One Gateway PlazaLos Angeles, CA 90012-2952

213.922.2000 Telmetro. net

June 16, 2009

TO:

THROUGH:

FROM:

SUBJECT:

ISSUE

BOARD OF DIRECTORS

ARTHUR T. LEAHY f'YCHIEF EXECUTIVE OFFICER

CAROLINGE ~5CHIEF PLANNING OFFICER

POST 1989 RETROFIT SOUNDWALL PROGRAM

At the March 2009 meeting, the Board requested additional information on (1)alternative soundwall materials or methods for the construction ofthe Post 1989Retrofit Soundwall Program; (2) rubberized asphalt pavement to determine if it is aneffective method in reducing traffic noise which results in the need to constructsoundwalls; and, (3) how other agencies, such as Florida Department ofTransportation (FDOT), are able to have lower soundwall construction costs and ifanything can be gained from their process to reduce the cost of our soundwallprogram. This Board Boxprovides the requested information.

DISCUSSION

Alternative Noise Barrier Materials

All soundwall materials have to be tested and approved with respect to aestheticalinstallation, acoustical performance, structural, safety, maintenance, and costs beforethey can be used on any state or national highways systems. The USDOT/FHWAand Caltrans has tested and certified several of the most viable materials. Theseinclude concrete (cast-in-place or precast), metal (steel, aluminum, or stainless steel),wood (pressure preservative lumber, plywood or glue laminated products),transparent panels (glass either tempered or laminated), plastics (polyethylene, PVC,fiberglass, Plexiglas, Butacite, Surlyn, Lexan, or acrylic products) , recycled rubber(scrap tires or any buffings from rubber product manufacturers), earthen materials(soil, stone, rock, rubble, rice straw-bale, etc.), and composites (two or more primarymaterials from above). The method ofconstruction would depend on the type ofmaterial used. Furthermore, some of the materials are not recommended as anoption over the bridge structures. A more detailed description of these different typesofmaterials including its features , examples of typical use, and other specialconsiderations are also presented in a memo to staff that was prepared by Mr. Steven

Wolfe ofParsons Brinkerhoff (PB) in 2003 for the soundwall project along the I-60Sfreeway (Attachment A). We also determined that the information contained in thismemo is still relevant based on FHWA's updated Noise Barrier Design Handbookthat is available on their website, which reflects state-of-the-art improvements andchanges in noise barrier design, materials, and installation techniques.

Caltrans' Highway Design Manual and Project Development Procedures Manualrequire the bid package for each soundwall project to include at least two noisebarrier design alternatives. Based on past experience, Caltrans District 7 staffhasfound that alternative soundwall materials are generally proprietary products and aresignificantly more expensive as opposed to masonry blocks, which are cheaper andcan be produced by multiple manufacturers. Thus, Caltrans District 7 includesmasonry block as the only material and design in the bid package. Further, based onprevious experience, Caltrans staff strongly feels that residents affected by the trafficnoise almost always prefer a masonry block wall over any other type of soundwallmaterial.

Additionally, we contacted DW Powell, the contractor who constructed our SR-134Design/Build Soundwall project, to inquire whether they considered the use ofalternative soundwall materials. The contractor informed us that masonry blocks arethe most cost-effective material to use for soundwalls. In addition, although masonryblocks require more labor to install, that cost is offset by the cost ofmore buildingmaterials (steel, beams, and posts) needed when using alternative materials such aspanels.

In order to ensure coordination and consistency with Caltrans' policies andprocedures to consider noise barrier design alternatives, we have contacted Caltransto determine ifalternative materials can be included in the design of Packages 5, 6,7,8, and 10. Caltrans is evaluating these packages and ifappropriate, would give theoption to contractors to use alternative materials other than masonry block walls.

Comparison to Other Agencies' Soundwall Program

With regard to the Board's request to how other agencies are delivering soundwallscheaper, we contacted FDOT. FDOT's costs ofdelivering soundwall projects aremuch lower than ours mainly because ofthe difference in the cost ofliving (labor)and materials in Florida compared with California. The State of Florida also hasdifferent environments where they build soundwalls, typically in accessible areas withavailable right-of-way which allows for easy maneuvering ofthe necessary cranes andtransport vehicles at the site.

