Experience with ASR in Practice and Testing in North America

Transcription

1 Experience with ASR in Practice and Testing in North America AKR Forum, Weimar October 21, 2014 Prof. R. Doug Hooton NSERC/CAC Chair in Concrete Durability & Sustainability UNIVERSITY OF TORONTO 1 DEPARTMENT OF CIVIL ENGINEERING

2 Tom Stanton ~1935: What is going on here? (California, USA) 2

3 The landmark ASR paper Tom Stanton was a civil engineer with the California Highway Department Stanton, T. E. Expansion of Concrete Through Reaction Between Cement and Aggregate Proc. ASCE Dec v 66 (10)

4 Stanton s findings Stanton, was the first to identify that concrete expansion and cracking in various highway structures was due to specific chemical reactions induced by high alkali content cement. He found that the reaction took place on certain types of shales, cherts, and impure limestones found along the coast of California between Monterey Bay and Los Angeles. He identified the primary components of the reactive rocks as opal and chalcedonic silica in the sands. He duplicated the expansion and cracking effects on mortar bars in the laboratory. 4

5 1950s-1970s ASTM C227 mortar bar test was developed and used to determine if aggregates had ASR potential. The effects of low-alkali cement and SCMs (pozzolans, slag) could be evaluated. These tests allowed agencies to deal with ASR if they thought it was a problem 5

6 Why does AAR still occur in 2014? 1. It is not recognized in some countries, states, or by some agencies (eg. Highway Agencies). 2. An aggregate source may not have been previously recognized as reactive (perhaps due to use of Low-Alkali PC in the past) or use of a new part of quarry 3. Inadequate test methods or bad testing. 4. Inadequate mitigation measures used to prevent AAR. 6

7 Occurrence of ASR in the United States (~ 1998) This map was never accurate ASR occurs in every state 7

8 Toronto 8

9 ~1200 km 9

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11 Lower Notch Dam 1971 No ASR problem after 40 years due to use of 20% fly ash in concrete with high-alkali cement Coniston Dam 1930 (Sudbury) 11

12 Timmins Ont. Random Cracking on Bridge Parapet Wall (no Restraint) and ASR gel exudation 12

13 Sudbury HWY #17 Overpass in 2010 Greywacke Gravel (built 1978) 13

14 Deseronto road, Hwy. 401 Ontario Longitudinal ASR cracks in prestressed beams C. Rogers 14

15 Oriented Cracks Due to Restraint (Quebec bridge demolished in 2010) 15

16 ASR Cracking Leading to Freeze/Thaw and Chloride Corrosion (in Quebec, replaced 2010) 16

17 s Test Methods The original ASR test methods (ASTM C227 mortar bar and C289 chemical test) were developed ~1950 appeared to work but were later found not to work (with limits adopted) with different types of aggregate. Some aggregates expanded slowly (and passed limits). Some C227 testing caused alkali leaching before expansion Some C227 testing did not maintain 100% rh, and bars underwent shrinkage---and no one looked at anything other than 6 or 12 month expansions 17

18 1980 s In Canada it was realized by the CSA AAR committee that current ASTM test methods were not adequate. New methods were evaluated for a suite of aggregates with known performance (Hooton and Rogers 1987). Based on that, Oberholster s 80 o C mortar bar test was developed and adopted, and the 38 o C concrete prism test was modified with a higher alkali loading. ASTM C227 and C289 were dropped by CSA 18

19 A. CSA Current Aggregate Tests 1. CSA A A Petrographic Examination of Aggregates (includes Petro Number Calc.) 2. CSA A A, ASTM C1260 Accelerated Mortar Bar Test (AMBT) (similar to RILEM AAR-2) 3. CSA A A, ASTM C1293 Concrete Prism Test (CPT) (similar to RILEM AAR-3) 19

20 B. CSA Guides for Mitigation of ASR If you test an aggregate and determine that is alkali-reactive,. What are the options? The Canadian CSA A A (Prescriptive)+28A (Performance) options were adopted in Similar approaches were then adopted by AASHTO (PP65) in 2010, and by ASTM (C1778) in

