Dynamic properties of early-age micro- and nanoengineered concrete for compliant railway structures

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1 Massachusetts Institute of Technology From the SelectedWorks of Sakdirat Kaewunruen December 14, 2015 Dynamic properties of early-age micro- and nanoengineered concrete for compliant railway structures Ratthaphong Meesit, University of Birmingham, UK Sakdirat Kaewunruen Paramita Mondal, The University of Illinois at Urbana-Champaign Available at:

2 Dynamic properties of early-age micro- and nanoengineered concrete for compliant railway structures Ratthaphong Meesit 1, Sakdirat Kaewunruen 2 and Paramita Mondal 3 1 School of Civil Engineering, University of Birmingham, Birmingham, UK, RXM496@student.bham.ac.uk 2 Birmingham Center for Railway Research and Education, University of Birmingham, Birmingham, UK, s.kaewunruen@bham.ac.uk 3 Department of Civil and Environmental Engineering, the University of Illinois at Urbana-Champaign, Newmark Civil Engineering Laboratory, Urbana IL, USA, pmondal@illinois.edu Cementitious materials modified by micro- and nano-engineered crumb rubber particles are robust and resilient materials capable of mitigating large-strain and large-amplitude vibrations in a dynamic compliant structure such as in railway traffic environments under heavy freight or high speed rail operation. The improvement of fundamental dynamic properties encourages the applications of engineered concrete to railway and civil constructions. Such the improvement has significant potential to mitigate pressing issues in modern railway industry such as rail seat abrasion and impact damages in concrete sleepers, thermal expansion crack of track slabs, and so on. Also indirectly, the utilisation of crumb rubber will enhance the recycling options of rubber tire wastes, which are not biodegradable. This will improve railway construction and maintenance to be more environmental friendly. In principle, the dynamic modal parameters and responses of compliant railway structures depend largely on the intrinsic material properties. This paper therefore investigates the dynamic properties of the early-age micro- and nano-engineered concrete using vibration responses of the materials to dynamic impact excitation. Experimental modal analysis has been used to evaluate the modal parameter changes of the concrete materials in the frequency band between 0 and 500 Hz. The concrete samples have then been subjected to ultimate static loading to evaluate their early-age compressive strengths. Dynamic modal parameters of three types of the novel concrete materials have been investigated. The comparative study to evaluate the effect of crumb rubber participles highlights meaningful changes in fundamental engineering properties, frequency response functions, dominant frequencies and associated modal damping coefficients. This fundamental insight will establish a novel material application guideline for rail track engineers and managers for maintenance and construction of railway tracks and their components. Corresponding author: Dr Sakdirat Kaewunruen - 1 -

3 Dynamic properties of early-age micro- and nano-engineered concrete for compliant railway structures Ratthaphong Meesit 1, Sakdirat Kaewunruen 2 and Paramita Mondal 3 1 Birmingham Center for Railway Research and Education, School of Civil Engineering, the University of Birmingham, Birmingham, UK, RXM496@student.bham.ac.uk 2 Birmingham Center for Railway Research and Education, School of Civil Engineering, the University of Birmingham, Birmingham, UK, s.kaewunruen@bham.ac.uk 3 Newmark Civil Engineering Laboratory, Department of Civil and Environmental Engineering, the University of Illinois and Urbana-Champaign, Urbana IL, USA, pmondal@illinois.edu ABSTRACT: Cementitious materials modified by micro- and nano-engineered crumb rubber particles are robust and resilient materials capable of mitigating large-strain and large-amplitude vibrations in a dynamic compliant structure such as in railway traffic environments under heavy freight or high speed rail operation. The improvement of fundamental dynamic properties encourages the applications of engineered concrete to railway and civil constructions. Such the improvement has significant potential to mitigate pressing issues in modern railway industry such as railseat abrasion and impact damages in concrete sleepers, thermal expansion crack of track slabs, and so on. Also indirectly, the utilisation of crumb rubber will enhance the recycling options of rubber tire wastes, which are not biodegradable. This will improve railway construction and maintenance to be more environmental friendly. In principle, the dynamic modal parameters and responses of compliant railway structures depend largely on the intrinsic material properties. This paper therefore investigates the dynamic properties of the early-age micro- and nano-engineered concrete using vibration responses of the materials to dynamic impact excitation. Experimental modal analysis has been used to evaluate the modal parameter changes of the concrete materials in the frequency band between 0 and 500 Hz. The concrete samples have then been subjected to ultimate static loading to evaluate their early-age compressive strengths. Dynamic modal parameters of three types of the novel concrete materials have been investigated. The comparative study to evaluate the effect of crumb rubber participles highlights meaningful changes in fundamental engineering properties, frequency response functions, dominant frequencies and associated modal damping coefficients. This fundamental insight will establish a novel material application guideline for rail track engineers and managers for maintenance and construction of railway tracks and their components. 1 INTRODUCTION The increased congestion of road and highway traffics and the current energy resources shortage in developed and developing countries around the world has posed the shift of transportation modes to railways for more sustainability and resilience. For example, over GBP50 billion is being invested in a new high speed rail line between London and Birmingham in the UK to improve transport sustainability. Over 90 million Euro has set up to promote work to shift - 2 -

