Pdf subbase is an important layer in flexible pavement which. The sub base consists of a layer of clean course aggregate, such. The importance of understanding concrete pavement behavior, such as material stresses and movements, lies in the design and functional characteristics of the pavement. Concrete pavement specifiers guidelines 2 foreword portland cement concrete pcc pavement refers to the rigid concrete layer of the pavement structure that is in direct contact with the traffic.
The preparation of the subgrade and base course is a very important step since these materials have a considerable impact on the ride quality of the concrete. Optimizing pavement base, subbase, and subgrade layers for cost and. The effects of properties of different base layers on concrete pavement performance were evaluated, based on an the mechanical and hydraulic. A wellconstructed subbase will aid drainage and prevent settlement. Other factors responsible for non uniform foundation include variability due to a number of reasons including, natural causes, excavation and. Pdf evaluation of subbase materials for mechanistic pavement. Following are the different components of road structure. Reclaimed concrete material user guideline granular. A parameter that plays a large role in the behavior of concrete pavements is subbase friction. Standard specification d294092, graded aggregate material for bases and subbases for highways or airports, annual book of astm standards, volume 4. Drylines serve as a guide to ensure that the subgrade has proper elevation. If the gradation or density does not meet specification requirements, the k value may be reduced below the design value resulting in inadequate pavement strength.
In highway engineering, subbase is the layer of aggregate material laid on the subgrade, on which the base course layer is located. When it comes to compacting a subgrade for a residential application, consistency, quality, and good practice by the contractor are. Its role is to spread the load evenly over the subgrade. The bearing capacity and permeability of the sub grade influences total pavement thickness. The properties of rca were compared with state road authority requirements to assess its performance as a pavement subbase material. Geotechnical properties of recycled concrete aggregate in pavement subbase applications article pdf available in geotechnical testing journal 355. The material quality requirements for a subbase are not as strict as. Installation steps typically include job planning, layout, excavating and compacting the soil subgrade, applying geotextiles optional, spreading and compacting the subbase andor base aggregates. The subbase layer is the main load bearing element in the system and is designed to spread the load of the cellular paving grids and any traffic thereon to the subgrade below. As shown in figure 4, loads applied to a pccsurfaced rigid pavement are spread over a large area of subgrade, compared to loads applied to an asphalt concretesurfaced flexible pavement. It is preferable that all materials, regardless of traffic category, conform to the requirements of clause 8. It provides stable platform to construct rigid pavement. Using recycled concrete aggregate in pavement base products.
Bases and subbases for concrete pavements aashto classification a6 or a7 soil groups or the unified soil classification system ch, mh, and oh soils. Bo4 geotechnical properties of recycled concrete aggregate in pavement subbase applications abstract. Typical road structure cross section sub grade, base. Minimize waste and hauling by using rca base across full pavement section including shoulders when excess material is produced e. This course helps the surface course to take additional loads. If the gradation of the base course deviates from the specifications, the base course may not prevent pumping of the subgrade material through the base course. Costeffective base type and thickness for longlife. It is also useful to provide sub surface drainage system. Homomorphic model pavement with sub base layer of foam. For example, minnesota allows up to 3% asphalt cement by weight of aggregate and california has no limit on the relative proportions of re.
Pdf the influence of base course types on rigid pavement. The material quality requirements for a subbase are not as strict as those for a base since, under concrete, the pressures imposed on this layer due to vehicle loadings are much lower than those under asphalt. A subbase works by distributing a point load over a larger area. Base and subgrade layers must provide adequate and moisture resistant strength that meets the design modulus, in. Proper subgrade prep concrete construction magazine.
A pozzolan material, such as fly ash, may be added to the. 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. Subbase is often the main loadbearing layer of the pavement. A typical fle xible pavement in malaysia consists of asphaltic concrete. The subbase, while not mandatory, can provide added benefits to the construction and performance of the slab. Basessubbases for concrete pavements transportation research. When using base aggregate open graded, refer to fdm 14515. Road pavement design guide home kent county council.