Since there are a number offactors which affect the cost of soundwalls and given thatthey can vary widely from area to area, we also contacted Orange CountyTransportation Authority (OCTA) regarding their soundwall delivery costs. We

Post 1989 Retrofit Soundwall Program 2

found their overall soundwall delivery costs to be comparable to ours and wedetermined that this is most likely due to the similar physical conditions and factorsconsidered in evaluating the cost ofsoundwalls. In addition, according to aCTAstaff, soundwall construction costs may vary significantly depending on thecircumstances. Some key considerations beyond the cost of the wall are the locationofthe soundwalls, and whether they are built on retaining walls or bridges, trafficcontrol requirements for walls built along the edge of traveled way, necessarydrainage or utility modifications, erosion control and landscaping.

Rubberized Asphalt Pavement

As part of their Highway Traffic Noise Abatement requirement, Caltrans is requiredto consider reduction of traffic noise at the source. Designers are encouraged toconsider emerging technologies intended to minimize noise emanating from thehighway. For example, quieter pavement surfaces such as rubberized asphalt arecurrently being researched for reduced tire/pavement noise on the highway.

Caltrans is conducting a four year Quieter Pavement Research study that wasinitiated in 2006. This study is intended to examine the impact of "quieterpavements" on traffic noise levels and establish which pavement characteristics havethe greatest impact on tire/pavement noise. We recently contacted Caltrans toinquire about any latest findings from completed repavement projects throughout thestate. According to Caltrans' District 7 Materials Engineer, the use ofrubberized hotmix asphalt would lessen traffic noise impacts, but the effect is short-term and thenoise returns to pre-overlay levels after five years. It is hoped that the study will helpidentify surface treatments, materials, and construction methods that will result in aquieter pavement that is also safe, durable, and cost-effective.

Currently, Caltrans' Pavement Research Division is preparing a draft QuieterPavement Policy Bulletin, dated March 27, 2009, which summarizes current practicesof quieter pavement surface treatments for flexible and rigid pavements. This draft,currently under review by Caltrans, presents the first and second year results of theQuieter Pavement Research study. Caltrans' Pavement Division also maintains awebsite that includes efforts being done by other states such as Washington, Texas,and Florida that are also testing how long the noise reduction lasts for rubberizedasphalt pavements. Arizona has reported a decrease in noise levels after quieterpavement is installed; however it is still being tested whether those results drop offasthe roadway wears.

Quieter pavement may not be a cheaper alternative to soundwalls ifthere is a need torepave more frequently to maintain federally accepted noise levels. According to thedraft Pavement Policy Bulletin, "pending the outcome ofthe ongoing nationwideresearch on the noise reduction benefits and longevity ofquieter pavements surface

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treatment strategies" the FHWA does not currently consider quieter pavements as aviable long-term mitigation for traffic noise impacts.

NEXT STEPS

We will continue to meet with manufacturers ofalternative materials and willmonitor Caltrans' Pavement research with regard to the use of rubberized asphalt asan alternative method for reducing traffic noise. We will also work with Caltrans tohave the design ofsoundwall Packages 5, 6, 7, 8 and 10 be completed to allowcontractors to bid on alternative materials to masonry block walls.

ATTACHMENTA. I-60S NBSSR - Alternative Noise Barrier Materials Memo to Staff

Post 1989 Retrofit Soundwall Program 4

ATI'ACHMENT A

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To:

From:

Date:

Eck Chaiboonma

Steven Wolf

October 28, 2003

Memorandum

Subject: 1-605 NBSSR - Alternative Noise Barrier Materials Report

A review of alternative noise barrier designs and materials are presented in this report.The most flexible soundwall design that can accommodate different types of materials isthe Post and Panel system. This type of system consists of noise barrier panelsmounted between foundation-supported posts. Primary elements of this type of barrierinclude: post and post/foundation attachments, panels, and panel to post connections.The foundations may be of reinforced concrete, unreinforced concrete or wood posts.The noise barrier panels, which can be of concrete, metal, wood or other materials, arenormally prefabricated and shipped to the project site. These barriers can beconstructed upright or at an angle where sound reflection may be an issue. Thehorizontal gaps created in this type of barrier must be considered in their relationship tothe aesthetics of the environment. Furthermore, connections between the panels mustpreclude sound leaks due to gaps.

Before discussing the alternative noise barrier materials that can be used as part of aPost and Panel soundwall, I have provided a description of the some of the other morecommon types of soundwall designs.

