Experimental Study on Autogenous Shrinkage of Concrete

Abstract

The concept of autogenous shrinkage has been around for over 100 years. Historically, it was not a concern since concrete was typically made at much higher w/c ratios and lower strength. In recent years autogenous shrinkage has returned to the forefront of concrete technology discussions, especially with the documentation of field cracking and durability problems in modern high performance concretes. Autogenous shrinkage was defined as a volume change resulting when there is no moisture transfer to the surrounding environment. Many researches has shown that autogenous shrinkage is strongly dependent on the water-cement ratios and the content of mineral admixture, such as blast-furnace slag, fly ash or silica fume, which has been used to replace cement by weight in designing the HPC proportion. However, it is surprised that so far there has not been any standard method available to measure autogenous shrinkage of concrete precisely. Many researchers have established various experimental methods based on their own investigations including the method proposed by JCI (Japanese Concrete Institute) to measure autogenous shrinkage from the setting time. Each method has got its own strong and weak points and none of them is really dominant. Besides, there also have been few researches on autogenous shrinkage under the effect of silica fume of 5% replacement. Therefore, this dissertation aims for designing an experimental method which can be applied to measure autogenous shrinkage accurately within hours after casting. Based on the method initiated by JCI, associated with the application of chamber to control the temperature history of surrounding environment and the use of embedded strain gage which has been designed and manufactured by Vishay Intertechnology in USA specially for measuring strain in concrete only, a new experimental method was proposed by the authors to investigate autogenous shrinkage of concrete under the influence of various w/c ratios and 5% ce...