What is a base and subbase in road construction?
What is a base and subbase in road construction?
Although the terms “base” and “subbase” are sometimes used interchangeably to refer to the subsurface layers of a pavement, base course is typically used in asphalt pavements, primarily as a structural load-distributing layer, whereas the subbase layer used in concrete pavements primarily serves as a drainage layer.
What is sub grade in road construction?
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 subgrade?
Subgrade Physical Properties
| Material (USC given where appropriate) | CBR | Elastic or Resilient Modulus (psi) |
|---|---|---|
| Aluminum | – | 10,000,000 |
| Wood | – | 1 – 2,000,000 |
| Crushed Stone (GW, GP, GM) | 20 – 100 | 20,000 – 40,000 |
| Sandy Soils (SW, SP, SM, SC) | 5 – 40 | 7,000 – 30,000 |
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 Type 2 Sub base?
Our Type 2 is a crushed aggregate with extra dusts and fines, which makes the perfect sub base for a range of domestic and commercial construction projects. Graded to 50mm down to dust and fines no specified grading, it is finer than our MOT Type 1 sub base, as it is composed of fewer larger angular scalpings.
What is the difference between subbase and base?
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 Type 2 Sub Base?
What is CBR subgrade?
The California Bearing Ratio (CBR) is a measure of the strength of the subgrade of a road or other paved area, and of the materials used in its construction. The ratio is measured using a standardized penetration test first developed by the California Division of Highways for highway engineering.
How do you prepare a road subgrade?
Other Subgrade Preparation Practices
- Ensure the compacted subgrade is able to support construction traffic.
- Remove all debris, large rocks, vegetation and topsoil from the area to be paved.
- Treat the subgrade under the area to be paved with an approved herbicide.
Which soil is best for subgrade?
A clayey soil generally has a low CBR value (less than 8). Sands are more granular and drain better and will generally have CBR values between 15 and 35. Gravel will have the best CBR values, generally 25 and up. That is why it is suggested to save the best material to cap 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 Type 3 sub-base?
Type 3 sub-base is a pure crushed granite, limestone or clean crushed concrete. Usually a 40mm product that has been screened to create a reduced fines aggregate. This product is fully certified according to the Specification for Highway Works. This is the most widely used sub-base where less fines are required.
What is type 1 sub-base material?
Type 1 Sub Base is generally a 40mm graded to dust material that is laid and compacted to form a level stable construction layer as a platform for asphalt or concrete. It is typically used in the construction of highways, car parks, footways and hard standing areas.
What is CBR road base?
The California bearing ratio (CBR) is a penetration test used to evaluate the mechanical strength of subgrade and roadbase materials. It was developed by the California Department of Transportation before World War II.
What is the minimum thickness of subgrade?
What is the minimum thickness of compacted sub grade? Explanation: The minimum thickness of sub grade required is 300mm and in highways it is 500 mm as they are provided with the maximum best facilities. 5.
What are the requirements of subgrade?
A subgrade’s performance generally depends on three of its basic characteristics (all of which are interrelated) as under:
- Load bearing capacity.
- Moisture content.
- Stabilization with cement or asphaltic binder.
- Additional base layers.
- Strength & Stiffness of Subgrade Soil.
- Construction Works.
What is Type 3 sub base?
What is Type 2 road base?
Class II Road Base is a Cal Trans Spec native rock with no recycled materials. It is generally used as a compacted base for roads, parking lots, interlocking pavers, sidewalks, asphalt, compacted rock surfaces, and as a sub base under retaining walls.
What is Type 2 sub-base?
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 are the different types of road structure?
Typical Road Structure Details. 1 1. Surface/Wearing Course in pavement cross section: The top layers of pavement which is in direct contact with the wheel of the vehicle. Usually 2 2. Base course. 3 3. Sub Base: 4 4. Sub Grade:
How thick is a subbase layer of a road?
Materials used in subbase layers. Many materials can be used to create a sub-base layer, and the thickness can vary according to the traffic that the surface layer is likely to experience. The thickness can range from 75mm for a simple path, 150mm for a driveway and 225mm or more on heavily used roads.
What are the characteristics of sub grade of road?
Material of sub grade should be strong enough to bear the loads, easily accessible and available in the vicinity and cheap. 2. Sub Base: 3. Road Base: 4. Surfacing: It is the upper most layer of road cross section.
