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INTERNATIONAL SEMINAR: The Thaumasite Form of Sulfate Attack of Concrete

THAUMASITE FORMATION IN LIMESTONE FILLER CEMENT MORTAR UNDER SULFATE AND CHLORIDE EXPOSURE

S M Torres 1,2 , C J Lynsdale1, R N Swamy 2 , J H Sharp 3

Ordinary Portland cement BS ENV 197-1 CEM I (0 and 5% CaCO3), Portland-limestone cement CEM II/A-L (15% CaCO3) and Portland-composite cement mortar CEM II/B-M (8.5% Metakaolinite and 15% CaCO3) have been tested in sulfate solution alone (0.60% SO4 as MgSO4.7H20), sulfate combined with chloride (0.5, 1.0 and 2.0% Cl as NaCl) and synthetic sea water at 5 and 20oC for 44 weeks. The mortar prisms - mix proportion 1:2.5:0.5 (binder:sand:water/binder)- were cured in water for seven days and 21 days in air at room temperature. Prior to immersion in each specific solution, the prisms were cut in to 2x2x2cm3 cubes. The conditions of the samples were assessed by means of visual inspection, X-ray diffraction (XRD) and Infrared spectroscopy (IRS).

Under the exposure conditions studied in this work, preliminary results suggest that the deterioration in samples exposed to combined sulfate/chloride solutions seems to depend on temperature, chloride concentration, carbonate content and cement type. At 20oC, chloride seems to mitigate the sulfate attack in all mixes in all concentration levels. Nevertheless, samples immersed in combined chloride/sulfate solution at 5oC presented much higher degree of deterioration, which increased as CaCO3 increased. All samples containing limestone presented higher levels of damage as the chloride/sulfate increased, but this trend does not seem to be linear. The most intense attack was found in samples with 15% CaCO3 that were immersed in 1.0%Cl, in which higher content of octahedron Si was found. The presence of Thaumasite/Ettringite type of phases indicates that a thaumasite type of sulfate attack caused the damage. The exact mechanism is still under investigation. OPC CEM I with 5% limestone filler was more damaged than OPC without any replacement. Mortars containing CEM II/B-M with Metakaolinite did not present any sings of deterioration throughout the period of this investigation in both sulfate alone or combined chloride and sulfate solutions, at both temperatures.

___________________________________________________________________________

Centre for Cement and Concrete

1 Department of Civil and Structural Engineering

2 Department of Mechanical Engineering

3 Department of Engineering Materials

University of Sheffield, Mappin Street,

Sheffield, S1 3JD.

ThaumasiteThaumasite formation in Limestone Filler formation in Limestone Filler Cement Mortar Under Cement Mortar Under SulfateSulfate and and

Chloride ExposureChloride Exposure

SandroSandro MardenMarden Torres Torres 1,21,2

Dr Cyril LynsdaleDr Cyril Lynsdale11

Prof RN SwamyProf RN Swamy22

Prof JH SharpProf JH Sharp33

The University of SheffieldThe University of SheffieldCentre for Cement and Centre for Cement and CroncreteCroncrete

1 Department of Civil and Structural Engineering1 Department of Civil and Structural Engineering2 Department of Mechanical Engineering 2 Department of Mechanical Engineering 3 Department of Engineering Materials3 Department of Engineering Materials

Scholarship sponsored by CAPES/BrazilScholarship sponsored by CAPES/Brazil

BackgroundBackgroundAs far as combined chloride and As far as combined chloride and sulfatesulfate is is concerned, it is well documented that chloride concerned, it is well documented that chloride usually mitigates usually mitigates sullfatesullfate attackattackThe general view is that chloride only affect The general view is that chloride only affect reinforced concrete due to corrosionreinforced concrete due to corrosionUnreinforcedUnreinforced concrete is only affected by concrete is only affected by ClCl at at extremely high concentrationextremely high concentrationTEGTEG--2000/2002 report identified the need for 2000/2002 report identified the need for further investigation on the effect of TSA on the further investigation on the effect of TSA on the chloride bind capacity of cements.chloride bind capacity of cements.No research has yet been published so far.No research has yet been published so far.

BackgroundBackgroundRegourdRegourd et al 1978,et al 1978, ThamasiteThamasite formation in a sea defence formation in a sea defence

(dike wall) after 40 years(dike wall) after 40 years

WalkleyWalkley et al 1983et al 1983WoodforditeWoodfordite in some dolomite, in some dolomite, unhydriteunhydrite and and mudstone grouts immersed in 30% mudstone grouts immersed in 30% ClCl brine after 56 brine after 56 daysdays

Slater et al 2002Slater et al 2002

Hobbs et al 2000Hobbs et al 2000

thaumasitethaumasite has probably not have any chloride has probably not have any chloride binding capacity, since higher concentration of binding capacity, since higher concentration of chlorides have been found at deeper sites across chlorides have been found at deeper sites across affected concrete sectionsaffected concrete sections

SibbickSibbick et al 2002et al 2002 ••Extensive damage of a pier few years Extensive damage of a pier few years after constructionafter construction

Brown et al 2000Brown et al 2000

Diamond 2002Diamond 2002

It formed at temperatures higher than It formed at temperatures higher than usually expected: In California state usually expected: In California state USA, where substantial amount of USA, where substantial amount of chloride was found among chloride was found among sulfatessulfates and and carbonatescarbonates

OBJECTIVESOBJECTIVESAssess the role of chlorides on the formation of

thaumasite in limestone filler cement mortar

Evaluate the performance of cement-based systems incorporating metakaolinite with respect to susceptibility to thaumasite formation

Evaluate changes in the engineering properties and microstructure of Portland cement mortar due to exposure to chloride and/or sulfate ingress and thaumasite formation

Explore the usefulness of non-destructive tests in predicting the onset of thaumasite formation.

