Author(s)

Toshifumi Sugama, Tatiana Pyatina

Brookhaven National Laboratory, Sustainable Energy Technologies Department, Upton, USA.

This study aimed at assessing the usefulness of carbon microfiber (CMF) in improving the compressive-toughness of sodium metasilicate-activated calcium aluminate/Class F fly ash foamed cement at hydrothermal temperatures of up to 300^°C. When the CMFs came in contact with a pore solution of cement, their surfaces underwent alkali-caused oxidation, leading to the formation of metal (Na, Ca, Al)-complexed carboxylate groups. The extent of this oxidation was enhanced by the temperature increase, corresponding to the incorporation of more oxidation derivatives at higher temperatures. Although micro-probe examinations did not show any defects in the fibers, the enhanced oxidation engendered shrinkage of the interlayer spacing between the C-basal planes in CMFs, and a decline in their thermal stability. On the other hand, the complexed carboxylate groups present on the surfaces of oxidized fibers played a pivotal role in improving the adherence of fibers to the cement matrix. Such fiber/cement interfacial bonds contributed significantly to the excellent bridging effect of fibers, resistance to the cracks development and propagation, and to improvement of the post-crack material ductility. Consequently, the compressive toughness of the 85^°-, 200^°-, and 300^°C-autoclaved foamed cements reinforced with 10 wt% CMF was 2.4-, 2.9-, and 3.1-fold higher than for cement without the reinforcement.

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

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.