This entire document, as detailed on the home or front page, comprisesMartech Final Report reference MB104903, dated 15.05.03. Thisinterpretative report is on a concrete and window condition survey andsafety works.

The works were carried out in accordance with the client’s tenderspecification and the client’s representative confirmed anyadditionals/alterations during the works.

TEST REPORT

PROJECT DETAILS

The document has been put together for you by:

The document was approved by:

SIGNATURE

Regional Manager

Roel van EsRoel van Es BSc(Hons), MCS, MICorrBSc(Hons), MCS, MICorr

Jerry NicholsJerry NicholsBA(Hons), MScBA(Hons), MSc

Divisional Director

Trellick TowerGoldbourne RoadRoyal London Borough of Kensington and ChelseaLondonW10

ADDRESS

Miss Sarah Smyth

John Shreeves & Partners66 Turnmill StreetLondonEC1M 5RR

(on behalf of the Royal London Borough of Kensington & Chelsea)

Phone no. 0207 596 0000

Fax no. 0207 596 0100

CLIENT

The structure consists basically of 2 multi-storey residentialmaisonettes/flats inter-linked by access link-bridges (walkways) and aservice/lift tower. The structure is a Grade 2* listed building andconstruction was completed in ~1972.

The taller block (A) has 31 storeys of housing units. The lower block (B)has 6 storeys of housing units with the ground level (1) and lower groundcontaining retail units.

The following photographs illustrate the structures:

Photograph 1: The main entrance which is to the service tower. Alsoapparent are access link-bridges to Block B.

STRUCTURE

Photograph 2: General view of the north elevation (front) of Block A.Note the access walkways at every 3rd floor level. At the far end is a stairtower.

Photograph 3: General view of the north elevation of Block A and theservice tower and connecting access walkways.

Photograph 4: General view of the east gable end of Block A with theshorter Block B in the background.

Photograph 5: General view of the south elevation of Block A and theservice tower. On this elevation of the Block there are private balconies.

Photograph 6: General view of the west elevation (front) of Block B. Notethe private balconies with retail units at ground.

Photograph 7: General view of the east elevation of Block B.

Photograph 8: General view of the service tower at lower ground level andthe interlinking walkways.

Photograph 9: General view of the south gable elevation to Block B.

Photograph 10: General view of a section of the south elevation of BlockA. Note the original timber cladding between the concrete and windowelements.

© Keller Group plc (2003). This report is copyright. Reproduction of the whole or any part thereofmust not be made without the express permission of Martech Technical Services Limited. This report,the results shown and any recommendations made herein are based upon the information, drawings,samples and tests referred to in the report. Martech Technical Services Limited accepts no liability,beyond three times the value of the original instruction, for any damages, charges, costs (including,but not limited to, legal costs) or expenses in respect of or in relation to any damage to any propertyor other loss (save for death or personal injury occasioned by reason of any negligence on the part ofMartech Technical Services Limited) whatsoever arising either directly or indirectly from the use of thereport, the carrying out of any recommendations contained therein, the following of advice or the useof any goods or materials referred to in this report.

COPYRIGHT

Key words: Concrete, windows, safety works, reinforcement corrosion, assessment,testing, cover, carbonation, chlorides, sulphates, cement content,samples, laboratory testing, strength, petrographic, corrosion potential,alkalinity, cracking, spalling, timber and metal frames, EuropeanStandard EN 1504, concrete repair, corrosion control.

Objectives: The structure basically consists of three main sections; Block A, Block Band the Service Tower and link-bridge walkways. These were assessedand tested in order to gain knowledge on the exact cause and trueextent of concrete deterioration and reinforcement corrosion present andwindow conditions. The testing regime was carried out in accordancewith the client’s specifications.

Findings: The structure was found to be suffering from localised low cover in areaswith carbonation most probably having reached the reinforcement inplaces, and hence a reinforcement corrosion problem possiblyexacerbated in some areas by the presence of cast-in chlorides. Thewindows were visually examined (externally) and graded according tothe specification. They varied in condition from “good, performing asintended” to “life expired/serious risk of imminent failure”. Allimmediately loose material at spalls was also removed in the interests ofhealth and safety.

Repairs: Proper concrete remedial works and effective corrosion control measuresmust be designed, in accordance with EN 1504, European standard forconcrete repair, to deal with visible and latent damage, together withconsideration of specific client requirements and expectations.Procurement of remediation services should, in our opinion, be inaccordance with the Egan Report.For the concrete elements we have recommended the use of traditionalrepair techniques for all visibly deteriorated areas. It must be noted thatthe structure is Grade 2* listed and any repairs would have to match theexisting finishes. With this in mind (and due to the overall state of theconcrete) it would also be of benefit to clean the structure to return it toits intended finish and remove staining due to deleterious materials andfumes, pollution and water run-off.It may also be considered appropriate to install/apply corrosion inhibitors(or even use electrochemical techniques) to treat areas of latentdamage.The defective windows should be repaired/replaced to ensure that theresidents are not subject to problems due to moisture ingress etc. All ofthe mastic joints should be reinstated to promote long-term durability.

Time scale: All necessary works (both glazing and concrete) should be carried out assoon as feasibly possible as deterioration is on going. This wouldpromote long-term durability for the structure.

Dateline: It is clear that the concrete deterioration observed has been caused by acombination of factors. This has resulted in the readily visible effects ofthe reinforcement corrosion seen on the structure, plus the latent, orhidden, damage identified. The information contained within the report isonly valid as presented in its entirety. The advice and interpretationgiven are representative of the state of the concrete as found at the timeof survey. As deterioration is clearly ongoing in the structure, the adviceand contents of the report are only valid for a period of 12 months fromthe date of issue.

SUMMATION

Martech were requested by Sarah Smyth of John Shreeves & Partners onbehalf of the Royal London Borough of Kensington & Chelsea to carry outa concrete and window condition assessment along with safety works onTrellick Tower, in accordance with their letter of instruction dated 28th

January 2003.

The works were carried out in accordance with the clientstender/specification as priced and tendered by us.

It was required to assess the nature and extent of concrete and windowdeterioration, to define the reinforcement corrosion condition, and to offerappropriate remediation and corrosion control proposals.

Our Engineers carried out the works from 17th February to 21st March2003 and in the week commencing 7th April 2003 and their findings arethe subject of this interpretative report.

Access to the external fabric was achieved through the use of IndustrialRoped Access Techniques.

INTRODUCTION

THE WORKS

Although an overall visual assessment was made, detailed work was onlycarried out in selected test areas as specified in the tender documents.

The Images Section of this report contains photographs relevant tovarious parts of the text. It is recommended that these be studied, inconjunction with their explanatory captions, before reading the balance ofthis text.

The most important test results are summarised, in a logical tabular form,in the Summary Tables section of this report.

The findings are recorded on survey sheets, to be found in the Imagessection of this report.

The Background section of this report contains more information on thetest procedures under Testing.

Assessment and testing was carried out employing the followingtechniques:

TEST RESULTS

GENERAL

Please note that our visual observations are based upon our Engineerscarrying out industrial roped access of all accessible areas.