ALTERNATIVE NOISE BARRIER SYSTEMS

Brick and Masonry Block - This type of system includes barriers constructed offabricated brick or masonry block units. Typically, these types of systems areconstructed by laying the brick or masonry block in a conventional fashion using acontinuous spread footing as a base. However, in certain instances, such barriers maybe constructed on a base beam supported at the ends by the posts or by the top of theconcrete caissons for the posts.

Direct Burial Panels - The direct burial panel type is a special panel system, whichinvolves burying a portion of one end of the panel (either precast concrete or wood)directly into the ground with no other means of foundation support. With this type ofsystem, the panels are usually full height and the connections to adjacent panels aretypically designed as a tongue and groove system. Since differential settlement of thepanels will most likely occur, a smooth top-of-wall profile cannot be expected. Therefore,a jagged profile should be considered during the design of this system. In some cases,this differential settlement may not be even throughout the length of each panel, thuscausing tilting of the panels and Ultimately resultinq in separating and gapping at thevertical tongue and groove joints.

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Cast-In-Place Concrete Noise Walls - these types of barriers are constructed at theproject site. The construction process includes excavating for the footing, erecting formwork, setting reinforcement steel, pouring concrete, surface finishing, and curing. Allmaterial testing and inspection procedures must be done in the field both duringconstruction and on an as-erected product. All casting and curing occurs under a varietyof weather conditions as compared to more controlled conditions for many of thecomponents of prefabricated barrier systems. Size limitations, shipping requirements,and traffic requirements must be considered in the construction of this type of barrier.Furthermore, application of concrete retarding chemicals to the vertical form worksurfaces for the purposes of obtaining an exposed aggregate finish is difficult.

Earth Berms - Barriers constructed from natural earthen materials such as soil, stone,rock, rubble, etc. in a natural, unsupported condition. These types of barriers aretypically constructed with surplus materials available on the project site or from materialstransported from an off-site location. The source and availability of such material arefactors, which can significantly affect the cost of such systems. Noise berms generallyoccupy more space than a wall type of barrier. The visual implications, landscaping, andacquiring of right-of-way should be considered in the construction of a berm.

ALTERNATIVE NOISE BARRIER MATERIALS

A variety of materials may be used for post and panels sound walls. This sectionprovides details of some of the more common materials: including a description of thematerial, its features, examples of typical use, and special considerations.

Concrete

Concrete is one of the most common material used for sound walls either cast-in-placeor precast designs. Almost half of the noise walls constructed in North America to dateare made of concrete. The proliferation of the use of concrete is not without reason.Concrete, if formulated, cast (precast or cast-in-place), and cured properly, is consideredto be one of the most durable materials currently used for many highway products,including noise barriers. It is rugged and able to withstand severe temperatures, intensesunlight, moisture, ice, and salt. It is a versatile material capable of being shaped,molded, and textured to take on the appearance of anything from weathered woodenboards to rock face to stone blocks to virtually any sculpted mural topic imaginable. Itsmass, even at a thickness of only 12 mm (0.5 in.), is well within any Sound Transmiss ionClass requirement.

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Metals

Three types of metals are most commonly used: (1) steel; (2) aluminum; and (3)stainless steel.

• Steel is the least expensive and most common of all metals used in construction.It is composed of a mixture, in varying proportions, of iron ore, carbon, and smallamounts of other metals depending on the physical characteristics desired.

• Aluminum is a lightweight alloy commonly made from bauxite and is typicallycoated with a bonded powder, enamel paints or anodized . It is not compatiblewith galvanized coatings.

• Stainless steel is a highly durable and corrosion resistant metal alloy. It is amixture of steel carbon, nickel, and chrome (in varying proportions). Since thismaterial is virtually corrosion resistant, the surface does not need to be coated.

Metal panels have a weight advantage which makes them particularly useful for verticalextensions of existing sound walls, for mounting on existing retaining walls which havelimited residual strength, or on bridge structures, because of their light weight.

Special Considerations

• Weathering Steel - Such unpainted, rusting panels are found to stain adjacentconcrete.

• Adjacent Vegetation - Plantings do not grow well next to sun-heated metalpanels. In addition, vines have difficulty in gaining a foothold on coated panels.

• Sound Transmission Class (STC) - Most metal sheeting materials do not meetthe typical minimum panel weight and/or sound transmission class required intypical noise barrier specifications. However, adding corrugations or ribs to theprofile of the panel material tends to improve the sound transmission class of thepanel.

