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Building Matters

Geopolymers and the Advancing Science of Building Materials

Geopolymers offer advantages over Portland cement for concrete production, so why aren't we seeing more widespread use of this promising material?

The author in Cario. The French scientist Joseph Davidovits developed the field of geopolymer chemistry in 1991. Although a burgeoning topic in modern material science as a replacement for Portland cement, Davidovits posited ancient origins. He proposed that the blocks of the Great Pyramid were not cut stone but a form of limestone concrete or artificial stone—poured, not carved—i.e. the original geopolymer.

First, let’s define the terms. What’s a geopolymer? Geo, like geology, implies materials from the earth, meaning minerals. Polymer is a bit trickier to define. Poly means many, and mers refers to many small, single molecules or “monomers” that combine into a larger macromolecule. Binding little molecules into a more extensive network is called polymerization. In this broad category exist many common organic elements, such as proteins, rubber, silk, and cellulose, as well as inorganic elements, such as polystyrene, latex, and silicone.

In short, geopolymer cement (GPC) is a material binding system that relies on minimally processed minerals and industrial products to achieve concrete with improved performance and a reduced carbon footprint.

While the adaptation of GPC moves slowly, some readily available concrete blends already use synthetic polymers to reduce a portion of Portland cement. These are called PPCs. You may have ordered Polymer Cement Concrete (PCC) if you ordered ready-mix with latex additives; this synthetic polymer enhances concrete workability and performance. You have no doubt used latex-cement in patching compounds. But a true geopolymer concrete is formulated with no Portland cement, thereby avoiding the high-carbon output required to produce the calcining temperatures above 1450°C (2640°F) required to produce Portland cement.

In environmental terms, the production of ordinary Portland cement yields almost one ton of carbon dioxide (CO2) for every ton of cement. So-called cold fusion concrete is made with more environmentally friendly geopolymers resulting in a carbon footprint of about 20% of Portland cement. World cement production of 1.4 billion tons annually produces 7% of the world’s current CO2 emissions.

Various formulas for geopolymer replacements exist, most derived from cementitious substances like fly ash, granulated blast-furnace slag, waste glass, and minerals like silica fume and alumina. These precursors create a binder, similar to Portland, when blended with an activator,…

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