Study On The Influence Of Fly Ash On Shrinkage And Crack Resistance And Crack Mechanism Of High-performance Concrete

Since High-performance concrete(HPC) appeared in 1990, it has been put toextensive application on building structure due to its favorable workability, favorablemechanics strength, excellent durability. In practice, for its low water-binder ratio, largecement dosage and large sand rate, the early-age shrinkage of the concrete are serious,especially the autogenous shrinkage. And that will result in the early-age cracks on theHPC. For the excellent performance of fly ash, if it is used properly, it should be aneffective admixture which can restrain the shrinkage of HPC. The variety and amountand dosage of fly ashobviously affect the shrinkage of HPC. The mechanism of influence of fly ash on the shrinkage and early-age crack ofHPC is discussed in this paper from the scope of macro and microcosmic by theflat-type test, water vaporization test, autogenous shrinkage test, drying shrinkage testand ESEM test. For the anti-cracking performance of HPC, the optimal dosage of fly ash is different due to thedifferent kind of fly ash. The optimal dosage of the different fly ash is basically determined in thispaper according to the cracking time, cracking area and largest cracking width as designedparameter, which can be beneficial to the practice. The anti-cracking performance of fly ash concrete has deep relationship with the physicalperformance and chemical component of fly ash. By analyzing the function of the physicalperformance and chemical component in the concrete, we can properly explain the mechanism ofthe shrinkage and crack of the fly ash concrete. The interface of the cement paste and aggregate is the weak tache of HPC. By using theEnvironmental Scanning Electron Microscopy(ESEM) method at 1st day, 3rd day, 7thday, 28th day, the micro appearance of the interface and cement paste of the different agefly ash concrete is studied. The investigation results show that different hydratedproduction and different volume of hydrated production have significant influence onthe performance of the concrete. Morpha effect and micro aggregate effect of the flyash are primary at early age. Its volcano effect is not so obvious. Fly ash can meliorate IIobviously the transient zone of interface of the cement paste and aggregate. Different typeand different quality of fly ash have different function.