Experimental Investigation on Material Properties of Ultra - High Performance Fiber Reinforced Concrete in Extreme Conditions

Abstract

Abstract. The Ultra -High Performance Fibre Reinforced Concrete (UHPFRC) is a very promising modern cementitious material suitable for application in special structures. The knowledge of performance of this relatively new material is limited. This paper deals in more detail with impact of extreme conditions (it means thermal loading) on bond properties between prestressing strands and UHPFRC and an influence of elevated temperature to final material properties of different UHPFRC mixtures. The first part of experimental work was focused on mechanical properties of UHPFRC and UHPC exposure to the high temperature (Tmax = 200°C -1000°C). Tested residual mechanical properties were compressive and flexural strengths, the fracture properties will be presented in this paper. Specimens in the first second experimental part were subjected to the cycling freeze-thaw testing. The relationship between bond behavior of both type of material (UHPC and ordinary concrete) and effect of cycling freeze-thaw tests was investigated. The obtained experimental data serve as a basis for further systematic experimental verification and more accurate information about the significantly higher material properties of UHP(FR)C and its behavior in extreme conditions. IntroductionExperimental research in the field of UHPC applications is very important. Based on current experience, this relatively new material with excellent mechanical and physical properties allows optimization of design rules of structural members and their details especially with regards to the anchorage length of the reinforcement [1]. Previous experiments that were been focused on the bond behavior between reinforcing bars and ordinary concrete and between prestressing strands and UHPC [2] confirmed the fact, that the excellent characteristics of UHPC material have very important effect on the bond properties. In the relation to this research, the article describes experimental verification of shear stress between prestressing strands and UHPC in extreme conditions. The effect of variable ambient temperature was investigated also on the specimens made from both type of material, UHPC and ordinary concrete C50/60. The specimens were exposed to cycling temperature in the range from -20°C to +20°C. The number of cycles varied from 100 to 400 cycles. Degradation of the material and related decline of material characteristics could have very significant impact on values of the bond stress.Exposition to elevated temperatures (Tmax = 200°C to Tmax = 1000°C) impact on degradation of material properties was content of second part of experimental program. High-temperature resistance is one of the particular importance of fire safety [9]. Adding steel fibers to UHPC matrix helps increase the values of compressive strength and mainly flexural strength. The effect of residual strength after high temperature exposure and comparison of steel fibers effect to final strength were main objectives of the second part of the article [4]. Specimens were exposed to temperatures 200-1000°C an...