Concrete Sleepers Research Articles

An acoustic emission-based approach to structural health monitoring of pre-stressed concrete railway sleepers

Railway sleepers represent an essential element of the track; indeed, their structural integrity is closely related to important technical and safety issues. Today, periodical visual inspections are the only method applied to check the status of sleepers but are limited to visible surfaces, whereas the early detection of in-service cracks in the whole volume of sleepers would provide great advantages in terms of maintenance and management. The aim of the paper is to propose an acoustic emission (AE)-based structural health monitoring (SHM) approach that is able to detect the initiation and propagation of cracks in in-service pre-stressed concrete sleepers. The investigation is carried out in the laboratory, comparing the results obtained by acoustic emission monitoring and digital image correlation when subjecting pre-stressed concrete sleepers, taken from production, to both static and cyclic loads. The main points dealt with in the paper include the sensitivity of acoustic emission to detect damage development and the signal processing approach needed for defining effective damage indexes. Given the encouraging results, the paper is the first step in developing an affordable monitoring system, to be embedded into sleepers, that is able to be part of a complete track monitoring system.

Buckling Analysis of Interspersed Railway Tracks

Nowadays, timber sleepers are still used for ballasted railway tracks to carry passengers and transport goods. However, the process of natural decay causes the problem of timber sleeper degradation over time. A temporary “interspersed” approach is used to replace rotten timbers with concrete sleepers. This implementation has several inadequacies, as interspersed railway tracks have inconsistent stiffness and experience significant deterioration over the years. Increased heat due to the change in the global climate can induce a compression force in the continuous welded rail (CWR), leading to a change in track geometry called “track buckling”. A literature review shows that track buckling on plain tracks has been widely studied. However, the buckling of interspersed tracks has not been fully studied. This study presents 3D finite element modelling of interspersed railway tracks subjected to temperature change. The effect of the boundary conditions on the buckling shape is considered. The obtained results show that the interspersed approach may reduce the likelihood of track buckling. This study is the world’s first to investigate the buckling behaviour of interspersed railway tracks. The insight into interspersed railway tracks derived from this study will underpin the life cycle design, maintenance, and construction strategies related to the use of concrete sleepers as spot replacement sleepers in ageing railway track systems. The outcome of this study will help track engineers to improve the inspection of the lateral stiffness of interspersed tracks in areas prone to extreme temperature.

Effects of under sleeper pads on dynamic responses of railway prestressed concrete sleepers subjected to high intensity impact loads

Exposed to operational uncertainties, the investment in railway infrastructure is increasing to improve track resilience, to mitigate long-term consequences, to prolong the track service life, and to reduce unplanned maintenance costs and carbon footprint. Under sleeper pads (USPs) have been widely used in several countries as a resilient component placed underneath concrete sleepers. However, it is well-known that, with any imperfection of either wheel or rail, railway tracks usually are incited by impact loading conditions. Accordingly, the application of USPs to mitigate the detrimental impact load consequences on track structure is unprecedentedly highlighted in this paper. Despite the common uses of USPs in various countries in Europe, the dynamic behaviour of the USPs under high-intensity impact loading conditions has not been fully investigated. Note that not only does this study focus on serviceability condition but it also instigates an extreme condition, which can occur when there are coupled effects of short and long wavelength defects (e.g. dipped rail joint coupled with track settlement, switches and crossings, etc.). This paper thus establishes a 3D finite element model of prestressed concrete sleepers with USPs, using LS-Dyna. This study has confirmed field measurement data that the sleepers with USPs tend to have lesser flexures, contact force and impact energy. However, this study is the world’s first to reveal that the vibration of sleeper with USPs could be amplified by the large amplitude impact force, which can be induced especially when excited by a high-speed train travelling over short-pitch rail defects, rail joints, coupled defects or crossings. It is also noteworthy that a very stiff pad with a bedding modulus of 1 N/mm3 can be alternatively used as USPs as recommended by the results obtained. Based on both numerical and field measurement results, it demonstrates that the applications of USPs should be very carefully considered since the USPs could trade off the desired benefits by aggravating dynamic behaviours of sleepers with USPs. The new insights will help track engineers to make appropriate decision on the design and usage of USP.

