Thompson Paper

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Thompson - September 2008 Page 1 of 20

ROAD REFLECTIVE CRACKING SYSTEM

UNDER COLD CLIMATIC CONDITIONS,EVALUATION AND STUDY OF THE FIBER-REINFORCED

EMULSION MEMBRANE

Martin Thompson

Midland Asphalt Materials Inc.

International Symposium on Asphalt Emulsion Technology, ISAET

September 24-26th

2008

Abstract

The paper will present the application and effects of a road maintenancetechnique combining polymer modified asphalt emulsion and glass fibers.

This process entered the North American market in New York State, 2003.New York State suffers from severe winter climatic conditions with abundant winter

snow plow activities affecting in particular surface treatments such as chip seals/surface dressings. Background data on these climatic conditions will be mentioned.

The fiber-reinforced membrane can be used as a stand alone enhanced chipseal system or as a Stress Absorbing Membrane Interlayer, SAMI. When used as aSAMI system, the process provides an alternative cost effective treatment to sometraditional techniques designed to delay reflective cracking.

A new piece of equipment that applies the fiber reinforced membrane wasdeveloped in order to increase production and effectiveness of the technique and thiswill be discussed.

Two studies at Texas Transportation Institute and Pennsylvania TransportationInstitute will be presented showing to date the benefits of this process.


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1. Introduction

In the United States the majority of pavements are composed of bituminous orasphalt concrete (AC). A large number of Portland cement concrete (PCC) also exist,

especially on high-traffic volume highways.

Two of the three major pavement distresses found in this region are fatigueand reflective cracking. Both these cracking mechanisms are considered low tomoderate temperature phenomena attributed to both load and thermal stresses in

pavements.

As is well known and documented, in the later periods of their life, both typesof pavements exhibit crack distresses: fatigue and thermal cracking in AC pavements,

joint faulting and mid-slab cracking in the case of PCC pavements.

Following an overlay application on an existing pavement, physicaldeterioration of this overlay takes place as a result of movement at the joints andcracks of the underlying pavement layer. When an asphalt overlay is placed over anexisting pavement surface the former should be fully bonded by the tack/bond coat tothe latter. Any movement taking place in the underlying pavement at a joint/crack will

produce stresses in the overlay, which can promote reflective crack propagation if thestresses in the overlay exceed its fracture resistance. Reflective cracking occurs innearly all type of overlays. Temperature induced horizontal movements concentratedat the underlying joints and cracks in the existing pavement lead to tensile stresses andis an important contributor to reflective cracking. Load or traffic induced verticalmovements lead to shear stresses in the overlay that also contribute to reflective

cracking.

This study will show that a fiber-reinforced product, readily available in theNorth American market, performs under severe winter conditions not only in terms ofseasonal and diurnal temperature ranges but also under aggression due to the effectsof snowplows in New York State as compared with a normal CRS-2p based ChipSeal. In addition this study will show the product when used as an interlayer, extendsthe life of the overlay subsequently applied, several fold as compared with notreatment.

Technical studies undertaken on this product will underpin the actualreality of using this product in New York and other similar States.


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2. Phenomena of Reflective Cracking

Asphalt concrete overlays and surface treatments are some of the mosteconomical forms of maintenance for a distressed pavement. However a problem

often encountered is when cracks start to appear due to traffic and temperatureinduced fatigue through and on the surface of the overlay.

While asphalt overlays and bituminous surface treatments are relatively cheapmaintenance techniques, they are however, considered a quick fix because the existingcracks in the underlying layers eventually propagate upward through the overlay andreappears at the surface and hence forms what are referred to as reflective cracks.Similarly surface shrinkage cracks may also initiate top down cracking and lead to

problems such as raveling and alligator cracking or crazing.

