Construction Institute

Topic: Materials
Sub-topic: Composites in Construction

Authors: Andrew Keene; Andrew Keene, x; Tuncer Edil, Ph.D., P.E., D.GE; Jim Tinjum, P.E., Ph.D.; Randy Brown, P.E., Ph.D.

Abstract:
In the U.S., the rail industry spends $500 Million per year for Class 1 railway maintenance due to degradation of the ballast layer supporting the track. Certain components of the railway require maintenance more frequently due to unpredicted or accelerated deterioration (i.e., bolted rail joints, crossings, bridge approaches, etc.). One primary contributor to substructure deterioration is ballast fouling. As the amount of fouling increases, the strength of the ballast layer decreases, leading to higher rates of track deformation and failure. Thus, prevention or mitigation of fouling would greatly reduce costs for railway track and ballast maintenance. A new but untested technology to stabilize the track substructure involves injection of polyurethane into the ballast layer. In this study, several new polyurethane injection techniques were developed and tested. The criteria by which polyurethane improvement of ballast mechanical properties were determined based on: 1) extent of ballast void space filling by polyurethane within the ballast layer skeleton, 2) strength and to what amount bonding occurred between ballast particles and polyurethane, and 3) limiting volumetric expansion of the ballast layer during injection. Injection of the polyurethane into the ballast layer creates a composite material of ballast bound with the polyurethane. Laboratory injection quantities were targeted that produced a minimal amount of RFP expansion/reaction pressure, the procedure is aimed at optimum void filling behavior that would resemble best practice for a field procedure. Ideal field practice would involve filling the ballast pore space in targeted areas while producing minimal expansion thereby retaining ballast layer geometry and minimizing quantity of RFP injected. Strategic polyurethane injection into defective substructure is; in essence, a surgical tool to enhance strength and performance of problematic railway elements, avoid disruptive and expensive maintenance activities, and lengthen track lifecycle.