hempcrete (life cycle analysis)

thread about life cycle analysis of hempcrete — all materials and processes to create it

any experience working with hempcrete along with any other tidbits about hempcrete are also welcome :)

Well, there are two (?) components in hempcrete right? Hemp and lime. The hemp could theoretically contain only the energy spent in the fuel for planting and harvest, this could be offset if the hemp was not grown for fiber and the stalks are a waste product. But these calculations will depend on the scale of the farm/processor and the efficiency of their equipment.

Lime requires some kind of mining/quarrying and some level of processing.

Then there is the packaging and distribution that brings these two things to your door.

i'm specifically interested in the lime life cycle

technically the hemp could be carbon neutral or negative (as hempcrete absorbs carbon over time) if it is acquired locally with machines run on biomass or something (dreaming 😂🌈)

and if local, then there's little to no packaging or transportation costs

but the lime i'm wondering about — certainly the mining will be intensive but how much so? and also the processing of limestone to like is intensive but how much so exactly?

can hempcrete ever become a more sustainable form of building than using local wood?

michael beyer wrote:i'm specifically interested in the lime life cycle

technically the hemp could be carbon neutral or negative (as hempcrete absorbs carbon over time) if it is acquired locally with machines run on biomass or something (dreaming 😂🌈)

and if local, then there's little to no packaging or transportation costs

but the lime i'm wondering about — certainly the mining will be intensive but how much so? and also the processing of limestone to like is intensive but how much so exactly?

can hempcrete ever become a more sustainable form of building than using local wood?

I found this link :
https://www.google.com/url?q=https://www3.epa.gov/ttn/ecas/regdata/IPs/Lime%2520Manufacturing_IP.pdf&sa=U&ved=2ahUKEwj6qZrs_JTrAhVCp1kKHXHYBC0QFjAJegQIDxAB&usg=AOvVaw0rUKgGyhlHm-7IU7Wltshp

Its a PDF about lime production from the EPA. Two things that stood out to me were a map.of lime production operations in the US which showed it being produced all over the place, meaning you can likely (only, realistically) source lime from relatively nearby. The other was that under ideal circumstances, the production of 1 ton of lime requires 2.77 million BTU. They qualified that only by saying, "In practice, the process is considerably less efficient". So who really knows what that means. I guess it means that at a minimum we are talking about 815ish kWh of electricity per ton, probably closer to 1200 kWh per ton.

How  much lime do you use per volume of hempcrete? Also, is it ag lime or is it some.other limestone product typically? Also, when considering the cost of local wood, it seems like the insulation requirements will be a big part of the ecological cost of.the house. I am under the impression that hempcrete can eliminate or reduce these requirements dramatically.

I'm interested to see where this goes. Where I live, I don't think you could.get much more eco groovy than a wofati type dwelling. However, I could imagine that in an area like the great planes a mix of locally grown hemp and locally mined limestone might contend for eco grooviness

According to statistics from Germany, quicklime (precursor to hydrated lime which is what you need) takes between 4.3 and 12 MJ per kg. lets be generous and say it takes 5 MJ of energy to produce 1kg of quicklime 1 kg quicklime turns into 1.32kg hydrated lime This energy is only the heat required it does not include loading or unloading the kiln pumping water or transporting any of the products.

Enough quicklime to make 1 short ton of hydrated lime takes 953KWh of energy to heat and convert from limestone, You still need to turn the quick lime into hydrated lime. this reaction is exothermic so there may be an opportunity to recover some energy here. but in practice it probably costs more energy to dry it out and powder it than they recover.

So the question would seem to hinge heavily on how much lime is needed to make a hempcrete house

this website makes some pretty hefty claims — here are a few..

"It has been estimated that a 35 cubic ft (1 cubic meter) hempcrete wall can absorb and lock 242 – 364 lbs (110 – 165 kg) of carbon. This negative carbon footprint alone is enough to state the benefits of hempcrete buildings for our environment. But if you needed more reasons to believe, hemp lime is 100% recyclable and reusable and can be used as fertilizer once destroyed."

it mentions how much hemp is needed for an average sized home but the search for how much lime is needed continues..

