islamic relief centre defect survey & concrete ... survey & concrete investigation 1.0...

Islamic Relief Centre

DEFECT SURVEY & CONCRETE INVESTIGATION

12B/1394

for TIC International Ltd

TIC INTERNATIONAL LTD ISLAMIC RELIEF CENTRE

Your Ref: TIC International Ltd 49 Landor Street Birmingham B8 1AG For the attention of Mr N HagMamed

Contents Pages

1 Introduction 1

2 Objectives 1

3 Methodology 1 to 3

4 Defect/Hammer Survey Results 3

5 Concrete Investigation Results 4

6 Construction Detail Results 4

7 Petrographic Examination Results 5

8 Discussion 6 & 7

9 Conclusions 7 & 8

10 Recommendations 8 & 9

Attachments No. of Pages

Sample & Defect Location Sketches 2

Appended Results & Photographs 25

Petrographic Examination Report, Reference: BCL/PR/020113 14

Electronic copy to Mr C Perry, Structural Design Partnership Ltd

Our Ref: 12B/1394

Date of Report: 4th January 2013


BIRMINGHAM CITY LABORATORIES - 1 - REPORT REFERENCE: 12B/1394

ISLAMIC RELIEF CENTRE

DEFECT SURVEY & CONCRETE INVESTIGATION

1.0 INTRODUCTION As requested, we have undertaken investigative works to the external elevations of the Islamic Relief Centre, 49 Landor Street, Birmingham, B8 1AG. The building, age unknown possibly constructed 1920’s or 1930’s, appears originally designed for an industrial purpose, but now serves as offices. The construction method comprises of beam and column reinforced concrete frame, with masonry cladding infill panels. Toward the front entrance recent refurbishment has been conducted. The remaining more historical elements show significant deterioration. The BCL site works were conducted 15th and 16th November 2012. 2.0 OBJECTIVES The objectives of the survey, as instructed by Chris Perry of the Structural Design Partnership Ltd, are as follows.

Perform a defect survey of the external elevations From selective concrete elements obtain dust samples for chloride ion and

cement content determinations Determine concrete cover to reinforcement Determine depth of carbonation Determine the extent of cracking occurring centrally to main beams and

ascertain the extent of reinforcement corrosion Remove samples for petrographic examination Conduct a photographic log throughout the investigative works

3.0 METHODOLOGY 3.1 Defect Survey A defect/hammer/soundness survey was conducted to the external elevations. This comprised of;-

Tapping the external elements with a hammer Removing spalled/loose material Recording defects

This work was conducted from either ground level or a mobile tower scaffold. 3.2 Concrete Sampling The concrete dust samples were taken by percussive drilling, in accordance with BS EN 14629: 2007. Concrete dust samples were taken either to a depth of 80mm in 25mm increments or to just 30mm. In both cases, the first 5mm was discarded.



3.0 METHODOLOGY 3.3 Covermeter Survey Site determinations of concrete cover to reinforcement were made using an Elcometer 331 covermeter, in accordance with British Standard 1881: Part 204: 1988. The particular model of covermeter employed is designed to locate steel within 100mm of the concrete surface. Minimum concrete cover to primary and secondary reinforcement was determined at sample locations. Readings were verified by the removal of sections of concrete to allow for the reinforcement cover to be physically measured. 3.4 Carbonation Survey Depth of carbonation was determined using phenolphthalein indicator in accordance, with BS EN 14630: 2006. The mean and maximum depth of the carbonation was measured to an accuracy of 1mm, using a depth gauge. 3.5 Cement Content A beam and a column concrete dust sample have been subjected to cement content determination, in accordance with British Standard 1881: Part 204: 1988. 3.6 Chloride Ion Content Samples have been analysed to determine the chloride ion content in accordance with BS EN 14629: 2007. Results are presented by weight of sample and by weight of cement. The results of the cement content analysis have been used to categorise the estimated risk of steel reinforcement corrosion associated with carbonation, cast-in chloride content and environmental conditions. The chloride risk levels have been classified in accordance with criteria given in Building Research Establishment Digest 444: Part 2 table 4b. The chlorides have been considered as cast in-situation and are based on circa sixty year old concrete, within a damp environment as all the elements investigated are external. 3.7 Construction Detail Investigation At two positions the extent of vertical cracking occurring centrally to main beams has been investigated. This has been achieved by using percussive equipment to remove sections of concrete in order to ascertain the full penetration of the cracks. At various locations, areas of significant spalling concrete with exposed corroding reinforcement were examined in order to ascertain the extent of corrosion occurring. The reinforcement bars were physically measured for loss of section. 3.8 Petrographic Examination Concrete core samples were removed from a beam and column using diamond drilling apparatus.



3.0 METHODOLOGY 3.8 Petrographic Examination (Continued) The core positions were reinstated using a proprietary concrete repair material. The core samples have been examined petrographically in order to ascertain the material quality, composition and the presence of any latent defects, such as fire damage or sulphate attack. This petrographic work has been conducted on our behalf by Aston University. 4.0 DEFECT RESULTS The results of the limited defect survey are presented as follows.

Locations – sketches 12B/1394-1 and 2 Results – appendices 1 to 11 Photographs – appendices 12 to 20 Tables 1 and 2 below

A total of 162 defects were highlighted. The total number of individual defects comprises of the following.

Defect Details No. of Defects

Concrete cracking 61

Spalling concrete & exposed reinforcement 51

Spalling concrete 21

Render cracking 20

Masonry cracking 3

Delaminating concrete 2

Previous investigation locations 2

Hollow render 1

Mortar eroding 1 Table 1: Summary by defect frequency The hollow render defects affect approximately 50% of all render to the left gable elevation. The 162 defects are affecting the following number of elements.

Element Affected No. of Defects

Beams 80

Columns 56

Render 21

Masonry 5 Table 2: Defect summary by element



5.0 CONCRETE INVESTIGATION RESULTS A total of six separate elements were investigated for concrete cover to reinforcement and carbonation depths, with samples for chloride ion content removed from each location. Two samples have been analysed for cement content. The site test and laboratory analysis results can be found in appendices 21 to 25, with the sample locations shown on the attached sketches 12B/1394 – 1 and 2. A summary of concrete cover to reinforcement, carbonation depths and chloride results are presented below in Table 3.

Min Max Ave Min Max Ave Min Max Ave

23 76 51 12 >50 31 0.07% 0.07% 0.07%

28 58 41 7 35 23 0.07% 0.13% 0.11%

Corrosion risk levels = 2 low & 1 moderate areas

Areas where reinforcement is located

within carbonated concrete = 2 (67%)

Corrosion risk levels = 1 low & 2 moderate areas

Beams Areas where concrete cover is less than

20mm = 0

Areas where reinforcement is located

within carbonated concrete = 1 (33%)

ElementChloride LevelsConcrete Cover (mm) Carbonation (mm)

Columns Areas where concrete cover is less than

20mm = 0

Table 3: Summary of concrete cover to reinforcement, carbonation depths and chloride results 6.0 CONSTRUCTIONAL DETAIL RESULTS 6.1 Exposed Corroding Reinforcement During the investigation, areas of significant spalling concrete with exposed corroding reinforcement were examined in order to ascertain the extent of corrosion occurring. The results of this examination are presented in appendix 23 and 24. As can be seen, all exposed reinforcement is in a corroding condition, with some areas exhibiting scaling and loss of section up to 2mm. 6.2 Beam Mid-Span Cracking Investigation At two positions, denoted as A and B on drawing 1, the vertical cracking occurring mid span to beams was investigated. The results of the crack investigation are presented below.

