Comparisons among magnetic and non-magnetic fly ash fractions: Strength development of cement-fly ash mortars

Magnetic extractions from aqueous-fly ash suspensions produced magnetic and non-magnetic fly ash fractions. Several fractions were obtained from an original fly ash (T0), from T0 and further grinding, and from a ground fly ash (T60). Magnetic and non-magnetic samples were characterized: chemical composition, granulometric data, specific gravity and specific surface area. Workability studies on mortars containing these fractions were carried out. Generally, non-magnetic fractions yielded mortars with similar or higher flowability than mortars containing the corresponding magnetic fractions. On the other hand, compressive strength development studies showed that non-magnetic fractions are more pozzolanic than magnetic ones; moreover, optimum replacing percentage of cement by fly ash fractions was 45% for non-mechanically treated samples, whereas for ground fractions optimum values were 30% for non-magnetic samples and 45% for magnetic ones.