ADVANCEMENTS IN PAVEMENT TECHNOLOGIES

Advancements in pavement technologies

1. INTRODUCTION

Many of the existing road networks all over the world are being widened and strengthened. Also new highways and expressways are being constructed to handle the demand of the rapidly increasing traffic volumes. With the increase in demand for efficient road network, awareness to use efficient strategies and improved pavement performances are being studied extensively by the transport officials all around the world. The ill treated pavements along with poor maintenances have lead to increased discomfort and safety for the potential road users. There has been an increasing demand for the road user safety as well as the time savings in travel because, generally, travelling is considered as a disutility. This demand is not constant over time. The reason can be simplified as the “ insatiability of the human needs”. This means the human needs can never be satisfied, as the olds say, it’s hard to fill a cup with a hole in it.

Many such developments have been made in the field of pavement technology such as drainable or permeable pavement system which are rapidly gaining popularity in Japan because of the high level of precipitation and the growing need for measures against the deteriorating road environment. In the field of interlocking block pavements, highly-porous permeable systems are expected to be increasingly used for constructing walkways and other facilities. In the case of crack treatments on pavements, there are two primary types of crack treatment materials currently in use: hot pour and emulsified. Hot pour materials require heating prior to application and cold pour materials generally pour at ambient temperature because they have been emulsified with water and do not require heating prior to application. Both materials are asphaltic in nature and may contain polymer, rubber, fibers as well as other proprietary additives. Much such innumerable advancement has been made in this field from researchers all over the world.

In our discussion, we shall mainly focus on the recent developments in the field of pavement technology in the evaluation procedure based on the type of pavement failures, the maintenance aspect of the pavements, and the recent advancements regarding the type of pavement interface.

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2. PERFORMANCE EVALUATION

For many years, state highway agencies (SHA) have been trying to assess which rehabilitation technology is best suited for their roadways. This research deals with the evaluation of field performance of new flexible pavement technologies all over the world. The alternatives considered by an agency for rehabilitation usually represent current practice. However, they almost invariably continue to change as new technologies become available. Very often, successful and cost-effective technologies seem to become part of the long-term practice.

A pavement is a complex structure, which is subjected to many diverse combinations of loading and environmental conditions. Adding to this complexity are; materials behaviour, varying pavement performance and their interrelationships. Traffic loading and environmental factors cause hot mixed asphalt (HMA) pavements to degrade and eventually fail in various ways. The modes of failure are typically categorized as permanent deformation, cracking, surface defects, and potholes, commonly referred to as pavement distresses.

Mixture design methods, structural design procedures, and construction specifications are designed to combat early failure of the HMA pavements. Fatigue cracking, rutting, and edge cracking are load related distresses. Thermal cracking, block cracking, and reflection cracking are caused principally by environmental factors and thus are considered non-load related distresses. Bleeding, ravelling, and potholes are caused by a combination of environmental factors and traffic loads. In any given situation, the feasible set of pavement rehabilitation alternatives may be much smaller than the total available options because of costs, physical constraints, or the condition of the existing pavement.

In this context, the performance evaluation is also done based on various other parameters such as performance grade binder temperature range, traffic volume, highway classification, maximum aggregate size and climate. We can also estimate the time of application of these rehabilitation work on the pavements based on their performances, that is, the expected life of the rehabilitation strategies utilized on the pavements may be shorter than could be expected had rehabilitation been done before distress reached this high level. Such considerations can also lead to an economic strategy for the rehabilitation work on pavements.

2.1 FLEXIBLE PAVEMENTS

The term flexible pavement composed of bituminous material and aggregate mixtures or various combinations of layers of these mixtures on layers of aggregate base or sub base. Although designs may vary in the combination of these materials, the flexible pavement functions in a definite manner under traffic loads. The flexible pavements generally doesn’t take up any load as such, instead they just transmit the load directly to the ground or subgrade. This load transfer mechanism is assumed to be a grain to grain transfer mechanism and it’s assumed to be trapezoidal variation from the point of application of load to the subgrade soil. It is the intent of the design that deflection of the pavement in reaction to wheel loads will not stress the materials to the point of fracture within a reasonable life expectancy of the pavement.

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Various design procedures are adopted all over the method. Some of those methods are empirical in nature and others are experimental determination of various properties such as the subgrade soil strength properties etc. The methods that comes under experimental determinations are California bearing ratio method (CBR), plate load test etc. Various empirical methods also has been developed by the researchers all over the world such as the US Corps of engineers have developed the Engineers formula for the design of the pavements considering the wheel load expected over the life of the pavement. The Indian Road Congress has also developed various empirical methods for the determination of the required thickness of the pavement for supporting the subgrade soil from deterioration.

Figure 1

2.1.1 Polymer Coated Bitumen

In this section, we shall look upon the performance evaluation done in the case of polymer coated bitumen build roads. Plastics waste constitutes a significant portion of the total municipal solid waste (MSW) generated in India. It is estimated that approximately 10 thousand tons per day (TPD) of plastics waste is generated. Their visibility has been perceived as a serious problem and made plastics a target in the management of solid waste. Plastics are non-biodegradable. They also have very long lifetime and the burning of plastics waste under uncontrolled conditions could also lead to generation of many hazardous air pollutants (HAPs) depending upon the type of polymers and additives used. However, the end-of-life plastics can be recycled into a second life application but after every thermal treatment, degradation of plastics takes place to a certain extent.

Plastics wastes consisting of mainly poly olefins from items such as carry bags, cups, thermocoles and packaging films pose a major problem for their disposal. In this study, the

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plastics wastes were shredded into small size, i.e. 2 mm to 4 mm, molten and thereafter coated over hot aggregate at 1600C. Several roads have been built in this manner in the State of Tamil Nadu, Puducherry, Maharashtra, Kerala and Andhra Pradesh using polymer-coated–bitumen aggregate

2.1.1.1 Plastics As A Binder

Waste plastic is shredded into required size and mixed with hot stone (150 – 1700c) with uniform mixing. When heated to around 1500c to 1700c, they melt and in their molten state they spread over the stone as a thin liquid, which acts as a binder.

2.1.1.2 Precaution

The plastics cannot be melted separately to use for coating. The stone is heated to 1700c and the shredded plastic film is sprayed over the hot stone. On contact with the surface of the hot stone the plastic gel softened and coated over the aggregate. It is important to note that the size of the shredded plastic should be in the range of 4.2mm to 1.18mm. The shredded plastics should be less than the surface area of the aggregate to get uniform coating. Otherwise the binding will not be effective. 2.1.1.3 COATING OF PLASTIC OVER GRANITE STONE

The stones can also be made to bind with bitumen strongly resulting in better mix for road construction likely; (i) The coating of plastics over stone reduces the voids in the stone and helps to reduce moisture absorption to a great extent. (ii) Solid deposition on the pores of stone results in degradation of stones. This is also prevented. (iii) The spreading of bitumen is also made easy.

2.1.1.4 PROCESS OF CONSTRUCTION OF FLEXIBLE PAVEMENT

Process: I

The roads were laid using both Mini Hot Mix Plant and central mixing plant. The aggregate mix prepared as per IRC specification, was heated in the cylindrical drum to 170 deg. C. It was then transferred to the puddling compartment where the plastics waste (size between 1.18mm and 4.36mm) was added. As the temperature of the aggregate was around 170 deg. C and the softening temperature of plastics waste was around 135 deg. C the plastics waste got softened and got coated over the aggregate within 30 to 45 seconds. Immediately the hot bitumen 60/70 grade (≈ 160° C) was added and mixed in the puddling chamber. The bitumen got coated over the aggregate. As the plastics and the bitumen were in the liquid state they got mixed. The mixture was transferred to the road and it was spread and compacted using 8 Ton roller.

Process: II

For the construction of long distance roads it is very important that the plastics coated aggregate should be tried with Central Mixing Plant. Using a mechanical device the plastics waste was mixed quantitatively with the aggregate at the cylindrical drum before the addition of bitumen. The material collected at the tipper was uniform and had a temperature of 140

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deg. C. This was transported to the spot and the road was laid using ‘paver’ and 8 Ton roller. The spreading was good and the laying was easy. During the process the materials got mixed at; 1. At the tipper 2. During the transfer from tipper to paver and 3. By the pavers during spreading for road laying. This ensures better distribution of plastics and help better binding

ROUGHNESS SURVEY

The surface unevenness of highway pavements refers to the regularity of surface finish both in longitudinal and transverse directions. Almost in all major highway works executed, control of surface unevenness has been introduced as a mandatory requirement. The existing standards and tolerances of surface unevenness are prescribed in IRC special publication 16-2004.

