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Jan Stindt, Luca-Alexander Kempf, Patrick Forman, Rolf Breitenbücher, Peter Mark

• High-performance concrete is often heat-treated to increase early \(\underline {strength}\). Standardized temperature conditions for at least 24 h and sulphate-resistant cement thereby preventing (\underline {delayed ettringite formation}\) (DEF). In contrast, this paper investigates the risk of DEF for rapidly heat-treated HPC with a minimum temperature duration of 1 h to achieve a rapid early strength for stripping. In addition, a binder is used that does not exhibit increased (\underline {sulphate resistance}\). For this purpose, standard prisms (L x W x H = 16 × 4× 4 [cm]) are heat-treated at 80 °C between 1 and 6 h without a pre-storage time. Samples with a temperature duration of 24 h serve as reference. First, the (\underline {pore structure}\) is analyzed using Mercury (\underline {porosimetry}\) to identify damage to the (\underline {concrete matrix}\) due to the rapid heat treatment. The investigation of DEF is achieved by two common approaches. The sulphate resistance is determined by means of wet-dry cycles on specimens for 90 days, whereby the changes in mass and strain as well as the cracking pattern on the concrete surface serves as a qualitative evaluation criterion. In addition, the SVA method on specimens directly after heat treatment, which determines the change in (\underline {mechanical properties}\) and the (\underline {swelling behaviour}\) of the concrete, leads to a quantitative evaluation of sulfate resistance. The measured pore distribution of the samples shows a significant increase of the capillary pores of up to 109% for decreasing temperature durations. However, the porosity does not affect the sulphate resistance of the concrete. The wet-dry cycles cause no damage due to DEF, since the change in mass and strains decreases with increasing cycles from up to 62.7% to − 2.5%. Furthermore, no visual differences were detected on the concrete surface between specimens with and without (\underline {sulphate attack}\). As a result of the SVA test, maximum absolute strains of about 0.1 mm/m occur that are below the limit value of 0.152 mm/m. Also, the mechanical properties do not show a reduction in strength, but even an increase in tensile strength. In conclusion, the high-performance concrete formulation used in combination with rapid heat treatment investigated here did not result in detectable damage due to DEF.