21 C. CSA: Dealing with AAR affected Structures CSA A864 Guide for Evaluation and Management of Concrete Structures Affected by AAR Discusses maintenance and repair options such as stress relief (saw cuts, diamond wire cuts), moisture control (surface coatings), and crack control (post tensioning) Currently being revised 21

22 Damage Rating Index test to determine degree of damage in existing structures (Prof. B. Fournier) 22

23 C) Risk Minimization: Canadian Guideline for ASR: CSA A A (revised 2014) Allows the use of reactive aggregates with following preventive measures: Limiting the alkali content of the concrete Use of fly ash Use of slag Use of silica fume Use of ternary blends The actual level of prevention varies with risk as defined by: Reactivity of the aggregate Nature of the structure (incl. design life) Exposure condition 23

24 Accelerated Mortar Bar Test CSA A A ASTM C 1260 ~RILEM AAR-2 Aggregate/cementitious material = 2.25 W/CM = 0.5 Portland cement = 0.8 to 1.0% Na 2 O e Mortar bars, 25 x 25 x 250 mm, stored in 1M NaOH at 80 C for 14 days 24

25 Concrete Prism Test CSA A A, ASTM C1293, ~Rilem AAR kg/m 3 cementitious material NaOH added to yield 1.25% Na 2 O e by mass of Portland cement 0.42 W/CM 0.45 Concrete prisms 75 x 75 x 250 mm (min) Stored over water at 38 o C (and nominally 100% RH) for 2 years 25

26 Accelerated Mortar Bar vs. Concrete Prism Test year expansion of concrete (%) Spratt Sudbury Potsdam Granite Nelson Republican Moore All Material Combinations Compiled by M. Thomas 14-day expansion of mortar (%) 26

27 ASTM C09.65 on Petrography C295 Guide for Petrographic Examination of Aggregates for Concrete C856 Practice for Petrographic Examination of Hardened Concrete C1723 Guide for Examination of Hardened Concrete Using Scanning Electron Microscopy 27

28 ASTM AAR Test Methods (subcommittee C09.26) 1. C227 mortar bar test in 38 o C, 100% RH: 3m, 6m limits 2. C289 Quick Chemical Test: ~2-days 3. C441 mortar bar test with pyrex glass sand (for testing pozzolans): 14 or 28 days 4. C586 ACR Rock Cylinder Exp n Test: up to 1 year 5. C1105 Concrete Prism test for ACR (23 o C): 3, 6, 12m limits 6. C1260 Accelerated Mortar Bar Test (80 o C) for Aggregates: 16-days 7. C1293 Concrete Prism Test (38 o C): 1-year for Aggregates: 2-year limit for SCM mitigation 8. C1567 Accelerated Mortar Bar Test (80 o C) for SCM mitigation: 16-days 28

29 Commonly Used ASR Test Methods ASTM C Standard Guide for Petrographic Examination of Aggregates for Concrete ASTM C Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates (Chemical Method) ASTM C Standard Test Method for Potential Alkali Reactivity of Cement-Aggregate Combinations (Mortar-Bar Method) ASTM C Standard Test Method for Effectiveness of Mineral Admixtures or Ground Blast-Furnace Slag in Preventing Excessive Expansion of Concrete Due to the Alkali-Silica Reaction ASTM C Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates (Accelerated Mortar-Bar Method) ASTM C 1567 Standard Test Method for Determining the Potential Alkali-Silica Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated Mortar-Bar Method) ASTM C Standard Test Method for Concrete Aggregates by Determination of Length Change of Concrete Due to Alkali-Silica Reaction (Concrete Prism Test) Aggregate Tests Mortar Tests Concrete Test Recommended Tests

30 ASTM ASR Guide (subcommittee C09.50) ASTM C1778 "Standard Guide For Reducing the Risk of Deleterious Alkali- Aggregate Reaction in Concrete Was just approved in Sept and should be published in the next month. This Guide is similar to AASHTO PP-65 (since 2010) and both are based on CSA A A / 28A (since 2000) 30