At position A, concrete was removed around the crack which was found to penetrate to a depth of 30mm.

At position B, concrete was removed around the crack which was found to penetrate to in excess of a depth of 100mm. To try and preserve the integrity of the beam the investigation was halted at a depth of 100mm.



7.0 PETROGRAPHIC EXAMINATION Initially, a concrete core sample was removed from a column and a beam for petrographic examination. However, during the defect survey large sections of concrete were readily removed from the roof beam. It was therefore decided that one of these pieces would be more representative for petrographic examination, as the failure/spalling mechanism could be investigated. The petrographic examination was conducted on our behalf by Aston University and the report, reference: BCL/PR/020113 is attached and should be read in full. Salient points taken from the report are presented below. Both samples are from the same type of concrete. The concrete is made with crushed epidosite (coarse aggregate),

quartz‐dominated sand and Portland Cement, probably OPC. There is no petrographic evidence of in situ aggregate instability or of

abnormal set. There is no excessive voidage. The mix design is within normal limits though the water: cement ratio, and

hence the capillary porosity of the paste, is high for concrete with ferrous reinforcement.

Reinforcement is placed at a depth of circa 40 mm. Because of the high capillary porosity carbonation penetration commonly

exceeds the depth of placement of ferrous reinforcement. In concrete with uncarbonated paste ferrous reinforcement is rendered

passive and protected from corrosion by the high pH of pore fluids. When the binder is carbonated the pH of pore fluids falls from > 12 to about

8.5. The reinforcement is no longer protected and, in the presence of atmospheric oxygen and moisture, it begins to corrode with concomitant expansion and cracking of the enclosing concrete.

Cracking facilitates ingress of air and moisture so if no remedial action is taken the rate of deterioration may accelerate.

Degradation may be exacerbated in severe winter conditions by freeze – thaw action of water trapped in the fractures.

This concrete is in poor condition for the following reasons.

o The paste has high capillary porosity and this has permitted deep carbonation.

o Ferrous reinforcement is placed too close to the surface of the concrete (approx. 40 mm).

o Photographs of the structure suggest it has not always been well‐maintained.

This petrographic investigation suggests concrete from beams and columns

need immediate remedial treatment and local replacement.



8.0 DISCUSSION 8.1 Corrosion Mechanisms General corrosion of reinforcement is caused by the loss of protection afforded to steel in concrete. Steel in concrete is protected (passivated) by the high alkalinity of the concrete. Carbonation of the concrete, due to atmospheric carbon dioxide, causes a reduction in the concrete alkalinity. This results in the steel reinforcement being susceptible to corrosion in the presence of moisture and oxygen. Corrosion can also be caused by chlorides, either introduced into the concrete from an external source or cast in at the time of construction. Chlorides within the concrete result in the formation of an electrochemical cell, which can result in pitting corrosion. 8.2 Carbonation Induced Corrosion (General Corrosion) Carbonation of concrete cover occurs when atmospheric carbon dioxide dissolves in the concrete’s pore solution and forms carbonic acid, which reacts with the calcium hydroxide generated in cement hydration and with the sodium and potassium hydroxides generated from the alkalis in cement. This precipitates calcium carbonate and reduces the pH to below the level required for the steel to be passive. The relatively low concentrations of soluble sodium and potassium carbonate produced from the alkalis offset this reduction somewhat, but are not sufficient to passivate the steel. Carbonation takes place most rapidly in conditions of low to intermediate humidity (50-70% relative humidity). At high humidity carbon dioxide cannot penetrate the water filled pores to react with calcium hydroxide and other calcium silicate phases. In very dry concrete there is insufficient water for the carbon dioxide to dissolve and form carbonic acid. When the carbonation zone reaches the reinforcing steel, the steel becomes at risk of corrosion in the presence of moisture and oxygen. 8.3 Chloride Induced Corrosion Corrosion due to chloride ions can be a much greater problem as it can occur even when the surrounding concrete is alkaline. Chlorides are a common species but are generally present in concrete from marine contamination, from de-icing salts or from the use of chloride-based admixtures. Calcium chloride admixture was widely used well into the 1970’s as an accelerating and cold-weather admixture for reinforced concrete. Chloride admixtures, introduced during mixing, are mostly bound by the aluminate phase in ordinary Portland cement concrete. Carbonation releases the bound chlorides and can cause them to concentrate ahead of the carbonation front. The problems associated with chloride admixtures are closely linked to the extent of carbonation. Hence reinforcement, located within the carbonation zone, due to poor bar spacing, will be at a far greater risk of suffering chloride-induced corrosion.



8.0 DISCUSSION 8.3 Chloride Induced Corrosion (Continued) When steel is in a passive condition, its oxide film is believed to be in a state of dynamic equilibrium, constantly undergoing local, small breakdown and repair processes, more or less randomly over the surface. Chloride ions interfere with this process, the local environment inside the zone of film breakdown is transformed to an acidic, chloride-rich solution. This causes the anodic activity of the metal to increase locally so that the region develops into a pit, which grows in size leading to localised penetration of the metal. This localised degradation of embedded steel is known as pitting corrosion. It can lead to rapid loss of cross sectional area and load bearing capacity of the metal, as well as causing expansive forces which can cause spalling of the concrete. However, in some instances the volumetric expansion of the corrosion products is minimal compared with the section loss caused by the pit formation. This can lead to significant loss in section before obvious surface cracking or spalling is noticed. 9.0 CONCLUSIONS 9.1 Defect Survey The concrete is in a severely deteriorating condition, with a significant number of defects distributed across the elements surveyed. The greatest number of defects relates to spalling and cracked concrete. The masonry and render also exhibit significant cracking. 9.2 Concrete Investigation The results of the concrete condition survey indicate that concrete cover to reinforcement for the columns and beams is adequate as the likely specified minimum concrete cover of 20mm has generally been maintained. Carbonation depths can be considered as exceedingly variable and generally severely penetrating, with an average of 27mm across all elements. This indicates either a concrete of variable quality, with moderate level of porosity and/or the concrete is not being afforded adequate protection by applied finishes. Carbonation depth was found to exceed the level of reinforcement at fifty percent of locations investigated. This is as a result of excessively penetrating carbonation depths and not low concrete cover to reinforcement. The reinforcement at one column and two beam positions will now have lost passivity. For all remaining elements surveyed the reinforcement should still be in a passive condition, as regards carbonation. The chloride analysis results can also be considered low. This indicates that chlorides have not ingressed from an external source and/or have not been cast-in at the time of manufacture. A summary of the corrosion risk levels obtained for all samples is presented in the table overleaf.