Membranes, as bituminous surface courses and/or as an interlayer as describedherein, have high shear and tensile strength in addition to high ductility and can act ascrack relieving layers when placed on/or in-between the old and new surface. Becauseof their strength, the crack propagation through that interlayer requires higher energyand stress concentrations, ultimately leading to a delay in the formation of thereflective cracks. The interlayers ductility allows it to absorb some of the strainenergy developed at the bottom of the new overlay as the wheel loads are appliedcyclically on the top of the pavement diagram 1.

Diagram 1

Cracked LayerJoint or crackCracked Layer

InterlayerAC Overlay

AC Overlay

Cracking also occurs through asphalt concrete pavements due to coldtemperatures and/or temperature cycling especially in the more northern states and

provinces of North America. Cracking that occurs from cold temperatures is referred

to as low temperature cracking whereas cracking due to thermal cyclic changes isreferred to as thermal fatigue cracking. Both forms can propagate through new asphaltoverlays or bituminous surface treatments as reflective cracks.

These thermal induced cracks allow the ingress of water into the layers below,deteriorating these layers through freeze thaw cycles and/or by freezing and expansionof ice focal points that may produce an upward force on the pavement overlay.

The result from both traffic and thermal induced fatigue is a deterioration ofpavement life and a reduction in ride quality for the end-user.


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3. New York State and Climate

Diagram 2 Map of NY State courtesy of MAGELLAN Geographix

3.1 Background

Eastern New York is dominated by the Great Appalachian Valley. LakeChamplain is the chief northern feature of the valley, which also includes the HudsonRiver. West of the lakes are the rugged Adirondack Mts. The rest of NE New York ishilly, sloping gradually to the valleys of the St. Lawrence and Lake Ontario, both ofwhich separate it from Ontario. The Mohawk River, which flows from Rome into the

Hudson north of Albany, is part of the New York State Canal System's Erie Canal,once a major route to the Great Lakes and the Midwestern United States as well asthe only complete natural route through the Appalachian Mts.

Most of the southern part of the state is on the Allegheny plateau, which risesin the SE to the Catskill Mts. New York City, in turn, attracts tourists from all overthe world. On the extreme SE, the state extends into the Atlantic Ocean to form LongIsland.

The western extension of the state to Lakes Ontario and Erie contains manybodies of water, notably Oneida Lake and the Finger Lakes. In the northwest theNiagara River, with scenic Niagara Falls, forms the border with Ontario betweenLake Ontario and Lake Erie.

3.2 The Physical & Climate of New York State

New York State contains 49,576 square miles, inclusive of 1,637 square milesof inland water, but exclusive of the boundary-water areas of Long Island Sound, NewYork Harbor, Lake Ontario, and Lake Erie.

The climate of New York State is broadly representative of the humidcontinental type, which prevails in the northeastern United States, but its diversity isnot usually encountered within an area of comparable size. The character of thetopography, and proximity to large bodies of water have pronounced effects on theclimate.


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Cold winter temperatures prevail over New York whenever Arctic air massesflow southward from central Canada or from Hudson Bay. High-pressure systemsoften move just off the Atlantic coast, become more or less stagnant for several days,and then a persistent airflow from the southwest or south affects the state. Thiscirculation brings the very warm, often humid weather of the summer season and themild, more pleasant temperatures during the fall, winter, and spring seasons.

The climate of New York State is marked by abundant snowfall. With theexception of the coast, the state receives an average seasonal amount of 100cm (40inches) or more. The average snowfall is greater than 178cm (70 inches) over some 60

percent of New York's area. Seasonal snowfall, averaging more than 4.5m (175inches), occurs on the western and southwestern slopes of the Adirondacks. Asecondary maximum of 3.8m to 4.5m (150 to 180) inches prevails in the southwesternhighlands, some 16 to 50 kilometers (10 to 30 miles) inland from Lake Erie. Heavysnow and lake effect squalls frequently occur, generating from 30 to 60cm (1 to 2feet) of snow and occasionally 1.2m (4 feet) or more in a single day.