As a general guide, factors elaborated in section 3. This finding was true for the full range of materials tested. Compaction of the soil subgrade and aggregate base materials are essential to the longterm performance of interlocking concrete pavements. Feasibility of reclaimed asphalt pavement rap use as. The pavement structure of a concrete pavement typically consists of a concrete sur face and subbases placed upon a prepared subgrade a base is part of an asphalt pavement struc ture, while a subbase is an optional element of a concrete. Concrete block surfaces are suitable for these applications. Optimizing pavement base, subbase, and subgrade layers for cost. The subgrade material should be clean and free from organic matter and should be able to be compacted by roller, to form stable subbase. Crushed concrete 90 percent crushed concrete that is substantially free of steel reinforcement and includes 75 percent asphaltic pavement or surfacing. Only class 2 dgb and dgs material traffic categories c and d material may be.
This paper presents a laboratory investigation of the geotechnical properties of recycled concrete aggregate rca. The sub grade is either natural, undisturbed earth or imported, compacted till. Whilst designs are based on type 1 subbase category a material, alternatives have been. Cement concrete pavements specifications and method of cement concrete pavement construction pqc importance of providing dlc as subbase and polythene thin layer between pqc and subbase. Subbase and subgrade performance investigation and design. Development of the numerical model a typical reinforced pavement system consists of hotmix asphalt layer, base course layer, subbase layer and subgrade layer as well as reinforcement layers. Recycling concrete pavement, american concrete pavement association, illinois, 1993. This also reduces the risk of tearing or puncturing the fabric. It may be omitted when there will be only foot traffic on the pavement, but it is necessary for surfaces used by vehicles. Well graded uniformity coefficient d60d10 should not. The construction of the base or subbase for the pavement construction is dependent on the type of base chosen and the equipment available. The primary objective of this report is to quantify the aggregate base properties required for concrete pavement foundations in accordance with currently established layer thickness requirements.
Facilities development manual wisconsin department of. In this article, some of the top base and subbase layers used for pavement construction are explained. The worker shown here is using a 2x4 to strike flat subgrade. Typical concrete is composed of coarse aggregate crushed stone and gravel, fine. Stabilized subbase friction study for concrete pavements. Based on the achieved material characteristics, the tensile strength in bending of previously used road construction materials was compared to innovative alternative of foam concrete and the suitability for the base layers of pavement roads was determined. A base course can be compacted aggregate, cement or asphalt stabilized aggregate, asphalt or concrete. Cement treated base unstabilised base asphalt treated base lean concrete base contents. The subbase is an optional layer located on top of the subgrade and beneath the slab bottom see figure 1. The pavers are laid on a oneinch 25 mm thick sand bedding layer over a compacted bound or unbound base and a granular sub base as required. Base construction for interlocking concrete pavements continued from p. Typical ranges of ls for various types of base materials.
Subgrade and subbase the subgrade is the ground on which the floor is built. The pavement is modeled as a multilayer structure subjected to static and dynamic loading. Installation interlocking concrete pavement institute. Understand european practices for basesubbase design and construction. Surface course or wearing course all these components belong to a typical flexible pavement, whereas rigid pavement usually consists of subgrade, subbase and a concrete slab. Grading first the site is graded to cut high points and fill low. A concrete pavement is only as good as the grade on which the pavement is. Reusing concrete pavement minimizes the amount of raw materials required for a new pavement structure. Geotechnical properties of recycled concrete aggregate in. Blend with virgin aggregate if designed base requirements exceed volume of recoverable rca base. The base course or granular base or stabilized base is the second layer from the top and is constructed using crushed aggregates.
Typically, recycled concrete aggregate rca is used as granular. Joe nasvik concrete slabs perform best when they are even thickness. A material of a designed thickness placed on a subbase or a subgrade to support a surface course. Subbases may be constructed of granular materials, cementtreated materials, lean concrete, or opengraded, highlypermeable materials. The surface conditions of pavements with subbase andor base layers made with rca were comparable to those made with na in terms of the international roughness index iri and pavement condition index pci ceylan et al. Rdgn042 pavement design for carriageway construction page 7 of 42 pavement type for different sections andor different lanes on the same road. Compacting the base icpi recommends that the base is installed. The construction and design of concrete slabs on grade. Index properties and probable volume changes for highly plastic soils after earth manual 1985.
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