Caracterização de um cimento álcali ativado monofásico a partir da ativação de escória de alto forno com hidróxido de sódio

Abstract

Alkali activated cements (AACs) are obtained by mixing materials rich in aluminosilicates, usually an industrial byproduct, with an alkaline activator and therefore can reduce CO2 emissions compared to Portland cement and also incorporate residues of other industries. Despite the chemical or mechanical properties equivalent or superior to Portland cement, conventional AAC has some disadvantages in its application because it requires an alkaline solution, which is highly corrosive and needs to be handled with caution. The one-part AACs, in turn, consist of preparing the cement through a dry blend of the solid activator to the precursor mineral. In the literature, there are no references of mechanical strength values of a one-part AAC produced from blast furnace slag activated by sodium hydroxide. Thus, the objective of this work is to obtain a one-part AAC of these materials and to compare its characteristics with conventional AAC. Furthermore, the behavior of the one-part AAC when prepared previously and stored for 90 days (pre-mixed one-part AAC) was evaluated. For this, pastes of the three different blends were made: conventional AAC, one-part AAC and pre-mixed one-part AAC. Tests of mechanical resistance at 7, 28 and 90 days; calorimetry up to 7 days; and microstructure analyzes by XRD and SEM at 28 days were performed. The one-part AAC presented the best result of compressive strength at 7 days (30 MPa) and remained similar to conventional AAC at the ages of 28 and 90 days. One-part AAC released higher amounts of total heat of hydration and also had a higher release rate than conventional AAC. The pre-mixed one-part AAC suffered high lump formation from the contact with the humidity of the air and in the calorimetric analysis released a very low amount of heat of hydration, showing not to have developed the reactions of hydration as expected. The main hydration product for the three mixtures was C-S-H and the presence of calcite was observed by XRD and SEM.