A NEW PATH TO THE ECOLOGICAL BELITE-RICH CEMENT

konferenční sborník (ne článek)

angličtina

Over time, humankind has become more trying to protect the planet against global warming and is looking for innovative ways to reduce the negative impact of the rapidly industrializing world. Ordinary Portland cement (OPC) with regard to the scale of its production around the world (annual production is around 3Gt) is considered as the dominant construction binder. One of the crucial problems with the use of OPC is the relatively high CO2 footprint related with the production of its main component - clinker. Approximately one tonne of CO2 is formed per tonne of produced clinker. [1] Given the current position in relation to the ecological and economic situation, alternative solutions are being sought to replace (completely or partially) the high-emission binder. One of this solution could be to replace most alite to belite innovative belite-rich cement. [2] There are 5 motivations: (i) lower maximum kiln operation temperature, ~1200–1350 °C, which saves up 20 % of energy (against required 1450 °C for alite rich clinker), (ii) lower limestone consumption leading to the lower CO2 emissions [3], (iii) lower water consumption, (iv) higher resistance to chemical corrosion, (v) the last but not least, lower hydration heat at the early stage of hydration and chemical shrinkage which minimizing cracking, that allows to use belite-rich cement or the constructions of massive structures such as dams, where the use of OPC would lead to cracking due to the large amount of the heat during the hydration process in initial stage. These savings result in a reduction of carbon dioxide emissions of up to 20 % and also a reduction in nitrogen and sulfur oxide emissions. [4] On the other hands there are couple drawbacks of using the belite-rich cements as: (i) lower reactivity with water resulting the long setting time and low initial strength (could be obstacle or drawback, depends on the application field), (ii) higher clinker colling costs due to the necessity of the high colling velocity, (iii) higher grinding energy to achieve required specific surface. [5] Mentioned drawbacks could be remedied by activation of belite-rich cement, where the initial strength could be improved and thus the biggest handicap will be fix-up. Chemical activation represents an option of achieving adequate hydration rate and mechanical properties, which will lead to an expansion the belite-rich cement range of use as an environmentally friendly alternative to Portland cement. Compared to many traditional solutions to improve the reactivity of belite-rich cement, alkaline activation does not increase the impact of CO2 emission or energy consumption. More detailed understanding of interaction between alkaline activators and belite-rich cement is also necessary to describe the hydration process. [6-8] In this study several points had been investigated: (i) the suitable C/S ratio of input material, (ii) the optimum firing temperature and (iii) then the influence of the alkaline activators. The crucial part of this work was to optimize the combination of the C/S ratio and the firing mode. As a raw material the raw flour from the Cement power-plant Mokrá (Heidelberg Cement) was doped with the diatomaceous earth to correct the C/S ratio. For the firing procedure the elevator furnace was chosen, which allowed to interrupt the firing process at the high temperature, due to the subsequently required fast cooling. The maximum kiln operating temperature was chosen as 1 300 °C. Suitable temperature and C/S ratio was assessed by subsequent XRD measurement, where the content of C2S, C3S and aluminate phases were monitored. The specific surface is one of the next necessary parameters for the further evaluation was specific surface, which was measured according to the EN 196-6 standard.

Belite-rich cement, alkali activation, isothermal calorimetry

ILIUSHCHENKO, V.; KALINA, L.; SEDLAČÍK, M.; CÁBA, V.

24. 11. 2021

Slovenská chemická knižnica

Bratislava

2

https://www.uiam.sk/~oravec/svk/e_zbornik_svk_2021.pdf?fbclid=IwAR2fs3twn1esSj0sLUoCC6x5aWt5OZfExnIESx90V78PVVyU4weISBxKs3k