Worldbuilding #15 – Concrete

So far we’ve discussed metals for the worldbuilding series, today we take a sidestep and look at another element important to our society, Concrete.

It’s hard to go anywhere today and not see some form of concrete, whether in building, roads, bridges, or a vast variety of other things. Like metal, it has been one of the key elements that has shaped our modern society, starting nearly 300 years ago. However, it is not a new concept and has been around since prehistoric times.


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First off, concrete is not a natural material, but rather a combination of materials that make something new. In this way, it is much like an alloy. For this reason, this is listed under technologies rather than a resource. While technically a resource, various techniques can be used to create concrete, which each have their own pros and cons.

Interestingly enough, the history of concrete shares a similarity with Copper. While used during prehistory and ancient age, it fell out of favor during the Middle Ages and didn’t resurface again until the beginning of modern history. However, the difference between Concrete and Copper, is that Copper had a profound impact when discovered, whereas concrete didn’t have a major impact on society until the modern age.



When people talk about concrete, they mostly think of its modern technique with the usage of cement. While that will be discussed in greater detail, when talking about concrete throughout history, we do need to discuss what concrete actually is.

Concrete comes from the Latin word concretus, meaning compact or condense. Now, while concrete does need to be mixed together to form, it doesn’t always need to be man made. It can occur in nature, albeit very rare.

The earliest usage of concrete was over 12 million years ago. It was formed through spontaneous combustion of limestone and oil shale. These deposits were discovered in the 1960s in Israel.


To understand what concrete is, we need to break it down into its core components. While there are a lot of techniques that can be used for concrete, we will start with the 3 basic components:

  • Aggregate
  • Binder
  • Water

Simply put: A binder is a mineral that when wet, acts like a paste that takes a hard substance like rock, and when it dries, becomes a hard material. In this way, concrete shares a similarity to cake. You mix some flour, water, and eggs together, and you get breading.

Other things can be used in addition to those 3 components:

  • Chemical admixtures
  • Reinforcements
  • Mineral admixtures

When we look at concrete in its most basic forms, we can see that almost anything can be used for concrete. Cement is often used as a binder in modern usage, but cement is a modern invention. Before Cement, a variety of other elements were used.

Our caveman ancestors used mud and clay as a form of cement that was used as a mortar, to put on stones to seal any holes in structure to protect against the elements. Assyrians and Babylonians used straw and clay for much the same reason.

Ancient Egypt improved upon this concept, using gypsum and limestone in combination with sand and water. This created cement to be used as a mortar that was used for many things, including the pyramids.

Ancient Greeks improved upon this, but the Romans took it to the next level, using Pozzolana as a binder, an important ingredient for Roman Concrete. It should be noted that Roman Concrete is comparable to the use of concrete today.

This will be discussed more in the history section, but I wanted to introduce you that cement is not necessary for the use of concrete. Other things can be used.



Put simply, aggregates is gravel. Rocks put into the mix to help give concrete its strength. What makes aggregates different from one another is namely the size of the rocks. The smaller the aggregates are, tend to be the more tough the concrete is. Generally, well ground aggregate is the best approach, though sand can be used as well. Often times, sand was used.


Concrete itself is 100% recyclable, provided it is just concrete and no other refuse. Concrete can then be used as an aggregate for new formations of concrete. Still need a binder with it.

Sometimes aggregates can be added during the curing process that might be shiny to give it a unique artistic look. It can also be done to concrete a robust look. This is more for the visible side of the concrete rather than the internal structure, as it is often done for aesthetics rather than function.

Aggregates don’t just have to be stones you find or recycled concrete. It can be manufactured, such as ash from a furnace or slag run off from smelting metals.

While a binder, such as concrete, is important for the task of concrete, it is very brittle. Aggregates can give concrete more durability.


Water is important for the Binder. Binder is just a powder, is most cases, and the water causes it to turn into a paste or glue to hold the aggregate. The the use of water is called hydration. Different levels of water is used for different applications. Too much and the concrete is weak. Too little, and the concrete is unworkable.

As you can imagine, you want to use pure water, as it will improve the final product of concrete, though you can add things into the water to improve concrete in other ways. However, just using water from a natural water source can have an impact on the overall quality, ore prevent it from properly setting.