31 AASHTO AAR Standards The FHWA and State DOTs have their own standards (so does the US Military) The test methods are essentially the same as ASTM test methods In 2010, the AASHTO PP-65 Guide was adopted. 31

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33 Types of ASR Optional Specifications Prescriptive Specifications If using reactive aggregate the type and level of prevention required is prescribed. For example: Limit concrete alkali content (e.g. 3.0 lb/yd 3 Na 2 Oe) Use a minimum of 25% Class F fly ash or 50% Slag Performance Specification If using reactive aggregate, testing must be conducted to determine what level of prevention is required. For example: Test combinations of the reactive and SCM in the C1567 accelerated mortar bar test to determine how much is required to meet the specified expansion limit

34 Basis for the CSA 27A Risk Guide Pooled concrete prism data from across Canada Data from Several Field Exposure Sites Field cases of mitigated ASR (eg. Lower Notch and Magpie Dams in Ontario) Data is being constantly added to update the guide (including US field and exposure site data). 34

35 Expansion (%) Greywacke coarse aggregate and pit sand from Lower Notch OPC OPC + Fly Ash Lower Notch Dam, Ontario 20% to 30% fly ash used with highalkali cement and highly reactive aggregate 0.00 Low Alkali OPC Age (years) Excellent field performance after 40 years (based on visual inspection and petrographic examination) (Hooton, Thomas, Rogers, Fournier Site Visit 2010) 35

36 Picton Field study 1998: silica fume and slag high-alkali cement (8 mixes) Spratt reactive aggregate field pavements vs. lab. performance Bleszinski, Hooton & Thomas 36

37 Outdoor Exposure Site Test Sites University of Texas at Austin CANMET, Ottawa Canada University of New Brunswick Treat Island, Maine

38 Site Established in Kingston, Ontario in different concrete mixtures reinforced and non reinforced blocks and slab for each mix Spratt coarse aggregate and local non-reactive fine aggregate Hooton, Rogers, et al, ACI Materials J

39 20-year old Pavement Slabs High-alkali PC 18% Class F Fly Ash Low-alkali PC 25% Slag 3.8% SF + 25% Slag 50% Slag Cracking in large beams noticed at ~ % expansion---similar to 38C concrete prisms 39 Hooton, Rogers et al, 2013

40 Mix 6: High-alkali Cement Concrete Lab Prisms vs 20-Year Field Exp ns 38 o C Prisms Beam 2 Beam 1 Pavement Reinforced Beam Total expansion ~same 40

41 CSA A A/28A, AASHTO PP-65 and ASTM C1778 Protocols for Preventing ASR Have both Prescriptive & performance alternatives Allow the use of reactive aggregates with the following preventive measures: Limiting the alkali content of the concrete Use of fly ash Use of slag Use of silica fume Use of ternary blends The actual level of prevention varies with risk as defined by: Reactivity of the aggregate Nature of the structure (includes. design life) Exposure condition

42 Flow Chart Yes Either Chemical Composition, CSA A A Is composition potentially alkali-carbonate reactive? Concrete Prism Test, ASTM C 1105 Expansion < limits in Section 6.6? No Yes No Petrographic Examination Is the aggregate potentially reactive? Yes Field History Is there a proven history of satisfactory field performance? No Yes Petrographic Examination Is the rock a quarried carbonate? No Accelerated Mortar Bar Test, ASTM C 1260 Is 14-day expansion > 0.10%? Yes Concrete Prism Test, ASTM C 1293 Is 1-year expansion > 0.04%? Yes Yes No No No Decreasing Risk of Failure to Identify Reactive Aggregate ASR Type of Reaction Is the expansion due to ACR or ASR? Evaluating Aggregate Alkali-Silica Reactive Take preventive measures or do not use ACR Alkali-Carbonate Reactive Avoid reactive components or do not use Non-Reactive Accept for use No precautionary measures necessary 3 Possible Outcomes Prevent Reject Accept

