Novel methods for testing the durability of eco-friendly concrete
C. Baldermann
Institute of Technology and Testing of Building Materials, Graz University of Technology
15:00 - 17:00 Monday 28 September 2015 Foyer Alte Technik The development of so-called eco-friendly concrete has a huge potential in reducing the global warming potential (by up to 30%) and in particular in the lowering of primary energy input, i.e. by substitution of cement by eco-friendly additives and optimization of packing density. This novel approach provides an important contribution to prevent further climate change. However, for eco-friendly concrete there exist no standards procedures based on the descriptive concept so far (EN 206-1 or ÖNORM B 4710-2) that are adequate to predict concrete durability and thus the latter can be only estimated by using the equivalent concrete performance concept (ECPC). Based on the ECPC the newly developed concrete is tested in relation to a reference concrete which fulfills the guideline limits. In this contribution we elucidate the equivalent performance of eco-friendly concrete by three test methods, named i) accelerated carbonation test (ACC-Test), ii) Cappillary Suction of De-Icing Solution and Freeze-Thaw Test (CDF-Test) and iii) resistance against lime-solving carbonic acid attack.
In the ACC-Test, samples are stored at 20°C, 65 % relative humidity and at a CO2(g) concentration of 2% for 28 days up to 196 days. After this period steady state has been reached and an inactive corrosion layer has been developed, which reduces ongoing progressive penetration of CO2 by the reduction of both porosity and permeability.
In accordance with the regulations of the CDF-Test, reference and eco-friendly concretes were stored in a 3% NaCl solution for 28 freeze-thaw cycles and subsequently the loss of mass was weighed. Results indicate that the eco-friendly concrete generally show a better performance, as evidenced by an approximately 34-85% lower loss of mass compared to that of the reference concrete.
The resistance of eco-friendly concrete against carbonic acid attack was studied in a flow-through reactor over a ~6 week period. During the experimental run, in-situ measurements of pH and electric conductivity were performed and the chemical composition of the solution monitored. The leached samples were analyzed by X-ray diffraction and electron microprobe. Results indicate that portlandite dissolved within < 100 hours, followed by calcite and CSH dissolutions. These processes resulted in the formation of a few mm-thick, mechanically weakened leached layer on the concrete`s exterior.
In summary, the three test methods are suitable to evaluate the equivalent performance of ecofriendly concrete according to the ECPC.
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Institute of Solid State Physics