As mentioned before, Binders are materials, that when mixed with water, act as a bonding agent with aggregates that then harden and become concrete. While Cement is the most used today, there are four general types of Binders:


Lime, also known as Quick Lime or Burnt Lime, is a calcium oxide which contain calcium, silicon, magnesium, aluminum, and iron. By itself, it acts as a good bonding agent for mortars and good in small applications, but not so greater in bigger applications.


Lime has been used since 4000 BC, used mostly for paint application and eventually mortars. Many other methods of creating a binder for concrete uses Lime in some way.


Used by the Egyptians primarily for the Pyramids. Gypsum is a soft mineral of calcium sulfate dihydrate. It reacts well to water and has a low temperature requirement, making it easier to use than Lime. However, it is often softer than Lime, which makes it more workable, but less durable in damp conditions. Put it in a dry environment, like Egypt, and you can see why the pyramids are still standing.


This is a silicate oxide and aluminum oxide material that is found in volcanic ash. When mixed with Limestone (which can be found naturally, or be created using quicklime), it helped enhanced mortar to be used as a concrete. Pozzolana was used in Roman Concrete. This added durability to concrete, allowing for bigger structures.

This is still used today, but is known as Pozzolan, which is just volcanic ash. It can be use to reduce the amount used of Portland Cement to increase durability, reduce cost and reduce pollution without sacrificing compressive strength or other performance features of concrete. Only 40% of Portland Cement can be replaced in favor of Pozzolan.

Portland Cement

Portland Cement is the standard. It is the best binder, as far as strength and availability. While other cements were made prior to Portland, it was the one of notable significance.

To process Cement, it requires it to be heated up and have a flux added to it, so it can change on a molecular level, resulting in a clinker. Then additional materials, such as gypsum, are added to it to become cement. The end process consists calcium, silicon and aluminum.

It was first patent in 1824 by Joseph Aspdin, named for how the cement resembled Portland Limestone. Like Roman Cement, it is useful for water applications and can be set underwater and be protected by various chemical elements.

Portland cement is unfortunately bad for the environment. As great as it is, it releases CO2 emissions and cause dust in the air. Which is why having another material, such as volcanic ash can help offset the pollution caused.

Chemical Admixtures

As great as concrete is on its own, sometimes you need it to do more than it is capable. Luckily, extra chemicals can be added, whether powders or liquids, that can change the final product. The various Chemical Admixtures types are:

  • Accelerators: Speed up the hardening of concrete. This is often used for making cement in cold weather.
  • Retarders: Slow down the hardening process. Used for large usage of concrete, where you want everything to set at relatively the same time. One part doesn’t get harden before other parts.
  • Air entraining agents: Adds tiny air bubbles to concrete. It will reduce its strength, but can protect against freeze-thawing cycle, adding to its durability
  • Plasticizers: Increases workability of concrete, making it easier to work with, as concrete can be quite rigid. Often called water-reducers as they can decrease the amount of water needed.
    • Superplasticizers: High-end Water-Reducers. Chemicals that can greatly increase workability while decreasing the amount of water.
  • Pigments: Used to change the colour of concrete, for aesthetic purposes.
  • Corrosion Inhibitors: Used to prevent corrosion of mental elements such as refined concrete
  • Bonding Agents: Used to bond new concrete with old concrete

There are also mineral admixers, added to concrete mostly to cut down costs or improve durability. Such elements are Fly Ash, Slag, Carbon Nanofibers, and other carbon products.

Special note is Silica Fume and Metakaolin, which can add to the strength of concrete, but requires the use of Superplasticizers. Silica Fume is dark in colour, where Metakaolin is light.



In the past, cement was produced in standing kilns, where you load it and once done, empty it. Now, concrete goes through a rotating kiln, that is tilted and rotating, and continuously moving 24/7. It goes through at the top and heated up as it goes down with the materials. That is when it is made into a croker, and finally made into a cement.


Now some facilities make their own cement before making their own concrete, other import the cement. The one thing to know about concrete is that it is time sensitive. Once you start mixing it, you have to use it before it hardens. Factories either send it off to a local area to be used, or puts it into a mold and makes their project in a controlled environment, and ships that off to where it is needed, such as bridges.

