Can You Use Old Concrete As Fill for New Concrete?

Giovanni Valle is a licensed architect and LEED-accredited professional and is certified by the National Council of Architectural Registration Boards (NCARB). He is the author and managing editor of various digital publications, including BuilderSpace, Your Own Architect, and Interiors Place.

Many DIY home builders ask the question: can I use old concrete as fill for new concrete? The answer is YES! If you have a large pile of leftover material from your last project, recycling it into your next one is both cost-effective and environmentally friendly.

You can use old concrete as fill for new concrete to create aggregate to add bulk, compressive strength, and stability, as well as for recycling purposes. Crush the old concrete or hire a company to remove it and smash it into small pieces. Clean and recycle the concrete by adding it to the new concrete’s mix before you pour it.

Throughout this article, you’ll learn the following information about using old concrete as fill for new concrete:

The step-by-step process to recycle or reuse old concrete
Several benefits of using old concrete as fill for a new layer
What you should know before starting

How To Use Old Concrete To Fill New Concrete

Whether you’re removing an old patio in the backyard or a concrete slab in the front of your home, there’s no reason to toss the old concrete. Contrary to popular belief, there’s a lot you can do with crushed concrete, regardless of how old it is. Make sure it’s clean and durable before you start, though.

Here’s how you can use old concrete to fill new concrete:

Crush the concrete by hiring a company, renting a mobile crusher, or breaking it apart with tools. Ozinga recommends hiring a third-part service since they’ll deal with potential damages to the machines. If you do the job and there’s nobody to blame when something goes wrong, you’ll have to foot the bill.
Inspect the concrete for dirt, grime, and powder. Crumbled concrete turns into a rocky, powdered substance. While you can use these bits as fill for new concrete, they’re not as tough as the chunks. Always clean old concrete before and after you crush it to ensure you don’t add anything to the new fill.
Mix the new concrete. Whether you’re hiring a company with a concrete truck or mixing it by hand, you should turn the concrete into a liquid prior to adding the rocks and chunks of crushed old concrete. They’re known as concrete aggregate, and they support the new concrete mix and remove air bubbles.
Check the liquid concrete mix to ensure the old concrete is thoroughly integrated. The last thing you want is to pour your new concrete and have a bunch of chunks clumped in the corner. Stir the concrete until it’s blended, then wheel or drive it over to the place you’re going to dump it.
Slowly pour the concrete as you usually would, but keep an eye on the old concrete aggregate. If it starts clumping, move it to a new location with a shovel or similar tool. If you’re using a concrete pouring truck, the spinning motion often keeps everything blended, so you don’t have to worry about it as much.

As you can see, reusing old concrete as aggregate to fill new concrete is easier than it sounds. As long as you keep it clean, evenly break it apart, and blend it thoroughly, you’ll be good to go. If you’ve never reused concrete and you’re considering it, review the next section to find a handful of undeniable benefits.

Benefits of Recycling Old Concrete As Aggregate

The benefits of recycling old concrete as aggregate are many. It is a great way to stop landfill waste and also recycle the material that would otherwise be wasted. Old concrete isn’t worth throwing away, especially since it can be used for dozens of applications.

By design, concrete is robust, durable, and you can typically expect a concrete structure to last decades. When you choose to remove and replace it, it is usually due to cracking or erosion at the corners (or for aesthetic reasons). But this doesn’t mean all of the concrete is defective.

By contrast, the center of the concrete area is likely just as strong as it once was, and using it as aggregate is the best option, both financially and environmentally speaking.

Let’s explore some of the advantages of reusing old concrete below.

Old concrete aggregate adds skid resistance and texture to new concrete. You don’t have to worry about slipping when walking on the new concrete pad, especially when it rains. The rocky texture makes it feel much more comfortable and easier to walk or drive on.
Old concrete adds an appealing aesthetic to new concrete. It looks excellent surrounding swimming pools, patios, walkways, driveways, and more. If you’re looking for a unique way to change your home without breaking the bank, the old concrete fill should be near the top of your modification list.
The old concrete will need to be broken down and removed regardless of whether it is being recycled. If you’re looking to replace a patio or remove old steps, it makes more sense to reuse the material you’ll soon have on hand.
It improves the durability of new concrete. Old concrete is already hardened, which means its chunks will support and hold new concrete without letting it slip or crack. It also evenly disperses the pressure of walking, driving, and operating heavy machinery on top of the new concrete slab.
Concrete aggregate can repel water from the surface, keeping it clean and safe to walk on. As mentioned earlier, it prevents slipping and sliding. The added texture also prevents the concrete from cracking due to excess moisture absorption. It even prevents long-term mold and mildew exposure.
Reusing old concrete to fill new concrete saves you a lot of money. It fills the gaps, removes air bubbles, saves you from having to pay for dumping fees, prevents long-term erosion, and more. All of these traits keep your bank in good condition from such a simple improvement.

New concrete is designed to handle the pressure, but old concrete that’s crushed and used as a filler can make a world of difference. If you have old concrete to remove, you might as well recycle it and use it as aggregate. Feel free to use different shapes and sizes to alter the new concrete’s appearance.

What To Know Before Recycling Old Concrete

Before you crush and fill the old concrete, it’s important that you don’t ruin the new mixture. After all, a small alteration can make the new concrete dirty, clumped, and unusable. You know how to recycle the old concrete, but it’s time to learn a few common mistakes and how to avoid them.

Always Clean the Old Concrete

It’s important to clean old concrete as it is often covered in dirt, oil spills, and other debris. If you leave all of that mess in the mix, your new concrete can become discolored, brittle, and unusable.

Any oil residue or dirt left on the aggregate can prevent the old concrete from properly bonding with the new. This can lead to weak spots in your new pour, gaps that let in water, and a higher risk of breakage under stress. Those who have extra-dirty concrete should consider hiring a professional company to crush, clean, and mix their aggregate.

Choose Your Concrete-Crushing Tools Wisely

You can use tools with jaws, picks, conveyors, and many other essential components. You’ll need to start by breaking down the concrete area, using either a sledgehammer or jackhammer to make smaller, movable chunks. Depending on the size of the area, a jackhammer might be the better option to save on time and energy.

Remember to cover the area with plastic to prevent debris from damaging anything nearby. If working with power tools, wear the appropriate safety gear, such as goggles and a face mask. Start at the edges and work your way into the middle until you have pieces that are easy to lift and relocate.

If you have a massive concrete pad or you’re not sure how to start, it might be a good idea to hire a professional. Otherwise, you could end up spending more money on rentals and repairs.

Concrete Aggregate Size Matters

Using aggregate that’s too big will cause clumping and uncomfortable, ugly textures. On the other hand, extremely small concrete aggregate is nearly pointless. With that in mind, consider consulting with an expert to ensure you have the right size and shape to avoid any wastage.

It takes a lot more time and money to make old concrete chunks smooth and round, but many homeowners and business owners find it’s more than worth it in the end.

Conclusion

Now that you know how to use old concrete as fill for new concrete and why it’s an excellent idea for many residential and commercial properties, you’ll reap countless benefits. Old concrete can be costly to remove, so why not reuse it and add a unique appearance, durability, and longevity to your new project?

Here’s a quick recap of the post:

Crush, clean, and reuse small chunks of old concrete as aggregate.
Dirt and grime can ruin old concrete, so inspect it beforehand.
You can save a lot of money by reusing old concrete.

Every year the world produces about 2.6 trillion pounds of concrete, and as our population grows, we are building more and more buildings with it. This means that there is a lot of old concrete out there that can be recycled to make new aggregate for construction projects.