All of the visible concrete defects were measured and are shown on theCAD drawings.

All of the windows were visually inspected externally and gradedaccording to the specification document and are shown on the CADdrawings.

The grades are as follows:A = Good, performing as intended,B = Satisfactory, performing as intended but showing minordeterioration,C = Poor, showing major defect/not operating as intended,D = life expired/serious risk of imminent failure.

Photographs of defects (both concrete and window) are contained in theImages section of the report.

Hammer Testing of all concrete surfaces was carried out and anyimmediately loose material (concrete spalling) was removed for healthand safety reasons.

VISUAL & HAMMERTEST

The covermeter results obtained have been corrected wherever possible inline with observations of visible reinforcement. The results aresummarised in the following tables:

Block A:COVER (mm)ELEMENT

Minimum Maximum MeanRoof Elements 43 74 59Roof Parapet

Walls5 77 42

Columns 19 120 44Floor Beams 18 67 33

Walkway Panels 34 68 50Walkway Beams 40 64 54Balcony Walls 32 56 44

Balcony Beams 16 37 26Balcony Soffits 9 47 26

Walls 4 120 52Window beam 48 55 50

Linkbridge soffit 21 55 36Linkbridge

panels15 52 36

Block B:

COVER (mm)ELEMENTMinimum Maximum Mean

Roof CanopyElements

33 78 52

Roof ParapetWalls

20 120 57

Roof Beams 23 120 72Columns 24 80 42

Floor Beams 19 120 44Walkway Panels 31 70 42Walkway Beams 40 50 45Balcony Walls 27 45 38

Balcony Beams 25 39 31Balcony Soffits 34 55 45

Walls 17 120 69Stairtower Roof

Elements35 58 45

Floor 2 Soffit 45 47 46

COVERMETER

Service Tower:

COVER (mm)ELEMENTMinimum Maximum Mean

Roof Beam 19 58 35Walls 14 120 53

The covermeter results indicated that where tested there were a relativelysmall number of localised areas of originally low cover (say <20mm). OnBlock A and the linkbridges there were a total of 40 readings below20mm, on Block B there were 3 and on the Service Tower there were 2.But the mean values were generally satisfactory being >30mm, in factoften greater than 40mm.

Please note that it is our policy to record carbonation results from in-situtests to the nearest 5mm only. We do this in recognition of the fact that,in our opinion, the results across any concrete structure can varysignificantly, as the concrete is frequently far from homogeneous acrossthat structure. It is also true that the so-called carbonation front is not aparallel plane to the surface of the concrete, rather it is locally seen to bea very irregular plane roughly parallel to the surface. Readings across asingle break out can vary by more than 5mm, which would be reflected inthe results.

In accordance with BRE Digest 444:Part 2:2000 the progress ofcarbonation obeys an empirical formula:

Simplified CBmm = k.�t

Where CBmm = carbonation depth in mmk = a constant reflecting

concrete qualityt = time, in years

The results obtained are summarised in the following tables:

Block A:CARBONATION (mm)ELEMENT

Minimum Maximum MeanRoof Elements <5 <5 <5Roof Parapet

Walls<5 10 <5

Columns <5 10 <5Floor Beams <5 20 5

Walkway Panels <5 <5 <5Walkway Beams <5 <5 <5Balcony Walls <5 <5 <5

Balcony Beams <5 <5 <5Balcony Soffits <5 10 <5

Walls <5 10 5Window beam <5 <5 <5

Linkbridge soffit <5 <5 <5Linkbridge

panels<5 10 <5

CARBONATION

Block B:

CARBONATION (mm)ELEMENTMinimum Maximum Mean

Roof CanopyElements

<5 15 5

Roof ParapetWalls

<5 <5 <5

Roof Beams <5 <5 <5Columns <5 <5 <5

Floor Beams <5 <5 <5Walkway Panels <5 <5 <5Walkway Beams <5 <5 <5Balcony Walls <5 <5 <5

Balcony Beams <5 <5 <5Balcony Soffits <5 <5 <5

Walls <5 <5 <5Stairtower Roof

Elements<5 <5 <5

Floor 2 Soffit <5 <5 <5

Service Tower:

CARBONATION (mm)ELEMENTMinimum Maximum Mean

Roof Beam <5 <5 <5Walls <5 10 <5

The carbonation results were generally very low being typically <5mm.There were a small number of deeper results (up to 20mm), whichindicated areas or elements with localised deeper carbonation levels. OnBlock A and the linkbridges there were only 42 results up to 10mm, tworesults up to 15mm and one result up to 20mm. On Block B there wasone result up to 10mm and one result up to 15mm. On the Service Towerthere were two results up to 10mm. Given the age of the structurecarbonation was found to be generally low.

Using the formula noted above for the progress of carbonation in concreteit can be assumed that the life expectancy of the structure in relation tocarbonation reaching the reinforcement will be long (say ~120 years forcarbonation to reach typically 20mm) given that at it’s current age of ~30years carbonation is typically <10mm.

Details of the laboratory test findings are to be found in the Lab Resultssection of this report.

In accordance with BRE Digest 444:Part 2:2000 the risks associated withchloride contamination of concrete are variable with source and age ofstructure. This has long been our opinion as the critical factor in chloridecontamination is in fact the total amount of free chloride ion available totake part in chloride attack on reinforcement.

In simple terms cast-in chlorides tend to combine with the hydrationproducts of the cement, and are therefore considered to be substantiallybound. It is known that the carbonation process releases this chemicalbond, which results in an accumulation of free chloride ion just ahead ofthe carbonation front.

Conversely, chlorides that have entered the concrete subsequent tohardening, referred to as ingressed chlorides, must be considered to besubstantially free, and available to take part in chloride attack. Ingressedchloride will accumulate with the passage of time, being present in ever-greater concentrations, at ever-greater depth. It follows that this form ofchloride contamination is the more aggressive in the normal run of events.

Classification of risk in accordance with BRE Digest 444:Part 2:2000 is acomplex procedure that we follow in general terms. The categories of riskare defined as follows: negligible, low, moderate, high, very high, andextremely high. Categorisation varies with source of chloride, age ofstructure, extent of carbonation and environmental exposure condition.