Prebuilding concrete could technically work for some smaller jobs, but it is not economical. For other jobs, it is not really feasible. As mentioned, you can poor it in a truck and deliver it, or make the concrete on the way. This require a Concrete Mixer, also known as a Cement Mixer.

NOTE: Concrete and Cement in everyday language is often interchangeable. Often when one speaks of cement, they are referring to Concrete and vice versa.

When it comes to Concrete Trucks, they either receive concrete already made and they keep stirring en route to prevent it from hardening, or the truck mixes the liquids and powders together en route. This way, construction sites can use it without worry of hardening.


Sites can also use portable mixers onside without the need of trucks, but is usually the output is lesser of trucks. There are a variety of trucks, trailers, portable on-site that can be used for concrete. Even a wheelbarrow can be used for creation of, and transport of, concrete.

Whether it is a plant or truck, concrete is prepared as a thick (or viscus) fluid, so it can be poured into the shape desired. As it pours, a variety of tools can be used to help prepare it for its final shape. Whether these are high powered machines, to hand tools. Some tools may be as simple and tall work boots to walk into the concrete. Other may involve a vibrating tool to try to push air bubbles out of concrete.

During the creation of the Hoover Dam, the concrete was poured in sections at a time. This concrete was very hot, but also quite massive. Anywhere concrete was poured, there were water pipes laid down first, so when the concrete needed to harden, it would blast very cold water through it to help reduce the temperature. Without this process, it might have taken well over 100 years for the concrete to cool down.



We have discussed this quite often in this article, but what is it? Put simply, how easy is it to work with. With our concrete in liquid form, how easy will it mold itself to a desired shape. A lot of careful planning goes into mixing concrete for a project, but even then, it is not always exactly what is needed.

If after testing, known as a slump test, the concrete mixture is not set to the standard needed, more water or admixtures can be added to get the desired workability. However, while adding more water can help, too much water can create bleeding (such as water going into the ground) or separation of cement and aggregates.


Once the concrete is the desirable quality, it can be poured and be cured.


Cured is basically cooling down and hardening. Important thing to note is that concrete takes time to cool down and to harden. It’s a process that can take a full day before it has any strength (albeit still weak), but will take up to 4 weeks to gain 90% of its strength. However, it can continue to gain strength over the years.

However, it is not something you can set and walk away from. Concrete needs the correct amount of moisture for the first few days. In the first three days, the concrete is kept moist, likely with spraying or flooding (ponding) the cement structure. This prevents tensile stress on the concrete, and allows it to gain strength to deal with those stresses properly. Skipping this step can result in shrinkage and cracking. This can be easily done in a controlled environment, but when done on site, not so much.

You can also use a moist tarp or plastic sheeting.


Concrete has high compression strength, but low tensile strength.

Compression strength is the measurement of forces being pushed on it and how well, say concrete, can withstand that pressure. Concrete is very good at this. Tensile Strength is a measurement of stretching, or pulling a part.

Because of it’s compression strength, concrete is ideal for the use of structures. However, build a structure too high, and it begins to break, as various forces start pushing and pulling the structure.

To combat this, we have reinforced concrete. Reinforced concrete is basically putting rebar or metal poles/strips in concrete, often steel. This gives concrete more tensile strength, and allows skyscrapers we know today. Reinforced concrete is the most common form of concrete.


Concrete can also make use of cables for concrete of long distances.

Shrinkage is not the only problem concrete faces when it comes to cracking. Perhaps the worst thing for concrete is ice. Ice by itself doesn’t affect concrete, but the process of freezing and thawing can cause the surface structure of concrete to fracture. Over time, this forms as cracks, and with cracks, greater opportunity for freezing-thawing process to get deeper into concrete.

Concrete also makes a good insulator. With it in walls, little air can get in or out, keeping a house at a consistent temperature. Concrete is also ideal for absorbing noise. Unfortunately, it can also be good at absorbing Internet WiFi signals in your home with a standard wireless router. Some stones can have crystals within them, that can absorb electronic signals, plus the thickness of the walls is a concern.

While concrete is good against wind such as tornados and hurricanes, it is bad against wind with higher structures. Concrete also has issues with earthquakes. Due to the inflexibility of concrete, it is easy to tear concrete, even with steel beams. However, reinforced concrete has a better chance at withstanding forces created by natural disasters than concrete without it.

