Laboratory investigation of the abrasive wear mechanism of concrete crosstie Rail Seat Deterioration (RSD)

Currently, there are divergent design and performance demands on railway infrastructure components due to increasing freight axle loads and cumulative gross tonnages, as well as increased investment in high-speed passenger rail development in North America. The divergence in loading and performance demands on shared infrastructure arises from the fact that while high-speed passenger trains exert lower loads at relatively high speeds, freight trains exert high loads at relatively low speeds. Improvements in infrastructure component designs are needed to achieve increased durability and tighter geometric tolerances. According to a rail industry survey administered by University of Illinois at Urbana-Champaign (UIUC) in 2008, Rail Seat Deterioration (RSD) is the principal performance problem limiting the service life of concrete crossties in North America. Rail infrastructure researchers and industry experts agree that abrasive wear may occur due to relative motion between the rail pad and concrete crosstie rail seat, potentially resulting in RSD. The complex tribological process of abrasion is further complicated and expected to be accelerated by the presence of abrasive fines and moisture, creating 3-body wear condition. Lack of understanding of the abrasion mechanism has resulted in a sub-optimal and iterative design of ties, causing reduced service life. This paper summarizes our efforts in understanding the effect of changing the mix design of concrete on the abrasion resistance of the rail seat which will eventually help us in modeling abrasive wear in RSD by constructing a mathematical relationship between the rail seat wear rate and input parameters including concrete mix design, mechanical/tribological properties of materials involved, normal load applied, presence of moisture, and abrasive fines. To simulate abrasive wear in RSD, a simple experiment is being carried out using a rotating wheel (lapping machine) capable of abrading concrete samples as a part of UIUC's Small-Scale Abrasion Resistance Test (SSART). The objective of this research is to develop wear performance curves (e.g. wear depth versus load/time/cycles) for lab specimens developed from concrete crosstie mix designs that are currently being used in the industry, as well as for the evaluation of new mix designs. These data will help the rail industry in mechanistically designing concrete crossties by improving the understanding of materials used for concrete crosstie mix designs, with the objective of decreasing life cycle costs for the crosstie and fastening system. Preliminary SSART results are in agreement with relevant literature documenting the relationships between concrete mix designs and curing conditions and the resulting rate of abrasion.