With a tailor-made test assembly by the company LABOSTRUCT from Guntramsdorf, Austria, the freeze-thaw resistance of the construction material concrete has been tested in the accredited Versuchsanstalt für Bautechnik Wiener Neustadt since the end of 2009 more economically and with absolutely standard-compliant temperature cycles in a Memmert TTC temperature test chamber.
It’s all about the right mixture! Even though the construction material concrete mainly consists of grains of stone such as sand or gravel, water and cement, there are in practise a wide range of concrete mixes, depending on static, physical and chemical loads, aesthetic requirements and areas of application.
The effects of various environmental influences and pollution are classified in Europe in DIN EN 206-1 and each of these so-called exposition classes in turn is expanded into a more detailed international and national set of regulations, for example on production, areas of application or quality testing. In Austria, the ÖNORM B 3303 describes the exact procedure in the freeze-thaw resistance test, which is undertaken by accredited laboratories such as the Versuchsanstalt für Bautechnik Wiener Neustadt on behalf of the concrete industry for the testing of new formulas for frost resistance.
Concrete samples are frozen a total of 56 times to a defined temperature drop ramp to -20 °C and after two to four hours, heated up again to 20 °C. At the end of the test cycles the loss of mass in the samples through weathering is determined along with structural change, using ultrasound examinations. To date the freeze-thaw resistance test has been a long and expensive procedure. Again and again samples had to be brought from the freezer chest to a waterbath in which warm water at a constant 20°C has to rinse the concrete components during the 8-hour thawing phases.
LABOSTRUCT developed a test assembly for the Versuchsanstalt für Bautechnik Wiener Neustadt that allows samples to be left in one place during the entire test procedure, that is, in a water-filled basin during the thawing phases. A side feed-through for the supply and drain hoses was fitted to a Memmert TTC temperature test chamber, so that with the aid of a circulating pump and a thermostat-controlled water heater, water can flow continuously between the supply tank outside and the inner basin.
The temperature ramps can be conveniently set via the Celsius software or stored on MEMory Cards. Additionally, programmed contacts take over electronic control of the watering procedures, i.e. the synchronisation of the watering with the thawing phase, as well as the draining of water prior to the start of the frost phase. Of special importance to those responsible at the Research Centre was the comprehensive logging and documentation of the entire testing process, including, and apart from the time cycles, the verification that all temperature ramps are exactly standard-compliant.