4. The fiber reinforced membrane process

The product at the center of this study is a made in-place membrane thatwaterproofs and produces a fiber impregnated and reinforcing layer that allows adissipation of some of the stresses generated in the pavement.

The fiber-reinforced membrane produced is all applied on one unit, wherebytwo layers of polymer modified asphalt emulsion sandwich fiberglass strands that arechopped in-place by a special chopping and distribution system.

Columns of fiber are held in a storage area on a trailer unit. Strands offiberglass are then taken and fed pneumatically through lines to a fiber chopping unit.In advance of the chopping unit a layer of polymer asphalt emulsion is appliedthrough a traditional slotted jet distributor spray bar arrangement. The strands offiberglass are then chopped in place and randomly orientated by air in a chamber andare lightly blown down onto the surface of the polymer modified emulsion. A secondlayer of polymer modified emulsion then seals in the fibers and completes themembrane component Diagram 3 over. An aggregate layer is then applied.


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Diagram 3 Process layout

Fiber reinforced membrane

2nd layer ofpolymer modifiedemulsion applied

Fibers blown downonto 1stlayer

1st layer of polymermodified emulsion

Strands of fibercut in place.

Storage ofcolumns of fiber

The fiber reinforced membrane process, FibreDec, was developed back in thelate 1980s in the UK and has been used in a number of countries world wide from theUK to Australia and now North America. Initially the unit was limited to 2.4m (8ft)wide for a single lane pass and was also limited to the production application rate perday, typically 12,500-17,000m2 (15-20,000Yd2). It was also difficult to work on andhence for the North American market had to be revamped making it more appropriatefor use.

The outcome was the trailer unit previously described, that contains fiber inthe storage area of the trailer unit capable of 38,000 to 64,000m2 (45-75,000 Yd2) offiber reinforced membrane before the need for re-loading. This means a daily

production rate of up to 85,000m2 (100,000Yd2).In addition the application width of the unit is now capable of making a 4

metre (13ft5) pass. This ensures in the majority of instances a full lane pass for theroads in North America.

We also addressed the problem of working on and maintaining the unit bymaking the spray bar and fiber configuration unit fold vertically in the middle foreasier access.


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e fiber-reinforced membrane has been used as the wearing course intraditio d as a

s was designed to delay the process of reflective cracking

and sea

acts not only as a wearing surface but can be used at various levels withinthe pav

;

.1 The fiber reinforced membrane as a wearing surface

Thnal chip sealing markets adding value by extending the life of the seal an

Stress Absorbing Membrane Interlayer, SAMI to compete against such products asGeotextiles and the like.

This whole proces

l alligator cracks within and on a pavement structure.

Itement structure from surfacing pre-primed gravel bases, to interlayers

before HMA, Ultra-Thin mixes such as NovaChip; Microsurfacing or Slurry Sealgiving in the interim before the final overlay, a resilient wearing surface.

4

he first type of application for this product is a bituminous wearing surfacecourse

ss

s with

he membrane is superior to traditional bituminous or chip sealing surfacetreatme

A 5-year evaluation study of the fiber reinforced membrane process wasperfor

ue

l

Ttreatment akin to a chip seal. This application combines a special polymer

modified asphalt emulsion at typically 1.8 to 3.2m2 (0.4-0.8Gal/Yd2), chopped glafibers of nominally 60mm (23/8) length at a rate of 30g/m2 to 120g/m2 (0.06lbs to0.22lbs/Yd2). This mixture produces a membrane that acts as a highly resilientwaterproofing layer that effectively bridges cracks with fiber and seals the cracka residual polymer asphalt membrane.