Type of road surface Conditions of road surfaceGood Average Poor

Surface dressing <3500 3500-4500 >4500Open graded premix carpet <3000 3000-4000 >4000

Mix seal surfacing <3000 3000-4000 >4000Semi dense bituminous concrete <2500 2500-3500 >3500

Bituminous concrete <2000 2000-3000 >3000Cement concrete <220 2200-3000 >3000

Table 1

The field experiments have revealed that none of the values have exceeded the permissible range specified by the Indian Road Congress.SKID RESISTANCE TEST

The portable skid resistance tester was designed by R.R.L. U.K, to provide a simple and rapid method for checking the skid resistance in local areas and entails measuring the frictional resistance between a rubber slider (mounted on the end of a pendulum arm) and the wetted road surface. In this case the loss in energy of the pendulum arm, after the slider has traversed the surface, is equated to the work done during the sliding process. The instrument measures directly the coefficient of friction on graduation scale. The measurements are recorded as 100 times the coefficient of friction. When the tester measures the polishing characteristics of road aggregates, the measurement is called the polished stone value (PSV). The test has been standardized in the UK under BS: 812-1967.

Guide to interpret Skid Resistance Values. Road Research Laboratory, Great Britain Type of site Min Value of Skid

Number (surface wet)

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Difficult site such as: Round-abouts ,Bends with radius less than 150 m on unrestricted roads, Gradients ,1in 20 or steeper, of lengths greater than 100m, Approaches to traffic lights on unrestricted roads

65 (A)

Motorways ,trunk roads, heavily trafficked roads in urban areas (carrying more than 2000 vehicles per day)

55 (B)

All other sites (city roads with more traffic) 45 (C)

Table 2

The Skid resistance values obtained for the roads made up of the plastic tar road declares that the roads are good in wet condition.

SAND PATCH TEST

The ability of bituminous surfacing to provide the required skid resistance is governed by its micro texture and macro texture. The macro texture of the surfacing, as measured by its texture depth, contributes particularly to wet skidding resistance at high speeds by providing drainage routes for water between tyre and road surfaces. The surface condition should include a qualitative assessment of texture in the wheel paths so that it can be used to trigger quantitative testing if required. The sand patch test is described in detail in BS 598 Part 105.

Texture Depth in mm Surface characteristics of pavement 0-0.4 Smooth 0.4-0.6 Medium >0.6 Rough

Table 3

BENKELMAN BEAM

Benkelman Beam is a device, which can be conveniently used to measure the rebound deflection of a pavement due to a dual wheel load assembly or the design wheel load.

Rebound Deflection (mm) Strength of pavement 0.5-1 Reasonably strong 1-2 Moderate 2-3 Weak >3 Very Weak (permanent Deformation)

Table 4

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The rebound deflection values of the plastic tar road are less than 1. This shows that these stretches are reasonably strong.

FIELD DENSITY ANALYSIS

The field density is studied to find the compactness of the road. The field is an important test to find the nature of the road and also the performance of the road after a prolonged period of open to the atmosphere. The ageing of bitumen and the crushing of aggregates is mainly responsible for the reduction in the field density.

SURFACE CONDITION SURVEY

Pavement condition surveys are generally conducted by any one of the following methods: (i) Walk survey- associated with or without actual measurement (ii) Drive survey

In a walk survey, a team of experienced highway engineers walks along the road and makes visual observations. The actual measurements may also be carried out on a representative and relatively shorter stretch. In a drive survey, the team travels along the road in a vehicle at a slow speed (say 10 to 15 km/hr) and records the surface condition by visual observations. The data is recorded at convenient interval (unit lengths of the stretch) say 200 m, by noting down distress in each interval. In view of time constraints and large length involved, the visual condition survey method was undertaken by driving in a slow vehicle moving slowly at a speed of about 10-15 km/hour. During the survey, the following items of distress were visually recorded for every 200m in terms of percentage of the pavement surface area.

CONCLUSIONS

Experiment tests were done for the roads constructed at various places in Cochin and Tamilnadu, and the test results observed were completely satisfactory and all the values were in the permissible range proposed by the IRC and UK standards.

2.1.2 REINFORCED STEEL FABRIC

A study on the reinforced steel fabric was done in Sweden where the design the road structure with steel fabric reinforcement in the asphalt concrete. Three fullscale100-meter test sections were built. Two test sections were reinforced with steel fabrics and one section was left without reinforcement as a reference road section. These sections were instrumented with strain gauges. The sections were tested by means of deflection measurements with Falling Weight Deflectometer, strain measurements at the bottom surface of the overlays, strain on the steel bars, unevenness and rut depth measurements, and manual distress surveys. The objective is to evaluate the performance of rehabilitated road structure reinforced with steel fabric. Strain measurements at the bottom surface of the asphalt layers show lower strains in the reinforced test sections than in the reference section without reinforcement. A particular road section was taken and the data was collected for the past 7 years of study on that particular road till 2007.

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Figure 2

2.1.2.1 STRAIN MEASUREMENTS

Asphalt strain gauges are located on the milled surface just below the levelling layers. After placement of the levelling, binder and surface layer, the strain gauges end up at different depths from the surface. The strain gauges are located at a depth of 150 mm and 170 mm in the reference and reinforced sections respectively. Placement of strain gauges at different depths complicates the comparison between test sections and the evaluation of the reinforced pavement.

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Figure 3

2.1.2.2 RUT DEPTH

A low speed laser profilometer called Primal, as shown in the figure 4, was used to measure

transverse profiles of the test sections. The profilometer produces highly accurate measurements of the transverse surface profile at intervals of 2 cm with an accuracy of 0.1 mm. The first measurements were performed in August 2000 before the road was opened to traffic. Figure 5 shows the average rut depth per section based on both wheel paths. The presented rut depths are the total rut depths measured on the surface and it is not possible to determine how much of the rut is generated by asphalt layer, unbound pavement layer, and subgrade, respectively. Figure 6, representative transverse profiles are presented and no indication of flow rutting can be seen in the shape of the profiles. This means that the rutting mainly depends on deformation/compaction of the layers. It is concluded from Figure 10 that rut development is smaller in the structures with the reinforced pavements than in the reference structure.

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Figure 4

Figure 5

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Figure 6

2.1.2.3 CONCLUSIONS

The comparison of deterioration between a reinforced and a traditionally constructed road

Structure has been presented above. The following can be concluded:

1. Results from Falling Weight Deflectometer measurements have not in this case been able to show any significant differences between the test sections with or without steel reinforcement.

2. Measured strains in the field show lower strain values for the reinforced structures.

3. Rut development is smaller in structures with the reinforced pavements than in the traditionally constructed road structure.

4. Referring to the strain levels and rut depth developments, the service life for the reinforced structure will be prolonged significantly in the studied case.

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2.1.3 GEOSYNTHETIC REINFORCED FLEXIBLE PAVEMENTS.

A study was done to characterize the deformation behaviour of geosynthetic-reinforced flexible pavements during dynamic surface loading. Cyclic plate load (CPL) tests were performed using a Vibroseis (shaker) truck, figure 7 on a low-volume, asphalt pavement frontage road in Eastern Arkansas (the Marked Tree Site). This site is among the most unique geosynthetic-reinforced pavement research sites in the country, consisting of sixteen 15-m long sections including different geosynthetic types, two base course thicknesses, and control sections. The goal of the CPL tests in this study was to understand the relative surface deformations in several of the test sections due to dynamic loading. Specifically, the Vibroseis was used to apply 100,000 loading cycles to the pavement at a peak dynamic force of 62 KN (a static hold-down force of 40 KN with a superimposed +/- 22 KN dynamic force). These loads were applied to a dual wheel-sized footprint resting on the pavement surface at a rate of 50 Hz. The permanent and dynamic surface deflections due to the applied loading were recorded every 500 cycles using nine LVDT’s located at incremental distances from the loading footprint. The results from the different sections clearly show improved pavement performance with increasing base course thickness. However, the influence of the reinforcement (unreinforced, geogrid, geotextile, geogrid over geotextile) was not clearly

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identified. It is possible that more surface deflection is needed before the contribution of the geosynthetic is mobilized.

