Precast Concrete Traffic Barriers

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OUTLINE Purpose of Traffic BarrierSpecificationsNCHRP 350 & RequirementsTypes of Precast Concrete BarriersPrecast Advantage & Cost SavingsQuality Considerations

PURPOSE of TRAFFIC BARRIER Reduce the risk of an out-of-control vehicle crossing themedian and colliding with opposing traffic or roadwayworkers.

PURPOSE of TRAFFIC BARRIER Reduce the risk of a vehicle deflecting back into thetraffic stream after colliding with the barrier.

PURPOSE of TRAFFIC BARRIER Decelerate theerrant vehiclewithin tolerablelimits. Directing traffic ina prescribedmanner.

PURPOSE of TRAFFIC BARRIER Security DevicesProtection againstunwanted vehicular trafficand terrorist activitiesaround governmentbuildings, utility facilities,historic landmarks andairports.

APPLICABLE STANDARDS ASTM C 825 –StandardSpecification forPrecast ConcreteBarriers NCHRP 350 –RecommendedProcedures for theSafety PerformanceEvaluation ofHighway Features

ASTM C 825 Classification of BarrierNew Jersey BarrierType-F Barrier

ASTM C 825 Basis of AcceptanceStrength Properties – Cylinders tested in accordancewith ASTM C39. Average f’c values for daily testingequal to or greater than the specified design strength.Dimensional Properties – Cross-sectional &longitudinal dimensions, and Location & positioningof anchoring devices and reinforcement.End Result – Acceptable to the purchaser at the pointof delivery.

ASTM C 825 MaterialsCement, aggregates, admixtures and steel reinforcementshall conform to applicable ASTM Specifications. ManufactureConcrete mixture shall be proportioned and mixed to meetthe minimum strength level and cured per the methodsoutlined in Section 7 of the ASTM C 825 specification. FormsSufficiently rigid to maintain dimensional parameters. Allcasting surfaces shall be of smooth, nonporous materials.

ASTM C 825 Design Concrete Design Strength – 4,000 psi in 28 days Air Entrainment – Unless otherwise specified, allconcrete will have an air content of 5 ½ /- 1% asmeasured by ASTM test method C 173 or C 231. Dimensions – Unless otherwise specified, theminimum length of each barrier section will be 10feet. It is common for DOTs to ask for lengths of20 feet or even 30 feet.

ASTM C 825 Design Steel Reinforcement – Unless designated by thepurchaser, reinforcement shall be designed by theproducer and be sufficient to permit handling,delivery and placement of sections without damage. Minimum concrete cover is 2.0 inches, except forend sections where cover may be less. Seeapplicable project or ASTM specifications forspecific details. Shall be assembled as a cage with sufficient matand bar to maintain shape during casting.

ASTM C 825 Design Reinforcement design for the endsof barrier sections should be inaccordance with the publication“Concrete Median BarrierResearch,” Volume 2, ResearchReport, prepared by the SouthwestResearch Institute for the FHA, toprevent fracture at the joints. Laps, welds and splicing shall beacceptable to the purchaser anddevelop full strength ofreinforcement.

ASTM C 825 Design Concrete Finishing – Shall be at the option of theproducer, produce a finish comparable to the steelform finish and be uniform for all sections in thecontract lot. Lifting Devices – Shall not be cast into the sidesurfaces of the barrier product. Anchorage to prevent lateral movement of thebarrier shall consist of dowels, keyway joints orinterlocking devices as may be specified by thepurchaser.

ASTM C 825 Physical Requirements Compression Testing – Identified with BarrierSections 2 cylinders for each 25 yd3, or a minimum of 2cylinders per day’s production in accordance withASTM C31, “Standard Practice for Making andCuring Concrete Test Specimens in the Field,”except when otherwise specified. Compressive Strength per ASTM C39,“Compressive Strength of Cylindrical Specimens.”

ASTM C 825 Permissible Dimensional Tolerances Cross-sectional dimensions shall not vary fromdesign by more than ¼ inch. Vertical centerlineshall not be out of plumb by more than ¼ inch. Longitudinal dimensions shall not vary from designby more than ¼ inch in 10 feet of barrier sectionand not exceed ¾ inch per section. Location of anchoring is specified by purchaser.

NCHRP 350 Summary Federal Highway Administration (FHWA) issued aguidance memo in July 1997 requiring crashtesting of all work zone devices on the NationalHighway System. This crash testing is outlined inNCHRP 350 (National Cooperative of HighwayResearch Programs). Visit the Web site at dept/road hardware/nchrp 350.htm

NCHRP 350 Work zone devicesare subdivided intofour categories. Precast concretebarrier falls inCategory 3.

NCHRP 350 Crash Testing Levels There are six levels forimpact performanceevaluation of various safetyfeatures based uponprincipal performancefactors: Structural adequacy Occupant risk Post-impact behavior ofvehicle

NCHRP 350 Crash Testing Levels Test Level 1 – Low-volume, low-speed localstreets and highways, and some work zones Test Level 2 – Most local and collector roads andmany work zones Test Level 3 – Wide range of high-speed arterialhighways Test Levels 4-6 – Based upon volume of truck andheavy vehicle traffic and/or the consequences ofpenetration beyond the barrier

NCHRP 350 CrashTestingLevels

TYPES OF PRECASTBARRIERSNew Jersey BarrierF-Shape BarrierSafety Shape Barrier(Constant Slope)

PRECAST ADVANTAGE Readily available Produced in a quality-controlledenvironment Durability from the elements Mass Modularity Faster and safer than slip-forming

PRECAST ADVANTAGE Durability upon vehicularimpact (unlike other types ofbarrier that contain sand orwater and be compromisedwhen impacted) Less Maintenance Superior Strength

PRECAST ADVANTAGE Cost Savings Alternative types of barrier are sacrificial and mustbe replaced when an impact occurs. Even low-energy impacts can bend and damagesteel rails and displace posts so that the barriermay not perform properly in a subsequent impact. Maintenance crews must spend considerable timemaintaining these systems, resulting in high costsand safety risks to motorists and highway workers.

QUALITY NPCA QualityControl Manualfor Precast Plants,Fifth Edition

QUALITY NPCA Plant Certification Program

measured by ASTM test method C 173 or C 231. Dimensions – Unless otherwise specified, the minimum length of each barrier section will be 10 feet. It is common for DOTs to ask for lengths of 20 feet or even 30 feet. ASTM C 825 Design Steel Reinforcement – Unless designated by the purchaser, reinforcement shall be designed by the producer and be sufficient to permit handling, delivery .

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