Subbases and subgrades american concrete pavement association. Subbase design manual for portland cement concrete. Concrete pavement construction basics compaction and trimming before compacting, subgrade material may have to be brought to the optimum moisture content. Mccullough, describes a comprehensive set of design methods for continuously reinforced concrete pave ments. Subgrade and subbases subbase layer of material directly below the concrete pavement. The main issue associated with this research is if cheaper alternatives can be configured for subbase construction. In some cases, as for most clays and some silty soils, it may be most economical and advanta geous to treat the subgrade soil and then to provide a unstabilized granular subbase as a construction platform. Construction of interlocking concrete pavements adequate compaction of the soil subgrade. To prepare for paving, the subgradethe native soil on which the pavement is builtmust be graded and compacted. Continuously reinforced pavements that have no contraction joints and are reinforced with continuous longitudinal steel. Smoothdrum roller equipped with onboard display unit. And one of the major functions of a highway pavement is to reduce the. A primecoat is a sprayed application of a cutback or emulsion asphalt applied to the surface of untreated subgrade or base layers asphalt institute, 2001 2.
After construction, the floor is likely to settle and crack because of poor subgradesubbase support. The major problems of concern in the design of rigid pavements are discussed. Exceptions and additional requirements are specified in those sections. Concrete pavement design for municipal streets load transfer slabs ability to share its load with neighboring. Subgrade and subbases design summary subgrade strength is not a critical element in the thickness design. Eb204 subgrades and subbases for concrete pavements acpa. Hence the performance of the pavement is affected by the characteristics of the subgrade. Subgrade stabilization the top of subgrade, as with other portions of an embankment, can be stabilized by two primary methods. Cost initial cost rehabilitation costs maintenance costs salvage value.
Subbase and subgrade performance investigation and design. The subgrade is required to be well drained at all times. Consortium national concrete pavement technology center partnership for geotechnical. Additional detailed information on subgrade investigation, subbases, and special subgrade problems can be found in appendix b. Concrete pavement and pavement foundations pavement plans and specifications pavement standard plans and specifications are the documents that implement the standards, policies, and best practices for pavements on california highways.
Technical report texas transportation institute available on this site. This paper describes how the analysis of the federal highway administrations fhwas longterm pavement performance ltpp data reveals that a pavement s foundation base or subbase and subgrade is one of the most critical design factors in achieving excellent performance for any type of pavement. It has been stated that improvement to the pavement s subgrade and subbase layers will extend pavement life, design guide for subgrades and subbases tr525. For highly trafficked highways, aggregate or stabilized subbases are commonly used to provide improved. The unique aspect of interlocking concrete pavements is that the pavers interlock to help spread the imposed loads. Concrete pavements, therefore, do not require strong foundation support. Publication details bases and subbases for concrete pavements. Compared with other types of paving materials, concrete is by far the most rigid, spreading applied wheel loads over large areas of the subgrade. Bases and subbases for concrete pavements this tech brief presents an overview of best practices for the design and construction of bases and subbases for concrete pavements and its effects on performance. Pdf models to estimate k subgrade reaction modulus values. It is much more important that the support be reasonably uniform with no abrupt changes in 8in. Subgrades and subbases for concrete slabs having good support for your concrete slab on ground is critical to success by bill palmer, concrete network columnist a wellcompacted subgrade keeps construction out of the mud and provides uniform slab support.
Eb204 subgrades and subbases for concrete pavements. Discuss the fundamentals of bases and subbases for concrete pavements. Bases, subbases, and subgrade aggregates section 301 base, subbase, and subgrade. Performance of concrete pavements on granular subbase w. Performance specifications scope of worksupplementary conditions pursuant to the provisions of o. The base course was changed from abc 2 to a blend of abc and millings. Introduction to rigid pavement design ced engineering. Requirements for flexible pavement design for frost conditions are presented in em 111038. Dont miss the upcoming webinar, subbases and subgrade considerations for concrete pavements, scheduled for april 7, from noon to 1.
Two new engineering bulletins subgrades and subbases 95th aashto subcommittee on materials. Subbases for concrete pavement effect of 3% cement on cohesive soils. Subbase layers have certain functions that need to be fulfilled in order to assure adequate pavement performance. Performance of concrete pavements on granular subbase. Soil classification and its limitations are discussed. Fly ash soil stabilization for nonuniform subgrade soils. Subgrades and subbases for slabs concrete construction. Concrete pavement engineer fhwa office of asset management, pavements, and construction. Bases and subbases for concrete pavements aashto classification a6 or a7 soil groups or the unified soil classification system ch, mh, and oh soils.
