Repair Consultancy

This page outlines some of the principles of concrete repair and notes BCRC expertise in each area.

People

BCRC consultants are amongst the worlds leading experts in concrete repair (refer to our “People” brochure). Our consultants have had led multi million dollar research programmes, been responsible for multi million dollar repair projects to buildings, bridges, and industrial plant, developed repair materials and managed highly regarded concrete repair training programmes.

Right: 3 day repair course arrange by BCRC’s Frank Papworth. Included 1 days practical on a demonstration structure

First step is to assess cause and extent of damage

The standard and correct approach to concrete repair is to assess the cause of failure and extent of damage first. Incorrect diagnosis can lead to expensive errors in repair. BCRC have the largest range of field concrete testing equipment in Australia. And are experts in the field of deterioration. They are the Durability Consultants on some of Australia’s largest projects.

Right – BCRC’s assessment of leaking cracks in a stadium floor slab found extensive delamination and traced the problem to overflowing down pipes and changed the nature of the repairs required.

Access

The quality of repair will be influenced by the access system. While small repairs can be undertaken from experts suspended on ropes major repairs have to be undertaken from stable platforms. BCRC are familiar with the affect on quality and time from working using different access systems.






 

Break Out

There are a wide variety of breakout systems available. These include jack hammers, explosives, water blasting, expansive chemicals and diamond sawing. BCRC are experienced in these methods and understand the difficulties with each. We are also aware of the high cost of breakout, particularly behind congested reinforcement, and the need to limit breakout by use of alternative repair systems in some circumstance.

Right – Explosives used to remove contaminated concrete

Reinforcement

Structural – Reinforcement is often included as temperature steel and it may be redundant from a structural perspective. By contrast it may have lost sufficient section that new reinforcement must be included in the repair.

Alternatives – There are alternative materials to the use of steel bar for reinforcement. In some repairs it may be advantageous to remove the steel and replace it with less corrosive types (eg stainless steel, carbon fibre or polymer types). In other cases the steel may be able to be made redundant by alternative designs.

Surface Treatment - There are various surface treatments available for reinforcement; epoxy, zinc rich epoxy, cementitious. All have there application depending on the overall design of the repair system. BCRC's approach is shown below:
 

 Reinforcement Treatment for Different Repair Situations

		Expected area of incipient anodes
		Low*	Moderate*	High (assumes adequate galvanic anode at edges of repair)
				Bar thoroughly cleaned	Risk of residual chlorides in pits
Risk of further chlorides to bar after repair	Low	Cement Unnecessary to protect bar from chlorides or surrounding steel from incipient anode. HP cementitious ensures passive bar and base level protection	Epoxy As the risk of incipient anodes increases the cementitious coating is not advisable is it provides a low steel potential and drives up the potential difference to surrounding steel. Epoxy insulates the bar and takes it out of the circuit.	Cement With the incipient anodes taken care of by anodes cementitious provides the necessary protection.	Zinc Rich Risk of continued corrosion under the cementitious reduced by zinc rich providing active protection
	High	Zinc Rich Gives excellent barrier plus galvanic protection. Low rate of consumption as only small incipient areas to protect	Zinc Rich + Epoxy There is some danger that epoxy alone will fail at minor damage and some danger that zinc rich will be consumed. The combination may be economic but either may be selected on its own based on the relative risk of damage and consumption.	Zinc Rich With the incipient anodes taken care of by anodes zinc rich provides the necessary protection

 

Crack Repair

The first step is assessing whether the crack requires repair and if so to assess the condition and movement at the crack. BCRC have many corrosion and penetrability models to determine if the cracks will be detrimental to the structure. We also have a range of devices for measuring crack width and movement.

Right –BCRC’s Tien Chang developed a microcement (6-12μm particle size) grout that was used successfully to repassivate steel & seal cracks in an immersed tunnel.

Impregnation – Cracks can be injected using polyurethanes, epoxy resins, acrylics, methacrylates, and micro-cements. The type and pressure depends on the application. BCRC have been involved in some of the most difficult crack repair projects and have developed systems for localised cathodic protection at  cracks and micro cement injection to re-passivate steel at cracks.

Below – Shopping centre car park where BCRC specified sealing of some cracks and deck coating in other areas due to leakage potential

Surface Sealing – In many instances it is wrong or unnecessary to impregnate cracks. Surface sealing may prevent the ingress of contaminants and be all that is necessary to prevent deterioration. One of the main issues is to ensure adequate movement capacity of the sealant material. Generally this means routing out the crack to provide an adequate width of repair that depends on the properties of the surface sealant. In some case the sealant may also provide a reservoir that feeds the crack to promote crystal growth at depth.

