Fracture energy of high-performance concrete at high temperatures up to 450°C: the effects of heating temperatures and testing conditions (hot and cold)

Abstract

The fracture energy of high-performance concrete (HPC) with a compressive strength of 67·1 MPa was studied by conducting three-point bending tests on eighty notched beams of 500×100×100 mm at high temperatures up to 450°C (hot) and in cooled-down states (cold). The temperatures in the furnace and inside the concrete and the weight loss of concrete were continuously monitored. If the exposure time was long enough, 16 h in this study, both thermal and hygric equilibriums could be reached. The fracture energy sustained a decrease–increase tendency with the increasing heating temperature for the hot concrete, and an increase–decrease tendency for the cold concrete. The modulus of rupture generally decreased with the heating temperature for the hot concrete but sustained an increase–decrease tendency for the cold concrete. There was a sudden drop at 105°C for the hot concrete owing to high vapour pressure inside the concrete. The residual compressive and tensile strengths both decreased with the increasing heating temperature, with sudden drops between 105°C and 150°C owing to residual stresses caused by high vapour pressures inside the concrete during heating. The tensile strength decreased more rapidly than the compressive strength for the same heating scenario. The residual Young's modulus of concrete monotonically decreased with the increasing heating temperature and this could be expressed using a linear relationship. The fracture energy and other material properties of concrete could be closely related to the ultimate weight loss.

Effects of fibres and rice husk ash on properties of heated HSC

“…At 1008C, a slight decrease of 6% occurred, mainly due to high vapour pressures inside the concrete; the microstructure of the concrete was not damaged significantly, so moisture was not able to evaporate easily and was trapped inside the concrete; this also led to high hygric gradients within the concrete. Higher humidity generally reduces the resistance of concrete to cracking at failure (Zhang and Bicanic, 2006). G F started to increase between 1008 and 5008C (from 137 .…”

“…7 AE 13% N/m to 246 . 6 AE 11% N/m), because moisture was able to escape freely (Zhang and Bicanic, 2006). Moreover, the temperature increase produced greater hydration of the cement paste, which raised the residual fracture energy of concrete.…”

“…Each tonne of paddy rice produces about 181 kg of husk, the combustion of which yields about 41 kg of rice husk ash (RHA). Due to growing environmental concerns and the need to conserve energy and resources, efforts have been made to burn rice husks in a controlled temperature and atmosphere and to utilise the ash produced as building material (Zhang and Bicanic, 2006). The aim of the present study was to add RHA to HSC at low dosages to analyse the possibility of recycling material this way and explore the influence of temperature in HSC containing RHA.…”

Determinación de las curvas de Wöhler en fatiga a flexotracción de un hormigón de muy alta resistencia sometido a temperatura elevada

“…Cuando se incrementa la temperatura del hormigón a 100ºC se generan tensiones internas debidas a la presión de vapor procedentes de la evaporación de la humedad interna de la matriz [8,9]. Esas tensiones generan microfisuras que dañan la matriz del material [8,9].…”

“…Esas tensiones generan microfisuras que dañan la matriz del material [8,9]. Tanto en el caso de los hormigones de control (Figura 6.a) como en los reforzados con fibras (Figura 6.b), la microfisuración originada por la temperatura provocaron tres efectos: un descenso del límite de fatiga, de 0.2 en D1 a 0.05 en D2 (Figura 6.a) y de 0.5 en DF1, a 0.26 para DF2 y 0.09 en DF3, un incremento de la dispersión de resultados, observados por el aumento de los intervalos entre las curvas del 75% y 25% de probabilidad, y un ablandamiento del material observado en la tendencia más suavizada de las curvas S-N.…”