Study of high volume circulating fluidized bed fly ash on rheological properties of the resulting cement paste

This paper investigated the rheological properties of cement paste containing high volume circulating fluidized bed fly ash (CFBFA) using a rheometer. The effects of fly ash (type, content, particle size distribution and surface characteristics) on the rheological parameters of the cement paste were analyzed. The test results showed that the rheological properties of the paste system exhibited Bingham fluid characteristics when the replacement level of cement by CFBFA (d50 = 56 μm) was less than 50%. When the content reached to 70%, the rheological properties were exhibited the characteristics of revised-Bingham fluid model. In contrast, the cement with ultrafine CFBFA (d50 = 5 μm) exhibited the fluid characteristics that follow the Herschel-Bulkey model. The results also showed that the particle size distribution and the surface characteristics of fly ash were the important influencing factors on the rheological parameters, where particle size distribution played a decisive role. Results from the Rosin-Rammler fitting analysis showed that the use of CFBFA would increase the d50 value of paste particles and widen the particle size distribution. When the content of CFBFA was 50%, the yield stress and plastic viscosity of the paste system were increased by 76% and 169%, respectively, however the fluidity of the paste system was lowered. On the other hand, the use of ultrafine CFBFA would reduce d50 value and narrow the particle size distribution. Owing to the ultrafine particles of FA3, the thixotropy of the paste increased when the content of ultrafine CFBFA in the paste was low. When the content of ultrafine CFBFA was 50%, the yield stress and plastic viscosity of paste system were reduced by 45% and 54%, respectively, and the fluidity of system was improved.