Adsorption properties of CFBC ash–cement pastes as compared with PCC fly ash–cement pastes

Abstract

Circulating fluidized bed combustion (CFBC) ash can be potentially used as supplementary cementitious materials for concrete production due to its desirable pozzolanic activity. The adsorption properties of CFBC ash–cement pastes were studied, and ordinary pulverized coal combustion (PCC) fly ash–cement pastes were used as control. The water-adsorption and superplasticizer (SP)-adsorption properties of the pastes were evaluated by water demand and UV-visible absorption spectroscopy respectively. The results show that CFBC ash–cement system has greater compressive strength as compared with PCC fly ash–cement system at a given curing age, although the water demand of the former is significantly higher than that of the latter. CFBC ash–cement pastes possess higher adsorption ability of aliphatic SP than PCC fly ash–cement pastes and the adsorption amount increases with an increase in ash replacement ratio. CFBC ash–cement pastes exhibit lower workability with higher slump loss. It is concluded that CFBC ash can be potentially used as supplementary cementitious material in concrete production, but the mix design of CFBC ash concrete needs to be appropriately adjusted. It is suggested that CFBC ash is used for the production of the concrete needing low flowability.