Subgrade and subbases design summary subgrade strength is not a critical element in the thickness design. Use of recycled concrete materials in basesubbase applications. Compared with other types of paving materials, concrete is by far the most rigid, spreading applied wheel loads over large areas of the subgrade. It is a layer required in many structures such as pavements and slabs, although it needs to have certain. 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. Subgrade the natural or prepared formation on which. Once the subbase has hardened sufficiently to resist marring or distortion by construction traffic, dowels, tiebars, or reinforcing steel are placed and properly aligned in. 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. 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. In the early days of rigid pavement construction, concrete slabs were placed directly on top of the subgrade without any basesubbase layers. Bases and subbases for concrete pavements aashto classification a6 or a7 soil groups or the unified soil classification system ch, mh, and oh soils. The main issue associated with this research is if cheaper alternatives can be configured for subbase. Design and construction of joints for concrete streets.
It has been stated that improvement to the pavements subgrade and subbase layers will extend pavement life, design guide for subgrades and subbases tr525. Performance of subbases for concrete pavements under. The structural design of concrete pavements according to aashto and pca methods makes use of modulus of reaction k from the subgrade and subbasesubgrade system as parameter to calculate. It is not permissible to adopt the cbr of just the thin layer immediately below the subbase. Pdf models to estimate k subgrade reaction modulus values. Vertical deflections are small, and the pressure on the subgrade is very low. When do you need to use a subbase under concrete pavements. How ever, it is important that the support be reasonably uniform with no abrupt changes in degree of support. The reinforcement design of jointed reinforced concrete pavements jcrp is dependent upon the frictional resistance between the bottom of the slab and the top of the underlying subbase or subgrade. 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. Subgrades and subbases for concrete pavements trid. Subgrade and subbases subbase layer of material directly below the concrete pavement.
Introduction to rigid pavement design ced engineering. A third measure of soil strength, westergaards modulus of subgrade reaction, k, is commonly used in design procedures for concrete pavements and floorsongrade that are not structural elements in the building floors not supporting columns and loadbearing walls. Subbase and subgrade performance investigation for concrete. 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.
Its role is to spread the load evenly over the subgrade. A subbase is a thin layer of material placed on top of the prepared subgrade. This includes thickness design, subgrade and subbase preparation, and jointing. 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. Subgrades and subbases for concrete pavements viii concrete, etc. Often industrial and port pavements are built on sites that have poor soil conditions. In some cases, however, design or construction errors or poorly selected materials have considerably reduced pavement life. Hence the performance of the pavement is affected by the characteristics of the subgrade. Eb204 subgrades and subbases for concrete pavements acpa.
Traffic lane markings can be incorporated into the jointing pattern where the concretes lightreflective surface improves visibility. March 20 page7 in concrete pavement design, all materials within one metre below the subbase are assessed for the determination of the. Concrete pavements exhibit high wear resistance and can be easily cleaned if necessary. Design and construction of joints for concrete streets to ensure that the concrete pavements we are building now will continue to serve our needs well into the future, it is essential to take into account all. The main issue associated with this research is if cheaper alternatives can be configured for subbase construction. Subbase design manual for portland cement concrete pavements. Imagine you have a very long slab of concrete sitting on a subbase. Subbase and subgrade performance investigation and design guidelines for concrete pavement. Because of the rigidity of concrete pavements, loads are spread over large areas of the subgrade and pressures on the subgrade are very low. Optimizing pavement base, subbase, and subgrade layers for cost.
Introduction to concrete pavements eesti betooniuhing. They can play a key role in mitigating the effects of climate and the stresses generated by traffic. It is therefore important for pavement engineers to understand. The k value for the subgrade so determined must be used in design whether the fatigue method ref 1, fig 2. Most native soils are not too uniform and thus require some. Dec 18, 2014 concrete pavements have been used for highways, airports, streets, local roads, parking lots, industrial facilities, and other types of infrastructure. Other factors responsible for non uniform foundation include variability due to a number of reasons including, natural causes, excavation and. March 20 page7 in concrete pavement design, all materials within one metre below the subbase are assessed for the determination of the average design subgrade cbr. The culmination of this study is to provide subbase friction profiles for determining concrete and steel stresses due to horizontally induced movements over stabilized subbases. Many pavements experienced failure due to pumping of loose. Basessubbases for concrete pavements transportation research. A wellcompacted subgrade keeps construction out of the mud and provides uniform slab support.
The subgrade must be thoroughly compacted, generally with a sheeps foot roller, to provide a strong platform for construction activities. Subbases may be constructed of granular materials, cementtreated materials, lean concrete, or opengraded, highlypermeable materials, stabilized or unstabilized. Design considerations for interlocking concrete pavements unilock specifications page 5 common to these applications. Lean concrete subbases stabilization helps to prevent migration of crusher fines, dissolution and transport of significant amounts of calcium hydroxide. Pdf models to estimate k subgrade reaction modulus. Pavement support basics firm, uniform, and nonerodible. Subbase is often the main loadbearing layer of the pavement.
