Concrete Pavement Bases and Sub-Bases

Posted on March 12, 2019

Whenever tasked with building a home, construction companies make sure the rafters and trusses have the strength to hold the roof. Likewise, when building bridges, the bridge piers require special attention as they are tasked with load distribution.

From parking lots to highways, anything that must bear weight should have a strong and stable foundation.

This is why pavements require a robust and solid foundation. Bearing the load of millions of vehicles that pass over them, pavements require strength and adequate load distribution to be able to provide a durable platform for transport.

Pavement construction techniques have evolved significantly over the years. This article will take a comprehensive look into the world of concrete pavement bases and sub-bases.


History of Concrete Bases/Sub-bases

The need for the use of bases and sub-bases is not a modern scientific achievement, but rather a commonplace fact among the earliest of constructors. The Roman Empire, famed for their advances in construction techniques, is accredited with building over 53,000 miles of roads to facilitate the movement of troops and supplies, as early as 500 BC.

The Romans had realized the importance of preserving the sub-grade from the continuous deterioration caused by their carts and chariots. Renowned tourist attractions, such as the Appian Way, were constructed with multiple layers of stones – which formed the sub-base, base, and surface.

As vehicles continued to evolve and increase in size and weight, the need for sturdier road surfaces grew, leading to key innovations in the road construction arena. Modern-day roads feature a stark difference from the Roman Appian Way, but the core – the need for a base – remains the same.

What Is A Concrete Pavement Base/Sub-base?

In concrete pavement terminology, the subgrade – the native soil on which the pavement is built – must be protected and compacted to ensure it stays in its place and isn’t damaged. This is done by laying down a sub-base, a layer of aggregate material that is placed above the subgrade to prevent soil displacement.

Acting as the primary load-bearer, the sub-base is critical to spreading the load equally over the subgrade. The quality of the sub-base is critical to the useful life of the pavement. In many cases, high-quality sub-base has outlived the life of the surface which means only a new surface layer needs to be applied once the surface has deteriorated.

Why Is The Base Important?

Modern construction is heavily dependent on concrete, and for a good reason. Concrete provides the strength and durability that constructors look for, and at cheap rates. However, the powerful compression comes with a downside – it lacks flexibility.

Roads are exposed to heavy traffic throughout the year, and when dealing with such an amount of traffic, it requires flexibility. If the concrete slabs that form the very top of the pavement are not adequately supported beneath, they may bend. Any potential ‘soft-spots’ in the subgrade can allow the concrete to sink from the center or turn up from the edges.

Owing to its inflexibility, the concrete slabs can crack. As concrete is highly compressed and heavy, it may crack under its own weight if not provided a suitable sub-base.

Is A Concrete Base Always A Requirement?

A sub-base beneath the pavement is not an inherent requirement, but ever since the first cement pavement was placed in America in 1891, the industry as a whole has shifted towards utilizing cement base and sub-bases.

An adequately prepared sub-base and base are a prerequisite in order to achieve uniformity across the pavement structure.

Even if a concrete slab is being placed on top of a granite subgrade, the lack of uniformity in the absence of a sub-base will pose several problems. For instance, it is harder to obtain a proper grade and an optimal flat structure without a thoroughly prepared sub-base.

In addition to uniformity, the surface shrinking also presents a grave problem. Concrete is prone to shrink, and as it shrinks, the presence of sub-base reduces the likelihood that the concrete surface will crack. Without the sub-base, the concrete surface will crack with relative ease owing to the lack of support.

What Is The Optimal Base Thickness?

The thickness of the base is not objective and rather depends on a variety of factors. Some of the factors are:

  • The stability of the subgrade underneath the pavement
  • The stability and topography of the surrounding terrain of the pavement
  • The type of load that the pavement will be subjected to

For instance, a three inch thick base on a residential driveway on a stable ground can suffice. However, in contrast, a concrete pavement at a truck stop needs an optimal base thickness of more than six inches.

Before deciding on the thickness of the base, it is important to understand that the base is just one element of the pavement construction. There are several other factors at play, such as the depth of the sub-base, and the type of construction material used, which can affect the thickness of the base.

Lastly, the planned thickness of the concrete pavement itself is also influential in determining the proper thickness of the base.

What Are The Advantages Of A Concrete Base and Sub-Base

There are several materials used in the construction of pavement, bases, and sub-bases, but concrete continues to be the most popular choice among constructors.

Compared to other materials, concrete continues to provide more safety assurance than any other construction material – owing to its extended lifespan.

Several studies have pointed out that concrete is a long-lasting material, which can last up to 50 years in the best-case scenario.

Concrete corrodes slower over time, as compared to other materials, which translates to lesser potholes, lesser need for repairs and lesser automobile skidding, as the surface of the concrete is more rugged and provides more friction.

Additionally, concrete is 100% recyclable and is one of the most recycled construction materials in the world. In stark contrast to other materials, such as Asphalt, it doesn’t add to your state land refills but can actually contribute to the environment and used for newer construction.

The strength and durability provided by concrete bases have contributed heavily towards their widespread use in the construction industry, and their popularity doesn’t seem to be fading.