Performed for:
Andres Belda
Department of Structural Engineering
Faculty of Engineering Science and Technology
Norwegian University of Science and Technology (NTNU) NO-7491 Trondheim
Norway
Performed by:
Ulla Hjorth Jakobsen
Danish Technological Institute Gregersenvej 4
2630 Taastrup Denmark
Project no.: 735718
Date: February 7, 2017
735718_NTNU_carbonation_uhj_070217.docx
Content
1. Introduction ... 1 1.1 Scope of Analysis ... 1 2. Result ... 2 3. Analytical Methods ... 7 3.1 Petrography ... 7 3.2 Scanning Electron Microscopy ... 7 4. PETROGRAPHIC ANALYSIS... 8 Attached: Plate 1-9; Photo documentation
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1 1. Introduction
The following report is prepared on the request of Andres Belda, NTNU, Trondheim, Norway.
Nine laboratory made concrete samples were, December 21th 2016, received for petrographic analysis. Details regarding the samples are in Table 1 below.
Table 1: Data supplied by NTNU.
The three analyzed binders contain various fly ash replacements: CEM I (0% FA), CEM II/B-M (18% FA), and CEM II/B-V (30% FA). The concretes were exposed to different conditions (Table 1).
The appearance of the samples as received.
Numbers in red are DTI identification numbers. Specimens made from the samples have the lab number 7842.
1.1 Scope of Analysis
The scope of this examination is to perform a petrographic analysis of each concrete sample using optical fluorescent microscopy and SEM-EDX.
Special emphasis is on the effect of 3 different exposure conditions on the appearance and composition of the cement paste.
Detailed petrographic analysis as well as photo plates are attached to this document.
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2 2. Result
The following observations were obtained during the petrographic analysis of nine concrete samples:
Generally, all the concrete appears with a plane and intact surface (Figure 1), though in most of the concrete several small micro-cracks formed in the plastic stage are present in the surface. The concrete containing CEM II, 18%FA seem to have the highest amount of surface defects.
CEM I 0%FA CEM II 18%FA CEM II 30%FA
60% RH, 1% CO290% RH, 5% CO2Natural carbonation
Figure 1: Appearance of the carbonated surface of the 9 concrete samples.Relatively many partially hydrated and non-carbonated cement grains are seen in the surface region of 4 of the concrete (light grey phases, arrows). All images are takein the same magnification and in backscatter mode.
A summary of observations is seen in Table 2a and 2b. All of the concrete has a relatively porous paste as well as having a somewhat inhomogeneous paste texture with alternating porous and less porous areas (patchy). Furthermore, adhesions defects (formed in the plastic stage) between paste and aggregate are observed in most of the concrete samples.
The paste of the concrete is, dependent on exposure condition carbonated to varying depths.
Deepest carbonation and the sharpest carbonation front is seen in concrete exposed to 60% RH and 1% CO2. The carbonation is also deep in concrete exposed to 90% RH and 5% CO2, but the
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3 carbonation front is very uneven varying from 4-15mm. Lowest depth of carbonation is seen in the natural exposed concrete where the max. carbonation depth is 5mm (Table 2).
Table 2a: Summary of petrographic observations; ordered after exposure condition
Table 2b: Summary of petrographic observations; ordered after binder type
Generally, the cement in the concrete samples are well hydrated, but in all sample larger partially hydrated cement grains are visible.
Partially hydrated and non-carbonated cement grains are present in the carbonated, especially surface region, of some of the concrete. This feature is most pronounced in concrete containing CEM I and CEM II w. 18%FA and exposed naturally and at 60% RH (Figure 1). In concrete containing CEM II w. 30%FA, and in concrete exposed to 90% RH most of the cement grains are fully hydrated.
Generally, no sign of calcium hydroxide, CH is seen in carbonated pasta.
As the paste in generally has a patchy appearance the carbonated paste also appears patchy with less carbonated #islands$ in a zone of carbonated paste (see Plate 1-9). The most distinct patchy feature is seen in concrete containing CEM I, and to some extent in concrete exposed to 90% RH.
Most of the concrete except those containing 30% FA, has a normal carbonation texture (Figure 2).
In concrete containing 30% FA a popcorn-like texture is observed (Figure 2).
