This is fascinating. I’ve just sent this article to a couple of structural engineers that I work. Thanks for shining a light on this innovative approach. Everything has an environmental impact, and frankly I’ve been concerned about mass timber ever since it became the next big thing. I’m eager to think about how a stone structure might be enclosed using modern building science. Maybe it’s just the same as for concrete.
How can you pretension stone? I know how they do that with concrete, but not stone.
Also what kind of stone can be used? Obviously not sandstone, but what is ideal? And, do we have enough in North America. You may think this is a dumb question, but I know a year stone has started leaving the ground there will be people squawking about how it's harming the environment.
And speaking of the environment, what kind a footprint is this going to leave. Perhaps not as large as concrete, but, there is still the mining, the transportation, etc. Not to mention the pre-stressing, which I assume uses steel cables as in concrete...
Stone ist stressed similar to post tensioned concrete with the difference that holes are drilled into the stone with huge diamond drills. Then the same strand or bar products are used as in concrete. Also stone doesn’t creep or shrink like concrete so the efficiency of PT stone is much greater.
There is a large variety of stone that has been used for PT elements. Even dense sandstone is an option. Most stone is much stronger both in compression and tension than concrete so you are quite free in choosing what stone you want.
Yes a few feel that stone extraction is like terraforming and hurting the environment. However you have to remember that any mineral building material has quarries at the start of their process and dimensional stone quarries have the least ecological impact, water is recycled, electric power is used for saws and a few quarries are already electrifying their forklifts. Furthermore quarries can be operated out of sight without harming any land by moving them a few meters underground and only extracting in a checkerboard pattern, leaving large columns to ensure safety for anything that’s happening above.
It should be mentioned that thin, highly processed cladding stone has high emissions, however that of dimensional stone is much lower, by as much as 10-30 times! Furthermore transport can be a large impact if one isn’t wise about picking the right quarry. The pt stands and bars make up about half of the emissions of modern structural stone products, however we can get away with a much lower degree of reinforcement than in pt or reinforced concrete as we don’t need any secondary reinforcements as stone cracks less and many have significant tensile strength compared to concrete.
In conclusion if the stone is locally quarried, transported around 300km and post tensioned the emissions are 80% less than reinforced concrete while having at least the same section size and structural capacity.
Limestone is dangerous for people who work with it, even when applying the best health and safety practices. Because of the well established cancer risks, Australia is phasing out all use.
Really? I thought Australia (and other countries following) are banning engineered stone because of silica dust. Limestone is made from calcium carbonate or seashells. I have never heard of it being dangerous. I wrote about this earlier: https://lloydalter.substack.com/p/counter-intelligence-australia-bans
It's funny - I came back here to share what one of the structural engineers I work with has to say, then I realized you posted this on April Fool's Day, so now I'm wondering . . . hmmmmm. Is this for real? 😂 Here are Justin's thoughts:
As always when I read about a new material being pushed, I try and read between the lines and find out what is being deemphasized for the purposes of selling the product. And stone certainly has a lot going for it for the right use case! It’s always tricky being in the industry where the expertise around stone construction isn’t readily available for input (for instance, I’d love to see the detail that uses stone in combination with pretensioned steel cables to make a floor). I feel like if I suggested using structural stone for just about anything I’d be laughed out the door, but that’s probably because I’m working in an area where concrete is king.
I’m glad someone is championing the material, it’s thankless work. Even mass timber, which we’re now sporadically using, often requires a lot of work from the design team to make viable. We’d need clients with a lot of ambition, and a really good partner stone manufacturer. I get bogged down in the practicalities of: how well does it respond to seismic activity? If you use it for a floor system, what spans and occupancies are you limited to? How deep does that stone+pretension system get, and how can it compete with 7” concrete post-tensioned slabs in the height restricted DC region? What’s the rating process for stone, does it have processes like wood for verifying the grade, adequate preparation, etc? Given stone is primarily a compression member, are we returning to the days of arch-based construction, and why did we leave that in the first place?
Thanks for taking me down a little structural rabbit hole!
Another huge advantage of using stone for structure is the lifespan of the building - hundreds of years instead of 55-60.
Planned obsolescence in building - not carbon-friendly!
