Fiber-Reinforced Concrete For Pavement Overlays Tech Brief
March 2019FIBER-REINFORCED CONCRETEFOR PAVEMENT OVERLAYSAUTHORSIntroductionBackgroundJeffery Roesler, ProfessorCivil and Environmental EngineeringUniversity of Illinois,Urbana-ChampaignThe objective of this tech brief is toprovide pavement engineers with theinformation necessary to use fiberreinforced concrete (FRC) for concreteoverlays. This tech brief explainshow to determine the appropriatefiber reinforcement performancevalues to specify and implement inthe structural design calculationsfor bonded and unbonded concreteoverlay projects.Fiber reinforcement technology forconcrete pavements was introducedseveral decades ago and has sincebeen applied to highways, streets,intersections, parking lots, pavementand bridge deck overlays, bus pads,industrial floors, full-depth slab patches,and airfields. The first US applicationwas a FRC pavement with steel fibersconstructed in 1971 at a truck weighstation in Ohio (ACI Committee544 2009). Additional early FRCapplications included overlays for USNavy airfields and commercial airportsin the 1970s and 1980s (Rollings 1986).Amanda Bordelon, Assistant ProfessorCivil Engineering, Materials PavementsUtah Valley UniversityAlexander Brand, Assistant ProfessorTransportation Infrastructure andSystems EngineeringVirginia Polytechnic Institute andState UniversityArmen Amirkhanian, Assistant ProfessorCivil, Construction, andEnvironmental EngineeringUniversity of AlabamaNational Concrete PavementTechnology Center2711 South Loop Drive, Suite 4700Ames, IA 50010-8664cptechcenter.orgDirector, Peter Taylor515-294-3230 / ptaylor@iastate.eduA spreadsheet tool called the ResidualStrength Estimator was developed tohelp pavement engineers use FRC inconcrete pavement applications. Thetool provides an estimate of the FRCperformance value to specify for aproject as well as the effective flexuralstrength to input into the mechanisticempirical (M-E) concrete pavementdesign software.A comprehensive technical reportaccompanies this tech brief. The reportprovides a more detailed summaryof the types of macrofibers used inFRC, the expected properties of FRCmaterials, the effects of differentmacrofibers on concrete pavementperformance, available FRC testmethods, best practice guidelinesand specifications for FRC materialsapplied to pavements, and backgroundinformation on the Residual StrengthEstimator spreadsheet tool.In the past 15 years, FRC has beensuccessfully implemented in concreteoverlays of roadways. Particularly, the useof FRC in bonded concrete overlays onasphalt or composite pavements has seensignificant growth in the past 10 years,with overlay thicknesses ranging from3 to 6 inches. The National ConcreteOverlay Explorer lists 89 FRC overlayprojects constructed between 2000 and2018 index.html).The known benefits of FRC forpavements include its abilities toprovide additional structural capacity,reduce crack widths, maintain jointor crack load transfer efficiency, andextend the pavement’s serviceabilitythrough reduced crack deterioration.