9.0 CONCLUSIONS 9.2 Concrete Investigation (Continued)

Element

Neg

ligib

le

Lo

w

Mo

der

ate

Hig

h

Ver

y H

igh

Ext

rem

ely

Hig

h

Beams N.A. 1

(33%) 2

(67%)

Columns N.A. 2

(67%) 1

(33%)

Table 4: Corrosion risk summary 9.3 Petrographic Examination The petrographic examination report confirms the findings of the site investigative works in that:-

The concrete is in a severely deteriorating condition Deeply penetrating carbonation exists

The reason for the above relates to high original water: cement ratio for structural concrete with ferrous reinforcement. This has resulted in a high capillary porosity which allows carbonation penetration to exceed the depth of reinforcement. Due to loss of passivity, general corrosion of the reinforcement ensues, leading to concrete cracking and subsequent degradation. 10.0 RECOMMENDATIONS All concrete repairs should be specified and undertaken in accordance with methods and materials complying with BS EN 1504. As chloride levels within the concrete are low, repairs can be undertaken using standard concrete repair techniques and materials. Due to the level of deterioration the repairs are likely to be significant and classified as structural and temporary propping may have to be considered. In accordance with the above standard, class R3 and R4 repair mortars should be specified for any patch repairs undertaken. Where the concrete cover afforded to the reinforcement is inadequate additional protection should be considered. In some instances, this could be addressed by the application of an anti-carbonation coating. However, where concrete cover is very low, say <10mm, application of additional concrete cover could be achieved more economically by the use of a high specification proprietary polymer modified cementitious fairing coat. These types of coatings are typically applied in two layers with a minimum thickness of 2 to 3mm.



10.0 RECOMMENDATIONS (continued) The control of further corrosion of the structure will rely on preventing additional carbonation and by reducing moisture levels to restrain corrosion rates. However, given the level of carbonation which has taken place and the general quality of the concrete used in the manufacture of the reinforced concrete elements, some continued deterioration is likely to occur and ongoing planned maintenance is likely to be considered necessary. We trust this report is to your satisfaction. If you require any further assistance please do not hesitate to make further contact. On behalf of: BIRMINGHAM CITY LABORATORIES

Prepared by: Verified by:

JOHN WALSH TREVOR BOX Senior Engineer Principal Engineer

TIC INTERNATIONAL LTD

APPENDIX 1DEFECT RESULTS


W L D

1 Front 1st Masonry Bottom centre Diagonal crack stepped through mortar 800 300 1 1

2 Front 1st Masonry Bottom left side Diagonal crack stepped through mortar 1200 420 1

3 Front Ground Masonry Top to bottom Vertical crack in mortar 3500 3 2

4 Front 1st Column Bottom right side Spalling concrete, exposed corroding reinforcement 500 130 50

5 Front 1st Column Top left side Spalling concrete, exposed corroding reinforcement 500 120 50

6 Front 1st Column Top right side Spalling concrete 150 50 10

7 Front Roof Beam Left side Previous investigation location 120 120 60

8 Front Roof Beam All Spalling concrete, exposed corroding reinforcement 1900 280 60

9 Front Roof Beam Right side Spalling concrete, exposed corroding reinforcement 290 150 25

10 Front 1st Masonry Right side Horizontal crack 1500 2

11 Front Ground Masonry Centre Eroding mortar joint 3000

12 Front 1st Column Top left side Spalling concrete, exposed corroding reinforcement 390 140 30

13 Front 1st Column Bottom left side Delaminating concrete 500 90

14 Front 1st Column Top right side Spalling concrete, exposed corroding reinforcement 600 180 35

15 Front 1st Column Bottom right side Spalling concrete, exposed corroding reinforcement 180 180 30

Photo Ref.

Defect Ref.

Size (mm)Elevation Floor Item Affected Approx Location Defect Details

BIRMINGHAM CITY LABORATORIESKEY

HL = Hairline Crack REPORT REFERENCE: 12B/1394




W L D

Photo Ref.

Defect Ref.


16 Front Roof Beam Centre Spalling concrete, exposed corroding reinforcement 3

17 Front 1st Beam Left side Multi directional cracking 400 300 1

18 Front 1st Beam Centre Vertical crack 400 1

19 Front Roof Beam Right side Spalling concrete, exposed corroding reinforcement 310 120 30

20 Front 1st Column Left side centre Spalling concrete, exposed corroding reinforcement 600 210 40

21 Front 1st Column Bottom left side Vertical crack (hollow) 290 2

22 Front 1st Column Right side centre Spalling concrete, exposed corroding reinforcement 390 200 50 4


24 Front Ground Column Centre Horizontal crack 300 1

25 Front Ground Column Centre Horizontal crack 320 1


27 Front 1st Beam Top left side Spalling concrete, exposed corroding reinforcement 400 200 30

28 Front 1st Column Bottom Vertical crack (hollow) 1200 2

29 Front 1st Column Top Vertical crack (hollow) 1500 2

30 Front 1st Column Top right side Spalling concrete, exposed corroding reinforcement 450 210 30






W L D

Photo Ref.

Defect Ref.


31 Front 1st Column Right side centre Spalling concrete 300 90 25

32 Front 1st Column Bottom right side Spalling concrete (around vent) 280 180 30

33 Front 1st Beam All Delaminating concrete 2200 250 20

34 Front 1st Beam All Vertical crack 300 1

35 Front Ground Column Bottom Previous investigation location 150 130 60

36 Front Roof Beam Centre Spalling concrete, exposed corroding reinforcement 2500 190 30

37 Front 1st Column Top Spalling concrete, exposed corroding reinforcement 250 200 20

38 Front 1st Column Left side Spalling concrete, exposed corroding reinforcement 1800 200 40

39 Front 1st Column Right side Spalling concrete, exposed corroding reinforcement 1800 200 40 5

40 Front Roof Beam Left side Spalling concrete, exposed corroding reinforcement 350 200 50 6

41 Front Ground Column Top Spalling concrete, exposed corroding reinforcement 400 350 40

42 Front 1st Beam Left side Spalling concrete 80 80 20

43 Front 1st Beam Centre Spalling concrete 80 80 20


45 Front 1st Beam Right side Spalling concrete 80 80 20






W L D

Photo Ref.

Defect Ref.




48 Front Ground Column Centre Spalling concrete, exposed corroding reinforcement 220 90 30

49 Front Roof Beam Left side Spalling concrete, exposed corroding reinforcement 250 80 20

50 Front Roof Beam Centre Spalling concrete, exposed corroding reinforcement 900 130 30

51 Front 1st Column Top Spalling concrete, exposed corroding reinforcement 300 100 20 7

52 Front 1st Column Centre Spalling concrete, exposed corroding reinforcement 550 180 50

53 Front Roof Beam All Spalling concrete 1700 200 30 8

54 Front 1st Beam Left side Vertical crack 500 1

55 Front 1st Beam Left side Vertical crack 500 1



58 Front 1st Beam Right side Vertical crack 500 1

59 Front 1st Beam Left side Spalling concrete 100 80 20







W L D

Photo Ref.

Defect Ref.


61 Front Ground Column Right side centre Spalling concrete, exposed corroding reinforcement 310 100 30

62 Front 1st Beam Left side Spalling concrete, exposed corroding reinforcement 510 120 80


64 Front 1st Beam Centre Multi directional cracking 1300 120 20

65 Front Ground Column Right side centre Vertical crack 400 1

66 Front Ground Column Top Vertical crack over previous repair 450 1



69 Front 1st Beam Left side Multi directional cracking 500 500 HL 9

70 Front 1st Beam All Spalling concrete, exposed corroding reinforcement 1100 400 40 10

71 Front Ground Column Bottom Spalling concrete, exposed corroding reinforcement 250 200 40

72 Front Ground Column Bottom Spalling concrete, exposed corroding reinforcement 250 200 40

73 Front 1st Column Top right side Vertical crack over previous repair (hollow) 320 1

74 Rear Ground Column Top Vertical crack 600 1

75 Rear Ground Column Top Spalling concrete 50 50 10






W L D

Photo Ref.

