Abstract:

Desulfurization gypsum is a kind of industrial wastes. When mixed with fly ash and slag， it can enhance the reaction efficiency， increase the cohesiveness of cementation systems and reduce the amount of cement. Furthermore， gypsum cement gel material has a slight expansion function， which contributes to improving the compactness of materials， delaying the shrinkage cracking. Currently， gypsum is just used as roadbed filler， which can not fully play its performance. Based on this background， in this paper， the gypsum cement stabilized aggregate formation mechanism and its engineering application were investigated to identify the mechanism of “excitation”， “enhancement” and “reduction” of shrinkage. Referring to the cement performance test， the effects of gypsum on the retarding effect， strength characteristics and stability of the composite gel system were analyzed. Scanning electron microscope images and X-ray diffraction patterns were applied to reveal the mechanism of the effect of gypsum on the chemical reaction of composite gel system. The results reveal the volumetric micro-swelling and the three-stage development of the composite gel system. The feature of volume swell is derived from the crystallization of gypsum and the formation of ettringite. The three-stage strength development characteristics are derived from the excitation of desulfurization gypsum to active ingredients in the slag， crystallization pressure generated by the ettringite formation， and gypsum filling. For medium-particle composite stabilized aggregates， the proportion of slag should not be lower than the proportion of cement incorporation and the proportion of gypsum should not be less than 3.0%， not be more than 6.0%.

Key words: flue-gas desulfurization gypsum, blast furnace slag, cement stabilized aggregate, shrinkage characteristics, strength characteristics