Fiber-Reinforced Concrete for Pavement OverlaysAn Illinois study of FRC overlays reported betterperformance compared to similar plain concrete overlays(King and Roesler 2014). Moreover, multiple laboratoryscale slab tests of macrofiber reinforcement have shown thatthe flexural and ultimate load capacity of FRC slabs and theload transfer efficiency between FRC slabs are significantlygreater than those of plain concrete slabs (Roesler et al.2004, Beckett 1990, Barman and Hansen 2018). Themagnitude of the increase is dependent on the fiber typeand content.Nevertheless, the use of FRC is still not considered forsome concrete pavement projects, sometimes becauseof the additional material costs, potential mix designmodifications, and constructability questions associatedwith FRC, but primarily because pavement engineers lackexperience with FRC.Given the advantages of FRC, an FRC inlay or overlay isuseful where a thinner slab is required, in high-traffic areaswith a significant number of repeated heavy loadings, whenvariable support conditions are required, or on projectsin need of a longer design or service life, as illustrated inFigure 1.In addition, FRC can help reduce slab movement, slabmisalignment, plastic shrinkage cracking, and crack widening.Smaller crackwidthsReduced crackdeterioration rateAdd macro-fibers(e.g., f150 150 psi)Thinner slab for samefatigue performanceORLonger fatigueperformanceFigure 1. Advantages of FRC inlays or overlaysHow does the use of FRC most benefit concrete overlays?The main advantages of FRC are improved residualstrength of the concrete material, smaller crack widths,and slower rates of crack deterioration. In addition, FRCcan help reduce slab movement, slab misalignment, plasticshrinkage cracking, and crack widening and can helpmaintain load transfer efficiency.2Pavement Design for Concrete OverlaysFRC can be applied to bonded or unbonded concreteoverlays. The most common design tools for bondedconcrete overlays on asphalt are bonded concrete overlayof asphalt mechanistic-empirical (BCOA-ME) design(Li et al. 2016), the American Concrete PavementAssociation’s (ACPA’s) Pavement Designer, and theAmerican Association of State and Highway TransportationOfficial’s (AASHTO’s) AASHTOWare Pavement ME. Forunbonded concrete overlays, AASHTOWare Pavement MEand Optipave 2.0 (Covarrubias et al. 2011) can be used todesign traditional-sized slabs and short slabs, respectively,with macrofibers.Several new M-E methods for designing unbonded overlayswith traditional jointed and shorter slab systems are underdevelopment and will become available soon. The jointspacing of unbonded overlays may need to be reduced whenmacrofibers are used to decrease the required slab thickness.The benefits of FRC are accounted for in all of the designtools by updating the plain concrete flexural strength,also known as the modulus of rupture (MOR), with aneffective flexural strength (feff ) that accounts for the effect ofmacrofibers on the slab’s flexural capacity, as follows:feff MOR f150Typical residual strength values ( f150 ) used in FRC overlaysare between 100 and 200 psi (Barman and Hansen 2018,Bordelon and Roesler 2012). The specified residual strengthvalue can vary depending on the traffic level, condition ofthe existing pavement, desired design life, slab geometry,slab thickness constraints, and requirements for crackwidth control. While the residual strength is specified for aparticular project and overlay design, different macrofibertypes require different dosage levels to achieve the sameresidual strength value. The macrofiber’s geometry, stiffness,surface texture, and other characteristics, along with theconcrete strength, all affect the residual strength.Research has shown that macrofibers can maintain theload transfer efficiency of contraction joints under repeatedloading (Barman and Hansen 2018, Barman et al. 2015),similarly to the mechanism of tie bars in contraction joints.However, FRC materials should not be substituted for tiebars in joints that require dowel bars to control faulting.
Fiber-Reinforced Concrete for Pavement OverlaysResidual Strength Estimator for Concrete OverlaysTo complement this work, a Residual Strength Estimatorspreadsheet tool (available at https://cptechcenter.org/publications/ under the Spreadsheets category), asillustrated in Figure 2, was developed to assist in theselection of a residual strength value (f150 ) for a given set ofconcrete overlay inputs.The pavement engineer enters the conditions and designrequirements of the project to determine the estimatedrange of residual strength for the overlay structural design,as well as to later verify the FRC material requirements.Because most FRC applications have been bonded overlays ofasphalt pavements, the software is based on this assumption.Therefore, the tool estimates a residual strength range for agiven set of inputs but warns the pavement engineer if anunbonded design should be considered instead.Figure 2. Residual Strength Estimator spreadsheet tool3
