The feasibility of estimation of mechanical properties of limestone concrete after fire using nondestructive methods U. Dolinar a , G. Trtnik b , G. Turk a , T. Hozjan a,⇑ a University of Ljubljana, Faculty of Civil and Geodetic Engineering, Jamova 2, SI-1115 Ljubljana, Slovenia b Building Materials Institute, IGMAT d.d., Polje 351c, SI-1000 Ljubljana, Slovenia highlights  Determination of residual mechanical properties of limestone concrete.  Influence of water to cement ratio and temperature on experimental results.  Relationships between results from destructive and nondestructive tests.  US pulse velocity and surface strength can predict the concrete residual strength. article info Article history: Received 26 March 2019 Received in revised form 6 August 2019 Accepted 22 August 2019 Available online 3 September 2019 Keywords: Concrete Nondestructive methods Mechanical properties High temperatures abstract The feasibility of estimation of mechanical properties of limestone concrete after exposure to high tem- peratures, 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 spec- imens 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 pre- sented 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 rela- tionship for estimation of flexural strength was determined based on combination of fundamental flex- ural 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 nonde- structive tests, is highly statistically significant for both mixtures. Posteriori test revealed that the major- ity of the measured quantities were significantly different on the temperature interval between 400 °C and 600 °C. Ó 2019 Elsevier Ltd. All rights reserved. 1. Introduction Concrete is the most widely used construction material. How- ever, the exposure to high temperature causes a decrease in mechanical properties of the material [1], which affects the bearing capacity of concrete structure. Determination of bearing capacity of concrete structure during fire is well known and documented, whereas the knowledge about bearing capacity after fire is quite limited. This can mainly be attributed to the lack of adequate data describing concrete mechanical properties after fire in combina- tion with duration of fire exposure, heating rate, and maximum temperature reached in the structural members during fire. Remaining bearing capacity after fire has to be taken into account when considering the rationality of the structural repair. https://doi.org/10.1016/j.conbuildmat.2019.116786 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: tomaz.hozjan@fgg.uni-lj.si (T. Hozjan). Construction and Building Materials 228 (2019) 116786 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat