Can igneous rocks replace the limestone (calcium carbonate) within cement? The cement industry is the largest carbon emission entity in the world, and the balance between the emission of carbon dioxide and the environment has been a major issue for various cement businesses. Stanford University has proposed a solution, which hopes to reduce the consumption of limestone and carbon emission, and eventually create a green concrete that does not require rebar for reinforcement.
Lime is an important composition of Portland cement as it provides calcium oxide that is required for cement production, though it is also the primary reason for environmental damages and carbon emission for the cement industry. Stones from the mountain are first detonated to obtain blocks of limestone, which are then smashed and shattered into fine powder that are fully mixed and calcined with shale, clay, and other substances under high temperature, where 1/3 of the carbon emission for concrete comes from the processing of cement clinkers, and the rest is contributed by limestone that releases carbon dioxide when heated at high temperature, before turning into calcium oxide powder.
Tiziana Vanorio, assistant professor of geophysics at Stanford University, and her research team have been dedicated in the research of limestone alternatives, and believes that igneous rocks can also be used to produce clinkers and become a part of cement. Although the use of igneous rocks would also require energy-intensive processing, the calcination process will not emit any carbon dioxide.
Vanorio commented that igneous rocks can be ground into find powder to produce clinkers using the same equipment and heating processes. The study points out that igneous rock clinkers can produce cement after being mixed with hot water, and it also helps to create long and dense molecular chains, which look like intertwined fibers under microscopes. This phenomenon was seen in cemented rocks from Roman ports 2000 years ago and hydrothermal environments, and possesses excellent endurance from preliminary observation.
▲Cementitious materials in fault rocks under electron microscope. (Source: Stanford University)
The research team hopes to eliminate the need of rebar reinforcement for concrete in the future through this study. Rebar concrete is the most common reinforcement method, where rebars, fabric reinforcement, steel plates, or fibers are added to the concrete, and the combination of materials is able to improve the insufficient tensile strength of concrete. As pointed out by Vanorio, the research team discovered that the micro mineral fibers are resistant to material brittleness, and she hopes to probe into how micro structures effectively reinforce rocks, as well as the conditions of natural growth, before implementing concrete reinforcement through nano engineering.
Scientists from all over the world are racking their brains as they seek alternatives to limestone, from coral reefs to lobster shells and mantis shrimps, in order to reduce the carbon emission of the cement industry; they are also looking to replace partial clinkers with fly ash that will contribute to “greenifying” the cement industry, which occupies 8% of the global emission of carbon dioxide. Alberto Salleo, professor of material science and engineering at Stanford University, commented that Earth is like a large laboratory. Who knows what other intriguing and useful structures await from the assimilation of various materials under high temperature and pressure?
(Cover photo source: pixabay)