Enhancing behavior of large volume underground concrete structure using expansive agents

• Large volume concrete structure with shrinkage crack.
• Expansive agents are used to create an internal stress.
• Restrained expansion ratio (RER) is measured in laboratory.
• Strain is measured in field and compared with the RER.
• Expansive strain to reach the peak value in field occurred earlier than the RER.

Many underground concrete structures suffer from issues of concrete cracking due to shrinkage during hydration, which furthermore results in water leakage. In order to improve the anti-crack ability of concrete, expansive agents were used to compensate for concrete shrinkage. This paper investigates enhancing the behavior of large volume underground concrete structures with expansive agents. Field measurements of strain and laboratory specimen tests were conducted. The results of concrete specimen in laboratory curing condition indicate that the restrained expansion ratio of concrete with expansive agents rapidly increases within the first 3 days. Restrained expansion ratio reaches the peak value after 14 days and then decreases with the elapsed time. The restrained expansion ratio was found to maintain a value of approximately 0.030% after 28 days. The developing trend of restrained expansion ratio of the field cured specimen was found to be similar as that of the specimen cured in laboratory. However, the peak value and average value of restrained expansion ratio of the field cured specimen was found to be smaller than those of the laboratory cured specimen. The field test results indicate that the post-poured strips and post-poured expansive reinforcing band with expansive agents can effectively increase the expansive strain of concrete, which furthermore indicates that expansive agents can enhance the crack prevention behavior of concrete structure in the field.