Characteristics of CFBC fly ash and properties of cement-based composites with CFBC fly ash and coal-fired fly ash

The aim of this study is to investigate the pozzolanic and cementitious characteristics of circulating fluidized bed combustion (CFBC) fly ash and the properties of cement-based composites with various combinations of CFBC fly ash and coal-fired fly ash. Setting time test, compressive strength test and length change test were performed to measure fresh and hardened properties. Test results showed that the CFBC fly ash cannot meet the chemical and physical requirements in ASTM C821-09 (Standard specification for lime for use with pozzolans), but is consistent with the requirements of ASTM C593-11 (Specification for fly ash and other pozzolans for use with lime for soil stabilization). It indicates that CFBC fly ash has the potential instead of cementing materials and as an alternative of pozzolan. The initial setting time increases with an increasing amount of cement replacement by CFBC fly ash and coal-fire fly ash. The lower compressive strength has been obtained in mortar with various combinations of coal-fired fly ash and CFBC fly ash than the comparable ordinary Portland cement (OPC) mortar. Coal-fired fly ash can be effectively used in reducing the length change. However, CFBC fly ash would results in a higher length change when adding over 30%. Thus, the amount of CFBC fly ash replacement cement was recommended to be limited below 20%.