Diagnosis of a Combined Alkali Silica Reaction and Delayed Ettringite Formation

Abstract

This paper presents a case study of diagnosing alkali silica reaction(ASR) and delayed ettringite formation (DEF) in mass concrete structures in order to identify causes of cracks in the concrete. In the investigation, cored concrete samples were taken from real concrete structures with 4 different levels of damage identified by none, moderate, severe, and very severe. Microscopic examinations were conducted to identify ettringite formation and ASR products in the concrete. Results revealed that the ettringite and ASR products were found in many locations of all concrete samples and their amounts were consistent with the damage levels of the concrete structures. Moreover, the semi-adiabatic temperature rise in these concrete structures was analyzed by using the authors’ heat model and finite element method (FEM). It was found that the temperature rise of the concrete was above 70°C, supporting the possible occurrence of DEF. From the results, it can be concluded that ASR and DEF are two of the mechanisms that contribute to cracking of concrete structures. The formation of ettringite was considered to be not involved with the external sulfate attack. This can be considered as the first evidence of a combined case of ASR and DEF in Thailand.

Keywords: alkali silica reaction (ASR), delayed ettringite formation
(DEF), microscopic examination, semi-adiabatic temperature rise