• Appearance - Occasionally, metal walls impart an industrial appearance, which isconsidered undesirable by some residential neighborhoods. This is particularlytrue for the back side where the girts and posts are exposed to the view of theresidents. To overcome this perception, a double faced wall may be used. Thissystem incorporates the use of steel panels on both sides of the post andframework.

Glare - All metal barriers are susceptible to glare from opposing light sources.This issue is addressed in more detail in.

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• Conductivity - Since all metals are electrically conductive, the installation of metalnoise barrier walls should be avoided near power lines unless all metalcomponents can be properly grounded.

• Panel Thickness - Metal noise barrier panels are typically in the range of 18 to 22gauge thickness making them quite susceptible to damage from vandalism,debris, errant vehicles, and other maintenance equipment. Therefore,consideration should be given to the thickness of the panel, the structuralstrength that can be achieved through corrugations, and the distance from theroadway that they are installed.

Wood

Most wood noise barrier walls are constructed of pressure preservative treated lumber,plywoods, and glue laminated products. Panels can be either installed piece by piece inthe field or partially assembled in a plant or on the ground prior to attachment to thepost. Some wood barriers can also be easily dismantled if future highway changes areneeded. This material blends well with natural or residential background and does notconduct electricity.

Special Considerations.

• Safety - Consideration to safety issues, such as shatter resistance, should begiven when mounting wood noise barrier walls on traffic barriers.

• Burning Characteristics - Wood noise barrier walls will burn under the sameconditions as any other wooden fence. The smoke and emissions that aregenerated from burning treated wood are considered toxic. The ash left from theburning of this type of wood is also toxic and can leach into the surrounding soiland water supply.

• Warping and Shrinkage - Wood products are not dimensionally stable and tendto warp/shrink leaving open cracks between joints, particularly if they have notbeen properly seasoned or kiln dried. The thicker the wood products are, themore problematic warping can become.

• Tongue and Groove Planking - To prevent the occurrences of gaps betweenplanks as the walls weather and the planks shrink or warp, specifications forwood plank walls should include deeper tongues and grooves than the industrystandards.

• Pressure Treating - Most wood will decay rapidly when in contact with moisture.To combat this, the common practice is to pressure treat the wood with achemical preservative. There are several acceptable chemical solutions used, all

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with relatively equal performance. Some of the more common ones are ACC,ACA, CCA, Penta, and Creosote.

• Wood Posts - Large posts have a tendency to check or split open, exposinguntreated surfaces to decay and attack by insects. Checking can be minimizedby allowing the posts to season properly before being pressure-treated. Inaddition, the butt end of the post should be kerfed to allow deeper penetration ofthe preservative solution.

Transparent Panels

The typical transparent noise barrier may use panel material made of either glass or aclear plastic product such as Plexiglas, Butacite, Surlyn, Lexan, or Acrylic. Glass panelsare commonly made of single tempered or laminated tempered glass sheets. Bothplastics and glass can be tinted and can also be etched or given a frosty appearance.

Tempering of the glass is a heat treating process, which strengthens the glass,producing a much more, shatter resistant product. When it does shatter, the shards aresmall and granular in appearance, with pieces typically not larger than 12 mm (~ in).These are much safer than the long knife-like shards produced from shattering commonnon-heat treated glass. In addition to the tempering, the glass panels can also belaminated. This type of glass panel is produced by adhering two sheets of temperedglass sheets to both sides of clear rubbery type flexible sheeting. When this type of glasspanel is shattered, the glass will break into small granular-like pieces, where the pieceswill remain adhered to the sheeting.

The transparent panel materials are an ideal way of reducing or virtually eliminating thevisual impact of a noise barrier for the following 3 reasons:

• To prevent hindering the scenic view for the driving public;

• To prevent hindering the scenic view for the residents adjacent to theroadway; or

• To prevent hindering the view of retail establishments for the driving public.

Since transparent noise barriers costs can be as much as 20 times that of commonconcrete or steel panels, the decision to use transparent noise barriers should not bemade lightly. Possibly, the only other reasons for their use would be to improve safety,where opaque noise barrier walls may have an adverse affect on stopping sightdistance, visibility in merge areas, lighting, and shading.

Special Considerations· Transparent noise barriers come with their own unique set ofengineering , safety, and environmental considerations which are significantly differentthan most other types of material normally used for noise barrier panels.

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• Vandalism - Plastic panels are particularly susceptible to vandalism not only fromthe typical paint can, but also from knives, lighters, or matches.