The concrete containing CEM I has an apparent very high capillary porosity similar or higher than our w/c reference of 0.70. The other concrete has an apparently lower capillary porosity. Generally, an increased porosity of the carbonated paste is seen in all concrete (Table 2).
An about 1mm wide, somewhat opaline zone containing very little CH, is recognized in most concrete except in the concrete containing 30% FA and lab-exposed.
Petrographic Observations
Patchy Porosity mm Front
Popcorn carb.
Non-carb.
areas Porosity mm Porosity In paste In voids
I-60 Distinct High 12 Even - Many Slightly increased 1.2 - High Present High Some
II-60 Somewhat Medium 12-14 Relative even - Some Slightly increased 1.2 - Medium None Low Many III-60 Weak Medium 20-22 Relative even X None Slightly increased - - Low None Low Some
I-90 Distinct High 4-14 Un-even - Many Increased 1 Decreased High Present High Few
II-90 Somewhat Medium 7-14 Un-even - Few Increased 1 Decreased Medium None Low Few
III-90 Somewhat Medium 11-15 Un-even X Some Increased - Decreased Low None Low Few
I-N Somewhat High 2-5 Un-even - Some Slightly increased 0.8 - High Present High Few
II-N Somewhat Medium 2-5 Un-even - None Slightly increased 0.8 Decreased Medium None Low Some
III-N Somewhat Medium 4 Even X Few Slightly increased 1 - Low None Low Some
Adhesion
Paste Carbonation zone Interface zone CH
Petrographic Observations
Patchy Porosity mm Front
Popcorn carb.
Non-carb.
areas Porosity mm Porosity In paste In voids
I-60 Distinct High 12 Even - Many Slightly increased 1.2 - High Present High Few
I-90 Distinct High 4-14 Un-even - Many Increased 1 Decreased High Present High Few
I-N Somewhat High 2-5 Un-even - Some Slightly increased 0.8 - High Present High Few
II-60 Somewhat Medium 12-14 Relative even - Some Slightly increased 1.2 - Medium None Low Some
II-90 Somewhat Medium 7-14 Un-even - Few Increased 1 Decreased Medium None Low Few
II-N Somewhat Medium 2-5 Un-even - None Slightly increased 0.8 Decreased Medium None Low Some III-60 Weak Medium 20-22 Relative even X None Slightly increased - - Low None Low Some
III-90 Somewhat Medium 11-15 Un-even X Some Increased - Decreased Low None Low Few
III-N Somewhat Medium 4 Even X Few Slightly increased 1 - Low None Low Some
Adhesion cracks Sample
ID
Paste Carbonation zone Interface zone CH
Air, amount
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4
CEM I 0%FA CEM II 18%FA CEM II 30%FA
60% RH, 1% CO290% RH, 5% CO2Natural carbonation
Figure 2: Appearance of the carbonated paste of the 9 concrete samples. A popcorn-like texture is seen in the concrete containing 30% FA. All images are takein the same magnification and in backscatter mode.
Phase analysis performed from EDX analysis on carbonated versus non-carbonated paste is presented in Figure 3.
The analysis shows generally that phase composition generally depends on the cement composition.
CEM I
Non-carbonated paste in concrete with CEM I, mainly consist of a mixture of CH and CSH and when exposed to 90% RH or natural conditions, ettringite seem to be more frequent.
CEM II 18%FA
Non-carbonated paste in concrete with CEM II 18%FA, consist of a mixture of mainly CSH, ettringite and monosulphate.
CEM III 30%FA
Non-carbonated paste in concrete with CEM III 30%FA, consist of a mixture of mainly CSH and monosulphate.
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5 A certain amount of mono-carboaluminate hydrate phases is present in all concrete.
The carbonate phases present in carbonated paste is quite similar in composition to CSH (when plottet in the S/Al diagram), except in concrete with 30%FA where the phases have a distinct lower and more uniform S/Ca ratio.
CEM I 0%FA CEM II 18%FA CEM II 30%FA
60% RH, 1% CO290% RH, 5% CO2Nat. carbonation
Figure 3: Phase analysis performed on carbonated and non-carbonated paste of the 9 concrete samples.
No distinct differences in phase composition is observed comparing binder type versus exposure condition (Figure 3).