Defect Ref.


76 Rear 1st Beam Top left side Spalling concrete, exposed corroding reinforcement 310 100 40

77 Rear 1st Beam Top right side Spalling concrete 100 30 10

78 Rear 1st Beam Right side Vertical crack 500 1

79 Rear 1st Column Centre Vertical crack (hollow) 350 1

80 Rear 1st Column Centre Vertical crack (hollow) 350 1

81 Rear 1st Beam Bottom left side Spalling concrete, exposed corroding reinforcement 450 190 100 11

82 Rear 1st Beam Centre Spalling concrete 100 80 20


84 Rear Roof Beam Centre Vertical crack 250 HL


86 Rear 1st Column Top Vertical crack 310 HL

87 Rear 1st Column Centre Vertical crack (hollow) 340 1 12

88 Rear 1st Beam Left side Spalling concrete 50 50 20

89 Rear 1st Beam Centre Vertical crack 500 1







W L D

Photo Ref.

Defect Ref.



92 Rear 1st Beam Right side centre Spalling concrete, exposed corroding reinforcement 650 230 50 13

93 Rear Roof Beam Right side Vertical crack 250 1




97 Rear 1st Beam Bottom centre Spalling concrete, exposed corroding reinforcement 850 100 30

98 Rear Ground Column Top left side Spalling concrete, exposed corroding reinforcement 500 250 30 14

99 Rear 1st Column Right side Vertical crack (hollow) 400 1



102 Rear Roof Beam Centre Vertical crack 250 1









W L D

Photo Ref.

Defect Ref.


106 Rear Ground Column Top Spalling concrete, exposed corroding reinforcement 280 150 20

107 Rear Ground Column Centre Vertical crack (hollow) 750 1-2

108 Rear 1st Beam Centre Vertical crack over previous repair 150 HL

109 Rear Roof Beam Left side Vertical crack 250 HL

110 Rear Roof Beam Left side Vertical crack 250 HL

111 Rear 1st Beam Bottom right side Spalling concrete, exposed corroding reinforcement 380 250 50 15

112 Rear 1st Beam Bottom centre Vertical crack over previous repair 160 HL



115 Rear Ground Column Bottom right side Spalling concrete, exposed corroding reinforcement 350 130 30 16

116 Rear Ground Column Top Vertical crack (hollow ) 350 1



119 Rear 1st Column Bottom right side Spalling concrete 190 80 20

120 Rear 1st Column Right side centre Vertical crack (hollow ) 320 1






W L D

Photo Ref.

Defect Ref.


121 Rear 1st Column Left side centre Spalling concrete, exposed corroding reinforcement 350 120 30

122 Rear 1st Column Left side centre Vertical crack over previous repair (hollow) 550 1




126 Rear 1st Beam Right side Vertical crack 450 1 17

127 Rear Ground Column Centre Vertical crack 390 1

128 Rear Ground Column Centre Horizontal crack 390 1 18

129 Rear Ground Column Bottom Horizontal crack 230 1

130 Rear 1st Column Centre Horizontal crack 240 1

131 Rear Roof Beam Right side Spalling concrete, exposed corroding reinforcement 180 100 20

132 Right Roof Beam Top left side Spalling concrete, exposed corroding reinforcement 300 200 20



135 Right Roof Beam Centre Spalling concrete, exposed corroding reinforcement 250 200 20






W L D

Photo Ref.

Defect Ref.




138 Right Roof Beam Right side Spalling concrete 100 80 10

139 Right Roof Beam Right side Spalling concrete, exposed corroding reinforcement 350 250 20

140 Right 1st Beam Right side Spalling concrete, exposed corroding reinforcement 350 300 30

141 Right Ground Column Top right side Vertical crack (hollow) 450 1

142 Left 1st Render (beam) Left side Vertical crack 150 HL



145 Left 1st Render (beam) Left side Vertical crack 450 1

146 Left 1st Render (beam) Left side Vertical crack 450 1

147 Left Roof Render (beam) Left side Vertical crack 500 1

148 Left Roof Render (beam) Left side Vertical crack 500 1

149 Left Roof Render (beam) Centre Vertical crack 500 HL







W L D

Photo Ref.

Defect Ref.


151 Left 1st Render (beam) Centre Vertical crack 500 HL




155 Left 1st Render (beam) Centre Vertical crack 500 1






161 Left Roof Render (beam) Right side Diagonal crack (hollow) 650 1

162 General note; approx 50% left gable render hollow




BIRMINGHAM CITY LABORATORIES REPORT REFERENCE 12B/1394

APPENDIX 12 DEFECT PHOTOGRAPHS

Photograph 1 – Defect 1 masonry diagonal stepped crack

Photograph 2 – Defect 2 masonry vertical crack




Photograph 3 – Defect 16 roof beam spalling concrete, exposed corroding reinforcement

Photograph 4 – Defect 22 column spalling concrete, exposed corroding reinforcement





Photograph 6 – Defect 40 beam spalling concrete, exposed corroding reinforcement





Photograph 8 – Defect 53 roof beam spalling concrete, exposed corroding reinforcement




Photograph 9 – Defect 69 beam multi directional cracking

Photograph 10 – Defect 70 roof beam spalling, exposed corroding reinforcement




Photograph 11 – Defect 81 beam spalling, exposed corroding reinforcement

Photograph 12 – Defect 87 column vertical crack





Photograph 14 – Defect 98 column spalling, exposed corroding reinforcement





Photograph 16 – Defect 115 column spalling, exposed corroding reinforcement




Photograph 17 – Defect 126 beam vertical crack

Photograph 18 – Defect 128 vertical crack in column


BIRMINGHAM CITY LABORATORIES REPORT REFERENCE: 12B/1394

APPENDIX 21

EXTERNAL BEAMS

CONCRETE COVER TO REINFORCEMENT, CARBONATION DEPTH & CHLORIDE RESULTS

Max Mean

4 44 52 60 23 35 23 9.7 0.01 0.10 LowHorizontal 10mm dia plain round bar with surface corrosion

6 48 55 45 74 76 45 9.7 0.01 0.10 ModerateVertical 30mm sq twist

bar with surface corrosion

9 53 49 45 50 45 9.7 0.01 0.10 ModerateReinforcement not

examined

Bold red type indicates reinforcement located within carbonated concreteSample 9 analysed for cement content.

Reinforcement Details

Sa

mp

le

Minimum Concrete Cover

to Vertical Reinforcement

(mm)


to Horizontal Reinforcement

(mm)

Minimum Concrete

Cover (mm)

Cement Content

by Weight of Sample

(%)

Depth of Carbonation

(mm)

Chloride Content

By Weight of Sample

(%)

Chloride Content

By Weight of Cement

(%)

Corrosion Risk Level

12

>50

>50



APPENDIX 22

EXTERNAL COLUMNS

CONCRETE COVER TO REINFORCEMENT, CARBONATION DEPTH & CHLORIDE RESULTS

Max Mean

5 52 58 51 50 48 48 10.8 0.01 0.09 LowVertical 16mm dia plain round bar with surface

corrosion

7 41 43 41 36 38 36 10.8 0.02 0.19 ModerateVertical 16mm dia plain round bar with surface

corrosion

8 35 28 30 35 34 28 10.8 0.02 0.19 LowVertical 30mm dia plain round bar with surface

corrosion

Bold red type indicates reinforcement located within carbonated concreteSample 7 analysed for cement content.

