Concrete Driveway Thickness: 5 Important Factors That Make it Strong!

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How Thick Should a Concrete Driveway Be?

The thickness of the slab of a concrete driveway should be at least 4”. Reinforced with steel wire mesh, it will have adequate strength to bear the load of passenger cars. 

Concrete Driveway Thickness is possibly the most important factor affecting strength. So, if you want a stronger, more durable concrete driveway that will not crack even under heavier vehicles, you should opt for a 6” thick slab reinforced with steel rebars.

Commercial concrete driveways and parking lots that have to bear the load of heavy trucks are typically 8” thick and are reinforced with steel rebars.

Increasing the concrete slab thickness, from 4” to 6”, increases the strength of the driveway in two ways:

• The higher thickness increases the compressive strength. To be fair, the compressive strength of even a 4” thick slab is sufficient for cars weighing 8000 lbs.
• The higher thickness of 6” allows the use of steel rebars as reinforcement. Steel rebars are far more effective in increasing the tensile strength as compared to steel wire mesh. A 6” thick concrete slab is, therefore, less likely to sink, heave or crack, under heavy loads or due to stresses created by movement of the ground below the driveway. 

The rule of thumb is that by increasing the concrete slab thickness from 4” to 6” the load bearing capacity is more than doubled.

Is There a Code for Concrete Driveway Thickness?

The International Residential Code or the International Building Code do not specify the thickness of the concrete slab in a driveway. 

ACI 332 Chapter 10 Section 10.4 states that 

“The minimum thickness of slabs-on-ground shall be 3.5 inches”.

TABLE 3.1 of ACI 318 gives guidelines for compressive strength for structural concrete for different applications. 

The specified compressive strength for driveways, garage and industrial floor slabs is 3000 – 4000 psi. 

However, local building authorities, that require you to obtain a permit before building a driveway, do have very clear driveway specifications. This includes the minimum thickness permissible for a concrete driveway.

Most local bodies require the minimum concrete driveway thickness to be 4 inches. 

Here are a couple of examples:

Township of Mansfield, NJ, Burlington County requires that 

“The concrete slab shall have a uniform thickness of not less than four inches”. 

City of Lancaster, CA requires that

“Residential Driveways shall be constructed of four (4) inches of Portland Cement Concrete, if curb has been constructed”.

However, there can be exceptions. For example:

Toledo Municipal Code, OH states that:

“All concrete walks shall be not less than four inches (4″) in thickness and six inches (6″) in thickness at residential driveways”. 

How Thick Should Concrete Be for Heavy Trucks?

An 8” thick concrete driveway will be able to support pretty heavy trucks such as fully loaded concrete mix delivery trucks.

A fully loaded concrete mix truck can weigh between 70,000 – 80,000 pounds but the weight is distributed over several tires.

Do not let a fully loaded concrete mix delivery truck on to your driveway if the concrete slab thickness is 6” or less. Your driveway may develop structural cracks!

However, a 6” thick rebar reinforced concrete driveway can easily withstand the load of heavier personal vehicles such as RVs and Camper Vans.

A concrete driveway has a life of 25 – 30 years, which can be even extended to 50 years with proper care. It therefore makes a lot of sense to go for a 6” thick driveway to accommodate your future needs.

A few years down the line you may just decide to buy an RV or a Camper Van! 

What Factors Affect the Strength of Concrete?

The load bearing capacity of a concrete driveway is, no doubt, very important. It not only dictates the type of vehicles that can safely use the driveway but ultimately affects the longevity of the driveway itself.

There are 5 important factors that affect the overall strength, that is the load bearing capacity of a concrete driveway.

THE 5 KEY FACTORS

Factor	Description
1. Concrete Driveway Thickness	The thickness of the concrete slab, as expected, determines the load bearing capacity. A thicker slab will be stronger than a thinner slab.
2. Compressive Strength of the Concrete (psi)	The compressive strength of the concrete is the inherent strength of the concrete. Concrete mix is graded by its compressive strength (psi). A higher compressive strength will result in a stronger concrete slab.
3. Reinforcement Using Rebar or Wire Mesh	Concrete has very high compressive strength but relatively poor tensile strength. Reinforcement helps to improve the tensile strength of the concrete slab.
4. Soil Support System	The soil support system is the foundation of the concrete driveway. A well-compacted soil support system will help to distribute the load from the concrete slab and prevent it from sinking or cracking.
5. Concrete Curing Conditions	The curing conditions affect the rate of hydration of the concrete and the development of its strength. Concrete should be cured in a moist environment to prevent the water from evaporating too quickly.

1. Concrete Driveway Thickness

Among the 5 factors, the concrete driveway thickness, without doubt, is the most important factor. All other factors being the same, thicker concrete driveway will have higher load bearing capacity. Thicker the concrete slab, higher the driveway strength.

2. Compressive Strength of the Concrete (psi)

This refers to the inherent strength of the concrete that is poured. Concrete mix is graded by its compressive strength (psi). You can order concrete mix as per your requirements.

As a rule of thumb the load bearing capacity of a concrete driveway will increase by 8% if you use 3500 psi concrete instead of 3000 psi concrete. Using 4000 psi concrete will increase the load bearing capacity by another 7%.

To understand the compressive strength of concrete (psi) better, check out my post, “What Is the Best psi for a Concrete Driveway?”

3. Reinforcement Using Rebar or Wire Mesh

Concrete has very high compressive strength but relatively poor tensile strength. Vehicle loads and ground movement try to bend or twist a concrete slab. This is tensile and flexural load. 

Concrete slabs, without any reinforcement, are likely to crack under such loads. Reinforcement can be in the form of steel wire mesh, fiber mesh and steel rebars.

Steel rebars are the strongest reinforcement material but can not be used in slabs that are less than 6” thick.

4. Soil Support System under the Concrete Driveway

They say that a building is only as strong as its foundation. In the case of a concrete driveway the “soil support system” is the foundation.

The “soil support system” consists of the subgrade, the sub-base and the base. 

Subgrade is compacted topsoil. 

Sub-base is layers of crushed stone or angular gravel, graded such that the largest pieces are at the bottom. Each layer must be compacted. 

The base is a layer of pea gravel topped with a layer of coarse sand. Once again each layer must be compacted or tamped.

To understand the “soil support system” better, check out my post, “What Is the Best Base for a Concrete Driveway?”

5. Concrete Curing Conditions

Concrete begins the process of setting immediately after water is added to the cement-aggregate mixture. Water reacts with cement by a chemical process called hydration. The process results in the formation of a web-like crystalline structure to encapsulate the aggregates and form rock solid concrete.

Concrete achieves 99% of its designed strength after curing for 28 days. However, the curing conditions and their impact on the water evaporation rate play a huge role in strength development.

Concrete Curing Blankets are often used to control the concrete curing process.

RECOMMENDED PRODUCT

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The Best Concrete Curing Blanket for Your Driveway

Concrete curing blankets help protect newly poured concrete from variations in temperature and humidity. They keep the concrete moist during the curing process, help develop strength and prevent the concrete from cracking & spalling.

Here is the Concrete Curing Blanket I recommend.

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Bottom Line

The bottom line is that a 4” thick concrete driveway will most likely meet the local building code requirements and also result in a driveway that is adequate for use by standard passenger cars.

However, by increasing the thickness to 6” you will get a driveway that is more than twice as strong, will withstand ground movement and freeze thaw cycles better and will last much longer.

5 Important factors affect the load bearing capacity of a concrete driveway.

Thank you very much for reading this post. I do hope you found it informative and helpful.