• Mounting - Depending on the type of material used for the panels, (glass, acrylic,etc.) and the size, the method of mounting can vary significantly. The generalprinciple for mounting this type of thin, flat sheeting is that the method used mustsufficiently reduce or remove the stresses on the material to eliminate thepossibility of the panels breaking or falling out from between the supports.

• Dimensions - In order to enhance transparency, it would be preferable to uselarge pieces of material and to limit the number of supporting brackets. Whiletransparent plastic sheeting materials are available in lengths exceeding 5 m (16ft), the same is not true for tempered or laminated glass. Manufacturingconstraints limit the maximum dimensions of glass plates. In addition, as the areaof the panel increases, the thickness must also be increased to maintainstructural integrity, thus increasing weight and cost. To reduce the need forthicker material, it is common to use smaller post spacing and/or framed panelsthat can be stacked between posts.

• Edge Conditioning - To avoid thermal and stress cracking, all edges must besmooth and without defects. This is extraordinarily critical if the edges are not cutin a straight line.

• Ultraviolet Light Stabilizers - Some of transparent plastic sheeting materials aresensitive to ultraviolet light. If exposed to sunlight for extended periods of timewithout being protected by UV stabilizer additives or coatings, the sheeting willhaze and discolor, leaving them translucent or even opaque in some cases. Notethat glass, by itself, is not affected by sunlight. However, if laminating material isused, this material may be sensitive to ultraviolet light.

• Shatter Resistance - Although most commonly used plastic products arerelatively shatter resistant, glass is not; even when the glass is tempered and/orlaminated, the panel will shatter

• Glare - All transparent barriers are susceptible to glare from opposing lightsources.

• Cost - Depending on the size and type of material selected, the cost oftransparent barrier sheeting can be anywhere from 10 to 20 times more than thatof other barrier panel materials.

• Cleaning - To maintain their transparency, these types of panels need to bewashed on a regular basis. Access for cleaning of the panels is normally not aproblem on the traffic side, which is usually the dirtier side of the wall. However,the opposite side may not be as accessible, and, in some cases, cleaning may

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not be feasible at all. This limitation should be considered when selecting barriermaterial. Cleanliness is particularly critical if the transparent noise barrier wasconstructed for safety reasons such as to improve visibility for stopping sightdistance or merging.

• Breakage - Damaged panels cannot be repaired by patching. The only option isto replace the damaged sections.

Plastics

There are several types of plastic materials available for use as a barrier material,including Polyethylene, PVC, and fiberglass. The most unique features of plasticproducts are their versatility and moldability. This material can be produced to performand appear the same as almost any construction material on the market today. Its lightweight nature improves ease of handling both in the plant and in the field. In addition,most of these products are recyclable. Plastic noise barrier panels can be installed inalmost any situation. However, due to their light weight characteristics, they areparticularly suitable for structure mounted applications.

Special Considerations.

• Burning Characteristics - Plastic noise barrier walls tend to be more flammablethan barriers made of other materials. The smoke and emissions that may begenerated from burning plastics should be considered toxic. The ash left fromany burnt material should also be considered as toxic and can leach into thesurrounding soil and water supply.

• Shrinkage - Some plastic products are not dimensionally stable and may tend toshrink leaving open cracks between joints or may be susceptible to acceleratedcreep and deformation.

• Ultraviolet Protection - Some plastic products are very sensitive to ultraviolet lightand tend to cause rapid deterioration of pigments, surface appearance, andmaterial strength. To avoid this, it is possible to slow down the deteriorationprocess by adding ultraviolet protection into the composition of the plastic at thetime of molding.

• Creep - Creep, which is evident in most plastics to varying degrees, should beconsidered during the design of the barrier system by reducing the amount ofstrain to which the plastic components may be subjected.

• Vandalism - Plastic panels are particularly susceptible to vandalism from paint,knives, and lighters.

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• Shatter Resistance - Although most commonly used plastic products arerelatively shatter resistant, this characteristic tends to deteriorate over time, andthe product becomes more brittle and may shatter on impact by flying objects orvehicles. Damaged panels can usually not be repaired by patching. The onlyoption is to replace the damaged sections.

• Glare - Depending on the surface texturing applied to the plastic surfaces, thebarrier panels may be susceptible to glare from opposing light sources.

Recycled Rubber

Recycled rubber can refer to a wide range of products, made from an equally wide rangeof rubber compounds. In practice, however, the rubber waste stream is dominated byscrap tires. There are two other significant sources: (1) tire trim and off-spec tires fromtire production and (2) buffings from rubber product manufacturers.