Tnts as greater tensile strength properties resist stresses placed upon it. This is

shown in the Photo Log below and over the next page where a side-by-side evaluation

was performed with a regular chip sealing emulsion in New York State back in 2003.This was subjected to progressive winters where extensive snowplow operations have

pronounced effects on all types of pavements because of their carbide blades.

med in upstate New York. One side of the chosen road was treated with aconventional chip seal overlay placed while the other with the FiberMat Type A

process as the fiber-reinforced membrane is called when used as an enhanced chipseal. This road surface had many reflective cracks likely caused by years of stress dto seasonal shifting and snow plow damage. After one year of wear and tear on thistest road, longitudinal reflective crack had started to reappear on the regular chip seaside while no cracks had appeared on the fiber-reinforced membrane side of the road.

Note that cracking was present on both sides of the road prior to application.


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The following year, longitudinal reflective cracking and snowplow damagewere evident on the chip seal side while the FiberMat Type A side was still in verygood condition.

On the third year of evaluation, further evidence of snowplow damage wasnoted on the chip seal side while only slight damage started to occur on the fiber-reinforced membrane side; all the while the FiberMat Type A membrane itself wasstill intact.

By year four, the chip seal side showed significant deterioration. It was nowbecoming a candidate for total rehabilitation. The FiberMat Type A side, after 4years of use, only just started to show some minor damage.

Year five showed that the original chip seal side had fully deteriorated, withaggregate loss and raveling along with all afore mentioned distresses; a candidatenow for full depth reclamation. However, the condition of the FiberMat Type A


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side altered minimally from the previous year. It was still years away from requiringany repairs or rehabilitation.

Work utilizing the Mini-Fretting test on this process was carried out back inthe 90s, and showed the benefit of using the polymer modified emulsions for this

process. It also showed that the aggregate layer applied firmly penetrated into themembrane and the fibers were able to lock-in the aggregate thus ensuring greateraggregate retention. Further work was carried out, this time showing in terms of theVialit Adhesion Test at 5oC a dramatic improvement when using a polymer modifiedversus non-modified asphalt emulsions

This resistance to general wear and tear on the surface is also linked to theexperiences in New York, that of, under normal practices & conditions a greaterresistance to aggression from such things as snow plows.

In addition the field study from Australia, (Lysenko & Scott, 1998), on variousbases showed that crack retardation was effective at a 3 fold improvement over non-fibered reinforced membrane treatments. One of the aspects here was the fact that the

membrane produced was held in tact after traffic loading and the aggregate retainedwas firmly set in place.

If we consider then a simple cost analysis, Equivalent Annual Costs, EAC,then for typically $ 2.25/m2 spent on the fiber process as a wearing surface and$1.80/m2 for a modified chip seal.

The EAC is calculated as = Price per unit or SY of material/ expected life of treatment.

For the Fiber Reinforced Membrane = $2.25/ 6 years = $0.38/yrFor a regular polymer modified chip seal = $1.80/ 3 years = $0.60/yr

This is just assuming a two fold improvement when using the fiber reinforcedmembrane versus a regular polymer modified chip seal. In reality the fiber process islasting three and more times longer than a regular chip seal surface; as in New York.

Therefore although the initial outlay is higher for the fiber process the actualreturn on that investment is short.


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4.2 The fiber reinforced membrane as an interlayer

When the fiber reinforced membrane is used as an interlayer treatment, known asFiberMat Type B, then again there are benefits to be had. But before considerationof this aspect the requirements of a successful interlayer system should possess must

be considered.

Diagram 4 - SAMI

The ability to provide a strong, waterproof membrane. The ability to absorb some stresses generated in the pavement and give

enhanced tensile properties.

To be installed easily, quickly without excessive preparation.

Cost effective in whole life costs of the pavement.

Easily recycled.As with all systems that act as SAMIs there is an imperative need for a tack or

bond coat to waterproof and seal the existing surface and provide an anchor ofadhesion for the subsequent layer(s). With the fiber reinforced membrane this

provides the polymer modified asphalt emulsions applied through a split bar givingthe waterproofing and sealing characteristics.