The results obtained are expressed as chloride ion by mass of cement,using an assumed cement content of 14% in the concrete. The resultsare summarised in the following tables:

DUST SAMPLES

Block A:

CHLORIDES (%)ELEMENTMinimum Maximum Mean

Roof Elements 0.05 0.10 0.08Roof Parapet

Walls<0.01 0.25 0.09

Columns <0.01 0.83 0.31Floor Beams 0.08 0.91 0.38

Walkway Panels 0.13 0.80 0.46Walkway Beams 0.18 0.51 0.33Balcony Walls 0.07 0.25 0.12

Balcony Beams 0.08 0.55 0.35Balcony Soffits <0.01 0.15 0.09

Walls <0.01 0.32 0.14Window beam 0.06 0.22 0.12

Linkbridge soffit 0.19 0.63 0.39Linkbridge

panels0.04 0.57 0.36

Block B:

CHLORIDES (%)ELEMENTMinimum Maximum Mean

Roof CanopyElements

0.05 0.49 0.19

Roof ParapetWalls

<0.01 0.12 0.06

Roof Beams 0.05 0.32 0.19Columns 0.08 0.94 0.33

Floor Beams 0.04 0.50 0.28Walkway Panels 0.22 0.50 0.41Walkway Beams 0.17 0.46 0.32Balcony Walls <0.01 0.04 0.03

Balcony Beams 0.37 0.73 0.51Balcony Soffits 0.09 0.29 0.19

Walls <0.01 0.19 0.07Stairtower Roof

Elements0.09 0.12 0.11

Floor 2 Soffit 0.13 0.13 0.13

Service Tower:

CHLORIDES (%)ELEMENTMinimum Maximum Mean

Roof Beam 0.06 0.27 0.13Walls 0.05 1.05 0.23

According to the BRE Digest 444 the results were classified as rangingfrom low risk to extremely high risk with the majority being of low risk,when considered in conjunction with age, carbonation and environmentalconditions.

The following assumptions were made using the BRE Digest:40 year old structure, typically in a “damp” environment, with cover

greater than carbonation.

Therefore the spread of the chloride results was as follows:

RISK OF CORROSIONLow Moderate High Very High

87.7% 10.2% 1.9% 0.2%

The BRE classifications are taken as follows:

<0.45%: low risk of corrosion0.45 to 0.70%: moderate risk0.71 to 1.0%: high risk1.1.to 1.5%: very high>1.5%: extremely high

The high risk results were for samples S85 (0.74), S88(0.94),S155(0.73), S225(0.72), S229(0.91), S262(0.83), S296(0.80),S332(0.72) and S378(0.92) whilst the one very high risk result was forS386(1.05).

The cement content test results were high and ranged from 14.3% to21.4%. If these higher individual results or the mean were used tocalculate the chloride results they would effectively lower the chlorideresults. Thus the chloride results in the tables above are the “worst case”scenario results.

The sulfate test results obtained by the laboratory were low and rangedfrom 2.20% to 3.61% by mass of cement. Concrete Society TechnicalReport No.32 suggests that concrete failure solely as a result of sulfateattack should not be inferred unless values are significantly greater than5%.

The testing of samples for the presence of High Alumina Cement (HAC)found none present.

The alkali testing of samples gave a range of results. The sodium oxide(by mass of cement) ranged from 0.38 to 0.96, which were consideredvery low. It was noted in the petrographic report (in the next section)that the aggregate contains rock types potentially reactive with alkalies incement paste but that no evidence for any such reaction was found.

Full details of the laboratory test findings are to be found in the LabResults section of this report.

The petrographic analyses of the concrete from the various elementsfound two distinct types of concrete present which were as follows:

Type 1: consisting of flint gravel coarse aggregate and siliceousmedium sand in dark grey Portland cement based paste of lowporosity.

Type 2: consisting of flint gravel coarse aggregate and crushedgranite fine aggregate in very light grey to white and porousPortland cement based paste.

The Type 1 cores were from main structure wall elements (e.g. stairtower, service tower, and gable) whilst Type 2 were from access elements(walkways and link-bridges).

The samples were found to contain aggregates that are potentiallyreactive with alkalis in cement. No evidence of this reaction was howeverseen in the sections examined. This situation gives no real cause forconcern as it occurs in a great number of concretes examined. Actualoccurrence of the reaction requires a number of variables to mutuallyexist, at given values, and consequently the reaction is rarely found in UKconcrete.

Type 1 samples had water/cement ratios of the order of 0.50 to 0.56.Type 2 samples had typically higher water/cement ratios of the order of0.60.

The Type 1 samples had low to moderate levels of macroscopicdeterioration (fine cracking, ettringite in cracks and voids) whilst Type 2samples had very low levels of deterioration.

The compressive strength of the concrete samples was found to vary froma low estimated in-situ compressive cube strength of 24.5N/mm2 to a highof 74.0N/mm2. The majority of the results were >40.0N/mm2.

One result was <30N/mm2 being 24.5N/mm2 (TA282 – walkway panel).One result was between 30 and 35N/mm2 being 34N/mm2 (TA287 – roofparapet). Four results were between 35 and 40N/mm2 being 36, 37, 39and 40N/mm2 (TA435 – walkway panel, TA423 – linkbridge panel, TA396– lift tower wall and TA457 – service tower wall, respectively). The other26 results were >40N/mm2.

Prior to crushing the concrete was visually described and these details arecontained in the laboratory report.

CORE SAMPLES

Please note that corrosion potentials of reinforcement are an empiricalmeasure of the probability of a corrosion condition existing, and thatresults are not always repeatable. Results may vary from day to day, andwill certainly vary by season, with the prevailing moisture condition of theconcrete in question.

Interpretation of the results, in accordance with ASTM C-876, is asfollows:

• More positive than –200mV Less than 10% probability of corrosion• Between –200 and –350mV Uncertain, or 50% probability of corrosion• More negative than –350mV More than 90% probability of corrosion

The half cell results obtained from the various elements spread over thetwo blocks and service tower etc ranged from a most negative of –195mVto a most positive of +192mV. Therefore the results were indicative of aless than 10% probability of corrosion occurring at the time of testing.

CORROSION

Details of these findings are to be found on the relevant detailed test areasurvey sheets, in the Images Section to this report.

The reinforcement pattern for the floor beam elements was mapped out inthree locations. The elements were found to be ~65mm thick. Generallyno gaps were found behind these elements except at one low area (floor 2– test area 276), where there was a ~10mm “gap” with debris in it.Despite mapping out the reinforcement no fixings were located.Borescoping of the elements was not possible as no gaps were foundelsewhere.

The testing of columns on the balcony elevations revealed a “U” shapedsection (in plan) in front of a wall end as detailed at Test Area 285, floor27, Block A. There was a gap between the U-shaped element and theinner wall (of 90mm at the sides and 50mm to the front face, wheretested). The U-shaped element itself was 75mm thick (and reinforced).

OTHER TESTING

The concrete investigation and test results for the structures indicatedthat the deterioration seen was predominantly due to a combination oflocalised areas of originally low cover, areas of poor compaction andcarbonation probably exacerbated in some areas by the presence of cast-in chlorides. There were also signs of cracking possibly due to thermalmovements and leakage due to moisture penetration.

It was also noted that the finishes to the concrete elements varied greatlydue to a combination of noticeable differences between precast and castinsitu elements, weathering and drainage (run-off) and contamination dueto fumes etc.

The majority of the mastic sealants were also noted to be degraded, oftenin the form of hardened, cracked or debonded.

The window frames varied in condition from “good, performing asintended” to “life expired/serious risk of imminent failure”. The vastmajority of the windows were considered to be of the “B” grade being“satisfactory, performing as intended but showing minor deterioration”.

