Abstract: The difference between biomass ash and fly ash on the particle size distribution, particle morphology, chemical compositions and activity index was studied.Cement mortar tests adding different biomass ash contents were conducted to evaluate the compressive strength of hardened cement paste.The results show that the particle shape of biomass ash is irregular, the average particle size and particle size distribution range is larger.It has the slender fibrous particles, and the active components of Al2O3 are less than a third of the ordinary fly ash.The pozzolanic activity of biomass ash is lower than fly ash.Under the same content, the compressive strength of biomass ash-cement complex mortar is less than fly ash-cement complex mortar at all ages, the more dosage, the greater the strength decreased degree compared with the pure cement group.The microstructure of adding biomass ash of hardened cement paste is more loose and porous than the sample of containing fly ash, especially the existence of its peculiar slender fibrous particles.

Key words: biomass ash;hardened cement paste;compressive strength;microstructure