Blood Concrete

Table of Contents

Concrete is the main material used to build installations incorporating magic! As such, it is an important tool and all engineers worthy of the name should know how to create and use it.

— Sergeant

Building materials

Building material is a very important aspect of engineering and technology. Metallurgy has always been a valued craft and science, and the progresses in chemistry and alchemy are constantly influencing it. Similarly, glass and materials like porcelain are subjects of intense studies so as to enhance crafting techniques. Even trees and how their care influence the quality of the wood they give is a popular subject of studies.
Therefore, it is rather surprising that this interest has not expanded to other materials such as stone. Beyond identifying the quarries giving the best quality stones and which type of stones is best fitted for each application, there has been little attempt to enhance the stones themselves. This is all because of the invention of concrete, a miracle material easy to create and with which mere stones cannot hope to compete.
While a multitude of concrete recipes exist, the main ingredients have barely changed since Roman time, when its invention created an architectural revolution by freeing them from the restriction of stones and resulting in marvels such as the Coliseum and the dome of the Pantheon.

The dome ceiling of the Pantheon, made of concrete by Macrons on Wikimedia Commons

The reason why concrete recipes have barely been updated in nearly two thousand years is that it's already bloody amazing! It's both lighter and stronger than regular rocks, and it can survive underwater, burning and even earthquake! Mere stones obviously cannot hope to compete and are only used for aesthetic value.

— Sergeant

Concrete recipes

Concrete is a composite material created by mixing water, aggregates (such as mixes of rubble, loose stones and sand) and additives with a fluid cement itself made from grinding and heating a mix of limestone (containing calcium), clay (containing silicon, aluminium and iron) and gypsum (containing sulphates). The mix of cement and water creates a chemical reaction (hydration) that makes it harden and set around the aggregates, while the additives control its properties.
2Ca₃SiO₅ + 7H₂O → 3(CaO)·2(SiO₂)·4(H₂O)(gel) + 3Ca(OH)₂
The first main additive added is pozzolana (volcanic ash). This allows the resulting concrete to be poured and to set underwater, creating an extremely solid material as can be observed by the Roman harbours still present around Europe. This effect is obtained by the sea water slowly dissolving the ash inside the concrete and new minerals such as tobermorite developing in the new space and interlocking with the rest to form a reinforced structure.
Other important additives are blood and animal fat. These additions have two effects. First, the blood and fat react with the rest of the mixture to both accelerate the formation of crystals and create air bubbles that allow the concrete to expand and contract with changes in temperature, thus making it more resistant.
Second, the use of sacrificial blood from either willing or unwilling donors allows for magic to be infused in the concrete so as to give him specific properties. Those properties mostly consist of different types of wards and resistance magic. The owner of the architecture in which the concrete is used can also add their own blood to the mix during a specific ritual so as to gain control of the building afterwards.

Vesuvius volcano

Blood by PublicDomainPictures on Pixabay

Blood binding with concrete is best left with engineers and architects, owners have no business attempting to control finicky magic they barely understand! We've all heard of lords and ladies spending fortunes creating sumptuous palaces and defensive installations with the extraordinarily powerful wards, only for them to immediately fall into the hands of enemies because they were not even able to activate their protections!

— Sergeant