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

Zhijuan Wang,Yuanming Song

doi:10.1007/s40789-016-0103-8

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.

Highlights

Circulating fluidized bed combustion (CFBC) ash is produced from the combustion of coal with injection of limestone for desulphurization (Gunka and Pyshyev 2014; Ni et al 2014; Tao et al 2014)
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

Summary

Introduction

Circulating fluidized bed combustion (CFBC) ash is produced from the combustion of coal with injection of limestone for desulphurization (Gunka and Pyshyev 2014; Ni et al 2014; Tao et al 2014). With rich content of active SiO2 and Al2O3, CFBC ash has been reported to exhibit good pozzolanic activity (Zheng et al 2009; Chindaprasirt and Rattanasak 2010; Li et al 2012) and recognized as a CFBC ash is produced at a much lower temperature (850–900 °C) than ordinary pulverized coal combustion (PCC) fly ash (1200–1400 °C), a widely used supplementary cementitious material in concrete. The content of unburnt carbon of CFBC ash is commonly greater than that of PCC fly ash and the shape of CFBC particles is irregular with loose and porous surface structure (Qian et al 2008; Wang and Song 2013). The unburnt carbon and porous surface of CFBC ash can potentially adsorb water and water-reducer in theory, and lowering the flowability when CFBC ash is used as supplementary cementitious material for concrete production

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