2.1.3.1 FIELD TEST SITE

A series of sixteen, 15-m long, geosynthetic-reinforced pavement test sections were constructed by the Arkansas State Highway and Transportation Department. The subgrade at the site is poor and generally classifies as fat clay (CH, UCCS; A-7-6, AASHTO) with an average PI of 42. Prior to construction, a significant amount of this material was obtained from a borrow source and compacted on-site to bring the road up to the desired grade. Due to differences in the initial surface elevations and the various base course thicknesses, the 25-cm base sections ended up with approximately 90 cm of compacted subgrade soil, while the 15-cm base sections ended up with approximately 150 cm of compacted subgrade. This subgrade soil was compacted to a dry unit weight of 18.6 kN/m3, and had a soaked CBR of approximately 1.5. The base courses were constructed as 25cm for the first 6 sections and as 15cm for the remaining 6 sections.

A traffic survey was conducted at the Marked Tree Site over a period of one week by AHTD in August 2009. The results of this survey show that the average number of ESAL loadings per year is 165 for Sections 1b to 6 (approximately 658 since the road was completed in 2005), and 115 for Sections 8 to 13b (approximately 459 since 2005). The 25 cm-base course sections have received 40% more loading that the 15 cm-base course sections because of a driveway leading to a retirement home intersecting the test road at the transition. The falling weight Deflectometer was used and the resilient modulus was back calculated from the FWD values. The following figure 8 represents the loading set-up of the truck and figure 9 represents the surface deflection measurement system.

Figure 7

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Figure 8

Figure 9

2.1.3.2 RESULTS

Every 500 cycles the peak dynamic deflections and the accumulated permanent deformations were recorded so that they could be plotted versus the total number of loading cycles up to that point. An example of the accumulated permanent surface deformations as a

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function of number of loading cycles from two of the LVDTs is shown in Figure 10. These results are for Section 13a, a geogrid-reinforced section with 15 cm of base course. Under static loading (i.e., under 40 kN before cyclic loading starts), a deflection of 1 mm was observed directly under the tire footprint, while at distances greater than 40 cm from the footprint a small amount of surface heave was recorded. Under application of the dynamic loads, the deflection under the footing continued to increase, reaching a maximum value of approximately 4 mm after 100,000 cycles. Correspondingly, increases in the surface heave at distances greater than 40 cm were measured with increasing number of loading cycles, reaching a maximum value of more than 1 mm after 100,000 cycles. No meaningful permanent deformation was measured at distances greater than 120 cm from the footprint regardless of the number of loading cycles. The data from all of the LVDTs can be synthesized to evaluate the permanent deformation profile after different numbers of cycles, as shown in Figure 11. This figure reveals that a substantial amount of permanent deformation occurs in the initial cycles of loading. A pronounced surface heave was noted at a distance of 60 cm from the loading plate, which may indicate the formation of a shear plane within the pavement layer.

Figure 10

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Figure 11

2.1.3.3 CONCLUSIONS

The results from full-scale cyclic plate load (CPL) tests on geosynthetic-reinforced pavements are interpreted and compared in this study. The CPL tests clearly indicate improved pavement performance with increasing base course thickness. The CPL test results were not significantly impacted by the subgrade. No clear difference in pavement performance was noted in sections with the same base course thickness but with different reinforcement type (geogrid, geotextile, or the lack thereof). The lack of improvement in the geogrid sections may be because of the location of the geogrid (at the bottom of the base course layer). It is possible that differences in the reinforced and unreinforced pavement sections may be more evident if the pavement is subject to greater strains. The maximum surface deflection imposed in these tests was 0.6 cm, less than a typical ‘failure’ rut depth of 2.5 cm. Under strains closer to those induced during loading of a “failed” pavement section, the effect of the geosynthetic reinforcement may be more evident in the deflection profiles (due to mobilization of lateral restraint and tensioned membrane mechanisms). However, under these ‘working’ strain levels the contribution of geosynthetic reinforcements to pavement deformation was only observed in terms of a change in heave for thinner base course sections. However, research is needed to evaluate if the magnitude of the permanent surface heave is an indicator that reflects the impact of geosynthetic reinforcement.

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2.2 RIGID PAVEMENTS

Concrete pavements have been used for highways, airports, streets, local roads, parking lots, industrial facilities, and other types of infrastructure. When properly designed and built out of durable materials, concrete pavements can provide many decades of service with little or no maintenance. Concrete generally has a higher initial cost than asphalt but lasts longer and has lower maintenance costs.

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In some cases, however, design or construction errors or poorly selected materials have considerably reduced pavement life. It is therefore important or pavement engineers to understand materials selection, mixture proportioning, design and detailing, drainage, construction techniques, and pavement performance. It is also important to understand the theoretical framework underlying commonly used design procedures, and to know the limits of applicability of the procedures.

2.2.1 PERFORMANCES

Concrete pavement engineering is the selection of design, materials, and construction practices to ensure satisfactory performance over the projected life of the pavement. Pavement users are sensitive to the functional performance of pavements – smoothness and skid resistance – rather than structural performance. Pavements, as a general rule, develop distresses gradually over time under traffic loading and environmental effects. An exception is when poor material choices or construction practices caused effects before or shortly after the pavement is put into service. In our discussion, the distresses will be mainly concentrated on four major types, they are

1. Cracking2. Joint deficiencies3. Surface defects4. Miscellaneous distresses.

CRACKING

Cracks may form in concrete pavements due to a one time overload or due to repeated fatigue loading.

CORNER BREAKS

Corner breaks only occur at corners of JPCP or JRCP. A triangular piece of concrete, from 0.3 m (1 ft) to half the width of the slab, breaks off. These are more likely with longer slabs, because as the slabs warp or curl upward the slab corners may become unsupported and break off when heavy vehicles travel across them. Huang(2004: 378) notes that “load repetitions combined with loss of support, poor load transfer across the joint, and thermal curling and moisture warping stresses usually cause corner breaks.” Corner breaks may be avoided by limiting slab lengths, particularly with stiffer sub bases, and by providing load transfer to adjacent slabs through dowels and tie bars.

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DURABILITY CRACKING

Durability or “D” cracking occurs near joints, cracks, and free edges, and is manifested as a “closely spaced crescent-shaped hairline cracking pattern”(Miller and Bellinger 2003: 37). The cracks are often darker than the remaining uncracked concrete. Yoder and Witczak note that the phenomenon is regional and due to use of non-durable materials and/or severe climatic conditions. It is a progressive failure mechanism than may eventually result in nearly total disintegration of the slab. According to Huang (2004: 387), it is caused by freeze-thaw expansion of some types of coarse aggregate. Mindess et al. note that the problem occurs frequently with limestones in Midwestern states in the United States.

LONGITUDINAL CRACKING

Longitudinal cracks are defined as those parallel to the pavement centreline (Miller and Bellinger). Huang suggests that longitudinal cracks are caused by a combination of heavy load repetitions, loss of foundation support, and curling and warping stresses, or by improper construction of longitudinal joints. If longitudinal cracks are not in vehicle wheel paths and do not fault appreciably, the effect on pavement performance may not be significant. Longitudinal cracks are also likely to occur at the crowns of crowned pavements if longitudinal joints are not provided.

TRANSVERSE CRACKING

Transverse cracks are defined as those perpendiculars to the pavement centreline (Miller and Bellinger. They are a key JPCP concrete pavement performance measure, because once a transverse crack forms its faulting and deterioration leads to severe roughness. JPCP does not have steel across the crack to hold it together. The cracking can progress and lead to a shattered slab, requiring slab replacement (Hoerner et al. 2001: 70). Huang notes that transverse cracks are “usually caused by a combination of heavy load repetitions and stresses due to temperature gradient, moisture gradient, and drying shrinkage.”

JOINT DEFICIENCIES

These are classified as seal damage or spalling. These damages mainly concentrate at the joints which lead to the weakening of the dowel bars or tie bars provided which ultimately results in the failure of the pavement at the joints.

JOINT SEAL DAMAGE

Joint seals are used to keep incompressible materials and water from penetrating joints. Incompressible materials can lead to stress concentrations when open pavement joints close, causing some of the concrete to spall off. Water leads to deterioration in the pavement

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and underlying layers. Typical types of joint seal damage include extrusion (seal coming up out of joint), hardening, adhesive failure (loss of bond), cohesive failure (splitting), complete loss of sealant, intrusion of foreign material, or weed growth in the joint (Miller and Bellinger 2003: 44). Joints must be periodically cleaned out and resealed, and this type of damage usually indicates a need to maintain the joints.

JOINT SPALLING

Joint spalling is defined as “cracking, breaking, chipping, or fraying of slab edges within 0.3 m (1 foot) from the face of the joint”. Spalls are a surface phenomenon and are generally caused by incompressible materials creating stress concentrations in joints as they close due to slab expansion or traffic loading. They may also be caused by “poorly designed or constructed load transfer devices”. Therefore, the best way to avoid spalls is to properly maintain joints. Spalls may also be caused by poor construction practices, such as failing to properly cure pavement joints after saw cutting.

