Application of Fly Ash in ASHphalt Concrete : from Challenges to Opportunities
Fly ash has been effectively used for many years in producing high performance concrete, with limited use in asphalt pavements. This is possibly because the performance benefits that fly ash provides to asphalt mixtures are under-investigated. The reported research investigated the interaction of fly ash with different types of asphalt binders and documented important improvements found in the critical properties of asphalt. Microstructural investigation demonstrated in previous work, that crack-arresting behavior was successfully induced by evenly distributed fly ash particles within the bitumen matrix. Investigation of the rheological performance of blends of asphalt binders with different types of ash using dynamic shear rheometer confirmed the feasibility of using fly ash to improve the performance of asphalt
Flow Properties of Fly Ash Modified Asphaltic Binders
This paper investigated the influence of fly ash (FA) on the rheological properties of indigenous Trinidad asphaltic base binders: the world renowned Trinidad Lake Asphalt (TLA) and Trinidad Petroleum Bitumen (TPB). The intricate relationship between the chemical composition of the binder and its influence of the Fly ash additive was evident as changes in the phase angle, δ (a measure of elasticity) and the complex modulus, G* (a measure of stiffness) was not generalized but were different for the modified blends for each of the asphaltic base binders. Incremental additions of Fly ash (up to 8% wt.) to TLA and TPB resulted in a general increase in the complex modulus (G*) indicative of the stiffening of both materials: the stiffening effect being more significant with TLA compared to TPB. Incorporating incremental amounts of Fly ash to TLA resulted in a general decrease in the phase angle (δ): an increase in the elasticity of the blends. Incremental additions of Fly ash into TPB resulted in an opposite trend as the modified blends exhibited marginally decreasing elasticity (phase angle (δ) increasing). A significant finding of this study was the occurrence of a relatively stiffer and more elastic (high G* and low δ values) TLA blend containing 1% fly ash. The rheological property of loss modulus (G″) exceeded the storage modulus (G′) in all instances indicating that the asphaltic blends behaved like a viscoelastic liquid. This study has provided previously unavailable key information which can facilitate the creation of customized asphalt-Fly ash blends to suit special engineering applications thus offering an environmentally attractive option for improving the use of the world renowned TLA as well as refinery TPB.
CHEMICAL REACTIONS OF GLASS CULLET USED AS CEMENT COMPONENT
The recovery of container glass (cullet) for recycling can often lead to the generation of surplus quantities of the material. The pozzolanicity of finely ground glass cullet (GGC) can be exploited by using it as a cement component in concrete. This paper examines two of the chemical reactions most significant to this mode of use, namely, the pozzolanic reaction and the potentially deleterious alkali–silica reaction. Although the presence of GGC has little effect on the reactions of portland cement, larger quantities of calcium silicate hydrate gel are formed, which are thought to contain quantities of sodium. Blends containing the largest quantities of calcium silicate hydrate gel also displayed the highest strengths. Expansion due to alkali–silica reaction of mortars containing GGC is reduced relative to controls. This can be understood when it is considered that the pozzolanic and alkali–silica reactions are chemically identical. The fine cullet particles have a high surface area and, hence, favor the rapid pozzolanic rate of reaction over the slower alkali–silica reaction rate.