A REPORT ON

DESIGN, FABRICATION AND TESTING OF AN ACCELERATED PAVEMENT TESTING INSTRUMENT BY

PRASHANT V RAM

2001B2A2649

P LAXMIKANTH

2001B5A2670

Under the guidance of Dr. V.R.Vinayaka Rao Thesis Submitted in partial fulfillment of the Requirements of the Course BITS C422T First Degree Thesis

ACKNOWLEDGEMENTS We would like to thank Dr. A.K.Sarkar, Dean Instruction Division for having given us an opportunity to work on this project and also provide us with complete funding to carry out our work. We are grateful to Dr. V. R. Vinayaka Rao for his invaluable support and guidance throughout the course of this project. We would like to acknowledge the help extended by Mr. Banwari Lal, Mr., Sharma, Mr. Raju, Mr., Yugendhar, Mr. Mahendar, Mr. Ramesh Das and all the other people in the workshop who helped us immensely in the fabrication of the instrument.

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ABSTRACT

Failures in multilayered flexible pavements structures are usually characterized by either rutting or fatigue cracking. Rutting, which is shown as a permanent deformation on the top of the riding layer is a result of plastic strains cumulated by all the individual component layers over a period of time. In addition, the shear induced by moving wheel loads along the wheel path will also contribute to the rutting. Though, the rutting is being contributed by all the individual component layers including the subgrade, majority of the rutting takes place due to the deficiencies in the riding surface layer. It is necessary to establish the rutting resistance capability of a design mix before it is being placed in the field. Several instruments have been developed to perform this function; however, they are quite expensive. It is with this background that the present study has been undertaken to develop an instrument with additional features involving temperature control of the sample being tested and also the frequency of loading application.

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TABLE OF CONTENTS Acknowledgements

i

Abstract

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1. Introduction 1.1 Background 1.2 Need for Present Study 1.3 Study Background

1 1 1 2

1.4 Scope of the study

2

1.5 Report Organization

2

2.Review of Literature

4

2.1 Introduction

4

2.2 Review of Accelerated Testing Facilities

4

2.2.1 VERTEK’S Accelerated Pavement Testing Machine

5

2.2.1.1 VERTEK’S APTM Features

5

2.2.2 Danish Road Testing Machine 2.3 Permanent Deformation Characteristics of Multilayered Flexible Pavements 2.3.1 Mechanisms of Development of Deformations in Flexible Pavements

6 9 10

2.3.2 Analytical Models available for Understating Flexible Deformations

10

2.3.2.1 The Wire Model

12

2.3.2.2 The Straight Edge Model

13

2.4 Factors Influencing Rutting

14

2.4.1 Effect of Moisture

14

2.4.2 Effect of Traffic

14

2.5 Effect of Temperature

15

2.6 Summary

15

3. Study Methodology

16

3.1 Introduction 3.2 Methodology for development of Accelerated Pavement Testing Facility

16

3.3 Methodology for calibrating and testing the Instrument

18

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4. Design and Fabrication of Accelerated Pavement Testing Instrument