There is much more to be said about concrete than what is listed here, but as always, this is meant more as an introduction rather than a complete picture. This should get you off to a good start in understanding how concrete works and how it would be used in your book.


Prehistory (2.5 million years ago to 3600BC)

Concrete was discovered to have been created through combustion in 1960’s dating back 12 million years ago. Concrete may form on its own naturally, but likely very rare.

Concrete was not really used during this time, except in the form of mortar. While Mortar and Concrete have differences, in a way, mortar is a binder and bricks/rocks for building are like an aggregate. For this, use of Mortar is part of the history of Concrete. However, any use of concrete as concrete itself was not used save for a few exceptions.

Syrians used a form of concrete in 6500 BC using fire pits made of limestone accidentally discovered of cooked limestone as a building material. This led to the use of rubble-wall houses with concrete floors by 700 BC.

Around 5600 BC, concrete was used near the Danube River for floors for huts. They used red lime, sand, gravel and water.

Ancient Age (3600BC to 800BC)

Better development of mortar was seen during this time.

3000 BC saw the Chinese use a form of cement in their boats, binding bamboo together, as well as the use of it in the Great Wall of China. It has been found that the Chinese used sticky rice in their mix.

Egyptians in 2500 BC began using gypsum in their mortars for many aspects of their society, including the great pyramids.


Age of Antiquity (800BC to 500AD)

Assyrians in Babylonian around 800 BC used a three different types of mortars:

  • Clay/mud with straw
  • Bitumen
  • Lime Cement

600 BC, the Greeks were using volcanic ash from Santorini Island for mortars, finding it superior for water protection.

However, in 300 BC, the Romans used volcanic ash called pozzuolana from Pozzouli near the bay of Naples. They begin to use this for concrete, likely used it mortars first and noted its use benefit when mixed with water. Early structures by the Romans were weak, but they soon developed Roman Concrete, which was used in the construction of the Coliseum in 82 AD and Pantheon in 128 AD. It had a 142ft dome diameter, which remained the largest one until 1900’s.


Romans also used animal fat, milk, animal blood, and even horse hairs as admixtures.

By 470’s, Rome fell and the techniques for Roman Concrete were lost. From this time, the use of concrete, rather than just as a mortar, was not used in the Middle Ages.

Middle Ages (500AD – 1500AD)

During the middle ages, only limestone mortar was used. All large building used stone and mortar. There is some suggestion that in 700 AD, Normans brought the use of cement to the English, and the Tower of London and the White Tower made use of concrete. I am unable to get more information on this.

Renaissance (1400AD – 1700AD)

By 1414, manuscripts of Roman Pollio Vitruvius contained information about pozzolan cement were discovered. Fra Giocondo would use pozzolan cement in construction of the pier of the Pont de Notre Dame in Paris in 1499. This would be the first use of concrete from a modern standard since the fall of Rome. (Over 1000 years).

Industrial Revolution (1700AD – 1900AD)

In 1759, John Smeaton, known as the father of civil engineering, finished work on Eddystone Lighthouse which used a substance he made called hydralic lime, as a mortar that can be harden underwater.

In 1824, Joseph Aspdin patent Portland Cement.

First concrete road was completed in Austria in the 1850’s.

1854 – William B. Wilkinson is credit for building the first structure using reinforced concrete, but only used it in the flooring.

In 1867, Portland Concrete was used in the London sewer system. In the same year, Joseph Monier patent the use of iron beams in concrete.

1884 – Earnest L. Ransom patent the use of twisted metal rods in concrete.

1884 – Frederick Ransome invented a rotary kiln, that made production of cement much easier.

1889 – First reinforced concrete bridge is built by Gyozo Mihailich.

1891 – George Bartholomew builds the first concrete road.

NOTE: Asphalt is considered to be a type of concrete that uses petroleum. However, concrete roads are far superior than that of Asphalt, it is also more expensive. Asphalt will be discussed in more detail likely in the petroleum in the near future.

Post-Industrial (1900AD – 1945AD)

1904 – Ingalls building is built, considered the first skyscraper. Made use of reinforced concrete.

1909 – Thomas Edison received patent for rotary kilns in the US.

1918 – Due to war and shortage of metal, a concrete ship was made. Named Atlantus.

1936 – Hoover Dam was built.