SURFACE DEFECTS

Unlike cracking and joint deficiencies, surface defects are usually unrelated to design. They are due to either poor materials selection or poor construction practices, or both.

MAP CRACKING

Map cracking is defined as a series of cracks that extend only into the upper surface of the slab. Larger cracks frequently are oriented in the longitudinal direction of the pavement and are interconnected by finer transverse or random cracks. According to Huang (2004:387), it is usually caused by over finishing of concrete. Mindess et al. (2003:507) note that map cracking can either be caused by excessive bleeding and plastic shrinkage from finishing too much or too early, which leads to fine cracks, or by ASR, which leads to coarse cracks.

It is useful to distinguish between map cracking due to finishing problems, which is unlikely to progress further, and map cracking due to ASR, which is likely to progress and lead to eventual destruction of the pavement. ASR is an increasingly important problem for concrete pavements, and is difficult to fix.

SCALING

Scaling is defined as the deterioration of the upper concrete slab surface, normally 3–13 mm (1/8-1/2 inch), and may occur anywhere over the pavement. Scaling may progress

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from map cracking. Scaling may also occur with repeated application of de-icing salts. This type of scaling may be prevented by using an adequately air entrained low permeability concrete with a low water/cement (w/c) ratio. Risk of scaling is higher on concrete surfaces that have not been finished properly.

POLISHED AGGREGATES

Polished aggregate problems refer to surface mortar and texturing worn away to expose coarse aggregate. This typically leads to a reduction in surface friction. The reduction in surface friction can make pavements unsafe, particularly in wet weather.

Because cement paste does not have good abrasion resistance, the wear resistance of concrete depends on the hardness of aggregates used. Poor finishing practices may also lead to a weak surface layer and lower abrasion resistance. Skid resistance may be restored by diamond grinding, but with soft aggregates the treatment may have to be repeated in a few years.

POPOUTS

Popouts are small pieces of pavement broken loose from the surface, normally ranging in diameter from 25–100 mm (1–4 inches), and depth from 13–50 mm (1/2–2 inches). Popouts may be caused by “expansive, nondurable, or unsound aggregates or by freeze and thaw action” (Huang 2004: 387). Popouts and D-cracking are caused by similar mechanisms.

2.2.2. NOISE CHARACTERISTICS OF OPEN GRADED FRICTION COURSES

This experimental feature documents the construction of two quieter pavements:

(1) An open-graded friction course (OGFC) modified with an asphalt rubber binder, hereafter referred to as OGFC-AR and

(2) An OGFC with a styrene-butadiene-styrene (SBS) polymer asphalt binder hereafter referred to as OGFC-SBS. OGFC, with a higher volume of surface voids (a minimum of 15 percent air voids), absorb some of the noise generated at the tire/pavement interface and are thus “quieter” than densely-graded pavements with fewer voids (around 4-8 percent). This aggressive proclamations regarding rubberized open-graded pavement as the answer to making pavements quieter has reached even to the public sector who are now asking for this type of pavement to be used on the highways that bisect their

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DOWNSIDES OF OPEN GRADED FRICTION COURSES

There are downsides with the use of open-graded pavements. Open-graded pavements are very susceptible to excessive wear from studded tires. This excessive wear produces ruts in the pavements that fill with water during rainy periods and pose the additional hazard of hydroplaning. The other downside is pavement life. The life of open-graded pavements is cut short by the studded tire wear.

Open-graded pavements also have benefits other than reducing the noise level. Drivers have improved visibility during rain storms on open-graded pavements due to the open void structure that drains away excess water. The quick drainage of water away from the surface of the pavement also improves the wet weather friction resistance of the roadway and decreases the potential for hydroplaning. At night the drainage capability of the pavement helps to improve visibility by reducing the glare associated with standing water on the pavement. Painted traffic markings are also more visible at night because of less water standing on the roadway.

2.2.2.1 MIX DESGIN

The mix design for the OGFC-SBS was performed in the WSDOT Headquarters Materials Laboratory. The starting point for the percent of asphalt was determined by an asphalt retention process which suggested using 6.8 percent. Samples were mixed at 6.3, 6.8 and 7.3 percent asphalt and evaluated using the FHWA pie plate drain down test. The results of the pie plate drain down test suggested using more asphalt than the initial target of 6.8 percent. However, before additional tests could be conducted, a recommendation was needed for the mix design that was to be used for the construction of the test section at the asphalt plant site in Everett.

Therefore, a preliminary design calling for 7.8 percent was issued for the test section construction. Additional samples were then mixed using 7.3, 8.3, and 8.8 percent asphalt and evaluated using the pie plate drain down test. All of the samples were in specification for volumetric properties, but the pie plate drain down test suggested that 8.3 percent was optimum; therefore, the asphalt content for the mainline paving was set at this level. The gyration level used for the mix design was 50 based on a recommendation from the ADOT.

The Special Provisions required that the asphalt binder for the OGFC-AR would be G58-22 or PG64-22. The crumb rubber must conform to the gradation requirements. .The crumb rubber will have a specific gravity of 1.15 ± 0.05 and will be free of wire or other contaminating materials, except that the rubber will not contain more than 0.5 percent fabric. Calcium carbonate could be added to prevent the particles from sticking together. The minimum amount of crumb rubber required in the mix was 20 percent by weight of the asphalt binder.

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The temperature of the asphalt binder at the time of the addition of the crumb rubber should be between 350 and 400°F. A one-hour reaction period was required after the mixing of the rubber with the binder. At the end of the reaction period the rubber particles must be thoroughly “wetted” without any rubber floating on the surface or agglomerations of rubber particles observable.

The temperature of the asphalt-rubber immediately after mixing will be between 325 and 375°F. The mixed asphalt-rubber must be kept thoroughly agitated during the period of use to prevent the settling of the rubber particles. In no case can the asphalt-rubber be held at a temperature of 325°F or above for more than 10 hours. Asphalt-rubber held for more than 10 hours must be allowed to cool and gradually reheated to the prescribed temperature. A batch of asphalt-rubber can only be cooled and reheated in this manner once.

2.2.2.2 EVALUATION

WEAR AND RUTTING

As mentioned, the performance of the OGFC decreases with the passage of time. This decay in performance has lead to the formation of rutting after the end of the design life period of 10 years.

2.2.2.3 NOISE MEASUREMENT

Noise measurement is a new concept to the paving community. There are three types of sound measurements currently used to characterize highway noise as noted below:

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1. Source measurement: measures the effect of pavement on tire/pavement interaction source level.

2. Sound absorption measurement: measures the effect of pavement on sound absorption.

3. Wayside measurement: measures the effect of pavement on communities.

SOURCE MEASUREMENT

There are three types of source measurements;

1. The Close-Proximity Method (CPX),

2. The On-Board Sound Intensity (OBSI), and

3. The laboratory drum method (DR).

The Close- Proximity Method uses microphones near the tire to measure sound pressure. The tire is mounted on a separate vehicle, usually a special trailer with enclosures around the tire to minimize contamination. This is the type of measurement used by the National Centre for Asphalt Technology (NCAT), ADOT, and throughout most of Europe. The On-Board Sound Intensity method uses two adjacent microphones mounted near the tire to measure sound intensity levels. The microphones are mounted on a vehicle, usually a rear tire, but no enclosure is used to reduce noise from outside sources. This method was developed by General Motors and has been used by the California Department of Transportation (Caltrans) and ADOT and is the method that was used in this study. The final method, the laboratory drum method, is used only in the laboratory. A pavement-lined drum rotates against a tire mounted external to the drum. Microphones near the tire measure sound pressure levels similar to the Close-Proximity Method.

SOUND ABSORPTION MEASUREMENT

There are also three types of sound absorption measurements; (1) impedance tube, (2) impulse response, and (3) ground impedance using effective flow resistivity. The impedance tube methods takes measurement in the laboratory on core samples from the pavement. A sound source (loudspeaker) is mounted at one end of an impedance tube and a sample of the pavement is placed at the other end. The loudspeaker generates broadband, stationary random sound waves that are reflected back from the sample. Sound pressure readings are taken at two points in the tube and from these the sound absorption coefficient can be determined.

The impulse response method can be used in the laboratory or in-situ. A source of sound is used to produce a response from the pavement surface which is then measured. It is similar to the impedance tube method except the measurement is taken in an essentially free field, that is, there is no confinement of the sound by a tube. There is only one microphone used and it measures both the intensity of the source and the amount of absorption by the pavement.