Experimental and Numerical Analyses of the Failure of Prestressed Concrete Railway Sleepers

This paper carries out the assessment of load-carrying capacity of prestressed concrete sleepers, in accordance with Brazilian Standard (ABNT NBR 11709) and AREMA Standard. In a lot of railways around the world, many prestressed concrete sleepers have failed due to Rail Seat Abrasion (RSA) and corrosion. RSA is the wear degradation underneath the rail on the surface of prestressed concrete sleepers. In this paper, a numerical study was carried out to evaluate the load-carrying capacity of the prestressed concrete sleepers, using ABAQUS software. The nonlinear using Concrete Damage Plasticity model was validated by 18 experimental results, in accordance to standards. Using the validated model, the influence of different wear depth RSA, combined with corrosion of the prestressed wires, is investigated.

Investigation of prestressed concrete sleeper’s vibration located at KM71.75 And KM79

Train has been one of the essential and convenient transportation choices for community nowadays. Instead of carrying a passenger, these types of facilities also can be used to transport material across our country. With the increasing usage of train every year, the rate of accidents has also increased dramatically. Therefore, the importance of studying about the railway can contribute to building better and comfort railway track which can deliver their services at its best for an extended period. This study focused on the measurement of the deflection of concrete sleepers which affect the performance of the railway track. Lack of actual deflection value from the site can be problematic to ensure the quality of the track itself. The method used for the analysis is by using the Sirius-M instrument which can be recorded and analyses the acceleration of the concrete sleepers when receiving the loading wave from a moving train. The data of acceleration then can be transformed into deflection form by applying double integration. From the data collection, it shows that the maximum deflection at northbound at KM79 is 13.72 mm for freight train and 1.5 mm at southbound for six set commuter train. As for KM 71.75, the maximum deflection at northbound is 0.57mm for ETS and 1.5mm at southbound for six set commuter train. Thus, from this research, the actual deflection value from both sites were achieved.

Study on Coupling of Glass Powder and Steel Fiber as Silica Fume Replacement in Ultra-High Performance Concrete: Concrete Sleeper Admixture Case Study

To investigate the substitution of silica fume (SF) with the coupling of glass powder (GP) and steel fiber (STF), a concrete sleeper admixture (CSA) contains SF is considered as the reference concrete admixture. The use of high SF content in CSAs has negative effects on concrete rheology. Furthermore, it decreases the extensive use of ultra-high performance concrete (UHPC) in concrete markets that can mainly be caused by the limitation in available resources and the high cost of SF production. The substitution of SF with GP is insufficient; therefore, the possibility of using the coupling of GP and STF as a SF replacement has been researched. In this regard, 0.5%, 1 % and 1.5% steel fiber by concrete volume and 5%, 10% and 15% glass powder and silica fume by weight of cement content have been investigated. It is found that concrete admixture with the coupling of STF and SF improves all the characteristics of the concrete. Additionally, the coupling effects of GP and STF are better than that of the SF and STF. Based on the synthetic consideration of the performance and cost, the combination of 10% GP and 1.5% STF is optimal in case of CSA mechanical performance.