Atomic Era (1945 – 1980)

1945 – Devastated countries of WWII made use of recycling concrete to clean up the streets and build new structures.

Information Age (1970 – Present)

1970’s – Fiber reinforcement introduced to concrete.

1985 – Silica Fume used in concrete.

1995 – Concrete used as an insulation for homes.

Future Age

To build a society, you need concrete. Very likely, nothing will ever beat concrete as a building material. Even futuristic societies will make use of concrete in some form or fashion, even with skyscrapers that go even higher than we thought possible.

The future of concrete is to find ways to overcome the weakness of concrete or improve the process to make processing more friendly to the environment.

For instance, Peter Trimble at the University of Edinburgh, discovered a way to use bacterium with binding properties as a cement that promises 70% of the strength of convention concrete. This process can be seen as a green alternative to making cement.

Other attempts at improving the compression strength, was the use of steel fibers and quartz as aggregates at the University of Tehran. It had a strength of 410 MPa, where Ultra-High Performance Concrete has a strength of 800 MPa. Giving the possibility to create even stronger concrete with new innovate uses with current techniques.

Another interesting technology being explored is self-repairing concrete. I’m sure you’re thinking of nanobots here, but nothing like that. At Ghent University, they are using special polymers, that when concrete is cracked, if you apply water to it, the polymers will expand and seal the crack.

Another approach to self-repairing concrete, similar to Peter Trimble, is the use of bacterium at Delft University of Technology. When a crack appears, with a little bit of water, a bacteria will produce calcium carbonate, which will then seal up any cracks.

With the possibility of space travel, anywhere you go in this universe, the one thing you will find is rocks. Rocks can be made as an aggregate. If you have a supply of water (whether at location or you brought it with you) and have a binder such as cement, then you can make concrete. There are plans to moon rocks, or Lunar regolith, as an aggregate material for concrete. While it wouldn’t be an alternative for Earth, it can be something to use for construction on the moon, which would make colonization of the moon easier.

Perhaps in going to other planets, you find a mineral that is more dense than anything we find on Earth. This might make concrete even more tough.

When you look at futuristic cities, I want you to pay attention to the fact that you are looking at a form of concrete. Whatever is used in the concrete to make it, it is basically a form of stone repurposed as a building material. If you choose to use another material for your story, realize that it must be as strong as and easily produced as concrete. Lacking that, any material as a replacement for concrete will likely be used as a partial replacement, rather than a full replacement, somehow used in conjunction with concrete. Unless of course, concrete is outlawed.


I realize that most worldbuilding is done for fantasy stories versus science fiction. While science fiction will still employ these elements, there is less need to do so for an entire galaxy or universe versus one planet. Fantasy definitely caters to one planet.

Many fantasy stories look at what life was like during the Middle Ages. Not a bad idea, but you will notice a pattern in our history. That many innovations in history were lost with the fall of Rome, and took the industrial revolution to recapture. While the Middle Ages had inventions to help them, most never recaptured what the Romans had.

When designing your fictional world, consider what our world would have been like if Rome hadn’t fallen, or the next civilization picked up where Rome left off. Rome had the use of concrete, and a technique that was reshaping their society. They used concrete to build roads. If those techniques had survived the fall of Rome, then perhaps your kingdom’s castle would be made of concrete rather than stone and mortar.

Concrete is an important building material that can help shape society. With it, metal can be a part of shaping society as well. To this effect, concrete and metal go hand-in-hand. As we can see, some cultures were using some form of concrete before history was written down. Many was in the forms of mortar, but some used actual concrete.

However, the use of concrete in your story will likely be limited, unless you are highly detailed oreintated and plan every detail you can of your story. While using concrete for your story might help make society more enhanced, it may not play anything to the overall plot. But then, you never know.

With concrete and your story, whether as a book or video game, ask yourself where concrete fits in. Just because a time period on Earth didn’t have it, doesn’t mean your story can’t. Remember that the fall of Rome in the 400’s AD to the reintroduction of concrete in the 1700’s, was over 1000 years of history that had to almost start over. If that 1300 years had built upon what the Romans had done, imagine how our society today would have been impacted.

Concrete is important. It can be used in a vast variety of ways, from sidewalks to boats. Perhaps even spaceships. It is very difficult to go anywhere in this world without seeing some form of concrete.

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