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Concrete mix percentage

The „concrete mix percentage” as an expression is related to the concrete made under domestic circumstances.

The information hunger however is common in each private person or company interested in manufacturing concrete: How much should I add of each concrete ingredient in order to get a quality material according to my expectations with the least possible cost?

The home made concrete preparation mostly uses the maison’s rule, that determines the concrete mix percentage similarly to grandma’s cake receipe: 3 lapát sóder, 1 lapat cement, water as much as it can take. We can tate with assurance that this is the way to prepare the most expensive concrete of the least quality.

What is concrete? Mineral pieces and mineral grains of various sizes (gravel and sand) [sometimes other materials like steel- or ironstripes, polistirol- or clay balls... ] glued together with a waterbase adhesive (cement [sometimes other chemicals]).


The concrete is therefore composed of:

  •  

    Aggregate mix: gravel and sand of various size – this in itself means more ingredients
    Cement
    Water
    Chemicals
    Additives

     

 

The first three materials can be found in all concrete types. Based on the price the water is the cheapest (we hope it stays like this), the cement is the most expensive. The target therefore is the least cement consumption.

 

The condition of a good concrete with simple words: the perfect gluing of the hard ingredients with filling of the inner spaces. The glue – so to say the mix of cement and water (cementmash) – we need exactly the quantity that fills this space. If it is less, it is obviously not good as the gluing is going to be insufficiant (unsaturated concrete). If we use more cementmash than the existing space, the gluable particles, grains are going to be further from each other and we utilized more cement tha necessary (oversaturated concrete – in special cases this could be needed in 5-10%, but generally it is in a vain).

The so called „inner space” officially is defined as the mash demand of the aggregate.. (This expression is explored more in another article of our site.)

The mash demand is a value given in liter that the manufacturer or distributor communicates in better cases about the aggregate mixes analized in a laboratory.

In case of an optimally saturated cement mash the strength depends on the quality of the cement (or other occasionally added chemicals) and on the proportion of the water and cement called as water/cement factor. Without going into further details: it id good to know: the higher the water content compared to the cement the less strength in the hardened concrete. (Beyond the chemical explanation of the phenomena we can easily understand that in a given volume having more of one component the other one will have less space.)

The suggested dosage percentages of the different chemicals are written amongst its characteristics.

 

The optimum mixing percentage of the concrete therefore depends remarkedly on the quality of its composition, their physical, chemical and geometrical characterisitcs. If we intend to act efficiently and we do not have a possibility to examine the materials and do adequate calculations, we can assume that – above a certain quantity – it is cheaper and safer to buy the concrete from a licenced concrete factory than mix it on the ground.


 

Stumpf Attila