SURFACE RESISTIVITY TESTING OF HARDENED CONCRETE PERMEABILITY: KANSAS DOT ANDREW JENKINS RESEARCH OPERATIONS SUPERVISOR BUREAU OF RESEARCH
OUTLINE Current Practice (at time of study) Outline Project Discuss Data Results/Outcomes Interesting Topics Future Work
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.
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
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
28-DAY SRM VS. 28-DAY BOIL 18.0 17.0 Boil (% Permeable Voids) 16.0 15.0 14.0 13.0 12.0 11.0 10.0 9.0 R² = 0.37666 28D SRM vs. 28D Boil Power (28D SRM vs. 28D Boil) 8.0 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 SRM (kω- cm)
SRM VS. RCP SAME AGES 10000 9000 8000 RCP (Coulombs) 7000 6000 5000 4000 3000 2000 y = 32188x - 0.975 R² = 0.88837 All "Same Age" Values AASHTO CorrelaMon 1000 0 0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 SRM (kω- cm)
28-DAY SRM VS. 56-DAY RCP 10000 9000 8000 7000 RCP (Coulombs) 6000 5000 4000 y = 35352x - 1.117 R² = 0.84098 28D SRM vs. 56D RCP 3000 2000 1000 0 0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 SRM (kω- cm)
28-DAY SRM VS. 56-DAY RCP 10000 9000 RCP (Coulombs) 8000 7000 6000 5000 4000 3000 28D SRM vs. 56D RCP TheoreMcal SRM- RCP RelaMonship 2000 1000 LTRC/LaDOTD Data 0 0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 SRM (kω- cm)
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 2000 4000 12 21 7.0 13.0 6.8 13.6 Low 1000 2000 21 37 13.0 24.0 13.6 27.0 Very Low 100 1000 37 254 24.0 190 27.0 272 Negligible <100 > 254 > 190 > 272 KDOT Standard Pre-2014 3500 13.2 7.9 7.8 KDOT Low Pre-2014 1000 37.5 24.4 27.2 **Not Final KDOT Specification Values
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
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
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
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 3000 12.0 9.0 KDOT MPC Spec 2000 11.0 13.0 KDOT LPC Spec 1000 9.5 27.0 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
INTERESTING TOPICS: EFFECTS OF SATURATION SRM at 28 Days (kω- cm) 14.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 Average 18% increase in 28-Day SRM if samples dried at any reasonable point during 28 day curing period 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 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
INTERESTING TOPICS: 28-DAY SRM RE-SATURATION 100.00 90.00 80.00 70.00 SRM (kω- cm) 60.00 50.00 40.00 30.00 13-1406 CLP 13-1406 CC 20.00 10.00 0.00 0 5 10 15 20 25 30 35 40 45 50 55 60 Minutes Soaking
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
QUESTIONS? Andrew Jenkins 785-296-2718 jenkins@ksdot.org