The development of modern highways has always depended upon the material available to build them by lawjuris

The development of modern highways has always depended upon the material available to build them CHAPTER 1 INTRODUCTION

1.1

GENERAL

The development of modern highways has always depended upon the material available to build them. Early attempts to seal a pavement with tar or pitch led to the use of bitumen and to the high performance materials currently in use worldwide. This process of development continues today for improvement of the existing materials to perform better by modification through addition of additives and admixtures. The primary function of the pavement is to give the users a smooth, comfortable and safe ride at economical cost. One of the main drawbacks of bituminous pavement materials is that they combine `elastic’ and `plastic’ behavior, that is, when they deflect under load, a small part of the deflection becomes permanent. After individual loads these permanent deformations are practically invisible, but repeated loading of this effect can lead to rutting. The phenomenon is particularly prevalent in warm climates where the growing weights or tire pressures of the transport vehicles are present. The behavior of flexible pavement is very complex due to the inter-relation between factors influencing its performance. Some of the major observed asphalt pavement problems can be listed as (Thompson et. al. 1983): •

Rutting

•

Thermal and fatigue cracking

•

Hardening of binder

•

Flushing

•

Moisture susceptibility and stripping

In order to deal with these problems, use of different types of additives in asphalt concrete mix is in use in various countries. For example, different types of “Filler Material” available

are one such type of additive, which is known to affect the properties of the Asphaltic Concrete (AC) mixes. Therefore any refinement of knowledge for use of such additives in AC mixes and their potential benefits, will find a good place in todayâ&#x20AC;&#x2122;s world where lot of concern exist for these in widespread problems of major importance.

1.2

PROBLEM DEFINITION

Bangladesh is climatically a tropical country with combination of all type of weathers and an average 2000 mm of precipitation annually. To provide communication between the towns, huge investment has been placed in constructing quality roads that covered great distances, under extreme climatic and topographical conditions. Road pavement of the national, regional and major feeder roads is mainly of AC surfacing and designed for a design life of 15-20 years before any major maintenance and rehabilitation is needed. However, during the past few years, these roads with AC layers have been experiencing early distress and deterioration leading to failures ultimately. Apart from heavy axle loads, high tire pressure and climatic conditions, use of locally available low quality aggregate in road construction is one of the major contributors to failures. The construction industry faces a difficult situation in finding good performance aggregate. On highways and urban roads many damaged spots can be seen after the seasonal rains, especially in eastern half of the country where aggregate are weaker comparatively and sensitive to water. Since the transportation of good quality aggregate from nearby country is uneconomical, in the eastern half of the country. Therefore, certain modifications in AC mixes produced by using the local aggregate of Bolaganj source is needed to ensure a durable mix by incorporating additives. There are a number of factors which may affect the performance of an AC layer. The major factors known to affect the material characteristics and behavior under traffic loading are; asphalt type and content, temperature variation, aggregate type and gradation, air voids, mix density, filler type and wheel loading or stress level. Among these the asphalt content and quality of the AC mix has direct effects on the stability and durability.

Considerable research and development has been done to achieve a mix which can satisfactorily resist the major distresses and water sensitively problems in pavements. One of the major steps towards this is achieved by incorporating additives in AC mixes to improve its temperature and water susceptibilities, especially for extreme and tropical climate regions. Use of additives to significantly improve the properties of the AC mixes such as temperature and water susceptibilities, strength and durability had been reported by researches in countries like USA, India and Saudi Arabia (Ronald et. al. 1989). Such promising results could present a cure for different types of distress and deterioration in the pavement in Bangladesh. Among various types of additives and modifiers “Filler Material” is one, which is considered to improve the AC mix properties without affecting much on the overall economy AC pavements. There are different kinds of filler material available and is in use in different regions depending upon the improvement needed and the relevant functions they provide. Although different kind of filler used in AC mixes may result in performance improvements or better economy. However, each one has it’s own limitation. For example: a)

Hydrated lime is widely used as an anti-stripping agent in AC mix, but it slightly increases the bitumen requirement in the mix thereby affecting economy. However, the achieved benefits in the improvement of properties and durability are considerable and feasible.

b) Asbestos fiber is reported to be an excellent filler material in AC mixes, but due to health hazard the use is discouraged References 1. Anderson, D.A., and Tarris, J.P., “Adding Dust Collector Fines to Asphalt paving Mixtures” NCHRP Report – 252 Dec. 1982. pp. 8-9 2. Aniruddha Vilas Shidhore, “ Use of Lime as anti-Strip additive for Mitigating Moisture susceptibility of asphalt Mixes containing Baghouse Fines”, M.S Thesis, North Carolina State University, Raleigh, 2005. 3. American association of state highway and Transportation Officials (AASHTO) 2000, “Standard Specifications for Transportation Materials and Method of sampling and Testing, Part I and Part II, 20th Edition, USA

4. American Society for Testing and materials (ASTM), 2000, “Annual Book of ASTM Standards, Road and Paving Materials”, Section 4, Volume 4.03, Philadelphia, USA 5. Asphalt Institute, USA, “Mix Design Methods for Asphalt Concrete and Other HotMix Types”, MS-2, Sixth Edition, 1995. 6. Asphalt Institute, “Asphalt technology and construction – Instructor’s Guide”, Education Series No. 1, College Park, Maryland. Pp. L23 7. Asphalt Institute, “Cause and Prevention of Stripping in Asphalt Pavements”, ES-10, Maryland, USA. 8. Asphalt Institute, 1992, “Model Construction Specifications for Asphalt Concrete and Other Plant-Mix Types”, Specification series No. 1 (SS-1), Maryland, USA. 9. Benson, F.J., “Appraisal of several methods of Testing Asphaltic concrete” Bulletin No. 126, Texas Engineering Experiment station. The Texas A&M University, 1952. p. 26-32 10. BS 598 Sampling and examination of bituminous mixtures for roads and other paved areas, Part 3 “Methods of Design and Physical Testing”, 1985, UK. 11. Corps of Engineers, symposium, “Investigations of the Design & Control of asphalt Paving Mixtures & their Role in the Structural Design of flexible Pavements” Dept of Army, Research report No. 7-b, HRB, 1984. 12. Craus, J., Ishai, I. and Sides, A. “Some Physico–Chemical aspects of the effect and Role of Filler in Bituminous Paving Mixes” AAPT, Proc. 47, 1978, pp. 558-559 13. Dorrence S. M. Plancher., and Peterson, J.C., “Identification of Chemical types in Asphalt’s Strongly Absorbed at the Asphalt-Aggregate Interface and their relative displacement by Water” proc. AAPT, vol-46, 1977. pp. 151-175 14. Hamad I. Al-Abdul Wahab., “The Effect of Bughouse Fines and Mineral fillers on asphalt mix properties”, M.S. Thesis, King Fahad University of Petroleum & Minerals, Dhahran. Sept. 1981 15. Hedman Resources. , “Information on Hedmanites”, Hedman Resources Limited, 106 Fielding Road, Ontario, Canada, 1983 16. Hudson, S.B., and Vokac, R., “Effect of Fillers on the Marshall stability of Bituminous Mixtures” HRB Bulletin 329, 1962, pp. 30-37 17. Hudson, W., and Kennedy, Thomas, W., “An Indirect Tensile test for stabilized materials”, research report 98-1, Center of highway research, the university of Texas at Austin, January 1968

18. www.lime.org, “Hydrated Lime-A solution for High Performance hot Mix asphalt” (http://www.lime.org/Asphalt.pdf) 19. Ishai I and craus, J., “effect of the filler on Aggregate – Bitumen adhesion properties in bituminous Mixtures” AAPT. Vol-46, 1977. pp. 228-258. 20. Jimenez R. A., “a look at the Art of Asphaltic Mixtures” AAPT, vol-55, 1986. pp. 323-352 21. Joe, W.B., “Summary of Asphalt additives Performance at selected Sites.” Transportation Research Board, TRR – 1342, 1991. pp. 67 – 75 22. Kamyar Mahboob, “asphalt concrete Creep as related to rutting” journal of materials in Civil engineering, vol-2, No.3, August 1990, pp. 147-163 23. Kennedy, T.W., “Characterization of asphalt Pavement materials Using Indirect Tensile Test”, Proceedings of Asphalt Paving Technologists, vol. 46, 1977. pp. 132150 24. Khanna, P.N., “Handbook of Civil Engineering”, Engineer’s Publishers, new Delhi, 1992 25. Ladis H. Csanyi., “Functions of Fillers in Bituminous mixes”, HRB Bulletin 329. Symposium Jan. 8-12, 1962, pp. 1-5 26. Little, Dallas N. and John Epps. “The Benefits of Hydrated lime in Hot Mix Asphalt”, Report for national Lime Association, 2001 27. L. R. Kadiyali Dr., “Principles and Practice of highway engineering”, Khanna Publishers, Delhi, pp. 763-774 28. Mirza Ghouse Beg, “Laboratory evaluation of Headmanites and Lime modified Asphalt Concrete Mixes”, MS Thesis, King Fahad University of Petroleums and Minerals, Dhahran, Saudi Arabia, 1995. 29. Mitchell, J.G., and Lee, A.R., “The Evaluation of Fillers for tar and other Bituminous Surfacings”. Journo chemical industry, vol-58, Oct. 1939, pp. 299-306 30. Monismith, C.L., Epps, J.A., and Finn, F.N., “Improved Asphalt Mix design” Proceedings of the Association of asphalt paving technologists, vol-54, 1985. 31. Peterson, J Claine., et. Al., “Lime treatment of Asphalt to reduce Age Hardening and Improve Flow Properties” Presentation at the Annual meeting of AAPT. Reno, Nevada, Feb. 23-25, 1987 32. Peter E. Sebaaly, Edgard Hilti, and Dean Weitzel, “Effectiveness of Lime in Hot-Mix aspalt

pavement”,

University

Nevada,

http://www.wrscunr.edu/WRSCMoisture_files/report.pdf).

