The application of NDT techniques to examination of thermally-induced cracking patterns of brick powder-Portland cement matrix

Abstract

The effect of an elevated temperature on the properties of thermally induced cracking patterns (CPs) of the brick powder-Portland cement system (CM-BP) was analyzed by NDT techniques. Various contents of brick powder (BP), ranging from 0 to 20%, as a partial replacement for cement, were evaluated. CM-BP was subjected to a cyclically increasing thermal load in the range of 105–500 °C. To evaluate the cracking patterns the image segmentation procedure was implemented. Parameters such as the total crack area (TCA), crack density (CD), and average crack width (CW) were used to characterize the CPs. To evaluate the CPs morphology and its complexity, a fractal approach was implemented by introducing the CPs fractal dimension (FDB). Additionally, after each thermal loading cycle, the CM-BP was subjected to the basic mechanical tests and the ultrasonic pulse velocity test (UPV). The results obtained allowed describing the process of CM-BP thermal degradation, and the FDB was found to be the most statistically significant parameter in the CPs quantitative description. In this paper, a damage assessment index (DAI) based on FDB and UPV was proposed to evaluate the degree of CM-BP thermal degradation. DAI was compared with the relative strength loss (RSL) and DAI was found to be more sensitive to the thermally induced chemo-physical transformation of the CM-BP microstructure.