Heat treatment of fresh concrete by radio waves - Avoiding delayed ettringite formation

Heat treatment of concrete during the early stages of hydration using the new radio wave technology enables a uniform energy supply at distinct rates under steady, closed-loop temperature control. This precise control of temperature makes it possible to implement accurately and uniformly any heat treatment regime based on existing or future guidelines over the entire volume of a concrete element. The article at hand presents this new technology briefly and focuses on the issue of possible delayed ettringite formation which might compromise concrete durability. By means of ESEM- and XRD-analysis the influence of the different heat treatment temperatures on the concrete microstructure could be comprehensively investigated. It was found that a maximum temperature of 60 °C should not be exceeded because higher temperatures cause severe delayed ettringite formation. Dielectric heating as such had no additional influence on microstructural damage, especially on the extent of the formation of delayed ettringite.