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The ground impedance method uses point source, two-microphone configuration set up on a pavement surface in the field. Data is captured for multiple frequencies to characterize the pavement. The impedance tube method is used strictly in the laboratory. The impulse response and ground impedance methods are used in the field but require a closure of a lane to make the measurements.

WAYSIDE MEASUREMENT

There are four types of wayside measurements;

1. Statistical Pass-By Method (SPB), 2. Controlled Pass-By Method (CPB), 3. Coast-By Method (CB) and 4. Time-Averaging Method.

All four methods use a microphone set at a prescribed distance away from and height above the roadway. The Statistical Pass-By Method measures the sparse highway traffic with a single sound level representing a minimum of 180 single vehicle pass-bys. Traffic (counts, categorizations, speeds) and meteorological data must be captured. The Controlled Pass-By Method is similar to the SPB except that a limited number of controlled vehicles are used to generate the noise. It has been used in both Caltrans and ADOT studies and in several European studies. The Coast-By Method is identical to the CPB except the engine of the control vehicle is switched off during the pass-by. The Time-Averaging Method measures the existing traffic over a prescribed time period. Traffic (counts, categorization, and speeds) and meteorological data must be captured. The method has been used by Caltrans, ADOT and ODOT for studies.

2.2.2.4 NOISE MEASUREMENT EQUIPMENT

The On Board Sound Intensity method was the one chosen by WSDOT because the noise produced by the tire/pavement is the only one that can be controlled by changes in the pavement characteristics. Two adjacent microphones are mounted vertically near a tire to measure the sound intensity level. Data from the microphones is sent to the computer. The computer collects the sound information as 11 separate data points corresponding to frequencies from 500 to 5,000 Hz.

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Figure 12

Figure 13

2.2.2.5 RESULTS

Initial measurements were made on the existing HMA pavement prior to the overlay to serve as a base line. This section ranged in age from eight to twenty years with an average of approximately twelve years. The sound intensity readings ranged between 103.8 and 105.3 with an average of 104.6 dBA. After completion of the open-graded overlays, sound intensity measurements were conducted on a monthly basis, weather permitting (noise measurements

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cannot be made when the pavement is wet) on all lanes of the three sections, OGFC-AR, OGFCSBS and Class ½ inch HMA. With the usage of OGFC, the sound intensity of the lanes got reduced by 22% over the design life. An average sound intensity of 92dBA was recorded over the design life of 10 years.

2.2.3 THIN BONDED OVERLAYS

The thirteenth full-scale Accelerated Pavement Test (APT) experiment at the Civil Infrastructure Laboratory (CISL) of Kansas State University aimed at determining the response and the failure mode of thin concrete overlays. Four pavement structures were built and tested in this experiment: two Thin Concrete Overlays (TCO) pavements, having 100 and 150 mm thick overlays constructed on top of a 125 mm thick PCCP and, two Thin White topping (TWT) pavements, with 100 and 150 mm thick PCC overlays constructed on top of 125 mm hot-mix asphalt layer. The pavements were equipped with instrumentation to measure the strains at selected locations in each PCC overlay. Each of the four pavements was loaded with approximately two million passes of the CISL APT machine, under in-door ambient temperature conditions. No moisture was added to the pavements. Response measurements and performance evaluations were performed at about every 100,000 passes.

Due to the effect of wheel loading, the TCO pavements failed due to the loss of support underneath the concrete slab. No loss of bond between the PCC overlay and the supporting slab was observed. The 100 mm TWT exhibited a transverse fatigue crack at the middle of the slab, while the 150 mm TWT exhibited no cracks at the end of testing. It was found that the magnitude and shape of computed strains matched well those of the strains measured before any APT loads were applied. It was, therefore, concluded that the three-dimensional finite element model built and the assumption made (linear elastic materials, fully bonded overlays) can estimate accurately the response of TWT and TCO pavements under wheel loading and therefore, can be used for predicting the performance of thin concrete overlays.

2.2.3.1 PERFORMANCE OF THE PCC OVERLAYS

The site was reported of excessive fatigue cracking and the solution for which was developed by the thin bonded overlays. The fatigue cracking was overall removed by this method. the cracking formed over the overlays was due to lack of proper grading of concrete and the excessive wheel loads that was deliberately put on the pavement.

The 100 mm TWT pavement section exhibited cracking. One transverse crack developed in the central slab, close to the middle of the slab, at about 400,000 passes of the APT machine. No significant joint faulting was recorded. At the end of loading (2.0 million passes), the 150 mm TWT pavement section exhibited no cracking or significant joint faulting. Due to budget and time constraints it was decided to stop loading on the TWT sections.

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The TCO pavement sections exhibited cracking. One transverse crack developed in the central slabs of both pavement sections, at about 1/3 in length for the West joint, at 1.1 million passes of the APT machine in the 100 mm TCO pavement section and, at 1.7 million passes in the 150 mm TCO pavement section. Several other cracks developed after that only in the 100 mm TCO pavement section. No significant joint faulting was recorded.

At the end of the loading phase of the experiment (after 2,000,000 load cycles), 100 mm diameter cores were extracted from central slabs of TCO on PCCP pavements at several locations near the edges and the corners of the slabs. The examination of the cores showed no de-bonding between the concrete layers. It was thus assumed, and confirmed by the modelling of the pavement response, that the failure of these pavement sections was due to the loss of support underneath the transverse joints, that lead to transverse cracking.

3. MAINTENANCE

Maintenance engineers have been applying treatments to both flexible and rigid pavements for as long as such pavements have existed. The types and application of various treatments for both corrective and preventive maintenance has been the subject of research studies over a number of years, and many publications have reported these findings. The practice of preventive maintenance, since there simply is not enough money available to continue the types of maintenance currently employed.

Pavement management systems (PMS) generally include a subsystem for pavement maintenance which may contain models to determine the most cost effective treatment. These are generally based on pavement type, condition, and other important factors. It is critical, however, that the proper maintenance treatment be placed at the right time for the pavement to function as designed and for the maintenance program to be cost effective. A limitation of many PMS systems is their inability to comprehensively analyze individual projects and determine the proper timing and cost of treatment.

Two types of pavement maintenance are generally recognized, they are preventive and corrective (or reactive). Preventive maintenance is used to arrest minor deterioration, retard progressive failures, and reduce the need for corrective maintenance. It is performed before the pavement shows significant distress to provide a more uniform performing pavement system. Corrective maintenance is performed after a deficiency occurs in the pavement; i.e., loss of friction, moderate to severe rutting, or extensive cracking. Although there are many different definitions for these terms, these are the ones used in this report.

Although each type of maintenance is needed in a comprehensive pavement preservation program, the emphasis should be placed on preventing a pavement from reaching the condition where corrective maintenance is required, since the cost associated with this approach can be substantial. What is really needed is a determination of the cost effectiveness of the preventive maintenance (PM) approach compared with standard practices of rehabilitation when the pavement wears out.

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Figure 14

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Figure 15

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Figure 16

3.1 ELEMENTS OF PAVEMENT PRESERVATION PROGRAMME

The following elements should be considered when developing pavement preservation

program:

1. ESTABLISH PROGRAM GUIDELINES - These guidelines become the instrument to express the overall strategies and goals of the preservation program by providing policy on such features as safety and environmental issues, and identifying a program coordinator. The technical elements of the program, such as what system will be used to determine needs, must also be included. Finally, a system to measure progress in relation to the stated goals of the program needs to be identified.

2. DETERMINE MAINTENANCE NEEDS - A system to determine the existing condition of the pavement network under the jurisdiction of the agency is an essential component of the management program. Pavement management systems (PMS) currently in use by agencies have this component, but they vary widely in their approach and sophistication. Generally, a condition survey is conducted on segments of existing pavements and various distress features are noted. This survey, conducted by trained individuals or with automated vehicles, may be supplemented by

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destructive sampling (i.e., cores and/or slabs) or non destructive testing means (i.e., friction trailer, falling weight Deflectometer, and profilometer/roughness meter). It should be emphasized that the traditional PMS distresses generally indicate failure conditions and do not provide early indicators for preservation.

3. PROVIDE A FRAMEWORK FOR TREATMENT SELECTION - It is important that the maintenance treatment selected is the proper one for the type and levels of distress, the climate, and the level of service expected for the project.

4. DEVELOP ANALYSIS PROCEDURES TO DETERMINE THE MOST EFFECTIVE TREATMENT – A number of procedures exist to determine the cost effectiveness of maintenance treatments (6, 7). These are based on several approaches and vary from simple to complex. A simplified approach, which is based on the decision tree or matrix process.

