ABSTRACT
In order to avoid crack inactivation of concrete structures due to tensile stress action, Slab ballastless track is designed according to the “no stretching resistance” principle, that is maintaining the structure in low or zero tensile stress as the base principle of design. There are many cracks in roadbed slab concrete, due to the interface between the old (sleeper) and new concrete (roadbed slab concrete), see Figure 1. Cracks happen 2-3 days after the initial setting time and the width of the cracks develop with the time. There are two kinds cracks in roadbed slabs, one type of crack appears in the four corner of sleeper, such splayed cracks universally occur at the interface between the corner of the sleeper and the roadbed slab concrete. The cracks between the corresponding twin block sleepers become into one crack crossing over the whole roadbed slab. And the other crack is in the cross direction or oblique direction cracks; some of them lie in the position of the expansion joint. Along the cast direction of the concrete, cross cracks appear at intervals. In addition, sometimes the hydraulic base layer cracked along the precracking, will cause the upper roadbed slab to form reflective cracks.