Sa

mp

le


to Vertical Reinforcement

(mm)


to Horizontal Reinforcement

(mm)

Minimum Concrete

Cover (mm)

Cement Content

by Weight of Sample

(%)

Depth of Carbonation

(mm)

Chloride Content

By Weight of Sample

(%)

7

25

38

Reinforcement Details

Chloride Content

By Weight of Cement

(%)

Corrosion Risk Level



APPENDIX 23

EXPOSED REINFORCEMENT BAR DIRECTION & CONDITION

4 Front 1st Column Vertical plain round bar 16mm dia, approximately 2mm section loss

8 Front Roof Beam Horizontal plain round bar 16mm dia, surface corrosion

8 Front Roof Beam Vertical square 20mm bar, surface corrosion

9 Front Roof Beam Vertical plain round bar 8mm dia, surface corrosion

14 Front 1st Column Vertical plain round bar 16mm dia & horizontal plain round bar 8mm dia, surface corrosion

16 Front Roof Beam Horizontal plain round bar 20mm dia, approximately 2mm section loss

19 Front Roof Beam Horizontal plain round bar 20mm dia, approximately 2mm section loss

20 Front 1st Column Vertical plain round bar 10mm dia & horizontal plain round bar 6mm dia, surface corrosion

23 Front Roof Beam Vertical square bar 20mm & horizontal plain round bar 16mm dia, surface corrosion

39 Front Ground Column Vertical plain round bar 20mm dia, approximately 2mm section loss

59 Front 1st Beam Vertical square bars 25, scaling & 2mm section loss

63 Rear 1st Beam Horizontal plain round bar 12mm dia, approximately 2mm section loss




Defect Ref.

Elevation FloorItem

AffectedDefect Details



APPENDIX 24

EXPOSED REINFORCEMENT BAR DIRECTION & CONDITION

78 Rear Ground Column Horizontal plain round bar 16mm dia, approximately 2mm section loss


90 Rear Ground Column Horizontal plain round bar 16mm dia, approximately 2mm section loss

94 Rear 1st Column Vertical plain round bar 16mm dia, approximately 2mm section loss

101 Rear Roof Beam Horizontal plain round bar 16mm dia, approximately 2mm section loss

105 Right Roof Beam Vertical square bars 30mm, scaling & 1mm section loss

106 Right 1st Beam Vertical square bars 30mm, surface corrosion

Defect DetailsDefect

Ref.Elevation Floor

Item Affected



APPENDIX 25

CARBONATION DEPTHS

Max Mean

4 Beam Front Elevation

5 Column Front Elevation

6 Beam Rear Elevation

7 Column Rear Elevation

8 Column Rear Elevation

9 BeamRight (East) Gable

Elevation

Bold red type indicates reinforcement located within carbonated concrete

>50

7

12

25

>50

38

ElementSample Location

Depth of Carbonation (mm)

PETROGRAPHICREPORT

DEGRADEDCONCRETETHEISLAMICRELIEFCENTRE49LANDORSTREETBIRMINGHAMB81AG

REPORTNUMBER:12B‐1394

Dr Alan Bromley

Aston Services

Report for Birmingham City Laboratories

Ref: BCL/PR/020113

2 January 2013

PETROGRAPHICREPORT



CONTENTS

1 Samples........................................................................................................................................1

2 Methods of Investigation.............................................................................................................3

3 Petrography..................................................................................................................................4

3.1 Composition of the Concrete.............................................................................................43.2 Aggregates..........................................................................................................................53.3 Binder.................................................................................................................................63.4 Voids...................................................................................................................................73.5 Fractures.............................................................................................................................8

4 Summary and Conclusions...........................................................................................................9

Appendix 1..............................................................................................................................................10

Plates 1 ‐ 3........................................................................................................................................12 ‐ 14

PETROGRAPHICREPORT



1 SAMPLES

Two samples of concrete, from a beam and column, were provided for petrographic investigation and analysis. Brief sample details are presented in table 1.

Table 1. Concrete from the Islamic Relief Centre, 49 Landor Street, Birmingham. Sample details.

Sample number Dimensions (mm) Mass (g) Surface Reinforcement Depth to reinforcement

12B‐1394 02 core: 75 (diam) x 90 762 plain finish 5 mm wire 45 mm

12B‐1392 03 chisel: 160 x 80 x 45 693 plain finish not identified 40 mm

Both samples are from the same type of concrete. It is made with crushed epidosite coarse aggregate, quartz sand and Portland Cement. The binder is uniform pale red in colour (Munsell Colour Index = 10YR 7/3). There is no segregation of the major components. There is no laitance. There are occasional clusters of large complex voids near the surface of the concrete in sample 12B‐1394 02 but there are no zones of honeycombing.

Surface‐related carbonation extends to a depth of at least 35 mm in sample 12B‐1394 02. The carbonation front is irregular and there are apparently isolated patches of carbonated binder at deeper levels in the core. The binder in sample 12B‐1394 04 is completely carbonated.

There are no fractures in sample 12B‐1394 02 and the wire at 45 mm is only superficially corroded. Discontinuous open fissures at the margins of coarse aggregate fragments are common and easily visible in hand specimen. Two faces of chisel sample 12B‐1394 03 are bounded by open fractures that originate from corroded reinforcement at a depth of 40 mm. The concrete adjacent to the corroded metal is iron oxide‐impregnated for a distance of 1 mm – 2 mm.

Photographs of the structure, provided by Mr John Walsh, City of Birmingham Laboratories, show the concrete is severely degraded (figures 1 – 4). Beams and columns show severe cracking, spalling and pop‐outs that often expose strongly corroded reinforcement. Paint on the concrete is cracked and badly flaked. There have been previous attempts at local repair (figures 1C and 1D). The repair mortar is locally cracked parallel with earlier failures, suggesting continued corrosion and expansion of the underlying reinforcement.

Page 1

Petrographic Report Degradation of Concrete 49 Landor Street, BirminghamReport Number: 12B‐1394

Figure 1. Concrete degradation. The Islamic Relief Centre, 49 Landor Street, Birmingham.

A Predominantly longitudinal fractures on surface of column, typical of expansion associated with corrosion of reinforcing bars.

B Severe spalling and cracking in beam above window opening.

C Repair mortar covering junction between column and beam. Cracking has continued after application of new mortar.

D Severe cracking and fall‐out of concrete at edge of column adjacent to a window opening. Repair mortar, applied between the column and the brick panel, has also cracked. Paintwork is in very poor condition.

Page 2

A B

C D


2 METHODSOFINVESTIGATION

Preliminaryinvestigation

Both samples were examined as received, and after removal of loose debris, using a Nikon SMZ‐U stereomicroscope. The microscope has a continuous zoom range of 7.5x to 75x and it is equipped with a 150W continuous ring, fibre optic illuminator. It is useful for the preliminary examination of samples and it is possible to discriminate and sometimes identify features as small as 100 µm in size. The microscope has a trinocular head and can be used for low power photomicrography.

