WI: Early Concrete Blocks?

[DominusNovus]

The ubiquitous concrete block, commonly called a cinder block, is one of the many tools of modern construction. They combine many of the best features of bricks and stones. They’re relatively easy to construct, too. Just pour concrete into a mold, let it set, and you’re done. Sears used to sell such molds to consumers in the 19th century. All you need is the ability to make a mold that is durable enough to be used repeatedly.

Could all of this have been developed earlier? Of course, given that we’re discussing concrete, the obvious candidate is Rome. And the Romans were no strangers to such methods. I’m imagining the Romans building some impressive fortifications with concrete blocks, filled with packed earth or sand for strength. Not to mention all the handy things they could with piping in the voids of the blocks for civilian construction.

 

[Brodydaboss]

A problem I see in this is that the transportation costs of such of a material might be more expensive then just using local blocks

 

[DominusNovus]

A problem I see in this is that the transportation costs of such of a material might be more expensive then just using local blocks

I’d be inclined to think they’d still be produced locally. Granted, being less dense than actual bricks, they could travel further, but there’s no need to.

 

[Dathi THorfinnsson]

I’d be inclined to think they’d still be produced locally. Granted, being less dense than actual bricks, they could travel further, but there’s no need to.

But clay exists in very many places, so you can make bricks locally using local material. Those places that didn't have good clay didn't build with brick, but used stone, wood, Adobe, or whatever else was handy. I believe that before trains bricks weren't transported very far or often.

The problem with concrete is cement is produced in many fewer places, and so you'd have to transport the cement, even if not the blocks themselves.

Transportation used to be EXPENSIVE away from waterways.

 

[DominusNovus]

But clay exists in very many places, so you can make bricks locally using local material. Those places that didn't have good clay didn't build with brick, but used stone, wood, Adobe, or whatever else was handy. I believe that before trains bricks weren't transported very far or often.

The problem with concrete is cement is produced in many fewer places, and so you'd have to transport the cement, even if not the blocks themselves.

Transportation used to be EXPENSIVE away from waterways.

I’m not suggesting this would be used in place of cheaper materials. I’m suggesting this as a way to make cheaper concrete construction available earlier.

That said, you wouldn’t need to transport the cement. Just whatever ingredients you can’t produce locally.

 

[FSB]

Do note that making cement is pretty energy intensive. Roman cement less so than Portland cement, but still. If you are fueling your industry with wood rather than, say, coal mines and making your blocks by hand rather than using mass production techniques and then transport them with aggregate already mixed in rather than using local stone, inexpensive is not the result I would expect.

 

[DominusNovus]

Do note that making cement is pretty energy intensive. Roman cement less so than Portland cement, but still. If you are fueling your industry with wood rather than, say, coal mines and making your blocks by hand rather than using mass production techniques and then transport them with aggregate already mixed in rather than using local stone, inexpensive is not the result I would expect.

Shouldn’t our cost comparisons be with the actual uses of concrete in history?

 

[FSB]

Ah, sorry, I derped. You are talking about MOLDS for concrete blocks rather than the blocks themselves.

Making cement takes a lot of fuel, so until that is cheaply available, concrete construction is going to be pricy. I'm not sure making things a bit easier with blocks is going to make much of a difference, but I'm no construction engineer.

EDIT

You also need to make your crushed stone aggregate with sledgehammers. So you may actually be better off with just making wooden molds to pour your concrete and then use larger stones.

 

[alexmilman]

The ubiquitous concrete block, commonly called a cinder block, is one of the many tools of modern construction. They combine many of the best features of bricks and stones. They’re relatively easy to construct, too. Just pour concrete into a mold, let it set, and you’re done. Sears used to sell such molds to consumers in the 19th century. All you need is the ability to make a mold that is durable enough to be used repeatedly.

Could all of this have been developed earlier? Of course, given that we’re discussing concrete, the obvious candidate is Rome. And the Romans were no strangers to such methods. I’m imagining the Romans building some impressive fortifications with concrete blocks, filled with packed earth or sand for strength. Not to mention all the handy things they could with piping in the voids of the blocks for civilian construction.

AFAIK, the Romans had been using concrete mostly for the apartment buildings - their concrete was crumbling too easily for fortifications, bridges, etc.

 

[FSB]

...There are Roman concrete bridges that are still standing. Piers also, it's much more tolerant of salt water than modern concrete.