Table 3 shows the average Si/Ca ratio of the carbonated and non-carbonated paste ordered after binder type and exposure condition. As seen, the Si/Ca ratio is in general lower in carbonated paste compared to carbonated paste. When ordered after binder type the lowest Si/Ca ratio in non-carbonated paste is in concrete with CEM I, and there is a tendency to it is also lowest in carbonated paste.
Table 3: Average Si/Ca ratios in carbonated and non-carbonated paste ordered after exposure condition and binder type, respectively
0,0
I60 0.25 0.35 I60 0.25 0.35
II60 0.32 0.43 I90 0.25 0.36
III60 0.29 0.43 IN 0.30 0.37
I90 0.25 0.36 II60 0.32 0.43
II90 0.27 0.38 II90 0.27 0.38
III90 0.29 0.45 IIN 0.29 0.40
IN 0.30 0.37 III60 0.29 0.43
IIN 0.29 0.40 III90 0.29 0.45
IIIN 0.30 0.40 IIIN 0.30 0.40
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6 February 15, 2017
Ulla Hjorth Jakobsen Phone: +45 7220 2198 Email: uhj@teknologisk.dk
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7 3. Analytical Methods
3.1 Petrography
The petrographic analysis (both macroscopic and microscopic examination) is carried out according
! #!!!"!!$The samples are for documentation photographed when received.
The microscopic examination is performed on totally 9 fluorescent impregnated thin sections. A section represents an area of 30 x 45 mm. The section is positioned from the surface and 45 mm into the concrete. The cast surface is indicated with an arrow on the section. All photographs taken, are positioned with the cast surface facing up.
The thin section is made by vacuum impregnating a slice of the sample with an epoxy resin containing a fluorescent dye. Subsequently, the impregnated slice is mounted on a glass plate, and ground to a
! %Finally, the section is covered by a cover glass. The thin section is then examined in a polarizing optical microscope using transmitted light, crossed polarized light, and blue transmitted light with a yellow blocking filter (fluorescent mode).
Three photographs using the three light modes have been taken from 3 position in each section;
carbonated paste, interface between carbonated and non-carbonated paste, and non-carbonated paste. The photographs are presented in nine Plates attached.
The vacuum impregnation of the sample with epoxy causes all voids and cavities in the sample to be filled with fluorescent epoxy. By transmitting fluorescent light through the thin section in the microscope, the fluorescent epoxy in the various porosities will emit yellow light that makes voids, cavities and cracks easy to identify. The fluorescent epoxy also impregnates the capillary pores in the hardened cement paste causing a dense cement paste with low water to cement ratio to appear darker green while a more porous cement paste with a high water to cement ratio appears lighter green. By this, the water to cement ratio (w/c) of the concrete is estimated, by comparing to known references, with an accuracy of ± 0.02.
The table below gives definitions of petrographic terms used in the text.
Terms Definition
Micro cracks Cracks that are less than 0.01 mm wide Fine cracks Cracks that are between 0.01 and 0.1 mm wide Coarse cracks Cracks that are more than 0.1 mm wide
Adhesion cracks Half moon shaped cracks (defects) along the paste/aggregate interface. The cracks mirror the aggregate surfaces. Forms in non-hardened concrete often as a result of bleeding
Totally carbonated All calcium hydroxide, and all CSH phases are carbonated
Partly carbonated All calcium hydroxide is carbonated but partly un-hydrated cement grains remain non-carbonated
Hadley Holes Term describing holes or imprints after former cement grains, now hydrated.
When viewed in fluorescent light they appear bright yellow (holes) with the shape of former alite grains. These features are especially distinct in the cement paste of rapid hardening cement
3.2 Scanning Electron Microscopy
SEM-EDX analysis is performed on 9 polished sections using a Quanta 400 from FEI at DTI.
An accelerating voltage of 15 KeV, spot size 5 and a working distance of around 10 mm are used during analysis. The data are Proza corrected. The analyses were performed using carbon-coated polished sections in high vacuum mode.
Paste analysis is performed on each sample by analyzing 50 point in carbonated area and 50 points in non-carbonated area.
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Paste: The cement is well hydrated. The paste appears distinctly patchy throughout with alternating highly porous and less porous areas. Generally, the paste appears highly porous with an apparent w/c ratio equal or higher to our 0.70 reference. A slightly higher porosity is seen in the carbonated surface area.
Ca(OH)2: Present throughout the paste and in many air voids as relatively large crystals.
