Qualification of prestressed concrete railroad ties is currently performed through testing at the design level following established AREMA guidelines, while important parameters, such as the strand transfer length, are typically not identified. Conventional testing practices are time demanding, expensive and labor intensive. Consequently, implementation of highly reliable, yet cost effective, quality control procedures at the tie production stage is highly appropriate and desired. In this work, the authors developed a stereo-vision system for both laboratory and industrial environments to measure the 3-D strain fields on the surfaces of prestressed concrete railroad ties. The proposed measurement system is based on the Digital Image Correlation (DIC) techniques developed in University of South Carolina (USC) laboratories over the past three decades. It is a non-destructive, non-contacting technique that has been successfully applied to obtain full-field measurements for a wide range of materials, loading types and temperature conditions. Known as 3D-DIC or Stereo-DIC, the method employs a stereo-vision system to successfully perform quality assessment of concrete ties in relation to the determination of: (i) the transfer length in both laboratory and production facility environments and (ii) full strain fields during product qualification tests to identify product defects. The proposed procedure is introduced and verified through application in a laboratory environment. The implementation of the method is presented and the cost effectiveness, accuracy, and versatility are discussed.

A High-Strength Reduced-Modulus High Performance Concrete (HSRM-HPC) for use in prestressed concrete rail ties has been developed by the authors. The HSRM-HPC material was originally considered for highway bridges but was rejected because of the accidental finding of the low modulus of elasticity. It is shown that the elastic modulus of the HSRM-HPC is reduced as much as 50% compared to the conventional HPC of the same strength while preserving all other properties of the conventional HPC. The use of the more flexible HSRM-HPC in concrete ties leads to reduced stress amplitudes and regularized stress fields at the rail seat area and the middle segment of the tie, which are the two most critical areas of tie failure. This work discusses the development and characterization of the HSRM HPC material, as well as current work on the performance assessment of such ties. The material development, material characterization, and performance assessment is conducted through experimental testing and computer simulations. The benefits of HSRM-HPC ties are quantified and discussed.