5. INCLUDE A FEEDBACK MECHANISM TO DETERMINE PROGRAM EFFECTIVENESS - This is a management process to assess how the program is working in relation to the established goals. It becomes a tool to help adjust factors that need to be changed because of program modifications. The feedback should include both individual pavement performance and overall system performance.

3.2 DECISION TREES

As the terminology implies, decision trees incorporate a set of criteria for identifying a particular treatment through the use of “branches.” Each branch represents a specific set of conditions (in terms of factors such as pavement type, distress type and level, traffic volume, and functional classification) that ultimately leads to the identification of a particular treatment.

Many decision trees use distress criteria of a composite nature to further simplify the selection process. The Pavement Condition Index (PCI) is an example of one of these composite distress indices. The problem with decision trees based on a composite distress index is that the treatments do not always appropriately address the actual distress conditions, particularly at the higher levels of deterioration associated with pavement rehabilitation.

The described flow chart provides an example of a relatively straightforward maintenance and rehabilitation decision tree for asphalt pavements using only a few treatments to illustrate the concept. In this example (intended for demonstration purposes only), five criteria are used as the basis for treatment selection. It should be noted, however, that inherent in a simplified decision tree of this type are certain environmental conditions and traffic levels which influenced the original determination of the recommended treatments. Accordingly, users should exercise caution in applying any decision tree for conditions that are outside the basis for its development.

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33


Figure 17

The detailed steps can be summarised as follows:

1. STRUCTURAL DETERIORATION. If little or no structural deterioration exists, the associated treatments are directed at maintaining the functional performance and preserving the intended life of the original pavement. This is the optimum timing for applying preservation treatments. If structural deterioration (in the form of fatigue cracking or rutting) does exist, then the associated treatments are directed more at improving the structural performance; i.e., retarding the rate of structural deterioration and extending the intended life of the original pavement.

2. ENVIRONMENTAL CRACKING. This refers to the transverse, longitudinal, and block cracking that develop in an asphalt pavement as it ages and undergoes the thermal stresses associated with daily temperature cycles. Treatments for this type of distress are intended to prevent moisture intrusion and retard the rate of crack deterioration that occurs at the pavement surface. The extent levels, in this case, are defined as follows:a. Low – The amount of cracking is so slight that there is little question as to the

feasibility of crack sealing.b. Moderate – The cracking has achieved a level where sealing alone may not be cost

effective.c. High – The extent of cracking is so great that crack sealing would definitely not

be cost effective and some other remedial work is required.

3. SURFACE WEAR. This refers to the pavement deterioration that takes place at the asphalt pavement surface (i.e., within the top 20 mm), primarily as a result of tire wear (e.g., polishing) and material degradation (e.g., ravelling). Treatments for surface wear remove and/or cover up the worn surface. The severity levels, in this case, are defined as follows:a. Low – Surface texture and frictional resistance are minimally affected.b. Moderate – Surface texture and frictional resistance are significantly affected. The

potential for wet weather accidents is increased.c. High – Surface texture and frictional resistance are heavily affected. The

probability of wet weather accidents is near (or above) the unacceptable level.

4. FATIGUE CRACKING. Wheel path cracking associated with the cumulative effects of wheel loads is a clear indication of structural deterioration and loss of load carrying capacity in a pavement. Accordingly, rehabilitation strategies tend to focus on removal and replacement of significant amounts of the HMA surface layer and, in some cases, base course. The extent levels are defined as follows:a. Low – Less than one percent of the wheel path area exhibits load-associated

cracking, which may start as single longitudinal cracks.b. Moderate – At least 1 and up to 10 percent of the wheel path area exhibit

cracking, likely in an interconnected pattern. The rate of crack progression is increasing.

c. High – Ten percent or more of the wheel path area exhibits load-associated cracking. Rapid progression to 100 percent of the wheel path area is likely.

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5. RUTTING. This type of permanent deformation can take place in any one or more of the pavement layers. If the HMA surface layer is of poor quality (either because of poor mix design or improper construction), rutting can be confined to the top 50 to 70mm of the pavement. If the structural design is inadequate or the pavement is overloaded, rutting can take place in the underlying pavement layers and natural subgrade soil. Generally, pavement rehabilitation strategies are targeted at replacing the deteriorated/deformed layers. The treatments described on the flowchart are based on the assumption that the rutting is confined to the HMA surface layer. The three rut severity levels are defined as follows:a. Low – Rut depth is less than 6 mm. Problems with hydroplaning and wet weather

accidents are unlikely.b. Moderate – Rut depth is in the range of 7 to 12 mm. Inadequate cross slope can

lead to hydroplaning and wet weather accidents.c. High – Rut depth is greater than 13 mm. The potential for hydroplaning and wet

weather accidents is significantly increased.

3.2.1 DECISION MATRICES

Decision matrices are very similar to decision trees in the sense that each relies on a set of rules or criteria to arrive at an appropriate maintenance or rehabilitation treatment. The major difference is that decision trees provide a more systematic and graphical approach to the selection process. The fact that decision matrices are tabular, however, makes them capable of storing more information in a smaller space.

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Figure 18

Figure 19

3.3 BENEFITS AND LIMITATIONS OF DECISION TREE

A deterministic decision trees are not a good idea (i.e., when someone identifies a set of conditions, including type and extent of distress, traffic, and environmental conditions, and then picks a treatment). The preferred way is to identify the conditions, identify feasible alternates (usually three to four are enough), evaluate the cost effectiveness of each alternate, and select the optimum treatment based on minimization of costs or maximization of benefits.

BENEFITS

1. It makes use of existing experience.2. Works well for local conditions.3. Good as a project level tool.

LIMITATIONS

1. Not always transferable from agency to agency.2. Limits innovation or use of new treatments.3. Hard to incorporate all factors which are important (e.g., competing projects,

functional classification, remaining life)4. Difficult to develop matrix that can incorporate multiple pavement distress types (i.e.,

does not always address the actual distress conditions)5. Does not include more comprehensive evaluation of various feasible alternatives and

LCC analysis to determine most cost effective strategy.

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6. Not good for network evaluation.

3.4 OPTIMUM TIMING OF MAINTENANCE TREATMENTS

One of the very recent approaches to initiate maintenance is by annual cost approach. The Figure 20 shows that the longer the maintenance is delayed, the more costly it gets as time proceeds. Alternatively, if the pavement is maintained too soon, then the initial cost of maintenance also increases, as shown in Figure 21. When the costs of delayed maintenance vs. those of early maintenance are superimposed (as shown in Figure 22) one can determine optimum timing to fix pavements.

Figure 20

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Figure 21

Figure 22

Generally, the optimum timing for applying the treatments are enlisted down.

TREATMENT YEARS

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FOG SEALS 1-3 YEARS

CRACK SEALS 2-4 YEARS

CHIP SEALS 5-7 YEARS

SLURRY SEALS 5-7 YEARS

THIN OVERLAYS 5-10 YEARS

The actual timing for the various treatments may vary depending on traffic level and environment. Each agency is encouraged to develop their own optimal timing for maintenance treatments to minimize life-cycle costs.

4. OTHER ADVANCEMENTS

4.1 COOL PAVEMENTS

Cities can be several degrees warmer than surrounding regions due to the built environment and the concentration of human activity, a phenomenon referred to as an urban heat island. Pavements have become an important contributor to this effect by altering land cover over significant portions of an urban area. Reducing the urban heat island effect can benefit air quality, lower air conditioning needs, and enhance human health and comfort. Using cool pavements also helps to improve water quality, noise, safety, and night time illumination.

Researchers have studied ways to reduce the urban heat island effect, and have identified vegetation, “cool roofing” materials, and “cool pavements” as mitigation strategies. While good ways to use vegetation are understood and cool roofing products have been identified, the idea of cool pavements has yet to gain wide dissemination and acceptance among local transportation and public works agencies and private-sector developers and

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owners. Several reasons account for this situation. First, there are technical hurdles in identifying the best cool pavement technologies and their different applications in varying climates. Second, the benefits from cool pavement are indirect. Third, institutional complexities surround pavement type selection throughout a metropolitan area, and more information on the economics of cool pavements, as well as funding mechanisms to support these technologies, are needed.

Cool pavements can be achieved with existing paving technologies and do not require new materials. Possible mechanisms for creating a cool pavement that have been studied to date are

a) Increased surface reflectance, which reduces the solar radiation absorbed by the pavement; b) Increased permeability, which cools the pavement through evaporation of water; and

c) A composite structure for noise reduction, which also has been found to emit lower levels of heat at night.