The content of CH is highest in the most porous areas. CH is observed in few voids of the carbonated zone.
Opaline paste: Not observed.
Carbonation (mm): 12mm, relatively even front. The zone contains many non-carbonated areas where the cement grains are only partially hydrated. Larger cement grains in the carbonated zone is non-carbonated.
A 1.2mm thick slightly opaline zone, with very little CH, is present in front of the carbonated paste.
Surface: The surface appears plane and intact with few plastic cracks.
Interior cracks: Few adhesion cracks are observed.
Ettringite: Not observed.
Air (type, est.
vol%): Many small air voids present, well-distributed, estimated to 5-6vol%.
Phase Analysis
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9 SEM-EDX analysis
Project No. 735718 Sample No.: I-60 Section #: 7842-1 Size: 30x45mm
Overview, carbonated surface; several
un-hydrated cement grains Carbonated paste
Carbonated paste Non-carbonated paste
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10 PETROGRAPHIC ANALYSIS
Project No. 735718 Sample No.: II-60 Section #: 7842-2 Size: 30x45mm
Petrographic Analysis
Binder type: CEM II, 18%FA
Paste: The cement is well hydrated. The paste appears somewhat patchy with alternating porous and less porous areas. Generally, the paste is porous, with a slightly higher porosity in the carbonated surface area.
Ca(OH)2: Present throughout the paste, small crystals. CH is not observed in air voids.
Opaline paste: Somewhat opaline in non-carbonated areas.
Carbonation (mm): 12-14mm, relatively even front. The zone contains some non-carbonated areas where the cement grains are visible. Larger cement grains in the carbonated zone, especially near the surface, is non-carbonated.
A 1.2mm thick slightly opaline zone, with very little CH, is present in front of the carbonated paste.
Surface: The surface appears plane and intact with many plastic cracks.
Interior cracks: Some adhesion cracks are observed.
Ettringite: Not observed.
Air (type, est.
vol%): Few, large air voids present.
Phase Analysis
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0 0,1 0,2 0,3 0,4 0,5 0,6
S/Ca
Al/Ca
II60-carb II60-non Gypsum
Ettringite
Thaumasite
Monosulfate
Monocarbo CH CSH
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11 SEM-EDX analysis
Project No. 735718 Sample No.: II-60 Section #: 7842-2 Size: 30x45mm
Overview, carbonated surface; several unhydrated
cement grains Carbonated paste
Carbonated paste Non-carbonated paste
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12 PETROGRAPHIC ANALYSIS
Project No. 735718 Sample No.: III-60 Section #: 7842-3 Size: 30x45mm
Petrographic Analysis
Binder type: CEM II, 30%FA
Paste: The cement is well hydrated. The paste appears relatively homogeneous throughout. Generally, the paste is porous, with a slightly higher porosity in the carbonated surface area.
Ca(OH)2: Difficult to observe due to the distinct opalinity of the paste, but present throughout. CH is not observed in air voids.
Opaline paste: Distinctly opaline in non-carbonated areas.
Carbonation (mm): 20-22mm, relatively even front. Only few larger cement grains in the
carbonated zone is non-carbonated. The texture of the carbonated paste looks like popcorn.
No distinct interface zone between carbonated and non-carbonated paste is recognized.
Surface: The surface appears plane and intact with few plastic cracks.
Interior cracks: Some adhesion cracks are observed.
Ettringite: Not observed.
Air (type, est.
vol%): Few, large air voids present.
Phase Analysis
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0 0,1 0,2 0,3 0,4 0,5 0,6
S/Ca
Al/Ca
III60-carb III60-non
Gypsum
Ettringite
Thaumasite
Monosulfate
Monocarbo CH CSH
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13 SEM-EDX analysis
Project No. 735718 Sample No.: III-60 Section #: 7842-3 Size: 30x45mm
Overview, carbonated surface Carbonated paste
Carbonated paste Non-carbonated paste
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Paste: The cement is well hydrated. The paste appears distinctly patchy throughout with alternating highly porous and less porous areas (bleeding?). Generally, the paste is highly porous with an apparent w/c ratio equal or higher to our 0.70 reference, however a distinct lower porosity is seen in the interface zone between carbonated and non-carbonated paste.