Special Considerations

• Flammability and Smoke - Rubber is notorious for its high flammability and thedense smoke, which is produced when it burns. If a noise barrier made from thismaterial should ignite as a result of such incidents as grass fires, accidents, orvandalism, the accelerated flame spread and the dense smoke produced couldresult in safety issues.

• Toxicity - Recycled rubber tire material has been found to be nontoxic underleachate testing. However, additives, such as binders, retardants, coatings, andcoloring, included in the mix to form and enhance the material, can createpotential toxicity problems. These additives are, in some cases, proprietary withthe specific formulations kept in confidence by the manufacturer.

• Structural Strength - Rubber material, on its own, does not have sufficient rigidityto be considered as a structural component of a noise barrier panel. Therefore,bonding agents must provide adequate stiffness to enable the panels to beconsidered strong enough to withstand wind loading, or the rubber material mustbe firmly attached to a suitable stiffener, such as channel backings, cores, orcasings.

• Binders - Rubber and some binders tend to oxidize over time when exposed tothe elements . They may also be susceptible to certain chemical or petroleumproducts. This increases the potential of premature disintegration of the panels. Ifconcrete is used as a binder, concrete modifiers and special treatment of thecrumb rubber are required before they will bond properly to each other. This isparticularly important when these panels are exposed to salt, cold weather, andflexing for a long period of time.

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• Coatings - Some coatings suitable for rubber have a questionable lifeexpectancy. They have a tendency to oxidize prematurely, particularly whenused in conjunction with certain pigments. If the surfaces of the noise barrierpanels are being manufactured to be sound absorptive, the coatings may clogthe surface openings thereby reducing the Noise Reduction Coefficient (NRC).

• Sound Transmission Class (STC) - Although the weight of the panels may besufficient to meet general requirements for minimum STC ratings, it may not besufficient when produced as a porous panel. Even when stiff backers or coresare used, the nature of this material may require the cores or backers to beextensively perforated to promote bonding.

• Recyclability - The recyclability of the final product may have been reduceddrastically by the type of additives needed to alter the physical properties of thepanel so that it can meet the various fundamental requirements for an effective,safe, and durable noise barrier product.

Composites

Composite noise barrier materials, in general terms, can be defined as any productcomposed of two or more primary materials, such as plywood with a fiberglass skin, orwood mixed with concrete and then layered onto concrete. Since the possibilities arealmost endless, this section will mainly focus on the special considerations, which shouldbe used in evaluating their safety, durability, and performance.

Special Considerations - The combining of basic materials has a tendency to changethe performance, durability, and, in some cases, the safety characteristics of the finalproduct. These changes should be investigated thoroughly before the compositematerials are used in an actual installation.

• Burning Characteristics - Some composite materials may have a tendency toburn, or be severely damaged under certain conditions. The smoke andemissions that may be generated from burning materials might also be toxic. Theash left from any burnt material may also be considered as toxic and will mostlikely leach into the surrounding soil.

• Shrinkage - The shrinkage rate of the primary materials differ significantly andmay cause dimensional instability and leave open cracks between joints orpromote accelerated creep, warping, or delamination.

• Ultraviolet Protection - Some products are very sensitive to ultraviolet light andtend to cause rapid deterioration of pigments, surface appearance, and materialstrength. To avoid this, it is possible to slow down the deterioration process byadding ultraviolet protection into the composition of the material at the time ofmolding.

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• Creep - If plastic is part of the composite material, creep should be consideredduring the design of the barrier system by reducing the amount of strain, whichthe plastic components may be subjected to.

• Vandalism - Some materials are particularly susceptible to vandalism from paint,knives, and lighters.

• Shatter Resistance - Although most commonly used products are relativelyshatter resistant, this characteristic tends to deteriorate over time and the productbecomes more brittle and may shatter on impact by flying objects or vehicles.Damaged panels can usually not be repaired by patching.

• Structural Strength - Some primary used in composite panels do not havesufficient rigidity to be considered as a structural component of a noise barrierpanel. Therefore bonding agents must provide adequate stiffness to enable thepanels to be considered strong enough to withstand wind loading, or the materialmust be firmly attached to a suitably stiff backing, core, or casing.

• Safety - Consideration to safety issues, such as shatter resistance, should begiven when panels are mounted on traffic barriers, such as Jersey barriers.

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