It may be omitted when there will be only foot traffic on the pavement, but. A slab on ground or slab on grade by definition is not intended to be selfsupporting. This is no different than the foundation for a building. A reasonably uniform subgrade or subbase, with no abrupt changes in support, is ideal for any concrete pavement. Subbase design manual for portland cement concrete. Subbases and subgrades american concrete pavement association. Design considerations for interlocking concrete pavements. Performance of pavements depends on the quality of its subgrade and subbase layers quality pavement foundation guidelines subgrade soils prepared subgrades with minimum cbr of 10 iowa soils generally provide poor support stabilized subgrades chemical reinforced, geosynthetics subbases. These soils often settle and consolidate unevenly under load resulting in serious damage to pavements. Design guide for subgrades and subbases iowa state university.
Municipal pavement design with streetpave software. This frictional resistance is characterized in the 1993 aashto guide by a friction factor f that is related but not equal to the coefficient of. See subgrades ond subbases for concrete pavements, prevention of mud. And one of the major functions of a highway pavement is to reduce the. When properly designed and built out of durable materials, concrete pavements can provide many decades of service with little or no maintenance. Subbase and subgrade performance investigation and design. In highway engineering, subbase is the layer of aggregate material laid on the subgrade, on which the base course layer is located.
In some cases, as for most clays and some silty soils, it may be most econom. Subbase layers have certain functions that need to be fulfilled in order to assure adequate pavement performance. The values of e bs from the base layers in the original aasho road test are summarized in table 540. For concrete pavements, the requirements may vary considerably depending on subgrade soil type, environ. As it cures, the concrete slab shrinks and would become shorter if it were floating. Design of basesubbase for rigid pavements strength and stiffness considerations. This paper describes how the analysis of the federal highway administrations fhwas longterm pavement performance ltpp data reveals that a. Construction specifications several other acpa publications,subgrades and subbases for concrete pavements 1, design and construction of joints for concrete streets2, and construction specification guideline for concrete streets and local roads3, discuss the. Most native soils are not too uniform and thus require some improvement or additional layers to compensate.
Alternatives to asphalt concrete pavement subbases for concrete pavement. 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. Compared to asphalt pavements, concrete pavements spread a given load over a larger area of the roadbed or foundation which, inturn, reduces the pressure on the support layer materials and subgrade. Subbase and subgrade performance investigation and design guidelines for concrete pavement one of 87 reports in the series.
Often industrial and port pavements are built on sites that have poor soil. Understand european practices for basesubbase design and construction. The quality of subbase is very important for the useful life of the road and can outlive the life of the surface, which can be scrapped off and after checking. Technical report texas transportation institute available on this site.
Subbases for concrete pavements1, design and construction of joints for concrete streets2, and. As a result, concrete pavements do not necessarily require strong support from below. These include provision for reasonably uniform support. Consortium national concrete pavement technology center partnership for geotechnical. The material quality requirements for a subbase are not as strict as. Stabilized subbase friction study for concrete pavements. Note that the e bs values are not only functions of moisture, but also of stress state. Performance of pavements depends on the quality of its subgrade and subbase layers quality pavement foundation guidelines subgrade soils prepared subgrades with minimum cbr of 10 iowa soils. Eb204 subgrades and subbases for concrete pavements acpa wiki. The importance is that the foundation strength is not as important to the performance of concrete as it is to asphalt pavement, even when. Optimizing pavement base, subbase and subgrade layers for. Eb204 subgrades and subbases for concrete pavements.
A third measure of soil strength, westergaards modulus of subgrade reaction, k, is commonly used in design procedures for concrete pavements and floorsongrade that are not structural elements in the. Concrete pavements can be placed directly on a compacted. 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. The subbases used many years ago were soft, loose, and unbound, such as sand, gravel, and clay. It briefly discusses subbase materials and their application to the design of crcp, and recommends the evaluation of the subgrade modulus of re. Technical report texas transportation institute available. Heavy duty pavements concrete construction magazine. Subgrade natural ground, graded, and compacted on which the pavement is built. Concrete engineers and the concrete industry must continue to face the challenge of building still heavier duty pavements needed for greater fleets of commercial, industrial, and military vehicles running at. 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. Dont miss the upcoming webinar, subbases and subgrade considerations for concrete pavements, scheduled for april 7, from noon to 1.
Mccullough, describes a comprehensive set of design methods for continuously reinforced concrete pave ments. As a result,concrete pavements do not necessarily require. A subgrade is made up of native soil that has been compacted to withstand the loads above it. Physical and mechanical properties of the rca must be considered in the design and production of cementstabilized subbases. What lies below your concrete slab is critical to a successful job. The materials used may be either unbound granular, or cement bound. Bases and subbases for concrete pavement transportation. As a result, concrete pavements do not require a buildup of foundation support. Concrete pavement construction basics compaction and trimming before compacting, subgrade material may have to be brought to the optimum moisture content. Download concrete pavement design, construction and. Optimizing pavement base, subbase, and subgrade layers for cost and.
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