CONREPNETA project 50% funded by the EU

Partners:• BRE, UK• Gifford, UK• CT Koulutos, Finland• Freyssinet, France• BBRI, Belgium• IETcc, Spain• STU-K, Czech Republic

PERFORMANCE OF REPAIRS IN PRACTICE

Proforma:

•Simple layout on one side of A4•Non-attributable•Mostly tick boxes•Up to 40 data points per response•45 % response

Distribution of Respondents230 (247) case histories

‘Consultants rarely involved subsequently’

Distribution of geographic locations

Distribution of Environments

THE STRUCTURES

Distribution of Case-histories by Structure(Numbers in brackets)

Ages of Structures

Ages of Structures when Repaired

Primary Causes of Original Deterioration

THE REPAIRS

TYPES OF REPAIR

Relative uses of different patch materials

•60% cementitious

•30% polymer modified

•10% other (fibre reinforced etc)

Relative uses of different types of coatings

Classification of Performance

As seen at last inspection:

•Successful•Evidence of deterioration•Failure

Performance of repairs in relation to deterioration

Performance of repairs in relation to time

Performances of Patches

Added Value of Coating

Patch repair after 5 years

Frost damaged underpass repaired with a sprayed polymer coating

Cathodic Protection

74 Installations, most UK–46 wholly successful–13 needed attention–15 failed

Cathodic Protection

•Accidentally switched off•Phone lines vandalised•Control box fire•Control failure•Anode failure•Unsuitable application

Modes of Failure – All Types of Repair

COMMENTS‘Partially wrong design of repair, partially wrong option of repair material, partially wrong design of concrete surface’

Poor workmanship :

‘the work had been a textbook example of how not to carry out a repair’.

‘coatings were incorrectly applied despite clear instructions being given’

‘the strength of the repair material was considerably greater than the substrate’

‘poor workmanship; too thin coating (against instructions)’and there were other instances where coatings were applied too thick or too thin.

Failure of Polymer Mortar Patches and Sprayed Polymer Coatings on an AAR Affected Bridge. Considered partly due to

incorrect diagnosis of the original problem and partly to incorrect design of the repair.

Failure of Polymer Mortar Patches and Polymer Coating Applied to Corroded Reinforcement.

Considered due partly to incorrect design of the repair and partly to incorrect application of anti-corrosion treatment to corroded

reinforcement.

Key Points •Performances of 230 concrete repairs have been collected and analysed

•Ages of structures when repaired were mainly in the range 10 to 40 years, the oldest was 100 years

•The most common problem was corrosion 60 per cent of repairs involved patching.

Key Points contd •50 per cent of the repairs had failed

•20 per cent failed in 5 years•55 percent failed in 10 years•90 per cent failed in 25 years

•Cracking, debonding and continued corrosion were the most common modes of failure •Incorrect design of the repair, poor workmanship and wrong diagnosis were the most common causes of failure.

CURRENT REPAIR PRACTICE

INSPECTION

•Visual methods are used in the majority of inspections.•20 to 30 per cent of inspection work is subcontracted•The most commonly used methods of NDT are measurements of depth of cover, carbonation and chloride content.•Some small repair works may start without any inspection

Repair Methods

Comment: ‘…sometimes had to apply a repair method specified by an owner or consultant while (we) would have proposed and used a more appropriate method if the choice had been up to (us)…’.

QUALITY CONTROLAbout 90 per cent of repair projects are subjected to some degree of quality control: •Trial repairs carried out beforehand to check the proposed method

•On-site checking of repair materials to ensure specifications are met

•The common site tests practiced by most repairers are visual inspection, acoustic tests, pull-off tests, laboratory tests on cores and in some cases, structural loading tests

•Special tests to verify the correct functioning of techniques such as chloride removal and cathodic protection.

•Thickness measurements of applied coatings

Grout Stability Testing

11 grouts tested:

•All passed the EN447 standard test

•Only 6 passed the BRITE EURAM test

PERFORMANCE BASED APPROACHKey research points:

o patches are a common repair method but require improved durability

o corrosion and AAR are difficult to stop and require more research,

o repair materials should be more forgiving and tolerant of misuse,

o guidance notes are required that are simple and easy for generalists to understand and use.

o research should address performances under all weathers, and improved acceptance testing to provide assurance of durability.

Performance based repair