Several conventional paving technologies now exist that can apply these mechanisms. For example, greater reflectance can be provided by conventional concrete, roller-compacted concrete, concrete-over-asphalt (“white topping” and “ultra-thin white topping”), asphalt concrete and asphalt chip seals with light-colored aggregate, and asphalt pavements with modified colour. Porous pavements can be built with asphalt concrete, Portland cement concrete, or unbound surfaces such as stone, brick, or grass. The composite structure used for noise reduction plus night-time temperature benefits comprises rubber asphalt surfacing over conventional concrete slabs. It should be noted that specific pavement technologies with cool attributes will not be appropriate for all uses; some may be better suited to light traffic areas, for instance; others to areas where noise management is considered crucial. In addition, certain paving technologies may not always be appropriate or feasible in a particular region of the country – whether technically, economically, organizationally, or institutionally.

4.1.1 BENEFITS OF COOL PAVEMENTS

As part of a heat island reduction strategy, cool pavements contribute to the general benefits of heat island mitigation, including increased comfort, decreased energy use, and likely improved air quality. Cool pavements also can be one component of a larger sustainable pavements program, or a “green” transportation infrastructure.

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Cool pavements can contribute to local as well as regional comfort improvements. For instance, they help make large paved areas such as parking lots more comfortable for users. Shopping centres may feel this enhances the shopping experience.

Quantifying the heat island mitigation benefits of cool pavements is complicated by several factors in a real urban setting. The reflectivity of pavement surfaces changes over time; buildings, trees, and vehicles cast shadows; some of the reflected light could be reabsorbed by surrounding structures, negating the effect of the cooler pavement; and the degree of cooling afforded by permeable pavements is not well quantified. There may be offsetting effects or tradeoffs in the several mechanisms at work, all complicating the estimate of the benefits that cool pavements can yield.

The benefits of cool pavements are not limited to heat island reduction. There also are a number of ancillary benefits that can be gained from the use of cool pavement technologies, which can make their use worthwhile in their own right or as additional factors contributing to sustainable or green pavement initiatives. These additional benefits of cool pavements include:

1. WATER QUALITY – They can improve the water quality by two ways. They are:

a. Permeable roadway pavements and especially parking facilities of all types (asphalt, concrete, and reinforced grass and gravel paving systems) can address water quality problems by reducing the percentage of land covered by impervious surfaces. When combined with water treatment wetlands, these pavements help to act as filters, improving water quality and providing greater groundwater protection. These improvements can translate into savings for urban areas by reducing the need to construct separate sewers or expanded water treatment facilities.

b. Both permeable and non-permeable cool pavements can help water quality through reduced heating of runoff. Laboratory tests with permeable pavers have shown reductions in runoff temperatures of two to four degrees Celsius in comparison to conventional asphalt paving.

2. NOISE - The open pores of permeable pavements have been shown to significantly reduce tire noise.

3. SAFETY - Permeable roadway pavements can enhance safety by reducing water spray from moving vehicles and increasing traction through better water drainage.

4. NIGHT TIME ILLUMINATION - More reflective pavements can enhance visibility at night, potentially reducing lighting requirements and saving both money and energy. European road designers often take pavement colour into account when

planning lighting needs. Better illumination from lighter pavements is sometimes considered valuable at private establishments as well, for security or customer appeal.

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Some sources cite night time illumination enhancements of 10 to 30 percent with more reflective pavements

4.2 QUIET PAVEMENTS

By definition, noise is any unwanted sound produced around the locality. Noise, especially transportation noise has become one of the most pervasive forms of pollution in today’s environment. It affects our lives at home, work or play. Urban noise is an indication of economic activity and commerce, and up to a point, improving the quality of life. But in extreme situations, it can lead to anxiety, stress and other health related problems. When that happens, noise needs to be controlled or abated.

4.2.1 NOISE REDUCTION TECHNIQUES

Potential innovative solutions include stamping, brushing, and other new texturing techniques; exposed aggregate concrete pavements; pervious concrete pavements; sprinkle treatment; and shot peening. Two of these promising innovative concrete pavement solutions, exposed aggregate concrete pavements and pervious concrete pavements, have been identified as potential candidates for fast-track advancement. These technologies require further study and detailed cost-effectiveness evaluation before becoming part of common practice all around the world.

A. Conventional texturing- done mainly when the concrete is still in plastic state.a. Drag texture.b. Tined texture.

B. Diamond grinding- done on the hardened concrete pavement.

DRAG TEXTURE

Pavement finishing was limited to shallow texturing techniques, such as brooming or dragging (Hoerner and Smith 2002). Broomed surface textures are created by dragging a handheld or mechanical broom along the surface of the pavement, creating a ridged surface. This texture typically consists of 1.5- to 3-mm-deep (0.06 to 0.12 in.) grooves, either longitudinal or transverse to the centreline of the roadway.

Artificial turf drag surfaces are similarly created by dragging an inverted section of artificial turf along the surface of the pavement. Today, this technique often employs a device that controls the time and rate of texturing, most commonly a construction bridge that spans the pavement. Grooves of 1.5 to 3 mm (0.06 to 0.12 in.) in depth are typically created.

Burlap drag (also known as Hessian drag) texturing is created by dragging moistened, coarse burlap across the surface of the pavement, typically creating grooves with depths between 1.5 and 3 mm (0.06 and 0.12 in.).

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Figure 23

Figure 24

Although the use of these shallower texturing techniques commonly leads to quieter pavements, concerns about adequate skid resistance have also been reported, particularly for high-speed facilities (Hoerner and Smith 2002). Studies have shown that dragged textures are sufficient for roadways with speeds less than 72 km/h (45 mph) (ACPA 2000). Furthermore, recent pavement evaluations in Minnesota have concluded that the use of drag texturing results in comparable noise levels and surface friction to conventional hot-mix asphalt

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(HMA) pavements (ACPA 2000). The required texture depth specification in Minnesota is reported to be 1.0 mm (0.04 in.).TINED TEXTURE

The pavement surfaces are tined using various tools in order to make them more noise absorbant surface and hence by providing adequate skid resistance as well. There are basically two types of tining being done all over the world. They are

a. Transverse tining.b. Longitudinal tining.

TRANSVERSE TINING

Transverse tining is one of the most commonly used texturing methods on higher speed concrete pavements. It is considered an inexpensive method for durable, high-friction surfaces on new concrete pavements. Favourable friction qualities of transverse tining are particularly pronounced in wet weather conditions, as deep macro texture is capable of reducing the water film thickness and thus the potential for hydroplaning. Depending on the properties of the concrete mixture, transverse tining can provide beneficial friction qualities over the life of the pavement.

Transverse tining has also been known to exhibit undesirable noise emissions due to the interaction of the pavement and vehicle tires. Noise emissions from transverse tined textures depend on tine spacing, depth, and width. A study conducted by the Wisconsin Department of Transportation in 2000 concluded that wider and deeper transverse tine textures often produce greater noise. Figure 25 shows uniformly spaced tining texture.

Transversely tined textures are created using a tining device, commonly a metal rake that is either controlled by hand or attached to a mechanical device. Tines are moved across the width of the pavement. Individual tines can be either uniformly or randomly spaced. Tine width is typically 3 mm (0.125 in.) while the depth is typically 3 mm (0.125 in.), but depth reportedly varies between 1.5 and 6 mm (0.0625 and 0.25 in.). figure 26 shows random tining

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Figure 26

LONGITUDINAL TINING

Longitudinally tined textures are constructed in a manner similar to that of transverse tining, except that the tining device is moved longitudinally along the direction of paving.

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Longitudinal tining is commonly reported to exhibit lower noise characteristics and is thus increasing in popularity. Some cautiousness to change has stemmed from data that have shown longitudinally tined surfaces to have lower friction numbers when compared to transversely tined pavements, all else being equal. One possible explanation of this may be the shape of the grooves with respect to the traction forces of the tire (compared to transverse tining). It should be noted, however, that longitudinal tining on horizontal curves has been shown to prevent vehicle skidding and improve safety. Furthermore, some DOTs have reported that if adequate cross-slope exists, the differences between the surface drainage on transverse and longitudinal tining are minimal.

In order for longitudinally tined textures to provide optimal noise reduction performance, some recommend the design of the texture as follows: uniform tine spacing of 19 mm (0.75 in.), tine width of 3 ±0.5 mm (0.125 ± 0.02 in.), and an individual tine depth of 3 mm (0.125 in.). Deeper tining reportedly exhibits more noise, regardless of the orientation of the texture. However, variability in tining depth currently makes this type of conclusion difficult to substantiate.

