Evaluation of Splitting Crack Propagation in Pre-Stressed Concrete Ties Made With Different Types of Coarse Aggregate

Pre-stressed concrete railroad ties must meet requirements during service life. Using pre-stressed wires in concrete members enhances load-carrying capacity of concrete ties. It is important to ensure that pre-stressed forcing is introduced well before rail seat where the high impact load is applied. The required length of wire to fully transfer pretension forcing to concrete member is referred as transfer length. In order to shorten the transfer length, wires with improved indentation are used. As the transfer length is shortened, the high amount of stress concentration at the interface of wire-concrete can lead to longitudinal splitting cracks in concrete railroad ties. Splitting crack can occur either right after de-tensioning or during service life. It has been observed that concrete properties and components can highly affect crack formation and propagation. In this research, the effect of coarse aggregate on the splitting cracks of concrete railroad ties was investigated. To assess the impact of coarse aggregate features on splitting crack performance, fracture toughness test was done on three-point bend prisms. The specimens were made of four different coarse aggregate including crushed aggregate and well-rounded aggregate. It was observed that angularity and coarseness of aggregate increases the fracture toughness of concrete by 20%. Then, the same mixes were used in fabrication of pre-stressed prisms with different cover length to evaluate actual performance of splitting cracks after de-tensioning. The wires were tensioned up to 7000 Ib per wire and de-tensioned when concrete strength of 4500 psi is reached. The results of crack area/length of splitting cracks showed that increasing angularity can significantly improve splitting cracks resistance.