20

4.1 Introduction

20

4.2 Design Details

20

4.2.1 Worm Wheel

20

4.2.2 Worm Screw

22

4.2.3 Motor

23

4.2.4 Bearing/Housing for Main Shaft

23

4.2.5 Coupling

24

4.2.6 Bearings / Housings for Vertical Shaft

24

4.2.7 Axles / Loading

25

4.3 Summary

27

5. Calibration and Testing of Accelerated Pavement Testing Unit

28

5.1 Introduction

28

5.2 Preparation of Pavement Cross Section for Testing

28

5.2.1 Preparation of subgrade

28

5.2.2 Preparation of Granular Sub-base Layer

29

5.2.3 Preparation of Bituminous Macadam

31

6. Summary and Conclusions

34

6.1 Introduction

34

6.2 Summary

34

6.3 Conclusions and Contributions

35

6.4 Scope for further improvement

35

Appendix A – Maintenance of the instrument

vi

References

vii

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1. INTRODUCTION 1.1 Background Major failure criteria usually observed in a multilayer flexible pavement is rutting. It is necessary to establish the rutting resistance capability of a design mix before it is being placed in the field. Several instruments have been developed to perform this function; however, they are quite expensive. It is with this background that the present study has been undertaken to develop an instrument with additional features involving temperature control of the sample being tested and also the frequency of loading application. 1.2 Need for the Present Study To determine the rutting, field based as well as analytical techniques have been developed by researchers all over the world. The techniques which are based on analytical modeling require accurate information regarding the individual material properties used in different layers. However, these methods are not very accurate as it is highly improbable to incorporate the material properties with the desired levels of accuracy and as a result, they suffer from inaccurate rut estimation. Hence, a number of instruments have been developed to tackle this issue of measuring the rut depth in both field and laboratory situations. On one hand, simple instruments like Straight Edge etc. are quite effective in estimating the rut depth in the field. However, on the other hand, rut measurement for the laboratory based pavement test tracks has been a challenging activity since it is required to simulate the loading and atmospheric variations of the field. As such, it is always a pre-requisite to test the efficacy of any innovation with respect to methods and materials with the small scale laboratory based simulation studies before being accepted for field application. It is with this background, that the present research activity has been taken up with the primary

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objective of developing an instrumentation which is both efficient as well as cost effective. 1.3 Study Objectives The primary objective of this research project was to investigate the relative contributions of the layers to rutting in multilayered pavements in the laboratory subjected to limited small scale accelerated testing. Based upon the performance of different mixes for the riding surface under accelerated testing, the best mix for a specific place can be suggested. . 1.4 Scope of the Study The scope of this study is confined to a limited small scale accelerated testing of multilayered flexible pavements. The developed instrument incorporates the capability to simulate different tyre pressures and varying traffic frequencies. The instrument also includes the simulation of rainfall and heat over the pavement surface. However, the size of the pavement that can be tested is restricted to a 1 metre diameter circular test track.

1.5 Report Organization The first chapter dealt with the need for the present study, study objectives and the scope of study. The second chapter will include a detailed literature survey which discusses the different accelerated pavement testing instruments developed all over the world. It will also give an insight into the permanent deformation characteristics of multilayered flexible pavements, mechanism of rutting, analytical tools for understanding rutting and the effects of temperature and loading frequency on flexible pavement performance.

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The third chapter will discuss the study methodology for the design and calibration of the accelerated pavement testing instrument. Chapter 4 will give the detailed design details of the accelerated pavement testing instrument which has been developed for the present study. The fifth chapter includes a detailed account of the calibration and testing of the instrument. It discusses the preparation of pavement cross section for testing, how the field conditions were simulated and the observations. All the analysis and results have been summarized in the sixth chapter.

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2. REVIEW OF LITERATURE 2.1 Introduction In the previous chapter, the study objectives and the scope of the study were discussed. This chapter will include a detailed discussion of literature review conducted on the subject of accelerated pavement testing and permanent deformation characteristics in multilayered flexible pavements. 2.2 Review of Accelerated Testing Facilities Various accelerated pavement testing instruments have been developed all over the world of which, a few popular of them are being discussed here in detail. 2.2.1

VERTEK’s Accelerated Pavement Testing Machine (APTM) (Applied Research Associates Inc., Vermont, USA)

It is a cost-effective, reliable and adaptable loading system for automated application of repeated wheel loading of highway and airfield pavements. The APTM takes advantage of modern technology, including a unique hydraulic loading control scheme, to provide high performance and reliability in a simple and easily maintained design. It can be adapted for use in a fixed laboratory environment, as a trailer that can be moved by a standard truck, or for self-propelled operation. The APTM is built around a steel load frame spanning the test section. The load carriage is automatically driven along a track attached to a load frame. Wheel loading is applied to the test pavement by either super single or dual truck tires attached to a constant force mechanism on the load carriage. The entire test machine is designed to operate under computer control. Pavement loading options include uni- or bidirectional loading, dual or super-single wheels, and programmed lateral wander. Instrumentation and limit switches constantly sense the position of the load wheels and detect the progress and completion of each operation. Instrumentation also records the history of each loading, including the magnitude of the applied load. The VERTEK APTM is electrically powered for quiet low-maintenance operation. To minimize the 4

complexity of the machine, the supporting mechanical and equipment can be housed in a separate trailer which is easily positioned near the machine, and if remote operation is required, can be supplied with a diesel-powered generator.

Fig. 2.1 Vertek’s Accelerated Pavement Testing Machine

2.2.1.1 VERTEK’s APTM Features •

Computer controlled wheel load simulator applies up to 30,000 pounds of load (optional configurations permit larger loads) with test speeds of up to 7.5 miles per hour.

•

Bi-directional operations of up to 500 load cycles per hour; unidirectional operations of up to 250 load cycles per hour.