4 freights and mass transits to rails. This has evidently increased the demand for heavier and faster trains, often at the expense of increased maintenance cost. Under heavy cycle train loads, the ballast deteriorates progressively, sometimes leading to formation of voids and pockets between sleepers and ballast. Effect of imperfect contact between railway sleepers (railroad ties) and ballast formation has not been investigated in detail so far, even though the interaction between sleeper and ballast plays an important role in railway track system dynamics. In a poorcondition track, large voids and pockets can easily be observed between sleepers and the underneath ballast, usually caused by the wet beds (highly-moist ground) from natural water springs or poor drainage (Fig. 1 [1]), while undetectable voids could also happen in the goodcondition tracks. Since a sleeper cracks typically as a result of vibration at its resonant frequencies, it is important to mitigate such the effect of various sleeper/ballast contact patterns at the resonant vibrations of the in-situ railway concrete sleeper. Several studies have shown that the resonant vibrations of sleepers could affect not only the sleepers themselves, but also the wheel rail interaction forces [2-4]. Dahlberg and Nielsen used an analytical model capable of analyzing the dynamic behaviour of concrete sleepers in both free-free and in-situ conditions [5]. Grassie [6] developed a two-dimensional dynamic model to perform vibration analysis of concrete sleepers in free-free conditions that was calibrated using experimental data. Many studies have shown that improvement of vibration damping mechanisms of materials is required to sustain the lives of track components and then the railway systems [5-12]. Based on the extensive literature search, very little knowledge is available on the dynamic properties of early age concrete, although these fundamental properties are the key critical criteria to design structural components in railway structure. rail rail pad rail rail pad sleeper ballast bed subgrade Figure 1. Railway tracks Environmental friendly structural concrete using recycle wasted tires, rubber and synthetics in structural concrete as either aggregate or filler have faced a number of challenges over the decade. The crumbed rubber concrete (CRC) was initially developed for low-profile nonstructural elements such as pedestrian pathway, acoustic wall panel, and furniture due to its low strength. It is reported that many have had serious issues of using aggregate crumb rubbers because they improve resiliency but scarify strength [13-14]. This means that certain structural applications are restricted. In contrast, a few research have shown that smaller size of crumb rubber can act as a filler and can maintain its strength while enhance the material resiliency. On this ground, there is clearly a need to carry out an experimental study to investigate influences on the engineering properties and dynamic resistance of the crumb rubber concrete. By means of experimental studies, it is possible to better understand the static and dynamic behaviour of the micro- and nano-engineered concrete associated with the crumb rubber particles. This study is the first to investigate the dynamic properties of high-strength crumb rubber concrete aimed for railway applications. The emphasis of this paper is placed on the early age of engineered concrete because such properties are essential in precast and prestressed concrete design