Reno,

2001,

33. Puzinauskas, V.P., ‘filler in Asphalt Mixes” Canadian Technical Asphalt association, Proc. 13 1968, pp. 97-125 34. Richardson, C., “The Modern Asphalt pavement”, Wiley Publications, New York, 1941 35. Rigden, D.J., “The Rheology of Non-Aqueous Suspensions”. Technical Paper No.-28. Hammond worth, Road Research Laboratory, 1954. 36. Robert S. Boynton., “Chemistry and technology of lime and limestone”, Second Edition., John Wiley & Sons, new York, 1980. pp. 193-194 37. Ronald, L.T., and Epps, A.J., “Using Additives and Modifiers in Hot Mix Asphalt.” National Asphalt Paving association, NAPA. Report No. –QIP 114A, 1989. pp. 03 -10 38. Tayebali, A.A., Huang, Y., “Material Characterization and performance Properties of Superpave Mixtures:, FHWA/NC/2004-11, May 2004 39. Terrel, R.L., and Walter, J.L., “Modified Asphalt Pavements Materials – The European Experiences”, AAPT, 55, 1986. pp. 482 – 518 40. Thomas L Speer and John H. Kietzman., “Control of asphalt pavement rutting with asbestos Fiber”, Symposium Proc. Jan 8-12, HRB bulletin 329, 1962. pp. 64-82 41. Thomas W. Kennedy., and james n. Anagnos. “Techniques for Reducing Moisture Damage in asphalt Mixtures”, Research Report, University of Texas at Austin, Nov. 1984. 42. Thompson, E.M., Haas, R.C and Tessier, G.R., “The Role of Additives in Asphalt Paving Technology.” Proceedings of the Association of Asphalt Paving Technologists. AAT, 52, 1983. pp. 324 -344. 43. Transport Research Laboratory (UK), Overseas Road Note 19, “A Guide to the Design of hot mix asphalt in tropical and sub-tropical countries”, November 2002. 44. Traxler, R.N., “The Evaluation of Mineral Powders as Filler for asphalt”, AAPT, proceedings. Vol-8, 1937, pp. 60-68 45. Van dear Poel, “a general system describing the viscoelastic properties of bitumen and its relation to routine test data”, Journal of applied chemistry, Vol-4, 1954, pp 221-236 46. Warden, W.B., Hudson, S.B., and Howell, H.C., ‘Evaluation of Mineral Fillers in Terms of practical Pavement Performance” AAPT, Proc. 28, 1959, pp. 97-125 47. Welch, B.H. and Wiley, M.L., “Effect of Hydrated lime on asphalt and aggregate Mixtures” Transportation research Board, TRR – 659, 1977. pp. 44. 48. Whiteout D (1990). “The Shell Bitumen Handbook”, London: Shell Bitumen, UK

49. Winn ford, R.S., “The Rheology of Asphalt – Filler Systems as shown by the Micro viscometer” STP 309, American Society for Testing Materials, 1961 pp. 109-120 50. Yoder, E. J., and Witzak, M.W., “Principles of pavement Design” Second edition, John Wiley, New york, 1975. pp 282-285 51. Ziauddin, A. Khan, “Laboratory evaluation of local concrete Mix Design procedures” M.S. thesis, KFUPM, Dhahran, Jan. 1988 demand Resources 1983). Therefore, correct selection and use of a particular type and amount of filler additive among various available and new emerging products becomes important to ensure a properly designed AC mix as per the local existing environmental and loading conditions. The study is designed to investigate the engineering properties of AC mixes modified with hydrated lime as part of the filler with regards to effectiveness and look for the improvements obtained as compared to conventional mix without lime.

1.3

OBJECTIVES OF THE STUDY

Bangladesh has a very limited choice of suitable locally available stone sources for producing aggregate for road pavement. The imported stone is consumed mainly in the Western part of country due to cost effectiveness. In the Eastern part of the country the local available stone of Bolaganj (Sylhet) is mainly used in aggregate production for the road pavement. Bolaganj stone have been reported to have an affinity towards water due to its hydrophilic character and AC mixes produced by using aggregate of these stone is susceptible to moisture and less durable thereby. In consideration of high annual rainfall and long rainy season, a necessity of modification of AC mixes is a need to control the moisture susceptibility aspects, which leads to stripping and raveling in the AC surfacing. Therefore this study is taken up with an objective to: i)

To review the available literature on the moisture susceptibility problems in the AC mixes, the types of the additives and modifiers and the effects of these on AC mixes in general and hydrated lime as modifier of AC mixes in particular

ii)

Conduct laboratory tests on the specimens of AC mix without lime and modified AC mixes in varying percentage of hydrated lime to determine the engineering properties with respect to water susceptibility aspects.

iii)

Compare the properties of AC mix without lime and modified AC mixes with lime to evaluate the effects on moisture susceptibility behaviour and come up with the conclusions.

1.4

SCOPE AND APPROACH OF STUDY

The findings of the study shall be applied in using the modified AC mixes with lime produced by using aggregate of crushed Bolaganj stone boulder with confidence in actual works to check and control the problems arising from water. The scope of the study involves the following tasks: 1.

Material characterization i.e., testing and evaluation of aggregate of Bolaganj origin and bitumen of Eastern Refinery (Bangladesh) in the laboratory for their quality and conformance with the specifications.

Mix design using Marshall Method to arrive at the optimum mix for the AC wearing course gradation of RHD specification (2001).

Study characteristics of the modified AC mixes with hydrated lime in different percentages and carry out comparative analysis with the control optimum AC mix without lime.

To achieve the study objectives, a systematic approach consisting of three main interconnected phases have been framed: The first phase consists of material collection and characterization to evaluate their quality with respect to conformance with applicable specifications. The second phase involves conducting mix design by Marshall Method and laboratory tests on control optimum AC mix without lime and modified AC mixes with lime in different percentages related to moisture

susceptibility. The third phase involves data analysis, interpretation of results, conclusions and recommendation.

1.5

THESIS LAYOUT

Chapter 1 presents the an overview of the problems being experienced with respect to moisture susceptibility in context of Bangladesh in AC mixes, the objectives, scope and approach of the study to arrive at conclusions. Chapter 2 is on a review if the literature on the subject matter with regards to modification of AC mixes by various additives in general and by modification using hydrated lime in particular. The chapter also covers the findings of researchers in the past to take account of those in the current study Chapter 3 presents the details related to characterization tests on constituent materials, mix design of AC mix for optimum mix and testing of Optimum AC mix without lime and modified AC mix with lime in varying doses for moisture susceptibility aspects. Chapter 4 presents test results, their analysis and evaluation adopting statistical approach and discussions for final conclusions on effects of modifications of AC mixes by lime. Chapter 5 presents the final findings and conclusions of the study. Recommendations for further researches and studies are also included in this chapter. CHAPTER 2 LITERATURE REVIEW

2.1

GENERAL

The concept of modifying asphalt mixtures is certainly not new, but has become much more prominent during the past few years due to frequent occurrence of problems in respect of early distresses and deteriorations in Asphalic Concrete (AC) mixes. To address theses problem for remedy one of the techniques being practiced in modern to modify the AC mixes by incorporation of various additives and admixtures. The factors that have some influence on an increased interest in modifying AC mixes include at least the following:

•

Traffic factors have increased including heavier loads, higher volume, and higher tire pressures.

•

To accommodate the shift from larger projects such as the Interstate System to smaller projects such as maintenance of the existing road network.

•

Higher costs have created a tendency to construct thinner pavements, thus reducing the service lives of pavements.

•

Environmental and economic pressure to dispose of certain industrial waste materials (i.e., tires, glass, ash etc) has prompted the idea of concerting them to additives in AC mixes.

A family of products and processes are aimed at a variety of pavement application. The highway engineer knows that the complexity of pavement distress requires a choice of repair or rehabilitation options (one or two methods may not suffice). The appropriate modification of AC mixes has broadened the choices available to the engineer. Engineers who are familiar with the field performance of bituminous pavements generally agree on three potential modes of distress (Ronald et. al. 1989): •

Distortion: i) Settlement, ii) Rutting

•

Cracking: i) Repeated load (fatigue cracking) ii) Non-load (thermal cracking)

•

Disintegration: i) Raveling (Loss of adhesion) ii) Stripping (moisture damage)

Although most bituminous pavements perform satisfactorily, problems still do occur. Consequently, there is an increased interest in making changes that include several possibilities:

•

Improved pavement design (structural, damage, materials, etc.)

•

Revision of specifications for paving materials and pavements.

•

Improvement in the quality control of construction

•

Improvement of binders systems through modifications by additives.

All of the above will contribute in improving the performance of the pavement system. However, the improvement of binder system through modification by additives has gained a primary interest (Terrel et. al. 1986)

2.2 ADDITIVE AND MODIFIERS An additive to the AC mix is a material which would normally be added during mix production, to improve the properties and/or performance. A bitumen extender is an additive which replaces a part of the mineral filler that would normally be used in the AC mix, and may additionally result in performance improvements or better economy (Terrel et. al 1986). The justification or reasons for using an additive or extender would include the following: •

Solve or alleviate a pavement problem

•

Realize some benefits such as: i) Economy ii) Environmental iii) Energy iv) Application and Performance

Vehicle weights, traffic volume, and tire pressures are steadily increasing and demanding more and more from the pavement structures. Engineers face with serious problems with the quality of paving material. Often aggregates are transported from long distances at high cost because local aggregate supplies of high quality have been depleted. As a result, additives to AC mixes have been widely accepted by the paving industry for the present time. The concept of additives is logical, and results from laboratory testing look positive. Even though field test results using many additives are incomplete, many of those responsible for pavement quality are willing to use because the results appear to be favorable (Joe, W.B., 1991).

2.2.1

Types of Additives and Modifiers

The generic classification has led to the following types of additives (Ronald et. al 1989): •

Fillers

•

Extenders

•

Polymers

•

Crumbed Rubber

•

Plastic

•

Fibers

•

Oxidants

•

Anti-oxidants

•

Hydrocarbons

•

Anti-stripping agents

•

Combinations

Each of the additives noted above provides benefits and improvements to the AC mix, either actual or perceived. The impetus to use one or more of these modifiers is generally based upon several factors. For example, a user agency may have a particular pavement problem and is in need of a solution. They in turn seek out additives or modifiers that provide some hope. Another approach has been to seek new markets for materials that are already available and have traditionally been used in other applications (Terrel et. al. 1986). 2.2.2

Filler as Additive and Modifier

Any fine powder added to bituminous mixture in the course of manufacture, and which has been processed to such a degree of fineness that not less than 85 percent by weight passes a 0.075 mm sieve is called “Filler” (Khanna, P.N., 1992). Examples of Filler are: 1. Mineral Fillers: i)

Crusher fines/dust

ii)

Lime

iii)

Portland Cement

iv)

Fly ash

Granite dust

2. Fiber material filler: i)

Natural Fibers: a) Asbestos (Hazardous) b) Rockwool (Non-Hazardous)

ii)

Man-made Fibers: a) Polyester b) Fiberglass c) Steel Fibers

3. Others: i)

Carbon Black

ii)

Sulfur

iii)

China Clay and Fullerâ&#x20AC;&#x2122;s earth

Mineral Fillers: They are generally considered to be fine inert mineral materials a high proportion (at least 65 percent by ASTM and AASHTO specifications) of which will pass the 0.075 mm sieveâ&#x20AC;? The description is improved by adding a statement to the effect that filler is important because of the surface area involved, and that properties of a pavement which may be improved by the use of filler include strength, plasticity, amount of voids, resistance to water action, and resistance to weathering. In short, if filler is to be adequately described it is necessary to turn to the literature to try to determine what others have learned about it, or to attempt independent analysis in the laboratory and field. Fiber material filler: Fiber provides some sort of reinforcement in the AC mixes. They also provide a finely divided material in the mix with a high surface area that permits the application of thicker than normal films of asphalt cement on the aggregate (Ronald et. al., 1989). Natural, Synthetic and Steel Fibers have all been used in AC mixes. The usual approach is to incorporate very fine, short Fibers into the AC mixture, depending upon their form, chemistry, and intended function.