Investigate the effect of carbonation on susceptibility of long-term mortar prisms to TSA in solutions containing chloride and/or sulfate ions.

Fine aggregate

German Normensand(a European Standard quartzite sand)

Cement BS ENV 197-1 CEM I (0 and 5% CaCO3)

Pozzolan MetaStar 501:Metakolinite (>95%)

Table 1: materials selected

Component Material

Filler Carboniferous limestone (>98%CaCO3)

Materials Materials

BS ENV 197-1 CEM II/A-L (15% CaCO3)BS ENV 197-1 CEM II/B-M (8.5%MK+15% CaCO3)

Chemical compositionChemical composition

OXIDES LIMESTONE(%)

OPC(%)

SiO2 0.86 20.82

Al2O3 0.08 5.30

Fe2O3 0.34 2.08

CaO 56.25 64.78

MgO 0.58 0.98

SO3 0.22 3.28

K2O 0.05 0.57

Na2O 0.08 0.20

Loss on ignition 42.01 1.36

CLINKER CONTENT(%)

C3S 49.41

C2S 22.42

C3A 10.53

C4AF 6.33

Metakaolinite(%)

55.4

40.5

0.65

0.01

0.12

-

2.17

0.13

1.0

Solution compositionSolution composition

g/l

% in

solution

by mass mol/l

sulfate

BRE

class

sulfate in all solutions 6.00 0.60 0.06 IVchloride M5 5.00 0.50 0.14chloride M10 10.00 1.00 0.28chloride M20 20.00 2.00 0.56chloride in sea 21.14 2.11 0.60sulfate in sea water 2.79 0.28 0.03 III

IVIVIVIII

MIXESMIXES

CEMENT LIMESTONE METAKAOLIN/BIND (cement)

SAND/BINDER

water/binder

Water/cement

1 0 0 2.5 0.5 0.5

0.95 0.05 0 2.5 0.5 0.53

0.85 0.15 0 2.5 0.5 0.588

0.765 0.15 0.085 2.5 0.45 0.588

Experimental ProgrammeExperimental Programme

0% 5% 15%

Metakaolin+Limestone filler

5oC20oC

Water

0.60%SO4

0.60%SO4 + 0.5%Cl

0.60%SO4 + 1.0%Cl

0.60%SO4 + 2.0%Cl

Seawater

Microstructure

Eng. Properties

•XRD•IRS •Visual inspection•SEM/BEI/EDS•pH

•Visual inspection•Change in mass•Change in length•Dynamic modulus of elasticity•Ultrasonic Pulse Velocity

CaCO3 concentration Temperature Ionic concentration

Parameters

5 years 15% in air

Samples after 12 weeks at 5oCW M M5 M10 M20 SEA

OPC

5%LF

15%LF

15LF+8.5MK

W M M5 M10 M20 SEA

0PC

5%LF

15%LF

15LF+8.5MK

Samples after 24 weeks at 5oCSamples after 24 weeks at 5oC

W M M5 M10 M20 SEA

0PC

5%LF

15%LF

15LF+8.5MK

Samples after 32 weeks at 5oCSamples after 32 weeks at 5oC

Samples after 44weeks at 5Samples after 44weeks at 5ooCCW M M5 M10 M20 SEA

0PC

5%LF

15%LF

15LF+8.5MK

Samples after 44 weeks at 20Samples after 44 weeks at 20ooCCW M M5 M10 M20 SEA

0PC

5%LF

15%LF

15LF+8.5MK

15%LF AT 515%LF AT 5ooC 24 weeksC 24 weeks

0.60%SO4

0.60%SO4 + 0.5%Cl

0.60%SO4 + 1.0%Cl

0.60%SO4 + 2.0%Cl

15% LF after 40 weeks15% LF after 40 weeks

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CONCLUSIONSCONCLUSIONSAfter 44 weeks, chloride seems to mitigate the After 44 weeks, chloride seems to mitigate the sufatesufateattack in all mixes exposed at 20attack in all mixes exposed at 20ooC, where C, where ettringiteettringiteprecipitated within the corroded material.precipitated within the corroded material.Combined action of chloride and Combined action of chloride and sulfatesulfate seems to be seems to be more deleterious than more deleterious than sulfatesulfate alone at 5alone at 5ooC, when C, when thaumasitethaumasite primary risk factors are present:primary risk factors are present:

Increases as calcium carbonate content increasesIncreases as calcium carbonate content increasesSeems to be nonSeems to be non--linear since 1.0%Cl caused more damage than linear since 1.0%Cl caused more damage than 2.0%Cl and also varied with CaCO2.0%Cl and also varied with CaCO33 content (15%>5%>0%)content (15%>5%>0%)Ettringite/ThaumasiteEttringite/Thaumasite type phases were responsible for the type phases were responsible for the attackattack

Mixes containing limestone filler and Mixes containing limestone filler and metakaolinitemetakaolinite did did not develop any sign of damage in any solution at both not develop any sign of damage in any solution at both 55ooC and 20C and 20ooC after 12 months of exposureC after 12 months of exposure