Influência do uso de cimento Portland como material suplementar em pastas de cinza volante álcali-ativadas

Abstract

Cement is the most commonly used binder in civil construction. However, a significant amount of gaseous pollutants is released into the atmosphere during its manufacturing process. On the other hand, alkali-activated materials have proposed a more efficient use of environmental resources, reducing cement consumption. However, some properties obtained from alkali-activated matrices still do not adequately meet usability standards in civil construction. Therefore, the main objective of this research is to evaluate the effect of adding Portland cement to alkali-activated fly ash pastes through tests of the material in its fresh and hardened state. To achieve this, pastes were prepared containing Portland cement (PC) in proportions of 5% and 10%, activated with a solution of sodium silicate and sodium hydroxide combined, as well as a solution of sodium hydroxide only. In the fresh state, the apparent specific mass, spread diameter through the mini slump test, yield stress, flow time, and initial setting time were evaluated. The mechanical behavior of the paste was assessed through compressive strength testing. An analysis of the microstructure was performed using scanning electron microscopy (SEM). The presence of sodium silicate in the solution increased the apparent specific mass, decreased the yield stress in the paste with 10% cement addition, and increased the spread diameter by 30% compared to the paste containing only sodium hydroxide. The initial setting time was longer in the pastes with 5% cement, with maximum values of 8 hours and 53 minutes for the paste activated with silicate and sodium hydroxide and 7 hours and 7 minutes for the paste activated with sodium hydroxide. The fly ash pastes activated with silicate and hydroxide containing 10% and 5% PC showed average compressive strengths of 43.1 and 43.5 MPa at 28 days, approximately 54% and 65% higher than the pastes activated with sodium hydroxide, respectively. The observed morphological changes indicate that activation with sodium silicate and sodium hydroxide affects the structure of the pastes, influencing their physical properties.