Characterization of net-zero pozzolanic potential of thermally-derived metakaolin samples for sustainable carbon neutrality construction

K C Onyelowe; A Naghizadeh; F I Aneke; D-P N Kontoni; M E Onyia; M Welman-Purchase; A M Ebid; E I Adah; Liberty U Stephen

doi:10.1038/s41598-023-46362-y

Characterization of net-zero pozzolanic potential of thermally-derived metakaolin samples for sustainable carbon neutrality construction

Sci Rep. 2023 Nov 2;13(1):18901. doi: 10.1038/s41598-023-46362-y.

Authors

K C Onyelowe^{1

2

3}, A Naghizadeh⁴, F I Aneke⁵, D-P N Kontoni^{6

7}, M E Onyia⁸, M Welman-Purchase⁹, A M Ebid¹⁰, E I Adah¹¹, Liberty U Stephen¹²

Affiliations

¹ Department of Civil Engineering, School of Engineering, University of the Peloponnese, 26334, Patras, Greece. kennedychibuzor@kiu.ac.ug.
² Department of Civil Engineering, Michael Okpara University of Agriculture, Umudike, Nigeria. kennedychibuzor@kiu.ac.ug.
³ Department of Civil Engineering, Kampala International University, Kampala, Uganda. kennedychibuzor@kiu.ac.ug.
⁴ Department of Engineering Sciences, University of the Free State, Bloemfontein, South Africa.
⁵ School of Civil Engineering, University of KwaZulu-Natal, Durban, South Africa.
⁶ Department of Civil Engineering, School of Engineering, University of the Peloponnese, 26334, Patras, Greece.
⁷ School of Science and Technology, Hellenic Open University, 26335, Patras, Greece.
⁸ Department of Civil Engineering, Faculty of Engineering, University of Nigeria, Nsukka, Enugu State, Nigeria.
⁹ Department of Geology, University of the Free State, Bloemfontein, South Africa.
¹⁰ Department of Structural Engineering, Future University in Egypt, New Cairo, Egypt.
¹¹ Department of Civil and Environmental Engineering, University of Calabar, Calabar, Nigeria.
¹² Department of Civil Engineering, University of Agriculture and Environmental Sciences, Umuagwo, Nigeria.

Abstract

Metakaolin (MK) is one of the most sustainable cementitious construction materials, which is derived through a direct heating procedure known as calcination. Calcination process takes place substantially lower temperatures than that required for Portland cement, making it a more environmentally sustainable alternative to traditional cement. This procedure causes the removal of hydroxyl water from the naturally occurring kaolin clay (Al₂Si₂O₅(OH)₄ with MK (Al₂O₃·2SiO₂) as its product. Kaolin naturally exists in large amount within 5°29'N-5°35'N and 7°21'E-7°3'E geographical coordinates surrounding Umuoke, Obowo, Nigeria. Alumina and silica are the predominant compounds in MK, which provide it with the pozzolanic ability, known as the 3-chemical pozzolanic potential (3CPP), with high potential as a cementitious material in concrete production and soil stabilization. Over the years, researchers have suggested the best temperature at which MK is derived to have the highest pozzolanic ability. Prominent among these temperature suggestions were 800 °C (3CPP of 94.45%) and 750 °C (3CPP of 94.76%) for 2 h and 5 h' calcination periods, respectively. In this research paper, 11 different specimens of Kaolin clay obtained from Umuoke, Nigeria, were subjected to a calcination process at oven temperatures from 350 to 850 °C in an increment of 50 °C for 1 h each to derive 11 samples of MK. The MK samples and Kaolin were further subjected to X-ray fluorescence), scanning electron microscopy (SEM) and X-ray diffraction (XRD) Brunauer-Emmett-Teller (BET) tests to determine the microstructural behaviour and the pozzolanic properties via the 3CPP as to exploit the best MK with the highest cementing potential as a construction material. The results show that the MK heated at 550 °C and 800 °C produced the highest pozzolanic potentials of 96.26% and 96.28%, respectively. The enhancement in pozzolanic potential at optimum calcination temperature is attributed to an increase in the specific surface area upon calcination of kaolinite confirmed by BET results. The SEM and XRD results further supported the above result with the strengthened crystal structure of the MK at these preferred temperatures. Generally, 550 °C is more preferred due to the less heat energy needed for its formulation during 1 h of calcination, which outperforms the previous results, that suggested 750 °C and 800 °C in addition to longer hours of heat exposure.