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PhD. Topics

Institute of Construction and Architecture

Carbonation of blended G-oil well cements under the simulated hydrothermal conditions
PhD. program
Inorganic technologies and materials
Name of the supervisor
Ing. Eva Kuzielová, PhD.
Receiving school
Faculty of Chemical and Food Technology SUT in Bratislava
Cementing in geothermal wells can be deteriorated by reactions of oil well cement (OWC) hydration products with CO2, which is, however, dependent on many factors acting simultaneously. Carbonation would not lead to the cement degradation, if only Ca(OH)2 (s) undergoes the reactions. On the contrary, higher compressive strengths and lowered porosity can be recorded. Besides, higher temperatures and pressures prevailing in the geothermal wells can have positive influence as hydration reactions are accelerated and higher degree of silicate polymerization is attained. However, above 100 °C, transformations of primary hydration products occur accompanied with the increase of permeability followed by the increased inclination to carbonation. In order to improve thermal stability of cementing, supplementary cementitious materials (SCMs; e.g. silica fume) are usually used. They act as fillers and improve pore structure of OWC also by acceleration of cement hydration, and formation of additional more thermal stable products. Pozzolanic or alkali activated reactions of SCMs consume Ca(OH)2, which causes the reduction of pH. Consequently, the rate of C-S-H decalcification is altered. Quantity of contradictory factors points out the importance of other investigation of carbonation in new cementitious materials and under the conditions simulating the real wells. Consequently, the present work will be focused on the investigation of the carbonation mechanism in new types of blended cements prepared by partial replacement of OWC by additives with pozzolanic or latent hydraulic properties at the temperatures higher than 100 °C. Experiments will be performed in the solution simulating composition of geothermal salt mineral water with high content of carbonates. Simultaneously, the accelerated carbonation of multicomponent cement pastes will be studied in CO2 chamber.