Effect of Desulfurization Ash with Different Gypsum Content on Rheology Characteristic, Hydration Structure and Rebar Protection of Cement Based Materials

Abstract

Depending on the desulfurization reaction temperature, it can be divided into fly ash generated at high- temperature furnace zone and at low-temperature flue gas zone. For simulating those two kinds of desulfurization ash, the ordinary fly ash mixed with different weight percentage of CaSO4·2H2O is divided into 2 groups, the first group is fol- lowed by calcining at 900°C, another drying at 100°C. And then by the experiment of workability, strength and steel rebar protection, the effect of morphology and amount of gypsum on material properties and the pretreatment method are studied. The results show that: compared with ordinary fly ash, those two kinds of desulfurization ash can improve workability, but the improving ability of desulfurization ash at high-temperature furnace zone weaker than another's, in addition, amount of gypsum in desulfurization ash on fluidity has a threshold; Secondly, the structure forming of the sample with 10% gypsum drying at 100°C are faster than that of control sample, however the structure forming is slower than the control sample when gypsum drying at 100°C increase to 20%. As for gypsum calcining at 900°C, the structure forming of sample with 20 mass% gypsum are fastest, with 10 mass% gypsum follows closely next, the control sample falls behind. Thirdly, desulfurization ash can decrease strength, and the early strength of desulfurization ash at high-temperature furnace zone higher than another's, but the development trend of later strength is in the opposite direction. Lastly, those two kinds of desulfurization ash are harmless for steel rebar, and the steel rebar's passive film compactness is followed desulfurization ash formed at low-temperature flue gas zone>desulfurization ash formed at high-temperature furnace zone>ordinary fly ash.