Cracks on concrete balconies- Where did they come from?

Posted by Pedram Mojarrad on

Late last year, GESS were engaged in forensic studies and then repair of balconies (8 of them) in a residential buildings in Sydney- Northern Beaches.

There types of cracks were quite obvious:

1- Side cracks; which we figured out to be due to chloride attack, and
2- Flexural cracks (soffit of slab); which are structural cracks.



Reinforcement corrosion has become a serious, widespread problem worldwide, with costly repair methods. The steel corrosion in reinforced concrete reduces its durability and can even result in failure of the structure.

Corrosion is a phenomenon which results in the deterioration or destruction of a material when they are exposed to different environmental conditions, such as chloride or carbonation.

Corrosion of concrete involves an electrochemical process in which both flow of electrical currents and chemical reactions occur. The steel in reinforced concrete structures is in passive conditions and are protected by a thin layer of oxide which is due to the alkalinity of concrete (pH between 12 to 13).


Chloride attack (or sometimes carbonation) are the main causes of corrosion of concrete rebars.

Corrosion of rebars is a very common problem in Sydney and all other coastal areas. When rebar is corroded, its volume changes (expands) and it will cause cracking in the concrete.


What did we do?

At first, we had to open up some of the cracks to figure out what the root cause of cracking is and to what extent this crack has been developed.

The main cause for this corrosion could be the airborne chloride from the sea breeze. 

Reinforced concrete can be protected against the invasive ions ingress that cause corrosion. But, what usually happens is that the concrete is not protected, and only once the rebar in concrete gets corroded and signs of corrosion pop out, the asset owner/manager seeks advice on what to do.

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