Right: Hypalon bandage system used for tunnels cracks under 90m water pressure head.

Concrete Reinstatement

Various methods of concrete reinstatement are available. Selection of which method to use will depend on cost and access.

Insitu Cast Concrete – For large repairs a repair concrete can be developed for most applications. The concrete must  flow well, be cohesive and have zero bleed. The placing methods are also important to ensure the concrete will remain in intimate contact with adjacent concrete. BCRC’s Frank Papworth has been involved in development of such mixes on various projects (right).

Proprietary Render - For smaller repair proprietary renders are often used. These have shrinkage compensation and low penetrability and properties that matching the parent concrete’s elastic modulus and coefficient of thermal expansion. BCRC’s Marton Marosszeky was responsible for a major research project on assessment of repair materials and developed a model for assessing crack propensity. This later resulted in a special expanding orthogonal ring test to determine cracking resistance.

Shotcrete – Shotcrete can be used for concrete repair but quality control is a primary issue. Shotcrete is particularly useful for soffits where access for formed concrete is difficult. BCRC’s Robert Munn has had extensive experience in the design of shotcrete mix design and BCRC’s Frank Papworth has published various papers on the use of fibre reinforced shotcrete.

Epoxy – Epoxy repairs are generally only suitable for very small patches. The difference in properties between epoxy and concrete have been found to lead to interface failure after a few years.

Right – BCRC’s design of mixed usage of remote anode and sacrificial anodes in stabilising corrosion on a wartime fortress.

Electrochemical Methods

BCRC’s Papworth and Broomfield led the pioneering research on paint based CP systems at TWRL in the UK. Broomfield went on to further research and development of CP systems as part of the US SHRP program while Papworth was  responsible for some of the first Cathodic protection, chloride extraction and realkalisation systems used in Australia approximately 20yeras ago.
Right - Repair using paint based CP system developed under BCRC’s Frank Papworth

Cathodic Protection – There are many types of CP systems. BCRC’s consultants are highly experienced in most types and can provide design and commissioning advice on Thermal Sprayed Since, Mesh Anode (slotted and surface systems), paint based systems, remote anode systems and internal anode systems.

Below – BCRC’s investigation of a bridge identified a small area of corrosion ideally suited to sacrificial anodes rather than more global impressed current CP systems.

Sacrificial Anodes – Galvanic anodes are simple to design and install and are ideal for small localised repairs where the installation cost of CP control equipment would be high. They are also very useful to prevent incipient anode failures in smaller repairs.

Chloride Extraction - Chloride extraction was first trialled in Australia by BCRC’s Frank Papworth in the 1980’s (right). It can be highly successful, particularly where the chlorides have not reached behind the bar.

Right – First Chloride extraction project in Australia managed by BCRC’s Frank Papworth

Realkalisation - BCRC’s John Broomfield has significant experience in the application of realkalisation.

Below- Anode mesh system for balconies designed by BCRC’s J.Au

Corrosion Inhibitors - Migrating corrosion inhibitors can be used for repair where the cover is low or the concrete is porous. Where concrete has spalled inhibitors can also be used in the repair concrete.


 

Chemical Attack

There are a wide range of repair methods associated with different causes of repair e.g. Lithium for AAR, moisture barriers for DEF and AAR, BCRC are familiar with most specialist repair materials and can bring the correct system to bear.

Right – BCRC advised on resistant concrete and high build epoxy coating for hydrogen sulphide induced acid attack in sewage digestor. BCRC also have experience in geopolymer concrete for acid resistance.

Historic Structures

One of the main causes of deterioration in historic structures is salt and ettringite crystals leading to bursting pressures. BCRC are familiar with the research on predicting salt etching and the research on materials used to prevent crystal growth pressures.

Other key issues are pointing, rendering, capping and grouting. Apart from BCRC’s materials experts we have a number of professional expert in requirements for matching materials in historic structures including the use of lime mortars.

Economic Assessment

Some repairs are put forward as being superior because they last longer. This is not the case. In 30 years of concrete repair we have found that most repair methods are legitimate and the decision on which method to use should be based on a whole of life costing, including all indirect costs, the clients budgetary restraints and consideration of the asset value affects. It all comes down to money.

BCRC are able to provide indicative costs of initial repair and maintenance over the life of a structure and through liaison with the client factor in costs such as lost rents, asset devaluation and public costs.

Options for different structures when deterioration begins to become noticeable at 10 years.

Below - Inspection and repair recommendations for three turn of the century reservoirs developed by BCRC’s Keiran Mathieu