BEHAVIOR OF SBR-LATEX MODIFIED POLYPROPYLENE FIBRE REINFORCED PSC RAILWAY SLEEPERS UNDER STATIC LOADING

G R Harish, University of Visvesvaraya and Bangalore University, India S A K Zai*, University of Visvesvaraya and Bangalore University, India

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35th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 25 – 27 August 2010, Singapore

BEHAVIOR OF SBR-LATEX MODIFIED POLYPROPYLENE FIBRE REINFORCED PSC RAILWAY SLEEPERS UNDER STATIC LOADING

G R Harish, University of Visvesvaraya and Bangalore University, India S A K Zai*, University of Visvesvaraya and Bangalore University, India N Munnirudrappa, Dayanand Sagar College of Engineering, India

Abstract This paper presents an experimental study on the behaviour of SBR-latex modified

polypropylene fibre reinforced prestressed concrete railway sleeper under static

loading and also nonlinear analytical study by finite element method using ANSYS-

10.0. Material nonlinearity has been considered for different concrete mixes and

prestressing wires, using solid 65 and link 8 elements respectively. The prestressed

concrete sleeper is an imperative component of ballasted railway tracks. Its main

function is to distribute axle loads on rails to the soil beneath. The prestressed

concrete sleeper is subjected to sagging moment at the rail seat section and hogging

moment at the mid section. The emphasis of this paper is on ductility aspect of new

advanced materials over conventional material used in the manufacture of railway

prestressed concrete sleepers. The test specimens are casted in sleeper factory at

Birur, Karnataka, India, in accordance with Indian Railway Standards (IRST-39-

1985). The PSC sleepers are tested under two-point static loading. From the

experimental study, first crack load, load - deflection behavior upto first crack load,

ductility factor, energy absorption capacity and toughness index upto first crack load

are observed.

Keywords: Railway pre-stressed concrete sleepers, static loading, ductility factor, energy absorption capacity, toughness index and R.D.S.O I. INTRODUCTION

A. Concrete Sleepers Railway tracks are being designed to resist heavy wagon loads and impact loads and hence need to possess high resilience to moment and impact. Usually, ballasted railway track which consists of rails, ballast formation and fastening system is widely constructed for transportation [4]. The railway sleepers are importantly functioned to: - Uniformly transfer and distribute loads from the rail to underlying ballast bed. - Sustain and retain the rails at the proper gauge by keeping anchorage for the rail fastening system;

-preserve rail inclination; - Provide support for rail; -restrain longitudinal, lateral and vertical rail movements by embedding itself onto substructures (see Fig.1). It is clear that the sleeper has a major. role in distributing axle loads to formation below. The axle loads could be considered static or quasi-static when the speeds of trains are quite moderate. However, in general, the axle loading tends to physically behave like the dynamic impact pulses due to the continual moving ride over track irregularities and higher speeds of trains.

Fig.1 Components of Railway tracks

B. Behaviour of Sleepers Although the dynamic effects have evidently prevailed over the failures of railway concrete sleepers, most of the design criteria are on the basis of the static sectional capacity of the concrete sleepers. Theoretical concepts of strength, ductility, stability and fracture mechanics refer to static behaviour of prestressed concrete sleepers. By nature, the concrete sleeper is subjected to sagging moment at the railseat zone and hogging moment at the middle section.