It is not suggested that all the stresses will be absorbed but just some stresses as

there are no SAMI systems in the market that can proclaim to absorb all the stressesgenerated in a pavement. The aim is to reduce the effect of the stresses within the

pavement layer and interlayer by absorption. Tensile properties are also important togive enhanced integral strength to the layers, especially when used as the enhancedchip seal wearing surface allowing greater retention of the aggregate. With the fiberglass cut and introduced between the spray bars this gives the ability to withstandsome of the stresses and give enhanced tensile properties.

Cost effective as shown from the previous example is more so when comparingthis membrane against traditional interlayer treatments such as geotextiles and

polymer rich mixes that may be as high as $12/m2 ($10/Yd2) or more installed in

comparison. In addition when used as an interlayer with an ultra-thin wearing course


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the need for mill and fill with HMA is eliminated and the cost savings areconsiderable- Diagram 5.

Diagram 5 Cost Comparison

Unlike many SAMI systems the layer ideally should be easily placed and shapedwithout the need for excessive preparation such as truing and leveling courses or extramilling. The fiber reinforced membrane can be quickly installed without the need forexcessive preparation. It is made on the move, cut to size and tailored to shape.

In subsequent years it needs to be recycled, easily milled and reprocessed back ata HMA plant without having to constantly remove wads of textile from a conveyor aswith some geotextiles for example. The fiber reinforced membrane can be easilyrecycled and used more usually in base RAP courses.

The fiber reinforced membrane truly fits into the family of what are known asStress Absorbing Membrane Interlayers, SAMIs and we would suggest is the onlytrue SAMI that encompasses what the customer be they a Contractor or aGovernmental DOT/County or Town really need.

We have applied nearly 4.25 million square meters (5 million square yards) offiber reinforced membrane in New York alone since 2003. About 60% of the projectsto date throughout North America have been as an interlayer application. Often thishas been overlaid with an ultra-thin hot mix overlay as shown in the photo of the coresample below. The rule of thumb, at least in New York State is that a pre-existingcrack will propagate through a new overlay at a rate of about 25.4cm (1 inch) peryear. Numerous projects with ultra-thin surfaces as the overlay, Photo 6, have been in-

place since 2003 and have no cracks re-appearing whereas nearby regular projects ofHMA with non fiber reinforced membrane treatment have cracks re-appearing withinthe 1 year period.


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FiberMat

Type B

Ultra-thin overlay

NOVACHIP

Photo 6 FiberMat Type B Interlayer with NovaChip Ultra-thin overlay

5. US based Research

The benefit of using the fiber reinforced membrane as the interlayer has notonly been proven in the field but also through laboratory studies here in the US.

5.1 The Texas Transportation Institute, TTI, study mimics the thermalcracking phenomena and is aimed at generating a cracking number which can becompared against other systems. At TTI use is made of the Overlay Tester that is adisplacement controlled repetitive loading machine to initially produce a small crack(due to tension) at the base of the test specimen and then continues to inducerepetitive horizontal displacements which causes the crack to propagate upwardthrough the specimen. This process is intended to simulate the cyclic tensile stressesof pavements due to periodic thermal variations. R.L Lytton has conducted studies onreflective cracking and fracture mechanics since the early seventies. The TTI overlaytester (simulating the cyclic horizontal displacement related to thermal shrinkage) has

been developed in the early eighties. Thermally induced fatigue is the primary cause

of reflective cracking initiating in pavements. Secondly Traffic Induced Fatigue


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comes into play followed by Bending/curling fatigue of the pavement. The testingprotocol developed is summarized below:

1.TTI Overlay Tester Dataoutput: 2.

Fracture mechanicsmodelization; predicted

cracking life

3.

Test section /Model validation.

- Linear horizontal Load P vs.time

- Horizontal displacement (u)- Crack length (c) vs. cycles (N)- Elastic/ relaxation Modulus of

the Complex (overlay +interface) @ initial loading.

Cycles at failure: N = h _ 1__ de

0 A(Ki)n

Where:- A, n fracture mechanics properties

deducted from Overlay tester data.- Ki Stress intensity factor deducted

from measured modulus thru finiteelements analysis.

