2018 Volume 72 Issue 1 Pages 77-82
The macroscopic fracture process of concrete due to high-speed impacts is understood well. However, the change in microscopic properties due to such impact load is not clear. In this study, an impact test was performed to understand the property change in concrete from collision of a high-speed projectile. Hardened cement paste was used in this study for easy observation and analysis. When the projectile impacts the sample, plasma was observed. The portion near the impact location changed to a brighter color compared to the portion far from the impact point and the color of the samples that were not tested. A pore structure analysis using mercury intrusion porosimetry showed that the brighter part was more porous and had larger pores. In the backscattered electron images, the brighter part had darker contrast compared to the darker part. There was almost no difference in the thermoanalysis and X-ray diffraction analysis results between the tested and not-tested samples. It was pointed out that the cause of the increase in porosity without a corresponding change in the property analyzed by thermoanalysis and X-ray diffraction analysis was probably due to the volume change or the drying of the sample caused by the instantaneous heat generated by the high speed collision.
