Surface Resistivity as a Performance Test for Transport Properties

Transcription

1 Surface Resistivity as a Performance Test for Transport Properties Francisco J. Presuel-Moreno, Y. Liu Florida Atlantic University, OME, Dania Beach, FL Mario Paredes Florida Department of Transportation, Gainesville, FL Andrew J. Boyd, McGill University, Montreal, QC, Canada

2 Motivation Deterioration of reinforcement concrete Cracking, spalling, reduction, Loss of structural capacity

3 Background Resistivity of the concrete is used to estimate the quality of concrete (High resistivity less permeable concrete) Low resistivity with corrosion initiated likely indicative of potentially high corrosion rate Recently a good correlation has been established between rapid chloride permeability test and Resistivity on laboratory specimens Good correlation chloride diffusivity vs. surface Resistivity on lab saturated conditions has been obtained

4 Background Surface Resistivity Non-destructive method. Used to estimate the quality of concrete. (permeability) K V 2 a V (semi infinite) KR I I Indicative of potentially high corrosion rate when corrosion has initiated. (Langford) 2 av I

5 Rebar Presence and Concrete Cover effect on SR 1 ρa kω cm a (% of bulk ) Cover Concrete = 2.5cm; 3x3x15cm Cover Concrete = 5cm; 3x3x15cm Cover Concrete = 7.5cm; 3x3x15cm Cover Concrete = 2.5cm; 1x1x1m Cover Concrete = 5cm; 1x1x1m Cover Concrete = 7.5cm; 1x1mx1m Electrode spacing (cm) Modeling of apparent resistivity of single layer concrete with single rebar with different cover concrete, specimen dimension: 1mx1mx1m vs. 3 cm x 3 cm x 15 cm

6 Surface Resistivity vs. RCP R.J. Kessler et.al. CBC28 *Normalized SR i.e. geometry corrected

7 Kessler et.al. Corrosion/25 Normalized

8 RCP (Coulombs) Accelerated Curing Concrete with Slow Reacting Pozzolans (Celik Ozyildirim 2) RT28days RT7/HR21 RT 1 year OPC 85/15FA 75/25FA 65/35FA FA: Fly ash w/cm =.45 No Surface Resistivity was performed by VTRC

9 1 Surface Resistivity vs. D Cl - *2 Lab-3yrDvsRho Field_RvsD 15yr D -FAU 15yr D FAU w/cn Kessler, 28 Sagues, 1992 Presuel, 211 Presuel, 211 Resistivity Kohm-cm 1 *3 Note: 15 yr w/cm.37 *2- Concrete with FA (2,35, 5), **3 Concrete with SF (6, 15, 27), not marked OPC Diffusivity (x1-12 m 2 /s) Surface Resistivity on saturated concrete

10 Resistivity (KOhm-cm) Normalized Surface Resistivity vs. D Cl - D measured after 3.3 yrs and 15 yrs yr yr DD - Presuel, yr yr D D - Hartt, Dapp (m 2 /s) Note: SR at 3.3 yr was not measured

11 Resistivity vs. Time under various Environmental Exposures Resistivity (kohm-cm) Resistivity (kohm-cm) Resistivity (kohm-cm) 2 Normalized Average Cylinders 1 to 3 - OPC group 3cm 5cm Lab T & RH ~95 RH Time (Days) 2 3cm Normalized Average Cylinders 4 to 6 - OPC group 5cm Stored in container with ~95% RH Time (Days) 2 3cm Normalized Average Cylinders 7 to 12 - OPC group 5cm Resistivity ρn kω cm (k -cm) Resistivity ρn kω cm (k -cm) Resistivity ρn kω (k -cm) Time (days) 3 Normalized Resistivity 2cy4 to 2cy6 25 3cm 5cm Stored in container with ~9 RH Time (days) 3 Normalized Resistivity 2cy7 to 2cy Normalized Resistivity 2cy1 to 2cy3 3cm 5cm Lab T & RH 3cm 5cm ρn kω cm 9 Normalized Resistivity 2cy1 to 2cy3 8 3cm 7 5cm High RH Time (days) Stored in fog room all the time Time (Days) OPC Concrete Time (days) 2% FA Concrete

12 Effect of NaCl on Surface Resistivity Resistivity (kohm-cm) cm-NaCl 5cm-NaCl 3cm-Fog 5cm-Fog Group 2 5cm-Fog Normalized Average Cyls - FA in 3.5 NaCl vs. Fog Room Time (Days) 4x8 -Concrete Cylinders. Those exposed to chlorides exposed to NaCl 6 days after casting.

13 Towards Performance Based Concrete Resistivity of Concrete with Slow Reacting Pozzolans Subjected to Accelerated Curing Immersed in Ca(OH) 2 at ~38 ºC Resistivity k cm day Resistivity - FL Limestone 2RT/26HT 7RT/21HT 14RT/14HT 28RT % 1% 2% 3% 4% 5% 6% % FA Compressive Strength MPa day Comp. Strength - FL Limestone 2RT/26HT 7RT/21HT 14RT/14HT 28RT % 1% 2% 3% 4% 5% 6% % FA Bulk diffusivity tests in 15% NaCl are being performed on these concretes.