In summation of the results the cover results indicated that there werelocalised areas of originally low cover (say <20mm) in numerous areas.But the mean values were generally satisfactory being >30mm, in factoften greater than 40mm. The carbonation results were generally verylow being typically <5mm. There were a few deeper results (up to20mm), which indicated areas or elements with localised deepercarbonation levels. Given the age of the structure carbonation was foundto be generally low and will probably penetrate at a continued very lowrate.

With regards to the chloride results and according to the BRE Digest 444,they were classified as ranging from low risk to extremely high risk withthe majority being of low risk, when considered in conjunction with age,carbonation and environmental conditions.

The spread of the chloride results was as follows:

RISK OF CORROSIONLow Medium Very High Extremely

High87.7% 10.2% 1.9% 0.2%

The petrographic analyses of the core samples found there to be twotypes of concrete. The Type 1 samples had low to moderate levels of

INTERPRETATION

TEST REPORT

macroscopic deterioration (fine cracking, ettringite in cracks and voids)whilst Type 2 samples had very low levels of deterioration.

The half cell results obtained from the various elements spread over thetwo blocks and service tower etc ranged from a most negative of –195mVto a most positive of +192mV. Therefore the results were indicative of aless than 10% probability of corrosion occurring at the time of testing.

The majority of the compressive strength test results were >40.0N/mm2,indicative of generally well compacted concrete.

GENERAL

WORKS REQUIRED

There are a number of options to be considered in dealing with a structuresuffering concrete distress as a result of reinforcement corrosion. Thesemay be outlined as follows:

• Do nothing• Do something temporary• Effect a proper repair

For the purposes of this report it is assumed that the sensible long-termoption of effecting a proper repair methodology will be adopted. It isnoted that the client wishes any repairs to ideally last a minimum of 20years, which should be achievable.

In effective long-term refurbishment one needs to deal with all the latent,or hidden, as well as visible damage. Passivation of the steel must in ouropinion be achieved for long-term durability. The repair advice givenbelow constitutes our best advice and opinion.

Please take the time to read our background information to this repairadvice, to be found variously under Concrete and Concrete Repair in theBackground section to this report.

REPAIR ADVICE

GENERAL

The following concrete repair and corrosion control advice for thestructures also assumes that all top surfaces of treated concrete slabs willbe made fully waterproof, e.g. roofs and balcony slabs and so forth.

In any event all instances of low cover must be attended to and all latentand visible corrosion damage repaired, such that any untreatedreinforcement is in a sound alkaline condition. For concrete repairpurposes any reinforcement found to be within 5 mm of the averagecarbonation front depth, must always be considered to be immediately atrisk of corrosion. Using these guidelines the areas of potential latentdamage can be estimated from the test data.

Traditional concrete repair methods are considered appropriate for dealingwith the visibly deteriorated concrete (spalls, cracks, visiblereinforcement, honeycombing etc).

This will involve identifying all carbonated or contaminated concrete at thetime of repair, which is in contact with reinforcement, which will of courseinclude an element of latent damage on top of the readily visible problemareas.

All such concrete will be removed and replaced with a concrete repairproduct, forming part of the full repair system in use. Due to the Grade2* listing it will most probably be required to match existing finishes. Thiswould probably be easier if the structure was cleaned (all staining anddeleterious contamination due to fumes, pollution etc) being removed in asuitable manner e.g. grit/jet blasting. Given the staining seen on someparts of the structure it would be desirable to install some form of dripdetails and suitable drainage system to limit further staining, especially ifthe structure was cleaned.

All cutting out for patch repairs will go well beyond the corroded lengthand behind the bar to ensure effective remediation.

A possible option for the limited areas of latent damage (due tocarbonation and/or chlorides) would be the use of electrochemicalremediation techniques although given the small areas requiring suchtreatment probably not viable in this instance.

This would involve identifying all hollow and delaminated areas ofconcrete for repair in areas to be treated in this manner. These will bevery simple repairs to delaminations, with no special requirements interms of reinforcement preparation. Steel is never coated when usingelectrochemical techniques, and mortars must have electrochemicalcompatibility, with the proposed installation.

Electrochemical remediation involves the application of a temporaryexternal anode system to the concrete, consisting of a titanium mesh in a

WORKS REQUIRED

shutter filled with electrolyte. This, as well as the reinforcing steel, isattached to a transformer rectifier unit designed to pass a current for agiven time period, dependent upon the exact concrete problems. Thesystem reinstates a robust and durable passivity to the reinforcement,and moves chlorides away from the reinforcement.

Alternatively it may be considered more appropriate to use corrosioninhibitors, which can be brush applied or inserted as pellets.

With the use of a corrosion inhibitor to deal with the latent damage it isonly necessary to identify all hollow and delaminated areas of concrete forrepair. Repairs must however be to a high standard in line with traditionaltechniques. The corrosion inhibitor deals with the latent damage viamigration through the pore structure of the concrete, and adsorption tosteel surfaces. A monomolecular layer coats the steel preventing moistureand oxygen reaching it, and hence corrosion.

It is important that a proprietary concrete repair system with a good trackrecord be used, in conjunction with a recognised specialist contractor.

All defective windows should be repaired/reinstated as necessary.

All of the mastic joints should also be reinstated.

If possible attention should be paid to the selection of decorative andprotective coatings. This route would enable the repairs to be hidden andalso allow options for changing the building appearance if so desired.

We would, upon request, be very pleased to arrange more detailed adviceand proposals, based upon our recommendations above.

CONCRETE SURVEYPHOTOS

The following photographs illustrate the structure and any defects notedduring the visual assessment of the concrete.

Photograph 1: The main entrance to the structure. There was noted to bevarying finishes to the concrete elements, which were also stained andaltered in places due to weathering and run-off. Note the columns eitherside of the entrance for example.

CONCRETE SURVEY

staining

Photograph 2: Part of the east elevation of Block B. Note the variousconcrete element finishes (colour changes and weathering). This will needcareful consideration if repairs are undertaken due to the listed nature ofthe structure. It was also noted that the parapet sections at roof levelappeared to have moved: were out of alignment.

Photograph 3: A section of the north elevation of Block A. Note thediffering windows (timber and metal framed). Also apparent again,notably on the access walkway elements, is the staining due toweathering.

Photograph 4: Given the size of the structure there were relatively a lownumber of visible defects to the concrete elements. This is a visible barend at a spall, drop 3, floor 9, top corner of window opening. (defect no.292).

Corroded bar

Photograph 5: There were a number of cracks with associated leakage.This was to the roof parapet soffit, drop 5, floor 31, (defect no. 10).

Photograph 6: A crack to a soffit corner, drop 6, floor 31, (defect no.14).

Photograph 6: A spall and exposed steel at a gable wall corner, drop 7,floor 21, (defect no.108). The concrete was also noted to behoneycombed (poorly compacted) at the spall.

Photograph 7: A crack (up to 15mm wide) and exposed steel, betweenparapet and gable wall, drop 7, floor 31, (defect no. 56).

crack

bar

Photograph 8: There were a few previous repairs/render on walls, notablyat roof level on Block A as seen here, where original elements had beenpreviously removed.

