Observation of Multiple Cracking in Hybrid FRCC at Micro and Meso Levels

Development of high-performance construction materials is one of the key issues for the sustainability of structures, and this is one of the reasons for the development of ductile fiber reinforced cementitious composites (FRCC). The purpose of this study is to observe microcracking in high-performance FRCC at the micro and meso levels to clarify the detailed mechanisms causing ductile behavior. In the experiments, a specially designed system was used to observe the surface of specimens under tensile loading by means of an electron microscope. X-ray technique with a contrast medium was also applied to observe internal cracking around a deformed bar. A formation of a number of microcracks on the surface of the FRCC was observed even before loading. These microcracks subsequently grew and/or other cracks occurred to generate multiple cracking as the load increased. The accumulation of multiple cracks produced extended nonlinearity of FRCC. In the vicinity of the deformed bar in the FRCC, multiple cracks were formed from the lug of the bar and the crack width was much thinner than in plain mortar. Thus FRCC surely contributes to dispersal of bond cracks and resistance to the expansion of cracks.