SURFACE RESISTIVITY TESTING PERMEABILITY: KANSAS DOT OF HARDENED CONCRETE ANDREW JENKINS RESEARCH OPERATIONS SUPERVISOR BUREAU OF RESEARCH

Transcription

1 SURFACE RESISTIVITY TESTING OF HARDENED CONCRETE PERMEABILITY: KANSAS DOT ANDREW JENKINS RESEARCH OPERATIONS SUPERVISOR BUREAU OF RESEARCH

2 OUTLINE Current Practice (at time of study) Outline Project Discuss Data Results/Outcomes Interesting Topics Future Work

3 CURRENT* KDOT PRACTICE Mix Design Prequalification Permeability 56-day RCPT And/Or 28-day Volume of Permeable Voids (Boil Test) Verification One set of samples per mix design per project Same test as was approved, samples pulled from project production at placement location.

4 KDOT SURFACE RESISTIVITY TESTING Initial Research: Add Surface Resistivity as alternative standard test for concrete permeability. Potentially replace existing tests long term. Follow-up Research: Investigate the field application (in-situ testing) of surface resistivity for field verification testing

5 INITIAL RESEARCH Develop a relationship between RCPT/Boil and Surface Resistivity (SRM) 28-day SRM vs. 28-day Boil Same age correlations (28 vs 28, 56 vs 56, etc.) with RCPT 28-day SRM vs. 56-day RCPT Data used to develop permeability specification Perform preliminary investigation on in-situ/core testing

6 28-DAY SRM VS. 28-DAY BOIL Boil (% Permeable Voids) R² = D SRM vs. 28D Boil Power (28D SRM vs. 28D Boil) SRM (kω- cm)

7 SRM VS. RCP SAME AGES RCP (Coulombs) y = 32188x R² = All "Same Age" Values AASHTO CorrelaMon SRM (kω- cm)

8 28-DAY SRM VS. 56-DAY RCP RCP (Coulombs) y = 35352x R² = D SRM vs. 56D RCP SRM (kω- cm)

9 28-DAY SRM VS. 56-DAY RCP RCP (Coulombs) D SRM vs. 56D RCP TheoreMcal SRM- RCP RelaMonship LTRC/LaDOTD Data SRM (kω- cm)

10 AASHTO VS. KDOT Chloride Ion Penetrability RCP AASHTO 56-Day RCP Charge Passed (Coulombs) AASHTO 4 X 8 Cylinder a = 1.5 in. (kω-cm) Surface Resistivity Test KDOT** 4 X 8 Cylinder a = 1.5 in. (kω-cm) Theoretical Value (kω-cm) High > 4000 < 12 < 7.0 < 6.8 Moderate Low Very Low Negligible <100 > 254 > 190 > 272 KDOT Standard Pre KDOT Low Pre **Not Final KDOT Specification Values

11 ROUND ROBIN 28-DAY SRM 21 Samples (3 samples for each District and M&R) Each set of 3 samples was tested by 3 Districts 4.8 % coefficient of variation for entire batch Multiple lab Due to small and controlled nature of round robin, multiple lab CV = 10% is being used. 4.5 % coefficient of variation for each set of samples ~ 1250 sets (3750 samples) Single lab

12 COST-BENEFIT Implementation Cost: ~$106,000 Study Cost: ~$81,000 Equipment: ~$25,000 Triennial Benefit: ~$1,065,000 KDOT: ~$205,000 Contractor: ~$860,000 Cost-Benefit Ratio KDOT: ~1.9 KDOT & Contractor: ~10.0

13 TAKEAWAYS Surface Resistivity is valid test on saturated samples Developed relationship to add Surface Resistivity to KDOT Specifications Correlated well to LTRC/LaDOTD Data and theoretical RCPT-SRM relationship Did not correlate well to Boil test Due primarily to the fact that they are measuring different properties SR Testing on saturated samples is repeatable and less variable than the RCPT Monetary saving to KDOT is present if RCPT and Boil are replaced with Surface Resistivity

14 KDOT SPECIFICATIONS Chloride Ion Penetrability RCP Boil SRM 56-Day Rapid Chloride Permeability Charge Passed (Coulombs) 28-Day Boil Test (% Volume permeable voids) 28-Day Surface Resistivity Measurement 4 X 8 Cylinder a = 1.5 in. (kω-cm) KDOT SPC Spec KDOT MPC Spec KDOT LPC Spec SPC Standard Permeability Concrete; Paving concrete and bridge sub-deck/structure MPC Moderate Permeability Concrete; Full depth bridge deck concrete LPC Low Permeability Concrete; Bridge deck wearing surface

15 INTERESTING TOPICS: EFFECTS OF SATURATION SRM at 28 Days (kω- cm) Average 18% increase in 28-Day SRM if samples dried at any reasonable point during 28 day curing period Day (From Cast Date) Control (100% Sat.) Set #1 Set #2 Set #3 Set #4 Set #5 Set #6 Set #7 Set #8 Set #9 Set #10 Set #11 Set #12 Set #13 Set #14 Set #15 Set #16

16 INTERESTING TOPICS: 28-DAY SRM RE-SATURATION SRM (kω- cm) CLP CC Minutes Soaking

17 FUTURE WORK In-situ testing on pavements (surface and cores) and bridge decks Evaluating several surfaces preparation types Re-saturation methods Vacuum saturation Boil Water bath Early age and long term surface resistivity Primarily LPC; low permeability concrete

18 QUESTIONS? Andrew Jenkins