Austrian concrete benchmark for increasing forecasting quality mechanical properties of modern concretes
Original Language Title: Österreichischer Beton Benchmark zur Steigerung der Vorhersagequalität mechanischer Eigenschaften moderner Betone
The predictability of properties of modern concretes, based on existing characteristic values and formulas, is challenging compared to more traditional concretes which are produced with ordinary Portland cements. Therefore, theoretical fundamentals of characteristic values of current standards and typical composition of modern concretes in Austria are investigated.
The results together with numerical simulations based on modern concrete models are used to define the details of the extensive test program on both material and structural level. Material tests are used to quantify the development of Young's moduli, creep, shrinkage, linear thermal expansion coefficients, uniaxial compressive strength, and splitting tensile strength of concretes that are conditioned to the standard temperature of 20 °C. Standardized material tests are carried out (1), 2, 7, 14, and 28 days after production. They will be complemented by innovative test methods that allow an hourly and, hence, quasi-continuous measurement of Young's modulus, creep, and shrinkage, in the period of 24 hours after production up to a material age of one week.
Overall, the experiments capture in detail early-age key properties of modern Austrian concretes under standard temperature. Additional material tests account for the fact that real temperature evolutions in concrete structures may deviate significantly from the standard temperature (20 °C). Calorimetry testing is used to determine the temperature-dependent hardening speed of the used binders. Combining the results with the development of concrete properties measured at 20 °C allows for predicting the development of concrete properties under variable temperature histories.
In order to validate these predictions, concrete samples are tested again in quasi-continuous experiments. This time, temperature histories are prescribed which are measured in the core of a massive concrete component, when the component is exposed either to typical Austrian midsummer or winter conditions. The massive concrete components are the focus of the structural test program. Two concrete bodies with dimensions of 0.60 m x 0.60 m x 1.00 m are produced during summer- and wintertime, respectively, and they are subjected to intensive monitoring during the first week after production. The temperature evolutions are recorded at the surface and in the interior of the components. After stripping of formworks, the surfaces will be treated according to the current state-of-the-art. Then, deformations of one surface will be monitored in a contact-free fashion, in order to document possible drying-induced cracking.
Numerical simulations based on the most modern concrete models support the design of the structural tests and their evaluation. Furthermore, numerical simulations serve as a vehicle to convey project findings up to the structural level of an exemplary investigated Engineering structure. The increase of prediction quality concerns the early-age and the long-term behaviour, whereby the latter is being evaluated in the framework of a life cycle analysis. Improved design formulas and planning principles summarize the project results. They are made available in a practically exploitable fashion. Key properties of modern Austrian concretes will be accessible in a much more reliable fashion compared to the current state-of-the- art.