•

Dual wheel or super single truck tire loading on pavement test sections or actual in-use road surfaces.

•

Test bed length of 45 feet (optional longer design).

•

Simulated wheel wander over a 20-inch range within operator-set parameters (optional larger ranges possible).

•

Design adaptability to a portable truck-mounted system.

•

Electronic emergency braking system.

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•

Laser profilometer measures pavement rutting and damage across pavement test sections.

•

Optional test facility to simulate environmental conditions with typical specifications of. •Temperatures from 10 to 130 degrees •Relative humidity up to 95% •Controllable water table in subgrade soil

2.2.2

The Danish Road Testing Machine (RTM) (Danish Road Institute, Ministry of Transport – Denmark)

The RTM, as pictorially shown in Fig. 2.2 is a linear pavement testing facility enclosed in a climate chamber. The actual test section has a width of 2.5 m and a length of 9 m. A longitudinal section, plan view and transverse section of the RTM (from top to bottom, respectfully) are shown in Figure 2.3 A dual wheel load was applied to the three test pavements. The structural details of the linear track and the tyre configuration used are illustrated pictorially in Figure 2.4.

Fig. 2.2 A view of the RTM in the climactic chamber

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Fig. 2.3 Structural details of the linear track Danish Road Testing Machine

Fig. 2.4 Dual tyre configuration utilized in the RTM

Response sensors installed in the test pavements included: Asphalt Strain Gauges (ASGs) to record horizontal strains at the bottom of the Asphalt Concrete (AC) surfacing, Soil Deformation Transducers (SDTs) to measure horizontal and vertical strains in unbound granular materials and Soil Pressure Cells (SPCs) to register horizontal and vertical stresses in unbound granular materials. Sketches of an SPC, an SDT and an ASG are shown in Figures 2.5 (a), (b) and (c), respectively. SDTs and SPCs were also installed in the unbound material layers in both the vertical and horizontal directions.

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Fig. 2.5 Sketches of the response instruments in the RTM test pavements

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2.3 Permanent Deformation Characteristics of Multilayered Flexible Pavements Rutting is defined as the permanent or unrecoverable traffic-associated deformation within pavement layers which, if channeled into wheel paths, accumulates over time (Paterson, 1987). A primary concern of most pavement structural design procedures is to control rutting.

This is achieved by estimating the cover

thickness of high quality materials required to protect the natural subgrade against the compressive stresses from traffic, and thus limiting deformation to within acceptable limits over time. This approach has led to the development of various relationships between acceptable rut depth limits and the various measures of material and traffic properties, enabling the design of adequate pavement structures. Due to the deterioration and ageing of road networks, these models (or the principles behind them) were also used for improved management and planning process and for the economic justification of expenditures and standards in the highway sector. Therefore, in modern pavement management systems, the routine measurement and prediction of rutting has become an important performance criteria as a result of the influence of rutting on road roughness, dynamic loads and safety (based on the hazard of ponding water), all of which influence the road user costs.

2.3.1 Mechanism of Development of Permanent Deformation in Flexible Pavements Traffic-associated permanent deformation and rutting in particular, results from a rather complex combination of densification and plastic flow mechanisms. Densification, according to Paterson (1987), is the change in the volume of material as a result of the tighter packing of the material particles and sometimes also the

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degradation of particles into smaller sizes.

Rutting due to densification is usually

fairly wide and uniform in the longitudinal direction with heaving on the surface seldom occurring, as illustrated in Figure 2.6. The degree of densification depends greatly on the compaction specifications during construction.

The

density

specification should be selected in accordance with the expected loadings and pavement type. Failure to reach the specified compaction during construction will result in an increase of densification under traffic, most of which occurs early in the life of the pavement. It is important to note that for similar rut depth values, the deformation within the pavement may be located within a single weak layer, or more evenly distributed through the depth of the pavement, as illustrated in Figure 2.6.

Fig. 2.6 Typical rut profile as a result of densification

Plastic flow involves essentially no volume change and gives rise to shear displacements in which both depression and heave are usually manifested. Plastic flow occurs when the shear stresses imposed by traffic exceed the inherent strength of the pavement layers (Paterson, 1987). The rutting in this case is usually characterized by heaving on the surface alongside the wheel paths, as illustrated in Figure 2.7. Plastic flow is controlled through the structural 10

and material design specifications, which are normally based on a measure of the shear strength of the materials used (for example, the California Bearing Ratio (CBR for soils, and Marshall and Hveem stability for bituminous materials). The best known example of plastic flow is shoving within the asphalt layers, as illustrated in Figure 2.7.

