Concrete: Salts, Shrinkage and Specification

Transcription

1 Concrete: Salts, and Specification Jason Weiss, Edwards Distinguished Professor of Engineering Head of the School of Civil and Construction Engineering December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 1 of 52

2 Lets Take a Second to Refocus December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 2 of 52

3 Concrete: Salts, and Specification Jason Weiss, Edwards Distinguished Professor of Engineering Head of the School of Civil and Construction Engineering December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 3 of 52

4 Some Quick Thoughts We generally approach durability in a very casual (empirical) way Dick Clark Approach Are we seeing the Gorilla? We can improve with a scientific approach Time is ripe for our profession to tackle this December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 4 of 52

5 We Need to Understand Structure and Sample Conditioning Gel Pores (2-5 nm) Tiny Pores Capillary Pores (5nm-10 mm) BFP Entrained/Entrapped Air Pores we specifically add then forget about once we take an air test December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 5 of 52

6 Volume Proportions (%) Graphical Version of Powers Model Water to Cement Ratio = Chemical Water Capillary Pores Degree of Hydration (%) Gel Water Hydrated Products Cement December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 6 of 52

7 The Simple Pore Take Away Gel Pores (2-5 nm) small, independent of w/c, increase in volume with hydration We have little control of gel pores Transport is very difficult is the main concern Capillary Pores (5nm-10 mm) large pores, very dependent on w/c, decrease in volume with hydration, what we control Controlled by W/C and Curing Critical for transport (salt ingress), freeze thaw and strength Entrained/Entrapped Air Largest pores from mixing, stabilizing bubbles Controlled by the Air Entrainment Dosage (proportion to gel and capillary pores is important) Impacts strength however the biggest impact is on freeze thaw durability December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 7 of 52

8 Breaking this Down to What Matters Gel Pores Little we can do Air Controlled By Air Capillary Controlled by w/c December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 8 of 52

9 Volume Proportions (%) Capillary Pores and W/C Water-to-Cement Ratio Excess Cement Excess Water December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 9 of 52

10 Volume Proportions (%) If Well Cured Water-to-Cement Ratio Excess Cement Excess Water December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 10 of 52

11 Transport Think Tony Saprano Transport mainly in large pores (BFPs) (practice cap, some lab tests cap and AEA) Capillary pores are large and connected W/C, SCM & Curing: Capillary Capillary Pores Lower w/c Higher w/c Assumes 100% Hydration December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 11 of 52

12 Main Concerns What We Discuss Today Freeze-Thaw December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 12 of 52

13 Photo In Concrete Cracks Abound is key Transverse cracking in 100,000+ bridges 62% of DOT s consider cracking as a problem (NCHRP) Cracks shorten service life, increase maintenance, and accelerate corrosion Increase in HSC Here we see cracks spaced at 2.5 ft on the approaches to a bridge December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 13 of 52

14 Measured of Components Looking at shrinkage of the components Aggregate generally does not shrink Paste is the portion that shrinks is a paste property Drying Time Aggregate Concrete Paste December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 14 of 52

15 This Work Required Battling Many Widely Held Thoughts V Paste Dutron (1956) shares data, followed by L Hermite (1960 stating little influence) Point to discussion on volume of paste which has been ongoing since the 1920s 1950 s see this come to many meetings (int l cement, TRB etc) Pickett ( 65) and others Concrete Paste 1 V Agg n December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 15 of 52

16 A Look at and Paste Volume Approach 1 Agg Volume 2 SRA (alter fluid) 50% red. 3 IC (keep pore filled) good for lower w/c, fp mat December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 16 of 52

17 A Look at and Pore Fluid Surface Tension Approach 1 Agg Volume (not w/c) 2 SRA (alter fluid) 50% red. Coefficient, N (m ) COV = Probability of T e t r a g u a r d w / c S R A C o n c e n t r a t i o n ( % ) Sh (m ) December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 17 of 52

18 A Look at and Keeping Pores Filled Approach 1 Agg Volume 2 SRA (alter fluid) 50% red. 3 IC (keep pore filled) good for lower w/c, and where finer pores are used Reduces Potential December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 18 of 52

19 Main Concerns What We Discuss Today Freeze-Thaw December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 19 of 52

20 General Model (Ice Formation - Saturation) Fagerlund pioneered this approach, followed by Li et al. (shown) here and Farnam, Lucero adding details When concrete reaches a critical degree of saturation (S CRIT ) it will become damaged Damage occurs fast Rate is related to the S and fracture 1-D December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 20 of 52

21 ASTM C Absorption Test method used to determine the rate of absorption (sorptivity) of water by measuring the increase in the mass of a specimen as a function of time when only one surface of the specimen is immersed in water December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 21 of 52

