Toughness Improvement of Geothermal Well Cement at up to 300°C: Using Carbon MicrofiberReport as inadecuate




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This study aimed atassessing the usefulness of carbon microfiber CMF in improving thecompressive-toughness of sodium metasilicate-activated calcium aluminate-ClassF fly ash foamed cement at hydrothermal temperatures of up to 300°C. When theCMFs came in contact with a pore solution of cement, their surfaces underwentalkali-caused oxidation, leading to the formation of metal Na, Ca, Al-complexedcarboxylate groups. The extent of this oxidation was enhanced by thetemperature increase, corresponding to the incorporation of more oxidationderivatives at higher temperatures. Although micro-probe examinations did notshow any defects in the fibers, the enhanced oxidation engendered shrinkage ofthe interlayer spacing between the C-basal planes in CMFs, and a decline intheir thermal stability. On the other hand, the complexed carboxylate groupspresent on the surfaces of oxidized fibers played a pivotal role in improvingthe adherence of fibers to the cement matrix. Such fiber-cement interfacialbonds contributed significantly to the excellent bridging effect of fibers,resistance to the cracks development and propagation, and to improvement of thepost-crack material ductility. Consequently, the compressive toughness of the85°-, 200°-, and 300°C-autoclaved foamed cements reinforced with 10 wt% CMF was2.4-, 2.9-, and 3.1-fold higher than for cement without the reinforcement.

KEYWORDS

High Temperature, Alkali Activation, Carbon Fibers, Fly Ash, Calcium Aluminate Cement

Cite this paper

Sugama, T. and Pyatina, T. 2014 Toughness Improvement of Geothermal Well Cement at up to 300°C: Using Carbon Microfiber. Open Journal of Composite Materials, 4, 177-190. doi: 10.4236-ojcm.2014.44020.





Author: Toshifumi Sugama, Tatiana Pyatina

Source: http://www.scirp.org/



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