Research has shown that the long-term effectiveness of longitudinally tined surfaces is impacted by the design of the pavement mix. Data have shown that longitudinally tined pavements should contain a minimum of 25% siliceous sand to improve the level and durability of the friction capacity (ACPA 2000). Regardless of the mixture design, the use of studded tires has been shown to diminish the texture of the longitudinal tining over time.

A Wisconsin DOT study further concluded that among all of the concrete pavements evaluated, those with longitudinal tining provided the lowest exterior noise while still providing adequate texture. When the texture is properly designed and constructed,

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longitudinally tined pavements can achieve friction characteristics and durability comparable to either transversely tined concrete pavements or dense-graded HMA pavements.

DIAMOND GRINDING

Diamond grinding is a technique that removes a thin layer of hardened concrete pavement using closely spaced diamond saw blades. The diamond saw blades are stacked side-by-side and generally remove between 3 and 20 mm (0.12 and 0.79 in.) from the surface. The blades are gang-mounted on a cutting head and can generate 164 to 197 grooves/m (50 to 60 grooves/ft.). This technique should not be confused with milling, which employs carbide teeth that “rip” into a pavement surface, leaving a very rough texture.

Although diamond grinding has traditionally been used to rehabilitate existing pavements by restoring smoothness, it has also been found to reduce tire-pavement noise and restore pavement friction. This raises the possibility of using this technique as an initial texturing method for newly placed concrete pavements. The grinding procedure results in the development of macro texture and, in some cases, exposure of increased micro texture. Furthermore, directional stability is more easily controlled, making this technique more appealing to drivers than longitudinal tining. Diamond grinding was used to remove a thin layer of the concrete surface. In some cases, thin fins of concrete were left behind and were subsequently broken off by a blade. Each grinding head consisted of 166 saw blades, 3.18-mm- thick (0.125 in.) separated by spacers with a thickness of 2.67 mm.

Figure 28

The study concluded that the longitudinal ground pavement was quieter than the transversely tined pavement by 2 to 5 dBA (measured on the side of the road). When noise measurements were conducted a year later, there was a negligible change in noise levels. When comparing different vehicle types, the ground surface led to a 5-dBA noise improvement for light trucks and automobiles, and a 2-dBA improvement for medium and heavy trucks. The lower noise

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reduction for larger vehicles is believed to be due to differences in the noise emission source; larger vehicles generate a greater percentage of noise from the engine and exhaust systems.

4.3 INTERNALLY ILLUMINATED PAVEMENT MARKERS

Pavement markers which self-activate in response to environmental conditions are one of the newer technologies being applied in efforts to promote the safety of road users. Self activated pavement markers are designed to provide enhanced road delineation in the event of wet weather, fading light, or ice formation by means of a solar powered LED. Three aspects of the performance of the self-activated pavement markers were assessed. They are

1. Laboratory tests were used to determine the consistency of the markers’ on/off thresholds in response to fading light, fog, and low temperatures.

2. The “in service” performance of the markers was assessed via inspection of several trial installation sites.

3. The impact of the pavement markers on driver behaviour was measured by means of a “before and after” observational study.

The on/off threshold of the pavement markers is accurate enough for their purpose and they do appear to encourage drivers to travel more slowly and to place their vehicles further from the centre of the road in some circumstances. Nonetheless, the self-activated pavement markers do not appear to be sufficiently robust, being susceptible to theft, vandalism, and damage by traffic.

One of the more recent technologies available for improving road delineation are solar powered LED illuminated pavement markers that activate in response to environmental conditions such as rain, ice, or fading light. Self-illuminated pavement markers offer certain advantages over conventional retro reflective markers, the most obvious being their visibility. Conventional retro reflective pavement markers function by returning light in the direction from which they are illuminated. To a driver, conventional retro reflective markers appear bright only when headlights are shining directly onto them. As such, there are limits to the extent to which effective delineation around a curve can be maintained using conventional retro reflective markers. Internally illuminated markers are designed to provide drivers with consistent light output from a wide range of viewing angles, thus giving a clear indication of road curvature throughout a curve.

4.3.1 TESTING

Each of the tested markers responded to either fading light (for delineation during darkness), low temperatures (for alerting drivers to the presence of ice on the road), or moisture (for delineation during rain and fog). Thirteen light sensitive pavement markers of a combination of four colours (red, green, amber, and white) and three housing types (surface mounted, flush mounted, and inset) were tested. Five blue surface mounted temperature sensitive markers and seven amber surface mounted moisture sensitive markers were also tested.

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The triggering consistency of the temperature sensitive and moisture sensitive pavement markers were tested in their climatic chamber. This allowed the atmosphere surrounding the markers to be controlled and monitored. During the testing of the moisture sensitive markers, humidity within the chamber was kept at 70%. The temperature in the chamber was lowered gradually and an injection of steam used to create fog. The response of all seven moisture sensitive markers was recorded.

During the testing of each of the five temperature sensitive pavement markers, a dish of water was placed near the markers to allow checking for ice formation. The temperature in the climatic chamber was lowered gradually until the marker was activated, at which point the temperature was increased again and the process repeated. The temperature of the pavement markers was monitored using a thermocouple.

Optometric and Photometric Technology (OPT) assessed the triggering consistency of the 13 light sensitive markers. The light sensitive pavement markers were arranged with sensors facing toward a light source and were illuminated from a distance of 25 metres. Initially the laboratory was dark and all of the units were on, then the illuminance was increased in steps and the illuminance level at which each marker turned off was noted. When all of the pavement markers had turned themselves off, the illuminance was decreased in steps and the illuminance at which each marker turned on was noted.

4.3.2 RESULTS

The moisture sensitive pavement markers activated before fog formed in the chamber. Within two minutes of the steam injection, and all within a narrow time frame, the seven moisture-sensitive pavement markers had activated. It appeared that the slight rise in ambient temperature caused by the steam injection resulted in the formation of moisture on the markers and this small amount of moisture was sufficient to activate the studs. The only circumstance in which fog would not activate the markers in the field would be when they were hot enough to remain above the ‘dew point,’ (at which moisture would form on their surface). Given that the self-illuminated pavement markers activated consistently in response to the formation of dew on their surface there is little reason to suspect that even light rainfall would fail to activate them.

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4.3.3 DRIVER BEHAVIOUR

To determine the effect of the installation of internally illuminated pavement markers on the behaviour of drivers, observations of traffic movement through a stretch of road between two bends, both before and after internally illuminated pavement markers had been installed, were conducted. A video trailer was used to collect the data. Using footage of 400 vehicles (200 in both the before and after periods) taken during darkness, data was collected in relation to five variables; Lateral placement, speed, brake use, high beam headlight use and travel on or over the centreline.

4.3.4 RESULTS

The “before and after” effects were estimates as a t-test. The data obtained were as given in the table.

The lateral placement of vehicles travelling through the observation site changed following installation of the pavement markers, four t-tests were conducted, one for each point at which lateral placement was measured.

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An alpha level of 0.1, the t-tests reveal that in two locations distance from the centreline was increased, a favourable outcome that may result in decreased risk of head-on collisions. In a third location however, distance from the centreline decreased after the pavement markers were installed. Perhaps in some circumstances clearer delineation of the centreline makes travel close to the centre of the road more comfortable than travel nearer to what may be a poorly delineated road-edge.

4.3.5 CONCLUSIONS

Based on the information gathered from the laboratory-based tests it appears that internally illuminated pavement markers perform the tasks they were designed to perform. The tested pavement markers activated in response to the environmental conditions to which they are designed to activate. They illuminated before ice formed, in response to the presence of moisture on their surface, and before light levels fell below that afforded by good street lighting. There is also little to indicate that the markers will not turn themselves off within an appropriate interval. Although they perform in the lab as specified, the performance of the tested pavement markers in the field is detracted from by their proneness to theft and damage.

Observation of driver behaviour revealed that some behaviours, such as high-beam headlight use and brake use were largely unaffected by the presence of the markers. The markers did seem to facilitate some reduction in the speed at which vehicles travelled through the installation site however, and this was a favourable finding, as was the apparent reduction in the tendency of vehicles to travel on or over the centreline. Findings in relation to changes in lateral placement associated with the installation of the pavement markers were mixed. In some circumstances installation of the pavement markers may facilitate travel closer to the centreline.

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ADVANCEMENTS IN PAVEMENT TECHNOLOGIES

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