Zhang Yamei

MECHANICAL PROPERTIES OF HIGH PERFORMANCE CONCRETE MADE WITH HIGH CALCIUM HIGH SULFATE FLY ASH

Abstract A high calcium fly ash with high SO3 content was used to produce high performance concrete. In all the mixes, the fly ash contents of 50% and 60% by weight were applied. Although fly ash cement pastes showed severe volume unstability and poor pore structure development, mortars and concretes incorporating high mass high calcium fly ash exhibited good performance in both fresh and hardened state as those with low calcium fly ash did. The 3d and 28d compressive strength of mortars reached 25.2 ∼ 42.2MPa respectively with the water binder ratio varying from 0.30 to 0.24. What is noticeable is that all the mortars and concretes showed good strength developing tendency with the 90d compressive strength up to 67.3 ∼ 85.5MPa. This investigation reveals once more the fact that some materials which are not up to standard can still play a special role so long as the components are carefully chosen and proportions properly designed.

Comparison of the fracture process of the rubberized concrete and plain concrete under bending load

Acoustic emission (AE) technique is employed to investigate the damage process of the notched plain concrete and rubberized concrete specimens under 3-point bending load. AE signals in the fracture process of notched specimens are illustrated by analyzing the distribution of amplitude and hit rate of AE signals. AE signals in the rubberized concrete have lower activity and amplitude than in the plain concrete. By AE location analysis, it is found that the high energy events mainly are distributed near the notch tip. According to AE energy, the fracture process zone (FPZ) is determined. By comparing the FPZ of both concretes, it is found that the incorporation of rubber particles in concrete can greatly alleviate the damage process of concrete specimens and the damage zone in the rubberized concrete is much smaller than in the plain concrete. The moment tensor is also used to analyze the type of cracks and it is found that tensile cracks dominate the early period of loading, while shear cracks become dominant with propagation of cracks in late load period.