Evaluation of mechanical properties of steel-fibre-reinforced concrete exposed to high temperatures by double-punch test

• The factors influencing the tensile properties of heated steel-fibre-reinforced concrete (SFRC) were investigated.
• The tensile properties of heated SFRC were measured by the double-punch test.
• Tensile properties of the heated SFRC were more sensitive to volume fraction and aspect ratio of fibre than to its type.
• The relative loss was highest in tensile strength, followed by compressive strength and rupture energy.

The aim of this investigation was to study the factors influencing the mechanical tensile properties of steel-fibre-reinforced concrete exposed to high temperatures. The properties were estimated by the double-punch test having a high accuracy. Specimens reinforced with fibres of two types (twisted or hooked), two aspect ratios (l/d = 60 or 80), and three fibre contents (volume fractions of 0.25%, 0.5%, or 1%) were tested after exposure to four different maximum temperatures (room temperature, 300 °C, 500 °C, and 700 °C). Test results show that the residual compressive strength, DPT tensile strength and rupture energy of the specimens decreased with their increased heating. After the SFRC was exposed to the high temperatures, the relative loss in tensile strength was higher than that in compressive strength, but the relative loss of rupture energy was comparatively lower. After exposure to high temperature, the behaviour of the samples was more sensitive to the volume fraction and aspect ratio of the fibre than to its type. The coefficients of variation (COVs) of the rupture energy for SFRC specimens heated to higher temperatures is similar to those of the tensile strength, although the results are considerably more scattered than the compressive strength. A model predicting the residual tensile strength of heated SFRC measured by the DPT was proposed based on the test results.