How to Make Roman Concrete - A Primitive Technology for Future Generations

I love history and enjoy watching videos about ancient technology, but the number of times the 'experts' say 'we don't know how they did it - must have been done by aliens' annoys me a lot. I think rocks are something that mankind was capable of figuring out without help from aliens. It's far more likely that people just stopped transferring the How-To's of primitive and ancient technology. So, for the sake of future generations, here's a How-To for making Roman Concrete. You never know when someone will need to build a stable - and not deadly - fieldstone dwelling using a home-made mortar. This method is simple, so tell your kids and friends.

How to Make Roman Concrete
Corporals Corner shows us how to take limestone or seashells, then burn and slake them.

After that, you'll grind up the volcanic ash in a blender to get a fine powder to mix with your dried quicklime/calcium hydroxide/slaked lime.

You'll need an aggregate. This video comparison-tests volcanic rock as aggregate and the alternative regular granite/quartz/limestone/other gravel and the end result was just as good as the version with volcanic rock used as more authentic aggregate, so there's room to improvise to use local resources.

You'll also need volcanic ash, which might be a bit tricky to source locally for most people. Volcanic ash consists of fragments of pulverized rock, minerals and volcanic glass. Perhaps pulverized locally available rock and quartz sand will produce a reasonable alternative. I also see that Portland Cement 'clinker' contains clay as the source of aluminosilicate.

Finally, the Romans used seawater, instead of freshwater to moisten their concrete. Seawater also contains an assortment of metals and minerals. You might try dissolving sea salt in water to substitute for seawater.

The ratio of quicklime to volcanic ash is 1:2 and water is added to make a putty, the consistency of clay and not the slurry of standard concrete blends made with Portland cement.

This video, covering the history of concrete, identifies the general constituents of Portland cement:

Minerals and metals, such as powdered iron and aluminum are added to strengthen the Portland cement blend. The video also discusses the secret ingredient in Roman Concrete, carried in the volcanic ash - possolan.

Pozzolana, also known as pozzolanic ash (pulvis puteolanus in Latin), is a siliceous or siliceous and aluminous material which reacts with calcium hydroxide in the presence of water at room temperature (cf. pozzolanic reaction). In this reaction insoluble calcium silicate hydrate and calcium aluminate hydrate compounds are formed possessing cementitious properties.

The designation pozzolana is derived from one of the primary deposits of volcanic ash used by the Romans in Italy, at Pozzuoli. Nowadays the definition of pozzolana encompasses any volcanic material (pumice or volcanic ash), predominantly composed of fine volcanic glass, that is used as a pozzolan. Note the difference with the term pozzolan, which exerts no bearing on the specific origin of the material, as opposed to pozzolana, which can only be used for pozzolans of volcanic origin, primarily composed of volcanic glass.
https://en.wikipedia.org/wiki/Pozzolana

Roman Concrete
https://en.wikipedia.org/wiki/Roman_concrete

Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates, (3 CaO·SiO2, and 2 CaO·SiO2), the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO2 shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed 5.0% by mass.
https://en.wikipedia.org/wiki/Portland_cement

Clinker
In the manufacture of Portland cement, clinker occurs as lumps or nodules, usually 3 millimetres (0.12 in) to 25 millimetres (0.98 in) in diameter, produced by sintering (fused together without melting to the point of liquefaction) limestone and aluminosilicate materials such as clay during the cement kiln stage.
https://en.wikipedia.org/wiki/Clinker_(cement)

Corporals Corner also has a version that uses terracotta and brick instead of volcanic ash. Here's the link for that video: