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Can You Lay Concrete Or Cement Over Bitumen?

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If you are looking for the best solution to fix a crack in the driveway, you may have thought about laying concrete or cement over bitumen. You know cement is just a binding agent and you might want to apply concrete instead of cement over bitumen. But are you sure it will work out well? We have researched this matter in-depth and have answers for you.

Yes, you can lay concrete over bitumen but you must first prep or repair the existing bitumen layer so the concrete will adhere to it. This process will increase the overall lifespan of your concrete.

If you are wondering how to lay concrete over bitumen, then you should know that the two are not compatible. It is imperative to have the initial layer of bitumen stripped off before you start working on laying new concrete. This will prevent you from having to do costly repairs later on. To learn more, continue reading!

Heavy vibration roller compactor press new hot asphalt on the roadway, Can You Lay Concrete Or Cement Over Bitumen?

What is Bitumen?

Bitumen is a thick black viscous substance derived from petroleum. It is used in road construction and in the manufacture of roofing membranes. Bitumen is also known as asphalt.

Protective bitumen mastic for concrete pavement

Typically, bitumen is used in the construction of roads, bridges, and parking lots. Bitumen is generally cheaper than concrete, which makes it the most preferred choice for road projects.

No wonder bitumen tends to crack and peel after a few years. We've witnessed how even a small crack today can turn into a major pothole in a couple of weeks, leading to dangerous driving conditions.

The cracking, peeling, and crumbling can be attributed not to the lack of proper maintenance, but to the structural properties of bitumen itself. It's not that bitumen is bad, but it just lacks the strength to last. 

In addition, the initial cost may give the impression of bitumen as cost-efficient, but the maintenance cost will make up for it, making bitumen a liability in the long run.

How Bitumen Mixture for Road Construction is Made

The first step is to heat the bitumen so that it turns into a liquid state. The heated bitumen is then pumped through pipes towards a mixing station where it will be combined with sand, gravel, or other aggregate materials. This mix is then dumped on the ground and compacted to make a new road surface. 

Asphalt road roller with heavy vibration roller compactor press new hot asphalt on the roadway on a road construction site

Reasons Why You Should Lay Concrete Over Bitumen

Fortunately, it is possible to lay concrete over bitumen. You may be able to replace a portion of your asphalt driveway or other paved surfaces with concrete if it is cracked, peeling, or broken. However, it can be difficult to get concrete applied over an existing bitumen surface.

The reason is that bitumen does not bond well with concrete, and it will usually require some prep work like stripping off the surface and mounting reinforcement bars. This way, the concrete will adhere to the rough bitumen surface and is kept in place.

How to Lay Concrete Over Bitumen

There are several ways to lay concrete over bitumen. Here are the basic steps to follow:

1. Evaluate the condition of the asphalt road surface

Potholes in the road looking like alien craters

You’ll need to consider the condition of the existing surface. It’s best to have a pre-survey done so you know what kind of surface you’re working with.

It's normal for asphalt roads to show signs of wear and tear like cracks and crevices. However, if you find that the road has wide, deep potholes and large crevices, then this could be an indication that your existing asphalt needs to be either resurfaced or removed.

You can do this by stripping 1 inch of the outer layer of the surface (for minor cracks) or totally removing it (for major cracks), depending on the outcome of your evaluation and circumstance.

If the asphalt is disintegrating badly as you strip the surface off, then it's a red flag telling you how much the asphalt has deteriorated over the years. It's better if you remove the entire asphalt surface totally in this case.

2. Optimize water outflow by drilling holes

Holes from drilling to measure asphalt road thickness

Proper drainage is crucial to ensure the concrete is resilient to external factors. Asphalt is naturally impermeable and does not allow for water to flow through the pavement, therefore making the surface susceptible to hydrostatic pressure and cracking.

Drilling holes on top of the asphalt will help release the water pressure. The standard depth of these holes is 12 inches and they must be spaced a foot apart.

3. Prep the surface so the concrete will bond

Since bitumen is non-porous, concrete will have a hard time bonding with it. It’s necessary to prep the asphalt surface to make it porous, allowing the concrete to adhere. This can be done by milling 1 inch of its outer layer. 

The rough surface that is the result of the stripping off of the outer layer will allow the concrete to bond properly. 

Additionally, mounting reinforcement bars (rebars) and building a framework around them will also ensure the concrete is held together in the proper place and won’t shift or move as the concrete cures. 

Ideally, rebars should be spaced 18 inches apart from each other in a grid pattern. They should be buried at least 2 inches vertically into the asphalt and exposed a few inches above it. 

Concrete reinforcement

4. Level the surface area where you want to pave

Once you're finished with prepping the surface, you'll need to level it. If you don't level the surface correctly, the concrete will begin to slump, leaving a noticeable dip in the uneven areas.

You can level the surface by adding more sand or gravel to the surface to even it out. Failure to level the surface correctly may lead to problems after the concrete hardens. 

5. Pour the concrete and smoothen using a bull float

Bull floating newly poured concrete

You should first determine where you are going to pour the concrete. You should also plan the depth of the concrete to ensure it is thick enough to support your structure.

You should also make sure you have all of the materials needed. These include a concrete mixer, wheelbarrow, concrete pump, wooden forms, tools, and safety equipment.

Before pouring the concrete, you should mix it to the correct consistency. You should add water gradually to the mix so it will become more fluid and easy to pour. 

You should then mix the cement and aggregate together. The ratio of cement to aggregate should be 1 part cement to 3 parts aggregate.

Avoid pouring concrete when the weather is inclement. You have to wait for the sun to shine and the clouds to disperse. Rain and snow will only make your concrete mixture get mixed together and turn into a lumpy, runny mess. It will be tough to level and smooth out.

Here's a quick video summary of the steps:

Disclaimer

These recommended steps are for reference purposes only. We do not encourage you to follow these steps unless you have tried them before.

The desired results can be best achieved if performed by a professional. Working with concrete requires a great deal of skill and experience because of its level of difficulty.

If you want to pursue this challenge as a beginner, you can click here to see this book on Amazon.

Are Cement and Concrete the Same?

In construction, concrete is one of the most popular building materials. It is made up of aggregates (sand and gravel) and a binder (cement). It is very versatile and can be used in many different ways. In fact, you could use concrete to construct anything from a house to a building.

Concrete is often used to refer to a denser heavy-duty building material that is designed for load-bearing uses, such as water dams and bridges.

Concrete pouring during commercial concreting floors of building

Cement, on the other hand, is a binding agent that is mixed with sand and gravel to make concrete. In addition to providing strength and stability, it makes concrete extremely durable and resistant to cracking and swelling. 

Worker filling a bucket with cement from a bag

When you add water to the cement, it becomes a paste that has a consistency similar to toothpaste. Sand and gravel need a binder to stick together. 

Cement or Concrete Over Bitumen?

As previously mentioned, cement is a binding agent that holds the concrete aggregates together. However, it is not intended to be used alone. This is because cement is prone to cracking. Therefore, the cement mortar must be reinforced with aggregates.

There are different types of aggregates that can be used in concrete. As mentioned earlier, the most commonly used ones are sand and gravel. However, there are other types of aggregates such as coarse granular stones or pebbles that can also be used as well.

If you're looking to fix and resurface a driveway, concrete is the way to go.

In Closing

Concrete and bitumen are two materials used to build pavement. Although they’re both strong, each one has its own advantages. We have learned about both concrete and bitumen and how they are made.

When it comes to using concrete and bitumen, it’s important to understand how each material is made and what its properties are.

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