1FRACTURE PROPERTIES OF CONCRETE UNDER CRYOGENIC CONDITIONS

In this paper, the fracture properties of a conventional concrete, at temperatures ranging from 20 to –170°C are reported. Two sets of test were carried out: a) stable three point bend tests on notched beams, conducted in CMOD control, and b) standard cylinder-splitting test. The tests were performed at 20, –20, –70, –120 and –170°C. To cool the specimens, two cryogenic chambers with automatic temperature control were used. From these tests, typical fracture parameters were determined according to cohesive crack model: tensile strength, fracture energy, softening curve, characteristic length and modulus of elasticity. The results show that low temperatures improve the fracture properties of concrete. As the temperature decreases, the tensile strength and the fracture energy increase markedly, especially until –70°C. Below this temperature, these properties tend to increase slowly or remain constant. From 20 to –170°C, concrete shows a two-fold increase in tensile strength and a three-fold increase in fracture energy. With regard to the softening curves, the results show that a bilinear approximation is a good estimate even for temperatures as low as –170 °C, and the shape of the curve is very similar at –120°C or higher temperatures. A significant difference in the shape, with a much shorter tail, is found at –170°C. The evolution of the characteristic length with temperature shows that the intrinsic brittleness of concrete decreases strongly as the temperature is reduced to –120°C, with a change in this trend when the concrete is cooled to –170°C