Concrete Railroad Ties Research Articles

Synergetic Influence of Microcrystalline Quartz and Alkali Content in Aggregate on Deterioration of Concrete Railroad Ties Used for 15 Years in High-Speed Railways

This study investigated the deteriorations of precast prestressed concrete (PSC) ties that were used for 15 years in high-speed railways in Korea and its damaging mechanism. The collected PSC ties with longitudinal cracks on sides and map cracks on surfaces exhibited strength degradation. The deteriorations were likely related to alkali-silica reaction (ASR) and delayed ettringite formation (DEF) together, given that the presence of massive ettringite crystals and the decomposition of ASR gel were found from microstructural analyses. Although there were no typical reactive siliceous aggregates for ASR in this study, ASR cracks were generated in the PSC ties. This is because the aggregates in the PSC ties with cracks were potentially reactive, and its high alkali-silica reactivity was likely attributable to the presence of microcrystalline quartz, supplying reactive SiO2 to trigger ASR. Furthermore, the alkali content in aggregates was associated with the deterioration of the PSC ties. The alkali-bearing minerals in aggregates (i.e., alkali feldspars) likely supplied enough alkalis for ASR. Besides, micas in aggregates could promote ASR due to their porous structure, which helps easy water ingress.

Improving serviceability of concrete railroad ties using prestressed AFRP strands

Prestressing with steel strands has been a key aspect in providing the required strength and durability for railroad ties (sleepers) needed to resist the loads on heavy haul lines in many countries. In spite of their improved durability in contrast to timber ties, a major flaw seen with concrete ties is deterioration due to the environmental or fatigue loading. Another issue found in concrete ties, not found in timber, is the electrical conductivity. The objective of this research is to design and to evaluate a class of concrete railroad ties utilizing aramid fiber reinforced polymer (AFRP) strand as the prestressing material. AFRP prestressed ties were constructed and tested for serviceability and strength following the guidelines provided by the American Railway Engineering and Maintenance-of-way Association (AREMA). Results demonstrated that AFRP strands are a potential substitute for steel strands. Some detail improvements may be necessary to mitigate cracking, this can be achieved by using smaller diameter strands.

Effect of concrete mixture components, proportioning, and compressive strength on fracture parameters

Splitting cracks in pre-tensioned concrete members often occur at the early stages after detensioning. To prevent these splitting failures, concrete members need to be resistant to crack growth at the strengths in which the beam is detensioned. In this paper, the effect of different concrete parameters including aggregate shape and content, water-to-cementitious (w/c) ratio, fly ash, paste and air void content on the crack resistance of concrete used in concrete railroad ties were investigated using Two-Parameter Model (TPM). For each mixture evaluated, twelve three-point prisms were tested at 27.5, 41.3 and 55.1 MPa concrete compressive strengths (4000, 6000 and 8000 psi) to determine the effect of concrete compressive strength on crack growth potential. In addition, splitting tensile tests were conducted on three samples at each compressive strength for all mixtures. Finally, the results were analyzed and the function of utilized method was discussed. The results show that increasing angularity, aggregate size and volume, and decreasing w/c ratio improve fracture toughness by 30% whereas changing paste, fly ash and air void content negligibly influence fracture toughness. However, all improving factors were seen to be most effective at low strengths. The obtained fracture toughness values from this study could lead to a significant improvement of splitting crack resistance in pre-stressed concrete members where high amount of transverse stress is often introduced at low compressive strengths.

Benefits of high strength reduced modulus (HSRM) concrete railroad ties under center binding support conditions

