Concrete Repair

BCRC Repair Consultants

For most concrete repair projects the owner should appoint a specialist consultant to assess the repair requirements and manage the repair. Specialist repair contractor may offer to undertake the assessment but 'owners beware'. Contractors have to win a project at the lowest price and may offer low cost, poor quality or short lived repair methods. BCRC consultants are amongst the worlds leading experts in concrete repair and understand how to elicit the type of repair that will best meet the owners needs and call for compettive tenders such that the lowest that meets client requirements will be obtained. Our consultants have:

  • led multimillion dollar research programmes into assessment of repair materials, structural failure mechanisms and prestress repair
  • been responsible for major repair projects to offshore structures, buildings, bridges, wharves, jetties, mines, and industrial structures
  • developed repair materials and cathodic protection systems
  • designed implemented highly regarded concrete repair training programmes

Repair Assessment Procedures

The standard and correct approach to concrete repair is to assess the cause of failure, extent of damage, and residual service life before finalising the repair and protection methods to be used. Incorrect diagnosis can lead to errors in repair specification that can be extremely costly. BCRC have the largest range of field concrete testing equipment in Australia and are experts in the field of deterioration. BCRC's Durability Consultants manage durability aspects on some of Australia’s largest projects.

Access Required for Quality Repairs

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 repair quality and project time when working using different access systems.

Breakout For Repair

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.

Reinforcement

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.

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. .

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.

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.

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.

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 30 years ago. BCRC are also able to advise on the Zebra paint based system currently available in Australia.

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 Zinc, Mesh Anode (slotted and surface systems), Casette ribbon anode, Zebra paint based systems, remote anode systems and galvanic anode systems.

Sacrificial Anodes – Galvanic zinc 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.

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

Corrosion Inhibitors - Migrating corrosion inhibitors can be used for repair where the cover is low or the concrete is porus. 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.

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.

Photograph of stadium where leaking cracks were assessedInvestigation of a stadium floors leaking cracks identifed delamination induced from overflowing down pipes.

Photograph of people on concrete repair course testing a mock up structure with defectsRepair course included practicals on demonstration structure.

Photograph of wharf beam with explosive charge set to remove sound but contaminated concreteExplosives used to remove contaminated concrete.

Photograph of leaking crack in an immersed tubeBCRC developed a microcement grout to repassivate reinforcement & seal cracks in an immersed tunnel.

Cut section showing intimate contact between repair and parent concrete. Development of repair mixes and methods to prevent separation is vital.

Photograph of Bridgette Beach Apartments where the first conductive paint based cathodic protection system was installed in AustraliaFirst paint based CP system application in Australia by F.Papworth.

Photograph of installation of first chloride extraction/realkalisation project in Australia

Photograph of tank wall attacked by sulphuric acid as a result of hydrogen sulphide formation.BCRC advised on resistant concrete and high build epoxy coating for hydrogen sulphide induced acid attack in sewage digestor.

Cross section through gun turret and magazine at Rottnest Island. BCRC’s design of mixed usage of remote anode and sacrificial anodes in stabilising corrosion on a wartime fortress.

Photograph of tank ring beam suffering corrosion.Inspection and repair recommendations for three turn of the century reservoirs developed by BCRC's NSW team.