According to the research, fiber linkage is a mechanism that may explain the resistance to rutting which asbestos imparts in bituminous paving mixtures. Selective adsorption on the short chrysotile asbestos fiber could bond or link together the heavy viscous bitumen fraction. Pavement stability against rutting would then depend on the strength of the heavy fraction, the amount present in the paving mix, and the proportion adsorbed by the asbestos fiber (Thomos et. al., 1962). Apart from asbestos, non-hazardous Rockwool fibers have been used in Great Britain and France, where fibers were added to the bituminous mixes during mixing, it was reported that it improved resistance to reflective cracking, deflection and there were no construction constraints (Terrel et. al., 1986). 2.2.3

Influence of Mineral Filler on AC mixes

Extensive research, most of it from the early part of the century, has been done on the properties of mineral filler and its influence on asphalt concrete mixtures. Richardson, C, (1941) was one of the first investigators to report on the effects of mineral fillers. He postulated that the function of the filler is more than mere void filling, inferring that some sort of physico-chemical interaction occurs when fine mineral dust is added to AC mixes. Traxler, R. N., (1937) considered size and size distribution as fundamental filler properties that affect the void content. More recent work by Traxler confirms his earlier findings (Anderson el. at., 1982). Mitchell et. al., (1939) also attempted to find a single parameter that would adequately predict the ability of mineral filler to stiffen the bitumen in the AC mix. The data were obtained for mineral filler asphalt mixtures with relatively small concentrations of solids. The results indicated that the bulk settled volume of filler in benzene is a good predictor of the performance of the mineral filler. A very extensive series of experiments on mineral fillers and mineral filler binder system has been reported by Rigden, (1954). In particular, he studied the relationship between filler properties and the viscosity of mineral filler binder mixtures. At filler bitumen ratios similar to those found in typical asphalt concrete mixtures, the fillers stiffened the asphalt by as much

as three orders of magnitude. His data also indicate that fillers affect the temperature and water susceptibility of the AC mixes, however, the stiffening effect did not correlate with any of the fundamental properties of the fillers. The theology of mineral filler asphalt systems has been studied by Winniford, R. S., (1961) using the sliding plate micro-viscometer. Winniford suggested that the role of the filler is more than volume filling, and postulated additional stiffening mechanisms including. 1)

A gelatin of the asphalt by the mineral surface, which increases the non Newtonian flow characteristics and lowers temperature susceptibility.

Formation of thick viscous coatings which increase the effective solids concentrations, and

Surface shielding by adsorbed asphaltenes. It was also shown that the stiffening effect of the mineral fillers was more pronounced with smaller sized materials.

Warden et. al., (1959) presented data on filler asphalt mixes in conjunction with filed observations. This study was motivated by field failures that were attributed to filler type. An easily measured parameter was sought that would predict the performance of the filler in the field. The tests performed on the fillers were empirical tests in use in the late 1950â&#x20AC;&#x2122;s. A reexamination of the early work by Traxler again demonstrated that no single parameter was sufficient to predict the behavior of different mineral fillers. The softening point of the filler bitumen mixtures was found to be critical with respect to filler type. Puzinauskas, V. P., (1968) reporting on The Asphalt Institute study of mineral filler concluded that the mineral filler plays a dual role in bituminous mixes. Stated that â&#x20AC;&#x153;they are part of the mineral aggregate and they fill the interstices and provide contact points between larger aggregate particles, when mixed with asphalt mineral fillers form a high consistency binder or matrix which cements larger aggregate particles togetherâ&#x20AC;?. Craus ET. al., (1978) dealt with the effect of the physicochemical properties of filler on mix performance. In particular, they examined the geometric characteristics (shape, angularity, and surface texture), adsorption intensity at the filler asphalt interface, and the selective adsorption of the filler asphalt system. They concluded that the physicochemical interaction between filler and bitumen increased with the adsorption intensity, geometric irregularities,

and selected adsorption of the fillers. The authors concluded that a single test on mineral filler cannot be expected to predict the behavior of the filler in the bituminous mixes.

2.2.4

Theory of Filler

Two fundamental theories, based on the results of studies, observations, and experience, have emerged regarding the functions of fillers in bituminous mixes: Filler theory: The filler theory postulates that â&#x20AC;&#x153;the filler serves to fill voids in the mineral aggregates and thereby create a denser mixâ&#x20AC;?. This theory presumes that each particle of the filler is individually coated with bitumen and that such coated particles, either discrete or attached to an aggregate particle; serve to fill the voids in the aggregate. By virtue of such filling of voids, mixes of higher stability and density can be attained (Ladis H. Csanyi, 1962). Mastic Theory: The Mastic theory proposes that he filler and bitumen combine to form mastic, which fill the voids and also bind aggregate particles together into a dense mass. When filler is added to bitumen, part of it will have a mechanical function where physical contact is not established and then filler and bitumen work together in the form of what can be called a binder. This finest portion of filler will be suspended in the asphalt, changing the properties of binder films. It will act as filler within the bitumen itself, since it will replace a certain amount of asphalt in the mixture. Mastic of this type is harder, stiffer, tougher, and possesses lower temperature and water susceptibility than the original bitumen (Hamad I. Al Abdul Wahab, 1981). 2.2.5

Filler Attributes

The desired practical and functional quality attributes in a filler material should include the following (Warden et. al., 1959): The filler in the bituminous mix must be non critical. Variations in the filler content which may be expected under normal plant operation must not cause undesirable fluctuations in the physical properties of the pavement. The yardstick or means of judging is the sensitivity of all the following quality attributes as a function of fillerâ&#x20AC;&#x201C;bitumen ratio. The quantity of filler desired for functional reasons must not unfavorably affect the mixing, placing and compaction of the bituminous mixture. In other words at the desired

concentration to meet design criteria the mortar softening point or consistency must not be so high that the mix is unworkable. Added mineral filler should be economical (availability and cost) and should be readily transported, stored, proportioned and mixed with customary equipment. Yardsticks for storing and proportioning are that the filler be non-hygroscopic and do not form lumps or cake or bridge in the bins. A completed pavement surfacing must be stable and durable over a wide range of temperature and over an extended period of time. This means that from the functional viewpoint the type and quantity of filler in the bituminous mixture must be such that the optimum void is maintained within the desired limits, both initially and after ultimate compaction, and that there is sufficient resistance to deformation by traffic at the highest service temperature. Concurrently the filler must not decrease the resistance to water or the bond of the bitumen or mortar to the aggregate and must not decrease durability through loss of flexibility by inducing cracking of the pavement. 2.2.6

Role of Filler in AC mixes

In general the functions of filler can be listed as follows (Khanna., P. N., 1992): 1.

To increase the viscosity of the binder and hence increase density and stability of the mixture.

To enable a thicker film of binder to be held by the mixes.

To improve the resistance of the binder to weathering.

To increase the effective volume of the binder

To reduce the apparent temperature and water susceptibility of the mixture (for dense surfacing-filler/binder mixtures have lower temperature and water susceptibility than straight binders of the same viscosity).

To reduce the brittleness of a mix in cold weather, where the quantity of the filler can be considerably increased.

To obtain a close texture on the surface after compaction

Researchers have related the void properties of the filler to the Marshall Mix properties. For example, Hudson et. al., (1962) have related the activity coefficient to Marshall Stability. The

activity coefficient is defined as the bulk volume of the filler to the solid volume of the filler. The bulk volume of the filler was determined from the settled volume of the filler in kerosene. For a given mixture, it was found that the activity coefficient is related to Marshall Stability. It was concluded, however, that the stability is a function of both filler type and concentration. Craus et al., (1978) concluded that the physicochemical interaction between filler and bitumen increased with the adsorption intensity, geometric irregularities, and selected adsorption of the fillers. These effects strengthen the filler bitumen bonds producing a mixture with a higher strength. Summarizing the key points from the state of the art review on mineral fillers it can be concluded that: 1.

Mineral fillers stiffen asphalt, and the degree of stiffening varies significantly between different fillers.

For a given filler source the finer the filler the greater the stiffening effect.

Although performance varies for different fillers, there are no exact tests that can adequately predict their performance.

