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This article talks as though Portland cement is the only cement. It isn’t. I’ve spent the past few years working in my free time on the restoration of several
by madaxe_again 8y ago
This article talks as though Portland cement is the only cement. It isn’t.
I’ve spent the past few years working in my free time on the restoration of several old buildings, under the guidance of my wife, who is a conservation mason, much of which has comprised removing cement and gypsum plaster and replacing them with lime mortar, lime plaster, and other lime products as appropriate.
While it’s true that most lime products aren’t as strong as cement, and are permeable to water vapour, their CO2 impact is much, much smaller - and many applications which currently see the use of Portland could as easily use appropriate lime-based products. Breathability is a good thing in most structures - most damp that you see in buildings arises from impermeable materials and condensation.
As to strength, lime-Portland blends exist which can create impermeable and strong concrete with less environmental footprint, and I’ve been experimenting with mixing lime with various different aggregates and plasticising agents - resulting in some interesting materials - ground pumice and slate in varying proportions produce very strong (high tensile and compressive properties) and impermeable materials - I was inspired by Roman concrete.
Here’s a tiny bit of further info on CO2 footprints, from a company I’ve bought several tonnes of NHL from:
http://ecolime.co.uk/c02-quick-facts/ http://ecolime.co.uk/c02-quick-facts/
- NeedMoreTea 8y agoRoman concrete also has loads of advantages over modern concrete. Cracks don't spread, better salt resistance, and better earthquake resistance. Modern concrete will not survive like Roman examples have. With the environmental advantages too I'm surprised it hasn't had a resurgence.
- rini17 8y agoCan't find the source now, the problem is that Roman concrete hardens slower than modern one.
- saalweachter 8y agoThat's also what killed Rosendale cement. ~1 month cures as opposed to putting a structure on the slab as little as ~1 day after pour.
- onetimemanytime 8y agoYp, 42.5 cement was used for concrete and 3 hours later the forms were removed. It was around 30celcius outside and that helped but still, you can walk on that thing hour later
- EADGBE 8y agoIf it has a 1 month curing time, I would assume weather would affect outside structures more often as well.
- saalweachter 8y agoRosendale cement is a natural hydraulic cement - it was used for the foundations of the Brooklyn Bridge, the US Capitol, and the pedestal of the Statue of Liberty. It's actually more durable and weather-resistant than Portland cement.
- coryrc 8y agoThey aren't comparable. The compression strength is too low to prevent oxidation of iron rebar (though epoxy-basalt rebar could replace), limiting you only to forms of ancient Rome: primarily vaults, domes, and vertical walls one or two stories tall (upon which wooden structures went higher). You also need much more limestone because the material is weaker, incurring higher environmental impact that way.
- NeedMoreTea 8y agoI don't know enough of the details but there were reports about using it for the Swansea lagoon barrier - a £1bn tidal energy project that was to be about 6 miles long. The government blocked the project just last week so we'll never know.
- coryrc 8y agoIt would perform admirably in that usage, though even modern concrete should be fine because you shouldn't need any rebar.
- bainsfather 8y ago"The government blocked the project just last week so we'll never know." To be more accurate - the government decided not to subsidise the project. It was emphatically the right decision - the economics of it were awful compared to wind, solar.
- NeedMoreTea 8y agoTo be even more accurate the government decided to ignore the clear advice of the independent cross-party committee of MPs they appointed, and after the announcement chairman of said committee said the government were not even comparing like with like in their economic comparison. Makes it look solely a political not economic or environmental decision.
- scythe 8y agoCompressive strength doesn't passivate steel. Alkalinity does. But pozzolanic cements don't absorb CO2 IIRC. Only cements with no acidic additives (e.g. silica, pozzolan, GGBFS) will absorb CO2, but in this case strength is always lost.
- sgc 8y agoAs someone outside your immediate target market: 1) what do you mean by single skin and double skin exterior walls? 2) are there any simple/quick and fast mixes to DIY a stronger lime mix?
- coryrc 8y agoIf you make a strong enough mix, you'll just replicate the existing problems with OPC. But generally, you can DIY a cement with roughly 1/3 hydrated lime and the rest graded dust-3/4" pozzolonic stone. Let me know the impact of acquiring that if you aren't in Italy or, apparently, southern Idaho. You can do it with non-pozzolonic stone but using ~2:1 lime:crushed terracotta, but it won't have the magic healing properties of the original. (Note, going off memory on the ratios; they're probably somewhat off).
- coryrc 8y agoUsing a naturally hydraulic lime is important for creating weaker joints, but it doesn't save that much CO2. You only heat the limestone a few hundred degrees cooler (though for longer) and you don't pulverize it as much, but hydraulic lime is using the minerals mixed with it to harden just like OPC (which is why it can harden in such thick pieces like the base of the Pantheon), not pull CO2 from the atmosphere like a non-hydraulic lime.