Effect of de-icing salt and aluminous supplementary cementitious materials on the mechanisms of the alkali-silica reaction in concrete

• Applicant: Professor Dr.-Ing. Detlef Heinz
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: from 2011 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 196752921

The aim of the second phase of this project is to characterize the damaging process of alkali silica reaction (ASR) with natural aggregates under field temperature conditions in the presence of sodium chloride taking into account that the aluminium content of supplementary cementitious materials (SCMs) in the binder contribute to the composition and the swelling properties of ASR gels.The project focusses on the damage mechanisms and processes in concretes with a highly reactive, artificial aggregate and concretes with less reactive, natural aggregates (e.g. diabase, granite). In particular, the formation of the ASR gel is considered, as a new approach, in the light of the effect of aqueous siliceous species in the concrete pore solution. What effects do the properties (especially mineralogical composition and microstructure) of the reacting aggregate have on the reactions? Furthermore, the effect of variations in temperature and in composition of the penetrating salt (e.g. NaCl or KCl) on the formation and the stability of the siliceous species is investigated. Based on these results, a correlation between the composition and swelling properties of the gels and therefore concrete damage can be made.To further the investigations of the first proposal, the storage period of the current concrete prisms will be extended. A further funding period would provide answers for the following open and new questions.1. What long-term changes occur in the concrete pore solution during an ongoing ASR in natural aggregates in the presence of NaCl?2. Can NaCl cause a damaging ASR in concrete when natural aggregates (e.g. diabase and granite) are used which are at present considered as non-reactive?3. What is the composition of ASR gels formed in presence of NaCl and how is it affected by the binder (cement and SCM) and the properties of the reacting aggregate?4. Which siliceous species form in the concrete pore solution in presence of NaCl or KCl and how do they affect the severity of the ASR?5. Is damaging ASR enhanced at winter temperatures (2 °C) in combination with de-icing salt owing to changes in pore solution composition, despite a slower chemical reaction at lower temperatures?

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Anne Heisig