Samplepreparation

Core sample 12B‐1394 02 was sawn in half parallel with its axis. Chisel sample 12B‐1394 03 was sawn normal to the surface of the concrete and arranged to include iron oxide‐impregnated binder adjacent to the corroded reinforcement. The cut face of one part of each sample was carefully ground, finishing with #900 grit carborundum powder. Digital images of ground surfaces were prepared using a flat bed scanner operating at a scan resolution of 1200 dpi. These images are useful for illustrating the general structure of the concrete and the position of any major fractures.

A single 75 mm x 50 mm thin section was prepared from the remaining part of each sample. Section 12B‐1394 02 was oriented parallel with the core axes and section 12B‐1394 03 was positioned normal to the surface of the concrete.

Sub‐samples, used for thin section preparation, were impregnated with epoxy resin containing yellow dye. This facilitates the identification of small voids, fractures and regions of porous binder. A high resolution, low magnification digital image of each section was prepared using a Nikon 9000 Superscan film scanner operating at a scan resolution of 4,000 dpi (plate 1). These images are useful for identifying and illustrating the lithologies of the aggregate and sand and assessing the general structure of the concrete.

Thinsectionexamination

Both sections were examined by conventional transmitted light microscopy and by reflected light fluorescent microscopy using a Nikon E600 Eclipse research polarising microscope. It is fitted with six strain free objectives having primary magnifications of 2.5, 5, 10, 20, 40 and 60. Digital photomicrographs were taken using a Nikon DS‐U1 five megapixel camera fitted to the trinocular head of the microscope. Image enhancement and processing were carried out using Adobe Photoshop CS6 Extended and Fovea Pro 4.0 image processing and analysis software.

Quantitativeinvestigations

Modal analyses were performed using a Conwy Valley Systems automatic stepping stage with Petrog® control software. The stage is capable of traversing the full area of the 75 mm x 50 mm thin sections at stepping and traverse intervals determined by the total count. One thousand points were counted from each thin section. Water:cement ratio was estimated by comparing the fluorescent intensity of the least altered uncarbonated paste in sample 12B1394 02 with that of standard mortars when viewed under high intensity reflected ultraviolet illumination.

Page 3


3 PETROGRAPHY

Both samples are from the same type of concrete. It is made with crushed epidosite (coarse aggregate), quartz‐dominated sand and Portland Cement, probably OPC. There is no evidence for the presence of cement replacements or admixtures though it should be noted that the latter are very difficult to identify by petrographic methods.

3.1 COMPOSITIONOFTHECONCRETE

The volumetric composition of the concrete was determined by modal analysis (point counting). One thousand points were counted from each thin section. Data are presented in table 2.

Table 2. Concrete from the Islamic Relief Centre, 49 Landor Street, Birmingham. Modal analyses.

Sample number Coarse aggregate Sand Binder Voids

12B‐1394 02 41.3 19.6 37.5 1.6

12B‐1394 03 40.7 19.2 37.5 2.6

Mean composition 41.0 19.4 37.5 2.1

Water:cement ratio was estimated by comparing the fluorescent intensity of the dye‐impregnated uncarbonated paste with that in thin sections of standard mortars when viewed under reflected high intensity ultraviolet illumination. Only a small area of thin section 12B‐1394 02 was suitable for the determination so results should be treated with caution. A range of values between approximately 0.6 and 0.8 were obtained. Water:cement ratio = 0.70 was used for the mix design estimation (table 3).

Table 3. Concrete from the Islamic Relief Centre, 49 Landor Street, Birmingham. Estimated mix design.

Component Volume percent

Density (kgm3)

Estimated mix design

Coarse aggregate 41.0 2670 Coarse aggregate 1095 kgm3

Fine aggregate 19.4 2620 Fine aggregate 508 kgm3

Binder 37.5 3140 Cement 368 kgm3

Voids 2.1 Water 258 kgm3

Total 100.0 Density 2229 kgm3

Cement content 16.5 %

Fluorescent intensity equivalent 0.6 – 0.8 Slump 60 ‐ 180 mm

Water:cement ratio 0.70 28‐day strength 31 N/mm2

Maximum aggregate size (mm) 12 crushed

No petrographic evidence for presence of plasticiser

Cement content of two samples were chemically determined by City of Birmingham Laboratories (Mr John Walsh – personal communication).

12B‐1394 04 (beam) 7.9%12B‐1394 07 (column) 10.8%

Page 4


The discrepancy between petrographically‐estimated and chemically‐determined cement content cannot be explained. The aggregate and sand are chemically stable and unlikely to interfere with the chemical analyses. Modal analyses of the two samples are very similar. The estimated volumetric composition is not influenced, for example, by local segregation of a major component. This aspect of the study requires further investigation.

3.2 AGGREGATES

The main features of the coarse aggregate and sand are summarised in table 4 and illustrated by plate 1.

Table 4. Concrete from the Islamic Relief Centre, 49 Landor Street, Birmingham. Aggregates.

Aggregates gap‐graded

Coarse aggregate epidotised quartz – feldspar porphyry (epidosite) Abundance 41.0%

Major components quartz, epidote, chlorite, plagioclase feldspar

Minor components magnetite, leucoxene

Size range 2.5 mm to 12 mm Average 7.5 mm

Grading good Rounding angular

Shape equant – oblate Sphericity low

Fine aggregate quartz‐dominated sand Abundance 19.4%

Major components quartz from acid igneous rocks, sandstone, quartzite and veins

Minor components chert (1% ‐ visual estimate), stable silicates (tourmaline, muscovite, K‐feldspar, glauconite), iron oxide

Size range 100 µm to 400 mm Average 300 µm

Grading good Rounding sub‐angular ‐ spherical

sub‐spherical morphologies predominate

Shape mainly equant Sphericity moderate – high

Percentage passing 600 µm > 90% (Visual estimate)

The coarse aggregate is a quarried product of unusual composition. Its provenance is not known. It contains no minerals that are normally considered reactive when used as concrete aggregate and there is no evidence of in situ instability or reaction with pore fluids in the concrete.

The sand contains about 1% chert. This is considered potentially reactive in terms of alkali – silica reaction (ASR). There is no petrographic evidence of in situ instability of chert or any other components of the sand in this concrete.

Page 5


3.3 BINDER

The binder is made with Portland Cement, probably OPC. In sample 12B‐1394 02 maximum surface‐related carbonation penetration is about 35 mm. The carbonation front is irregular and there are some apparently isolated patches of carbonated paste at deeper levels in the concrete. The binder in sample 12B‐1394 03 is completely carbonated. Mineralogical and textural features of the uncarbonated binder suggest the concrete is between about 40 and 60 years old. Its main properties are summarised in table 5 and illustrated by plate 2.

Table 5. Concrete from the Islamic Relief Centre, 49 Landor Street, Birmingham. Uncarbonated paste.

