Research On Moisture Stability Of Flue Gas Desulphurization Ash Modified Asphalt Mixture

Flue gas desulphurisation ash (FGDA), a kind of industrial by-product, isproduced by desulfurization agent (CaCO3/Ca(OH)2) slurry absorbing SO2duringthe process of coal-fired flue gas desulfurization. FGDA has increasingly become aburden for power plants since it causes both a shortage of storage space andenvironmental problems to surrounding areas. A reasonable way to re-use FGDAwould have environmental and economic significance. This paper focuses on usingFGDA in the asphalt mixture as inorganic anti-stripping agent, and compare with themodified asphalt mixture prepared with traditional used anti-stripping agent–cement.The moisture stability of FGDA asphalt mixture was investigated. At thesame time, the acting mechanism of the desulfurization ash in improving the moisturestability of asphalt mixture by researching the component changes of desulfurizationash and the effect of each component in asphalt mixture.Scanning electron microscope (SEM) was used to observe the microstructure ofFGDA, the fluorescence analysis and X-ray diffraction (XRD) was carried out on thedesulfurization ash to investigate its chemical compositions. The mass change ofFGDA during the mixing process and differential thermal analysis (TG and DSC)(0-250℃) were used to investigate the thermal stability performance of FGDA. Withthe improved boiling method and tensile experiment the effect of FGDA onimproving the adhesion between asphalt and aggregate was researched. ImmersingMarshall test, freeze-thaw cycling test and immersion rutting test were carried out toevaluate the water stability of FGDA modified asphalt mixture; pavementperformances of FGDA asphalt mixture was investigated by rutting test, three pointbending test and four-point bending test. In the end, the pure dihydrate calciumsulphate and calcium hydroxide were used to prepare of asphalt mixture toexploretheir effects on improving water stability respectively.According to the micrograph, the FGDA particles have no obviousagglomeration, but do present narrow particle size distribution and irregular spheroidshape. The chemical composition analysis of FGDA shows that its main components are CaSO4·2H2O, CaCO3, Ca (OH)2and a small amount of CaSO3·0.5H2O. Improvedboiling test showed that FGDA modified asphalt mortar had a better adhesion withthe aggregate than the limestone powder asphalt mortar. the mass rate of residualasphalt (RRA) mortar of FGDA modified asphalt mortar reached55.4%,7%higherthan limestone powder one. FGDA can significantly improve the strength and thedeformation capacity of asphalt mortar.The results of immersing Marshall test, freeze-thaw cycling test and immersionrutting test showed that the asphalt mixture with FGDA had a better water stabilityperformance than limestone powder one or cement mixture. High temperature ruttingtest, low temperature three point bending test, four-point bending fatigue test showedthat high temperature deformation resistance, low temperature cracking resistance andfatigue resistance of the FGDA asphalt mixture can meet the requirements of thespecification and is comparable to cement asphalt mixture. Therefore, it is concludedthat the FGDA used in the asphalt mixture can significantly improve the waterstability of asphalt mixture, and its pavement performance is as good as traditionalasphalt mixture.