What are Geopolymers?
The Science
Geopolymer is a term coined by Joseph Davidovits over thirty years ago. It means inorganic, typically ceramic, materials that form long-range, covalently bonded, non-crystalline (amorphous) networks. Obsidian (volcanic glass) fragments are a component of some geopolymer blends.[1] Commercially produced geopolymers may be used for fire- and heat-resistant coatings and adhesives, medicinal applications, high-temperature ceramics, new binders for fire-resistant fiber composites, toxic and radioactive waste encapsulation and new cements for concrete. The properties and uses of geopolymers are being explored in many scientific and industrial disciplines: modern inorganic chemistry, physical chemistry, colloid chemistry, mineralogy, geology, and in other types of engineering process technologies. Geopolymers are part of polymer science, chemistry and technology that forms one of the major areas of materials science. Polymers are either organic material, i.e. carbon-based, or inorganic polymer, for example silicon-based. The organic polymers comprise the classes of natural polymers (rubber, cellulose), synthetic organic polymers (textile fibers, plastics, films, elastomers, etc.) and natural biopolymers (biology, medicine, pharmacy). Raw materials used in the synthesis of silicon-based polymers are mainly rock-forming minerals of geological origin, hence the name: geopolymer.
In History
Geopolymer cement was originally called roman cement, after the long standing structures of the late roman empire. It’s been used in the limestone aqueducts and many of the ancient structures that are still standing today dating back to the 2nd century AD.
Uses of geopolymer has also been found in Ancient Egypt. Research has shown that the Egyptian pyramid stones might not have all been transported from afar for the construction project, but that some were man-made geopolymer blocks and so might have been mixed and cast on location.
As Building Material
Concrete is the most voluminous material made by all mankind. It’s used all around the world in roads, bridges, dams, and buildings. The key binding ingredient in today’s concrete – Portland cement – has a terrible carbon footprint. We make so much Portland cement that it’s alone responsible for 12-15% of all the world’s pollution.
Portland cement was invented in England in the mid 18th century and is made by superheating limestone and a few other ingredients in giant kilns. The enormous CO2 footprint emerges in two ways. First, lots of fossil fuels are required to achieve kilning temperature above 2,000 degrees Fahrenheit. Second, the chemical reaction that produces Portland cement involves baking CO2 out of the limestone, CO2 that was originally sequestered in the skeletal fragments of marine organisms that formed the limestone. The CO2 emissions from the production of Portland cement are so significant that producing a pound of Portland cement emits almost a pound of CO2 into the atmosphere. Billions of tons of Portland cement are produced every year.
Portland cement is the second dirtiest industry on the planet, trailing behind #1, which is gas-burning vehicles.
The math is downright scary.
A greener alternative, inorganic polymer concrete (geopolymer) fits into an emerging class of cementitious materials that utilize ‘fly ash’, one of the most abundant industrial by-products on earth, as a substitute for Portland cement.
Geopolymer concrete has a number of benefits. The first is it has the potential to substantially curb CO2 emissions. It can also produce a more durable infrastructure capable of lasting hundreds or thousands of years, instead of tens. And by utilizing the fly ash, it can conserve hundreds of thousands of acres currently used for disposal of coal combustion products, and protect our water ways from fly ash ‘contamination’, too.
In comparison to ordinary Portland cement (OPC), geopolymer concrete (GPC) has better resistance to corrosion and fire (up to 2400°F), high compressive and tensile strengths, a rapid strength gain, and lower shrinkage.
Researchers believe the geopolymer concrete’s greatest appeal could be its life cycle greenhouse gas reduction potential; as much as 90 percent when compared with OPC.