Kari | Concrete tealight holder

A ready-mixed product was out of the question for us from the start, as it leaves little room for adjustment due to the lack of a list of ingredients. So we designed our own concrete using cement, sand and other ingredients.
We started with prior knowledge of the composition of concrete in construction, but determining a concrete recipe for a concrete wall with a thickness of 200 mm is quite different than for a vessel with a wall thickness of 10 mm.
The first and probably easiest step is to adjust the so-called "maximum grain size" to the grading curve of the concrete. The grading curve describes the composition of different grain sizes, from sand to gravel in the concrete. In construction, a maximum grain size of 8 mm is usually chosen for delicate components, but in exceptional cases this can also be smaller. For thick components, such as foundations, a maximum grain size of 32 mm is often chosen. In general, it can be said that the larger the selected maximum grain size, the cheaper the same amount of concrete can be obtained. Due to the nature of the component, however, it is not always sensible to choose the largest possible grain size. This becomes clear when you concrete a container with a wall thickness of 10 mm with a maximum grain size of 8 mm. It just about fits in, but when processing it, you will very quickly notice that the individual grains wedge together and the mold is not filled properly. To avoid this, we use a maximum grain size of 2 mm for most of our products, but for some very delicate pieces we reduce the grain size to less than 1 mm to achieve even better results.
But this only lays the foundation for the concrete recipe, as the maximum grain size only describes the dimensions of the largest grains. However, it is very important to incorporate the right mixture of different grain sizes in the range of 0 - 2 mm into the recipe, as this is the only way to create the densest concrete matrix possible.