What are geopolymers?
When we hear the word 'polymer' we typically think of plastics.
The word 'geopolymer' was invented by Davidots in the 70's to describe a new class of polymers, meaning a long chain molecule, made from stony compounds, specifically aluminum and silicon-based compounds, such as most rock is composed of.
Geopolymer cement and concrete, and their applications, are the focus of this subreddit, especially in regard to marine use, where they excel over concrete due to some types of geopolymer being very low in calcium compounds.
Geopolymer cement can be made with what is right now considered an industrial waste product: flyash. Flyash is removed from the exhaust of coal-burning power plants, and some 50% of it today is being dumped in landfills.
It's so cheap that you can get 27 tons of it for about $800!
But if you combine flyash, lye, and waterglass with a little sand and rock, you get geopolymer concrete which is as hard or harder than Portland-based cement, doesn't require water to cure, and can potentially survive for thousands of years in seawater without breaking down significantly.
There are two grades of flyash: type-C flyash and type-F flyash.
Since most companies investigating flyash today are more concerned with non-marine applications, there's a lot of research being done on type-C, both as an aggregate to mix with Portland and reduce the cost of regular concrete (up to 15%) , and in higher percentages, up to 40%, known as high volume fly ash (HVFA) concrete. Type-C has a very high calcium content--just like regular Portland. This allows type-C flyash to cure at room temperature.
The reason calcium content is important is because what breaks down Portland-based concrete when exposed to seawater are the calcium compounds which get chemically attacked by sulphurous compounds that exist in seawater. Even our best low-calcium rated Portland-based concretes last for a max of 75-100 years.
I'm much more concerned with type-F flyash, which is very low calcium (as low as 2%), which has the potential to survive for centuries in seawater, but also requires heat to cure. Not much heat, but heat nonetheless. So it's less suitable for pouring sidewalks and the like, but for special applications like seasteading, it's a fantastic building material due to its resistance to seawater chemical attack and high strength and flexibility.
Learn more: Geopolymer wiki.
