Study And Application Of High Performance Concrete Containing Ultra-Fine Fly Ash Designed For Railway Prestressed Bridge Girders

With the development of bridge structure towards long-span, heavy load, light-weight, high strength and good durability, High Performance Concrete (HPC) has been becoming the first choice material of concrete bridge today. Ultra-fine Fly Ash (UFA) has been collected by electro-static precipitators and airflow classifying technology, the specific surface area of UFA ≥500m~2/kg, it is a good kind of mineral admixture for preparing HPC. Because of specifications of relevant standards, the application of fly ash in prestressed bridge girder is limited, especially for railway prestressed bridge girder. In general, fly ash is refused for railway prestressed girder. In this paper, a series of research is done against engineers' anxiety. The specification of current national standards is broken through, UFA replaces equally 25% of cement by mass, HPC for railway prestressed girder was prepared successfully and applied to LuoYang-ZhanJiang railway prestressed concrete girders for the first in China.The main work and achievements in this paper are as follows: 1 , Physico-chemical characteristics, morphologies and Zeta potential et al. were investigated systematically, the action effects of UFA was analyzed. Early strength of HPC with UFA (UFA-HPC) depends on W/C, and its long-term strength depends on W/B. The acting effects of UFA, especially the effect of water reducing and enhancement, can compensate concrete early strength decreasing due to incorporating UFA. UFA-HPC preparing by optimization meet the requirements of railway prestressed concrete bridge girder. The workability of UFA-HPC is good, the shape of stress-strain curves is approach to that of ordinary high strength concrete with same strength grade, its Young's modulus is larger, creep and dry shrinkage is smaller, and its durability is excellent.2, The fatigue properties of C50-C80 UFA-HPC model beam was tested and studied. It was proved that the fatigue properties of UFA-HPC prestressed girder meet the requirements of railway code when 20-40% of cement was replaced equally by UFA. Those concrete beams which have undergone 2,000,000 fatigue tests did not crack, still being in elastic...