Fiber-Reinforced Concrete for Pavement OverlaysThe following are the key inputs considered in the FRCresidual strength recommendations: Roadway functional class Equivalent single-axle loads (ESALs) in the design life Asphalt pavement condition prior to overlay placement;this is a subjective rating, but it can be internally selectedbased on characteristics such as a resilient modulus,stiffness, percent cracking, structural number, etc. Remaining thickness of existing pavement after preoverlay surface preparation Approximate new concrete overlay thickness New slab size, with slab sizes of 4 ft recommended onlyfor non-channelized traffic such as parking lots Design flexural strength (MOR) for the plain concretemixture Enhanced performance option in terms of reduced crackdeterioration rate or enhanced load transfer efficiency,which increases the specified residual strength for extrafiber toughness performanceIn addition to the residual strength range, the tool alsocalculates an effective flexural strength value that accountsfor the benefits of the macrofibers. The effective flexuralstrength can be entered into a concrete design procedure.The macrofiber type and content can be separately selectedand tested with a paving concrete mixture to verify thespecified residual strength.What is the difference between bonded and unbondedoverlays with FRC?FRC overlays can be bonded or unbonded. The addition ofmacrofibers should not be used to convert an unbondedoverlay design to a bonded overlay design. If the existingasphalt pavement is in fair to good condition, a bondedoverlay can be designed. However, if the existing pavementis in a poor and deteriorated condition, an unbondedoverlay design should seriously be considered.A number of possible ME design methodologies areavailable depending on whether a bonded or unbondedoverlay is chosen. The Guide to Concrete Overlaysprovides a thorough discussion of the selection processwhen considering an unbonded versus a bonded overlay(Harrington and Fick 2014).4Concrete Overlay and FRC MaterialDesign ProcessThere are several ways for the designer and contractor/material supplier to determine the required fiber contentgiven a target FRC performance value. An agency canestablish a qualified product list based on laboratory residualstrength tests for a standard concrete paving mixture,or an initial estimate of the required fiber dosage can beobtained from the fiber manufacturer or past laboratorytests (Barman and Hansen 2018), and then be verified usingASTM C1609-12. Fiber content can be adjusted linearly toachieve the target residual strength value.The following steps, divided into designer and contractor/material supplier responsibilities, summarize the processfor selecting the FRC performance value (f150 ) for a newconcrete overlay.Designer responsibilities:1. Determine existing pavement conditions and collectdesign inputs.2. Decide whether the new concrete overlay is a bonded orunbonded system based on the existing conditions andpavement design inputs.3. Use the Residual Strength Estimator tool to determinethe FRC’s residual strength (f150 ) and effective flexuralstrength (feff ) (see Figure 3).4. Design the concrete overlay thickness in a pavementdesign program using the effective flexural strength.How many macrofibers do I need to add?Typical fiber content for concrete overlays can rangefrom 0.2% to 0.5% by volume, and the amount depends onmany technical factors (e.g., slab flexural capacity, desiredservice life, crack width criteria, and joint load transferefficiency) and costs. For bonded concrete overlays ofasphalt, a minimum residual flexural strength (f150) of 100to 150 psi should be specified depending on the designrequirements. The fiber type and volume fraction canbe adjusted accordingly to meet the specified residualstrength requirement.
Fiber-Reinforced Concrete for Pavement OverlaysMacrofiber Types and Contents1. Run concrete overlaydesign softwareCompare plain and FRCoverlay thickness2. Use key inputs inResidual StrengthEstimator Software3. Determine effectiveflexural strength foroverlay design4. Determine concreteoverlay thicknesswith fibersFigure 3. Designer process flow for FRC overlayperformance specificationContractor/material supplier responsibilities (see Figure 4):1. Select potential macrofiber types and fiber contentsbased on published laboratory data, a qualified productlist, or data from the fiber manufacturer.2. To verify fiber performance, cast a concrete mixturewith macrofibers for each fiber type. If the estimatedfiber content is not known, it is recommended that FRCbeams with at least two volume fractions be cast.3. Use ASTM C1609-12 at a fixed age and calculate theresidual