# Field Tests on Eco-Friendly Railway Precast Concrete Slab
## 1 Introduction  
In the railway engineering field, two basic types of railroad track structures are most commonly used: (1) a ballasted railway track structure with either concrete prestressed sleepers or wooden sleepers and (2) a ballastless track structure. Over several decades, the ballasted track structure has been widely used as one of the important track structure systems. However, the ballasted system has inherent drawbacks such as (1) ballast fouling, (2) uneven support conditions to the track structures, and (3) negative effects on ties and rails. Ballast fouling is identified as one of the main causes that can negatively affect the integrity of the track structure [1]. Therefore, it has been of great interest to evaluate and detect the level of fouled ballast and its condition. A non-destructive testing method using ground penetration radar (GPR) has been developed and its great potential has been presented in the railway industry [1, 2]. The fouled-ballast greatly affects the drainage capacity of the railway infrastructure [3]. After investigating derailment accidents (e.g., accident no. DCA13 FR009 in Bronx,New York, NY, USA on 18 July 2013), the investigation report indicated that the accidents were associated with the damage of concrete sleepers including reduced the cross-section of the ties due to abrasion, fouling, and others [4,5]. Recent studies have focused on identifying different failure mechanisms of prestressed concrete crossties including splitting/bursting, center biding, and rail seat deterioration [6, 7, 8, 9, 10]. In order to ensure the structural integrity and the safety of the track structure including substructures and superstructures, a ballasted track requires high maintenance cost. As opposed to the ballasted track, the maintenance cost of a continuous, ballastless, or slab track is lower than the traditional ballasted track, although it initially requires higher construction costs [11, 12]. Recently, field applications of a slab track have become more popular in Japan, South Korea, China, and Europe, since a slab track system shows superior performance such as higher longitudinal and lateral resistance, less buckling issue, even substructure settlements etc. [13]. In addition to the high-speed train applications, a slab track has been used for special track systems such as tunnel, bridges, and transit [11,14,15]. As the loading demands have increased over the last decades, in addition to the interest of increasing speed for a high-speed train system with an environmentally-sustainable next-generation railroad track system in South Korea, the authors developed an eco-friendly concrete, which was adopted to develop an eco-friendly railroad structural component. The developed eco-friendly concrete utilizes the industry slags (i.e., ground granulated blast furnace slag and electric arc furnace oxidizing slag) while minimizing the amount of cement and natural resource usages [16,17]. Therein, 30% of Portland type III cement was replaced by ground granulated blast furnace (GGBF) slag and 100% of fine aggregate was replaced by electric arc furnace (EAF) oxidizing slag. They used the newly developed cement-based material to manufacture eco-friendly prestressed concrete sleepers and the new railway structural component was successfully installed in the field of a high-speed train track in South Korea. They conducted a series of experimental tests to evaluate the structural performance of the eco-friendly concrete sleepers and compared to conventional prestressed concrete sleepers according to domestic/international standard tests. Static and dynamic load tests were performed and the test results demonstrated that the bending capacity and crack initiation of the eco-friendly concrete sleepers were higher and much delayed as compared to the conventional sleepers [16]. In addition, the authors measured the transfer length of the developed eco-friendly concrete sleepers, since it was critical for the railseat section to have fully developed effective stress after de-tensioning tendons.