what is sub base course in road construction

Full Answer

What is base course in road construction?

Base course It is the layer immediately under the wearing surface (Applies whether the wearing surface is bituminous or cement concrete and or more inch thick or is but a thin bituminous layer). As base course lies close under the pavement surface it is subjected to severe loading.

What is a sub base course of rigid pavement?

Sub Base Course of Rigid Pavement. This is the layer (or layers) under the base layer. The properties and function of this layer are similar to those under flexible roads/pavements. A sub-base is not always needed and therefore may often be omitted.

What is sub base in road?

Sub Base: It is layer of granular material provided above subgrade generally natural gravel. It is usually not provided on subgrade of good quality. It is also called granular subbase. a. Function of Sub base in Road Cross Section

What is a sub-base course?

Sub-Base course is the layer (or layers) under the base layer. A sub-base is not always needed. A proper sub-base consists of various sizes of crushed stone aggregate, commonly known as crusher run.

What is a base and subbase in road construction?

A road base is defined as a layer or layers of bound material intended to give structural integrity to a pavement. The base consists of well-graded material, usually crushed stone. Sub-base consists of a lower quality material, sometimes crusher-run product, or the finer fraction of crushed stone production.

What is subgrade course?

The foundation of the pavement structure is known as subgrade. Preparation of subgrade consists of all operations before the pavement structure could be placed over it and compacted. The subgrade may be situated on an embankment or excavation or at the existing ground surface.

What is Sub base coarse?

Subbase Course. The layer between the base course and subgrade. It functions primarily as structural support but it can also minimize the intrusion of fines from the subgrade into the pavement structure and improve drainage.

What is a subbase in construction?

In this publication, a subbase is defined as the layer of material that lies immediately below the concrete pavement. Some engineers call this a base course since that term is used to designate the first layer beneath an asphalt surface.

What is the difference between subgrade and sub base?

The subgrade is the soil that is usually compacted when preparing for slab installation. Thus, you find this soil at the bottom of the slab system. The subgrade may refer to the native soil or the improved soil delivered from a different source. The subbase refers to the layer placed on top of the subgrade.

What is the purpose of sub base?

Subbase is often the main load-bearing layer of the pavement. Its role is to spread the load evenly over the subgrade. The materials used may be either unbound granular, or cement-bound.

What is a sub base?

What is a Sub Base? In construction, a Sub Base is the layer of aggregate material laid directly on top of the subgrade, on which the base course layer is positioned. The role of a Sub Base is to act as working platform for the ground slab to be constructed.

What is the difference between sub base and base course?

Base may consist of unbound materials, such as gravel or crushed stone, or stabilized materials, such as asphalt-, cement- or lime-treated materials. The subbase course is typically a granular borrow that is placed between the base and subgrade. It can be constructed as either a treated or untreated layer.

What is subgrade in road?

Subgrade is that portion of the earth roadbed which after having been constructed to reasonably close conformance with the lines, grades, and cross-sections indicated on the plans, receives the base or surface material. In a fill section, the subgrade is the top of the embankment or the fill.

What material is used for subbase?

Sub-base material is produced by crushing either limestone or granite rock. The sub-base is designed to evenly spread the load on traffic bearing areas such as pavements and roads. Made up of a load-bearing layer of aggregate, the sub-base is laid on the sub-grade layer below.

What material is used in base course?

The base course is generally com- posed of granular material such as crushed aggregate, gravel, selected soil, or a mix- ture of selected soil and aggregate.

Is Sub base necessary?

Do I really need a Sub-base? The short answer is: if the pavement will be trafficked by vehicles, then yes, but if it will be foot-traffic only, then not necessarily. The type of paving or surfacing that will be used is one of the key factors in determining whether a sub-base will be required.

What is subbase in engineering?

In highway engineering, subbase is the layer of aggregate material laid on the subgrade, on which the base course layer is located. It may be omitted when there will be only foot traffic on the pavement, but it is necessary for surfaces used by vehicles. Subbase is often the main load-bearing layer of the pavement.

Why is subbase important?

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 that the subbase is still in good condition, a new layer can be applied.

What is unbound concrete?

Unbound granular materials are usually crushed stone, crushed slag or concrete, or slate . Cement-bound materials come in multiple types. Mass concrete is used where exceptional loads are expected, with thickness usually 100 to 150 millimetres (4 to 6 in ), and optional reinforcement with steel mesh or polymer fibers.

Sub Base Course of Rigid Pavement

This is the layer (or layers) under the base layer. The properties and function of this layer are similar to those under flexible roads/pavements. A sub-base is not always needed and therefore may often be omitted.

Base Course of Rigid Pavement

This is the layer directly below the PCC layer and generally consists of aggregate or stabilized sub-grade.

What is sub base paving?

The sub-base layer is often the main load-bearing layer of a pavement. It is designed to evenly spread the load of the paving, and any traffic thereon, to the sub-grade below. A well-constructed sub-base will aid drainage and prevent settlement and channelisation - the phenomenon common on cheap installations of block paving, where two 'ruts' develop in the paving. These 'ruts' are caused when a car travels over the same line of paving to the garage, every morning and every night. Channelisation is also apparent on carriageways, particularly at the approach to traffic lights and on upward gradients. The sub-base is intended to prevent channelisation and settlement.

