Evaluation of different fly ash samples on the production of alkali-activated materials

Abstract

In this work, different samples of fly ash (FA-A and FA-B) classified as type F as used to produce the AAM samples. The FA-A presented a higher Fe2O3 content than FA-B, 6.1 to 3.8 wt.%, and a slightly higher SiO2/Al2O3 ratio of 3.52 in comparison to 3.34 of FA-B. The average particle size (D50) of fly ash A was 19.7 µm and of fly ash B 30.8 µm, while the specific mass of the ashes A and B were 2.38 and 2.21 g/cm3, respectively. The results revealed that the mechanical strength of the AAM produced with fly ash A was higher than fly ash B, close to 80 and 44 MPa, respectively. The variation of the strength has been attributed to the different SiO2/Al2O3 ratios and different particle sizes. The mechanical strength decreased with increasing curing time, which is attributed to excess alkali in the system. Only very small differences in porosity and density have been found.