Is Old Concrete Stronger Than New Concrete?

In some cases, old concrete is much stronger than new concrete. This is due to the materials that were used to create it. We don’t know the exact formula, but we do know it contained volcanic ash, lime and seawater. These ingredients contained lots of rare Earth minerals not found in modern concrete. This old mix created a crystalline structure that grew strong and more durable over time. It eventually became as hard as a natural rock and resistant to seawater. Modern concrete uses Portland cement, sand and stone mixed with fresh water. This creates a concrete that’s very strong and durable when new, but it doesn’t last nearly as long.

Have you ever visited or seen pictures of Italy. Most of its ancient monuments, statues and architecture were built using an extremely durable material called Roman Concrete. It’s similar to the concrete we make today only much stronger and more durable.

In fact, Roman concrete actually grows stronger and denser over time. This is why so many ancient Italian monuments are still in such great condition thousands of years after they were built.

Unfortunately, we don’t know exactly how it was made. If we did, builders would be using it instead of modern concrete to build foundations, walls and large structures.

Modern concrete grows weaker and breaks down over time. This is mainly due to water absorption, which is why concrete needs to be sealed. But ancient Roman concrete doesn’t. It’s much stronger and more durable than the concrete we use today.

However, even modern concrete grows stronger as it ages up to a point. As freshly poured concrete cures, it dries, hardens, and becomes stronger. But eventually it starts to deteriorate and look rocky. It does not grow stronger for thousands of years like ancient concrete does.

Why Is Old Concrete Stronger Than New Concrete?

Old concrete is much stronger and more durable than new concrete because of how it’s made. Some scientists say Roman concrete could be poured and hardened under water. That’s definitely not something today’s concrete can do.

So what makes old concrete so strong and resilient?

Old concrete is stronger than new concrete because it was made from volcanic ash. The ash contained rare minerals such as Al-tobermorite and Phillipsite. These minerals cure the concrete continuously which makes its chemical structure grow denser and stronger over time. This creates a much stronger, more durable concrete that actually gets better with age.

Once old concrete cures long enough, it becomes dense and solid like a rock. New concrete doesn’t do that. This is one of the reasons modern concrete is so easy to crack. New concrete’s chemical bonds aren’t nearly as strong as old concrete because it doesn’t contain the same ingredients.

A mixture of volcanic rock and lime was used to make old concrete. The mixture was ground up into a powder and mixed with seawater. This triggered a hot chemical reaction that formed incredibly strong bonds similar to a stone.

Rare minerals from volcanic ash formed tight bonds during the curing process. These minerals form into crystals which have a similar shape and strength to volcanic rock. As a result, the concrete hardens into a solid structure capable of withstanding incredible amounts of wear.

Unlike today’s concrete that’s damaged by salt, Roman concrete grew stronger when mixed with seawater because it contained even more minerals. Many Roman seawalls are still standing today even though they’ve been fully submerged in water for over a thousand years. They continue to grow stronger as the seawater strengthens the concrete’s bonds.

Old Concrete Vs New Concrete

Modern concrete is typically made with Portland cement, stone aggregate and sand mixed with fresh water. Cement is the active ingredient that chemically reacts with water to form a paste. The paste hardens over time and binds the sand and stone together. Sand gives concrete a gritty texture and makes it stickier. Stone is what gives concrete it’s great strength.

Portland cement is a man made material. It’s a mixture of silica sand, limestone, clay, chalk and other ingredients melted together at very high temperatures to form clinker. The clinker is ground down into a cement powder. In concrete, cement is what binds aggregate rock and sand together.

The aggregate used to make concrete has to be inert. Any unwanted chemical reaction that occurs while the concrete is curing can cause cracks. These cracks then lead to erosion and deterioration. This is a major reason why concrete doesn’t have the longevity of natural rocks or Roman concrete.

Old Roman concrete works in a different way.

Old concrete was created using volcanic ash, lime and seawater to create a mortar. The mixture mimics the chemical reaction Romans may have observed in naturally cemented volcanic ash deposits called tuff rocks. Lots of rare Earth minerals are naturally present in volcanic rock that aren’t used in modern concrete.

Volcanic rock aggregate was then added to the volcanic ash mortar along with seawater. The mortar would react with the seawater and aggregate making super strong and dense Roman concrete.

Check out the picture shown above. It shows a set of steps built out of new concrete next to steps built thousands of years ago out of Roman concrete. The difference is clear. Roman concrete is much stronger and more durable.

Why Don’t We Use Old Concrete Anymore?

Modern concrete is a fantastic building material. Just about all of our foundations, sidewalks, buildings, bridges and damns are made out of concrete. It’s one of the most popular building materials and used throughout the world. But there’s no doubt that old Roman concrete was much stronger. So why don’t we use it anymore?

We don’t use old concrete anymore because we don’t know exactly how it was made. Scientists have been running tests on ancient concrete for years, and they’ve made some great progress, but still don’t have the formula.

There is also the issue of cost. Concrete is such a widely used material because it’s cheap and readily available. Just about every country on Earth has the basic ingredients required to make it. But rare minerals found in old concrete, such as Al-torbernite which gives Roman concrete its strength, is very expensive to produce in a lab.

In addition to not knowing the exact ingredients used to make Roman concrete, scientists are unsure about the process. For example, adding the mineral Al-torbernite into a cement mixture causes the concrete to crack when curing. This is a big problem because they know Al-torbernite is in Roman concrete. What they don’t know is how to add it without cracking the concrete.

Scientists from around the world are trying to find a way to make old concrete again. But despite the progress researchers have made, they still can’t reproduce it.

