Construction of rigid pavement – Base materials
Construction of rigid pavement
The construction of a rigid pavement involves the incorporation of concrete which requires a careful design due to its nature. A good concrete pavement should provide an excellent riding surface while retaining good surface texture and skid resistance. The following among others are important things to note in the construction of rigid pavement.
In other to achieve a quality concrete pavement, adequate preparation must be carried out on the existing soil surface. The soil should be properly compacted and graded to the correct elevation for the project. Depending on various factors, there might be needs to place a layer of base material on top of the subgrade. This is because; the subgrade grade soil has great effects on the pavement design
There are no specified stones as regard the subgrade materials for rigid pavement. On this, any type of graded stone can be added as base material. Stone like rounded river gravel, quarried stone, crushed stone, or any material that can achieve the proper density with as few voids as possible when compacted. Often time, this material comprises of whatever is available locally. It doesn’t have to be especially dense but just needs to be stable
Concrete for rigid pavements should be designed to a standard quality of M40 compressive strength at 28 days. The most important characteristic of a quality concrete is durability. Concrete used for road pavement construction must stand the test of time through all kinds of traffic, wet and dry weather. The following are among others, things that contribute to durability of concrete.
- Quality aggregates
- A well graded mix (for low permeability) adequate strength
- Proper air-entrainment (well-dispersed and typically around 6%)
- workability and fluidity of the concrete
Aggregates are the constituent of a composite material such as concrete and asphalt concrete that resists compressive load and provides bulk to the composite material. Aggregates should be clean, hard and free from absorbed chemicals or coatings of clay and other fine materials when added to cement for a good concrete mix. Without this cleaning, it can cause the deterioration of concrete quality.
A well graded mix
The mix for a concrete pavement should be well graded according to the design. This is to provide an excellent ridding surface and a retaining good surface texture
An air entrainment is the intentional creation of tiny airbubbles in a concrete. These bubbles are introduced by adding to the mix an air entrainingagent. Air entrainments protect the concrete against freezing and also serve as air valves in the concrete during freezing. These are like little ball on the concrete when the concrete is being worked fresh, before it’s hardened
Workability and fluidity of the concrete
This is an integral part of the concrete mix. When a good workability is achieved, it shows that the slump is in the range of design. To achieve this, the water-cement ratio should be maintain at 0.45 or below as a higher ratio will reduce the durability of the concrete.