Different fillers may react differently with different bitumen

2.3

LIME AS FILLER AND MODIFIER TO AC MIX

2.3.1

Chemistry

Hydrated Lime, Calcium Hydroxide Ca (OH) 2, commonly used in soil stabilization have also traditionally been used in AC mixes as a filler to improve the properties. Lime perhaps has special binding qualities in addition to the role of filler. It has been used for the purpose of providing stiffening or reinforcement to the bitumen as well as ‘Filling in’ the voids in the aggregate matrix (ES-2, Asphalt Institute). “Hydrated lime” is a dry powder obtained by hydrating quicklime with enough water to satisfy its chemical affinity, forming a hydroxide due to its chemically combined water (Robert S. Boynton, 1980). It has a surface area of 17-24 m2/gram. 2.3.2

Effect of Lime in AC Mixes

Hydrated lime has gained considerable recognition as a useful additive for improving the performance of bituminous pavements. It is added to some low grade aggregate to render them suitable in bituminous mixes for use in highway construction. Sometimes, it is difficult to coat certain aggregate with bitumen because of their siliceous or acidic surfaces. Hydrated lime, which is highly alkaline, starts a chemical reaction that changes the character of the aggregate surfaces and neutralizes any acidic properties present in the aggregate. Adding hydrated lime often improves the coat-ability and bonding properties of bitumen to these aggregate (Robert S. Boynton, 1980). Thomas W Kennedy et. al., (1984) in their study on “Techniques for reducing moisture damage in AC” reported that hydrated lime has been found to be a very effective additive. Indirect Tensile test results indicated that hydrated lime was effective in reducing stripping and moisture damage effects. Plancher, et. al., (1977) in their research suggested that hydrated lime absorbs carboxylic acids in the bituminous mixes which increase the water resistance and asphalt aggregate bonds. Welch et. al., (1977) studied effect of hydrated lime on bitumen and aggregate mixtures and found that hydrated lime changes the mechanical properties of the mixtures. It has been shown by investigators that the addition of a small quantity of basic oxides such as calcium hydroxide, calcium oxide, and Portland cement helps to maintain adhesion in the presence of water, and retard oxidative hardening (Ishai et. al., 1977). The report on “Lime Treatment of Asphalt Mixes to reduce age hardening and improve flow properties” by a distinguished scientist, Peterson J. Claine indicated that lime treatment on AC mixes reduced asphalt age hardening, increased the high temperature stiffness of un-aged asphalts, reduced the stiffness in aged asphalts at higher temperatures and increased the asphalt tensile elongation at low temperatures. These effects benefit asphalt pavements by increasing asphalt durability, reducing rutting, shoving and other forms of permanent pavement deformation, improving fatigue resistance in aged pavements, and improving pavement resistance to low temperature transverse cracking. These benefits are in addition to the well documented effect of lime in increasing the resistance of pavements to moisture damage (Peterson, J Claine., et. el., 1987).

2.3.3 Method and stage of lime addition The batch of mineral aggregate shall be dried to 300o F, the required quantity of additive shall be added to the aggregate, and the entire mass shall be thoroughly mixed until a uniform distribution of additive has been achieved. Care shall be taken to minimize loss of lime to the atmosphere in the form of dust. It is unified that the addition of hydrated lime to AC mixes does increase stability and reduce the hardening rate of bitumen present in the mixes. Hydrated lime is usually added to aggregate at the pug-mill. It may serve as filler in the aggregate material. Researches have established that the addition of hydrated lime can increase bitumen content in the AC mixes over the normal bitumen content without risks of raveling or bleeding in the completed pavement. This produces a firmer, denser and more durable surface and considered effective in improving the water resistance of asphalt concrete (Peterson, J Claine., et. al., 1987).

2.4

MIX DESIGN AND EVALUATION METHODS

The major properties of AC paving mixtures are stability, durability, flexibility and skid resistance (in case of wearing surface). The mix design methods are the process and procedures to establish the aggregate particle size distribution and to determine the corresponding design asphalt content that would let the AC mix to perform satisfactorily, particularly with respect to stability and durability aspects. Stability is defined by many engineers is the â&#x20AC;&#x153;resistance to deformationâ&#x20AC;? with an implied emphasis towards resistance to flow or rutting, including resistance to tensile, compressive, and shear stresses that causes failure in a pavement surface. Durability has been defined as the resistance to the effects of weather and its combination with other forces. Durability is enhanced with high content of bitumen, however, resistance to flow or deformation is impaired with high bitumen content. As a consequence, the amount of bitumen to be used in a bituminous paving mix must be in a balance to optimize durability but yet maintain adequate stability (Jimenez, R. A., 1986). There are many mix design methods used throughout the world such as Marshall Mix design method, Hubbard field mix design method, Hemet Mix design method, Asphalt Instituteâ&#x20AC;&#x2122;s

Triaxial method of mix design etc. Out of these Marshall Mix design method is used in this study and discussed in detail.

2.4.1

Mix Design by Marshall Method

The Marshall procedure as applied to design and control of bituminous mixtures used was evolved during the period from World War II to late 1950’s by U. S Army Corps of Engineers. Motivation for its development came from the need for a mix design procedure to proportion aggregate and bitumen border to sustain increasing wheel load and tire pressure of military aircrafts during World War II. In order to achieve these needs, Corps began an investigation to select a test apparatus that was simple and easily portable and could be used in the field for control purposes. The second phase of this study was to determine the method of compacting laboratory specimen in order to achieve the density as that obtained in field. The third phase of this investigation was the establishment of satisfactory design criteria and control procedure (Ziauddin, A. Khan, 1988). The Corps of Engineers selected a testing machine and a method of bituminous mix design conceived by Bruce Marshall of Mississippi State Highway Department. The Marshall Test procedure has been standardized by the American Society for Testing and Materials by ASTM designation D-1559 “Resistance to Plastic Flow of Bituminous Mixtures Using Marshall Apparatus”. The procedure and design criteria, is adopted by RHD with some modifications to suit the environmental conditions in Bangladesh and shown in Table 2.1. The use of these criteria must be limited to hot bituminous paving mixes using penetration grades of bitumen and containing aggregate size of 1 inch or less. The corps of Engineers found that, in order to have the proper balance between durability and stability, the air voids in the total mix should be limited to between 3 and 5 percent and the voids in the aggregate mass filled with bitumen 75 and 85 percent. The RHD standards requires the air voids to be between 3 and 5 percent for AC wearing course mixes and between 3 and 7 percent for base coarse mixes. Since its development in 1940’s the Marshall method has increasingly been accepted by highway agencies throughout the world to design and control the bituminous paving mixtures. A review of literature indicates that Marshall Stability is a measure of tensile

strength. Smith V. R, (1984) wrote in his research paper that the Marshall Stability values are affected primarily â&#x20AC;&#x153;by the tensile strength or cohesion properties of a mixtureâ&#x20AC;?. Benson, (1952) found a linear relationship between Marshall Stability and cohesion-meter value. It would seem to be apparent that the Marshall test does give a measure of tensile strength and that the success in preventing shear deformation (rutting) failure come form the control of aggregate texture and gradation, bitumen content, and compaction. During the past few years, other supplementary tests such as indirect tensile test, resilient modulus and creep test etc. have been used to evaluate the engineering properties of AC mixes. Table 2.1: Mix Design Criteria for AC Wearing Course (RHD Project Specification â&#x20AC;&#x201C; 2006) for heavy traffic > 1 msa. Marshall Mix Criteria Compaction (No. of blows on each face) Stability, kN Flow, mm Percent Air Voids Percent voids in mineral aggregate Marshall Stability Flow Ratio Percent Voids filled Percent Bitumen Content Percent Loss of Stability on immersion

Min. 8.2 2.5 3 15 2.5 75 5.5

Max. 75 4.5 5 20 85 6.5 25

2.4.2 Indirect /Diametral / Split Tensile Strength The indirect tensile test is one type of tensile strength test used for stabilized materials. The indirect tensile test can be used to characterize bituminous mixes in terms of (Kennedy, T.W., 1977): a)

resilient elastic properties,

properties related to thermal cracking,

properties related to fatigue cracking, and

properties related to permanent deformation

The test is non-repetitive Indirect Tensile Strength and conducted by loading a cylindrical specimen with a single compressive load which acts parallel to and along vertical diametrical plane. This loading configuration develops a relatively uniform tensile stress perpendicular to the direction of applied Load and along the vertical diametrical plane, which ultimately causes specimen to fail by splitting along vertical diameter. The development of stresses within cylindrical specimen subjected to load is reported by (Kennedy et. al., 1977). The test has been standardized as AASHTO T 283 under the title “Resistance of Compacted Asphalt Mixtures to Moisture Induced Damage”. Diametral Tensile Strength is also called Split Tensile Strength is a form of Indirect Tensile strength for measuring the change in diametral tensile strength resulting form the effect of saturation and accelerated water conditioning of compacted mix to simulate with field condition. The tests are conducted on the unconditioned test specimens and on conditioned test specimens after immersion in water at controlled temperature to find the Tensile Strength Ratio (TSR) parameter. The result is used for prediction of long term stripping susceptibility from water on the bituminous mix and evaluating the performance of Anti-Stripping additives. The equation employed in calculating the tensile strength is: in FPS units

σT

2P max/πhD

in SI units

σT

2000P max/πhD

…….. (2.1) …….(2.2)

Where: (σT) is Indirect/split tensile strength; (Pmax) is the load at failure, (D) diameter and (h) the thickness of test specimen. Tensile Strength ratio (TSR) =

(σT2 / σT1)

………. (2.3)

Where: (σT1) is average tensile strength of unconditioned subset of test specimen and (σT2) is the average tensile strength of the conditioned subset of test specimens 2.4.3 Resilient Modulas The elastic modulus of asphalt treated material can be determined by means of the diametral resilient modulus (MR) device. This test is basically a repetitive load test using the stress distribution principles of the indirect tensile test. Like the non-repetitive indirect tensile test,

the main advantage of this test procedure is the simplicity of the test equipment as well as the ability to test asphalt specimens similar in size to those used for the widely known Marshall and Hemet tests. A repetitive (pulsating load) of 0.1 second duration and 0.9 second dwell time is applied diametrically to the test specimen. The dynamic load, in turn, results in dynamic deformations across the horizontal diametrical plane. These deformations are recorded by transducers mounted on each side of the horizontal specimen axis. Knowledge of the dynamic load and deformation allows the MR value to be calculated. Thus, for an applied dynamic load of ‘P’ for the duration‘t’ to produce a resulting horizontal dynamic deformation (δ h), the modulus or MR value is (Yoder, E. J., et. al., 1975): MR = P (μ + 0.2374) / (t δh)

……… (2.4)

A commonly used value of Poisson’s ratio (µ) for AC mix materials is 0.35 2.4.4 Fatigue and Permanent Deformation “Fatigue” is the phenomena of repetitive load induced cracking due to a repeated stress or strain level below the ultimate strength of the material. Fatigue tests may be conducted by several test methods and various specimens. Repeated load indirect tensile (split tensile) test have also been used. The research work had been carried out at Ohio State University also which is based upon fracture mechanic principles applied to a more mechanistic solution of the fatigue problem (Yoder, E. J., et. al., 1975). A common method for evaluating the fatigue characteristics of the AC mix is by repeated flexural testing. In this testing the specimen is applied with a repeated load having sine wave, with a certain adjusted loading and unloading (rest) time. Because of the effect of varying stiffness upon AC fatigue tests, a temperature control system is used around the flexural load device. The range in stress level is selected so as to yield a range in fatigue life between 100 to 1,000,000 repetitions. Fatigue testing may be conducted under two types of controlled loading. They are either (i) Controlled stress or (ii) Controlled strain. In the controlled stress mode a constant load is continuously applied to the specimen. Because of progressive damage to the specimen, a

decrease in stiffness results in. This, in turn, causes an increase of the actual flexural strain with load applications. For the controlled strain (deflection) approach, the load is continuously changed to yield a constant beam deflection. This results in a stress that continuously decreases with load applications, However, since controlled stress conditions give more conservative estimate of the fatigue life (Nf)and is easy to apply, this test may be safely employed. For controlled stress testing, conducted in the laboratory, the effect of stiffness may be accounted for by plotting the fatigue results in a critical tensile strain applied (ε) versus (Nf) relationship on logarithmic scale. This results in a relationship for fatigue tests of the form (Tayebali et. al., 2004): Nf = 4.9016 x 10-2 x (e)0.03029 VFB x (ε)-3.8034 x (S0)-0.98505 …….. (2.5) S0 = 8.560 x (G0)0.9130

.…….. (2.6)

Where (S0) is the Dynamic flexural stiffness and (G0) is dynamic shear stiffness “Permanent Deformation” is a longitudinal depression that forms in the wheel track due to consolidation in one or more of the pavement layers due to repeated traffic load applications. The depressions or ruts are of concern for at least two reasons: i)

if the surface is impervious, the ruts trap water and at depths of 0.2 inch, hydroplaning (particularly for passenger cars) is a definite threat.

ii)

As the ruts progress in depth, steering becomes increasingly difficult, leading to added safety concern.

