What is the difference between base and subbase?

What is the difference between base and subbase?

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 the purpose of the subbase?

The subbase layer is typically used to protect the pavement from the effects of frost heave and/or used to improve the constructability of the pavement layers above the subbase.

What are the requirements of a subbase?

Subbase material has specific size requirements (<45mm with a specified fines level), must have been stored for at least 1 month, have a loss on ignition (LOI) of <10%, and water content between 17% and 25%.

What is the minimum CBR value for subgrade?

10%
According to the subgrade characterization which recommends 10% as minimum CBR value for the layer [1], the subgrade material proved adequate as this value appears to have been exceeded by a wide margin at most of the sections along the road. …

How is subgrade prepared?

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.

Can you use sand as a subbase?

Generally speaking, building sand is an unsuitable material to use for bedding; it does not allow for enough free draining and doesn’t provide as stiff, or as stable mortar mix as sharp sand.

What can I use for a sub-base?

The most common granular aggregate sub-base is DoT (Department of Transport) Type 1 and Type 3 Limestone. They are both crushed stone: Type 1 has a maximum permitted top size of 63mm, graded down to dust; and Type 3 is an open-graded 40mm unbound mixture with a reduced amount of fines.

What is CBR value?

CBR is the ratio expressed in percentage of force per unit area required to penetrate a soil mass with a standard circular plunger of 50 mm diameter at the rate of 1.25 mm/min to that required for corresponding penetration in a standard material. The ratio is usually determined for penetration of 2.5 and 5 mm .