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
Study of structure formation in bitumen-mineral compositions based on fly ash under water saturation
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.
ELIMINATING OR MINIMIZING ALKALI-SILICA REACTIVITY
This investigation into various aspects of alkali silica reactivity (ASR) as it affects performance of highway structures, emphasized the practical needs of the concrete engineer with respect to the evaluation of the potential of aggregate for expansive ASR in new concrete, procedures to evaluate material for safe use in new concrete, and means to mitigate ASR and associated adverse effects in existing concrete. A rapid test method, based on immersion of mortar bars in sodium hydroxide solution, originated by the National Building Research Institute of South Africa was evaluated and extended to identify cement alkali levels and pozzolan proportions required to prevent deleterious ASR with particular aggregate. The efficacy of using lithium salts in concrete to suppress expansion due to ASR was researched. Reaction chemistry and dosages were studied. Results were favorable and the approach is highly recommended. Means to mitigate ASR were also studied. Restraint to expansion and application of lithium hydroxide solutions are possible means to control expansion due to ASR.