C. Research Significance Strength and ductility are the two major important factors to be considered in the design of structures subjected to static and impact loads, hence many attempts have been made in the recent past to develop a new material, which exhibits higher strength and ductility than the conventional concrete. It has been understood from the literature that many of the engineering properties such as tensile strength, compressive strength, flexural strength, fracture toughness, energy absorption capacity, etc of the conventional concrete could be improved by the addition of fibers. Similarly incorporation of polymers into concrete has also been attempted for the combined effect of fibers and polymer on the strength and ductility of concrete. Considering this existing knowledge, an attempt has been made to study the combined effect of polymers and fibers on flexural behaviour of Pretensioned Prestressed concrete (PSC) sleeper. The polymer considered in this study is Styrene Butadiene Rubber (SBR) Latex. The main aim of present study is for a detailed experimental investigation of conventional Pre-Tensioned PSC sleeper and modified PSC sleepers with advanced construction materials such as SBR-latex, polypropylene fibres, silica fume and new generation superplasticizer, for enhanced structural properties, ductility and durability aspects, so that introduction of such composite material in the field of sleeper manufacturing industries will benefit in increased life span and loading carrying capacity of PSC sleepers with quality production. II EXPERIMENTAL PROGRAMS Experimental setups were carried out complying with Indian Railway Standards: IRS-T-39-1985 for Pretensioned Prestressed concrete sleepers. A. Materials used - Special grade 53-S cement (As per IRST-39). - Coarse aggregate with fraction 52%:23%. - Natural river sand (Confirm to Zone-I). - Water. - Silica Fume (Microsilica 920-D). - Superplasticizer (Glenium ACE-30). - SBR-latex. - Polypropylene Fibres. - High Tensile Wires.

B. Mix proportions The M-60 grade concrete is designed by Entroy and Shacklock’s Empirical Graphs. The mix proportions obtained are 1:0.92:2.65:0.31. Then the modified M-60 grade concrete is achieved by adding 10% of SBR-latex, 0.25% of polypropylene fibres, 10% of silica fume and 0.6% of superplasticizer by weight of the binder. Finally the mix proportions for modified M-60 grade concrete is 1:1.02:2.94:0.28. C. Test Specimens The nine standard size sleepers (3/SS, 3/MS-1 &3/MS-2) are casted with trapezoidal cross section at railseat of 150mm X 250mm X 210mm and at the centre 150mm X 220mm X 180mm with a span of 2750 mm, at Malu Sleepers. Pvt. Ltd, Karnataka, India. D. Static Bending Test for Sleepers Tests were conducted as per IRS: T-39-1985 (Third Revision-May-1996). The arrangement is shown in Fig.2. The sleepers are tested under different supports conditions such as centre top, centre bottom and railseat bottom. The PSC sleepers were tested under two point loading. All PSC sleepers were tested in the loading frame of capacity 500 KN with gradual increment of load at the rate of 30 to 40 KN per minute up to the first crack load.

Fig.2 The Arrangement of Static bending test on Sleeper. III. EXPERIMENTAL RESULTS A. Load- deflection behavior of Sleepers

Fig.3 Load versus Deflection Curves Fig. 3 shows the first crack loads of sleepers, it varies from 100KN to 130 KN. The deflection corresponding to first crack loads are 0.26mm, 0.6mm and 1.7mm for M-55, M-60 and modified M-60 grade concrete sleepers respectively.

B. Static Bending Strength of Sleepers Table - 1 Static Bending strength values

Sleeper Designation

Centre Top

Rail Seat Bottom

Moment of

Resistance

Moment at Failure

SS(M55) 100 335 435

MS-1(M60) 110 350 >500

MS-2(M60+SBR+Fibre) 130 382 >500

As per RDSO 60 220 370

The static bending test results values are shown in Table-1. There is a 30% increase in load carrying capacity in centre top condition, 14% increase in moment of resistance and more than 35% for moment at failure, in rail seat bottom condition for modified M-60 concrete sleepers, as against the specified values of the same for standard sleepers of RDSO (Research Design and Standard Organization-ISO 9001) acceptance criteria. C. Ductility Factor Ductility factor defined as ratio of ultimate deflection to first yield deflection. Table-2 Ductility Factor values

Sleeper Designation Ductility Factor

SS(M55) 2.5

MS-1(M60) 4.6

MS-2(M60+SBR+Fibre) 7.3

From Table-2, it can be seen from the values of ductility factors, computed from the load-deflection curve upto first crack load, that the ductility of the modified M-60 grade concrete has appreciated immensely, justifying high ductility as compared to the standard sleepers. D. Energy Absorption Capacity In general, the term “Energy absorption capacity” of given material could be obtained only from the load versus deflection curve of the specimen. Energy absorption capacity is obtained from area under the curve up to first crack load. Table-3 Energy Absorption Capacity values

