Testing Concrete Since Setting Time Under Free and Restrained Conditions

Abstract

Restrained deformations in concrete structures induce the development of stresses and sometimes cracking. Therefore the whole service life of concrete structures is influenced by the appropriate consideration of the early age behaviour of concrete under restrained conditions. For that reason, several devices were developed in the past to characterize the risk of cracking of cement-based materials. In the 1990s, a new experimental concrete testing concept has been designed: the Temperature Stress Testing Machine (TSTM). The device is able to monitor several parameters such as the age of cracking, the stiffness development and the stress relaxation. Between 1990 and 2010, less than fifteen laboratories worldwide have developed or acquired this kind of experimental equipment. All devices bear some similarities but major differences remain in the test set up designs, in the testing processes and also in the scale of the material used. This chapter summarizes all existing technics used to assess the behavior of concrete under restrained deformation, a comparison of the different existing TSTM is presented. New advanced techniques aim at monitor the cracking risk of cement-based materials such as the active ring test or the elliptical ring test are also presented.