Fig. 2.7 Typical rut profile as a result of plastic flow (shoving)

2.3.2 Analytical Models available for understanding Permanent Deformation This section discusses the various analytical tools for understanding permanent deformation. 2.3.2.1 The Wire Model This method simulates a string or wire being stretched transversely across the road profile following convex curves and overlaying hollows as a straight line, as illustrated in Figure 2.8. The rut depth is then calculated as the greatest perpendicular distance from the simulated wire, shown as W1 and W2. The advantage of this method is that it is mathematically easy to use, and it gives very good results for convex road profiles because it follows the general shape of the transverse

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profile and still takes hollows at the top into consideration (Larsen et al., 1994).

This model has the disadvantage in that it can give very large rut

depths where the mid-profile is one large basin, as illustrated in Figure 2.9. Although resulting in larger rut depths for the above case, it might be argued that this method gives a more accurate indication of the depth of free water for the large basin. Secondly, only the largest rut depth value will normally be calculated for each cross-profile; thus for the large basin in Figure 2.9, only the rut depth value W1 would be calculated. Based on these anomalies the rut depth calculated by the wire model could differ substantially from the rut depth measured under a straight-edge. A discrepancy between manual rut measurements and measurements calculated with the wire model are also noted in New Zealand (Cenek 1994).

Fig. 2.8 Wire Model applied to concave cross profile

2.3.2.2 The Straight Edge Model This method simulates a straight line of a given length similar to a straight-edge being attached to the transverse profile. Various methods exist of attaching this straight line; some attach it to the outer-most laser at each end, after ensuring that the reading at this point is not that of a curb, and then calculate the largest vertical difference between the transverse profile and the reference line (Larsen

12

et al., 1994). This results in two rut depth values, of which only S2 is illustrated in Figure 2.9.

Also illustrated is the difference in rut depth calculated by the two

models. The other method simulates rapidly moving a straight line of a given length over the profile, performing up to over 200 rut calculations to identify the greatest rut depth in each wheel path. Both methods are able to simulate different straight-edge lengths, and as such allow the evaluation of the influence of straight-edge length on the calculated rut depth.

Fig. 2.9 Wire / Straight Edge Models applied to cross profile with large basin

2.4 Factors influencing Rutting The resistance of pavement structures to rutting is dependent on a number of factors which either relate to applied loads (traffic type and traffic volume), the environment (temperature, rainfall), the pavement structure (materials used and their composition), the construction process, or to a combination of the above. The factors of importance for the various pavement types included within HDM-4 are discussed

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in this section. The general influences of the factors are based on the findings of laboratory and field observations of numerous experiments.

2.4.1

Effect of Moisture

Over time, the pavement surface may crack. The increased moisture content due to ingress of water through a cracked surface layer will result in a decrease in shear strength of granular pavement layers which, when over- stressed by traffic, will result in the shear failure of the layers and thus the increased deformation observed in the final phase. The rate of increase is once again dependent on material quality (high quality materials are less susceptible to ingress of water), the amount of water ingress (rainfall), and traffic loading. 2.4.2

Effect of Traffic

The traffic loading is a combination of the magnitude and volume of the loads; these are combined into the number of standard loads through the fourth power law. Traffic loading is one of the most important factors contributing to rutting. Traffic induces stresses within the pavement structure that have to be withstood, and thus determines the quality of materials required, as well as the behaviour of the pavement in various phases. It is important to note that a few excessive loads or tire pressures for which the pavement was not designed may cause stresses exceeding the shear strength of the material and thus plastic flow, resulting in the premature failure of the layer.

2.4.3 Effect of Temperature The dependence of the flow properties of bituminous mixtures on temperature is due to changes in the theological properties of the binder, the dominant factor being the great dependence of viscosity on temperature. From simulation tests and general experience it is well known that the resistance to deformation of bituminous materials decreases rapidly as temperature increases, especially if the 14

ambient temperature approaches or exceeds the softening points of the binders used in such mixes. 2.5 Summary In this chapter, a review of the various accelerated pavement testing facilities was done. The chapter also discusses in details about the permanent deformation characteristics in flexible pavements, the mechanism and the factors affecting performance of flexible pavements. The next chapter will deal with the study methodology for the development and calibration of the Accelerated Pavement Testing facility.

