Supplementary Cementitious Materials

Supplementary cementitious materials (SCMs) are pozzolanic materials that are used to replace a portion of Portland cement, a key ingredient in concrete. Pozzolans are defined as siliceous or siliceous and aluminous materials that, while having little or no cementitious properties themselves, when finely ground will react with calcium hydroxide in the presence of water to form compounds having cementitious properties. Pozzolans can be of natural or artificial origin. Natural pozzolans can be of volcanic origin, such as pumices, or sedimentary origin, such as clays and diatomaceous earth. 

This Common Product focuses on artificial pozzolans used as SCMs.These SCMs include fly ash, blast furnace slag, silica fume, and ground glass pozzolan. Fly ash is a byproduct formed in coal fired power plants. Blast furnace slag is a byproduct formed from the production of pig iron at high heat and pressure in blast furnaces. Silica fume consists of small spheres of silica that are formed in electric arc furnaces as a byproduct of elemental silicon or silicon metal alloy production. Ground glass pozzolan can be sourced from both post- and pre-consumer glass sources. 

SCMs can replace a portion of Portland cement in order to utilize these materials that would otherwise be sent to landfills. They also can reduce the cost of the concrete mixture and affect properties of the concrete such as reducing permeability and increasing strength. The use of SCMs is often cited as a way to reduce greenhouse gas emissions, although emissions from industrial processes (e.g. production of coal ash) are not always considered in these estimates. The percent weight below is the maximum percentage of Portland cement that may be composed of each reported SCM. 

Additional types of recycled content can be incorporated into cement as aggregates. These include mixed sources of recycled concrete from demolition of previous structures and various types of plastic including polyethylene terephthalate (PET) bottles, PVC pipes, thermoset plastics, polyurethane foam, polycarbonate, glass-reinforced plastic, and recycled polystyrene insulation. Mixed plastic waste from curbside recycling (numbers 1 - 7) can be processed and supplied as concrete aggregate as well. While these types of content are beyond the scope of this Common Product, some additional information on plastics recycling has been added to the resources tab.