Drying shrinkage of early-age concrete for twin-block slab track

Abstract

Moisture and early-age mechanical properties in hydrating track slab present a significant risk for cracking. Based on the prediction model of concrete drying shrinkage and the moisture transport, a hygro-mechanical-chemical coupled model of twin-block slab track was developed by taking into account of dissimilar mechanical properties and humidity diffusion performance between prefabricated concrete twin-block sleepers, hardened concrete support layer and cast-in-place fresh track slab. The model can depict the cracks occurring at track slab such as the splayed cracks around sleepers, the gaps between sleeper and track slab and the irregular cracks inside the track slab. The numerical results show that: (1) The ambient drying condition will cause underestimated relative humidity gradient on the surface of the track slab, and the maximum relative humidity gradient can reach about 400%/m. (2) The embedded twin-block sleepers reduced the longitudinal continuity of the track slab around the twin-block sleepers. This results in greater displacement but smaller stress than other regions. (3) Splayed cracks may easily extend from the gap between twin-block sleepers and track slab within 2–3 days after initial setting of the track slabs for chemical shrinkage. (4) 14 days after pouring the track slab, the stress inside the track slab will increase to 8 MPa, and non-uniform drying shrinkage on the surface of track slab may be the primary cause for irregular cracks.