Effect of fineness of palm oil fuel ash on compressive strength and microstructure of alkaline activated mortar

Abstract

The influence of different palm oil fuel ash (POFA), specifically treated POFA (t-POFA), fine POFA (f-POFA) and ultrafine POFA (u-POFA) with different fineness on the compressive strength and microstructure of POFA-based alkaline activated mortars has been investigated. The POFA-based alkaline activated mortars were prepared using 10 M of NaOH, Na₂SO₃ with silica modulus (Ms = SiO₂/Na₂O) of 2.2 and sand/POFA ratio of 1.5. The alkaline activated mortar samples were then cured at 75 °C for 24 h before testing for the compressive strength at 7, 14 and 28 days, respectively. The POFA grinding and calcination decreased the carbon content and loss on ignition also, improved POFA fineness and increased the mineral (oxide) compositions. The utilisation of POFA with different fineness for the synthesis of alkaline activated mortar affected the morphologies of its microstructures as well as its compressive strength. From the study, the use of POFA with greater fineness leads to higher strength of the alkaline activated mortar. This observation is verified by the creation of more C–S–H and N–A–S–H in the alkaline activated mortar which utilised POFA with higher fineness.

Keywords:

• palm oil fuel ash
• alkaline activated mortar
• compressive strength
• FTIR
• XRD
• FESEM/EDX

Acknowledgements

The authors thank United Palm Oil Industries Sdn. Bhd. for providing the palm oil fuel ash.