 

[Max Sinister]

The Romans had concrete - if they didn't use blocks, how did they build with it then?

 

[FSB]

If you look at pictures of the aforementioned bridges, you'll see concrete used like mortar - large stones connected together with concrete. There is also the standard way, build a box out of boards, pour it full of concrete and after it has been hardened a bit remove the boards.

 

[Dathi THorfinnsson]

That said, you wouldn’t need to transport the cement. Just whatever ingredients you can’t produce locally.

I.e. the cement, no? I believe cement raw materials aren't nearly as wide spread as clay.

 

[cmakk1012]

I.e. the cement, no? I believe cement raw materials aren't nearly as wide spread as clay.

Yeah, wasn’t the Romans’ important ingredient in cement volcanic ash? That’s only common in a few places in Europe—granted Italy is one of those places.

 

[RogueTraderEnthusiast]

It'd probably be really effective if you wanted to build something quickly, even if it isn't cheap. Say the Romans want to capture a position - having a stockpile of concrete blocks to rapidly build a fort out of, and filling the gaps in with dirt and mortar would likely be much faster than other construction methods, making it easier to fortify a captured frontier.

Plus, pound per volume, they'd be much lighter than bricks, making them a much easier material to move in comparison, which also makes them easier to move up to higher places.

Basically, they'd make great construction material in unsafe areas simply because they're able to build big structures more rapidly, even if they're replaced later on.

 

[DominusNovus]

It'd probably be really effective if you wanted to build something quickly, even if it isn't cheap. Say the Romans want to capture a position - having a stockpile of concrete blocks to rapidly build a fort out of, and filling the gaps in with dirt and mortar would likely be much faster than other construction methods, making it easier to fortify a captured frontier.

Plus, pound per volume, they'd be much lighter than bricks, making them a much easier material to move in comparison, which also makes them easier to move up to higher places.

Basically, they'd make great construction material in unsafe areas simply because they're able to build big structures more rapidly, even if they're replaced later on.

Agreed, though I doubt they’d be replaced later. We rarely replace such construction ourselves, and we’re far more able to afford replacing structures regularly.

Also, does anyone know how common concrete construction was outside of Italy, historically?

 

[Carl Schwamberger]

Actually, all you would need to transport far are the material for molds, and the cement. Rocks and other bits can be found locally. Making cement requires cooking crushed limestone in a kiln. If there is a local source for the limestone then you can burn lime for cement locally too.

If you look at pictures of the aforementioned bridges, you'll see concrete used like mortar - large stones connected together with concrete. There is also the standard way, build a box out of boards, pour it full of concrete and after it has been hardened a bit remove the boards.

Correct. Roman concrete was not the slurry we use. large aggregate or rocks were pounded into layers of a stiff cement/sand mix. Roman concrete lasted longer as the lime or calcium compound (& other minerals) was a larger portion in the cement mix. Up to a point you increase the strength or durability of concrete or the cement component this way. Modern concrete is not intended to last 2000 years & its specced for specific levels of compressive strength depending on the use.

...

Also, does anyone know how common concrete construction was outside of Italy, historically?

There were similar construction techniques here & there. I suspect the Roman advantage was the particular mix of calcium & other minerals. Others had not stumbled onto that particular bit of chemistry & their 'cement' component was inferior, so less used.

 

[FSB]

Lime mortar was common. You could use it like concrete, but it will set slowly and not do so underwater. Roman concrete has amazing longevity because it uses some of the reactions that causes modern concrete to crack to harden in the first place. Modern concrete is stronger and sets faster, though.

I looked at some images of weathered Roman concrete structures, and the aggregate was indeed large. Looks reasonable that they were made by spreading a layer of cement mixture, adding large pieces of aggregate and then spreading another layer of cement mixture. And this makes sense, since they did not have machines to crush and sieve aggregate rock.

 

[andys]

You don't need machines to crush and sieve rock. The early macadamised roads were built using hand crushed and sized stones. Romans have plenty of slaves - job done.

 

[Dathi THorfinnsson]

You don't need machines to crush rocks to gravel, but cement production grinds it's materials to a powder. How much that's a necessity and how much a convenience, i don't know.
Also. Cement kilns heat the material to 2700C as opposed to a brick kiln which only needs to get to 900-1200C. Also, the cement kilns are rotary, where brick kilns are stationary.

I will admit to being wrong about the need for special rock.