Sleeper Designation Energy absorption capacity in kN-mm

SS(M55) 1.68

MS-1(M60) 4.55

MS-2(M60+SBR+Fibre) 16.01

From Table-3, it can be seen from the energy absorption values, computed from the load-deflection curve upto first crack load, that the energy absorption capability of the modified M-60 grade concrete has appreciated immensely, justifying high malleability, as compared to the standard sleepers.

E. Toughness Index Toughness index is defined as area under curve up to first crack load divided by area under curve up to yield point. Table-4 Toughness Index values

Sleeper Designation Toughness index

SS(M55) 2.5

MS-1(M60) 3.5

MS-2(M60+SBR+Fibre) 23.03

From Table-4, it can be seen from the values of toughness index, computed from the load-deflection curve upto first crack load, that the toughness of the modified M-60 grade concrete has appreciated immensely, justifying high resistance to impact loads as compared to the standard sleepers. IV. FINITE ELEMENT MODELS OF PSC SLEEPER under CENTER TOP & CENTER BOTTOM boundary condition A three-dimensional model of a typical railway prestressed concrete sleeper of standard dimensions recommended by RDSO, INDIA, with loads & boundary condition was developed for the finite element analyses by ANSYS 10 as illustrated in fig 4 and fig 5.The solid bricks(SOLID 65) represent the concrete and the embedded three dimensional spar elements(LINK 8) represents the prestressing wire. The pretensioning was modeled using an initial strain in the tendons corresponding to the prestressing forces at the final stage.

Fig 4 finite element model of the p.s.c railway sleeper with pre-stressing strands.

Fig 5 finite element model of the p.s.c railway sleeper with meshing.

Fig 6 Load vs Deflection behaviour up to first crack load for combination of all the mixes used in sleeper specimen, obtained from FEM analysis.

V CONCLUSIONS The experimental programme deals with the study of static bending strength, electrical resistance test, load deflection behaviour, energy absorption capacity and toughness index. Some conclusions are given below. 1. Load carrying capacity 30% more than the control specimen. 2. The electrical resistivity is good for the all the test specimens tested. 3. It is experimentally evident that from results obtained for static bending test, load carrying capacity, ductility factor, energy absorption capacity and toughness index for the material chosen in present study is more than conventional material used in control specimen. 4. The static behaviour of PSC sleeper can be increased by using higher toughness and higher fracture capacity, which can be achieved by addition of fibre and SBR- latex to concrete matrix. VI. REFERENCES

A.G.Madhava Rao, V.S.Parameswaran and E.Abdul Karim, “Experimental Investigation on Pre-

Stressed Railway Sleepers”, International symposium on PSC pipes, pressure & sleeper, PP SL/3.

Dr.Amlan.k.Sengupta & Prof. Devdas Menon, “Pre-stressed concrete structures”, IIT-Madras

Dr. Sadath Ali Khan Zai, “Impact Behaviour of Steel Fibre Reinforced High Strength Concrete

Beams”, Ph.D report, Bangalore University, U.V.C.E, November -2006.

Indian Railway Standard: T-39-85 Third Revision Indian railway Standard specification for Pre-

tensioned prestressed concrete sleepers for Broad gauge and Meter gauge.

Sakdirat Kaewunruen and Dr.Alex. M.Remennikov, “Rotational Capacity of Railway Prestressed

Concrete Sleeper under Static Hogging Moment”, University of Wollongong, Year 2006, PP 399-404.

Sakdirat Kaewunruen and Dr.Alex.M.Remennikov, “Post-failure mechanism and residual load-carrying

capacity of railway pre-stressed concrete sleeper under hogging moment”, University of Wollongong,

Year 2006, PP 331-336. SIS: 1343 -1980 Practice for Prestressed concrete