A study of drying shrinkage for securing durability of PC bridges

Recently, cracks have been found in a few prestressed concrete (PC) structures at early ages in Japan and it was determined that the cracks were caused by large drying shrinkage of concrete. In the current design standards, the relationship between the shrinkage strain of actual structures and that of small test specimens obtained by the Japanese Industrial Standards (JIS) test method has not been clarified. Therefore, large test specimens whose sizes are the same as actual PC box girders were constructed and the drying shrinkage strain was measured over an extended period of time. These measurements provided an understanding of what happens in the actual structures, and a clue to solve the problem due to large drying shrinkage strain was gained. In addition, the validity of the measurements was verified by the analysis based on the moisture diffusion in concrete.