strength (f150 ) versus fiber volume fraction foreach fiber type.A wide variety of fibers are commercially available for usein FRC. The two primary types of macrofibers used forpavements and overlays are synthetic and steel (see Figure 5).Synthetic macrofibers are overwhelmingly used in concreteoverlay applications. Macrofibers come in differentgeometries, shapes, and surface textures. Generally,macrofibers are 1 to 2.5 in. long with an aspect ratio of 30to 100.The required macrofiber content, volume percentage, ordosage rate depends on the specified residual strength value,concrete constituents and proportions, and the requiredstrength of the concrete. Typical macrofiber ranges usedin past concrete overlay applications have been between 3and 8 lb/yd3 for synthetic and 25 to 75 lb/yd3 for steel, orapproximately 0.2% to 0.5% by volume.Residual strength ( f150 ) is the primary performanceparameter used to quantify the benefits of FRC materialsand is used as an input for the structural design of concreteoverlays with macrofibers. Ideally, the selection of the fibertype and content should be the contractor’s decision, andthe pavement engineer should only specify the residualstrength that is required to achieve the objectives of theoverlay design.Macrofibers should not be specified based on the fibers’geometries, shapes, or surface textures but on theireffect on the concrete’s residual strength value (see theaccompanying report).4. Select the fiber volume fraction (%) or fiber content(lb/yd3) based on the specified residual strength.5. During construction, check the macrofiber content in thefield by weighing the fibers contained in a unit volume.Select fiber types to evaluateCreate trial concrete batches with two fiber contentsPerform ASTM C1609 on FRC beams to determine f150 valueFigure 5. Examples of differentmacrofibers, top to bottom: crimped,embossed, and bi-tapered synthetic;twisted synthetic; straight fibrillatedsynthetic (two images); and hookedend and crimped steelDetermine required fiber content for each fiber based on specified f150 valueFigure 4. Contractor/material supplier process flow for FRCoverlay specificationMeasurements in inches5
Fiber-Reinforced Concrete for Pavement OverlaysWhich specific fiber type should I use and how does the fibertype affect dosage?While both steel and synthetic fibers have successfully beenimplemented in FRC overlays, synthetic macrofibers havebecome the most commonly used because they are easier tohandle and less prone to balling.Fresh and Hardened Properties of FRCSeveral of the standard fresh and hardened concreteproperties change with the addition of macrofibers.Fresh Properties Workability should be expected to decrease with theaddition of macrofibers. In some cases, slump can be reduced by up to 4 in.,but the magnitude of the reduction depends on thefiber type and content as well as the concrete mixture’sconstituents and proportions. Generally, the additionof water-reducing admixtures or other mixturemodifications can easily compensate for the slumploss so that the effect on workability is minimal. Theseadjustments also improve finishability. Air content has been reported to be affected by theaddition of fibers. Adjustments in air content can bemade through changes in the air-entraining admixturewhen mixing the FRC trial batches. Trial batches are always recommended to confirm thatthe FRC mixture can meet all of the fresh propertyspecifications.Regardless of the fiber type, the fiber content can be adjustedto achieve the specified residual strength performance.Therefore, the concrete residual strength (ASTM C1609-12)should be specified and then verified through laboratory testingto determine the fiber content for a particular fiber type. The durability of FRC may be improved comparedto plain concrete, particularly given the reduction inaverage crack width. FRC has also been shown to retain significant residualstrength even after a large number of freeze-thaw cycles.Test Method for FRC PerformanceThe primary test method used to quantify the performancebenefits of macrofibers in concrete pavement design isASTM C1609-12 (Figures 6, 7, and 8).L/3L/3L/3dLFigure 6. Geometry of the ASTM C1609-12 beam setupHardened Properties For fiber volume contents used in pavements (less than0.5% by volume), the compressive and flexural strengthsare not expected to change relative to plain concrete. The post-cracking strength and toughness are theprimary hardened concrete properties that are improvedwith the addition of macrofibers. Fibers have been shown to improve the flexural fatigueperformance of concrete. The load transfer efficiency of FRC can increase by30% compared to plain concrete, especially when crackwidths are relatively large, i.e., greater than 1.0 mm(Barman and Hansen 2018). Macrofibers have also been shown to reduce the numberof cracks and the average crack width under restrainedshrinkage testing.6Figure 7. ASTM C1609-12 testing apparatusb
