Avaliação da temperatura gerada pelo calor de hidratação de pastas de cimentos Portland fabricados com nanotubos de carbono

Abstract

Cement production is responsible for 7% of carbon dioxide (CO2) total emissions. With the goal of reducing this emission, the decrease in consumption of Portland cement clinker is the natural way. Several investigations in the last years have been conducted in developing cementitious composites that provide partial substitution of clinker. Since their discovery in 1991, carbon nanotubes (CNT) have promoted major changes in different areas. In the specific case of Portland cement composites, these nanoscale elements can improve their performance. In this scenario, the objective of this work was to evaluate the variation of the temperature generated by the heat of hydration of Portland cement pastes made with carbon nanotubes. The CNTs were synthesized directly on the cement clinker in a continuous process. For the assessment of the effects of CNTs, cement pastes were produced with 0.1% and 0.3% of CNTs with respect to cement mass. Pastes made with Brazilian type CP V and CP III 40 RS cements without CNTs were also produced for comparison. A semi-adiabatic chamber, developed in this project, was used in which the cement pastes were kept during hydration. Thermocouples placed in samples were employed from which the temperature values were collected with the aid of the PicoLog recorder. This way cement paste temperature profiles were generated using a non-conventional differential thermal analysis (NCDTA). In addition, the initial and final paste setting times were measured by Vicat analysis and calorimetry. The carbon nanotubes did not change the thermal profile of the pastes produced with both cements: Brazilian type CP V and CP III 40 RS. On the hand, for pastes produced with CP III 40 RS cement and both CNT ratios, the initial and final setting times were reduced