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Concrete patina

About High Performance Concrete

Concrete patina

Concrete is a vivid and natural material that changes over time. 

Hi-Con products are made of high performance concrete, which as regular concrete, must be expected to change over time. The color and texture change during the lifetime of the concrete and this variation is the aesthetic strength of concrete and contributes to a vivid and varied expression. 

The concrete patinates over time and changes its appearance. This change is a part of the aesthetic expression of the concrete. The patina concerns only the outer few milimeters of the surface and has no effect on the construction or durability of the concrete. It is only an aesthetic issue.

Products from Hi-Con will also patinate, but often slower and less than regular concrete. 

Erosion

Surfaces erode over time due to normal weather conditions as rain and wind. Concrete erode primarily through a cycle of frost and thaw as the chalk is washed out. 

The result is that the cement paste of the concrete vanishes while the sand and stone become more visible at the surface of the concrete. The surface appears more rough and porous and also often darker. The increased porousity is contributing to an accelleration of other types of patina: Soiling and fouling.

Soiling of concrete

As long as the surface of the concrete is dense and smooth (the cement paste is intact) particles as soot etc. will be deposited at the surface, but also easily be washed off by the rain.

When a surface erodes, small pores and cracks will be accessible. Soil sticts easily to an eroded surface and is also washed into cracks and pores by the rain. It must be expected that a concrete surface over time will be difficult to keep entirely clean. 

Fouling

Fouling is a term used for the growth of small plants on surfaces as concrete. Fouling requires sun light, water and nutrition like any other plants. When the surface of the concrete is exposed to these factors, fouling will happen after a few years. 

A few years will typically pass before the first signs of fouling show. The reason for this is that the water inside the concrete is very alkaline and prevents plant growth. During time the alkaline level lowers due to an reaction with CO2 from the air. When the pH-value is low enough, algae, mosses and other plants will be able to take root at the surface. 

Efflorescence

Efflorescence can take place on all kinds of concrete in a period of time after casting. The efflorescence is recognised as a white vail on the surface that temporarily colors the concrete into a lighter tone of color. The efflorescence is harmless to the concrete and usually disappears by itself after one to two years, as long as the concrete is exposed to weather and wind. Efflorescence is alone an aesthetic challenge. 

When the concrete is young the surface is porous and the calciumhydroxide in the concrete will form chalk as a result of a chemical reaction. This reaction would in principle go on and on, but in reality the process ends when the pores are blocked by chalk.  This happens after one to two years. 

To avoid efflorescence it is very important to keep the newly cast concrete indoors - especially if the elements are for indoor use. 

Read more about efflorescence at the Concrete Blog

 

Do you want to know more about patina of concrete?

Tommy Bæk Hansen
Group Product Development Manager

Bendt Kjær Aarup
Group Material Development Manager