For pavements in hot tropical climates and subjected to large number of heavy vehicles and/or vehicles operating at high tire pressures, rutting can be a controlling factor. The relationship at a particular number of load repetitions can be stated as: εp = f( σij ) = (5.9055 x 10-3) x Yt

……….. (2.7)

Where (Yt) is the total vertical deformation, mm 2.4.5

Creep

Shell researchers have developed a pavement design system in which rutting potential of asphalt concrete is characterized by a simple “Creep Test”. This has lead to the establishment of an empirical link between rheological properties of bitumen and visco-plastic behaviour of

asphalt concrete. The test has been designed for the following purposes (Kamyar Mahboob, 1990): i)

To measure compressive stiffness or compliance properties of mixture

ii)

To establish plastic flow potential of AC mixes under various stress states in terms of visco-plastic strains.

Based on the research of Van der Poel, (1954) the Creep deformation of cylindrical specimen under a uni-axial, static compressive load is measured as a function of time. In this test, a constant stress (σ0) is applied to the specimen and the resulting time dependent strain (ε t) is measured. For permanent deformation characterization the relevant quality is the stiffness modulus of mix (Smix) defined as (Ziauddin A Khan, 1988): Smix = (σ0 / εt)

………….. (2.8)

Where: (σ0) is Applied Stress, (εt) is measured strain at time (t) and equell to Δh / h 0, Δh is Change in height of specimen and h0 is the Original height of the specimen. Based on the studies, the researchers had recommend a minimum creep modulus of 80 Mpa (120,000 psi) at 40 oC and stress of 200 kpa (30 psi) for conditions of heavy, slow moving traffic.

2.5

SUMMARY

Stripping and damages from water susceptibility is a serious problem faced by the Road project implementing agencies. Two types of testing procedure have been developed to predict the moisture susceptibility of AC mixes: strength and subjective. In strength test, the TSR data have been widely accepted. The Marshall Test equipment can be used by replacing the testing head with an accessory suitable to test the Indirect Tensile Strength in accordance with procedure AASHTO T 283 without major additional expenditures. CHAPTER 3 MATERIAL CHARACTERIZATION, MIX DESIGN AND MOISTURE SUSCEPTIBILITY TESTS 3.1

GENERAL

Material characterization consists of evaluation of engineering properties of component materials i.e., bitumen and aggregate, mix design include determination of design Asphalt

content for layer gradation by Marshall procedure and moisture susceptibility tests covers Marshall stability and Indirect tensile strength determinations. The sequence of testing is shown in Figure 3.1

Material Selection Bolagonj Boulder Crushed Aggregate (coarse & fine ) 80/100 Pen Bitumen Stone gravel (fine)

Material Characterization

Test on Aggregate • Gradation • Specific gravity • L. A. Abrasion • Soundness • Sand Equivalent • Plasticity

Hydrated Lime Characterization

Test on Bitumen • Specific gravity • Softening point • Penetration • Flash Point • Ductility • Solubility

Marshall Mix Design

Water Susceptibility Tests (Stability loss andTSR)

Figure 3.1: Flow Diagram of Material Testing and Mix Design 3.2

MATERIAL SELECTION AND TESTING

3.2.1

Aggregate

Bolagonj Boulder stone is the only source of stone, locally available in Eastern Part of the Bangladesh. Hence the aggregate of this stone source is chosen for the present study. The aggregate fractions for the study have been colleted from stone crushing plant Dhaka. Crushed stone fine aggregate containing fines which is a by-product from stone crushing also

collected from the same plant for use as fine aggregate and filler in the experimental work of this study. The aggregate were subjected to testing as per ASTM standard test methods to evaluate the properties which are of significance for AC mix aggregate. The tests include Los Angles abrasion test, Water absorption test, Sand Equivalent, plasticity, and specific gravity test for coarse and fine aggregates. The test results together with project specifications limit of RHD are summarized in Table 3.1. These results are in agreement with RHD project specifications (2006) for AC wearing course. Table 3.1: Test Result of Aggregate TEST

Wearing course

Los Angles Abrasion, % (ASTM C-131) Specific Gravity Bulk O.D. (ASTMC-127) Apparent (C-128) Water Absorption, % Soundness, % Loss (ASTM C-88) Apparent Specific Gravity of Lime (ASTM C-128) Coating and Stripping of Bitumen (AASHTO T182), % Broken faces (retained 4.75 mm) 2 or more faces, % Flakiness Index (BS 812 part 7.3) Plasticity Index (AASHTO T-90) Clay lumps and friable particles, % (ASTM C-142) Lightweight pieces, % (AASHTO T113) Sand Equivalent (ASTM D-2419)

CA 2.677 2.757 1.08 8.2

33.4 FA 2.614 2.707 1.29 5.2

RHD Project Specifications 35 Maximum

PG 2.633 2.735 1.40 6.3

2.5 minimum 2 Maximum 10 Maximum

2.727 95

Minimum 95% retained

75% minimum

24 Non-plastic

25 Maximum 3 Maximum

0.09

1 Maximum

0.10 53

1 Maximum 50 Minimum

CA: Crushed Stone Coarse Aggregate (10 mm Nominal size), FA: Crushed Stone Fine Aggregate (includes fines as filler), PG: Natural Stone Gravel 5 mm Nominal Size (pea Gravel)

3.2.2

Bitumen / Asphalt Cement

Bitumen of grade 80/100 penetration is used in experimental works of this study and collected from the sealed container/drum manufactured by Eastern Refinery, Chittagong. The main reason of using this grade is its wide use in all road projects in the country being the single refinery in Bangladesh. A series of RHD specification recommended tests including penetration, specific gravity, softening point; thin film oven (TFO) test, flash point, ductility, and solubility in carbon

tetrachloride were conducted for the basic characterization properties of penetration grade asphalt. The test results are shown in Table 3.2, which complies with the requirement of RHD specifications (2001). Table 3.2: Test Results of Bitumen Physical Properties & Test Designation Fresh Sample Specific gravity, @ 25 oC (ASTM D-70) Penetration dmm @ 25o C (ASTM D-5) Softening Point in oC (ASTM D-36) Flash Point, Cleavland Open Cup, o C (ASTM D-92) Solubility in carbon Tetrachloride (ASTM D-4) TFO Sample Percent loss (TFO) (ASTM D-1754) Penetration dmm @ 25oC (ASTM D-5),

3.2.3

Test Results

RHD Specifications (2001)

1.025 82 49 320 99.8

1.01 â&#x20AC;&#x201C; 1.05 80 - 100 45 â&#x20AC;&#x201C; 52 oC 250 Min 99 Minimum

0.057 65

0.5 Maximum 64 Minimum

Filler

This study is initiated to evaluate the effect of Lime as a modifier in AC mixtures to compare the AC mix without lime and modified AC mixes with lime. As such the two types of fillers used in this study are: 1)

Crushed Stone fillers

Crushed stone filler with hydrated lime

Crushed stone filler (0.075 mm finer material) supplemented to the combined mineral aggregate from crushed stone fine aggregate (FA). Hydrated lime was added in four different percentages (1%, 1.5%, 2% and 2.5%) in mineral aggregate of Modified AC mixes. The weight of the crushed stone filler (0.075 mm finer material) reduced by the amount of added lime from the mineral aggregate for test specimens preparation. Hydrated Lime collected from local vendors to ensure availability in future. In both types the percent finer than 0.075 mm determined and found to greater than 75 and acceptable in reference of specifications for filler.

3.3

MIX DESIGN

The optimum design of paving AC mixes is one that best satisfies a set of desirable mix properties at optimum construction and maintenance costs. These properties can be summarized as (Asphalt Institute, MS-2, 1995):

Stability to meet traffic demands without distortion or displacement.

Skid resistance to meet the need for traffic safety, particularly under wet condition.

Fatigue and rutting resistance with longer life under repetitive traffic loading conditions without cracking or permanent deformation.

Durable mix resistant to climate including moisture effect without wear or cracks and stripping yielding better ridding conditions and lower maintenance costs.

Mix with sufficient voids to allow additional compaction under traffic loading without flushing or asphalt bleeding and loss of stability.

