Comparative investigations of influence of chemical admixtures on pozzolanic and hydraulic activities of fly ash with the use of thermal analysis and infrared spectroscopy

The aim of this work is to investigate the influence of selected alkaline activators on pozzolanic and hydraulic activities of fly ashes using thermal analysis (TG/DTG) and infrared spectroscopy (FTIR). Two types of fly ashes differing in chemical compositions, especially content of calcium components, were selected for investigations. The study was carried out for two types of samples: (1) fly ash–lime paste performed with low-calcium fly ash and (2) a paste performed with high-calcium fly ash and water without introduction of additional amount of Ca(OH)2. Chemical admixtures NaOH, Na2SO4, and Na2CO3 were added to both the types of samples. It was confirmed that influence of chemical activators on pozzolanic and hydraulic properties of fly ashes strictly depends on the kind of fly ash and availability of Ca(OH)2. For example, in case of high-calcium fly ash, the most active action was exhibited by NaOH solution.