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Circulating fl uidized bed combustion (CFBC) ash exhibits the desirable pozzolanic activity which makes it a potential supplementary cementitious material to replace cement for concrete production. However, the high unburnt carbon content and porous surface structure of CFBC ash may adsorb water reducer and thereby signifi cantly reduce the effi ciency of water-reducing agents. The adsorption mechanism of polycarboxylate superplasticizer in CFBC ash-Portland cement paste was investigated by ultraviolet-visible spectrophotometer, and the conception of "invalid adsorption site" of CFBC ash was presented. The results show that the adsorption behavior of polycarboxylate superplasticizer in coal ash-Portland cement paste can be described by Langmuir isothermal adsorption equation. The adsorption capacity of CFBC ash-Portland cement paste is higher than that of pulverized coal combustion (PCC) fl y ash-Portland cement paste. Moreover, the adsorption amount of polycarboxylate superplasticizer increases with the ratio of ash-to-cement in the paste. At last, the fl uidity of CFBC ash-Portland cement paste is lower than that of the PCC fl y ash paste. This work suggests that when CFBC ash is used as concrete admixture, the poor fl owability of the cementitious system due to the high adsorption of water and water-reducing agent should be taken into consideration. SONG Yuanming (宋远明): Assoc. Prof.; Ph D;

Circulating fluidised bed combustion (CFBC) fly ash contains plenty of anhydrite, so it is important to investigate the hydration behaviour of the anhydrite for the reutilisation of the ash in autoclaved products including autoclaved aerated concrete. X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to study the effect of curing conditions on the hydrates and existence form of the anhydrite in CFBC fly ashcement clinker pastes. Results show that autoclave curing can significantly limit hydration activity of the anhydrite in CFBC fly ash, and the hydration ability of the autoclaved anhydrite cannot be recovered, even if the anhydrite is submerged in water for the subsequent curing, because it is completely covered by fine hydrates. This work confirms that autoclave curing can effectively limit the expansion of anhydrite in CFBC fly ash, and suggests that CFBC fly ash is suitable to be used for the preparation of autoclaved products. NotationP pressure Q reaction quotient R gas constant, 8 . 314 J/(mol K) S Ł m standard molar entropy T thermodynamic temperaturẽ G Gibbs free energy changẽ f G Ł m standard molar Gibbs free energy of formatioñ r G Gibbs free energy change of chemical reactioñ r G m molar Gibbs free energy change of chemical reactioñ r G Ł m standard molar Gibbs free energy change of chemical reactioñ H enthalpy changẽ f H Ł m standard molar enthalpy of formatioñ r H enthalpy change of chemical reactioñ r H Ł m standard molar enthalpy change of chemical reactioñ S entropy changẽ r S entropy change of chemical reactioñ r S Ł m standard molar entropy change of chemical reaction Ł as superscript, indicates standard state

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