Concrete pavement design, political userdefined subgrade. When do you need to use a subbase under concrete pavements. In cut sections, the subgrade should be scarified and re. Subgrade, subbases, and bases january 2005 300 general. However, even for such simple projects, it may be advisable to add a gravel subbase to improve drainage and help level the surface. Cement stabilization of reclaimed asphalt pavement aggregate for road bases and subbases article pdf available in journal of materials in civil engineering 143 june 2002 with 4,077 reads. Intelligent compaction for concrete pavement bases and subbases. As a result, deflec tions are small and pressures on the subgrade are very low. Eb204 subgrades and subbases for concrete pavements acpa wiki. Understand european practices for basesubbase design and construction. Several conditions can lead to non uniform support and damage to the pavement. This tech brief presents an overview of best practices for the design and construction of bases and subbases for concrete pavements and its effects on performance fhwa publication number. It emphasizes the major objective of obtaining longlasting uniform.
Since lowvolume roads do not fail in this manner, they do not require subbases to prevent subgrade pumping, in most cases these concrete pavements can be placed directly on the compacted subgrade. No pavement or subbase may be placed if the subgrade is frozen or muddy. For hma pavements, the graded subgrade or the top granular base layer may be prepared with a primecoat if necessary. All installed pavement systems must meet the code and regulatory requirements and recommendations of the most current edition of. Subgrade preparation for new pavements pavement interactive.
Effective with the december 2019 letting 116 2020 standard specifications part 3. Due to the high level of strength provided by concrete pavements. When concrete pavement is placed directly on a subgrade, more accuracy is required. Department of transportation federal highway administration research and development turnerfairbank highway research center 6300 georgetown pike mclean, va 221012296. Considerations for construction of subgrades and subbases for. Relation of soil index properties and probable volume changes for highly plastic soils after earth manual 1985. For pavement thickness greater than 400 mm, specialised software design tools should be used to determine the optimum pavement. Design pamphlet for the determination of design subgrade in support of the 1993 aashto guide for the design of pavement structures publication no.
Subbase and subgrade performance investigation and design guidelines for concrete pavement. Primecoats have three purposes asphalt institute, 2001 2. The webinar will include essential information about the design and construction of subbases and subgrades, which are important to the quality of the finished pavement. It is intended for use in designing flexible pavements subject to the geometric design criteria set forth in em 11103. Common subgrade theories used for concrete pavements.
Vertical deflections are small, and the pressure on the subgrade is very low. This material is generally of lower quality than any course placed over it, but it still carries and distributes the wheel loads. A reasonably uniform subgrade or subbase, with no abrupt changes in support, is ideal for any concrete pavement. See subgrades ond subbases for concrete pavements, prevention of mudpumping with a relatively thin untreated or cementtreated subbase on projects where the expected truck traffic will be great enough to cause pumping. The influence of the spatial variability of subgrade subbase on pavement performance was then evaluated by modeling the elastic properties of the pavement and subgrade using the islab2000 finite element analysis program. Design methodology for subgrades and bases under concrete. Optimizing pavement base, subbase and subgrade layers for.
Subgrades and subbases for concrete pavements viii concrete, etc. It is not intended as definitive treatise, and it does not encompass the design of flexible pavements. This engineering bulletin provides the necessary background information for the proper selection and application of subbases and the appropriate consideration of subgrade variables for concrete pavements used for streets, roads and highways. It emphasizes the major objective of obtaining longlasting uniform support for a concrete. Alternatives to asphalt concrete pavement subbases for concrete pavement. During construction youll either waste concrete or end up with a floor thats too thin in spots because the subgradesubbase is uneven. A highway pavement is said to be only as good as the base under it.