Therefore, using old concrete is nearly impossible to pay for. Then on top of this, the old concrete that we can make today isn’t practical for buildings or projects. Nevertheless, researchers continuously aim to resurrect this ancient building material, the key to some of Rome’s most incredible feats of engineering.

What’s In Old Concrete?

To find out what Roman concrete is made of, scientists map samples using an Electron Microscope and techniques such as Microdiffraction and Raman spectroscopy. Using these advanced techniques they can identify all the minerals found inside old concrete.

A silica-based mineral called aluminous tobermorite was one of the minerals scientists found. It’s rare and difficult to make in a lab but abundant in old concrete. Aluminous tobermorite and a related mineral called phillipsite grow in the concrete because of the sea water used to create it. The water slowly dissolves the volcanic ash and gives it space to develop a reinforced structure from interlocking crystals.

The Romans created a rock like concrete that thrives in seawater. This is the opposite of what happens with modern concrete which breaks down from salt or rusted rebar.

Making old concrete again would be incredible for the modern building industry. Especially in coastal structures like seawalls that are constantly hit by waves. This would be a great aid in the fight against rising tides and climate change.

Unfortunately the exact recipe and process used to make old concrete isn’t known anymore. So scientists continue to take samples and reverse engineer it’s construction.

Romans were lucky that they had the type of volcanic rock needed to make Roman concrete. That isn’t the case all over the world. So lab made materials will have to be used instead. This will make the concrete cheaper and readily available. However, scientists have to figure out the formula and process first.

How Strong Is New Concrete?

Modern concrete is an excellent building material that’s extremely strong and durable. Just not when compared to Roman concrete. So how strong is modern concrete?

The amount of strength modern concrete has is measuring in PSI or Pounds Per Square Inch. When you look at a bag of Quikrete concrete, it’ll have a number on it like 3500. That means it’s 3500 PSI concrete. The higher the number, the stronger the concrete is.

There are a few factors that effect concrete strength:

• Mix: Almost nothing effects the strength of concrete more than the mix. Concrete is made from Portland cement, stone, sand and water. Varying the ratios and materials used changes the concrete’s strength.
• Ingredients: The actual ingredients you use matters too. For example, course sand and large stones produce a stronger concrete than fine sand and small stones.
• Additives: Additional ingredients can be added to concrete to increase it’s strength.
• Water: A key ingredient in making strong concrete is water. Use too much and you’ll greatly weaken the concrete.
• Reinforcement: Concrete that’s been reinforced with steel rebar is much stronger than concrete without it.
• Thickness: The thickness of the structure also effects it’s strength. The thicker it is the more weight it can typically hold.

Concrete grows in strength during curing which usually takes 28 days to complete. That bag of Quikrete 3500 concrete is actually 3500 PSI after 28 days of curing. At 10 days it’s only about 1500 psi. Make sure you cure the concrete properly if you want it to be as strong as possible.

If you read an architect or engineers structural plan it will tell you how strong the concrete needs to be for your project. Make sure you follow the designers instructions and use the proper concrete for the job.

How To Make New Concrete Stronger?

Since Roman concrete isn’t an option you’ll have to make due with a modern mix. It won’t be as strong as Roman concrete, but there are lots of things you can do to improve modern concrete’s strength and durability.

Here are some ways to make new concrete stronger and more durable:

• Use a pre-mix like Quikrete or buy concrete from a plant. All the ratios will be correct, the ingredients will be of high quality and you won’t have to worry about making mistakes.
• If you mix your own concrete, choose the ingredients carefully. Use clean sand and stone. Impurities can weaken the concrete.
• Use large stones. The larger the stones the higher the PSI will be.
• Use chemical additives to increase concrete’s strength.
• Try non-chemical additives like micro rebar or fiber to add even more strength.
• Coarse sand makes stronger concrete than fine sand.
• Use the proper amount of water.
• Cure the concrete correctly. This is a very important part of making strong concrete.

The best way to make a concrete structure stronger is using steel rebar. Rebar is a hard metal rod placed within the concrete structure. Usually rebar is tied together with other rebar to form a skeletal structure for the concrete. Concrete has high compressive strength but low tensile strength. Adding rebar boosts the concrete’s tensile strength which increases the strength of the structure.

While rebar doesn’t actually make the concrete stronger, it makes the structure stronger and more durable.

Summary: Is Old Concrete Stronger Than New Concrete?

In some cases, old concrete is much stronger than new concrete. This is due to the materials that were used to create it. We don’t know the exact formula, but we do know it contained volcanic ash, lime and seawater. These ingredients contained lots of rare Earth minerals not found in modern concrete. This old mix created a crystalline structure that grew strong and more durable over time. It eventually became as hard as a natural rock and resistant to seawater. Modern concrete uses Portland cement, sand and stone mixed with fresh water. This creates a concrete that’s very strong and durable when new, but it doesn’t last nearly as long.

Have you ever visited or seen pictures of Italy. Most of its ancient monuments, statues and architecture were built using an extremely durable material called Roman Concrete. It’s similar to the concrete we make today only much stronger and more durable.

In fact, Roman concrete actually grows stronger and denser over time. This is why so many ancient Italian monuments are still in such great condition thousands of years after they were built.

Unfortunately, we don’t know exactly how it was made. If we did, builders would be using it instead of modern concrete to build foundations, walls and large structures.

Modern concrete grows weaker and breaks down over time. This is mainly due to water absorption, which is why concrete needs to be sealed. But ancient Roman concrete doesn’t. It’s much stronger and more durable than the concrete we use today.

However, even modern concrete grows stronger as it ages up to a point. As freshly poured concrete cures, it dries, hardens, and becomes stronger. But eventually it starts to deteriorate.

If you have any questions or comments about concrete, email any time.