IN PLACE DURABILITY ASSESSMENT FOR THE NEXT MILLENNIUM - LONG-TERM STUDY

Within the framework of the "BHP 2000" French National Project, a long-term experimental study is carried out in order to assess the durability of fifteen concretes with 28-day compressive strength ranging from 20 to 130 MPa. The properties of these concretes are first studied on samples in laboratory conditions. Also, reinforced-concrete test specimens are monitored over the years at four different field exposure stations. The experimental results of compressive strength, gas permeability, and carbonation depth obtained in the laboratory on the water-cured 28-day old samples are compared here with some of the available field data. The ranking of the different concretes with respect to their durability is deduced in both cases. Other laboratory measurements, such as chloride diffusivity, capillary coefficient, and deicing-salt scaling resistance, are also presented and discussed in this paper. For each type of concretes, the influence of mixture-parameters, such as the water-to-cement ratio, the presence of entrained air or of pozzolanic admixtures, on the different properties is analyzed. The influence of the environmental conditions on the field data is also discussed. The various trends observed on the durability-related properties are interpreted on the basis of the microstructural characteristics of the materials. The paper focuses on the behavior of high-performance concretes. A superior ability to limit gas or liquid transfers within the material is observed for these concretes. But, it is found that the presence of entrained air increases their gas permeability, indicating an increased potential risk of corrosion of the reinforcement, without systematically enhancing the deicing-salt scaling resistance of the concrete. Most of the non-air-entrained high-performance concretes do not exhibit good performance when submitted to accelerated freezing and thawing cycles in the presence of salts. All of these results have to be confirmed by the long-term monitoring of the structural elements.