On site assessment of concrete strength, sorptivity, permeability and diffusivity

Transcription

1 In situ monitoring and assessment of structures: June 2010 QUB On site assessment of concrete strength, sorptivity, permeability and diffusivity Dr Sree Nanukuttan Prof. P.A. Muhammed Basheer Dr Lulu Basheer Prof. Adrian Long

2 Outline of the Presentation Need for measuring the transport properties of concrete cover in situ In situ tests developed by Queen s Autoclam Permeability System Permit Ion Migration test Limpet Conclusions

3 Manifestation of Lack of Durability Infrastructure problems Energy/Environmental Impact of new structures and rehabilitation of existing structures

4 Corrosion of Reinforcement Due to Chlorides Due to Carbonation

5 Common Causes of Deterioration of Concrete Abrasion and erosion 10% 5% 5% 7% 33% 10% 9% 4% 17% Alkali-aggregate reaction Chemical attack Corrosion (Carbonation) Corrosion (External chlorides) Corrosion (In-built chlorides) Freezing/Thawing Shrinkage and settlement Other (Infrequent)

6 Factors Contributing to Concrete Deterioration Low cover 21% 19% Poor quality concrete Poor design detailing Poor workmanship 13% 2% 7% 12% 26% Wrong specification Failure of joint/waterproofing Wrong material selection

7 Specifications for Durability? What should we specify? How should we test for compliance?

8 Significance of In Situ Measurement of Transport H 2 O CO 2 O 2 Cl - SO 3 - Variation of properties Ingress from the environment Sorptivity Permeability Diffusivity Strength Abrasion resistance Porosity Permeation properties Cover Concrete Depth from the surface

9 Interaction Between Transport and Durability Concrete Manufacture: Constituents, Method & Treatment Microstructure/Microcracks Transport Mechanisms/Permeation properties Alkali Water Oxygen Chlorides Carbon dioxide Sulphates Water Salt or Carbonation Modification of pore structure Alkali attack ASR Gel expansion Corrosion of Reinforcement Sulphate attack Frost attack Salt attack Microcracking/ Cracking/ Spalling Fracture Strength

10 Importance of Cover and Its Quality

11 Cover Concrete is the Achilles Heel of Concrete!

12 Ensuring Durability of Concrete Structures What should we specify? Workability Strength Permeation Properties Absorption Permeability Diffusion Fracture Strength How should we test for compliance? In laboratory using test samples? In situ on structures?

13 Outline of the Presentation Need for measuring the transport properties of concrete cover in situ In situ tests developed by Queen s Autoclam Permeability System Permit Ion Migration test Limpet Conclusions

14 In situ Tests Developed by Queen s Permeation Properties Absorption Permeability Diffusion Fracture Strength Autoclam Permit Limpet

15 Autoclam Permeability System Bonding Type Bolting Type

16 Permit In Situ Ion Migration Test

17 Limpet Pull-off Test

18 Outline of the Presentation Need for measuring the transport properties of concrete cover in situ In situ tests developed by Queen s Autoclam Permeability System Permit Ion Migration test Limpet Conclusions

19 The Autoclam Permeability System Measures air and water permeability water absorption Can be used to test concrete structures and products stone masonry surfaces treated with coatings Easy to use on site Skilled operator not required Results related to service life

20 Sorptivity vs Corrosion Initiation Time Corrosion Initiation time (weeks) 40 High degree of correlation of Autoclam test results with indicators of durability of concrete 25mm cover 40mm cover Sorptivity Index x 10-7 (m 3 / min)

21 Outline of the Presentation Need for measuring the transport properties of concrete cover in situ In situ tests developed by Queen s Autoclam Permeability System Permit Ion Migration test Limpet Conclusions

22 Chloride Profiles in Long-term Exposures 0.7 Chloride concentration (% mass of concrete) Reinforcement level Critical concentration year 5 years 10 years Long-term penetration of chlorides 0.1 depends on the chloride ion diffusivity of the near surface concrete Depth from surface (mm)

