The first step in the selection of the most effective concrete repair technique is diagnosing the cause of failure, and ensuring that the technique used makes the repaired area resistant to this original cause of failure. If this is not done, the repair will fail; it is also likely that the damage will be extended to the adjoining parts of the structure.

Through inspection, testing and analysis, we at BDS formulate long-term cost-effective repair solutions based on a structural design life desired by the client.

While the repairs we carry out usually follow traditional repair practices, often we have to implement advanced corrosion control techniques as well.

Due to its vast experience in large project execution, BDS has developed expertise in repairs in the following areas:

• Repairs to multi-storeyed buildings
• Repairs to hospital buildings
• Seismic retrofitting to building structures like hospitals and manufacturing plant building
• Repairs to elevated storage reservoirs (ESR)
• Repairs to jetties
• Bridge repairs
• Repairs to typical industrial structures, etc.

The following additional related information is available on this page:

• Accommodating special needs of educational, hospital, commercial and residential buildings
   
• Marine structures
   
• Causes of concrete failure
   
• Traditional repair techniques
   
• Corrosion control techniques
 

EDUCATIONAL, HOSPITAL, COMMERCIAL AND RESIDENTIAL BUILDINGS
Educational, hospital, commercial and residential buildings require a creative, innovative and caring approach, which is sympathetic to the particular operational environment encountered. This includes issues related to noise, dust and safety due to the close interface with the public. BDS’ integrated management system for health, safety, and environment (HSE), enables it to provide a very high standard of customer service for such buildings, and the renovation activities are carried out with minimum disruption to building occupants and users like students, patients, staff and residents.

The projects can often be programmed to be undertaken whilst the building remains operational, so that disruptive work such as concrete demolition is done outside of the building’s normal operating hours.

In industrial and commercial buildings however, an additional very important consideration is the long-term durability of the work. BDS can implement a range of solutions at different levels of the durability-cost scale.

BDS is often required to undertake work during shutdown periods, which requires detailed programming and mobilisation of sufficient resources to complete the work on schedule. At other times the work must be undertaken whilst the plant remains operational, which may require working in very high temperatures and under strict environmental control. Here again, BDS’ integrated management system for health, safety, and environment (HSE), enables successful and safe implementation of the projects.

<<RETURN>>

MARINE STRUCTURES
With its long coastline, India has several marine structures, which are an important part of the country’s infrastructure. These structures are usually made of reinforced concrete and steel. Due to the very aggressive marine environment, over time, chlorides in the seawater penetrate the concrete and set off corrosion of the reinforcement. Similarly, steel structures suffer from accelerated corrosion, which can cause significant loss of steel section.

BDS fully understands the deterioration mechanisms of marine structures and how to deal with them. The repairs to the deteriorated areas of concrete are usually substantial and require careful planning to maintain the integrity of the structure.

To ensure long-term durability of a marine structure, BDS is able to design and install a range of corrosion control systems, which may include protective coatings, or cathodic protection systems, or a combination of both.

The execution of repair works for marine structures needs to be planned carefully with special scaffolding and removable platforms, especially for jetties. At BDS, this is rigorously implemented at site for safe and efficient working.

COMMON CAUSES OF CONCRETE FAILURE
Generally, the cause of concrete failure is one or more of the following reasons:

• Built-in design problems
• Poor construction , defective use of materials
• Environmental & chemical attack
  
• Damage from shrinkage, creep, settlement and thermal contraction
• Mechanical damage due to abrasion and erosion
• Indiscriminate structural modifications & alterations
• Change of loads, overloading
• Poor maintenance
• Failure of sealants and waterproofing membranes
  
• Freeze/thaw damage in cold areas, etc.

Apart from physical damage to the concrete, the other main reason for deterioration is corrosion of the reinforcement. The most common causes for this are:

• Carbonation, and
• Chloride-induced attack.
  

For older buildings with stone or masonry cladding, the problem usually lies in steel frame corrosion, which can cause cracking of the facade.

Corrosion can occur in even the best designed and constructed structures and can be worsened by lack of maintenance. Early assessment of the structure’s condition is vital.

TRADITIONAL REPAIR TECHNIQUES

Step 1: On Site Survey
With traditional repair systems, only the cracked and spalling areas of concrete are repaired. These are identified by close visual inspection and hammer testing of the concrete.

Step 2: Concrete Breakout
Electric or pneumatic breakers are used, wherever possible, to completely expose the corroding reinforcement. Saw cutting is carried out around the perimeter to ensure correct concrete profile with suitable edges in the repair area.

Step 3: Concrete Reinstatement
The exposed steel is cleaned and treated. The concrete is then reinstated in accordance with the manufacturer’s instructions. The method of reinstatement can be either hand placed mortars, shuttered repairs, or sprayed concrete.

Hand placed mortars are typically used where the repair areas are small. Larger repairs can be shuttered and re-cast using a flowable concrete. Alternatively they can be sprayed back using either a wet or dry gunite process. Sprayed concrete can offer several advantages, including quick construction, as shuttering is reduced or eliminated, plus it can be rapidly placed. It also offers a good bond to the substrate.

Step 4: Surface Coatings
The corrosion of reinforcement steel in concrete requires both oxygen and water. The application of a good protective coating will slow down this corrosion process and substantially reduce further carbonation or chloride contamination.

<<RETURN>>

CORROSION CONTROL TECHNIQUES

Corrosion of the reinforcement steel bars is one of the main reasons for deterioration of concrete structures. This steel corrosion costs India crores of rupees every year.

It is important that while we write the specifications for structural repairs, the provison of corrosion control techniques are incorporated.

While traditional repair techniques are perfectly adequate when there is no risk of further corrosion due to carbonation or chlorides, in high corrosion risk areas, it is important to use a corrosion control system for long term durability.

BDS uses the latest systems that offer effective cathodic protection to the reinforcement steel in repair projects. This includes sacrificial coatings, sacrificial anodes, bulk anodes, etc.

The selection of an appropriate cathodic protection system requires expert knowledge, and depends on the existing condition of the steel, surrounding environmental conditions, the type of structure, and the durability required. For example, very critical structures in an aggressive climatic zone require far better and robust techniques to arrest the progress of corrosion.

With our expertise in corrosion control, BDS are able to advise on the most appropriate system.

Our initial condition survey includes the following:

• Visual survey
• Hammer test
• Depth of carbonation
• Chloride profiles
• Half cell potential surveys
• Covermeter

This survey identifies possible corrosion risk in certain elements of the structure. A more detailed survey may be used to focus on these areas. The more detailed survey would include corrosion rate monitoring to assess the rate of reinforcement corrosion, and provide an assessment of the corrosion risk for the structure.

<<RETURN>>