- Sample depth: h.Reinforcing factor & Crack speed

Index

Test section with TXDOTVerification of material fracturemechanics properties on coresamples.

-Section monitoring: PredictedCracking Life verification.

However the Finite Element Analysis model used by TTI assumes that thecrack propagated will do so vertically this is not to date the case however withthe fiber reinforced membrane.

The findings from the study concluded that

- There was horizontal crack propagation along the FiberMat Type Binterface, Photo 8, rather than by cracking vertically above as in controlsamples, Photo 7. This is consistent with previous studies at NottinghamUniversity in the UK.

Photo 7 Control Photo 8 FiberMat Type B SAMI- Generally, specimens containing FiberMat Type B improved cracking

resistance in the small overlay testers 3 to 4 times more than control samples.The large overlay FiberMat Type B samples survived 14 times morecompared to the control.

Diagram 6 - Small Overlay Tester


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5.2 Pennsylvania Transportation Institute, PTI, -

Work was also carried out at Penn State Test Track where they evaluatecommercial buses for use in the US. This is part of the Pennsylvania DOT approval

process for Municipal Services with Pennsylvania Transportation Institute, PTI.

HHMMAASSeecctt iioonnss

PPCCCC

SSeecctt iioonnss

FiberMat Type B FiberMat Type A

Several areas were applied with fiber reinforced membrane of the types A & Band to date, as the sections were laid last year, are performing very well. In additionthree live sites where chosen throughout Pennsylvania and again these are

performing well.

A preconstruction distress survey was also done for all the sections. Thesections were divided into a grid of 6x6 ft parcels. Monthly distress surveys were andare conducted during this period for the sections constructed at the PTI test track.Distress observations and pictures are routinely taken as part of the visual survey

process. The observed cracks are identified, measured, and matched with the original

cracks that existed before the overlay.

Some of the techniques employed as part of the approval process includedAccelerated Pavement Testing is performed using the Mobile Model LoadSimulator Scale 3, (MMLS3), unit that determine loss of aggregate on the testsections. Chipping or aggregate loss was inspected for the FiberMat Type A &control and experimental sections using the MMLS3 as seen in Figure 7. Evaluationis done by weighing the mass of aggregates chipped from the pavement after a certainnumber of wheel cycles are applied.

HMA Overla

Cracked HMA Cracked HMAPPCCCC

WWeeaakk BBaasseeSSttrroonngg BBaassee

PPCCCC


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(a) (b)Photo 9 a) MMLS3 testing over a designated area for aggregate loss; b) MMLS3covered with a tarp to prevent any loss of aggregate from leaving the area. For thefiber-reinforced chip seal section versus the control no major differences wereobserved initially but are continuing to be monitored periodically.

However field cores were taken from the fiber-reinforced SAMI experimentaland control sections. A thin ring corresponding to the polymer modified emulsion can

be seen in Photo 11(b)

Photo 10(a) Cored control Photo 10(b) Cored FiberMat SAMI

11(a) 11(b)

Fiber-bitumenemulsion

Photo 11(a) Core from FiberMat Type B section; and b) FiberMat Type B section(black ring consisting of the fiber-bitumen emulsion)

It can be seen in the top two photos 10 that there is a substantial differencewhen the fiber-reinforced system is employed as a SAMI, Photo 10(b). Crack

propagation is delayed for the fiber-reinforced samples after 18months, while crackspropagate through the control section Photo 10(a).


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In addition and not part of the formal evaluation, X-ray Tomography wascarried out on some of the core specimens. These clearly showed the layer of fiber-reinforced membrane containing the fibers; aggregate fracture of the old underlyinglayer; and distinguish between voids within the mix. This was more from an academicstandpoint than anything else but shows the uniformity of the fiber-reinforcedmembrane produced.

