UTILIZATION OF INDUSTRIAL BY-PRODUCTS TO DEVELOP A VARIETY OF CEMENT-FREE COMPOSITES VIA CHEMICAL ACTIVATION

Date

2023-7-13

Author

Seyedian Choubi, Sepehr

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The production of ordinary Portland cement (OPC) - an essential material in the construction sector - is one of the most significant antropogenic CO2 emitters in the world. This research aimed developing cement-free binders based on alkali-activation of industrial by-products such as coal fly ash (CFA) and ground granulated blast furnace slag, that could replace OPC in certain applications. Research was carried out at four stages. At stage I, CFAs with varying calcium content collected from different thermal power plants in Türkiye were alkali-activated with sodium hydroxide and cured at 80 ºC for one day. High-calcium CFAs demonstrated better mechanical performance than low-calcium CFAs. Furthermore, the finer particle distribution of CFA results in a higher mechanical performance. The micro-characterization experiments revealed N-A-S-H and (N,C)-A-S-H as the important activation products. At stage II, fixated scrubber sludge (FSS) was used to activate slag. The main activation products of Slag-FSS mixtures were C-A-S-H and ettringite. Mixtures with FSS:Slag ratio larger than 1 resulted in 90-day compressive strengths higher than 50 MPa. In stage III, slag and Sugözü CFA were activated by anhydrite/Ca(OH)2 mixture. The main products of activation were amorphous phases like C-A-S-H, enveloping slag and fly ash particles and filling pores. The mixture containing 50% slag, 25% fly ash, 20% anhydrite, and 5% Ca(OH)2 resulted in 90-day compressive strength of 40 MPa. At stage IV, selected mixes from previous stages were exposed to high-temperatures. While slag based mixtures activated with FSS or anhydrite/Ca(OH)2 showed rapid reduction after heat exposure, CFAs activated by sodium hydroxide performed much better.

Subject Keywords

Alkali-activation, Fly ash, Blast furnace slag, Fixated scrubber sludge, Anhydrite,

URI

https://hdl.handle.net/11511/104824

Collections

Graduate School of Natural and Applied Sciences, Thesis