Effect of SCMs on durability. With input from Professor Mike Thomas University of New Brunswick Canada

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1 Effect of SCMs on durability With input from Professor Mike Thomas University of New Brunswick Canada

2 Causes of concrete degradation 1% 4% 5% Others Freeze / Thaw Alkali Silica Reaction Corrosion 90%

3 Impact of SCMs degradation 1 st mech 2 nd mech General Impact SCMs Carbonation binding transport Negative Chloride Transport Binding Positive ASR Pore solution Alumina Positive ph Freeze thaw saturation?? Negative Sulfate Conversion of Afm embedded in CSH to ettringite transport Claimed positive

4 CARBONATION

5 Reducing calcium content; reduces buffer to carbonation Mg S Na K rest +H 2 O CaO Ca(OH) 2 O Reduce Ca Ca CO 2 +CO 2 Si CaCO 3 Fe Al All CaO content can react with CO 2, not just portlandite CH + CO 2 CaCO 3 + H 2 O C-S-H + CO 2 various intermediates CaCO 3 + SiO 2 nh 2 O + H 2 O Aluminate hydrates + CO 2 CaCO 3 + hydrated alumina Ferrite hydrates + CO 2 CaCO 3 + hydrated alumina + iron oxides

6 Effects more pronounced with poor curing From BRE via MDA Thomas, UNB

7 Fly Ash Content vs. Outdoor Carbonation 10-Year Outdoor Carbonation (mm) day cure 3-day cure 7-day cure Fully Carbonated 25-MPa 35-MPa 45-MPa Fly Ash Content (%)

8 Effect of SCMs on carbonation Capacity to bind CO 2 is most important. Cement with less chemical CO 2 inevitably has less capacity to bind CO 2 Transport (through carbonated layer) is secondary. Good curing can partially offset effects of lower binding capacity The balance between these effects needs to be further explored These considerations are important for reinforced concrete, but there is no obstacle to using low CaO binders in non reinforced applications: blocks, bricks, pavers roof tiles

9 CHLORIDE INGRESS

10 Effect of SCMs on chloride transport Now transport is dominant Binding is secondary, but important C-S-H (a lot which binds a little) and Freidel s salt (a little which binds a lot), overall play roughly equal roles in binding. SCMs with high alumina content will give significant increase in binding capacity

11 Effect of Fly Ash on Permeability Permeability (m 2 ) Lab. Concretes W/CM = Fly Ash OPC Age (days)

12 Harmon G.S. Ontario Deck Concrete Mass Exterior OPC (kg/m 3 ) Fly Ash (kg/m 3 ) - 63 W/CM d strength (MPa) Built in 1962/5 Sampled in 1993

13 Effect of fly ash on permeability long term effect Permeability (m 2 ) Source Mike Thomas Lab. Concretes W/CM = Fly Ash OPC Age (days) Field Concretes W/CM =

14 Effect of slag on RCPT W/CM = 0.50 RCP (Coulombs) Control (no slag) 25% Slag 50% Slag Source Mike Thomas Age (days)

15 Effect of SCM on RCPT Values W/CM = 0.40 RCPT (Coulombs) PC Age (days)

16 Effect of SCM on RCPT Values W/CM = 0.40 RCPT (Coulombs) PC 25 FA Age (days)

17 Effect of SCM on RCPT Values W/CM = 0.40 RCPT (Coulombs) PC 8 SF 25 FA Age (days)

18 Effect of SCM on RCPT Values W/CM = 0.40 RCPT (Coulombs) PC 8 SF 25 FA 4 SF & 20 FA Age (days)

19 Example of influence of fly ash on binding

20 CORROSION OF STEEL IN OPC & 30FA CONCRETE 35 N/mm 2, 11 years FAMCET Exposure OPC Source: CSIR Contract nr:bb OPC/30FA Slide from

21 ASR, PhD Theodore Chappex, EPFL

22 Effect of blended pastes on ASR expansion SCMs are effective in reducing deleterious ASR (empirical additions): Field & Lab experience: Samples in alkaline solution OPC 5% 10%SFQ 10%MK 15%SFQ 15%MK Silicon and Aluminium addition are involved in the reduction of expansion Aluminium rich SCMs are more effective against ASR The exact mechanism by which it happens is unclear!

