Variation in hybrid cements over time. Alkaline activation of fly ash-portland cement blends

摘要

The primary aim of the present paper was to determine the variations over time (one year) in the main ce-mentitious gels forming during the alkaline activation of hybrid cements (70% FA/30% OPC). The 28 and 365 day hydration products were characterised by different techniques. The findings showed that the C-S-H/ N-A-S-H mix of gels precipitating did not precipitate in a pure state, but rather that their composition was affected by the presence of dissolved species. In the presence of aluminium C-S-H gel development was: C-S-H →C-(A)-S-H→ C-A-S-H, whilst in the presence of calcium, N-A-S-H gel evolved as follows: N-A-S-H → (N.C)-A-S-H →C-A-S-H. This last conversion is not complete in these systems because the amount of calcium present is thought to be insufficient. On the grounds of the findings, a microstructural model is proposed to describe the development of the reaction products forming in these hybrid cements.