Photograph 9: A spall and exposed steel to a roof parapet slot, Block A(defect no. 257).

bar

Photograph 10: Spalling and exposed steel at originally very low cover(<5mm) to a balcony return wall, drop 8, floor 30, (defect no’s 73, 74 and75).

Photograph 11: Spalling and exposed steel to a column return face(indicative of originally very low cover), drop 13, floor 24, (defect no. 97).

Photograph 12: A spall, exposed steel and crack to a balcony parapet wall,drop 13, floor 22, (defect no’s 106 and 107).

Photograph 13: A spall and cracking associated with hand rail fixing to abalcony parapet wall, drop 13, floor 19, (defect no’s 120 and 121).

Photograph 14: A spall (and honeycombed concrete) to the lower edge ofa balcony, drop 13, floor 10, (defect no. 148).

Photograph 15: Spalls and visible bars (at originally low covers) to a wall,drop 18, floor 30 (defect no’s 17 to 21).

Photograph 16: General view of a typical private balcony (in this instanceon Block A).

Photograph 17: General view of another private balcony area on the southof Block A. Note the timber panelling and the pigeon netting.

Photograph 18: A typical visible corroded bar at originally very low cover,Drop 11, floor 23, (defect no. 99).

Photograph 19: A spall and visible bar on a window return wall, drop 12,floor 31. (Also note the poor condition of the window frame). (Defect no.84).

Photograph 20: A previously removed area of spalling and paintedreinforcement (at originally very low cover), Drop 12, floor 29 (defect no.293).

Photograph 21: A typical crack to a balcony soffit.

Photograph 22: Previous repairs/skims, spalling and cracking to a slabsoffit over the loading bays of Block B.

Photograph 23: There were a number of spalled ferrule plugs noted andremoved from the cast insitu elements (walls).

Photograph 24: An exposed bar, top level, service tower, north elevation,(defect no. 17).

Photograph 25: Cracking emanating from a pipe opening, service towerchimneys, (chimney no. 4), west elevation (defect no. 26).

bar

Photograph 26: Exposed bars (at originally low cover), service towerchimneys (chimney no. 1) (defect no. 27).

Photograph 27: A small spall and visible bar, floor 27, east elevation,service tower, (defect no. 10).

Photograph 28: A crack at the joint of a parapet and the lift tower, floor 8,(defect no. 6).

Photograph 29: A spall and visible bars at level 3, south elevation, left oflinkbridge, from Block B (defect no. 9).

Photograph 30: Two spalls and a crack to a parapet wall, north, Block B(defect no’s 81, 82 and 84).

Photograph 31: Two visible bars (at originally low covers), right hand side,2nd column canopy support, Block B, (defect no’s 6 and 7).

crack

Photograph 32: A typical deteriorated mastic joint, in this instancedebonded from one surface.

Photograph 33: An exposed bar at ground level, west elevation, Block B,(defect no. 65).

Photograph 34: A notable crack/gap at a column joint, ground level, westelevation, Block B, (defect no. 73).

crack

Photograph 35: A spall and visible bar, wall behind entrance column, westelevation, (defect no. 7).

Photograph 36: An exposed bar (at originally very low cover) on a“gargoyle”, level 2, south elevation, Block A, drop 10, (defect no. 178).

Photograph 37: An example of the staining (extensive in some areas), inthis instance to the east elevation of the service tower.

WINDOW SURVEYPHOTOS

The following photographs illustrate the windows and typical defects notedduring the survey. Please refer to the CAD drawings for the full windowsurvey grading.

Photograph 1: Typical windows at 31st floor level.

WINDOW SURVEY

Photograph 2: Another view of a typical window. The mastic sealantswere noted typically to be either hard, cracked, debonded or missing.

Photograph 3: A typical walkway window with deteriorated sealant.

Photograph 4: A typical cracked mastic joint at a concrete/windowjunction.

Photograph 5: The paint to the timber window frames was often flakingoff.

Photograph 6: Typical cracked mastic to a window/caldding panel.

Photograph 7:A number of the timber window frames were rotten as seenhere (west elevation, Block B).

Summary of Test Results Block A Trellick Tower

Element Depth of Cover Depth of Carbonation Chloride Content(mm) (mm) (%) *

Min Max Mean Min Max Mean Min Max MeanRoof Elements 43 74 59 <5 <5 <5 0.05 0.10 0.08Roof parapet walls 5 77 42 <5 10 <5 <0.01 0.25 0.09Columns 19 120 44 <5 10 <5 <0.01 0.83 0.30Floor beams 18 67 33 <5 20 5 0.08 0.91 0.37Walkway panels 34 68 50 <5 <5 <5 0.13 0.80 0.41Walkway beams 40 64 54 <5 <5 <5 0.18 0.51 0.33Balcony walls 32 56 44 <5 <5 <5 0.07 0.25 0.12Balcony beams 16 37 26 <5 <5 <5 0.08 0.55 0.35Balcony soffits 9 47 26 <5 10 <5 <0.01 0.15 0.09Walls 4 120 52 <5 10 5 <0.01 0.32 0.14Window beam 48 55 50 <5 <5 <5 0.06 0.22 0.12Linkbridge soffit 21 55 36 <5 <5 <5 0.19 0.63 0.39Linkbridge panels 15 52 36 <5 10 <5 0.04 0.57 0.36

*Chlorides expressed as % ions by mass of cement assuming a cement content of 14%

Summary of Test Results for Block B - Trellick Tower

Element Depth of Cover Depth of Carbonation Chloride Content(mm) (mm) (%) *

Min Max Mean Min Max Mean Min Max MeanRoof Canopy elements 33 78 52 <5 15 5 0.05 0.49 0.19Roof parapet walls 20 120 57 <5 <5 <5 <0.01 0.12 0.06Roof Beams 23 120 72 <5 <5 <5 0.05 0.32 0.19Columns 24 80 42 <5 <5 <5 0.08 0.94 0.33Floor Beams 19 120 44 <5 <5 <5 0.04 0.50 0.28Walkway Panels 31 70 42 <5 <5 <5 0.22 0.50 0.41Walkway Beams 40 50 45 <5 <5 <5 0.17 0.46 0.32Balcony Walls 27 45 38 <5 <5 <5 0.01 0.04 0.03Balcony Beams 25 39 31 <5 <5 <5 0.37 0.73 0.51Balcony Soffits 34 55 45 <5 <5 <5 0.09 0.29 0.19Walls 17 120 69 <5 <5 <5 <0.01 0.19 0.07Stairtower Roof elements 35 58 45 <5 <5 <5 0.09 0.12 0.11Floor 2 Soffit (Walkway) 45 47 46 <5 <5 <5 0.13 0.13 0.13

*Chlorides expressed as % ions by mass of cement assuming a cement content of 14%

Summary of Test Results for Service Tower - Trellick

Element Depth of Cover Depth of Carbonation Chloride Content(mm) (mm) (%) *

Min Max Mean Min Max Mean Min Max MeanBeams 19 58 35 <5 <5 <5 0.06 0.27 0.13Walls 14 120 53 <5 10 <5 0.05 1.05 0.23

*Chlorides expressed as % ions by mass of cement assuming a cement content of 14%

Concrete is a highly alkaline substance and it is this alkalinity thatprotects the reinforcement from corrosion, despite the almost inevitablesimultaneous presence of oxygen and moisture - the fuel of corrosion. Theair around us is however relatively acidic, mainly by virtue of the carbondioxide content, and tends to neutralise any concrete it comes into contactwith gradually from the surface inwards. A chemical reaction takes placein which alkaline hydroxide compounds are converted into carbonatecompounds - hence carbonation.