Photo 12 (a) - Cross section of core Photo 12(b) Top view

Bending Beam Rheometer, (BBR), analysis was carried out on the fiber-membrane albeit with a great deal problems associated with sample preparation. Theresults showed a definite increase in stiffness of the residual binder due to theinclusion of the fibers. The fibers act with the residual binder and reduce the

deflection caused due to the load. Furthermore, it was seen that the stiffness of thespecimens with fibers is greater than the case of samples without fibers. The creeprate (m value) is lower in case of samples with fibers (0.192 and 0.173) and higher incase of samples with without fibers (0.462 and 0.431), suggesting an increase inelastic behavior when the glass fibers are added.

Photo 13 BBR Samples


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After applying one million cycles on top of pre-existing cracks on bothFiberMat Type Band the control sections, no visible reflective cracks appearedinitially. However, after taking the cores on top of the pre-existing pavement cracks, ahairline crack was visible on the control section. Therefore, it was decided to furtherinvestigate that area using the Portable Seismic Pavement Analyzer (PSPA).The PSPA is an instrument designed to determine the variation in modulus with depth

of exposed layer be it concrete or asphalt.The operating principle of the PSPA is based on generating and detecting

stress waves in a medium. The device consists of two transducers and a sourcepackaged into a hand portable package, photo 14(a), which performs the UltrasonicSurface Wave (USW), and Impact Echo (IE) tests. The USW method was used on the

project to determine the modulus of FiberMat Type Band the control section. Anumber of areas were chosen to calculate the modulus of the top 2 using the PSPA.

Photo 14(a) Portable PSPA Photo 14(b) Transducer and source over crack

Moduli from the four sections were determined at -7oC and at 7oC (Table 5).At -7oC, it was observed that for locations without pre-existing cracks, the modulus of

the FiberMat Type Bsection was similar to that of the control section, photo 14(b).However for locations with pre-existing cracks, the modulus at -7oC of the

Control section is higher than that of fiber-reinforced. This intimates that the pre-existing crack reflected to the upper layers of the control section while it did not in thefiber-reinforced. The higher modulus of the control stems from the high modulus ofice entrapped; frozen water entrapped; in the reflected crack in the top 2 of thecontrol section which implies more voids or the reflective crack is more prominent.Comparing crack and no crack sections, both crack sections are higher to the oneswithout cracks, because of this high modulus of ice..

For the higher temperatures on top of the pre-existing crack, the fiber-reinforced section has a higher modulus than the control due to absence of the

reflective crack. For the section on top of no pre-existing cracks, the fiber-reinforcedsection has a lower modulus, due to the inclusion of the interlayer which has a lowermodulus than regular HMA overlay. This fact makes the treated section less stiff andmore ductile and self-healing.


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6. Conclusions

Pavement preservation is one of the key tools for road engineers around theworld to prevent the complete fatigue of their network and to optimize their road

budget. In this field of pavement preservation, the fiber reinforced membrane chip

seal (surface dressing in the UK) or as a SAMI will bring one of the most importanttechniques to the fore. The use of fiber reinforced systems with polymer modifiedasphalt emulsion will enhance this process and will give another appropriate tool intheir range of maintenance products.

The new applicator unit developed is more ideal and applicable for the NorthAmerican market than previous versions. This allows coverage of single lane widths,higher production per day and easier to maintain.

The long term resilient characteristics of the fiber reinforced membrane, as

shown in New York State during five winters, gave local road engineers an excellenttechnique to help them maintain their pavements. At low temperatures, the resultsobtained in New York State after three winters showed a combination of advantages:

1. Economical in terms of Equivalent Annual Costs when compared withtraditional systems.

2. Resilience under winter conditions and maintenance (snow plough effectsand low temperature).

SAMI (Stress Absorbing Membrane Interlayer) systems are also a domainroad engineers can gain by using the fiber reinforced membrane system with hot mixasphalt. The action of the polymer modified asphalt emulsion will bond both materials

and therefore give good reflective crack resistance when used with the fibers. Thepolymer modified asphalt emulsion is the best bond component for this application.The use of this system with an ultra-thin overlay can give the road engineersubstantial savings over traditional mill and HMA fill practices and effectively reducethe environmental impact of road construction.