에트린자이트 지연생성에 의한 고속철도 PSC 침목 콘크리트의 손상

제작 후 10년 이내의 PSC침목에서 맵균열(map-cracking)에 의한 조기손상이 관찰되고 있다. 이러한 경화된 콘크리트에서 발생한 균열의 원인 중 하나는 콘크리트 내부의 에트린자이트 지연생성(delayed ettringite formation, DEF)에 의한 이상팽창인 것으로 알려져 있다. DEF는 일반적으로 양생 시 콘크리트가 고온이력을 받고, 사용 중 수분에 노출된 경우 수년이 지나서 나타난다. 본 논문에서는 국내 고속선 PSC침목의 맵균열 원인을 조사하기 위해 손상 침목에서 시료를 채취하여 SEM/EDS 분석을 이용한 미세구조 특성과 침목 생산 공장 두 곳에서 콘크리트의 양생 온도이력을 직접 측정하여 분석하였다. 그 결과, 맵균열 손상 콘크리트의 시멘트 페이스트와 골재 경계부에서 다량의 에트린 자이트가 관찰되었으며, 양생 중 일부 침목 콘크리트의 온도가 70°C 이상으로 측정되었다. 이러한 결과는 국내 고속철도 침목의 맵균열 손상 원인 중 하나는 DEF에 의한 재료적 팽창이며, DEF의 발생 원인은 콘크리트 양생 중 고온 노출에 의한 것임을 뒷받침할 수 있을 것으로 판단된다.

A carbon footprint analysis of railway sleepers in the United Kingdom

This paper provides an assessment of the lifecycle Greenhouse Gas (GHG) emissions associated with the four most common sleeper (railroad tie or cross-tie in North America) types present in the UK rail network. It estimates the embodied material, process and transport emissions linked with the lifecycle activities of construction, relay/renewal and end-of-life of these variants at low and high traffic tonnage. The analysis suggests that at low traffic loads, the softwood sleepers perform the best over the whole simulated-period. At high traffic loads, the concrete sleepers outperform all other variants in terms of lifecycle CO2e emissions, followed by hardwood, softwood and steel. Regardless of the scenario examined, the steel sleepers perform the worst due to the carbon intensive nature of their manufacturing process. This performance gap is amplified at high traffic loads, as their service life is excessively compromised. The analysis reveals that the end-of-life pathway of timber is a critical determinant of its footprint. Results suggest that the impact of disposing of these sleepers results in their footprint being magnified. Nevertheless, if a minimum of 50% follows the combustion pathway with subsequent heat recuperation, then a GHG reduction potential of between 11% and 18% of their footprint is feasible. From a whole-lifecycle cost lens, for higher tonnage routes, the choice of concrete sleepers results in considerable financial savings. If the infrastructure manager was to install sleepers with stiff under sleeper pads (USPs), it may achieve additional economic and GHG savings, with potential for increasing the latter using recycled carbon-neutral USPs.

The influence of sleeper material characteristics on railway track behaviour: concrete vs composite sleeper

Composite sleepers and bearers formed of polymers and sometimes steel or fibre reinforcement are an alternative to traditionally used timber or prestressed concrete counterparts. Composite materials offer the combined benefits of the compliant sleeper/ballast contact of timber with the longer service life of concrete. However, composite and timber sleepers have lower bending stiffness compared with concrete, and this affects their track performance. To better understand the influence of sleeper material on performance, a concrete and a composite sleeper were tested in the Southampton Railway Testing Facility. Test results were interpreted with the aid of finite difference and discrete element method numerical modelling. It was found that composite sleepers can provide a more compliant sleeper/ballast interface with increased numbers of ballast grain contacts of larger area that attenuate the peak contact forces. However, owing to their lower bending stiffness, they have more exaggerated deflection profiles and a tendency to become centre-bound compared with stiffer prestressed concrete counterparts.

Ultra high performance concrete (UHPC) sleeper: Structural design and performance

Both structural and material performance of railway sleepers are critical to ensure the safety of railway track structures. In this study, for the first time, ultra high performance concrete (UHPC) is adopted to the post-tensioning type of sleeper to prolong design life and reduce the maintenance of sleepers. A structural design is carried out to fully utilize the material benefits of UHPC, including superior compressive strength and tensile ductility, and reviewed the critical sections of the sleeper based on strain compatibility analysis. Sixteen UHPC sleepers were fabricated using the developed UHPC mixture, incorporating coarser aggregates and ground granulated blast furnace slag, to perform structural verification tests according to the European standard, including bending strength tests under static, dynamic, and fatigue loading. The series of structural tests conducted on the UHPC sleepers show that the ductile characteristic of UHPC reinforced with steel fibers resulted in stable structural behavior and outstanding crack resistance capabilities even after the initial cracks developed. This experimental study may provide new insight into the structural applications of UHPC under railway loading conditions.