22 Absorbed water (mm 3 /mm 2 ) ASTM C1585 Typical Results Units odd volume of water/surface area, frequently misinterpreted (Lucero et al.) Frequently plotted as a time^0.5 Fluid impacts Initial slope g, h (Spragg et al. 2008) Geometry impacts time at Nick point Absorption Nick Secondary Sorptivity Initial Sorptivity Time (min 0.5 ) December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 22 of 52

23 Absorption and the Role of Air Just measuring mass absorbed (ASTM C1585) is not sufficient Need to know the sample degree of saturation Link to the critical degree of saturation and to the service life S Sat S Nick December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 23 of 52

24 Degree of Saturation Water Absorption and Pores S Int S Nick = S Mat S Sat Time Lucero et al. December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 24 of 52

25 Degree of Saturation Water Absorption and Pores S Sat 5 3 S Nick = S Mat 2 1 S Int Time Lucero et al. December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 25 of 52

26 What We Can Control Role of Resistivity December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 26 of 52

27 Phase Diagram of NaCl Solution NaCl salt most common deicers used on concrete. Typical NaCl Water Phase Diagram Farnam et al. 2012b December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 27 of 52

28 Hydrated Cement and Calcium Chloride/Magnesium Chloride Similar but more damage is observed for salts like CaCl 2 MgCl 2, more complex but similar (Farnam et al., 2014a,b) December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 28 of 52

29 Identification Tests and Mitigation Low Temperature Differential Scanning Calorimeter (LT-DSC) Uses cement powder with a Solution of CaCl 2 Good Screening Test Related to the Chemistry of Cement (C 3 A, CH) Role of SCM (good, watch scale in high slump mixes) Can use sealers also (Villani et al., 2015) December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 29 of 52

30 Where Why is SCM this Works headed Effect of Dilution (Less CH) Effect of Reaction (Less CH) Limiting Factor Dilution Pozzolanic Mixture Design Monical et al. 201 December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 30 of 52

31 Test and Materials Longitudinal Guarded Comparative Calorimeter (LGCC) A new test method Two mechanisms proposed during F/T cycles depending on the concentration 1) low concentration hydraulic, osmotic 2) high concentration chemical reactions December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 31 of 52

32 Plain Take Aways on Salts Some salts can react with cement binder Potential Solutions are: Reduce reactive components (C 3 A, Sulfate, CH seems the big one) Change cement chemistry? Not likely Use SCM more frequently YES, YES YES (Class F Ash, potential to add silica fume, Class C Ash) etc Watch out for scaling (high slump mixtures on next slide, SCM year round?) seal (keep solution out) 2004 to now December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 32 of 52

33 A Comment on Full Year SCMs (Neuwald et al 2004) Slip form SCM All year? Proper Curing - Vital December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 33 of 52

34 Main Concerns What We Discuss Today Freeze-Thaw December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 34 of 52

35 Photo Credit Dolch Can We Write Equations 1970 s deicing salts become widely used for clear pavements US: 8-12 mil. annual tons of salt Ions travels through concrete, depassivates steel, & corrodes Can we write an equation to predict when chloride reaches a critical level at the bar? December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 35 of 52

36 Chloride At the Bar Fick s Second Law For Diffusion In 1855 Adolf Fick introduced an equation (2 nd law) regarding diffusion C t D Cl 2 C 2 x C is the concentration, t is time, x is position, D is diffusion coefficient Critical Value Time December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 36 of 52

37 Where Do We Find Tests Much like Indiana on the search for the holy grail We want a test for transport (or durability) that is fast, accurate, inexpensive easy to interpret but also scientifically valid Diffusion is lengthy but also has pitfalls (binding, units, leaching, duration, age, lack of fit, exposure dependent, etc) We think that electrical measurements can be a significant part of this approach December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 37 of 52

38 Electrical Methods Food For Thought V IR Ohms Law (Cavendish) Ionic conduction Conduction related to how fast the ions move in pores December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 38 of 52

39 Resistivity as a Test Fast (seconds to minutes) Low cost ($ dollars) Portable (put it in your pocket) But most importantly it is useful as it measures what we are interested in Remember - Tony Soprano Transport is related to the volume of pores and the connectedness of the pores December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 39 of 52

40 Review of the Impact of Geometry Uniaxial, surface, embedded, and RCPT electrical measurements all yield results that can be directly compared if done properly Proper reporting is essential To - Lead Epoxy Coating To + Lead Copper Mesh Electrodes RA L December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 40 of % NaCl 0.3 M NaOH Concrete Q V I A L 6h V 0h dt

