Microstructural and thermal characterization of concretes prepared with the addition of raw and milled fly ashes

The influences of mechanically activated fly ash on the microstructure and thermal behaviour of atmospheric-cured concrete panels have been evaluated. For this purpose, comparative analyses of concretes prepared with and without addition of raw and milled fly ashes were performed. The raw fly ash was activated with an attrition mill for 1 h. Cylindrical concrete specimens with and without 20% fly ash substitution and large concrete panels with the same compositions were prepared. Mechanical properties of the concrete specimens were measured after 3, 7, 28 days, 2 and 4 months. After preparation the cylindrical specimens were cured in water while the concrete panels were kept in an open atmosphere outside the building for 1 year. The 28-day compressive strengths of the non-fly ash added cylindrical concrete specimen was 61.1 MPa, raw and mechanically activated fly ash added specimens were 54.4 and 64.7 MPa, respectively. Microstructural and thermal studies of the concrete panel were performed in the core drilled specimens after 1 year curing. The compressive strength of the core drilled specimens was 26.6, 25.4 and 35.9 MPa for the non-fly ash added, raw and mechanically activated fly ash added concrete panels. A beneficial pozzolanic reaction and improved mechanical properties of the milled fly ash-substituted concrete cured under harsh weather conditions were observed and determined by differential thermal analysis-thermogravimetry and mercury intrusion porosimetry. Improved mechanical properties of the milled fly ash added panel indicates its potential applicability in industrial practice due to the simplicity of the process.