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3. STUDY METHODOLOGY

3.1 Introduction The previous chapter dealt with the detailed review of the literature which has been collected. This chapter will include a discussion on the study methodology which has been adopted in the present study. 3.2 Methodology for development of Accelerated Pavement Testing Facility The methodology adopted for the design and fabrication of the accelerated pavement testing machine has been discussed in the form of a flowchart shown in Fig. 3.1.

Main Base: Fabrication of the rectangular framed steel base, 41 inch X 21 inch and covering it with a 0.25 inch MS sheet. Fitting the base with angles below to strengthen it and to allow the bolting of the motor and other components placed on the base.

Circular Base: Fabrication of the circular base, 1 m dia to support the bituminous concrete slab and the wheel loads , cut out from a 3/8 inch thick MS Sheet.

Axles: Fabrication of the axles using 1 inch dia MS rods. Press Fitting of the wheels (diameter 15 cms) in to the axle.

Worm Wheel and Worm Screw: Design and fabrication of the worm wheel with 48 teeth and the worm screw with 6 TPI according to AGMA standards.

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Bearings and Housings: Fabrication of housings using GI pipes for the bearings of internal diameters 20mm, 20mm and 19mm to support the rotation of the main shaft.

Main Shaft: Fabrication of the main shaft to be coupled to the motor using a 7/8 inch MS rod. Turning of the shaft on the Lathe to allow the press-fitting of bearings and the worm screw at appropriate locations.

Supports for the Housings: Determination of the heights of the supports for the bearings of the main shaft. Fabrication of the supports using MS plates, .25 inch thick.

Coupling the Shaft with the Motor: Welding of the supports to the housings and press-fitting of the worm screw and the bearings at the appropriate locations and coupling of the shaft with the motor.

Fixing the Circular Base: Supporting the circular base on the main base by means of angles.

Fabrication of Perpendicular Shaft: Fabrication of the perpendicular shaft using a 1 inch MS rod and fixing the axles to the perpendicular shaft by means of screws.

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Fabrication of the weights: Fabrication of the weights by boring holes in the center of 20 cm dia plate loads to slip the weights in to the perpendicular shaft.

Incorporation of temperature and speed control mechanisms: Incorporation of temperature and speed control mechanisms to provide for testing the sample at various temperatures and different frequencies of loading. Fig. 3.1 Methodology for development of Accelerated Pavement Testing Instrument

The design details for each of the stages discussed above is explained in detail in the next chapter. 3.3 Methodology for calibrating and testing the Instrument The different layers of the pavement structure are to be laid over the circular base. Then, the axle is to be slipped into the perpendicular shaft. The desired number of plate loads have to be slipped over the axle and then the Allen studs on the axle have to be tightened so that the axle rotates with the perpendicular shaft. The motor is then switched on. The deformation on the pavement surface for ever 500 revolutions are to be noted by the dial – gauge arrangement which has been provided. 3.4 Summary In this chapter, the study methodology and the methodology for the calibration and testing of the instrument was discussed. The next chapter will deal with the design and fabrication details for the Accelerated Pavement Testing Instrument.

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4. DESIGN OF ACCELERATED PAVEMENT TESTING FACILITY 4.1 Introduction In the previous chapter we dealt with the study methodology being adopted in the present study. This chapter will include in detail the design and fabrication of the Accelerated Pavement Testing facility, being designed and developed as a part of the present study. 4.2 Design Details A circular accelerated test track simulator has been developed which has the capability of simulating different contact pressures, adverse climatic conditions like varying temperatures, moisture levels etc. and frequency of loading with cost effective materials. The feature of changing / simulating the varying climatic conditions and frequency of load application is expected to make the simulator more versatile for application. For testing the efficacy of the simulator, a few pavement slabs are also being laid on the field and are being tested under different conditions. Basic laboratory tests including mix designs have also been performed in the laboratory as a pre-requisite before finalizing the mix designation for making the pavement slabs. Rut measurements at a frequency of 500 wheel repetitions have been taken and the results have been analyzed for different slabs being tested on an experimental basis. A few minor modifications have also been made to the simulator to test the quality of road paints also. It is hoped that the developed simulator will have acceptability in the field as it has both economy as well as versatility in its use. 4.2.1

Worm wheel

The Worm Wheel shown in fig 4.1 was fabricated from a cylindrical block of cast Iron. The Design parameters were calculated according to American Gear Manufacturers Association (AGMA) standards. The worm wheel was press fitted into the vertical shaft and was supported by means of Allen stu

