11 Comments
Nov 3, 2022Liked by Brian Potter

Structural concrete work is especially resistant to change because of the consequences if your new innovation fails, and no one wants to be the guinea pig for it.

A somewhat related personal example - We were building a very typical 5 story concrete office building. Since the first floor had higher ceilings for retail than the office floors above, the concrete contractor built his formwork to the typical 2-5 floor height and then slipformed the columns coming off the ground floor so they were usable on all floors, which his drawings did not show.

Our structural engineer absolutely blew a gasket when he learned there would be cold joints in the columns. It became a huge ordeal that nearly ended with us tearing out and re-pouring the columns and required extra testing and I believe we had to drill and epoxy extra bar for the engineer to accept it. The concrete sub claimed means and methods, they do it all the time, it saves cost and time, etc etc - which was true! - but this relatively minor deviation got them absolutely drug through the ringer, so its no surprise that innovation isn't growing by leaps and bounds in the concrete trade.

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By that standard, a column poured onto the slab/column/rebar of the floor below is just as much of a "cold joint". As long as there exist rebar continuity that connects both pours, it's irrelevant because concrete should not be stressed in tension.

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Very thorough and interesting.

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I've hear there is a vast difference too in the quality of concrete, though I know nothing about that. I have long wanted to build a concrete and stone house, though it is easier to dream about than build. This is a nice primer on concrete construction. Thank you.

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>(it's not obvious to me what sort of project this would make sense on - it seems like it would require a relatively large volume of relatively small pieces).

I have done it on a large bridge project, where we needed many small pieces of concrete barriers to go up and down the sides. We established a temporary precasting yard at one end of the bridge. However (if my memory serves me correctly) this was still our second choice, behind utilising our company's permanent precasting yard, but the permanent yard was too busy with orders for large planks for other bridges at the time, and establishing a secondary yard was preferable to losing more schedule time to waiting.

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I thought that lift slab construction around a central core was pretty standard nowadays. I know a lot of buildings in NYC have been built that way including many this century. Since it starts with a stable central core and forms and lifts the slabs around it, it seems pretty solid. Maybe ten years ago, the New York Times had an article on how NYC builders had optimized the process to build two floors a day rather than one.

I also gather that reinforced concrete has replaced steel in a lot of construction. This was from the book High Steel. According to the book, this replacement started in Cuba where steel was hard to come by, but was soon adopted world wide. Even a building like the Time Warner Center supposedly has relatively few all steel components. Most of the building is reinforced concrete. The glory days of iron workers riveting girders into place is long past.

How far off base am I?

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Nov 11, 2022·edited Nov 11, 2022

An interesting article, and Automatic Construction seems to be going down a similar line for the company I work for: Concrete Canvas (https://www.concretecanvas.com/), we originally manufactured inflatable shelters, but have moved into infrastructure projects as the primary market

We make a concrete impregnated fabric; which is a fabric combined with dry cement powder during manufacture. This is then sold as a roll and can be manipulated into the required shape on site and then sprayed with water to set it

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The last few times I've had contractors come in to do concrete work, for a heavy duty slab for a pool and then to replace a sidewalk, they used fiber reinforced concrete. The second contractor didn't even mention he did so, I just saw it when I had to break off some overflow to put in the guard rail posts. Anyway, not only was their a strength advantage but, more importantly for them I think, the forms didn't have to be tight fitting at the bottom, etc. The concrete was viscous enough that it didn't flow out through 1 to 2 inch gaps on the bottom of the forms. This certainly saved them labor!

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I would like to see a modular system that unites composite concrete decks and foam stay-in-place forms like Hercuwall, and extends these concepts for the foundation & roofing.

It could be the dimensional lumber of the 21st century: a limited number of universal foam & steel shapes you can order in quantity to your site, assemble with small crew, then call the concrete truck to form the resistance structure and superior flooring in a single step. Next day, you continue assembling the next floor, etc.

You local distributor has no idea what you are building, they just deliver a certain number of corner forms, flat wall panels, T wall joints, floor decks etc., that are standardized, easy to manufacture in small factories, and available from a large number of suppliers that can adapt to cycles in the construction industry. As Brian shows, this coordination and complexity issue is a major problem with modular construction methods, because a complex system ties you to a certain supplier, which may or may not be around next cycle, killing uptake.

To be effective, it would need to dispense with as much site-work as possible, while maintaining universality. For example, exterior fibercement siding could be applied in the factory to the foam, designed for a snug and esthetic fit at the site. So you trade manual siding effort to factory time, while guaranteeing quality of water insulation etc.

The interor foam structure would have pre-cut channels that you can place services in, Romex & pex conduits etc. then cover it with traditional plasterboard that screws directly into the raised portions of the foam.

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Fantastic article! I hadn't heard of Automatic Construction, although I work for www.mesh.ch (we work on making arbitrarily-shaped concrete structures less expensive to build by using robots to make meshmoulds which replace formwork - with the goal of making concrete structures more material efficient). This is the most comprehensive post on the topic I've read so far, thanks a lot for your writing! In our case, we use the metal reinforcement to hold the concrete when pouring, so we end up not needing external formwork: we just build the internal rebar structure, pour the (increased viscosity) concrete inside, and cover the rebar with a shotcrete finish. It's exciting to see all the new methods that are emerging in this space, and also the potential for more intricate architecture to make it into our daily lives. (https://www.dezeen.com/2022/11/02/amnh-studio-gang-construction-new-york/)

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Thanks for sharing, one of my favorite newsletters on substack.

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