Utilization of calcareous fly ash with Lopburi calcined clay as high Portland cement replacement supplementary cementitious materials

Calcined clay and calcareous fly ash were used as supplementary cementitious materials to replace Portland cement at 50% by weight to produce a more environmentally friendly binder with a lower carbon footprint. Up to 30% of calcined clay was used while calcareous fly ash was used at 20-50%. Compressive strength and phase characterizations were investigated for these samples at 7 and 28 days to provide understandings of the phases formed during hydration. It is found that at both ages, the use of calcined clay in addition to fly ash resulted in an increase in the hydration phases as early as 7 days when compared to the reference fly ash mix and is more pronounced at 28 days. This relates with the increase in compressive strength of the mixes where the compressive strength of fly ash mixes with 15-20% calcined clay are found to be 40 to 41 MPa compared to 27 MPa of reference fly ash mix (50% fly ash). Using both thermogravimetric analysis (TG) and X-ray diffraction (XRD), a number of phases were detected such as calcium silicate hydrate (C-S-H), calcium aluminosilicate hydrate (C 2 ASH 8 ) and monocarboaluminate hydrate. A noticeable reduction in calcium hydroxide (CH) was also clear when increasing calcined clay.