Effect of Incorporating Tire Rubber Waste on the Mechanical Behaviour of Railway Ballast Layer: Experimental and Modelling Studies

In order to delay the degradation of railway tracks, several techniques have been developed in recent years; the best known of which are: under sleeper pads, geogrid and the use of polymers as elastic elements between ballast particles. The objective of the research described in this paper is to evaluate the effectiveness of incorporating tire rubber waste into the ballast layer in reducing its settlement. For that purpose, a small-scale testing laboratory setup has been developed, which consists of a bi-block concrete sleeper surrounded by a layer of ballast. The developed apparatus is subjected, through the actuator of a servo-hydraulic machine, to a vertical cyclic force reproducing the passage of a train bogie. This study has been performed in two stages: the first is to identify a suitable existing model that well-describes the ballast settlement with cycle applications and the second is to study the influence of the variation of the percentages of addition of rubber on the behaviour of the ballast layer. Finally, a finite element model was developed to simulate the experimental setup. The results show that using 10% of tire waste rubber could decrease the track settlement and reduce the breakage of ballast particles.

Drying shrinkage of early-age concrete for twin-block slab track

Moisture and early-age mechanical properties in hydrating track slab present a significant risk for cracking. Based on the prediction model of concrete drying shrinkage and the moisture transport, a hygro-mechanical-chemical coupled model of twin-block slab track was developed by taking into account of dissimilar mechanical properties and humidity diffusion performance between prefabricated concrete twin-block sleepers, hardened concrete support layer and cast-in-place fresh track slab. The model can depict the cracks occurring at track slab such as the splayed cracks around sleepers, the gaps between sleeper and track slab and the irregular cracks inside the track slab. The numerical results show that: (1) The ambient drying condition will cause underestimated relative humidity gradient on the surface of the track slab, and the maximum relative humidity gradient can reach about 400%/m. (2) The embedded twin-block sleepers reduced the longitudinal continuity of the track slab around the twin-block sleepers. This results in greater displacement but smaller stress than other regions. (3) Splayed cracks may easily extend from the gap between twin-block sleepers and track slab within 2–3 days after initial setting of the track slabs for chemical shrinkage. (4) 14 days after pouring the track slab, the stress inside the track slab will increase to 8 MPa, and non-uniform drying shrinkage on the surface of track slab may be the primary cause for irregular cracks.

An Examination on Performance of Railway Sleepers

The main focus of railways is of all economies, transporting items, and passengers. The important role of sleepers is the performance of track and rail transport safety. In sleeper manufacturing, different kinds of materials (Timber, Concrete, and Steel) are utilized. The most widely used sleeper material is Hardwood Timber. The demand for sleepers will move on lots better side in time to come back due to the failures of the Sleepers. The production and maintenance cost of the sleeper is higher. This paper discusses the different failures of classic concrete, steel, and timber sleepers and the capacity of defensive action to minimize those failures. This paper comprehensively evaluates with the recommended solutions for the three typically used sleeper materials of its failure mechanisms. In order to make cost-effective sleeper, the waste materials from industries can be used as supplementary raw material with a purpose to result in enhancing the great for the environment as properly. For the approaching years, every production activity needs to focus on sustainable engineering and this study tries to present the alternative smart solution for the destiny infrastructure engineering region

Measurement of deformation of the concrete sleepers under different support conditions using non-contact laser speckle imaging sensor

Prestressed concrete sleepers play a significant role in distributing wheel loads from the rails to the ballast layer. Cyclic wheel loads may cause local deterioration of the ballast layer which would affect the support conditions beneath the sleepers. Therefore, understanding the influence of different support conditions on the deformation of sleepers is necessary for maintaining safe railroad operations. In this study, a non-contact and non-destructive laser speckle imaging sensor (LSIS) was developed and successfully applied to investigate the flexural behaviour of concrete sleepers under various support conditions, including “full support”, “partial support” and “centre binding”. The results show that LSIS was in agreement with foil strain gauges of achieving high-resolution strain measurements with a maximum mean absolute error of 5.41±3.12με (equivalent to a mean absolute error of 7.15%) as the detection threshold (20 με) is exceeded. More than three times change in the negative bending moment was observed at the mid-span of the sleeper as the support condition was changed from “full support” to “centre binding”, which indicates the potential risks of voided ballast support and importance of ballast tamping in railway maintenance.

