Concrete Repairs
Concrete repair has been the core activity of the business since 1963. Reinforced concrete is a very durable construction material but it needs to be maintained like most other products if it is to achieve its design life.
Apart from physical damage to the concrete the main reason for deterioration is corrosion of the reinforcement. Steel reinforcement in the highly alkaline environment provided by the concrete remains in a passive state because a stable oxide film on the steel surface prevents corrosion activity. However this oxide film becomes unstable if the concrete carbonates and it can also be broken down when there are sufficiently high levels of chloride.
Carbonation of the concrete occurs when carbon dioxide in the atmosphere dissolves into the concrete pore water to form carbonic acid. This reduces the alkalinity of the concrete and eventually when the process reaches the reinforcement it destabilises the oxide film. The process is time dependent and the rate is a function of concrete quality.
High chloride ion levels at the reinforcement can locally disrupt the protective oxide film and initiate pitting corrosion. The chlorides may have been added to the concrete when cast in the form of calcium chloride, which was used as an accelerator up until 1970 or unwashed marine aggregate may have been used. Alternatively chlorides from an external source such as marine environment or de-icing salts may enter the concrete over a period of time. Before repairing a reinforced concrete structure it is important to undertake a detailed survey to identify the reasons for the deterioration. TA Taylor is able to provide a comprehensive consultancy service to inspect and report on concrete deterioration.
Areas of speciality
- Spalling concrete repairs
- Structural repairs
- Marine structure repairs
- Grout injection
- Construction repairs
Repair Techniques
(1) On Site Survey
With traditional repair systems only the cracked and spilling areas of concrete are repaired. These are identified by close visual inspection and hammer testing of the concrete.
(2) Concrete Breakout
The defective concrete is normally repaired using electric or pneumatic breakers to completely expose the corroding reinforcement. Saw cutting around the perimeter will avoid any feather edges to the repair area.
An alternative method of breakout is to use high-pressure water, which is called hydro demolition. This removes the concrete and also cleans the steel at the same time. It is particularly effective for high volume repair areas or in environmentally sensitive situations where noise and vibration may be a problem. However it is also a dangerous procedure requiring very careful control at all times.
(3) Concrete Reinstatement
The exposed steel is cleaned, and treated and then the concrete is reinstated in accordance with the manufacturers instructions. The method of reinstatement can be either hand placed mortars, shuttered repairs, or sprayed concrete. Hand placed mortars are typically used for building repairs where the repair areas are small.
Larger repairs can be shuttered and re-cast using a flow able concrete. Alternatively they can be sprayed back using either a wet or dry granite process.
(4) Surface Coatings
The corrosion of reinforcement requires both oxygen and water to support the activity. The application of a good protective coating will slow down any corrosion and reduce further carbonation or chloride contamination.
To ensure a good bond the concrete substrate needs to be correctly prepared. Existing paint surfaces will need to be removed by grit blasting and the exposed surface prepared using a thin coat leveling mortar. Unpainted surfaces are cleaned by high pressure water jetting or possibly light grit blasting.
The protective coatings can be applied by brush, roller or spray depending on requirements.