Binder

Cement type Portland Cement (probably OPC)

Replacement none found

Optical properties of least altered paste Munsell Colour Index

Colour (thin section) medium brown (often opaque) Isotropy weakly anisotropic

Texture mottled Disseminated calcite replaced portlandite locally

Dye absorption variable, generally strong Fluorescence variable, generally strong

Portlandite

In paste present Distribution irregular

Maximum size (µm) 75 Shape mainly tabular

Replacement calcite

At aggregate margins common Distribution irregular

Maximum size (µm) 50 Shape outgrowths

Replacement dissolution, calcite

Cement clinker grains alite ~ belite

Alite common Maximum size (µm) 50

Max. birefringence not determined Colour colourless

Hydration completely hydrated Reaction rims broad brown rims (common)

Alite (clusters) present Maximum size (µm) 300

Matrix dark brown ferrite‐rich glassy phase, granular iron oxide

Hydration variable, weak – strong Reaction rims broad brown – opaque rims (common)

Belite common Maximum size (µm) 50

Max. birefringence not determined Colour dull brown

Hydration moderately hydrated Reaction rims narrow opaque rims

Belite (clusters) common Maximum size (µm) 250

Matrix sparse brown glassy phase

Hydration weak – strong Reaction rims narrow opaque rims

Ferrite/ferrite‐rich glass present Maximum size (µm) 30

Alteration strongly oxidised Colour dark brown ‐ opaque

Other minerals unidentified blue‐green crystalline phase in some alite clusters

Page 6


The main properties of the carbonated paste in both samples are summarised in table 6.

Table 6. Concrete from the Islamic Relief Centre, 49 Landor Street, Birmingham. Carbonated binder.

Carbonated Binder

Transition zones complex, irregular (sample 12B‐1394 02)

Carbonation fronts diffuse

Width of transition zones 250 µm – 1 mm (weak anisotropy of uncarbonated paste suggests widespread incipient carbonation)

Mineralogy and texture

Colour pale yellowish brown – medium brown Texture furfuraceous

Calcite size range 1 µm to 10 µm Porosity variable, locally very high

Relict clinker grains common (replaced by CSH, calcite and opaque iron oxides)

Residual gel irregular patches up to 100 µm maximum size

Granular iron oxide abundant (flakes and irregular grains up to 50 µm maximum size)

Microporosity variable, generally high – very high Pore size range 5 µm to 200 µm

Secondary minerals microcrystalline calcite

Dye absorption strong Fluorescent intensity high

Mineralogical and textural features of the uncarbonated paste (12B‐1394 02) suggest the concrete is between about 40 and 60 years old. These include presence of coarse cement clinker grain clusters and high belite content (plate 2A and B). Fineness and alite:belite ratio have increased progressively over several decades. The fluorescent intensity of the paste is variable but generally high, indicating high water:cement ratio. Portlandite is only moderately abundant and its crystal size is smaller than that usually found in old concrete made at high water:cement ration (plate 2C). This may be partly explained by leaching. Both uncarbonated and carbonated binders have high secondary microporosity and peripheral fissures are common locally round coarse aggregate fragments. The latter are almost certainly a result of dissolution of portlandite.

There is no obvious petrographic evidence of abnormal set. There is no post‐hardening degradation other than that related to deeply‐penetrating carbonation and corrosion of reinforcement.

3.4 VOIDS

The main properties of the air void system are summarised in table 7.

Table 7. Concrete from the Islamic Relief Centre, 49 Landor Street, Birmingham. Voids.

Void system

Mean modal volume 2.1% Shape spherical ‐ sub‐spherical

spherical voids predominate

Size range 100 µm to 2.5 mm Average size 500 µm

Distribution regular (visual assessment)

Interconnectivity generally isolated

Secondary void filling minerals in uncarbonated paste

Minerals calcite Abundance trace

Secondary void filling minerals in carbonated paste

Minerals calcite Abundance present

Page 7


There is no excessive voidage or zones of honeycombing. There are no secondary minerals in voids that might indicate aggregate – cement reaction or degradation resulting from ingress of reactive fluids (soluble sulphate or chloride).

3.5 FRACTURES

There are no fractures in core sample 12B‐1394 02.

Two faces of sample 12B‐1394 03 are bounded by open fractures that originate from corroded reinforcement and extend to the surface of the concrete.

Fracture aperture cannot be assessed. They follow the margins of coarse aggregate fragments rather than cutting through them. Their walls are coated with 50 µm – 100 µm thick layers of brown iron oxide for a distance of 1 mm – 2 mm from their point of origin at the edge of the corroded reinforcement (plate 3A). Carbonated paste adjacent to the walls is impregnated with iron oxide. Binder at the edge of the sample, presumably adjacent to the reinforcement is similarly impregnated with iron oxide.

A few subsidiary fractures branch and reunite with the major open fractures. They have apertures between a few micrometres and about 500 µm (plate 3B). Some cut impartially through aggregate fragments and the binder (plate 3C). Most of the subsidiary fractures are open but a few are partially‐filled with secondary calcite (plate 3D).

Page 8


4 SUMMARYANDCONCLUSIONS

1. Two samples of concrete from the Islamic Relief Centre, 49 Landor Street, Birmingham were submitted for petrographic examination and analysis.

2. The samples are from a reinforced beam and column respectively.

3. Photographs of the structure (Mr John Walsh, City of Birmingham Laboratories – personal communication) show severe cracking and spalling of the concrete that appears to be associated with corrosion of reinforcement and concomitant expansion.

4. Both samples are from the same type of concrete.

5. The concrete is made with crushed epidosite (coarse aggregate), quartz‐dominated sand and Portland Cement, probably OPC.

6. There is no petrographic evidence of in situ aggregate instability or of abnormal set.

7. There is no excessive voidage.

8. The mix design is within normal limits though the water:cement ratio, and hence the capillary porosity of the paste, is high for concrete with ferrous reinforcement.

9. Reinforcement is placed at a depth of circa 40 mm.

10. Because of the high capillary porosity carbonation penetration commonly exceeds the depth of placement of ferrous reinforcement.

11. In concrete with uncarbonated paste ferrous reinforcement is rendered passive and protected from corrosion by the high pH of pore fluids.

12. When the binder is carbonated the pH of pore fluids falls from > 12 to about 8.5. The reinforcement is no longer protected and, in the presence of atmospheric oxygen and moisture, it begins to corrode with concomitant expansion and cracking of the enclosing concrete.

13. Cracking facilitates ingress of air and moisture so if no remedial action is taken the rate of deterioration may accelerate.

14. Degradation may be exacerbated in severe winter conditions by freeze – thaw action of water trapped in the fractures.

15. This concrete is in poor condition for the following reasons.

● The paste has high capillary porosity and this has permitted deep carbonation.

● Ferrous reinforcement is placed too close to the surface of the concrete (approx. 40 mm).

● Photographs of the structure suggest it has not always been well‐maintained.

16. This petrographic investigation suggests concrete from beams and columns at the Islamic Relief Centre, 49 Landor Street, Birmingham needs immediate remedial treatment and local replacement.

17. In terms of the scheme of concrete classification provided by Eden (2010) this concrete is assigned to grades 5 – 8 (Appendix 1. Table 8). In the classification system used by this laboratory it is placed in Class B2/C (Appendix 1. Table 9).

Page 9


Appendix 1 – Classification of Concrete

A classification scheme for concrete degradation by petrographic investigation and analysis is outlined in A Code of Practice for the Petrographic Examination of Concrete (Eden, M.A., SR2, Geological Society of London, 2010). Details are presented in table 8.

Table 8. Grades of concrete degradation.

Coherent concrete with no macroscopic evidence of deterioration

1Normal homogeneous concrete with few microcracks. Void content in keeping with the amount of paste. Paste structure in keeping with water:cement ratio. Paste abundance in keeping with water:cement ratio.

