Synthesis and characterization of mortars with circulating fluidized bed combustion fly ash and ground granulated blast-furnace slag

• CFBC fly ash has the potential replacement of partial cementing materials.
• Addition of CFBC fly ash reduces the compressive strength and increases length change.
• GGBFS can be effectively used in reducing the length change.
• The amount of CFBC fly ash replacing cement was recommended to be limited below 20%.
• The amount of GGBFS replacing cement was no less than 70%.

The purpose of this study to investigate the synthesis and characterization of cement-based composites with circulating fluidized bed combustion (CFBC) fly ash and ground granulated blast-furnace slag (GGBFS). Firstly, CFBC fly ash shall be examined to confirm to the chemical and physical requirements according to ASTM C821-09. Secondly, the properties of mortars mixed with cement, CFBC fly ash and GGBFS as cementitious materials were explored. Test results showed that CFBC fly ash does not comply with the chemical and physical requirements in ASTM C821-09 (Standard specification for lime for use with pozzolans), but accords with the requirements of ASTM C593-11 (Specification for fly ash and other pozzolans for use with lime for soil stabilization). Based on the test results, CFBC fly ash has the potential replacement of partial cementing materials and as an alternative of pozzolan. The initial setting time of mortars increases with an increasing amount of cement replacement by CFBC fly ash and GGBFS. The compressive strength of mortars with GGBFS and CFBC fly ash is lower than that of ordinary Portland cement (OPC) mortar. The more the CFBC fly replaces OPC, the less the compressive strength obtains. Meanwhile, CFBC fly ash would results in a higher length change when adding up to 30%. In terms of engineering property, environment and economic, the amount of OPC replacement by CFBC fly ash was recommended to be limited below 20%, while by GGBFS it was recommended to be limited below 70%.