Ca(OH)2: Present throughout the paste and in many air voids as relatively large crystals.
Opaline paste: Not observed.
Carbonation (mm): 4-14mm, highly un-even front, difficult to draw a line. The zone contains many non-carbonated areas where the cement grains are visible. Many larger cement grains in the carbonated zone is only partially hydrated and non-carbonated.
An approximate 1mm thick slightly opaline zone, with very little CH, is present in front of the carbonated paste.
Surface: The surface appears plane and intact with few plastic cracks.
Interior cracks: Few adhesion cracks are observed.
Ettringite: Observed within the non-carbonated paste of the carbonated zone.
Air (type, est.
vol%): Many small air voids present, well-distributed, estimated to 5-6vol%.
Phase Analysis
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15 SEM-EDX analysis
Project No. 735718 Sample No.: I-90 Section #: 7842-4 Size: 30x45mm
Overview, carbonated surface, some un-hydrated
cement grains Carbonated paste
Carbonated paste Non-carbonated paste
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Paste: The cement is well hydrated. The paste appears somewhat patchy with alternating porous and less porous areas (most distinct in non-carbonated paste). Generally, the paste is porous, with a slightly higher porosity in the carbonated surface area. A distinct lower porosity is observed at the interface between carbonated and non-carbonated paste.
Ca(OH)2: Present throughout the paste. CH is not observed in air voids.
Opaline paste: Somewhat opaline in non-carbonated areas.
Carbonation (mm): 7-14mm, relatively un-even front. The zone contains few non-carbonated areas where the cement grains are visible. Few larger cement grains in the
carbonated zone appears non-carbonated.
An approximate 1mm thick slightly opaline zone, with very little CH, is present in front of the carbonated paste.
Surface: The surface appears plane and intact with some plastic cracking.
Interior cracks: Few adhesion cracks are observed.
Ettringite: Not observed.
Air (type, est.
vol%): Few, large air voids present.
Phase Analysis
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17 SEM-EDX analysis
Project No. 735718 Sample No.: II-90 Section #: 7842-5 Size: 30x45mm
Overview, carbonated surface Carbonated paste
Carbonated paste Non-carbonated paste
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18 PETROGRAPHIC ANALYSIS
Project No. 735718 Sample No.: III-90 Section #: 7842-6 Size: 30x45mm
Petrographic Analysis
Binder type: CEM II, 30%FA
Paste: The cement is well hydrated. The paste appears somewhat inhomogeneous with patchy areas (especially in non-carbonated areas). Generally, the paste is porous, with a somewhat higher porosity in the carbonated surface area.
Ca(OH)2: Difficult to observe due to distinct opalinity of paste, but present throughout.
Opaline paste: Distinctly opaline in non-carbonated areas.
Carbonation (mm): 11-15mm, somewhat un-even front. Non-carbonated paste is present along some of the coarse aggregate particles. Only few larger cement grains in the carbonated zone is non-carbonated. The texture of the carbonated paste appears like popcorn.
No distinct interface zone between carbonated and non-carbonated paste is recognized.
Surface: The surface is plane and intact with few plastic cracks.
Interior cracks: Few adhesion cracks are observed.
Ettringite: Not observed.
Air (type, est.
vol%): Few, large air voids present.
Phase Analysis
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0 0,1 0,2 0,3 0,4 0,5 0,6
S/Ca
Al/Ca
III90-carb III90-non
Gypsum
Ettringite
Thaumasite
Monosulfate
Monocarbo CH CSH
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19 SEM-EDX analysis
Project No. 735718 Sample No.: III-90 Section #: 7842-6 Size: 30x45mm
Overview, carbonated surface, popcorn
carbonated Carbonated paste
Carbonated paste Non-carbonated paste
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20 PETROGRAPHIC ANALYSIS
Project No. 735718 Sample No.: I-N Section #: 7842-7 Size: 30x45mm
Petrographic Analysis
Binder type: CEM I, 0%FA
Paste: The cement is well hydrated. The paste appears patchy throughout with alternating highly porous and less porous areas. Generally, the paste is highly porous with an apparent w/c ratio equal or higher to our 0.70 reference.
Paste: The cement is well hydrated. The paste appears patchy throughout with alternating highly porous and less porous areas. Generally, the paste is highly porous with an apparent w/c ratio equal or higher to our 0.70 reference.