23 Permit Ion Migration Test Lab-based test

24 Validation against D mig (1-D) for OPC Mixes 3.5 One dimensional migration coefficient (x10-8 cm 2 /s) y = 1.86x R 2 = 0.95 Mix: w/c, a/c 1: 0.45, 2 2: 0.45, 3 3: 0.45, 4 4: 0.55, 4 5: 0.55, 5 6: 0.65, 4 7: 0.65, 5 8: 0.65, In-situ migration index (x10-7 mol/cm 3 s)

25 Migration Coefficients: 1-D vs In Situ In situ migration coefficient, Din situ (10-12 m 2 /s) y = 0.55x R 2 = Steady state migration, D 1Dssm (10-12 m 2 /s) w/b mix age 0.45 opc 28D 0.52 opc 56D 0.45 pfa 28D 0.52 pfa 56D 0.40 ms 28D 0.40 ms 2yrs 0.52 ms 56D 0.45 ggbs 28D 0.45 ggbs 2yrs 0.52 ggbs 56D

26 Charge Passed vs Migration Coefficient current temperature Current (ma) non-steady state Steady state Attenuate Temperature ( C) w/b ggbs Time (hours) 6 hours charge passed (coulombs.m) y = 2.36x + 30 R 2 = RCPT- ASTM C opc 0.52 opc 0.45 pfa 0.52 pfa 0.40 ms 0.52 ms ggbs Steady state migration coefficient 0.52 ggbs D 1Dssm (x m 2 /s)

27 Charge Passed vs Chloride Flow Chloride concentration (ppm).. concentration charge passed 1400 Time lag Steady state Attenuate Time in hours 0.52 w/c opc Charge passed (coulombs). Chloride concentration of the anolyte.. (mmol/l) y = x R 2 = 0.91 All mixes Charge passed (coulombs)

28 Outline of the Presentation Need for measuring the transport properties of concrete cover in situ In situ tests developed by Queen s Autoclam Permeability System Permit Ion Migration test Limpet Conclusions

29 On site strength assessment Pull-out testing Lok, Capo, Internal Fracture Pull-off testing -- Limpet Penetration resistance testing Windsor Probe

30 Limpet: Pull-off Test

31 Pull-off Strength vs Cube Strength

32 Comparison of different partially destructive tests. Test method Range of Predicted to Measured Strength Ratios Coefficient of Variation C v Pull-off Internal Fracture Windsor Probe

33 Pull-off Test Assessment Convenient mechanical loading for on site Cored and uncored specimens OPC and HAC concrete tested Compared against standard compression test Good compressive/tensile strength relationship

34 Recommendations for on site strength assessment

35 Outline of the Presentation Need for measuring the transport properties of concrete cover in situ In situ tests developed by Queen s Autoclam Permeability System Permit Ion Migration test Limpet Conclusions

36 Ensuring Durability Current Situation Design Practice Control Cover Thickness Specify Minimum Cover Careful placement and fixing Covermeter survey Quality of Cover (= Transport Properties) f c Min. CC Max. w/c Concrete production Tests on standard cubes/ cylinders Execution Placement Compaction Finishing Formwork removal Curing Surface treatments Core tests Site Tests?

37 The Case for Regular In Situ Testing Performance in measurable terms 2 Duration of exposure (years) Intermittent Repair/maintenance Minimum acceptable level 1 3 Service Life

38 The Case for Regular In Situ Testing Whole life cost (million ) 2 Duration of exposure (years) 3 1

39 Assessment of Service Life from In situ Testing In-situ Permeation index Idealised curve Possible spread of results Not fit for service? Carry out repair? No. of cycles (or Duration of exposure) To be agreed for different exposure conditions

40 Ensuring Durability Future Situation Design Practice Control Cover Thickness Specify Minimum Cover Careful placement and fixing Covermeter survey Quality of Cover (= Transport Properties) Specify Concrete Class and k max, D e Concrete production Tests on standard cubes/ cylinders Execution Placement Compaction Finishing Formwork removal Curing Surface treatments Core tests (Optional) Site Tests: permeability, sorptivity & ion migration

41 Thank you