43 Table 1 Expansion Values for Identifying Potentially Alkali-Silica Reactive Aggregates Test Method C 1293 Test Method C 1260 Greater than 0.040% at 1 year (See Note a) Greater than 0.10% at 14 days (See Notes b, c and d) CSA uses 0.15% Note a: In critical structures such as those used for nuclear containment or large dams, a lower expansion limit may be required. Note b: Many aggregates that expand greater than 0.10% after 14 days have not caused deleterious expansion in field structures and gave less than 0.040% expansion in Test Method C Therefore, expansion in excess of the recommended limit calls for further testing of concrete specimens. Note c: Some aggregates, in particular, granites, gneisses, metabasalts (greenstones), and granodiorites of Grenville age, and also some horizons of the Potsdam sandstone (found in upper New York State and Southwestern Quebec), that have reacted deleteriously in field concretes exhibit less than 0.10% expansion at 14 days in Test Method C Note d: Some dolostones from the Beekmantown Group expand significantly in Test Method C1293 (> 0.040% after one year), while expanding between 0.10% and 0.15% after 14 days in Test Method C1260. Deleterious expansion in field structures has not been confirmed (Berube et al, 2000). 43

44 AASHTO PP-65 and ASTM C1778 Prescriptive Approach Step 1 Determine Aggregate Reactivity Table 1 Classification of Aggregate Reactivity Aggregate- Reactivity Class Description of aggregate reactivity One-Year Expansion in CPT (%) 14-day Expansion in AMBT (%) R0 Non-reactive < R1 Moderately reactive > 0.10, 0.30 R2 Highly reactive > 0.30, 0.45 R3 Very highly reactive > > 0.45 If CPT and AMBT results are available CPT results govern

45 ASR Expansion Tests Concrete Prism Test Expansion (%) Highly-reactive Moderately-reactive Non-reactive Age (months) 45

46 AASHTO PP-65 and ASTM C1778 Prescriptive Approach Step 2 Determine Risk of ASR Table 2 Determining the Level of ASR Risk Size and exposure conditions Non-massive 1 concrete in a dry 2 environment Massive 1 elements in a dry 2 environment All concrete exposed to humid air, buried or immersed Aggregate-Reactivity Class R0 R1 R2 R3 Level 1 Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Level 4 Level 1 Level 3 Level 4 Level 5 All concrete exposed to alkalis in service 3 Level 1 Level 4 Level 5 Level 6 1 A massive element has a least dimension > 3 ft (0.9 m) 2 A dry environment corresponds to an average ambient relative humidity lower than 60%, normally only found in buildings 3 Examples of structures exposed to alkalis in service include marine structures exposed to seawater and highway structures exposed to deicing salts (e.g. NaCl) or anti-icing salts (e.g. potassium acetate, sodium formate, etc.) CSA A A does not include the bottom row

47 AASHTO PP-65 and ASTM C1778 Protocol for Preventing ASR Prescriptive Approach Step 3 Determine the Level of Prevention Table 3 Determining the Level of Prevention Level of ASR Risk (Table 4) Classification of Structure (Table 4) S1 S2 S3 S4 Risk Level 1 V V V V Risk Level 2 V V W X Risk Level 3 V W X Y Risk Level 4 W X Y Z Risk Level 5 X Y Z ZZ Risk Level 6 Y Z ZZ It is not permitted to construct a Class S4 structure (see Table 1) when the risk of ASR is Level 6. Measures must be taken to reduce the level of risk in these circumstances.

