brittle and it may crack in the same circumstance. In very hot summers however, we may see it heat up to a very high temperature so much so that it is close enough to the melting point temperature to have more give in the road than you really want to. I walked in Madrid and Spain once during the summer. I had the impression that my shoes were slightly sticky to the tarmac. Maybe I was just imagining it. I don't know but it was a weird feeling man. So what can be done here? How can we make our binding substance, the stuff that holds our road reality together? How can we make that have a wider temperature range in which it shows all the great features that we need? Well there are a couple of things you could do. The two main ones I would say is you either modify the Bichiman's molecular structure, that is you do some chemical reactions. Change the molecules in there until you have what you want or you mix other stuff into it that has the physical properties that you want. Well since Bichiman is already a complex mixture of various things the latter route was taken and what do they add in? In fact rubber, different types of rubber. You know polymers that are elastic to some extent. There are loads and loads of different types from rubber bands and hair bands found in households over the rubber used to make car tires all the way to the rubber material used in ropes for bungee jumps. Would you need those?
is a rubber-like material that can be heated up and mixed with a bitch of it at high temperatures and then cool down and be like a cool down liquid mix. You know so effectively something called a thermosetting polymer, something that doesn't change on heating and cooling down again. This is not as easy as it sounds. Many polymers just don't mix well or they don't flow well when melted and so on. The one that is now typically used called styrene butadiene styrene fulfills all these criteria and it achieves all we need. This so-called polymer modified asphalt is now characterized as neither being viscous when being heated nor being fragile when cooled of great plasticity and property of aging resistance and that is a quote from the in 2011 published book Building Materials in Civil Engineering. So now with polymer modified bitumen we have an asphalt concrete that according to the mixing ratios can be adjusted to the weather zone that you find yourself in. An absolutely versatile product but damage is still to happen especially with so much traffic going over to Rhodes daily. I mentioned before the main causes for damage are mainly two long exposure to sunlight which makes the bitumen age and become more brittle and so-called freeze-thaw cycles of water that manage to get into the cracks. They say you have to renew a road surface every 15 years but the time in between is just as important to keep the road in a serviceable state. And how can that be done? Well typically you use a very specific type of asphalt concrete that can be applied at colder temperatures as low as 80 to 100 degrees Celsius. Again 176 to 212 degrees Fahrenheit which that temperature is more easily handleable by a small crew to fix a pothole or stuff like that and consequently can be more easily flattened out and fitted into all the cracks. Which leaves us with a final problem. What to do with the roads that were broken up and put aside to breathe renewed afterwards? The answer to me is just great. You recycle it back into the process. Not all asphalt concrete can be recycled back but in general we can say that the bitumen that was not overly affected by sunlight and weather conditions can be reprocessed and reused several times. And the aged bitumen will be just part of the structural pieces in the concrete next to gravel and sand. I personally find that really neat. How many of those processes do you know where everything is recycled back in? And there you have it. A quick and dirty discussion on asphalt also called bitumen and how to incorporate into roads. To me honestly what a surprisingly useful material. This was more of a material science episode than a chemistry one truth be told but the two are related cousins and a surge belong together. As I mentioned this was an episode that I wrote thanks to a fan mail that requested it. I will still not be able to reactivate this podcast but if you have a topic that you're interested in and do not mind an extended waiting time until I get round to it drop me a mail under a
[email protected]. And yeah until then I say thanks to you all for listening and especially thanks to Carla for the suggested topic. For me this was a fun episode that looked into a topic I had little to no knowledge about in the beginning. So thanks again and take care folks. You've been listening to chemistry in everyday life. A podcast about chemistry that happens all around us explained in layman's terms. Thank you for listening. [Music]
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