Concrete ties, also referred to as sleepers or crossties, have become a promising alternative to timber ties for freight lines in demanding territories with high curvature, high grade, and high axle loads. Concrete ties have also become popular in rail transit systems. High strength (HS) concrete is the material of choice in the fabrication of prestressed concrete railroad ties. The higher strength of the concrete is directly related to higher values of the elastic modulus, thus increasing the rigidity of the material. The combination of increased strength, rigidity, and the material brittleness may lead to premature cracking and deterioration which has raised major concerns within the rail industry. With experience in frontier concrete material research, researchers at the University of South Carolina (USC) have developed a High Strength Reduced Modulus (HSRM) concrete by introducing weathered granite aggregates into concrete mix designs. A comprehensive study has been conducted at USC to quantify the benefits of using HSRM concrete in railroad ties. Both laboratory experiments and computer simulations at the material, component, and structural levels were performed. HSRM can improve the cracking resistance and fatigue performance and extend the service life of the concrete ties. This paper presents the details of the computer simulations used to quantify the benefits of using the HSRM material in ties subjected to center binding conditions. Three-dimensional nonlinear Finite Element (FE) models have been developed for the HSRM and the “Standard” concrete ties. Nonlinear material models based on concrete damaged plasticity are implemented. The concrete-steel bond interface is also modeled. The numerical models are first validated through comparisons with laboratory testing results of prestressed concrete prisms and commercial prestressed ties, which showed excellent agreement. Results from a parametric study simulating the center binding conditions in a tangent track have shown that the HSRM concrete tie outperforms the Standard concrete tie by: (i) showing smoother stress distribution, (ii) delaying the initiation of cracks, and (iii) failing at higher ultimate loads.

Ballasted Track versus Ballastless Track

First concrete sleepers were made of normal reinforced concrete and used during the 1930s and 1940s. Concrete railroad ties became popular in Europe after World War II because of the advances in design, material quality and production of pre-stressed concrete. Now as before, concrete sleepers on ballast represent the primary basis of track construction, around the world, but the twin block concrete sleepers are also popular and widely used. The continuously increasing operational loads and speeds forced the railway companies to update their technical and economic system to keep their vital role in transporting passengers and merchandise. In this development a very important role played the superstructure of the railroad system, and this modernization process led to appearing of the ballastless track system approximately 60 years ago. The article presents a comparison of two main types of track systems, including technical and economic aspects.

Noncontact Inspection Method to Determine the Transfer Length in Pretensioned Concrete Railroad Ties

The traditional experimental method to determine the transfer length in pretensioned concrete members consists of measuring concrete surface strains before and after detensioning with a mechanical strain gauge. This method is prone to significant human error and inaccuracies. In addition, because it is a time-consuming and tedious process, transfer lengths are seldom if ever measured on a production basis for product quality assurance. A rapid noncontact method for determining transfer lengths in pretensioned concrete railroad ties has been developed. The new method uses laser-speckle patterns that are generated and digitally recorded at various points along the pretensioned concrete member. A prototype was fabricated as a portable self-contained unit for field testing, which incorporates a unique modular design concept that has several preferable features. These include flexible adjustment of the gauge length, easy upgradability to automatic operation, robustness, and higher accuracy. A laser-speckle strain sensor was applied to the transfer length measurements of typical pretensioned concrete railroad ties in a railroad tie plant. These prestressed concrete tie members are expected to withstand repeated axle loadings of 290 kN, totaling 250 million gross tons annually and occurring at speeds in excess of 110 km/h. The technique achieved a microstrain resolution comparable to what could be obtained using mechanical gauge technology. Surface strain distributions were measured on both ends of 12 ties, and their associated transfer lengths were subsequently extracted. The measurements of the transfer length using the laser-speckle strain sensor were unprecedented because it was the first time that the laser-speckle technique had been applied to pretensioned concrete inspection, and particularly for use in transfer length measurements of concrete railroad ties. It was also demonstrated that the technique was able to withstand the harsh manufacturing environment, making transfer length measurements possible on a production basis for the first time.

Optimization of a Prestressed Concrete Railroad Crosstie for Heavy-Haul Applications