48 AASHTO PP-65 and ASTM C1778 (& CSA rev.2014) Protocol for Preventing ASR Prescriptive Approach Step 4 Classify Structure(adapted from RILEM TC191-ARP)

49 AASHTO PP-65 and ASTM C1778 Protocol for Preventing ASR Prescriptive Approach Step 5 Select Preventive Measure Table 5 Limit Alkali Content of Concrete Table 6 Use Supplementary Cementing Material (SCM) Table 7 Adjusting Level of SCM Based on Cement Alkalis Table 8 Limiting Alkali Content of Concrete and Using SCM (to provide exceptional levels of prevention)

50 AASHTO PP-65 and ASTM C1778 Protocol for Preventing ASR Prescriptive Approach Step 5 Select Preventive Measure Table 5 Maximum Alkali Contents (from Portland Cement) to Provide Various Levels of Prevention Prevention Level Maximum alkali content of concrete (Na 2 Oe) lb/yd 3 kg/m 3 V No limit W X Y Z ZZ Go to Table 8

51 Alkali Loading of Concrete To calculate the alkali content of the concrete: Multiply the maximum acid-soluble alkali (total sodium oxide equivalent, which is Na 2 O + [0.658 x K 2 O]) content of the portland cement, expressed as per cent by mass, by the portland cement content of the mixture in kg/m 3 divided by 100. Allowance should be made for likely variations that will occur in the alkali content of the cement and for variations that will occur in the cement content of the concrete. 51

52 AASHTO PP-65 and ASTM C1778 Protocol for Preventing ASR Prescriptive Approach Step 5 Select Preventive Measure Table 6 Minimum Levels of SCM to Provide Various Levels of Prevention Type of SCM Alkali level of SCM (% Na 2 Oe) Minimum Replacement Level (% by mass) Level W Level X Level Y Level Z Level ZZ Fly ash (CaO 18%) < Slag < Table 8 Silica Fume (SiO 2 > 85%) < x LBA or 2.0 x KGA 1.5 x LBA or 2.5 x KGA 1.8 x LBA or 3.0 x KGA 2.4 x LBA or 4.0 x KGA The minimum level of silica fume (as a percentage of cementing material) is calculated on the basis of the alkali (Na 2 Oe) content of the concrete contributed by the portland cement and expressed in either units of lb/yd 3 (LBA in Table 6) or kg/m 3 (KGA in Table 6).

53 Effect of Calcium Content of Fly Ash on ASR Expansion Concrete Prisms with 25% Fly Ash (All ashes < 4.0% Na 2 O e ) 0.20 Expansion at 2 years (%) U of T CTS Calcium in Fly Ash (% CaO) 53

54 Expansion of Concrete Prisms with Slag Spratt % Na 2 O e (by mass of PC) 0.3 Slag (%) Expansion (%) Thomas & Innis 1998 Age (months) 54

55 AASHTO PP-65 and ASTM C1778 Protocol for Preventing ASR Prescriptive Approach Step 5 Select Preventive Measure Using Combinations of SCM s When two or more SCM s are used together to control ASR, the minimum replacement levels given in Table 6 for the individual SCM s may be reduced provided that the sum of the parts of each SCM is greater than or equal to one For example: If Table 6 indicates that either 30% fly ash or 50% slag or 10% silica fume is required it is permissible to use a blend of A% fly ash + B% slag + C% silica fume provided: eg. In Ontario, MTO does A B C not want to use 50% slag, but are ok with 25% slag + 5% silica fume blends

56 AASHTO PP-65 and ASTM C1778 Protocol for Preventing ASR Prescriptive Approach Step 5 Select Preventive Measure Table 7 Adjusting Minimum SCM Level Based on Cement Alkalis Cement Alkalis (% Na 2 Oe) < 0.70 Level of SCM Reduce the minimum amount of SCM given in Table 6 by one prevention level 0.70 to 1.00 Use minimum SCM levels in Table 6 > 1.00 Increase the minimum amount of SCM given in Table 6 by one prevention level > 1.25 No guidance is given

57 AASHTO PP-65 and ASTM C1778 Protocol for Preventing ASR Prescriptive Approach Step 5 Select Preventive Measure Table 8 Using SCM and Limiting the Alkali Content of the Concrete to Provide Exceptional Levels of Prevention Prevention Level SCM as sole prevention Minimum SCM level Limiting concrete alkali content plus SCM Maximum alkali content, lb/yd 3 (kg/m 3 ) Minimum SCM level Z SCM level shown for Level Z in Table (1.8) SCM level shown for Level Y in Table 6 ZZ Not permitted 3.0 (1.8) SCM level shown for Level Z in Table 6

