Thursday, April 21, 2016

Concrete, Briefly

Cement and concrete are not the same thing. Cement is one of the ingredients for making concrete, along with sand and gravel (in most countries). The sand and gravel are the “aggregate.” Oh, and water, that’s important. Water not only makes it fluid and formable, but also causes the chemical reaction that binds it all together. It’s amazingly practical stuff.

Concrete has been around for a long time, something like 8,000 years. The recipe was very different, but the idea was the same: aggregate and some kind of binding agent, activated by water. Some of the trading people around present day Syria and Lebanon had a pretty good recipe and used it for “rubble wall houses,” and underground cisterns. People are clever.

The Romans really put concrete on the map. They had a great recipe and used it for great things. Like the Colosseum and the Parthenon in Rome. The Parthenon is still the biggest free-standing concrete dome in the world. And non-reinforced, too. Everything from the giant public baths that they liked to the big apartment houses that they invented was made from concrete. Or opus caementicium, as they called it. From 300 BC (or BA as I like to call it, “Before Augustus”) to 476 AD they used the hell out of the stuff. Then came the big crash and the art of making concrete was lost to the world for over a thousand years. How stupid was that?

The Germans make some great concrete. I’d venture to say that they have consistently made the best super-hardened concrete in history. Remember when the Berlin Wall “came down?” Cheering crowds with huge German sledge hammers rushed the wall and set about to smashing it. Well, that was easier said than done. I’m sure you will recall the news footage of strong, young men with big hammers hauling away at the wall and the wall just standing there yawning. “That the best you got, asshole?” the wall seemed to be saying. Every few blasts they would get a small chip to flake off.

The Germans, of course, had had a lot of practice, and a lot of reasons for wanting the best concrete in the world. I spent the summer of 1984 studying German in Kiel, a lovely city in the very north of Germany that had been completely flattened during World War II. Completely, except for the civilian and military bomb shelters and the headquarters building of the Kriegsmarine (The German Navy). One of the bomb shelters was left in place and a park was built around it, as some kind of memento. And the entire vast bulk of the Navy Headquarters is still there, too. It’s still a Navy base. We could just walk on, there was no security at all at the time. It’s a huge rectangle of concrete, the best super-hardened, reinforced concrete that the minds of German science could devise. It’s about thirty or forty meters high, maybe a couple of hundred meters across, and several hundred meters long. And it’s there, still there, after furious aerial bombardment that lasted a couple of years, being subjected to bombs of up to a ton in weight. Sure, there are chunks blown off, it really does look like it’s been in a fight, but the building was never close to being compromised and the staff working inside were never threatened. That, my friends, is concrete at its finest.

Thailand is a wonderful place to observe the progress of concrete. The Thais are very adept with the stuff. Most of the bigger buildings in Thailand are built from reinforced concrete. They must use a great recipe, because drilling a hole in a wall is a daunting task that requires a huge drill and a long time. Just hanging a picture is a big ordeal. They reinforce the hell out of it, too. I watch them at construction sites, and when they’re putting down the forms and laying in the rebar it’s a sight to see. All of that rebar, elaborately interconnected and laced together. Thais mean business when they do almost anything. And anything that is important is done with great care. Building tall buildings is, of course, very important.

And, almost surprisingly, there never seems to be any chiseling going on in the amount of cement used. In many countries around the world the construction supervisors or somebody will steal some of the cement and just use more sand. Bags of cement are worth money. Boy, it’s trouble when they have an earthquake in some of those countries. Whole building just turn to dust and fall around the inhabitants. Sometimes it happens without even the agency of an earthquake. That stuff never happens in Thailand.

I lived for eight years on the fifth floor of a twenty-three story condo building made entirely from reinforced concrete. I worried for five minutes once, when I considered the weight above my head. Then I got over it. Thais are too proud to fool around with something so important.

Thailand is interesting in its countryside innovations in concrete, too. When I was with the Peace Corps I frequently visited a small school in a non-prosperous, agricultural province in the northern mountains. The principal got some money and built a computer room. About eighteen by twenty-five feet, a modest room off the main building. Did he contract it out to professionals? No, he did not. He just had the maintenance man build it, singlehandedly. The fellow was talented and resourceful, and it came out fine. I watched him prepare the concrete for the foundation and the uprights to hold the walls and the roof. He built good forms and a good matrix of rebar, and he used good cement, and good washed sand, and . . . river rocks bigger than golf balls!  Smooth as a baby’s ass they were, too! Not technically correct, but it’ll probably work out okay. It’s got a light load on it.

It’s fascinating stuff, concrete. But then, I find everything fascinating.   

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