This is fascinating. I’ve just sent this article to a couple of structural engineers that I work. Thanks for shining a light on this innovative approach. Everything has an environmental impact, and frankly I’ve been concerned about mass timber ever since it became the next big thing. I’m eager to think about how a stone structure might be enclosed using modern building science. Maybe it’s just the same as for concrete.
How can you pretension stone? I know how they do that with concrete, but not stone.
Also what kind of stone can be used? Obviously not sandstone, but what is ideal? And, do we have enough in North America. You may think this is a dumb question, but I know a year stone has started leaving the ground there will be people squawking about how it's harming the environment.
And speaking of the environment, what kind a footprint is this going to leave. Perhaps not as large as concrete, but, there is still the mining, the transportation, etc. Not to mention the pre-stressing, which I assume uses steel cables as in concrete...
Enquiring minds want to know.
Great questions!
Stone ist stressed similar to post tensioned concrete with the difference that holes are drilled into the stone with huge diamond drills. Then the same strand or bar products are used as in concrete. Also stone doesn’t creep or shrink like concrete so the efficiency of PT stone is much greater.
There is a large variety of stone that has been used for PT elements. Even dense sandstone is an option. Most stone is much stronger both in compression and tension than concrete so you are quite free in choosing what stone you want.
Yes a few feel that stone extraction is like terraforming and hurting the environment. However you have to remember that any mineral building material has quarries at the start of their process and dimensional stone quarries have the least ecological impact, water is recycled, electric power is used for saws and a few quarries are already electrifying their forklifts. Furthermore quarries can be operated out of sight without harming any land by moving them a few meters underground and only extracting in a checkerboard pattern, leaving large columns to ensure safety for anything that’s happening above.
https://m.youtube.com/watch?v=DUBLl_h2MKM
Furthermore stone is almost infinitely reusable.
It should be mentioned that thin, highly processed cladding stone has high emissions, however that of dimensional stone is much lower, by as much as 10-30 times! Furthermore transport can be a large impact if one isn’t wise about picking the right quarry. The pt stands and bars make up about half of the emissions of modern structural stone products, however we can get away with a much lower degree of reinforcement than in pt or reinforced concrete as we don’t need any secondary reinforcements as stone cracks less and many have significant tensile strength compared to concrete.
In conclusion if the stone is locally quarried, transported around 300km and post tensioned the emissions are 80% less than reinforced concrete while having at least the same section size and structural capacity.
(Sources are available for all statements)
Thank you! I was talking about this article with some friends and you answered most of the questions that came up.
Limestone is dangerous for people who work with it, even when applying the best health and safety practices. Because of the well established cancer risks, Australia is phasing out all use.
Really? I thought Australia (and other countries following) are banning engineered stone because of silica dust. Limestone is made from calcium carbonate or seashells. I have never heard of it being dangerous. I wrote about this earlier: https://lloydalter.substack.com/p/counter-intelligence-australia-bans
Ah, there you go, shows my ignorance!
I thought limestone had the same issues. Good to know I was wrong, because using stone, as actual stone, makes so much common sense.
It's funny - I came back here to share what one of the structural engineers I work with has to say, then I realized you posted this on April Fool's Day, so now I'm wondering . . . hmmmmm. Is this for real? 😂 Here are Justin's thoughts:
As always when I read about a new material being pushed, I try and read between the lines and find out what is being deemphasized for the purposes of selling the product. And stone certainly has a lot going for it for the right use case! It’s always tricky being in the industry where the expertise around stone construction isn’t readily available for input (for instance, I’d love to see the detail that uses stone in combination with pretensioned steel cables to make a floor). I feel like if I suggested using structural stone for just about anything I’d be laughed out the door, but that’s probably because I’m working in an area where concrete is king.
I’m glad someone is championing the material, it’s thankless work. Even mass timber, which we’re now sporadically using, often requires a lot of work from the design team to make viable. We’d need clients with a lot of ambition, and a really good partner stone manufacturer. I get bogged down in the practicalities of: how well does it respond to seismic activity? If you use it for a floor system, what spans and occupancies are you limited to? How deep does that stone+pretension system get, and how can it compete with 7” concrete post-tensioned slabs in the height restricted DC region? What’s the rating process for stone, does it have processes like wood for verifying the grade, adequate preparation, etc? Given stone is primarily a compression member, are we returning to the days of arch-based construction, and why did we leave that in the first place?
Thanks for taking me down a little structural rabbit hole!