In response to rising energy costs, there is increased demand for efficient and sustainable transportation of people and goods. One source of such transportation is the railroad. To accommodate the increased demand, railroads are constructing new track and upgrading existing track. This update to the track system will increase its capacity and make it a more reliable means of transportation compared to other alternatives. In addition to increasing the track system capacity, railroads are considering an increase in the size of the typical freight rail car to allow larger tonnage. An increase in rail car loads will, in turn, require the design of track components to accommodate these loads. This design change is especially pertinent to crossties that support the rail and serve to transmit loads down to the substructure. Today, the use of concrete ties is on the rise in North America as they become an economical alternative, competitive with the historical wood ties used in industry, providing performance that surpasses its competition in terms of durability and capacity. Because of the increased loads heavy-haul railroads are considering applying to their tracks, current designs of prestressed concrete railroad ties for heavy-haul applications may be undersized. In an effort to maximize tie capacity while maintaining tie geometry, fastening systems, and installation equipment, a parametric study to optimize the existing designs was completed. The optimization focused on maximizing the capacity of an existing tie geometry through an investigation of prestressing quantity, configuration, stress levels, and other material properties. The results of the parametric optimization indicate that the capacity of an existing tie can be increased most efficiently by increasing the diameter of the prestressing and concrete strength. Findings of the study demonstrate that additional research is needed to evaluate the true capacity of concrete ties because of the impacts of deep beam effects and inadequate development length in the rail seat region.

Delayed ettringite formation in Swedish concrete railroad ties

A petrographic examination of cracked Swedish concrete railroad ties identified delayed ettringite formation (DEF) as the damaging mechanism. This was unexpected because the concrete railroad ties were steam-cured with a maximum concrete temperature below 60 °C. The consensus in the published literature is that DEF only occurs in concrete subjected to heat curing above 70 °C. However, DEF is not only influenced by the curing temperature, but also by various other factors, such as cement composition (alkalis, C 3S, C 3A, SO 3, and MgO), fineness, etc. If an unfavorable combination of these parameters exists, delayed ettringite may occur at lower temperatures than 70 °C. In this paper, the influence of various parameters on DEF is discussed with reference to the investigated concrete.

Microstructural Features of Railseat Deterioration in Concrete Ties

Deterioration has been observed in concrete railroad ties, producing a loss of up to 40 mm at the railseat and leaving a rough surface formed mainly by aggregates. This deterioration occurs largely in cold and wet regions of western Canada and northern United States. The purpose of the present investigation was to deduce the processes responsible for this deterioration. Proposed mechanisms included abrasion, erosion, hydraulic pressure, freeze-thaw cycles, and chemical deterioration. Microstructural features associated with each mechanism were explored using laboratory concrete subjected to known deterioration processes or through computer simulations. Microstructural studies utilized scanning electron microscopy and x-ray diffraction. Based on the microstructural evidence, it was concluded that the railseat deterioration is produced by a combination of abrasion and freeze-thaw or hydraulic pressure.

Composition of alkali silica gel and ettringite in concrete railroad ties: SEM-EDX and X-ray diffraction analyses

Alkali silica gel and ettringite observed in concrete railroad ties were analysed by SEM-EDX and X-ray diffraction. The compositions, represented in the Si CaNa + K system, of clear gel were in the range of 53 to 63 atomic% Si and 20 to 30 atomic% Ca. The K + Na contents were constant and about 15% (excluding oxygen, water and trace elements). Analyses of crystallized gel showed a constant ratio between Si, Ca and Na + K of 70: 15: 15. Analyses of the Si and Ca content, of crystallized gel in cracks inside the aggregate particles, and clear gel at the mouth of the cracks and in air voids revealed a compositional difference with the crystallized gel as higher Si and lower in Ca. The content of Si decreases and Ca increases in gel away from the aggregate particles. The gel compositions are in the range published in the literature. The composition of ettringite is close to stoichiometrical values for ettringite, however, slightly lower in sulfur. The X-ray diffraction analyses identified the ettringite as crystalline.

Effect of loading rate and support conditions on the mode of failure of prestressed concrete railroad ties subjected to impact loading

In order to explore the dependence of the cracking mode of prestressed concrete railroad ties on the support conditions and the loading rate, particularly under impact loading, both static and impact tests were carried out. During static testing, the order in which different types of cracks developed as the load increased was: (1) flexural cracks; (2) flexural-shear cracks: and (3) shear cracks. Under impact, the loads at which the first cracks appeared were of about the same magnitudes as the loads required for the same mode of cracking to occur under static loading. However, the type of cracking that first appeared depended on the level of the impulsive load and the loading rate. At low levels of impulsive load, the first cracks to appear were flexural. At higher levels of impulsive load, flexural-shear cracks occurred first, and at still higher levels, shear cracks were the primary mode of failure.