14 Field work objective Investigate the feasibility of extending correlation D Cl vs. Lab. Surface Resistivity to field surface resistivity measurements Approach Surface resistivity measurements on bridge substructures Surface resistivity measurements on cylindrical cores obtained during field visits Chloride Diffusivity from field cores

15 Field: Surface Resistivity Measurements Measured: Profiles of ρ vs. elevation. Approach: Increased moisture content with water. Method: 1.6 gallons plastic containers. Edge-grip rubber seal on containers, tied down to piles, and filled with fresh water. Track of SR during 3 to 4 days. Additional Measurements: Concrete cover Moisture meter (-2 scale) First measurements as-is. Then containers placed and measurements taken every 24 hours.

16 Conditioning using: 1.6 gallon filled water container, tie-down.

17 Field Obtained Concrete Cores 2 to 4 cores drilled per selected pile 2 purposes: SRwet (high humidity) DCl More than 3 cores in ± 8 pile structures

18 Field results: Turkey Creek, Melbourne FL. Bent 5, Pile 14 1 year-old SR normalized 21 C) 135 orientation SR decreases as moisture increases

19 1 SRfield vs. SRwet a=3cm a=5cm Field (KOhm-cm) Wet (kohm-cm)

20 1. SR wet vs. Age Wet Resistivity (Kohm-cm) Lower SR for > 2 year-old Higher SR for < 2 year-old Bridge Age (years)

21 1.E-6 D Cl vs. Age 1.E-7 Diffusivity (cm 2 /s) 1.E-8 1.E-9 1.E Bridge Age (Years) Most newer bridge structures have low D Cl Older bridges show higher D Cl

22 1. SR Wet vs. D Cl 1-2 years 21-4 years >4 years Wet Resistivity (k -cm) E-1 1.E-9 1.E-8 1.E-7 1.E-6 D (cm 2 /s)

23 Conclusions Concrete with Fly Ash replacement cured in a fog room needs more than 4 days to reach final resistivity value. Immersion in 3.5 NaCl solution reduced the SR value measured by 2% on FA concrete when compared to saturated SR measured value. Environmental conditions have a significant effect on the SR value measured. Exposure to laboratory temperature and relative humidity produces a monotonic increase in the measured SR value.

24 Conclusions Conditioning method increase the moisture content of the concrete layer closer to the surface. SR wet < 1 Kohm-cm for bridges > 2 year-old, SR wet usually > 1 Kohm-cm for newer bridges SR wet vs. D cl showed a good correlation, older bridges had higher D cl and lower SRwet When comparing SR wet to SR field, showed that conditioning approach does not completely saturate the outer-surface concrete

25 Thank you for your attention! Any Questions? Acknowledgments The authors are indebted to the Florida Department of Transportation (FDOT) for financial support of this research. The opinions expressed in presentation are those of the authors and not necessarily of the FDOT. FP also acknowledges travel assistance thru FAU RSY.

26 1 D app values vs. Resistivity Resistivity (Kohm-cm) 1 1 PseudoD-UF Hamilton, 27 Hamilton-27 Hamilton, 27 ECR-USF Sagues, 1994 Bamfoth8y Bamforth, 1999 Force8s Force, 1985 Polder-16yIm Polder, PolderFog Polder, Polder-Rilem2 1.E-9 1.E-8 1.E-7 1.E-6 D app cm 2 /s

27 Moisture content effect on Resistivity 2. Resistivity (KOhm.cm) a. UFA 41c. FA 42d. SF 43a. BFS 44b. MET 45d. OPC Weight increase due to water uptake after 1 day at 6ºC, then exposed in high humidity environment. UFA gained the most Weight 4. OPC clearly the lowest SR wet, followed by BFS..%.5% 1.% 1.5% 2.% Weight increase (%) Note # in Series is CoreID

28 Towards Performance Based Concrete Resistivity of Concrete with Slow Reacting Pozzolans Subjected to Accelerated Curing Immersed in Ca(OH) 2 at ~38 C Resistivity k cm Day Resistivity- Granite 2RT/26HT 7RT/21HT 14RT/14HT 28RT % 1% 2% 3% 4% 5% 6% % FA Compressive Strength MPa 28-day Comp. Strength- Granite RT/26HT 7RT/21HT 14RT/14HT 28RT % 1% 2% 3% 4% 5% 6% % FA Back-up slide

29 Moisture content effect on Resistivity Normalized Resistivity (k -cm) %.5% 1.% 1.5% 2.% 2.5% 3.% 3.5% 4.% M% Note # in Series is CoreID 6D 61D 85A 52B 34A 24A 45D Normalized Resistivity (kohm-cm) Normalized Resistivity (k -cm) 3 32C 2A 25 22A 23C 44B 2 41C 85A %.5% 1.% 1.5% 2.% 2.5% 3.% 3.5% 4.% M% 16 72D 54D 53D 14 33A 31D 3D 8 9 4A 12 42D 43A %.5% 1.% 1.5% 2.% 2.5% 3.% 3.5% 4.% M%

30 RCP (Coulombs) Accelerated Curing Concrete with Slow Reacting Pozzolans (Celik Ozyildirim 1998) RT28days RT7/HR21 RT 1 year FA: Fly ash 1 OPC 85/2FA 1/2FA w/cm= No Surface Resistivity was performed by VTRC