My pond will be right next to our house. Since I want it to stay level “forever”, I will build my pond walls out brick, and I’ll need a concrete foundation.

Basics of concrete

Concrete is made with two main ingredients: aggregate and paste.

The paste contains (portland) cement and water. this is the glue that will bind the other ingredients when it sets. Basically, cement turns into a synthetic rock when it hydrates.

The aggregate usually is a mix of gravel and sand. This serves as filler or bulk material. The type of aggregate, among many other factors, influences the strength of a concrete.

Sand mining

Ever since I read an article about the Indian sand mafia, I’ve been intrigued by the surprising scarcity of a seemingly endless resource. According to a 2023 UN report, humans use 50 billion tonnes of high quality sand every year, mostly for construction. At over 6 tonnes per person, that’s unfortunately more than Earth’s geological cycle regenerates. Therefore, I felt kinda bad overusing this material and I started thinking about alternatives…

Soil cement

A while ago, I stumbled upon a YouTube video about soil cement. This is a cement-based product made with local dirt instead of builders’ sand. It’s often used in road stabilisation and airports.

What a beautifully simple idea. Why would you use high grade, uniform sand to build something that is structurally quite trivial? Using local soil as an aggregate makes so much sense. It saves money, it saves me from finding places to get rid of the soil I dig up, and it avoids using a critical resource.

My situation

I am doing some basic concrete research now, and I haven’t found anything yet to discourage me from trying to replace the builders’ sand in my concrete mix with my own soil. The research is more busywork than anything else, since, deep inside, I have already decided that I’m just gonna try it anyways. I might even try replacing the sand in my mortar.

Be aware though, my soil is a loamy sand. This makes it more suitable for mixing into a concrete mix than a soil with a high clay content.

• The mixing itself is easier, since I won’t have too much difficulty breaking up clumps. And I’m buying a concrete mixer.
• The result is also stronger for this type of soil than for a clay soil. Besides, I’ll probably still use regular gravel as coarse aggregate.

Finally, as I already mentioned, the structure won’t bear high loads. I would be more cautious if I was designing a building.