6. 3.3.1

Sufficiently workable to allow efficient placement without segregation. MIX DESIGN BY MARSHALL METHOD

Establishment of Design gradation: Sieve analysis of the component aggregate fractions and filler carried out and combined gradation worked out by trial and error or graphical methods. Design gradations is achieved by proportioning the component fractions, in proportion of 55 %, 25 % and 20 % of 10 mm nominal size crushed stone, Crushed fine aggregate consisting of fines also and natural gravel 5 mm nominal size (pea gravel) respectively. The design grading satisfies the grading range of RHD Specification for AC wearing course and shown in Table 3.3 and Figure 3.2. Details of these are also shown in Appendix-1 Table 3.3: Individual aggregate fraction and Combined Design Gradations: Sieve (mm) 12.5 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075

Coarse Aggregate 100 80.3 15.1 6.6 3.5 2.5 1.9 1 0.6

Fine Aggregate 100 100 99.3 97.3 86.6 71.5 50.4 26.3 15.5

Pea Gravel 100 99.4 88.7 46.1 13.9 4.5 1.9 1.2 0.8

Combined (55, 25, 20) % 100 89.0 50.9 36.8 26.4 20.2 14 7.5 4.4

RHD Specification (2001) 100 60 – 90 45 -65 25 – 45 15 – 35 12 – 30 9 – 20 5 – 15 3-7

Figure 3.2: Design Gradation Curve of mineral Aggregate Preparation of Test Specimens: Proportioning and batching was done to obtain 1200 gram combined mineral aggregate for each specimen separately according to established gradation and shown in Table 3.4. Prepared combined aggregate batches were then placed in the oven maintained at a constant temperature of 160oC for eight hours. Sufficient quantity of bitumen for a day’s work was heated up upto 150oC prior for adding with aggregate. Use of re-heated bitumen was avoided in the research work in order to achieve consistent results. Mechanical Mixer was used for mixing the aggregate and bitumen to ensure uniform coating of bitumen on the aggregate. Table 3.4: Batch weights of Aggregate and Bitumen for test specimens Fraction Size (mm)

Individual Weight (gms.)

12.5 – 9.5 9.5 – 4.75 4.75 – 2.36 2.36 – 1.18 1.18 – 0.6 0.6 – 0.3 0.3 – 0.15 0.15 – 0.075 < 0.075

132.0 457.2 169.2 124.8 74.4 74.4 78.0 37.2 52.8

Cumulative weight (gms.) 132.0 589.2 754.4 883.2 957.6 1032.0 1110.0 1147.2 1200.0

Weight of Bitumen (by weight of mix) for 1200 gm of combined aggregate (gms.), at different percentages 4.5 % 56.6 gms. 5.0 % 63.2 gms. 5.5 % 69.8 gms. 6.0 % 76.6 gms. 6.5 % 83.4 gms. 7.0 % 90.3 gms

Correct amount of bitumen added to the hot combined aggregate in the bowl, placed in position on the mixer and allowed to mix for two minutes. Standard Marshall Moulds of 4 inch (10 cm) diameter, 2.5 inch (6.3 cm) height, were heated in the oven upto 140 oC. The

thoroughly mixed material then placed in the mold, treated with strokes of spatula in and around and compacted with 75 blows (for heavy Traffic) of hammer on each face of the specimen. The mixing and compaction temperature of test specimen was maintained 155 oC and 145 oC corresponding to viscosities of 170 Âą 20 and 280 Âą 30 centistokes kinematics respectively as recommended in (Asphalt Institute, MS-2, 1995) USA. Triplicate test specimens for the bitumen content were fabricated for a range of bitumen contents (5.0 to 7.0%) with increment o.5%. Compacted specimens were left to cool down for at least four hours before extrusion. Specimens were left to cure at room temperature for 24 hrs before testing. Mix Design Tests Procedure: Marshall Test was conducted on each cylindrical specimen 4 inch (10 cm) diameter by 2.5 inch (6.3 cm) height. Prior to stability test, all specimens were weighed in air and submerged in water. From this information the bulk specific gravity (Gmb) of compacted specimen was calculated as described in ASTM D2726. The specimens were then placed in a controlled temperature water bath at 60oC (140oF) for 35 minutes. Upon removal from the water bath, the specimen was placed on its side in the breaking head of the Marshall test Apparatus, as shown in Fig. 3.3, and a load was continuously applied on the outer circumference of the specimen at a rate of 2 inch (5 cm) per minute until failure. The maximum load (kN) recorded as the stability and the corresponding deformation in the specimen (mm) measured by the flow meter reported as flow. Percentages of air voids in the specimens calculated from bulk specific gravity of the specimens as per ASTM D2726 and the maximum theoretical specific gravity of the mix determined from test designation ASTM D2041 and shown in Appendix-2 and 3. Stability loss, after 24 hours immersion in water at 60 oC (140oF), also determined to evaluate the resistance to stripping. This was estimated on the basis of Marshall Strength loss of the conditioned specimen in water at 60oC for 24 hours with respect to the stability determined after 35 minute immersion in water at 60oC for 35 minutes.

Figu re

3.3:

Marshall

Stability and Flow Tests Apparatus Design Asphalt content: The results on AC specimen are shown in the Table 3.5 and plotted against % bitumen content on a liner scale and presented in Figure 3.4. Each point shown on the plot is a numerical mean of triplicate tests on specimens. Bitumen contents from the graphical plots corresponding to maximum Stability, Maximum Bulk Specific gravity and the median of specified voids (i.e. 4%) is noted. The optimum bitumen content of the AC mix then calculated as the numerical mean of the bitumen contents as noted above and found to be 5.9%. This procedure of determining the optimum bitumen content has been revised by a new procedure. The MS-2 (Asphalt Institute, USA, MS-2, 1995) and ORN-19 (Transport Research Laboratory, UK, Overseas Road Note 19, 2002) renamed the optimum bitumen content as Design Bitumen Content which is a value which satisfies all the design criteria and also corresponds to the median of specified range of voids. The design bitumen content as worked out is found to be 5.8% (by weight of mix) and shown in the Figure 3.5. Table 3.5: Mix design data from tests and calculations % AC by wt of mix 5.0 5.5 6.0 6.5 7.0

Comp. SG (Gmb) 2.298 2.342 2.367 2.372 2.365

Max SG of Mix Gmm) 2.49 2.471 2.453 2.435 2.417

Air voids (%) 7.71 5.22 3.51 2.59 2.15

VMA (%) 17.68 16.55 16.1 16.37 17.06

VFA (%) 56.39 68.46 78.2 84.18 87.4

Stability (kN) 14.54 18.13 16.51 15.25 15

Flow (mm) 3.5 3.7 3.9 4.2 4.5

The AC mix properties, then read from the characteristics curves shown in Figure 3.4 corresponding to design bitumen content. The properties corresponding to design bitumen contents are summarized in Table 3.6 together with RHD specifications limits for AC wearing coarse mix. At the design bitumen content, the mix design criteria parameters are well satisfied the RHD specification requirements. Bitum en Conte nt v/s Com pacted Bulk Spe cific Gravity

Comp. Bulk Sp. Gravity

Marshall Stability (kN)

Bitum en Content v/s Marshall Stabliity

18 17 16 15 14 13 5

5.5

6.5

2.38 2.36 2.34 2.32 2.3 2.28 5

Bitum en conte nt v/s Air voids in com pacted m ix

7 6 5 4 3 2 1 5.5

6.5

Bitum e n Content (%)

6.5

Bitum e n Conte nt v/s Voids filled w ith Bitum en Voids Filled (%)

Air Voids (%)

9 8

5.5

Bitum en Content (%)

90 85 80 75 70 65 60 55 50 4.5

5.5

6.5

Bitum e n Content (%)

7.5

Bitum en Content v/s Flow

Bitum en Content v/s VMA 4.7

4.5 Flow (mm)

VMA (%)

17.5 17 16.5 16

4.3 4.1 3.9 3.7 3.5 3.3

15.5 5

5.5

6.5

5.5

6.5

Bitum en Content (%)

Bitum en Content

Figure 3.4: Characteristics Curves of AC mix Properties 4.5

4.6

4.7

4.8

4.9

5.0

5.1

5.2

5.3

5.4

5.5

5.6

5.7

5.8

5.9

6.0

6.1

6.2

6.3

6.4

6.5

Bitumen % Bitumen Content @ 4% air voids, 5.8%

Design Bitumen Content

Flow mm) VMA (%) Voids Filled with Bitumen (%) Air Voids (%) Stability (kN) Range of % Bitumen satisfying all design criteria (5.6 – 6.3) %

1. Design Bitumen Content corresponding to 4 % voids in laboratory compacted mix: 5.8 %

Figure 3.5: Determination of Design Bitumen Content for Optimum mix Table 3.6: Properties of Optimum AC Mix at Design Bitumen Content. Mix design Criteria Design Bitumen Content, % (by wt. of mix) Marshall Stability, kN Air voids, % Voids filled with Bitumen, % Flow (mm) Filler-Bitumen ratio Loss of Marshall Stability after 24 hours submersion at 60 oC as compared to 30 minutes submersion, % Rigidity ratio: Stability/Flow (kN/mm)

AC Wearing

RHD Project

Course mix 5.8 17.3 4.0 77 3.8 0.76

Specification (2006) 4.5 – 6.5 8.2 Minimum 3-5 75 - 85 2.5 – 4.5 0.6 – 1.2

25 Maximum

4.55

2.5 minimum

After studying the test results, it is found that for the designed aggregate gradation, the Design Asphalt Content required is 5.8% (by weight of the mix). This Design Asphalt Content will be used in preparing further mixes and test specimens with addition of different percentages of lime to substitute the crushed stone filler. The prepared mixes will be

subjected to further tests, such as Marshall Stability loss, Dimetral/Split /Indirect tensile strength on lime modified mix in varying doses of lime.

3.4

MOISTURE SUSCEPTIBILITY TESTS

Following tests shall be carried out on the Optimum AC mix without lime and modified AC mixes with lime in varying doses to characterize the mix behaviour in respect of moisture susceptibility aspects. The tests which are conducted to analyze the effects are: 1.

Marshall Stability and Flow test of conditioned and unconditioned compacted mixes for Loss of Stability.

Indirect / Split / Diametral Tensile Strength of conditioned and unconditioned compacted mixes for Tensile Strength Ratio.

3.4.1

Experimental Programme

Establishment of Compaction Effort for 7 % voids: Standard Test procedure for Indirect Tensile Strength requires testing on specimen having voids 6 to 7 %. As such the compaction effort, the number of blows to be applied on the test specimen during its preparation has to be established. To establish this, test specimens at design bitumen content 5.8% (by weight of mix) prepared by applying 25, 40 and 55 number of blows of Marshall Hammer on each face of the specimens. Percent air voids in the compacted test specimen computed using bulk SG of specimen and the maximum SG of the mix. A characteristics curve, number of blows verses air voids drawn and corresponding to 7% air voids the numbers of blows as 44 blows obtained and shown in Figure 3.6.

% voids in compacted mix

8.5 8 7.5 7 6.5 6 20

No. of compaction blows applied on Te st Specimen

Figure 3.6: Number of Blows applied on the Specimen v/s Air voids

Schedule of Tests: To study the effect of lime as modifier on characteristics of designed mixes, AC mixes with 0%, 1%, 1.5%, 2.0% and 2.5% of lime as a replacement of crushed stone fines filler were prepared. AC mix with no lime (0% lime) represents the control mix and lime added mix represent the lime modified mix A set of six test specimens were prepared using 75 blows of hammer on each face to determine the loss in stability each for no lime and added lime in varying doses. Similarly a set of eight test specimens were prepared using 44 blows of hammer to get 7 %air voids in the compacted mix for no lime and added lime in varying doses of lime. The test specimens prepared with 75 blows were tested for stability after immersion in water at 60 0C for 35 minutes and 24 hours to determine the loss in Stability. The test specimens prepared with 44 blows of hammer were subjected to Indirect / dimetral / split tensile strength test on unconditioned (after 2 hours soaking in water at 250C) and conditioned specimens (24 hours immersion in water at 600C plus 2 hours immersion in water at 25 0C) to determine the tensile strength ratio (TSR). Distribution of the test specimen for each type of test is shown in Table3.7. Table 3.7: Schedule of tests for water susceptibility of AC mixes Test

Control Mix

Marshall Stability for Loss of Stability @ 60o C

@ 25oC (2 hrs)

@ 60oC (24 hrs)

Indirect / Split / Dimetral Tensile Strength for Tensile Strength Ratio

+ @ 25oC (2 hrs)

Total

Modified AC Mix with lime 1% 1.5% 2.0% 2.5%

Mixes with no lime (0% Lime) indicate the â&#x20AC;&#x2DC;Control Mix (Having crushed stone fines filler only).

ii)

Mixes with 1%, 1.5%, 2% and 2.5% of Lime indicate the percentage of crushed stone

fines filler replaced by hydrated lime. Marshall Stability for Loss of Stability: To correlate the effect of water on the AC mixes, loss of stability determination is one of the methods usually practiced. The loss of stability is obtained as the decrease in stability after 24 hours immersion of test specimen in water at

600C with respect to stability determined after 35 minutes immersion. Thus, in this study the Marshall Stability tests performed on modified mixes after 35 minute immersion and 24 hours immersion in water maintained at at 60 0C temperature. The result shall be used to know the effect of lime on the stability loss characteristic of the AC mixtures for comparison with loss of stability of optimum AC mix without lime. Indirect / Diametral /Split Tensile Strength for Tensile Strength Ratio: Test Specimens prepared by Marshall Mix design procedure using 44 compaction blows of Marshall Hammer on each face to achieve an air void of 7 percent (within 1% variation), using Optimum AC mix without lime and modified AC mix with lime in varying doses to replace crushed stone filler. The test specimens were subjected to the indirect tensile test as per test procedure AASHTO T 283. The test involved loading the specimen with a compressive load acting parallel to and along vertical diametrical plane through 0.5 inch (13 mm) wide stainless steel strips which are shaped at the interface to match with the specimen for uniform distribution of stresses. The strain rate of 2 inches (50.8 mm) per minutes is used as recommended in the standard test procedure. The set up of the test and the test specimen failed by splitting along the vertical diameter are shown Fig. 3.7 and 3.8. Split tensile strength and Tensile strength ratio are estimated using the equation 2.1, 2.2 and 2.3 and explained in chapter 2. To determine the TSR of the various AC mixes, specimens were tested after 2 hours immersion in water at 25oC and 24 hrs at 60oC + 2 hrs at 25oC. Ratio of Indirect tensile strength of the specimens after (24 hrs + 2 hrs) immersion in water to the strength of specimens after 2 hrs immersion in water is expressed as the Tensile Strength Ratio (TSR). Various International officials and authorities had suggested the limiting value of TSR. ORN 19 (Transport Research Laboratory (UK), Overseas Road Note 19, 2002) suggests a figure of at least 80% for tropical countries while several State Highway Departments, (USA) adopt a figure of at least 85% (Aniruddha Vilas Shidhore, 2005) for TSR.

Fig. 3.7: Specimen in Testing Machine for ITS

Fig. 3.8: Failed Specimen along vertical diameter

3.5

SUMMARY

After studying the test results of Marshall mix design method it is found that for the selected aggregate gradation, the design asphalt content required is 5.8 %. The design asphalt percentages will be used in preparing further mixes with different percentages of lime as substitute to the conventional crushed stone filler. The prepared mixes will be subjected to further tests, such Stability loss, Split tensile strength for estimation of effects of water susceptibility on AC mixes. Test result indicates that addition of lime upto 2.5 % is effective in increasing the Tensile Strength ratio and reducing the loss of stability of AC mixes. The trend of increase in TSR and reduction in

Loss of stability are commensurate to the percentage of lime added. These results are supported by the statistical analysis performed on the tests data. CHAPTER 4 TESTS RESULTS AND DISCUSSION

4.1

GENERAL

Results of laboratory testing carried out to evaluate the engineering properties of the optimum AC mix without lime and modified AC mixes with lime in varying percentages is discussed in this chapter . A statistical approach has been adopted in the analysis of test data using the standard deviation values adjusted for 90 % confidence level. The evaluation of results has been carried in reference to the results for same properties of the optimum AC mix without lime to quantify the benefits achieved for resistance to adverse effect of water.

4.2

MARSHALL STABILITY FOR LOSS OF STABILITY

Marshall Stability Analysis at 60o C after 35 minutes and 24 hours of immersion in water is performed estimate the loss of stability of the modified mixes. This has led to the results shown in Table 4.1 for the Optimum AC mix without lime (control mix) and modified AC mixes with lime in varying percentages (lime modified mixes). The details are shown in Appendix-4. The loss of stability as obtained for control mix is in the order of 23 percent. This value is very close to the maximum permissible value of 25 percent, set forth by the Roads and Highway department (Bangladesh) specifications. The analysis of the results of loss of stability of lime modified AC mixes by adding upto 2.5% lime show that there is reduction in loss. The stability losses with 1.0%, 1.5 %, 2.0% and 2.5% addition are 19.7%, 16.6%, 12.7 and 11.2 respectively and show a trend of proportionate reduction with increase in added percentage of lime. A reduction of 0.1 mm to 0.3 mm in the flow value of the lime modified AC mixes is observed in comparison of control mix. The reduction in flow value is proportionate to the percentage of added lime replacing the stone filler. This is an indication for the improvement in resistance to rutting on the road, while experiencing the repetitions of traffic load under hot climate. Percent reduction in loss of stability of lime modified AC mixes in doses of 1%, 1.5%, 2%, 2.5% while comparing with loss of stability of control mix (without lime) are14.58, 28.08, 44.92, 51.54 respectively. The comparisons of the results are shown by graphical wizards in Figures 4.1, 4.2 and 4.3.

Table 4.1: Loss of Stability Data from Marshall Tests Mix Type Control mix

No lime 1.0 % Modified 1.5 % AC mix 2.0 % with lime 2.5 %

M. Stability M. Stability Loss of Improvement (kN), at 600C (kN), at 600C Stability (%) in Stability for 35 min. for 24 hrs. (%) 17.18 13.21 23.11 0 17.17 16.91 16.80 16.61

13.78 14.21 14.66 14.75

19.74 16.62 12.73 11.20

14.58 28.08 44.92 51.54

Figure: 4.1: Marshall Stability after 35 minutes and 24 hours

Figure 4.2: Effect of addition of Lime on Loss of Stability

Figure 4.3: Effect of addition of lime on % Reduction in Loss of Stability

4.3

INDIRECT TENSILE STRENGTH FOR TSR

The results of Indirect Tensile Strength test of control mix with no lime and lime modified mixes in varying percentages of lime are shown in Table 4.2 and details in Appendix 5. It is observed from the results that addition of lime can increase the Indirect Tensile strength of conditioned specimens (soaked in water at 60 0C for 24 hours plus at 25 0C for 2 hours) of modified AC mixes to achieve the desired target of Tensile Strength Ratio (TSR). In comparison to the TSR of control mix (without lime), there is increase in TSR of lime modified mixes by 3.3%, 5.3%, 6.6% and 8.1% when 1%, 1.5%, 2% and 2.5 lime is added respectively to replace the crushed stone filler in AC mix. Various Comparisons of the results are shown by graphical wizards in Figure 4.4, 4.5 and 4.6. Table 4.2: Split Tensile Strength and Tensile Strength Ratio of various AC mixes Split tensile Split Tensile Strength Tensile Strength after 2 after (24 hrs at 600C + Strength hrs at 250C. 2 hrs at 250C) Ratio (%) 540.4 426.5 78.9

Mix Type Control

No lime 1.0 % 1.5 % 2.0 % 2.5 %

Lime modified

Ind.Tensile Strength (kPa)

700

616.7 554.6 548.4 566.0

502.8 460.6 461.4 483.0

ITS of Unconditioned Specimen

% gains

81.5 83.1 84.1 85.3

0.0 3.30 5.32 6.59 8.11

ITS of Conditioned Specimens

600 500 400 300 200 100 0 0

1.5

2.5

% lim e added to replace filler

Figure 4.4: Ind. Tensile Strength of Conditioned and un-conditioned specimen

Tensile Strength Ratio (%)

86 84 82 80 78 76 74 0

1.5

2.5

% lim e added to replace filler

Figure 4.5: Effect of Lime on Tensile Strength Ratio (TSR)

% improvement in TSR

9 8 7 6 5 4 3 2 1 0 0

1.5

2.5

% lim e added to replace stone filler

Figure 4.6: Effect of Lime in improving the Tensile Strength Ratio (TSR)

4.4 STATISTICAL ANALYSIS The effects of lime addition in varying percentages to modify the AC mixes are analyzed statistically using the data obtained from the tests performed on the control optimum AC mix without lime and modified AC mixes with lime. The data from the Marshall Stability test and the Indirect Tensile Strength test for estimating the percent loss of stability and Tensile Strength Ratio has been adjusted for statistical corrections and deviations to define the Limits. The Upper Limit (UL) and the Lower Limits (LL) for population mean has been established using the computed Standard Deviation for 90% confidence levels separately (L. R. Kadiyali Dr., 1998). The results are as discussed below. 4.4.1 Results of Statistical Analysis