58 AASHTO PP-65 and ASTM C1778 Protocol for Preventing ASR Performance Approach Performance Testing using the CPT (ASTM C1293) Evaluating Lithium Admixtures using the CPT 1. Total cementitious content = 708 lb/yd 3 (420 kg/m 3 ) with or without SCM s 2. Alkali content of portland cement component raised to 1.25% Na 2 Oe 3. LiNO 3 solution added to mix water at various levels 4. W/CM = 0.42 to 0.45 (include water in LiNO 3 solution) Use high-range WRA if slump too low Use VMA if high slump causes segregation in mix 5. Expansion limit 0.04% at 2 years.

59 AASHTO PP-65 and ASTM C1778 Protocol for Preventing ASR Performance Approach Performance Testing using the AMBT The accelerated mortar bar test cannot be used to determine the influence of portland cement alkalis on ASR expansion, in other words: ASTM C1260 AMBT cannot be used to determine the safe alkali level for a particular aggregate In many cases, ASTM C1567 AMBT can be used to determine the safe level of SCM needed to mitigate ASR But ASTM C1567 AMBT cannot be used to evaluate a combination of low-alkali cement and SCM

60 AASHTO PP-65 and ASTM C1778 Using the AMBT for Evaluating Preventative Measures First establish correlation between AMBT & CPT for aggregate 14-d Expansion in AMBT (%) AMBT will overestimate preventive measures If AMBT vs CPT data fall within this range - the AMBT may be used to evaluate preventive measures Y Expansion in CPT (%) AMBT should not be used. Use C1293 for selecting preventative measures

61 Real structures Exposure block tests Concrete prism tests Petrography Mortar bar tests Accelerating Alkali-Silica Reaction in the Laboratory Solution tests alkali availability from SCM Decreasing Reliability Increasing Time The IDEAL Test Method Rapid Reliable Capable of determining performance of real job mixtures influence of aggregate reactivity alkali contribution from cement and/or SCM exposure conditions We don t have an Ideal Test so we rely on a suite of tests and best practices, guidance documents 61

62 Agency Testing Requirements In Canada, highway agencies require aggregate producers to conduct rapid mortar bar (AMBT) and concrete prism tests (CPT) annually. In the USA, FHWA, State DOTs, FAA, etc. do not require this testing. Testing is only required on a project basis so there is no time for CPT tests--so the less-reliable AMBT is typically used. 62

63 80 o C Problems The 80 o C mortar bar test is only accurate about half the time. At temperatures above 60 o C, ettringite becomes unstable and the sulfates are released into the pore solution--- reducing [OH - ]. This appears to prevent expansion of some ASR aggregates, that do expand at lower temperatures Current research is addressing this. 63

64 Alkali Leaching in Concrete Prism Tests In structures & large blocks of concrete, alkali leaching is not large, so ASR reactions will keep going. In 75x75x300 mm concrete prisms, up to 30% of alkalis can leach out over 2 years of test at 38 o C (ASTM C1293). Therefore, if low-alkali cement is used, and there is no expansion, you will not know if this is because the low-alkali cement is effective or the alkalis were leached out of the concrete. Refs. Rogers and Hooton 1991; Fournier et al New research is evaluating changes to reduce leaching 64

65 Summary 1. The CSA, AASHTO and ASTM Guides for identifying ASR aggregates and selecting mitigation make use of current knowledge and can prevent most cases of ASR. 2. Long-term field site data and field experience are being used to improve the guidance. 3. The current test methods are not perfect but research is ongoing to improve them. 4. Highway agencies are now using fly ash or slag in concrete pavements and bridges to mitigate ASR (and improve chloride resistance). 5. The US agencies need to require aggregate producers to perform annual ASR concrete prism testing and not just rely on rapid mortar bar tests.

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