Concrete damages

Time has shown that concrete is not as resistant against ageing as first expected. There are different reasons to this occurrence, and we will here give a brief summary of the main reasons.

Chloride penetration

Chloride (salt) brought by winds or spread on roads and bridges in order to prevent ice from being created on road surfaces, is penetrating the concrete by cracks or sucked in with water. Once inside, the chloride causes corrosion at the rebars. The rebars expand when they corrode and consequently crack the surrounding concrete. These damages lead to an increased penetration of water and chloride, which speed up the ageing procedure. Soon big pieces of bad concrete are falling down. The higher concentration of chloride, the bigger pieces falling down.

Freeze-thaw cycles

A similar cracking procedure of the concrete is occurring when water and moist inside the concrete freeze and thereby expand. The concrete can just withstand a specific amount of freezing cycles. This means that a construction of concrete e.g. a bridge in an area where the temperature will go up and below the freezing point will be ageing much faster than one in a warmer or cooler place. In fact you can put a piece of sound concrete in a freezer and, without any other affection, let the temperature varies over and below the freezing point. When the specific resistance against freeze-thaw cycles is reached, all that remains of the once so solid concrete is a just a heap of dust.

Consequently, the demolition first occurs in the surface area. Since concrete is a complex material the penetration of salt and water, and thereby the damages, differs from one place to another in the same construction. Some parts can be almost intact while others are seriously and deeply injured. When repairing a damaged construction it is of utmost importance to remove all of the bad concrete to avoid encapsulation of these parts and thereby create hidden weakness in the construction. A proper removal of the bad concrete will therefore give a surface with various depths.

Due to a geographical position where such temperature changes, as mentioned above, may occur more than hundred times a year, the Scandinavian countries have been forced to focus on this problem. Accordingly there is a continuous and aggressive research in this subject, not only about the damages, but also to develop methods for practical repairing of the damaged parts in the best and most efficient way. This research and development has created a sophisticated process called the Conjet Method or Hydrodemolition. This method will make it possible to save time and money by fast demolition of only the bad concrete and leaves the sound concrete intact. The reconstruction work of damaged concrete constructions all over the world thereby benefits of this progressing research and development.

Carbonization

Concrete is naturally basic but in contact with the air a chemical reaction caused by the carbon dioxide (CO2) is decreasing the pH value. When decreasing too low (pH < 9) the corrosion of the reinforcement will accelerate (compare with the chloride penetration mentioned above). When this phenomenon occurs the carbonated concrete must be replaced.