RISE has presented the results of a study on sustainable high-performance concrete (HPC) development and problematic of combined carbonation-frost resistance in concrete with high replacement of cement with granulated blast-furnace slag (GGBS) at the XXIV Nordic Concrete Research Symposium 2022 in Stockholm, which took place 16-19 of August.
Frost resistance is essential for structures built in the nordic climate, especially in marine conditions where in the tidal and splash zones the surfaces are constantly exposed to wettening with chloride salts and negative temperatures. The WECHull sustainable HPC with high slag replacement performed excellently in the harsh frost scaling test and was classified as "very good" according to the Swedish standard SS137244.
However, concrete is also subjected to carbonation (the natural process of CO2-uptake from the air changing hydrated cement into calcite). That process is affecting the microstructure of cementitious materials and is recognized to cause significant changes, especially for slag-based materials. Those changes affect the frost resistance depending on the replacement levels and level of carbonation. The current research was focused on normal concrete and no data on HPC was available.
The study within WECHull project compared HPC with different slag/cement ratios and indicated a threshold where frost resistance is affected by carbonation. The image below presents the sections of two HPC materials with different cement content painted with fluorescent paint after carbonation and frost exposure. The sample on the right exhibited large frost damage on the surface and microcracking developed inwards on the depth of the carbonated surface.
The study will be continued and a research paper will be prepared for more detailed information.