Were the carbonation front to reach the reinforcement, the protectivepassive layer around the bars maintained by alkalinity would be lost andactive corrosion would ensue. This occurs in the form of microcellcorrosion, or generalised surface corrosion, which leads to latent (orincipient) damage, and later to the classic symptoms of reinforcementcorrosion - cracking and spalling of the cover concrete. For this reasonthe steel should have adequate cover (say 40 mm+) when built.

The presence of free chlorides in significant quantities can lead to localisedbreakdown of the passive layer on reinforcement, often in otherwisesound alkaline concrete, which results in intensive localised pittingcorrosion of the steel. This is often termed macrocell corrosion, and canoccur irrespective of cover. This form of reinforcement corrosion hasassociated with it a considerable excess of cathode over anode area, andcorrosion rates can be relatively high. Care is needed in the rare situationswhere the oxygen supply to the steel is limited, as a non-expansive formof corrosion (black rust) can occur, which could ultimately lead todissolution of the steel in the absence of the usual surface manifestations.

BACKGROUND

CONCRETE

Visual Observations

Pertinent observations on the structure are generally recorded on a briefoverall visual assessment, mainly on a walk around survey of accessibleareas, supplemented by areas accessed during the course of the detailedtesting.

Covermeter Survey

A representative portion of each detailed test area is generally subject toa covermeter survey, which measures the concrete cover, in millimetres,over the reinforcing steel. Measurements were carried out in generalaccordance with BS1881: Part 204.

The instrument used by us is a Protovale CM5, Protovale CM52, ProtovaleCM9, or Kolectric Micro Electronic Covermeter. In order to obtain preciseresults exact bar sizes need to be known or assessed, otherwise smallerrors in cover readings can result. This effect is however, much moremarked with shallow depths of cover concrete, where there can beevidence of correct bar sizes. Multiple, parallel or intersecting bars, giveincorrect readings unless identified and avoided, or adjusted for.

Carbonation Testing

The depth of carbonation of the concrete is generally assessed andmeasured in situ in all detailed test areas. This is carried out in generalaccordance with BRE recommendations, from information paper IP 6/81.We always carry out the test on freshly broken concrete surfaces, as it isour opinion that this gives the most accurate results. The broken surfaceis blown clean and sprayed with phenolphthalein indicator solution. Thesolution gives a vivid pink coloration on sound alkaline concrete, with nocolour change on carbonated surfaces, which merely look wet.

The mean depth of carbonation is measured, within 30 seconds ofspraying, as the distance from the concrete surface to the boundary of theuncoloured zone.

It is important to record any slow development of colour, or creep back ofcoloration towards the surface of the concrete, as either condition can beindicative of partially carbonated concrete.

TESTING

Concrete Dust Sampling

Concrete dust samples are generally collected in the detailed test areasfor laboratory analysis in respect of chloride content, plus in someinstances sulfate and cement content. The samples are drilled using aheavy duty rotary-percussive drill and 20 mm bit from at least two holesper location, with the first 5 mm of sample from each hole discarded asbeing non representative. Sampling is carried out in general accordancewith BRE recommendations, from information paper IP 21/86.

If the location of the structure is such that any chloride present in theconcrete is likely to have been cast-in at the time of construction, thesamples are obtained in single increments of 5-50mm.

Conversely the location and nature of the structure could be such thatchloride is likely to have ingressed the concrete, from an external source,and subsequent to construction. In this instance the samples are collectedin 3no. separate depth increments of 5-25, 25-50 and 50-75mm, andsuffixed A, B, and C respectively.

The nature of a car park structure is such that chloride is likely to haveingressed the deck concrete surfaces, from vehicular traffic bringing in de-icing salts. The samples on these elements are therefore collected in 3no.separate depth increments of 5-25, 25-50 and 50-75mm, and againsuffixed A, B, and C respectively. The other concrete elements on car parkstructures are generally such that any chloride present in the concrete islikely to have been cast-in at the time of construction. The samples inthese areas are therefore obtained in single increments of 5-50mm.

Dust samples for chloride, sulfate, and cement content analyses aregenerally collected in plastic sample bags, labelled appropriately, andsubmitted to a UKAS accredited laboratory for analysis, in accordance withBS1881: Part 124.

Concrete Core Sampling

Concrete core samples, when required, are generally collected in anumber of test areas, for submission to the laboratory for furtheranalyses.

A UKAS accredited laboratory can be requested to analyse the cores inrespect of a description and photograph, prior to compressive strengthtesting in accordance with BS1881: Part 120.

In addition a specialist laboratory cab be requested to analyse the coresvia petrographic techniques. This involves the vacuum impregnation ofcore slices with fluorescent resin, which are then further prepared.Generally polished slices are prepared for observation under a relativelylow powered microscope. They also prepare thin section microscopyslides, in which a small but representative sub-sample of the concrete,

often including the surface, is glued onto a glass slide. The concrete isthen ground down until translucent and examined under a high-poweredspecialist petrological microscope.

This process enables exact detail of aggregate types, cement types,original mix, and so forth to be determined, but also details of all chemicalchanges, cracking and deterioration to be recorded. Photomicrographs atvarious magnifications are normally provided.

Corrosion Potential Measurements

Each detailed test area of 2 or 4m² or so, or a whole element such as acar park deck, can be subject to corrosion potential measurements, alsoreferred to as half-cell testing. Essentially this technique measures theelectrical potential of the reinforcement in the concrete, in millivolts (mV),via a surface applied instrument coupled to a high impedance multimeter.

The measurements are generally carried out on every node of a 0.5m or1.0m orthogonal grid, generally employing a Copper/Copper Sulfate half-cell.

Corrosion of the reinforcement is an electrical phenomenon, with a buildup of electrical potential in corroding or anodic areas, and a negativecharge by convention on the affected portion of steel.

The presence of chlorides, where associated with loss of passivation,results in the development of very active corrosion cells, often withintense localised pitting of the reinforcement.

Our corrosion potential measurements are carried out in generalaccordance with ASTM C-876, Standard Test Method for Half-CellPotentials of Uncoated Reinforcing Steel in Concrete. We do howeverrecognise that the method only gives corrosion potentials, i.e. theprobability of corrosion occurring, as opposed to rates; and it must beunderstood that the method is empirical, or qualitative.

We additionally recognise that the given parametric criteria really onlyapply to an external chloride contaminated concrete. Any other applicationwill require fresh criteria to be established by visual correlation.

