Concrete comes under attack from both natural and man-made forces almost from the time it is first formed and poured. The relative rate of degradation resulting from these assaults depends on a wide variety of factors of which only some are controllable.

Man-made forces affecting degradation are often controllable and fall into two general categories: those that cause deterioration because the marketplace was less knowledgeable about concrete 40 years ago and those that cause degradation due to obvious design deficiencies or subsequent neglect. Foremost among all causes of concrete degradation is the internal damage caused by the corrosion of the embedded reinforcing steel. In addition to deterioration of the steel itself, the corrosion also affects the concrete surrounding it, which results in cracking, delamination and spalling. Since virtually all of the concrete found in structures is steel-reinforced, this is a widespread problem. The science surrounding this phenomenon is still evolving. However, it is critical to learn from previous misconceptions to avoid these same pitfalls in the repair process (see Figure 1).

Unfortunately, the methods in which concrete deterioration manifests itself typically do not indicate the true severity of the problem. The first small crack in its protective lining invites intrusion by moisture or corrosive agents. Eventually, the outward symptoms of scaling, cracking and spalling gradually begin to appear.

Deterioration process

One area that frequently experiences deterioration is concrete balconies. With an average rainfall of more than 1.5m per year with high chloride content, the climate in Florida aggressively attacks steel-reinforced materials. Typically wind-driven, the rain is blown onto exterior balconies and walkways. Furthermore, many balconies are now carpeted, which creates problems for the concrete since carpet can retain the moisture and the inherent salts that eventually impact the steel and begin the deterioration process. Water, steel and salt create a simple battery and the steel acts as the anode that sacrifices itself in a galvanic reaction. This reaction changes iron to iron oxide and the larger molecule requires more space. Therefore, the steel expands and forces the concrete cover off, allowing for further water intrusion and acceleration of the deterioration process.

Minimised disruption

Concrete repair integrates new materials with existing materials to form a composite structure that can withstand environmental conditions and operational processes, while at the same time providing extended service life. Obviously, in this market a successful repair undertaking is also one in which disruption to residents is minimised while the repairs are taking place.

Originally constructed in 1976, the 8-storey Lido Surf and Sand condominium development is located on the shores of the Gulf of Mexico. It is subjected to harsh environmental conditions and over the course of its lifetime has been the subject of three concrete restoration projects. A quick and cost-effective solution was needed. Structural Preservation Systems was able to complete the repairs on the balcony slab edges and columns that were cracked and spalled for less than $1 million and also shaved three months off the construction schedule.

Preventative measures

If signs of damage are visible, any delay in seeking repair can only make matters worse. However, visual inspection is how most concrete deterioration is noticed. A host of preventive measures can increase the life of the facility and the time between repairs.

Waterproofing

If this is carried out prior to the appearance of any visible damage, the occurrence of severe problems can be minimised. It is relatively inexpensive to waterproof a concrete deck but costs rapidly accelerate if it becomes necessary to repair deteriorated concrete.

Regular visual inspections

These help identify small problems before they become large. For example, rust stains on slab edges indicate corrosion and cracks on the top of decks could allow water intrusion. Other signs to note are peeling paint or coatings and failed sealants, loose or delaminated tiles or decking, lumps under the carpet, loose grout at handrail post pockets, leaks around doors or windows, wet interior carpet adjacent to exterior walls, damp or musty odours and damp or wet drywall adjacent to exterior walls or openings.

Concluding remarks

The technologies available to repair concrete have advanced far beyond the simple concrete patch and a range of solutions can be used to implement an effective concrete repair programme. A basic understanding of these options - surface repair, protection, stabilisation, strengthening and waterproofing - will allow selection of the best programme. A concrete repair specialist can also help determine both the underlying cause of the problem and the optimal solution.