In cold climates, reflective cracks can reveal the status of the pavement.Fatigue cracks indicate the end of the life of the wearing course if there is nodeformation, these techniques will help the road engineer; by keeping water out andinsuring a good protection of the pavement to crack propagation. Thermal cracks alsocan be dealt with. Those cracks especially during the thaw period will be abated as the

fiber reinforced membrane gives great imperviousness and flexibility to and thereforehelps prevent water penetrating into the pavement. The higher flexibility given by thecombination of the polymer modified asphalt emulsion and fibers will insure good

performance for longer than usual.

Research done in the USA showed the great advantage of this technique todelay crack propagation coming either from fatigue or thermal effects.

The findings from the TTI study concluded that

There was horizontal crack propagation along the FiberMat Type B interfacerather than by cracking vertically above as in control samples. This is

consistent with previous studies.


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Generally, specimens containing FiberMat Type B improved crackingresistance in the small overlay testers 3 to 4 times more than control samples.The large overlay FiberMat Type B samples survived 14 times morecompared to the control.

From the PTI study -

BBR results suggest a higher ductility at lower temperature for the fiber-reinforced membrane interlayer which would delay the onset of cracksreflecting upwards.

Cores removed from both sections having pre-existing cracks show thatreflective cracks occur in the control section; whereas, reflective cracks areabsent in the fiber-reinforced sections. X-ray Tomography also showedevidence of fiber-reinforcement homogeneity and characteristics of existingsubstrates not normally seen. An interesting tool for evaluation of mixes in

general. One million cycles of MMLS3 on top of pre-existing cracks did not induce

any visible cracks neither on the treated nor the control sections.

Results from Portable Seismic Pavement Analyzer show that more voids andmicro/macro cracks are present in the overlay surfaces in the control section ascompared to the fiber-reinforced sections. Visual observations of both studiedsections suggest that cracks are more likely to reflect in the control sectionthan in the fiber-reinforced section.

Research undertaken in the USA will continue on in order to understandbetter, through American tests, the behavior of both systems. Finally with the future

use of mechanistically driven pavement structural design in the US market, we shouldbe able to give data in order to introduce this SAMI system in the design.


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References

I.L.Al-Qadi, M.M.Elseifi, (2003), A Simplified Overlay Design Model againstReflective Cracking Utilizing Service Life Prediction, TRB 82nd Annual MeetingJanuary 12-16 2003, Washington D.C.

W.G.Buttlar, D.Bozkurt, B.J.Dempsey, (2000), Cost-Effectiveness of Paving Fabricsto Control Reflective Cracking, Journal of the Transportation Research Board,

No.1730, National Research Council, National Academy Press, Washington D.C.

G.S.Cleveland, R.L.Lytton, J.W.Button, (2003), Reinforcing Benefits of GeosyntheticMaterials in Asphalt Concrete Overlays using Pseudo Strain Damage Theory, TRB

82

nd

Annual Meeting January 12-16 2003, Washington D.C.

K.E. Cooper, S.L. Held, (1987), The evaluation of fibre reinforcement techniques toinhibit reflection cracking in overlays, Nottingham University Dept of CivilEngineering.

P.Jayawickrama, R.L.Lytton, Methodology for Predicting Asphalt Concrete OverlayLife against Reflection Cracking.

J. Lysenko, G Scott (1998), Are your roads getting enough fibre?, AAPAPavements Industry Conference.

C.Yeates, ( 1994) Evalaution of fibre-reinforced membranes., Colas Limited.

F.Chaignon & M.Thompson, (2006), Road Reflective Cracking System Under ColdClimatic Conditions, World Congress On Emulsions October 2006, Lyons, France

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