Towards Extending the Range of Supplementary Cementitious Materials in ASR Regulations

In 2020, the Danish concrete industry established a roadmap to reduce its CO2 emissions by 50% compared to 1990, by 2030. The plan highlighted the necessity to introduce new supplementary cementitious materials (SCMs) to face the expected shortage of coal fly ash. This paper reports the main outcomes of an industrial PhD project, which aimed to suggest an update of the Danish ASR regulations to allow the use of more SCMs without putting concrete durability at risk. The Danish regulations for binders are based on the total alkali content, with a few exemptions for well-documented materials. Since current regulations hinder the use of most alternative SCMs due to their high alkali content, this project focused on other ways to compare binders on an ASR-relevant basis. For this purpose, Cold Water Extraction (CWE) was carried out to determine the free alkali content in blended cement pastes. CWE was selected due to its relative simplicity, which makes it a promising method to be implemented by industrial stakeholders. As the study intended to be generic, various SCMs were tested to cover a wide range of material composition: coal fly ash, two calcined clays, two biomass ashes, sewage sludge ash, crushed brick and glass beads. The results were compared with ASR expansion tests (ASTM C1567, TI-B 51, AAR-10) and field exposure cubes to assess the ASR performance of the same binders. The project emphasised the need for new guidelines, better suited for screening and assessing all types of SCMs.