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PROPERTIES OF CEMENTS WITH CARBON NANOFIBERS GROWN ON KAOLIN CLAY

Ekaterina Potapova, Yuri Krivoborodov, Sergey Sivkov, L. I. Sycheva, Ivan Burlov

Abstract

At present, the issue of environmental protection is very important in the world. In Portland cement production a large amount of greenhouse gas is released, namely 8 % of all world anthropogenic emissions. CO2 emissions from cement production are associated with fuel combustion and decomposition of limestone during firing of the raw mixture. Scientists around the world are trying to reduce the amount of carbon dioxide released by replacing the main component of cement ? clinker with various additives. In recent years, "cement science" has paid much attention to thermally activated clays, which can act as pozzolana additives. Heat-treated clays contain amorphous oxides of silicon and aluminum, which interact with Ca(OH)2 , formed as a result of hydration of cement, which leads to the formation of additional amounts of silicate and calcium aluminate hydrated. Additionally formed hydrate phases seal the cement stone, and this leads to an increase in strength and improvement of other various characteristics of the binder. The most famous are kaolin clay, by heat treatment which produces metakaolin. Cement stone, which resists compressive loads well, does not work well on stretching and bending ones. The value of the tensile strength of this stone is only 7-8 % of the value of the compressive strength. To increase the resistance of cement stone to bending loads, it is reinforced by fibrous materials. As such materials, researchers are increasingly attracted to carbon nanotubes (CNTs) and nanofibers (CNFs), which are known to have particularly high tensile strength, high elastic modulus, and electrical and thermal conductivity. Thus, CNTs and CNFs are promising materials for creating high -strength construction and multifunctional composites of the new generation ones. Currently, the most suitable method for producing carbon nanofibers for large-scale production is catalytic pyrolysis of hydrocarbons, which is divided into two types according to the method of introducing the catalyst: 1) with a catalyst on a carrier (substrate) and 2) with volatile catalysts. The first method makes it possible to achieve higher UNF yields per unit mass of the catalyst. However, this method has a disadvantage. It needs in the separation of the carbon fibers from the catalyst substrate. The main requirements for the substrate are chemical and thermal stability under pyrolysis conditions, as well as a high specific surface area of the substrate. In this paper, as a substrate which satisfies the above conditions, it is proposed to use burnt clay (kaolin clay), used in cement technology as an active mineral additive.

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DOI resolver: doi.org/10.5593/sgem2020/6.1/s24.016

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