The famous Pantheon in Rome boasts the world's largest unreinforced concrete dome—an architectural marvel that has endured for millennia, thanks to the incredible durability of ancient Roman concrete. For decades, scientists have been trying to determine precisely what makes the material so durable. A new analysis of samples taken from the concrete walls of the Privernum archaeological site near Rome has yielded insights into those elusive manufacturing secrets. It seems the Romans employed "hot mixing" with quicklime, among other strategies, that gave the material self-healing functionality, according to a new paper published in the journal Science Advances. //

It was believed that the Romans combined water with lime to make a highly chemically reactive paste (slaking), but this wouldn't explain the lime clasts. Masic thought they might have used the even more reactive quicklime (possibly in combination with slaked lime), and his suspicion was born out by the lab's analysis with chemical mapping and multi-scale imaging tools. The clasts were different forms of calcium carbonate, and spectroscopic analysis showed those clasts had formed at extremely high temperatures—aka hot mixing.

“The benefits of hot mixing are twofold,” Masic said. “First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form. Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction.”

It also seems to impart self-healing capabilities. Per Masic, when cracks begin to form in the concrete, they are more likely to move through the lime clasts. The clasts can then react with water, producing a solution saturated with calcium. That solution can either recrystallize as calcium carbonate to fill the cracks or react with the pozzolanic components to strengthen the composite material.

Masic et al. found evidence of calcite-filled cracks in other samples of Roman concrete, supporting their hypothesis. They also created concrete samples in the lab with a hot mixing process, using ancient and modern recipes, then deliberately cracked the samples and ran water through them. They found that the cracks in the samples made with hot-mixed quicklime healed completely within two weeks, while the cracks never healed in the samples without quicklime. //

mgsouth Seniorius Lurkius

DJ Farkus said:
So many questions... Did they pour the hot-mix, is it required to be poured hot? How high of temperatures are we talking here? I wonder how they heated batches on-site (or did they transport it for pouring)?

Thank you. Now I have a mental image of a wagon pulled by a brace of oxen, with a huge oak barrel slowly rotating in the back. Meanwhile, the drover is flicking a whip about, cursing the throng of people in the street, screaming he has a *!@#! load setting up and get out of the !#@!! way. (In Latin, of course.)

At its peak in the second century, the Roman Empire dominated nearly two million square miles of the world. As with most such grand achievements, it couldn’t have happened without the development of certain technologies. The long reach of the Eternal City was made possible in large part by the humble technology of the road — or at least it looks like a humble technology here in the twenty-first century. Roads existed before the Roman Empire, of course, but the Romans built them to new standards of length, capacity, and durability. How they did it so gets explained in the short video above. https://www.youtube.com/watch?v=z1aFWtBXHII

On a representative stretch of Roman-road-to be, says the narrator, a “wide area would be deforested.” Then “the topsoil would be removed until a solid base was found.” Atop that base, workers laid down curbs at the width determined by the road plan, then filled the gap between them with a foundation of large stones.

Atop the large stones went a layer of smaller stones mixed with fine aggregates, and finally the gravel, sand, and clay that made up the surface. All of this was accomplished with the old-fashioned power of man and animal, using tipper carts to pour out the materials and other tools to spread and compact them.

https://www.openculture.com/2022/12/how-to-make-roman-concrete-one-of-human-civilizations-longest-lasting-building-materials.html

The ancient Romans were masters of building and engineering, perhaps most famously represented by the aqueducts. And those still functional marvels rely on a unique construction material: pozzolanic concrete, a spectacularly durable concrete that gave Roman structures their incredible strength.

Even today, one of their structures – the infamous Pantheon, still intact and nearly 2,000 years old – holds the record for the world's largest dome of unreinforced concrete.

The properties of this concrete have generally been attributed to its ingredients: pozzolana, a mix of volcanic ash – named after the Italian city of Pozzuoli, where a significant deposit of it can be found – and lime. When mixed with water, the two materials can react to produce strong concrete.

But that, as it turns out, is not the whole story. An international team of researchers led by the Massachusetts Institute of Technology (MIT) found that not only are the materials slightly different from what we may have thought, but the techniques used to mix them were also different.

The smoking guns were small, white chunks of lime that can be found in what seems to be otherwise well-mixed concrete.

Curing is the maintenance of a satisfactory moisture content and temperature in concrete for a period of time immediately following placing and finishing so that the desired
properties may develop

AirCrete is inexpensive, easy to make, and easy to work with.  It requires only basic skills. 

It's easy to make.  And, like baking a cake, you have to get the recipe right. The quality and density of the foam is important. Use an accurate postal or kitchen scale to check the weight of your foam. It should be between 90 - 100 grams/liter (about 3 ounces/quart). 

You can use good quality dish detergent to make the foam with Little Dragon, our continuous foam generator. Look for a high foaming degreaser detergent. We tested Seventh Generation Natural Dish Liquid, Dawn Ultra and Safeway Home concentrate.  They all produced adequate foam diluted 40/1 with water. (5 gals water / 2 cups foaming agent).  Add the detergent to the water and mix thoroughly.

You need an air-compressor rated for at least 2.5cfm@90psi, which is a relatively small compressor. Of course you can use a bigger compressor if you have one.

Mix one 94lb bag of cement with 6 gallons (US) water. Put all the water in your container first and add the cement while you are mixing to avoid clumping. When the cement and water are well mixed, turn on the Little Dragon and add foam to the mixture. Add enough foam to make a total of 45 gallons of AirCrete. That's about 30" high in a standard 55 gallon drum. The foam is very light weight and so it wants to float on top of the cement mixture. Our foam injection mixer works great because it injects the foam directly into the mixing paddles at the bottom of the barrel where it is mixed into the cement before it can float to the top.

Foam Concrete (FC) is made by mixing foam into mortar. The mortar is a cement mix with sand and water. As a result you end up with a mix that is lighter than “normal” concrete. The mass, or density as we call it here, (weight per cubic meter) depends on how much foam is added to the mortar. The more foam we add the lighter it is, but also the weaker is becomes. The “Ideal” mix would have at least 20 MPa at a density of 1000 Kg/m3, however the best results I have found in studies was 18 MPa and a density of 1200Kg/ m3. A simple FC with no additives is usually around 5-8 MPa with a density of 1000 Kg /m3. There are FC “Brands” on the market that make the claim to be better than this.

The lighter the FC is, the better the thermal insulation becomes. The combination of the strength and the insulation value makes FC an ideal building material.  For the advantages and dis-advantages of FC go to:  Why Foam Concrete is an ideal building material