23 Systems Studied Experimental systems: Si SF 7.65, % 5, 10, 15% MK w w Al Q - Filler 7.35, % w 95, 90, 85% w OPC OPC EDS Pore solution extraction TGA Paste sample Pore solution Piston

24 C-S-H EDS analysis 300 days: The Si/Ca increase with increasing substitution for both systems (MK and SF Q) The Al/Ca is constant for SFQ at all substitutions levels and increase with MK substitution Pastes can be compared in term of pore solution concentration

25 Pore solution analysis K [mmol/l] Na [mmol/l] MK 5SFQ 10MK OPC 5SFQ 5MK 10SFQ 10MK 15SFQ 10SSFQ 15MK 15SFQ 15MK The silanol binding capacity is confirmed No improve of fixation is observed up to 2 years in Al rich systems Al doesn t increase the alkali fixation capacity of C S H in blended pastes! Another phenomena is involved to control ASR in presence of Al! me [day]

26 C-S-H fixation capacity estimation 90 days: 300 days: Comparatively, the fixation capacity of SFQ and MK are similar. Aluminium has no influence on the fixation capacity of alkalis New approach: focus on the aggregates

27 Pore solution composition of MK pastes Al [mmol/l] OPC 15MK 10MK 5MK me 300 [day] MK systems provide aluminium ions in the pore solution A peak of aluminium appears during the first 90 days

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30 30 There is a clear influence of aluminium ions on aggregates gel formation!

31 Effect of SCMs on ASR First effect is lowering of ph of pore solution Lower C/S C-S-H absorbs more alkalis SCM high in alumina also inhibit directly dissolution of amorphous silica

32 SULFATE ATTACK,

33 Why worry about sulfate attack Others Freeze / Thaw Alkali Silica Reaction Corrosion 1% 4% 5% Rarely a problem in the field 90% WHY Because we use sulfate resisting cements? Because concrete has w/c < 0.45? Because exposure conditions not the same as in tests? Causes of degradation in reinforced concrete

34 Also an excellent example of how performance tests designed for Portland cements can be totally misleading for blended materials novel solutions

35 Conventionally sulfate resisting cements are those with a low content of C 3 A To improve sustainability we now see an increasing amount of cements containing supplementary cementitious materials (SCMs). Can such cements be qualified as sulfate resisting? Wide diversity of prescriptive approaches throughout Europe. CEN TC 51 charged with finding a performance test >10 years of round robin testing failed to find a reproducible test

36 Development of EN standard for sulfate resisting cements Performance Approach 10 CEMENT NO 1 4th ROUND ROBIN COMPARED TO 2nd Cement no 1 Expansion [%] Source: Time in solution [weeks] Graeme Moir, CEN TC51

37 For Pure Portland cements seems to be fair indicator of degradation But what about slag blends 37

38 Expansion w/c= S cm 3g/L 10g/L 30g/L Surface spalling

39 What happens in the field

40 Effect of sample size w/c=0.55 3g/L 40

41 Expanded Area EA S penetrated S original When EA is large than a certain value, noticeable expansion occurs cm sample, When EA = 0.5, affected depth is around 3mm. 41

42 Loss of surface is dominant FIELD SAMPLES P-0.53 CEM I w/c=0.53 S-0.53 CEM III/B 80wt.-%slag w/b=0.53

43 Field samples Degradation is now only by loss of surface no bulk expansion For this particular slag blend at w/c = 0.53 greater depth of sulfate penetration than plain Portland reference No relation to what is seen in laboratory tests

44 Observation of threshold W/C results of US Corps of Engineers 40 years tests C 3 A seems to be irrelevant! Kurtis and Montiero

45 Effect of SCMs on sulfate resistance Complicated Cannot say that blended cements have chemical resistance to sulfate attack if they contain alumina. Need for test methods more representative of reality where surface loss is more important than macroscopic expansion

46 Impact of SCMs degradation 1 st mech 2 nd mech General Impact SCMs Carbonation binding transport Negative Chloride Transport Binding Positive ASR Pore solution Alumina Positive ph Freeze thaw saturation?? Negative Sulfate Conversion of Afm embedded in CSH to ettringite transport Claimed positive

47 Summary Durability is not a materials property depends on environment SCMs may improve or worsen durability depending on exposure condition It appears that 1.5 C/S CSH may slow down transport of water and chloride Carbonation can be a potential problem, for reinforced concrete due to lack of buffering capacity. ASR undoubtedly improved by SCMs Sulfate attack (and probably Freeze Thaw) are complex and need to be better understood.

48 EXEMPLES d UTILISATION

50 Viaduct au Cameroon utilisation de ciment avec fumée de silice importé du Canada pour amelioration d étanchéité

51 Confederation bridge, Canada: ciment+fs pré-mélangé +cendres volantes ajoutées à stage de fabrication du béton pour augmenter la durabilité, améliorer pompabilité, réduire chaleur, meilleur résistance. + ice load

52 Causeway en Floride Cendres volantes utilisées pour augmenter résistance à la pénétration des ions chlore.

53 Barrage au Canada Cendres Volantes (Type F) pour minimiser risque d expansion par réaction alcali granulats (ASR)

54 Voutre pour tunnel ciment avec FS pré-melangé plus laitier, pour réduire pénétration des ions chlore.

55 End

SULPHATE ATTACK AND CHLORIDE ION PENETRATION: THEIR ROLE IN CONCRETE DURABILITY

SULPHATE ATTACK AND CHLORIDE ION PENETRATION: THEIR ROLE IN CONCRETE DURABILITY Concrete durability continues to be a subject of controversy among design professionals, specifiers, Government instrumentalities,