Research On Preparing High Strength And Performance Concrete With UFA As A Replacement Of SF

In order to reduce the cost of preparing high strength and performance concrete,increase the added value of fly ash and improve the utilization rate of fly ash, the fly ash was grounded to 2μm-6μm for preparing ultra-fine fly ash(UFA). As mineral admixtures, the silica fume(SF) and UFA were used to replace cement respectively for preparing high strength and performance concrete(HSPC) with the same replacement rate of 10%.Comparative research on the working performance, mechanical properties,shrinkage performance and durability(including frost resistance and resistance to sulfate attack) of these two kinds of concrete were carried out. The main results were as follows:The work ability of HSPC mixture containing UFA showed significant improvement than the concrete mixture blended with SF. Among all the specimens, the work ability of the fresh concrete mixture blended with 2μm UFA was the best, the slump and expansion of this fresh concrete mixture were increased by 6.7% and 20%separately than the fresh concrete mixture blended with SF.HSPC with the strength grade of C80 could be prepared by using both UFA(The average particle size ranged from 2μm to6μm) and SF as mineral admixtures separately.The flexural strength of concrete containing UFA was significantly higher than concrete containing SF. And among the specimens, the concrete blended with 4μm UFA possessed the highest flexural strength, whose flexural strength on 7 day and 28 day were 51.4% and 13.9% higher respectively than SF concrete.The application of UFA could reduce the shrinkage deformation of concrete, which was helpful for the long-term performance of concrete, while SF would sharpened theshrinkage deformation of concrete and brought adverse effect on the long-term performance of concrete. After being cured for 90 days, the concrete samples containing UFA with the average particle size of 6μm presented the smallest shrinkage deformation whereas the concrete samples containing SF showed the largest ones.The frost resistance performance of concrete containing UFA was enhanced with the decrease of the average particle size of UFA. When the average particle size of UFA was reduced to 4μm, the frost resistance performance of UFA concrete was better than SF concrete. Both using UFA and SF could reinforce the resistance of concrete to sulfate attack, and the effect of UFA was better than SF.As a substitute of SF, using UFA could reduce the production cost of HSPC and improve the performance of concrete on workability, mechanical property and durability,which indicated good economic and social benefits.