41 A thought as we begin Many people are asking for a resistivity value that can be used to insure durability Can relate resistivity to RCPT (known value) - 1 st principles V 1 t Q 5cm 2 5 cm This results in a table 2 60V 60min 6hr 2000Ampsec 1hr However is this really what we want.. think back to the gorilla 60sec 1min ASTM C1202 Classification (1) 10.4 k cm Charge Passed (Coulombs) (1) Resistivity (kohm cm) (2) High >4,000 < 5.2 Moderate 2,000-4, Low 1,000-2, Very Low 100-1, Negligible < 100 > 207 (1) from ASTM C (2) calculated using first principles December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 41 of 52 Q 6h 0h V 1 dt Spragg et al. 2010

42 Relationship Between Q (Columbs) and Resistivity ( ) Many relationships have been developed over the years (the black - theory) While all have a reasonable shape, details are very important when one tries to use this in spec s We will come back to this Spragg et al December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 42 of 52

43 Archie s Law and The Formation Factor Empirical relationship that is the ratio of the bulk resistivity ( ) of a saturated medium and the fluid ( O ) that is in the medium F This makes the assumption that it is only the fluid that is conductive (Weiss et al.) There are solutions for other cases; but this works most of the time December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 43 of 52 O

44 What is the Formation Factor Really Describing Gel Pores (2-5 nm) Not a Challenge generally for transport Capillary Pores (5nm-10 mm) BFPs that we can control by water, w/c Entrained/Entrapped Air in practice these do not saturate (else FT) Formation Factor is all about Total (f) and Tortuosity ( ) F 1 f O What Do We Need to Remember? Transport mainly in large pores Capillary pores are large/connected W/C, SCM and Curing December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 44 of 52

45 Maybe We Should Look at the Formation Factor Maybe it makes sense to look at the formation factor instead for specifications ASTM C1202 Classification (1) Charge Passed (Coulombs) (1) Resistivity (kohm cm) (2) Formation Factor High >4,000 < ? Moderate 2,000-4, ? Low 1,000-2, ? Very Low 100-1, ? Negligible < 100 > ? (1) from ASTM C (2) calculated using first principles These numbers are just place holders however they illustrate how to get to the most fundamental value With this one can to go in two directions 1) This relates to service life 2) This enables various constituents December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 45 of 52

46 1) Direct Relation to Service Life Walther Nernst ( ) German physical chemist/physicist Won 1920 Nobel Prize F Bulk Soln D i D m i 1 F D m i Soln Bulk December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 46 of 52

47 2) Enables Various Constituents Conduction requires an electrolyte Free ions making solution electrically conductive Na +, K +, Ca 2+, Mg 2+, Cl -, HPO 4 2-, HCO 3 Heavily influenced by Cement source + SCM Three approaches to obtain O (for const.) 1) Extraction Doable 2) Sensor Promising (Rajabipour et al) 3) Calculation December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 47 of 52

48 Lets Take a Second to Review Geometry correction is key ( ) Many want a table for RCPT vs Easy to do but is it the best thing I say no A Possible Thought F is the way to go for a specification is the way to go for QC/QA Requires O to be stated using a procedure in specification (much easier) or determined experimentally (harder) December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 48 of 52

49 Components of Variation Machine/Operator/Material Traditionally estimated in a single lab as 3-4% (Purdue, LaDOT) Production Important when used as a QC/QA tool Dependent on contractor quality 10% is a typical value Data shown is from a central mix plant with one mixture run frequently, low variation Spragg et al December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 49 of 52

50 Components of Variation Attention to Curing is Critical State Study Within-lab: 4.36% Machine/Operator/ Material Multi-lab: 13.22% Machine/Operator/ Material and curing Believed Curing Variation: 12.5% State Variation Shown (top young, bottom old samples) Spragg et al December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 50 of 52

51 Accelerated Curing Effects (Get 91 day data in 23 days) Transport testing and service life prediction usually performed on specimens of later age (91 days). Ea 1 1 ( ) R T Tr t e t Same maturity (DOH) could be achieved with shorter time using a higher curing temperature. 91 days 23 days December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 51 of 52 e E a = 37 kj/mol Bu et al. 2014

52 Pores Different Size (Gel Small, no Control, Capillary - Big, w/c, Air Enormous) Related to Agg Volume (5-6% per % paste), SRA, IC Freeze-Thaw DOS is Key, relates to proportion of air in the mixture, matrix controls filling rate (resistivity) Rate of salts travelling to bar Resistivity - is easy to measure, can replace RCPT, F should be specified, can be used for accelerated acceptance December 3 rd 2015 Slides Prepared by W. Jason Weiss, jason.weiss@oregonstate.edu Slide 52 of 52