"On average, it takes around 2.5 acres of hemp to produce enough hemp hurd to build a house of 1,250 square feet."

https://hempcretedirect.com/hemp-houses/

here is a write up of general hempcrete research i've done...

The carbon dioxide absorbed by lime as it turns back into calcium carbonate (limestone) will only ultimately equal the amount emitted when the source material was fired to produce quicklime. So the LCA is net neutral on this factor.

Phil Stevens wrote:The carbon dioxide absorbed by lime as it turns back into calcium carbonate (limestone) will only ultimately equal the amount emitted when the source material was fired to produce quicklime. So the LCA is net neutral on this factor.

net neutral in terms of the lime/limestone but the hemp sequesters carbon in the growing process

so it seems to come down to whether the processing (and transportation costs) of hemp release more co2 than that hemp sequesters in its life cycle of growing

if the hemp sequesters more carbon than is used in processing it, then it may indeed be a net negative substance to use in building

is my logic seeming right?

Michael - assuming the transport and processing component is minimal, if you use a carbon-neutral energy source to calcine the lime then hempcrete would indeed have a net negative footprint. Running a lime kiln requires a lot of heat, so that will either come from renewable electricity, biomass, or possibly a solar furnace. There's a potential industry for sunny places with limestone at hand...solar limeworks.

The first info I found on a ratio was this:

`We mix our hempcrete at a ratio of 1 part chopped hemp hurd by weight, with 1.5 parts of the binder by weight. After translating these weights to volume measurements, it was 4 buckets or hemp hurd going into the mixer with 1 bucket of binder (1/2 lime, 1/2 metakaolin`

(http://endeavourcentre.org/2016/04/hempcrete-developments/)



The first info I found on calculating hemp usage for a given wall was this; note that the ratio is fairly close, 6:10 rather then 6:9 above:

'1 x 15 kg bag of Hemp mixed with our 25 kg bag natural cement will make ~4.5 to 5 cubic feet of ”Hempcrete”

Q. How many bags of Hemp do I need for a 12" thick Hempcrete wall ?

A. Calculate length of wall x Height of wall = total square footage.
Now divide by 4.5 to get number of 15 kg (33 lbs) bags of hemp you'll need for a 12" thick wall.'


(https://hemptechglobal.com/page15/page16/page16.html)


so... a modest but not tiny house of say 30x30 with 8' high by 1' thick walls(30*4*8=960 cubic ft), might use about 213.33 batches per the latter figures above. 25KG binder per batch... IF this binder has a ratio per the first link of 50% lime, you are looking at 2666.625KG of lime for this arbitrary dwelling... assuming interior walls are something else, and there are no doors and windows!




Phil, this is an important point, and as you say could be practical in the real world in the right place...

Phil Stevens wrote:Michael - assuming the transport and processing component is minimal, if you use a carbon-neutral energy source to calcine the lime then hempcrete would indeed have a net negative footprint. Running a lime kiln requires a lot of heat, so that will either come from renewable electricity, biomass, or possibly a solar furnace. There's a potential industry for sunny places with limestone at hand...solar limeworks.

hmm do you think a solar furnace could heat it enough? solar limeworks sounds like a good idea...

Is 3500 C hot enough for you?

https://en.wikipedia.org/wiki/Odeillo_solar_furnace

Calcining lime requires 825 C, and I think you could achieve that pretty easily with mirrors and a well-insulated refractory vessel. Is there BB potential here?

Phil Stevens wrote:Is 3500 C hot enough for you?

https://en.wikipedia.org/wiki/Odeillo_solar_furnace

Calcining lime requires 825 C, and I think you could achieve that pretty easily with mirrors and a well-insulated refractory vessel. Is there BB potential here?

this is great! so then the final step to make this even more localized and sustainable is a machine that can be used to harvest one's own limestone — does such a thing exist or is it necessary to only buy the limestone from companies capable of harvesting it?

Pickaxe, shovel and wheelbarrow! Although we can also make explosives from bird droppings if you're keen to experiment....

Phil Stevens wrote:Pickaxe, shovel and wheelbarrow! Although we can also make explosives from bird droppings if you're keen to experiment....

seriously explosives from bird droppings?! does that create any harmful emissions? 😂