Results and Learnings of 15 Years Management of 25 Bridges with Precast Beams Affected by Delayed Ettringite Formation

In 2006, Cofiroute, a French highway concessionaire, discovered that a series of 25 bridges with precast prestressed girders were affected by the pathology of delayed ettringite formation in concrete. Faced with this still poorly understood phenomenon, Cofiroute surrounded itself with scientists and carried out multiple monitoring and diagnostic studies.

After a brief presentation of the 25 bridges, the article presents the results and the learnings drawn from these actions with regard to the evaluation of the evolution of the cracking through cracking index measured during several years, the evaluation of the swelling potentials through residual expansion tests on several tens of concrete cores, the evaluation of the effects of the pathology on the structures by means of numerical modeling (thermal, hydric, thermodynamic, mechanical) and reassessment. The article presents the methodology adopted to approach a classification of the current state of 200 of the 848 beams correlated to their probable evolution, with the objective of defining methods and priorities of treatment. In addition, are presented the experiments of treatment by water protection carried out on some of them. The article discusses the difficulties encountered during these various operations and in particular the “lack” of data/information, recognized as relevant, on the concrete at a young age (cement data, curing temperatures, concrete temperature curves, etc.), the assumptions considered to model the effects of the reaction on the characteristics of the concrete in order to appreciate their degraded functioning, the evaluation of the sensitivity to the water influx, and the evaluation of the performances and the efficiency of the solutions of protection by impermeable coatings.