2Slight deterioration, possibly through slight excess voidage, excess microcracking, uneven paste composition, low levels of alkali – aggregate reaction, drying shrinkage, low temperature curing, possibly slightly lean mixture.

3Moderately low deterioration, possibly with enhanced voidage, microcracking frequency fairly high, excessive paste porosity, evidence of leaching or other forms of secondary alteration, possible lean mixture.

Coherent concrete with macroscopic evidence of degradation

4Moderate deterioration, possibly with evident macrocracking or fine cracking, enhanced voidage, high frequencies of microcracking or fine cracks, evidence of significant leaching or other forms of secondary alteration, evidence of ettringite in cracks and voids, evidence of significant alkali – aggregate reaction with gel in cracks.

5Moderate deterioration, possibly with much fine cracking and some macrocracking, very high excess voidage, evidence of paste recrystallisation, excessive porosity, carbonation highly penetrative, evidence of significant alkali – aggregate reaction in some abundance.

6 As for 5, but with enhanced level of deterioration but with concrete remaining intact.

Concrete lacks coherence and is friable or readily decomposed

7 Concrete shows deterioration and may be partly decomposed or friable.

8 As 7, but enhanced friability and tending to break into fragments. Loose aggregate particles, honeycombed.

9 As 8, but enhanced deterioration. Much cracking and fragmentation.

10 All cementitious value, coherence and strength lost.

The system is complicated and often difficult to apply, especially if only one thin section is available per sample. For this reason a simplified three‐fold classification is offered here (Table 9). Each class of concrete corresponds approximately with the major divisions presented in the code of practice.

It must be remembered that petrographic classification of concrete is often based on intensive investigation of a thin section measuring only about 65 mm x 40 mm and more general study of a single core or other sample with a mass of about one kilogramme. Even good quality concrete has some short‐range inhomogeneity. Severely degraded material may grade into apparently sound concrete over distances of a few tens of millimetres.

Page 10


Successful application of petrographic classification is heavily dependent on the quality of fieldwork and careful selection of an adequate number of sample positions.

Table 9. A simplified scheme for the petrographic classification of hardened concrete.

Class A concrete. The concrete is petrographically sound. (All of the following conditions are satisfied.)

The petrographically estimated mix design is within acceptable limits.

There is no evidence of in situ aggregate instability.

There is no excessive segregation of the major components of the concrete.

There is no excess voidage or zones of honeycombing.

Carbonation penetration is not excessive and must be less than the depth of placement of any reinforcement.

There is no significant corrosion of ferrous reinforcement.

There is no macro‐ or microcracking other than low density shrinkage microcracking.

There is no replacement of the binder by secondary minerals or gel.

There is no extensive growth of secondary minerals or gel in voids.

Class B1 concrete. The concrete shows petrographic evidence of unsoundness but appears serviceable.

(One or more of the following conditions is satisfied.)

Petrographically estimated mix design and/or derived parameters are outside acceptable limits.

The concrete contains unstable aggregate lithologies that show evidence of in situ reaction.

The concrete shows serious segregation of one or more major components.

The concrete has excess voidage, large voids below reinforcement or zones of honeycombing.

Class B2 concrete. The concrete shows petrographic evidence of post‐hardening degradation.

(One or more of the following conditions is satisfied.)

Surface‐related carbonation penetration is close to or deeper than the level of placement of ferrous reinforcement.

Reinforcement shows evidence of corrosion and associated expansive microcracking.

The concrete has pervasive, high density microcracking associated with severe aggregate shrinkage.

The concrete has pervasive, high density microcracking resulting from growth of secondary minerals and/or gel with concomitant expansion.

The concrete shows spalling and/or high density microcracking resulting from other causes (salt crystallisation, fire or frost damage).

The binder has zones of high secondary porosity.

There is extensive growth of secondary minerals and/or gels in voids.

Class C. The concrete is deemed unsound. (One or more of the following conditions is satisfied.)

Serious corrosion of reinforcement with associated spalling of concrete and growth of long‐range open fractures.

Extensive dissolution of unstable aggregate lithologies with widespread expansion cracking, growth of secondary minerals and/or gel in voids and fractures, and gel‐impregnation of the cement paste. The concrete is locally or generally incoherent.

Frequent long range open or partially open fractures extend from the surface to depths beyond the level of placement of reinforcement.

Serious surface‐parallel spalling that may lead to detachment of flakes or slabs of concrete.

The binder is replaced by soft secondary minerals or gel in large domains that are at least locally interconnected, leading to loss of coherence and compressive strength.

Page 11

Plate 1. Sample number 12B-1394 03.

High resolution low magnification digital image of part of the thin section. The image shows the general

structure of the concrete and the lithology of the coarse aggregate (epidosite: epidotised quartz -

feldspar porphyry). The sand is mainly quartz (white). It is very fine-grained. The binder appears medium

brown. Voids are filled with epoxy resin containing yellow dye.

Most edges of the section lie outside the scanned area though the inclined upper right margin is defined

by the wall of a fracture that originates from a corroded rebar.

Petrographic Report Degradation of Concrete 49 Landor Street, Birmingham

Report Number: 12B-1394

25 millimetres

epidosite

epidosite

fracturesurface

Plate 2. Mineralogy and texture of the binder.

A, B Sample 12B-1394 02. Uncarbonated paste at a depth of about 55 mm below the surface of the

concrete. Coarse partly hydrated alite and belite clusters in strongly mottled paste are visible in

plane polarised light (A). Sparse tabular portlandite crystals may be seen between crossed

polars (B). Pale yellow domains (especially adjacent to some quartz particles) are secondary

micropores, probably formed by partial dissolution of portlandite.

C Same field of view as above seen under reflected high intensity ultraviolet illumination. The

fluorescent intensity of the paste is variable over short distances but generally corresponds to

that of standard mortars having water:cement ratio between 0.6 and 0.8.

D Sample 12B-1394 03. Carbonated paste with coarse furfuraceous (bran-like) texture and high

secondary porosity. The texture is typical of atmospheric carbonation of Portland Cement

concrete made at high water:cement ratio. High secondary porosity facilitates penetration of air

and moisture into the concrete.

A - plane polarised light. B, D - crossed polars. C - reflected high intensity ultraviolet illumination.

A B

C D



100 µm

100 µm100 µm

100 µm

alitecluster

alitecluster

belitecluster

quartz

quartz

micropore

void

portlandite

Plate 3. Fractures associated with corrosion of reinforcement.

A Sample 12B-1394 03. Coating of brown iron oxide and oxide-impregnated binder at the

wall of an expansion-induced fracture about 2 mm from the edge of a corroded rebar.

B Sample 12B-1394 03. Subsidiary open fracture cutting binder about 5 mm from the

edge of a corroded rebar.

C Sample 12B-1394 03. Network of open microfractures cutting impartially through

epidosite aggregate fragment and binder about 5 mm from the edge of corroded

reinforcement.

D Sample 12B-1394 03. Subsidiary fracture partly filled with secondary calcite, about

10 mm from the edge of the reinforcement.

Thin sections photographed in plane polarised light.

A B

C D



100 µm

quartz

oxide-impregnatedbinder

iron oxidecoating

250 µm

250 µm 250 µm

openfracture

openfracture

epidosite(aggregate)

binder

openfractures calcite

islamic relief centre defect survey & concrete ... survey & concrete investigation 1.0...

Documents