Statistical analysis of the results of Marshall Stability on test specimen after 35 minutes and 24 hours when soaked in water at 60 0C reveals that â&#x20AC;&#x153;different percent of added lime have equal meansâ&#x20AC;?. This indicates that there is an effect on the results when lime is added to replace the crushed stone filler and to modify the AC mixes with lime. The Loss of stability is getting reduced proportionately with increase in percentage of amount of added lime. Details of these are shown in Tables 4.3 for stability after 35 minute immersion in water and that of stability after 24 hours in Table 4.4, when soaked in water maintained at 60 0C. Loss of Stability as estimated from the results is shown in Table 4.6.Upper Limit and Lower Limit have been defined by the adding and subtracting the standard deviation value adjusted for 90 % confidence level from the arithmetic mean value. In estimation of loss of stability three situations from the Upper Limit, Lower Limit and combination for most critical situation have been considered for 90% confidence levels and shown in Table 4.5. The comparisons of results are shown by graphical wizard in the Figure 4.7. Table 4.3: Marshall Stability (kN) after 35 min immersion in water at 600C

Test Specimen - 1 Test Specimen - 2 Test Specimen - 3 Mean Variance Standard Deviation UL for 90% Confidence Level LL for 90% Confidence Level

% Lime added to replace Stone Filler 0.0 1.0 1.5 2.0 2.5 17.34 16.88 16.88 16.73 16.70 16.88 17.46 17.06 16.78 16.12 17.32 17.17 16.78 16.88 17.02 17.18 17.17 16.91 16.8 16.61 0.0676 0.081 0.0202 0.0059 0.2082 0.260 0.285 0.142 0.077 0.456 17.600 17.64 17.14 16.92 17.36 16.750 16.7 16.68 16.67 15.86

Table 4.4: Marshall Stability (kN) after 24 hrs immersion in water at 60 0C

Test Specimen - 1 Test Specimen - 2 Test Specimen - 3 Mean Variance Standard Deviation UL for 90% Confidence Level LL for 90% Confidence Level

% Lime added to replace Stone Filler 0.0 1.0 1.5 2.0 2.5 13.35 13.79 14.5 14.52 14.97 13.05 13.94 14.21 14.82 14.35 13.22 13.64 13.93 14.64 14.92 13.21 13.79 14.21 14.66 14.75 0.0227 0.0225 0.0813 0.0228 0.1187 0.15 0.15 0.285 0.151 0.344 13.46 14.04 14.68 14.90 15.32 12.96 13.54 13.74 14.41 14.18

Table 4.5: % Loss of Stability after 24 hours immersion in water at 60 0C 0.0 23.52 22.63 27.7

on UL basis on LL basis on Critical basis

% loss of Stability

1.0 20.41 18.92 24.55

% Lime added 1.5 14.35 17.63 20.38

2.0 11.94 13.56 15.06

2.5 11.75 10.59 20.05

Upper Limit @ 90% confidence level Low er limit @ 90% confidence level Most Critical situation @ 90% confdence level

25 20 15 10 5 0 0

1.5

2.5

% lim e added to replace stone filler

Figure 4.7: Statistical Evaluation of Loss of Stability data Statistical analysis on the test data of Indirect / Split / Diametral Tensile Strength after immersion in water at 2 hours at 25 0C and (24 hours at 600C+2 hours at 250C) also reveals that there is an effect of lime addition on the results. The results of Indirect Tensile Strength are shown in Table 4.6 for unconditioned (2 hours of immersion) specimen and in Table 4.7 for conditioned (24 hours + 2 hoursâ&#x20AC;&#x2122; immersion) specimens for different AC mixes. The Tensile Strength Ratio (TSR) results as estimated from the results in consideration of standard deviation adjusted for 90% confidence level are shown in Table 4.8. The comparisons of results are shown by graphical wizard in figure 4.8. Table 4.6: Indirect Tensile Strength (kPa) after 2 hrs immersion in water at 25 0C, UnConditioned Specimens) Test Specimen - 1 Test Specimen - 2 Test Specimen - 3 Test Specimen - 4 Mean Variance Standard Deviation UL for 90% Confidence Level LL for 90% Confidence Level

% Lime added to replace Stone Filler No lime(0) 1.0 1.5 2.0 2.5 545.3 606.6 563.2 548.6 555.60 556.7 620.5 550 546 579.7 536.1 632.6 563.8 544.9 558.1 523.4 607.1 541.2 554 570.4 540.38 616.7 554.55 548.38 565.95 199.062 151.807 119.771 16.469 125.871 14.109 12.402 10.944 4.058 11.219 563.59 637.1 572.55 555.06 584.41 517.17 596.3 536.55 541.7 547.49

Table 4.7: Indirect Tensile Strength (kPa) after 24 hours immersion in water at 60 0C, followed by 2 hours at 25 0C (Conditioned Specimens) % Lime added to replace Stone Filler No lime(0) 1.0 1.5 2.0 2.5 433.2 505.5 458.4 457.5 494.10 423.6 500 467.1 461.6 473.9 433.2 509.8 453.3 456.1 475.3 416.6 495.7 463.7 470.5 488.6 426.65 502.75 460.63 461.43 482.98 65.371 28.633 36.663 42.049 98.889 8.085 5.351 6.055 6.845 9.944 439.95 517.55 470.59 472.69 499.34 413.35 493.95 450.67 450.17 466.62

Test Specimen - 1 Test Specimen - 2 Test Specimen - 3 Test Specimen - 4 Mean Variance Standard Deviation UL at 90% Confidence Level LL at 90% Confidence Level

Table 4.8: Tensile Strength Ratio (TSR) % Lime added to replace Stone Filler No lime(0) 1.0 1.5 2.0 78.06 81.24 82.19 85.16 79.93 82.84 83.99 83.1 73.34 77.53 78.71 81.1

on UL basis on LL basis on Critical basis

88 86 84

2.5 85.44 85.23 79.84

Upper Limit of TSR data @ 90% confidence level Low er Limit of TSr data @ 90% confidence level Most critical situation @ 90% conf idence level

% TSR

82 80 78 76 74 72 70 68 66 0

1.5

2.5

% Lim e added to replace stone filler

Figure 4.8: Statistical Evaluation of Tensile Strength Ratio (TSR) data 4.4.2 Repeatability and Reproducibility The precision to be expected in test values as determined from various tests involved in this study has been evaluated with reference to the recommended values and figures for repeatability and reproducibility in Standard Test procedures of AASHTO (USA) primarily. In case of absence of provisions in AASHTO the provisions of BSI (UK) has been adopted.

4.5 SUMMARY The behavior of the Optimum AC mix without lime and the modified AC mixes with lime designed by Marshall Method, under static loading are analyzed using Marshall Stability and Indirect Tensile Strength characterization tests. Test results indicate that addition of lime in varying doses to replace the crushed stone filler by the same amount is effective in improving the engineering properties of the AC mixes. The loss of stability is getting reduced and Tensile strength ratio enhanced of the modified mixes proportionate to the amount of lime added. From the results of Stability Loss and Tensile Strength Ratio, it can be concluded that high quality asphalt concrete mixes and more resistant to adverse water susceptibility effects can be prepared by using lime as modifier in AC mixes using aggregate of crushed Bolaganj boulder stone. High Stability Loss and poor Tensile Strength Ratio are the main cause of stripping in AC mix with aggregate of Bolaganj crushed stone and lime modified AC mixes has shown resistance against the damaging effect of water. Therefore, use of lime as a modifier in AC mixes shall provide the desired benefits. Similar researches have been done in Kingdom of Saudi Arabia and the addition of hydrated lime in AC mix has been found to be effective in reducing the damaging effect of water (Mirza Ghouse Beg, 1995). Also the damaging effect of water has been also studied in USA on lime modified AC mixes containing Baghouse fines and designed by Superpave mix design method and found to be more resistant to the effects of water (Aniruddha Vilas Shidhore, 2005).

CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS 5.1

GENERAL

The objective of this study is to evaluate and quantify the effects of water susceptibility from lime modification of AC mixes, and to compare those effects with the AC mix without lime. AC Mixes both the without lime and lime modified with varying doses tested for Stability and Split / Indirect / Diametral Tensile Strength on Un-conditioned and conditioned specimens. The test data were further used in estimation of the loss of stability and Tensile Strength Ratio parameters. Subsequently, these estimated parameters evaluated for, to come up with the results showing the effectiveness of lime in modifying of AC mixes produced by using aggregate of Bolaganj stone boulder.

5.2

CONCLUSIONS

Based on the laboratory tests, its interpretation and evaluation, the following conclusions are drawn: i).

Incorporation of hydrated lime in varying doses to replace the crushed stone fines filler by the same amount has resulted in change in the engineering properties of the AC mixes with respect to moisture susceptibility effects.

ii)

Results of modified AC mixes with lime show a resistance towards the adverse effects of water on compacted mix on the pattern of, increase in quantity of added lime, increases the resistance against the adverse effects of water. In comparison to the AC mix without lime, an increase in Tensile Strength Ratio is achieved by 3.3%, 5.3%, 6.5% and 8.1% corresponding to 1.0%, 1.5%, 2.0% and 2.5% lime addition respectively. Also a reduction in the loss of stability of 14.8%, 28.1%, 44.95 and 51.5% corresponding to 1.0 %, 1.5%, 2.0% and 2.5% lime addition is observed. The reduction in loss of stability and enhancement in TSR are in comparison of the properties of AC mix without lime and.

iii)

The increase in TSR and increase in resistance towards loss of stability are commensurate with increase in quantity of added lime. The TSR values as obtained by adding 1%, 1.5%, 2.0% and 2.5% of lime are 81.5%, 83.1, 84.1 and 85.3 % respectively. The added lime shall be decided to satisfy the applicable specifications which varies from 80% to 85% of TSR depending on the climatic conditions

5.3

RECOMMENDATIONS

In view of the observations made from this research work, the following recommendations are made: 1. In this study, Lime modified mixes were tested at temperature range 25oC and 60oC as recommended in the standard test procedure. Tests at lower temperature range 25 oC

and 45oC may also be conducted and evaluated for. The effect of the lime addition as modifier and to replace the stone filler proportionately in AC mixes in lower temperature range 25oC and 45oC could better simulate the prevailing temperatures in Bangladesh during peak winter and summer seasons. 2. In this study the test are carried out in the laboratory static loading, the study works could be extended for dynamic and repetitive loadings also. 3.

The research work could also be extended to observe the effects on shear properties, dynamic modulus, modulus of resilient, fatigue, plastic deformation and creep of lime modified mixes to the establish the performance behaviors.

4. The research study may also be extended, for designing AC mixes using “Superpave Mix Design” procedure developed under “Strategic Highway Research Programme, USA” using Superpave gyratory compactor in preparation of test specimens. Test specimen prepared using gyratory compactors are considered more representative of compaction during construction than the Marshall Hammer prepared test specimen.

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