What to do if sub base isn't required?

If your contractor tells you that a sub-base isn't required beneath your new drive, then ask how the sub-grade (soil beneath drive) is going to spread the load of the paving and what guarantee is offered with regard to settlement. Alternatively, get a different contractor to give their opinion.

How long does it take for concrete to set?

A 'slab' of mass concrete, usually 100mm or 150mm thick is spread and compacted, then allowed to set. A few days later (2-7 days, depending on time of year and weather conditions), the paving is laid on a bedding material over the now solid concrete. A medium strength concrete is used in most applications.

What happens if you water a base course?

Excess watering is wasteful, but more importantly, it may result in serious damage to the subgrade. Most of the water that falls on granular material penetrates to the subgrade almost immediately and this could create serious problems. This "sponginess" and resultant movement under wheel loads is usually first noticed as excessive looseness of base materials. The Inspector should be on guard for any soft spots that may develop in the roadway following rains or excessive watering. If this condition should occur, a thorough investigation shall be made and corrective measures taken before paving.

Why is lime admixture used in subgrades?

The subgrade may be treated to improve its ability to support traffic loads. The improved load carry capability occurs because the lime admixture reduces the volume change characteristics and plasticity of the soil.

When clearing or stripping of a pit is required at a Department Furnished Source, should the Resident

When clearing or stripping of a pit is required at a Department Furnished Source, the Resident Engineer should direct where the waste is to be placed. Stripping may be deposited beyond the area intended for use, but not beyond the pit right-of-way boundaries. A survey should be performed to establish pit boundaries beforehand. Some material sources may have environmental restrictions that are shown in the licensing agreement. See the Standard Specifications for final placement of stripping.

Can you use salvaged concrete for aggregate?

The Special Provisions may allow use of salvaged asphaltic concrete or Portland cement concrete materials for aggregate subbase and aggregate base. Requirements for salvaged materials are not the same as Standard Specifications for aggregate subbase and aggregate base. The contractor may request use of salvaged materials on a project where specifications were not included in the Special Provisions. A copy of the normal requirements can be obtained from Contract and Specifications Section. If Special Provisions do not include salvage material specifications, then the engineer should contact Materials Group before initiating a Supplemental Agreement to allow use of salvage material for aggregate subbase and aggregate base.

Is highway pavement good?

highway pavement is said to be only as good as the base under it. This material is generally of lower quality than any course placed over it, but it still carries and distributes the wheel loads. The need to be concerned with its quality and finish is very important.

Is the riding surface of a completed pavement dependent on the base surface upon which it is laid?

To a great extent the riding surface of the completed pavement is dependent on the base surface upon which it is laid. Since smoothness of the pavement is one of the qualities most desired by the road users, the Resident Engineer should be satisfied that every means possible has been expended to obtain a finished base course having a cross section true to line and grade within the specified tolerance.

What is a subbase in a concrete slab?

A subbase will go on top of the subgrade, which typically is native soil or improved soil that has been compacted. It is important for a subbase to have solid edges and joints to prevent cracking and concrete spalling.

What is subbase material?

Subbase materials preferably might consist of naturally occurring, coarse-grained soils or blended and processed soils. When possible, avoid using materials which have more than 15 percent fines. Lift thickness is dependent on the type of material, the compaction equipment used, and the method of construction.

What is the difference between subbase and subgrade?

There is no consistency in regards to the terms of subbase and subgrade, but normally the subgrade is the native soil while the subbase is the layer of soil or aggregate on top of the subgrade.

How are subgrade materials improved?

Normally, subgrade material is improved by installing geotextiles. They are used to prevent mixing of soft or inadequate soil that might affect the structural capacity of the subgrade. Geotextiles must have specific mechanical and hydraulic properties to ensure they have the right characteristics for their intended use.

What are the advantages of a solid subbase layer?

A solid subbase layer should offer the following advantages: Provide strength and support to the overlying pavement. Provide drainage and frost protection. Prevent settlements to pavement and slab on grade. Be reusable if you decide to change your pavement surface. Keep workers out the mud.

What is a solid subbase?

A solid subbase is a key to a successful building project. A slab on ground and pavements normally are designed to be supported by a solid subbase, which needs to be uniform by nature to support the structure above it. A subbase will go on top of the subgrade, which typically is native soil or improved soil that has been compacted.

Why do subbases need to be uniform?

Subbases need to be uniform to support the structures above them. Juan Rodriguez is a former writer with The Balance who covered large-scale construction. He is an engineer with experience managing and overseeing large civil works construction. A solid subbase is a key to a successful building project.

What is sub grade material?

Material: Material of sub grade should be strong enough to bear the loads, easily accessible and available in the vicinity and cheap. 2. Sub Base: Consists of: Upper Base Course. Sub or Lower Base Course.

How high should a sub grade be?

If natural surface is below the formation level then the sub grade will be above the ground level. It should be constructed at least 60 cm (2ft) high from highest flood level of the area.

What are the components of a road?

A road structure consists of the following components: 1. Sub Grade: Subgrade is the foundation of the road, thus its the lowest and most important component of road structure.