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Design Parameters: Speed Reduction : 1440 rpm to 34 rpm Number of Teeth (N) = 42 Linear Pitch = 0.25” Bore = 25 mm Pitch Diameter (PD) = N * 0.3183 * 0.25 = 3.34215 “ Throat Diameter (TD) = PD + ( 0.636 * LP ) = 3.50115 “ Outer Diameter = TD + ( 0.4775 * LP ) = 3.6205 “ Hub Diameter = 1.875 * Bore = 1.640625” Face Width (FW) = ( 2.38 * LP ) + 0.25 = 0.845” Hub Extensions = 0.25 * Bore = 0.21875” Hub Length = FW + ( 0.5 * Bore ) = 1.2825” Radius of Wheel Face = ( 0.882 * LP) + 0.55 = 0.7705” Radius of Wheel Rim = ( 2.2 * 0.25 ) + 0.55 = 1.1” Edge Round = 0.25 * 0.25 = 0.0625” Centre Distance = ( Pitch Dia of worm + Pitch Dia of Gear ) * 0.5 Normal Pressure Angle = 14.5o

Fig. 4.1 Worm Wheel

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4.2.2 Worm screw The worm screw as depicted in fig 4.2 was fabricated from a cylindrical block of Mild Steel. The design parameters were calculated according to AGMA standards. The worm screw was press fitted into the main shaft and was supported by means of Allen studs. Design Parameters: Linear Pitch (LP) = 0.25” Pitch Diameter = (2.4 * 0.25) + 1.1 = 1.7” Outside Diameter = (3.036 * LP) + 1.1 = 1.851” Root Diameter = (1.664 * LP) + 1.1 = 1.516” Hub Diameter = (1.663 * LP) + 1 Bore = 19 mm Face Length (FL) = (4.5 * N/50) * LP = 1.335” Hub Extension = LP = 0.25” Hub Length = FL + (2*LP) = 1.335 + 0.5 = 1.835” Addendum = 0.3183 * LP = 0.079575” Whole Depth of tooth = 0.686 * LP = 0.1715 Lead = 0.25” Lead Angle (VL) = (PD*3.1416) / Lead = 21.36 o Normal Tooth Thickness = 0.5 * LP * Cos VL = 0.125 * 0.99” = 0.125” Top Round = 0.05 * LP = 0.0125 “ Normal Pressure Angle = 14.5 o

Fig. 4.2 Worm Screw

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4.2.3 Motor The Motor which is being used is a 2 HP, 1440 RPM. Single phase induction motor. The motor was bolted to the main base as shown in fig 4.3.

Fig 4.3 Motor

4.2.4 Bearings / Housing for Main Shaft Ball Bearings of internal diameters 20mm and 19mm were chosen to guide the main shaft. The housings for the bearings were made from GI pipes. The supports for the housings were made from 0.25” MS Sheets. The housings were welded to the supports and bolted to the main base. as shown in fig 4.4.

Fig 4.4 Bearing / Housing

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4.2.5 Coupling The Motor was coupled with the main shaft by means of a coupling as shown in fig 4.5. Holes were drilled on either side of the coupling corresponding to the diameter of the shafts of the motor and the main shaft and they were bolted together.

Fig 4.5 Coupling

A photograph showing all the individual components together is shown in fig 4.6 :

Fig. 4.6 All the individual components shown above, supported on the base plate

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4.2.6 Bearing / Housing for Vertical Shaft The housing for the vertical shaft depicted in fig 4.7 was made from Solid 4 inch MS rods. The ball bearing of internal diameter 25 mm was press fitted into the housing which would allow for free rotation of the shaft. The vertical shaft was a 1.25 inch diameter MS rod, 5 ft 2 inch high. The vertical shaft was turned in the lathe for a length of 90 mm from the bottom and the bearings and worm wheel were press fitted into it.

Fig 4.7 Bearing / Housing for the vertical shaft

4.2.7 Axles / Loading The Circular Base was supported on the Main Base Plate by means of angles as being depicted in fig 4.8 . The axles of radius 27 cm, made using 1 inch MS rods which were slid into the vertical shaft. Provision for sliding the axle and supporting it at any point on the vertical shaft was made by means of Allen screws. Pins were also fitted on either ends of the axles to prevent the wheels from sliding out. Cylindrical loads were loaded on the axle through the vertical shaft to achieve required contact pressures. Axles of variable radius can be made to test the pavement at different locations.

