The feasibility of estimation of mechanical properties of limestone concrete after fire using nondestructive methods

Abstract

The feasibility of estimation of mechanical properties of limestone concrete after exposure to high temperatures, using nondestructive methods, was investigated. Experimental study was carried out on two concrete mixtures that differed in water to cement ratio (w/c). After standard curing time, specimens were exposed to various temperature levels, i.e. 20 °C, 200 °C, 400 °C, 600 °C or 800 °C. Basic mechanical properties of concrete specimens were determined prior heating at ambient temperature. Once the specimens were cooled down to the ambient temperature, various nondestructive tests including ultrasonic (US) method, determination of rebound number, and resonant frequency method were performed. Further on, specimens were visually inspected to assess the damage of the concrete surface. To determine the residual mechanical properties of specimens after exposure to high temperature, the compressive and flexural strengths were determined on cubic and prismatic specimens, respectively. The main goal of presented research was the estimation of the compressive and flexural strengths of limestone concrete after fire based on developed relationships between results of destructive and nondestructive measurements performed on limestone concrete mixtures 1 and 2. The best relationship for estimation of compressive strength was determined based on measured fundamental torsional frequency, whereas the best relationship for estimation of flexural strength was determined based on combination of fundamental flexural frequency and US pulse velocity, both measured on prisms. The analysis of variance (ANOVA) showed that the influence of temperature on experimental results, obtained from destructive and nondestructive tests, is highly statistically significant for both mixtures. Posteriori test revealed that the majority of the measured quantities were significantly different on the temperature interval between 400 °C and 600 °C.