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Few data are available concerning tensile creep of concrete, a property that can have considerable influence on shrinkage-induced cracking, for instance in repair works. This paper presents the results of tests carried out to evaluate the influence of stress level, age at loading, steel fiber reinforcement, and paste content on the tensile creep of concrete. These results show that, as in compression, creep of concrete in tension increases sharply under drying conditions. They also show that the tensile creep coefficient decreases with the age at loading, and that up to 50% of the ultimate short-term strength, tensile creep of concrete varies linearly with the applied load, either under sealed or drying conditions. However, tensile creep is apparently more sensitive to fiber reinforcement than compressive creep, and it was observed to increase as the paste content is reduced. Further research is necessary, particularly to determine the ultimate creep capacity, but the reported data indicate that it could be possible to optimize the composition of cement-based repair materials to reduce their cracking potential when subjected to restrained shrinkage.
Keywords: cracking; drying shrinkage; elastic modulus; fiber reinforcement; tensile creep; tensile strength.
INTRODUCTION
The viscoelastic behavior of concrete in tension is particularly important when concrete is subjected to restrained shrinkage, as is the case in bonded overlays. During the drying process, the contraction of the overlay is hindered by the generally much stiffer and hygrometrically stable concrete substrate. If concrete was purely elastic, the ultimate shrinkage, which for field concretes can range from 250 × 10^sub -6^ to 1000 × 10^sub -6^, would inevitably overcome the ultimate elastic strain, which typically is between 100 × 10^sub -6^ and 150 × 10^sub -6^. Durable nonreinforced superficial repairs (bonded overlays) would thus be impossible to achieve. There are many examples, however, of concrete overlays that have performed very well for many years.1 This has to be in some way related to tensile creep.
To allow a rational analysis and a more appropriate design of concrete repairs and, globally, of all elements where hygrometric and thermal strains are restricted, a better understanding of the tensile creep behavior of concrete is required. Such an understanding would also be helpful in the solution of many other practical problems, for example, in the design...