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Fig 4.8 Axles / Loading

Initially a base of dimensions 104 cm x 57 cm was chosen and a base plate of the same size was welded on it. The motor was bolted to the base plate by means of screws. Ball Bearings of internal diameters 20mm and 19mm were chosen to guide the main shaft. The Motor was coupled with the main shaft by means of a coupling. Then the bearings, worm screw and the coupling were tight fitted to the main shaft. The coupling and the worm screw were also supported by the means of Allen studs. The housings for the bearings were made from GI pipes. The supports for the housings were made from 0.25” MS Sheets which were welded to the housings and bolted to the main base at their respective positions. The housing for the vertical shaft was made from Solid 4 inch MS rods. The ball bearing of internal diameter 25 mm was press fitted into the housing which would allow for free rotation of the shaft. The vertical shaft was a 1.25 inch diameter MS rod, 5 ft 2 inch high. The vertical shaft was turned in the lathe for a length of 90 mm from the bottom and the bearings and worm wheel were press fitted into it. The worm wheel was also supported by means of Allen studs. A Circular Base of one meter diameter was supported on the Main Base Plate by means of angles. The axles of radius 27 cm, made using 1 inch MS rods were slid into the vertical shaft. Provision for sliding the axle and supporting it at any point on the vertical shaft was made by means of Allen screws. Pins were also fitted on either ends of the axles to prevent the wheels from sliding out. Cylindrical loads were loaded on the axle through the vertical shaft to achieve required contact

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pressures. Axles of variable radius can be made to test the pavement at different locations. A MS sheet of thickness 1/8 inch and height 20cms was welded to the base plate to give it a tub like arrangement. The instrument was painted black as shown below. A cylindrical bush had been welded with the circular plate to damp the vibrations in the vertical shaft. A nipple and socket arrangement had also been provided to the drain the water in the tub.

Fig 4.9 Accelerated pavement testing instrument

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4.3 Summary In this chapter the detailed study of the design, fabrication and testing of an accelerated pavement testing instrument was done. The next chapter will discuss about the Calibration and testing of Accelerated pavement testing unit.

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5. CALIBRATION AND TESTING OF ACCLERATED PAVEMENT TESTING UNIT 5.1 Introduction In the previous chapter we discussed in detail about the design, fabrication and testing of Accelerated Pavement Testing unit. In this we will be dealing with the calibration and testing of Accelerated Pavement Testing unit. 5.2 Preparation of Pavement Cross Section for Testing The pavement simulated in the laboratory consisted of 3 layers, subgrade, sub-base, and bituminous concrete layer. There is also a layer of sand which is compacted between the sub base and the subgrade for drainage purposes. 5.1.1 Preparation of subgrade To simulate 54mm of subgrade 68 kgs of clayey soil was taken and OMC of 12% was added and compacted in the circular base with the help of rammers and cylindrical rollers as shown in fig 5.1 and fig 5.2. Then a layer of 6mm of sand was compacted on the subgrade for drainage purposes using 7 kg of coarse sand.

Fig 5.1 Preparation of subgrade

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Fig 5.2 Drainage layer of 6 mm

5.1.2 Preparation of granular sub-base To simulate the Granular Sub-base layer of 50mm as shown in fig 5.3, the following gradations of aggregates were used as shown in table 1. Passing through

Retained on

Quantities

26.5 mm

10 mm

11.66 kg

10 mm

4.75 mm

8.875 kg

4.75 mm

2.36 mm

7.729 kg

2.36 mm

425 microns

14.578 kg

425 microns

75 microns

16 kg

Table 1 Aggregates used for GSB

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Fig 5.3 Granular Sub-base layer

Before laying the bituminous macadam layer a thin layer of bitumen was sprayed on the Granular Sub-base layer as shown in fig 5.4

Fig 5.4 Thin layer of bitumen as a Tack Coat

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5.1.3 Preparation of bituminous macadam To simulate 50 mm of bituminous macadam the following gradations of aggregates were used as shown in table2. Passing through

Retained on

Quantities

26.5 mm

20 mm

10 kg

20 mm

13.2 mm

34 kg

13.2 mm

4.75 mm

40 kg

4.75 mm

2.36 microns

12 kg

Table 2 Aggregates used for Bituminous Macadam

The aggregates were heated to a temperature of 140-165 degrees Celsius and mixed with 4 kg of 80/100 grade bitumen heated to a temperature of 140-160 degrees Celsius at a mixing temperature of 155 degrees Celsius. The layer was then rolled and compacted at a temperature of 80 degrees Celsius as shown in figures 5.6 and 5.7. To simulate the shoulder portion a 10 cm layer of aggregates was laid as shown in fig 5.5.