Fiber-Reinforced Concrete for Pavement Overlaysis recommended that ASTM C1609-12 be used to evaluatethe residual strength value for a given concrete mixture,fiber type, and fiber content for concrete pavement overlaydesigns (ACI Committee 544 2018).6.35% Hooked End Steel Fiber.50% Crimped Steel Fiber.32% Synthetic Fiber.48% Synthetic FiberPlainStress (MPa)54Mixture Proportioning and ConstructionModifications for FRC Overlays321000.511.522.53Beam Deflection (mm)Figure 8. Typical load-deflection responses for several macrofiberbeams with a typical width (b) and cross-section depth (d) of 6 in. andspan (L) of 18 in.ASTM C1609-12 is very similar to the flexural beam test(ASTM C78) but with several important differences: The test is controlled by mid-span vertical displacementinstead of load. The test is continued beyond when a macro-crack formsuntil a total displacement equal to L/150 is achieved.Typically, the deflection is 0.12 in. ASTM C1609-12 specifies a low-friction roller assembly(ASTM C1812). A 6-in. square cross-section beam depth isrecommended for pavement applications instead of the4-in. beam depth recommended in ASTM C78. The specification should state a testing age and identifythe target (average) residual strength (f150 ) for the FRCmaterial. Experience has shown that later testing agesmay require a stiffer and higher-capacity testing frame toproperly control the ASTM C1609-12 test.In ASTM C1609-12, the residual strength (f150 ) iscalculated from the load-deflection plot (see Figure 7 for anexample) as follows:where P150 is the corresponding load when the displacementreaches a value of L/150, L is the span of the beam betweenthe supports, b is the width of the beam, and d is the heightof the beam.While alternative test methods for characterizing thepost-cracking performance of FRC have been proposed, itIn general, for the typical low to moderate fiber dosagesused for FRC pavement overlays (i.e., less than 0.5% byvolume), the concrete mix design does not necessarily needto be adjusted except to accommodate the volume of thefibers. Best practices for standard proportioning of concretepaving mixtures should otherwi
4. Design the concrete overlay thickness in a pavement design program using the effective flexural strength. How many macrofibers do I need to add? Typical fiber content for concrete overlays can range from 0.2% to 0.5% by volume, and the amount depends on many technical factors (e.g., slab flexural capacity, desired
reinforced concrete for pavement applications. However, Merta et al., (2011) studied wheat straw reinforced concrete for building material applications. They concluded that there is an increase (i.e. 2%) in fracture energy of wheat straw reinforced concrete. Thus, wheat straw reinforced concrete needs to be investigated for rigid pavements.
Recommended Practice for Glass Fiber Reinforced Concrete Panels - Fourth Edition, 2001. Manual for Quality Control for Plants and Production of Glass Fiber Reinforced Concrete Products, 1991. ACI 549.2R-04 Thin Reinforced Cementitious Products. Report by ACI Committee 549 ACI 549.XR. Glass Fiber Reinforced Concrete premix. Report by ACI .
Jun 01, 2020 · FIBER TYPE The first step to choosing the right fiber is to understand the type of fiber required for your application. The main standards for fiber reinforced concrete are ASTM C 1116 and EN14889. ASTM C 1116, Standard Specification for Fiber Reinforced Concrete, outlines four (4) classifications of fiber reinforced concrete;
Airports in North Dakota are a combination of asphalt concrete (AC) pavement and Portland cement concrete (PCC) pavement with there being slightly more AC pavement than PCC pavement. These two pavement types have unique pavement distresses and repairs. The following is a brief description of commonly observed
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vary the overall capacity of the reinforced concrete and as well as the type of interaction it experiences whether for it to be either over reinforced or under reinforced. 2.2.2.1 Under Reinforced Fig. 3. Under Reinforced Case Figure 3.2 shows the process in determining if the concrete beam is under reinforced. The
Properties of strain hardening ultra high performance fiber reinforced concrete (UHP-FRC) under direct tensile loading. Cement and Concrete Composites, 48, 53-66. Applications of Fiber Reinforced Concrete Fiber reinforced concrete are primarily used for applications that toughness of
experimental flexural behavior of concrete beams reinforced with glass fiber reinforced polymers bars" is done. D.Modeling . ANSYS Workbench 16.1 is used to model the concrete beams and 28 different models are considered. Concrete beams reinforced with reinforced with steel bars of circular cross