5 2 MATERIALS In this study, the materials used to make concrete specimens consisted of ordinary Portland cement type I with characteristic strength of 52.5 MPa. (Accordance with BS EN 197-1), clean water, crush gravel with maximum size of 10 mm (Coarse aggregate), sand with maximum size of 5 mm (Fine aggregate), undensified microsilica and crumb rubber with particle size of 75 Micron (Figure 2). Figure Micro crumb rubber 3 CONCRETE DESIGN 3.1 Mix Design Three concrete mixes were designed based on method explained in the Design of Normal Concrete Mixes [15]. For the reference concrete, it was designed by using water-cement of 0.44 in order to achieve a target mean strength of 63 MPa at 28 days (RFC). The second mix is the reference concrete which 10 weight percent (wt%) of cement was replaced by microsilica (CMS10). The last mix is a crumb rubber concrete which is modified from second mix by replacing 5 wt% fine aggregate with 75 micro rubber powder (CMSR10-5). All of mixture portions are presented in Table 1. Table 1. Mixture proportions of concrete No. Mixes Cement Water Gravel Sand Microsilica Rubber 1. RFC CMS CMSR Remark: The unit of all materials is in kg/m Concrete Specimens After designing stage, the concrete specimens of each mix were produced. The shapes and dimensions were 100 mm cube and 45 x 20 x 120 mm prism (Figure 3). These samples were used for the compressive strength and vibration testing respectively

6 Compressive Strength (MPa) (a) Figure 3. Shapes and dimensions of specimen (a: 100 mm cube and b: 45 x 20 x 120 mm prism) 4 RESULTS AND DISCUSSION 4.1 Compressive Strength The 7 days compressive strength of concrete was tested according to BS EN Before testing, the concrete specimens were cleaned and dried. Then, each sample was placed into the compression testing machine, and the constant loading rate of 0.7 MPa/s was applied to the sample until it failed. The last loading shown in the monitor was recorded as a compressive strength of the sample. From the results shown in Figure 4, it can be illustrated that replacing 10% of cement with microsilica can improve the compressive strength of the concrete by 16.9%. However, for the CMSR10-5 which contains both microsilica and 75-micro crumb rubber, the compressive strength significantly reduced by approximately 13.3 and 25.9% compared to RFC and CMS-10 respectively. (b) RFC CMS-10 CMSR10-5 Figure 4. 7-days compressive strength of all mixes 4.2 Damping Property of Concrete The damping property can be defined as phenomena which causes loss of vibration energy in material [16]. In this study, the damping ratio of each concrete mix was measured according to vibration theory. As shown in Figure 5, the 45 x 20 x 120 mm prism was clamped to the stable support. Then, the accelerometer was mounted at end of the concrete sample. After that the PCB impact hammer was used to excite vibrations in the sample over the frequency range 0 to 1,

7 Hz, and the 5-time average vibration responses represented by the FRFs and natural frequency were obtained using the PROSIG system. a) Test setup Tra nsfe r Function 10 0 Ine rtance [g /N] P ha se [ ] F re q ue n cy [Hz] b) Frequency responses and phase differences of RFC Figure 5. Vibration testing for concrete At the next stage of the experiment, the vibration signal obtained from the experiment was analysed (Figure 6). Then amplitudes of the signal was plotted, and the amplitude response will be followed Equation 1 below [16]. A = A 0e -ζѡt (1) where A is an amplitude which can be displacement, velocity or acceleration, A 0 is peak amplitude, ζ is damping ratio, ѡ is natural frequency (rad/s) which is equal to 2πf n (f n is natural frequency, Hz), and t is time (second). In addition, the damping ratio can be calculated from basic logarithmic decrement function [16] as presented in Equation 2 and 3. δ = 1 n ln A 0 A n (2) - 6 -

8 Damping Ratio Acceleration (g) and ζ = 1 1+( 2π δ )2 δ 2π (3) where δ is damping coefficient, A 0 is initial amplitude, A n is amplitude after passing n number of cycles and ζ is a damping ratio A = A 0 e -ζѡt = 51.18e t Time (s) Figure 6. Example of the vibration pattern obtained from RFC As results, the CMSR10-5 seems to have the highest damping ratio compared to RFC and CMS10 (Figure 7). The damping ratio increased dramatically when the microsilica and micro crumb rubber were added into the concrete. This is because 1) microsilica particles and cement matrix create the large interface are which can dissipate the vibration energy [17], and 2) the micro crumb rubber can help the concrete dissipate the vibration energy [13] Graph Formula RFC CMS10 CMSR10-5 Figure 7. Damping ratio of each concrete mix 5 CONCLUSIONS Large-strain and large-amplitude vibrations in a dynamic compliant structure such as in railway traffic environments under heavy freight or high speed rail operation prompt the need to reinvent a novel material that is strong, durable, resilient and tough. Among the desirable characteristics, a property might compromise the other. Cementitious materials modified by micro- and nano-engineered crumb rubber particles are found to be capable of mitigating such demanding problems within railway sectors in the 21 st century. Such problems as railseat abrasion and impact damages in concrete sleepers can lead to train derailments as they undermine the ability to secure rail gauge. Thermal expansion crack of track slabs can lead to - 7 -