Exploratory Breaking Out

In selected detailed test areas exploratory breakouts are generally madein order to gain further knowledge of reinforcement condition, and otherdetail.

This also allows correlation of other test data, and in particular physicalchecks on reinforcement size, plus of course correct measured concretecover. Surface corrosion condition of the reinforcement is alwaysrecorded.

The concrete remediation and corrosion control process must generallyensure that the concrete becomes stable and the reinforcement passive.Clearly the original condition of the now deteriorated concrete was suchthat failures have occurred well within the designers projected life for thestructure.

Successful concrete repair involves the treatment and control of allcorrosion on the reinforcement, i.e. all the latent (or hidden), as well asthe visible deterioration identified. It is not unusual for the latent damageelement to be considerably more extensive than the visible damage.

Having identified the exact nature and the true extent of the corrosionproblem, a method of concrete remediation and corrosion control must bearrived at by reference to BS DD ENV 1504:Part 9:1997, the Europeanstandard for concrete repair. This is done in accordance with the clientswishes and expectations as regards issues such as: life expectancy of therepair, life expectancy of the structure, intended use, as well as issuesregarding cost and funding, in conjunction with the frequency and numberof repair cycles desired. There is nowadays no reason why a durablerepair should not be achieved straight away in the majority of cases.

The European Standard lists eleven repair principals, of which five arespecifically related to reinforcement corrosion, as opposed to defects inconcrete, and these five are as follows:

Principal 7 [RP] Preserving or Restoring Passivity

This involves creating conditions in which the surface of thereinforcement is maintained or is returned to a passive condition.This can be achieved via additional cover, replacing contaminatedor carbonated concrete, or electrochemical remediation ofconcrete.

Principal 8 [IR] Increasing Resistivity

This involves increasing the electrical resistivity of the concrete,for instance by limiting moisture content via surface treatments,coatings or sheltering.

Principal 9 [CC] Cathodic Control

This involves creating conditions in which cathodic areas ofreinforcement cannot drive an anodic reaction. It may be achievedby limiting oxygen content by saturation or surface coating.

Principal 10 [CP] Cathodic Protection

This involves corrosion control via the establishment of an externalanode, and may be via an applied current (ICCP) or by galvanicmeans (GCP). The method is dealt with by BS EN 12696:2000,Cathodic Protection of Steel in Concrete.

CONCRETE REPAIR

Principal 11 [CA] Control of Anodic Areas

This involves creating conditions in which anodic areas ofreinforcement are not able to take part in the corrosion reaction. Itmay be achieved by coating the reinforcement or applyingcorrosion inhibitors to the concrete.

General Note The above is not reproduced verbatim from the standard, it is ourprécis. It is noted in the standard that the inclusion of methodsdoes not imply their approval, and that the methods may makeuse of products or systems not covered by the EN 1504 series.

The principals are listed in full for completeness, some are rarely,if ever, used by our sister company Makers UK Ltd.

The full range of successful concrete repair and remediation techniquesthat may be employed in corrosion control, are best viewed as a toolbox,and one must seek to select and apply techniques appropriate to thevarious parts of the structure, having given consideration to specific clientrequirements and expectations.

It is usual in concrete repair for a coating to be applied to the carefullyrepaired and prepared surface, being free of blowholes and other surfacedefects, which resists further carbonation, and the ingress of aggressiveagents. It is often preferable for this product to be elastomeric anddurable.In our opinion the preferred route forward, in procuring the necessaryrepair services, is in the formation of partnerships and term contracts witha suitable contractor. It is important to seek a satisfactory outcome for allparties, in which the client’s needs and wishes are fully encompassed.Negotiation and Construction Partnering, as advocated in the Egan Report,should really take a preference over the traditional method of competitivetendering, which in the final analysis can only serve to reduce everyaspect of a job to its lowest common denominator.

GLOSSARY

BIBLIOGRAPHY

HEALTH CHECK

It is important to treat concrete to an occasional health check or MOT likeone would a vehicle. Whilst properly designed and built concrete might beconsidered to be maintenance free, it is in practice an extremely rarecommodity.

Just like other components of a structure the concrete should beperiodically examined by an expert and if necessary subjected to aprogram of testing.

This would often include at least a detailed visual examination, aswell astests for cover depth, carbonation, chlorides, and could possibly alsoinclude tests for HAC, sulfates, ASR and any other tests deemednecessary.

COVER DEPTH

This is a term applied to the depth or thickness of concrete over the layersof reinforcing steel that are closest to the exposed surface. It is importantthat this parameter is appropriate to the concrete quality and the degreeof exposure of the concrete, in order in particular to prevent carbonationfrom reaching the steel.

In UK construction it is historically not uncommon for inappropriate coverto result from poor standards of design and/or build. Shallow covers leadto early deterioration.

PASSIVATION

This is a term that is applied to the protection of reinforcing steel inconcrete by the high alkalinity of concrete as cast. This alkalineenvironment supports a film of passive oxides on the steel, which, despitethe almost inevitable simultaneous presence of oxygen and moistureprevents reinforcement corrosion.

GLOSSARY

COMMON TERMS

CARBONATION

Concrete as cast is highly alkaline which affords the reinforcing steelcorrosion protection. The atmosphere around us, mainly by virtue of thecarbon dioxide content, is slightly acidic which tends to neutralize theconcrete from the surface inwards. This is the natural weathering processof concrete and is termed carbonation.

The carbonation process in no way harms concrete, in fact in many waysit enhances the physical properties, but it does reduce the high alkalinitythat results in a loss of passivation, should the process reach the steel.

This in effect means that active corrosion of the steel will ensue with theall too familiar signs of corrosion in the form of cracking, spalling, andphysical distress to the concrete cover.

The process of carbonation progresses into concrete as a somewhatirregular front, as concrete is not truly homogenous, in approximatereverse exponential advance in relation to time, at a true rate dependantupon concrete quality.

CHLORIDES

Chlorides in concrete are present either because they were cast in at thetime of construction or because they have ingressed the concrete afterconstruction.

Cast in chlorides tend to be present in the UK historically in precastconcrete construction where they are derived from the use of calciumchloride based accelerating admixtures commonly used in the 1960’s.They could also of course be present due to contaminated ingredients,such as for instance marine dredged aggregates. This form of chloridecontamination tends to combine with the hydration products of cement,and hence tends to exist in a substantially chemically bound condition.

Ingressed chlorides can be present from a variety of sources such asdeicing salts on trafficked surfaces, spray and leakage of deicing salts,marine environments, salt laden air in coastal areas, aswell as influencessuch as industrial processes. This form of chloride contamination tends tobe present in a free ion form. The amount of chloride present in concretefrom external contamination is ever increasing with time, as is the depthof penetration.

It should be noted that it is the free chloride ion content of concrete thatdictates the vulnerability to chloride attack. The mechanism of attack isthe localized break down of the passivation of the steel, which leads tooften intensive pitting corrosion. It is not possible to easily specify alimiting chloride content below which corrosion will not be initiated, asthere are so many other factors to take into consideration.

