Study of structure formation in bitumen-mineral compositions based on fly ash under water saturation

Abstract

-The industrial powder waste from thermal power plants such as fly ash is used as asphalt or mineral filler due to its properties and dispersibility. However, the conflicting data on the fly ash usage are due to the different compositions, dispersibility, reaction capacity of the used fly ash. This paper presents the detailed research of the structuring process in bitumen-mineral compositions experimentally studied under the water saturation tests. The water saturation for the asphalt cements evaluates the strength of adhesion of the binder film to the particle surface as well as the stability of the bitumen-mineral structure when saturating water under the reduced pressure and elevated temperature. Depending on the fly ash composition, the structure formation operates differently at the component cohesion stage and during the swelling test. In bitumen-mineral composites, based on the high-lime ash, the mineral hydration leads to the binder film liftoff as well as to the change of the ash phase composition due to the low adhesion of bitumen and mineral particles. That results in undesirable formations in the system such as calcium sulfate dihydrate and ettringite, particularly. These formations cause the structural softening and the swelling of asphalt cements. The higher bitumen -low-lime ash adhesion provided the more stable structure of asphalt cements under testing. That resulted just in the binder film deformation without its liftoff. The swelling of the bitumen compositions was provided by the low packing density of ash particles in the asphalt cement.Keywords-the thermal power plant fly ash, swelling test; asphalt cement; structure formation; new formation.

Long-Term Water Saturation of Asphalt Binder Based on Fly Ash

“…4). Similar changes in the composition and structure were identified after the swelling experiment, where processes of hydration and phase formation were accelerated by exposure in hot water [10].…”

“…Previously the significant differences in the formed structure and characteristics of asphalt binder when using fly ash with different composition (differ in calcium oxide content), dispersity [9] and adsorption capacity were determined. The last factor has a significant effect on properties of asphalt binders under water saturation, which was shown in swelling test [10]. This article presents the results of study that are similar to described ones in the last article, but they are devoted to detailed research of changes in composition and structure of asphalt binders, occurred at the time of long-term water saturation.…”

“…So, for 30 days of water saturation the asphalt binders after vacuuming, their strength was reduced by 54% vs. initial strength. This can be explained by low adsorption capacity of original fly ash that determines the bad adhesion of bitumen to surface of mineral particles [10]. Flaking of bitumen film can lead to changes in composition of filler due to hydration of active minerals.…”