9 the downtime (i.e. speed reduction) of high speed trains in the curved section of high speed line. Modification of concrete materials to improve the dynamic properties will increase the adoption and application in construction and maintenance of passenger, freight and high-speed railway networks all around the world. The utilisation of crumb rubber will also enhance the recycling options of non-biodegradable rubber tire wastes, and eventually promote environmental friendly and green rail infrastructures. The structural design of compliant railway structures is governed dominantly by the intrinsic material properties. This paper therefore investigates the dynamic properties of the early-age micro- and nano-engineered concrete using vibration responses of the materials to dynamic impact excitation. The concrete samples have been developed in accordance with British Standard and later subjected to ultimate static loading to evaluate their early-age compressive strengths. Experimental modal analysis in a frequency band between 0 and 500 Hz yields dynamic modal properties for three concrete material types. The comparative study to evaluate the effect of crumb rubber participles highlights meaningful changes in dynamic damping coefficients without scarifying the strength needed for serviceability and ultimate limit states design. It is found that the damping characteristic can be improved by more than 45% based on the standard control concrete. This fundamental insight will encourage a novel material application guideline for rail track engineers and managers in maintenance and construction of railway tracks and their components. 6 ACKNOWLEDGEMENT The author would like to gratefully acknowledge the University of Birmingham s BRIDGE Grant, which financially supports this work as part of the project Improving damping and dynamic resistance in concrete through micro- and nano-engineering for sustainable and environmental-friendly applications in railway and other civil construction. This project is part of a collaborative BRIDGE program between the University of Birmingham and the University of Illinois at Urbana Champaign. The micro crumb rubber powder was kindly provided by Lehigh Technologies Company. The authors would also like to thank David Cope for their assistance during the course of this project and wishes to thank Royal Thai Government for the scholarship to read his masters degree at the University of Birmingham. 7 REFERENCES [1] Grassie, S.L. and Cox, S.J. The dynamic response of railway track with unsupported sleepers. Proc Instn Mech Engrs, Part D, 1985, 199(2), [2] Clark, R.A., Dean, P.A., Elkins, J.A., and Newton, S.G. An investigation into the dynamic effects of railway vehicles running on corrugated rails. J of Mech Engr Sci, 1982, 24, [3] Grassie, S.L. and Cox, S.J. The dynamic response of railway track with flexible sleepers to high frequency vertical excitation. Procs Instn Mech Engrs, Part D, 1984, 198, [4] Knothe, K. and Grassie, S.L. Modelling of railway track and vehicle/track interaction at high frequencies. Vehicle System Dynamics, 1993, 22, [5] Dahlberg, T. and Nielsen, J. Dynamic behaviour of free-free and in-situ concrete railway sleepers, Procs Int Symp on Precast Concrete Railway Sleepers, Madrid, Spain, [6] Grassie, S.L. Dynamic modelling of concrete railway sleepers. J of Sound Vib, 1995, 187, [7] Kaewunruen, S. and Remennikov, A.M. Applications of experimental modal testing for estimating dynamic properties of structural components. Procs of Australian Structural Engineering Conference 2005, New Castle, Australia, 2005, [CD Rom] [8] Kaewunruen S. and Remennikov A.M. Sensitivity analysis of free vibration characteristics of an insitu railway concrete sleeper to variations of rail pad parameters. J. Sound Vib. 2006, 298, [9] Kaewunruen S. Monitoring structural deterioration of railway turnout systems via dynamic wheel/rail interaction. Case Studies in Nondestructive Testing and Evaluation, 2014, 1(1), [10] Kaewunruen S. Effectiveness of using elastomeric pads to mitigate impact vibration at an urban turnout crossing. Noise and Vibration Mitigation for Rail Transportation Systems, 2012, 118, pp

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