CARBONATION AND CHLORIDES

The process of carbonation in a concrete containing chlorides ispotentially much more serious. This occurs because the carbonationprocess effectively releases the chemically bound chloride leaving it freeto attack the reinforcing steel. It can be seen that the carbonation canthus be a trigger for chloride attack. This form of chloride attackfrequently occurs just ahead of the carbonation front.

SULPHATES

The presence of sulfates in above ground concrete construction in the UKis most frequently due to external contamination such as industrialsources. In sufficient quantity sulfates break down the binding qualities ofcement by chemical attack, which will ultimately result in a dangerous lossof strength.

HIGH ALUMINA CEMENT

This HAC form of cement differs from ordinary portland cement (OPC) inthat it has a higher alumina content. This results in cement that setsmuch more quickly, a property that was historically exploited in themanufacture of precast concrete construction in the UK.

It has more recently come to light that under certain conditions oftemperature and moisture this type of cement undergoes certain chemicalchanges, often termed conversion, which results in a drastic and oftenunacceptable loss of strength. Some degree of, if not total conversion,tends to be the norm in UK HAC.

ALKALI SILICA REACTION

This is a form of alkali aggregate reaction, which was seized upon by thenon-specialist press in the UK when it first came to prominence, andcommonly termed concrete cancer by them. It is ironically only reallyfound in limited geographical areas, most frequently in parts of thesouthwest and midlands.

The reaction requires a particular combination of cement and aggregateproperties to coexist to trigger it, and consists essentially of a chemicalattack on the aggregate leading to the formation of an expansive gel,which in sufficient quantity can disrupt the concrete matrix. The reactionis very much moisture dependant and frequently has a finite life.

Ironically there have been less than a handful of notorious cases in theUK, which have required demolition. The reaction is by no means commonand can frequently be controlled by elimination of moisture. It is

sometimes found microscopically that a degree of the reaction is presentin a minor way, which may need some preventative measure.

It is however fairly common in UK aggregates to find types present inconcrete under petrographic examination which are said to be classified aspotentially reactive with alkali. This is not normally a cause for concernunless the reaction itself is observed to any significant degree.

MECHANICAL DAMAGE

Mechanical or physical damage to concrete is commonly seen due tovehicular or industrial plant impact. It could however include abrasion. Onsome precast concrete one can find physical damage, particularly oncorners, as a result of erection damage.

This kind of damage requires to be treated like a proper concrete repair,particularly where the reinforcement has become exposed. It is alsoimportant to ensure that any repair includes protection from reneweddamage.

FROST DAMAGE

This kind of damage is seen frequently on very exposed and oftensaturated components of concrete construction. It manifests itself in theform of lots of pop outs on a generally friable surface, often also includinglineations of calcareous deposits. It is important to deal with thesesituations and install preventative measures.

LEAKAGE

Signs of leakage through concrete often manifest themselves in the formof calcareous deposits and stalactites, frequently on cracks in soffits. Inthe long term, particularly if salts are present, this can lead to significantdurability problems. The continuous saturation and passage of waterthrough concrete can lead to undesirable chemical changes. It is thereforeimportant to deal with these situations and install remedial measures.

FIRE DAMAGE

The effects of fire upon a concrete surface will vary greatly dependantupon the proximity of the fire, the heat, and the physical qualities of theconcrete. On the one hand the effects can be limited to severe sootcontamination but on the other hand to extensive and deep physicaldamage.

The main effect of exposure of concrete to fire is the differential expansionof the constituent parts leading to physical distress. This can range fromsurface pop outs over aggregate particles, to a friable surface, to spalling,

and ultimately possibly even to the permanent deformation of anyexposed reinforcing steel. It is common for the surface layer of exposedconcrete to exhibit a discoloration to pink, but this is dependent upontemperature reached.

Most frequent repair is in the form of removal of all loose, friable, anddiscolored concrete followed by reinstatement in an appropriate manner.

1. BS DD ENV 1504:Part 9:1997 Products and systems for the protection andrepair of concrete structures- Definitions,requirements, quality control and evaluation ofconformity. Part 9- General principals for theuse of products and systems.

2. BS EN 12696:2000 Cathodic Protection of Steel in Concrete.

3. BS1881: Part 120 Testing concrete- Method for determination ofthe compressive strength of concrete cores.

4. BS1881: Part 124 Testing concrete- Methods for analysis ofhardened concrete.

5. BS1881: Part 204 Testing concrete- Recommendations on theuse of electromagnetic covermeters.

6. ASTM C-876 Standard Test Method for Half-Cell Potentialsof Uncoated Reinforcing Steel in Concrete.

7. Concrete Society Technical ReportNo.32

Analysis of Hardened Concrete.

8. BRE Digest 444, in 3 parts Corrosion of Steel in Concrete.

9. BRE IP 6/81 Carbonation of Concrete made with denseNatural Aggregates.

10. BRE IP 21/86 Determination of the Chloride and Cementcontents of Hardened Concrete.

11. BRE Report BR 254 Repair and Maintenance of ReinforcedConcrete.

12. BRE IP 8/00 Durability of pre-cast HAC concrete inbuildings.

13. BRE Digest 392 Assessment of existing high alumina cementconcrete construction in the UK.

BIBLIOGRAPHY

MartechThe Technical Division of Makers UK Ltd21 Church StreetSawtryHuntingdonCambridgeshire, PE28 5SZ

Telephone: 01487 832288Fax: 01487 832739

E-mail: technical@makers.co.ukWeb-site: www.makers.co.uk

Makers UK LimitedManaging Directors Office and Marketing3rd Floor, North WingLyon CourtWalsworth RoadHitchinHertfordshire, SG4 9SX

Telephone: 01462 477333Fax: 01462 477339

E-mail: marketing@makers.co.ukWeb-site: www.makers.co.uk

Accounts Department1st Floor, Building 3Rye Hill Office ParkBirmingham RoadAllesleyCoventry, CV5 9AB

Telephone: 02476 405600Fax: 02476 405625

Keller Group PlcOxford RoadRyton-on-DunsmoreCoventry, CV8 3EG

Telephone: 02476 511266Fax: 02476 305230

E-mail: coventry@keller-ge.co.ukWeb: www.keller-ge.co.uk

COMPANY DETAILS

MartechThe Technical Division of Makers UK Ltd21 Church StreetSawtryHuntingdonCambridgeshirePE28 5SZ

Telephone: 01487 832288Fax: 01487 832739

E-mail: technical@makers.co.ukWeb-site: www.makers.co.uk

Roel van Es – Divisional Directorrve@makers.co.uk 07798 768899

Jerry Nichols – Regional Manager Team Bj.nichols@makers.co.uk 07798 768907

Mark Heales – Senior Site Engineer Team Bm.heales@makers.co.uk 07774 754436

Jo Barnes – PA to Divisional Directorj.barnes@makers.co.uk

or technical@makers.co.uk

Gemma Scott – Office Administratorg.scott@makers.co.uk

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