Concrete using Siliceous Fly ash at very High Levels of Cement Replacement: Influence of Lime Content and Temperature

摘要

Potential for producing viable binders at very high levels udof cement replacement (60% and above) with fly ash is udexplored. The role of lime content and temperature on udthe efficiency of fly ash in contributing to strength gain udis investigated using quantitative X-ray diffraction (XRD) udanalysis. Results of fly ash characterization are presented udusing quantitative X-ray diffraction (XRD) to identify udits reactive potential associated with the amorphous udsilica content. A new method for quantitative phase udanalysis of the amorphous phase contributions in the udXRD spectrum is presented. A strength-based efficiency udfactor which provides a measure of the contriubtion of udfly ash is introduced. Temperature is shown to increase udthe efficiency of fly ash by accelerating the dissolution of udthe reactive amorphous content. Efficiency of fly ash in udthe binary high volume fly ash-cement blend is limited udby the availability of lime. Increasing the lime content in udthe system provides significant enhancement in strength, udbut it does not influence the dissolution of fly ash With udthe availability of lime, the efficiency is limited by the rate udof contribution of reactive Silica from fly ash, which is udinfluenced strongly by temperature. Concrete strengths of ud30 MPa and higher were achieved with 65% replacement of udcement with fly ash and total cement content of 100 kg/m3. udThe strength gain in concrete is shown to be related to the uddepletion of lime in the system, formation of amorphous udhydration products and the depletion of Si/Al content from udfly ash. An investigation of the underlying mechanisms udreveals the potential for further strength enhancement by udeffectively engaging all the reactive components of fly ash.