Behaviour of Prestressed Monoblock Concrete Sleepers (PMCS) Subjected to Static Loading

In Malaysia, there have been many mode of transportation created to ease the movability of its people from one place to another in short period of time. One of them is rail transportation as it provides many services along the countries. Not only it can transport passengers, train services also transport goods everyday in large quantitties and allocate in short period of time. Many people fond of this transportation due to its low service charge but provides comfortable and safety riding experience whether in short or long destination. Due to high demand of train transportation, it is important to have their structural integrity remain in high quality to avoid any damage and accident occur in the future. One of the most important component in railway structures is Prestressed Concrete Sleeper (PCS). Therefore, it is important to investigate its load capacity and capabilities to avoid any high risk to occur not only to train and its cargo, but to the safety of the passengers as well. Prestressed Monoblock Concrete Sleeper (PMCS) mainly involved in this research paper due to its majority usage in Malaysia by KTMB and positive and negative moment test were chosen to investigate the design and ultimate load under static loading referring to Australian Standard (AS 1085.14 – 2012).

Validation of a dynamic wheel load factor and the influence of various track irregularities on the dynamic response of prestressed concrete sleepers

Prestressed concrete sleepers are generally designed taking into account the influence of the dynamic wheel load. In Japan, the dynamic wheel load factor of 2.0 has been typically used for the serviceability limit state since the 1950s. However, there are few examples that have proved its validity. In this study, field measurement tests and three-dimensional numerical analysis were conducted for prestressed concrete sleepers laid on a straight section of a railway track with continuously welded rails. According to the results of the field tests, the measured dynamic wheel load factor was less than the conventionally used dynamic wheel load factor of 2.0, and the bending moments exceeding the full prestress condition, i.e. the compressive stress on all sections, were generated in some cases. Furthermore, even with the prestressed concrete sleepers of the same type laid continuously, the bending moment was increased more than three times due to the support conditions of the prestressed concrete sleepers and the rail roughness. Results of the numerical analyses also revealed that the bending moment was increased more than two times because of the hanging (unsupported) sleepers, and the tensile stress of the prestressed concrete sleeper exceeded 3 N/mm2 when the rail roughness was approximately 2 mm or more. Based on this investigation, the validity of the dynamic wheel load factor of 2.0 was proved.

Improving the resistance of concrete for sleepers to the formation of delayed and secondary ettringite, the alkali-silica reaction, and electric corrosion

The paper reports results of examining the influence of modifier admixtures on the corrosion resistance of concrete for reinforced concrete sleepers based on the criteria of electric resistance, resistance to alkaline corrosion and corrosion due to the crystallization of delayed and secondary ettringite. This study was conducted within the framework of resolving the issue on premature destruction of reinforced-concrete sleepers caused by the progressing crack formation at the stage of heat treatment and subsequent operation. It has been established that the introduction of pozzolanic admixtures containing active Al 2 O 3 in their formulation to the composition of concrete for sleepers makes it possible to minimize the risk of corrosion predetermined by the reaction between aggregates’ silica and alkali and corrosion as a result of crystallization of delayed and secondary ettringite. The high efficiency of pozzolanic admixtures containing active Al 2 O 3 regarding the specified types of corrosion is due to binding alkali into the insoluble alkaline hydroalumosilicates, contributing to the compaction of the system with a decrease in the content of Na + /K + ions in the solution. A decrease in the content of alkali in the porous solution predetermines blocking the «alkali-silica reaction» and increasing the temperature of ettringite stability to higher values. This reduces the potential number of secondary ettringite forming cycles and the probability of delayed ettringite formation. The alternative mechanism of action of active Al 2 O 3 on pozzolan implies binding the SO 4 2– and Ca 2+ ions from a porous solution into low-sulfate forms of calcium hydro-sulfoaluminates, which excludes the crystallization of delayed and secondary ettringite. Reducing the consumption of cement and water through the use of admixtures-plasticizers makes it possible to increase the electrical resistivity of the modified concrete for sleepers above the level of a control composition without admixtures. The obtained results provide an opportunity to ensure the design durability of concrete in reinforced-concrete sleepers through their comprehensive modification by plasticizers and active mineral admixtures that contain active Al 2 O 3

