Application of Results of Nondestructive Testing Methods in the Investigation of Microstructure of Refractory Concretes

The aim of this investigation is to establish the correlation between concrete porosity, compressive mechanical strength, and microstructure using the results of nondestructive testing methods, i.e., ultrasonic pulse velocity (UPV) and image analysis. Researchers and engineers usually use results of standard laboratory procedures in order to obtain mechanical properties of a material. That process is long and it requires large number of samples, i.e., a lot of time and lot of material. Image Pro Plus (IPP) and UPV are methods which can provide equally accurate results. These methods are much more simple, rapid, and cheaper. Nondestructive test methods were applied on the corundum and bauxite based refractory concretes. Investigated concretes are varying in chemical and mineralogical composition. Mechanical compressive strength of concrete samples after thermal treatment at various temperatures (110, 800, 1,000, 1,300, and $1,500°\text{C}$ ) was investigated using standard laboratory procedure and afterward with UPV technique. Loss of strength and degradation occurs when refractory concrete sample is subjected to increased temperature and compressive load; therefore, measurement of mechanical properties can indicate and monitor the changes in the microstructure. Level of surface deterioration after thermal treatment was determined using optical microscope and IPP. Nondestructive ultrasonic measurement was also used as a means of monitoring of increasing porosity in refractory specimens. UPV technique and image analysis are reliable nondestructive methods for characterization of microstructural defects and can be useful when type of refractory concrete is to be chosen for an application.