Fig 5.5 Shoulder portion

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Fig 5.5 Mixing of bituminous macadam

Fig 5.6 Bituminous macadam layer

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Bitumen was then mixed with coarse and a thin layer of seal coat was prepared on top of the bituminous macadam layer as shown in fig 5.8 and fig 5.9

Fig 5.8 Seal coat

Fig 5.9 The final Pavement

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6. SUMMARY AND CONCLUSIONS 6.1 Introduction In the previous section we had discussed on the Calibration and Testing of Accelerated Pavement. In this section we will give a brief summary of the instrument so far and recommendations for further improvement of the instrument. 6.2 Summary The first chapter dealt with the need for the present study, study objectives and the scope of study. In the first chapter we saw that rutting is the major failure criteria in flexible pavements and the need to develop a cost effective instrument for measuring the rut depth in flexible pavements. The second chapter included a detailed literature survey which discussed the different accelerated pavement testing instruments like VERTEK’S Accelerated Pavement Testing Machine ( APTM ) and the Danish Road Testing Machine ( RTM ) in brief. It also gave an insight into the permanent deformation characteristics of multilayered flexible pavements, mechanism of rutting, analytical tools for understanding rutting and the effects of temperature and loading frequency on flexible pavement performance. The third chapter discussed the study methodology for the design and calibration of the accelerated pavement testing instrument. In Chapter 4 the design details of the accelerated pavement testing instrument had been discussed in detail which has been developed for the present study. In this chapter the design of every part has been explained in detail along with suitable diagrams. The fifth chapter included a detailed account of the calibration and testing of the instrument. It also discussed in detail about the preparation of pavement cross section for testing.

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6.3 Conclusions and Contributions For the accelerated flexible pavement testing facility developed during the present thesis, all the spares excluding the motor and the tyres are being indigenously fabricated and used. The testing facility is expected to be quite effective in testing multilayered flexible pavement sections with different combinations of materials and layers. The instrumentation developed will be quite useful in establishing the quality of the pavement marking paints as an additional feature. The features of adjustable loading frequencies, contact pressures and varying temperatures make the instrument quite versatile from the point of view of simulating the field conditions. The developed instrumentation is quite cost effective when compared with similar such instruments available in the market, since its fabrication involves simple and cost effective spares. 6.4 Scope for Further Improvement Though the instrument is complete there is a lot of scope for improvements that can be made to improve the instrument. The following are some of the improvements suggested: 1. A sprinkler could be attached to the instrument for rainfall simulation. 2. By means of a Variac the frequency of rotations of the axles can be controlled. 3. A heater or blower could be attached to simulate higher temperatures. 4. Different mixes of bituminous concrete can be prepared and tested for permanent deformation.

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APPENDIX A: MAINTANENCE OF THE INSTRUMENT Introduction This section elucidates the various maintenance steps to be taken to ensure smooth functioning of the instrument. Bush Guiding the Perpendicular Shaft It should be ensured that the bush which guides the perpendicular shaft should be oiled every time before the instrument in used. Bearings The bearings should be greased at least once in two weeks. Allen Screw It should be ensure that the Allen screw which holds the coupling to the motor and the main shaft should be tightened every time the instrument is being used. Axle / Loads First the Axle is to be slipped into the perpendicular shaft then the axle is to be loaded. Only after this, the Allen studs in the axle should be tightened. Perpendicular Shaft Never shake the perpendicular shaft. General If it is required that the axle be rotated manually, never force the axle to rotate by pushing it, Always rotate the shaft of the motor, then the axle will automatically rotate.

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References 1. Contributions of Pavement Structural Layers to Rutting of Hot Mix Asphalt Pavements, National Cooperative Highway Research Program, Report 468 2. Yang Huang, Pavement Analysis and Design, 2nd Edition, Prentice Hall, 2003 3. http://www.lpcb.org/lpcbdownloads/isohdm_pdwe/1995_kannemeyer_rut_modell ing.pdf 4. Specifications for Road and Bridge Works, Fourth Revision, Ministry of Road Transport and Highways, India.

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