Reuse of coal combustion ashes as alternatives to cement and natural fine aggregate in green building bricks production for sustainable development

The coal thermal power plant generates a lot of ashes, including fly ash (FA) and bottom ash (BA), which potentially pollute the environment. Thus, to promote sustainable development, this research assesses the feasibility of converting these ashes into green building bricks (GB). In detail, BA was utilized to fully replace natural fine aggregate in the GB mixes, and FA was utilized as a binder material to partially replace cement at various weight percentages of 0%, 30%, 50%, 70%, and 85%. The designed grade of GB in this study is M7.5, as classified in the TCVN 6477:2016, which is commonly used in non-loading bearing wall applications. The influence of FA replacement level on the GB’s properties, such as compressive strength, ultrasonic pulse velocity (UPV), electrical resistance (ER), and thermal conductivity (TC), was investigated. Moreover, the mineralogy change and microstructure of the GB samples were identified using X-ray diffraction and scanning electron microscopy techniques. The experimental findings demonstrate that replacing cement with FA had a substantial effect on all of the GB sample performance. At 28 days, GB samples had compressive strength, UPV, ER, and TC values ranging from 3.1 to 14.8 MPa, 1526 to 3360 m/s, 5.1 to 18.3 kΩ.cm, and 0.29 to 0.69 W/mK, respectively. These findings illustrate the viability of employing FA and BA in the manufacturing of GB for sustainable construction. As a result, the GB with ≤30% FA replacement met the target strength of ≥7.5 MPa, qualifying for use in a non-loading bearing wall in real practice.