Basics of concrete pavement thickness design pe civil exam for. Additional detailed information on subgrade investigation. The subgrade must be thoroughly compacted, generally with a sheeps foot roller, to provide a strong platform for construction activities. Subbase and subgrade performance investigation for concrete. The structural design of concrete pavements according to aashto and pca methods makes use of modulus of reaction k from the subgrade and subbase subgrade system as parameter to calculate slab. Subgrades and subbases for concrete pavements careful attention to the design and construction of subgrades and subbases is essential to ensure the structural capacity and ride quality of all types of pave ments. Subbase design manual for portland cement concrete pavements. Ihrb tr640 optimizing pavement base, subbase and subgrade layers for cost and performance on local roads. Lean concrete subbases stabilization helps to prevent migration of crusher fines, dissolution. This tech brief presents an overview of best practices for the design and construction of bases and subbases for concrete pavements and its effects on performance. The approach to the study of subgrades and subbases the nationwide variation in soil types. For concrete pavements, the requirements may vary considerably depending on subgrade soil type, environ. A sidewalk or other concrete surface that isnt taking heavy loads can stand to have only a subgrade layer under the concrete. Proper subgrade prep when it comes to compacting a subgrade for a residential application, consistency, quality, and good practice by the contractor are critical to prevent concrete cracking and sinking concerns for the homeowner.
Conventionally reinforced pavements that contain steel reinforcement and use dowels in contraction joints, and. Section 301 base, subbase, and subgrade aggregate 301. Background the need and use of bases and subbases for pavements has been well known for thousands of years. When expansive soils are compacted in too dry a con. The subgrade is required to be finished to within 12 in. A subbase is a thin layer of material placed on top of the prepared subgrade. Subgrades and subbases roadbed subgrade and subbase design is key to longterm performance and. Poor subgradesubbase preparation can not be overcome with thickness. This is an introduction to rigid pavement design for engineers. Any concrete pavement, built of any thickness, will have problems on a poorly designed and. Pavement performance can be largely attributed to the care given in designing and preparing its foundation, which is comprised of the subgrade and base layers.
A layer of granular material provided in between the subgrade and the base course in a road. This paper describes how the analysis of the federal highway administrations fhwas longterm pavement performance ltpp data reveals that a pavements foundation base or subbase and subgrade is one of the most critical design factors in achieving excellent performance for any type of pavement. Practices vary from state to state, but dowel bars are typically required in eightinch or thicker pavements. Sqft in a flexible pavement, the pavement surface and base have the ability to move slightly or flex under load then recover when the load is removed. The thickness and type of pavement structure depend upon the supporting power of the subgrade because the entire load of the pavement, including the load of traffic transmitted through the pavement, is ultimately taken up by the subgrade. Subgrade the roadbed materials beneath the pavement structure. Subbases and subgrades for concrete foundations networx. General information pavement systems generally consist of three layers. This guide captures the fundamental parameters, recommendations, and considerations for subgrades and subbases for concrete pavement. The analytical relationship between a soils resilient modulus and it modulus, of subgrade reaction is a follows.
Discuss the fundamentals of bases and subbases for concrete pavements understand the design, construction, and cost considerations of bases and subbases understand european practices for basesubbase design and construction understand the performance of various bases at experimental sections constructed at mnroad. Finally, it is likely that as this document is printed and distributed, some new and emerging technologies are advancing within the grading and paving industries. Nov 22, 2017 place a concrete floor on an unstable subgrade or subbase and youll probably pay for it two ways. Concrete pavement construction basics placing dowel baskets dowel bars transfer heavy loads across joints in the pavement, preventing faulting at the joint that can lead to pavement damage. Design pamphlet for the determination of design subgrade in. Therefore, based on that study, the life cycle costs of a pavement placed on subbase or on treated subgrade should be lower than that of a pavement on natural untreated subgrade. Engineers are cautioned that much of pavement design is governed by codes, specifications and practices of public agencies. These include provision for reasonably uniform support. It emphasizes the major objective of obtaining longlasting uniform support for a concrete pavement. As a result, concrete pavements do not require a buildup of foundation support. Intelligent compaction for concrete pavement bases and.
Natural subgrade soils, fly ashstabilized subgrade, reclaimed hydrated fly ash subbase, and granular subbase were studied. Most native soils are not too uniform and thus require some improvement or additional layers to compensate. Statewide urban design and specifications 6f1 design manual chapter 6 geotechnical 6f pavement subbase design and construction page revised. Subbase and subgrade performance investigation and design guidelines for concrete pavement one of 87 reports in the series. Design guide for subgrades and subbases iowa state university. Subgrade natural ground, graded, and compacted on which the pavement is built. Pdf cement stabilization of reclaimed asphalt pavement. Unfortunately, many concrete pavement failures in the united states are related to inadequate foundation layersthe soils and aggregates in the natural subgrade and. Other factors responsible for non uniform foundation include variability due to a number of reasons including, natural causes, excavation and.
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