Rigid Pavement Overview_Concrete Type

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Rigid pavement introduction

Text of Rigid Pavement Overview_Concrete Type

Project Management Concept

1Concrete Pavement Type & Selection2Concrete Pavement TypesJointed plain concrete pavements (JPCP)Jointed reinforced concrete pavements (JRCP)Continuously reinforced concrete pavements (CRCP)22As mentioned before, these are the three main concrete pavement types3JPCP3.7 to 6.1 m (typ.) (12 to 20 ft)Transverse Joints(with or without dowels)Longitudinal Joint (with tiebars)PLANVIEW3.7 to 6.1 m (typ.) (12 to 20 ft)33This figure schematically illustrates some of the design characteristics of JPCP--short joints, no distributed steel (but dowels and tiebars). JPCP is the most common concrete pavement type constructed; it is a reliable, easy to construct design (1999 ACPA survey showed it is constructed by 38 of 41 responding state highway agencies).4JPCP

44Overview photo of a JPCP with distresses that are common to the design (faulting and transverse cracking)5JRCPPLANVIEW7.6 to 18.3 m (typ)(25 to 60 ft) Transverse Joints(with dowels)Welded WireFabric Reinforcing(0.15 to 0.25%)Longitudinal Joint (with tiebars)55This figure schematically illustrates some of the design characteristics of JRCP--longer joints, distributed steel (typ. 0.15 to 0.25%), dowels and tiebars. The steel is non-structural and is not intended to actually carry traffic loading, but instead to hold cracks tightly together. The use of deformed steel bars or mesh is recommended.JRCP was widely used in the 60s and 70s, but many of these had excessive joint spacing and insufficient steel, resulting in failures (ACPA survey showed 9 of 41 construct JRCP, although some not routinely). JRCP is not being included as part of the 2002 design guide.6JRCP

66Overview photo of a JRCP with common distresses (deteriorated joints and deteriorated transverse crack)7CRCPLongitudinal Joint (with tiebars)PLANVIEWTypical Crack Spacing(0.9 to 2.4 m)(3 to 8 ft)Continuous Longitudinal Reinforcement(Deformed Bars)(0.6 to 0.8%)77This figure schematically illustrates some of the design characteristics of CRCP--no regular transverse joints, heavy reinforcing steel (typ. 0.6 to 0.8%). Again, this steel is non-structural. CRCP are anywhere from 20 to 50 percent more expensive than JPCP (initial construction costs). CRCP have been tried by many agencies, but today are used by only a few agencies (ACPA survey showed 8 highway agencies). IL and TX are the biggest users, and they commonly use CRCP in urban areas such as Chicago and Houston where the need for a long-lasting, low maintenance pavement is acute.

8CRCP

88Photo of CRCP (notice crack spacing) and major structural distress in CRCP (punchout)9Pavement CharacteristicsJPCPPavement TypeDisadvantagesAdvantagesCRCPJRCPReliable designApplicable in all locationsFewer jointsLess concern about random crackingNo transverse jointsSmooth ridingLong service lifeLow maintenanceIncreased joint costIncreased joint maintenanceJoint deteriorationCrack deteriorationHigh initial costRehab is difficult99A few of the advantages/disadvantages of the different pavement types are listed here (and on page 10 in the Technical Digest).What items can you add?10Considerations in SelectionTraffic levelsSubgradeClimateInitial construction and life-cycle costsService lifeFuture maintenance/rehabilitationReliabilityContractor experienceLocal experience/past performance1010In selecting a concrete pavement type,what are some of the factors to consider?Here are just a few of the factors that might be considered (see also list on pages 9-10 of the Technical Digest).What factors are most important to your agency?11NCHRP 1-32 Pavement Type Selection Guidelines0 5 10 15 20 ESALs, millionsUndoweled or Doweled JPCPDoweled JRCPCRCP1.51.5-3.03.0-6.0Doweled JPCPDoweled JRCPCRCPUndoweled JPCPUndoweled or Doweled JPCPDoweled JRCP>6.01111A study was recently completed under NCHRP 1-32 in which a pavement design catalog was developed. Here are the general recommendations on type selection (see page 12 of the Technical Digest). Not a lot of guidance, but does suggest that all PCC types can provide satisfactory performance provided that:--it is effectively designed--it is properly constructed--it is routinely maintainedThe results of the NCHRP 1-32 study are available on a CD-ROM from TRB.

12Design FeaturesDesign elements contributing to performance, such as dowel bars, drainage, edge supportVarious studies have shown the positive effect of design featuresEuropean experienceLTPP findings1212Weve made reference to design features in the previous module and want to emphasize the impact on performance. Various studies have been conducted that have shown the positive effect of pavement design features.13European ExperienceEuropean researchers identified four key design featuresNonerodible base coursePositive drainageStrengthened structure (thick slab, doweled joints, or CRCP)Slab stress relieving features (widened slabs, trapezoidal cross section)1313Weve made reference to design features in the previous module and want to emphasize the impact on performance.European researchers have found that the following items contribute to the performance of their concrete pavements:--Nonerodible base--Positive drainage--Strengthened structure--Widened slab or trapezoidal cross section14LTPP Study of Relative Effect of Design FeaturesInitial smoothnessLoad transferSubdrainageBase typeSlab wideningJoint spacingSlab thicknessSlab modulus/strengthIncreasing Effect on JPCP Performance1414A preliminary performance study was conducted on the concrete pavement data collected under the Long-Term Pavement Performance (LTPP) program (Khazanovich et al 1997). The relative effect of design features as they contribute to JPCP performance are listed here (most important features listed first). Although these are preliminary findings, they are intriguing. Based on your experience, what factors do you feel are most important?It is interesting to note that slab thickness and concrete strength fall near the bottom of this list. That is, two of the main design items that we consider in pavement design do not, according to this study, have as significant effect on pavement performance as some of the other factors. One possible reason for this is that of all the elements in concrete pavement design, slab thickness is designed rather conservatively with a factor of safety built in; other elements do not have a factor of safety built in so this may explain why they have a more significant effect on pavement performance. This also might explain why most concrete pavements fail by some other mode than fatigue.15LTPP Study of Design and Construction FactorsFactors Contributing to PerformanceDesign FactorsConstruction FactorsDoweled jointsErosion-resistant basesPositive drainagePCC shouldersPCC strengthATBMultiple base layersDowels on basketsCoarse agg. content1515A similar LTPP study was done looking at what design and construction factors affect concrete pavement performance, and some of the findings are listed here. Again, it should be emphasized that these findings are preliminary.16LTPP Study of Design and Construction Factors (contd)Site conditions adversely affecting performanceWet climates > 39 in annual precipitation > 140 wet daysAverage temperatures > 60 oFAverage number of freeze-thaw cycles > 110Fine-grained subgrades1616The same LTPP study also identified site factors that adversely affected concrete pavement performance17LTPP Study of Joint FaultingUse of dowel bars had the greatest effect on reducing faultingUse of skewed joints did not show a significant difference in faulting for doweled jointsDoweled joints exhibited little faulting after many years of service1717A study on LTPP joint faulting was also conducted and revealed these findings.18Cost EffectivenessAddition of design features may increase performance, but also will increase costsMust consider COST EFFECTIVENESS of design features

1818It is important to recognize that adding design features will increase the cost of the project. Therefore, it is important that the addition of these design features be cost effective. What do we mean by cost effectiveness? How can it be determined?