Investigation of the Elastic Modulus of Polymer Sleepers Under a Quasistatic and Cyclic Loading

Abstract In ballasted track, the wheel load is transmitted to the subgrade via sleepers commonly made of impregnated wood, prestressed concrete, steel or recently developed polymer sleepers. Mentioned material types of sleepers are characterized by different elastic moduli being a key parameter in any numerical model. Hence, this paper aims to determine the elastic modulus of sleepers subjected to a laboratory four-point bending test. Traffic resembling load level of 60 kN adopted from a typical axle load distributed by the rails to the sleeper was applied in a quasistatic and cyclic loading. The samples included sleepers made of polymers complemented with wood and pre-stressed concrete. The results of this paper are based on the elastic modulus investigation. Main conclusions are focused on the sleeper’s elastic modulus under changing loading frequencies. Wood and prestressed concrete sleepers indicated mainly elastic behaviour resulting in a constant elastic modulus. However, polymer sleepers showed a loading frequency dependent elastic modulus as a result of their viscous elastic behaviour. Moreover, the conclusions of this paper involve E-modulus measurements of impregnated beech sleepers in order to describe their piece by piece elasticity variation due to their natural origin.

Estimation and test assessment of the rail pads effect on the indicators of dynamic impact of the rolling stock on the track in the joint area

Increasing axial loads including the development of heavy movement on Russian railroads network require the best solutions for improvement of the railway track structure. Research by Russian and international scientists indicates that rail elastic pads reduce vibrations transferred from reinforced concrete sleepers to crashed stone, including the joint area. This study examines possibilities of using rail pads for reducing the dynamic effects of the rolling stock on the track in the joint area. Assessment of the rail pads construction material shock-absorbing properties was conducted considering the elastic properties of the rail support with static and dynamic loads. Results of mode ling the elastic properties of the rail support with rail pads of different rigidities using the software complex “Universal mechanism” are presented. The results were used as basis for calculation of indicators of dynamic interaction of the track and rolling stock at the joint using the coeffi cient establishing the link between bendings of the solid rail and the rail with joint. The expediency of using rail pads at the place of the joint is justifi ed based on assessment of the results.This study reveals that elastic rail pads based on isoprene rubbers are suitable for track structures that improve indicators of the track and rolling stock interaction. When using rubber pads, the growth of accelerations on the sleeper is less dependent on the speed, causing the track stability to increase. The results are supported by tests consistent with calculations and justify the necessity for further studies in this fi eld.

Investigation on the behaviour of prestressed concrete sleepers (PCS) under negative static loading

Railways in Malaysia are undoubtedly a various incorporated element that can possibly assume as an imperative part in the advancement of a manageable transportation framework in the nation. Therefore, failure of prestressed concrete sleepers under the negative static loading need to be investigate due to its role as one of the important part in railway. In this study, negative moment test was established to investigate the design load of the prestressed concrete sleeper (PCS) under negative static loading. Three (3) samples of PCS were used and one (1) PCS contains two rail seat, called KTMB and EPMI sides. It is found that new crack appeared on EPMI sides with the length of 100 millimeters. Meanwhile, the highest displacement for EPMI and KTMB sides were found to be 7.332 and 6.606 millimeters. From three (3) samples tested, only one PCS shows the failure to cater the design load of 176.94 kN subjected to rail seat.