Maintenance-Free Service Life Design of Concrete subjecting to Carbonation

Transcription

1 Maintenance-Free Service Life Design of Concrete subjecting to Carbonation Somnuk Tangtermsirikul and Jittbodee Khunthongkeaw School of Civil Engineering and Technology

2 Carbonation of concrete -CO 2 diffuses into concrete and react with Ca(OH) 2 in in concrete. Ca(OH) 2 + CO2 CaCO3 + H 2O - Reduces alkalinity of concrete, thus corrosion protection is is destroyed. Problem in Reinforced Concrete

3 Effect of carbonation on chloride condensation in concrete

4 Situation of Carbonation Problem in Thailand

5 Research area Central Thailand Bangkok Nakornsawan Ratchaburi Lob-Buri Ayudtaya Samutsongkarm Pathum Thani Seaside areas Samutprakarn Cholburi Environmental Classification condition Number of structures Percent Central Thailand Seaside area Total

6 In Bangkok

7 Carbonation induced steel corrosion

8 Carbonation induced steel corrosion

9 Carbonation induced steel corrosion

10 Steel Corrosion due to Carbonation

11 Early steel corrosion due to Carbonation (not enough concrete cover)

12 Effort toward durability design in Thailand A new Building Acts for Design of RC Structures by Department of Public Works & Urban Planning (Enforced in 25) Design considering long term properties (durability, creep, fatigues, ductility), easiness of construction and maintenance

13 Though, various design codes are available at present Different condition in Thailand - Materials - Environment - Standard of practices

14 Urgently Require Tools for Durability Design (Software/Design Charts)

15 To establish a suitable design to suit condition of Thailand Carbonation Performance Based Analysis and Design of Concrete Mix Proportion (Computer Software for Mix Design) At SIIT, Thammasat University

16 Performance Prediction s for Analysis and Design of Concrete Mix Proportion Overall Concrete Properties Fresh Plastic Early Age Hardened Long term orkability -Bleeding -Temperature - f c Durability - Drying shrink -Settlement -Auto shrink - ft - Cl Corrosion -Plastic shrink -Setting -Strength - fr - Ec ν - Carbonation** - AAR - Sulfate attack -Acid attack -Freeze-Thaw - Erosion Others - Creep

17 Examples of Computer Software for Performance Based Analysis and Design

18 21 EGAT and SIIT For workability and strength design

19 Software for Temperature Calculation in Mass Concrete

20 Input interface for temperature calculation

21 Output interface for temperature calculation

22 Software for Calculating Chloride Concentration in Concrete

23 Input interface for for calculation of of chloride distribution (I) (I)

24 Input interface for for calculation of of chloride distribution (II) (II)

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26 Carbonation Simulation for Fly Ash Concrete

27 (ii) Flow chart of of the model

28 The model consists of 3 main parts 1. Water migration 2. CO 2 diffusion 3. Hydroxide generation/consumption and ph calculation

29 1) Water migration (i) (i) formulation -- Concrete is is initially saturated with with water. During drying, vapor migrates from concrete through the the interconnect capillary pores, according to to the the gradient of of vapor pressure (RH). water x Fick s Law FH (x,t) = DH RHc (x,t) x

30 (ii) Diffusion coefficient of of water vapor Parameter affecting DH 1. Pore characteristic of concrete 2. Water content in concrete 3. Aggregate content 4. Boundary condition DH (t) = DH (t) = i. 72 d(t) n(t). 7 d(t) n(t) Concrete to concrete Water Concrete to environment ( 1. 6wb 1. 6) ( 1. 6wb 1. 6) C C. 11 w. 11 w η (x,t) η (x,t) Water vapor Low porosity High porosity Water vapor Water vapor High degree of saturation in pore Water Low degree of saturation in pore Water vapor Water Water vapor

31 ii) i) State of of equilibrium between liquid water and water vapor Relative Humidity (RH) 1 % (4 o C) (2 o C) % Relative water content (C w ) 1 % Cw = 1 W (x,t) W e sat (x,t)

32 (iv) Verifications (5%RH, T=4 C) (a) r = % (65%RH, T=3 C) 4 (5%RH, T=4 C) (65%RH, T=3 C) Distance from open surface (cm) Cw (%) (5%RH, T=4 C) 6 (b) r = 2% (65%RH, T=3 C) 4 (5%RH, T=4 C) (65%RH, T=3 C) Distance from open surface (cm) Cw (%) (5%RH, T=4 C 6 (65%RH, T=3 C (c) r = 6% 4 (5%RH, T=4 (65%RH, T= Distance from open surface (cm) Relative water content in in pastes after drying for for days Cw (%) 1 1 (w/b=.3) 8 8 (w/b=.4) (w/b=.5) 6 (a) r = % (w/b=.3) (b) r = 2% 6 (w/b=.4) (w/b=.5) Distance from open surface (cm) Distance from open surface (cm) Cw (%) Cw (%) (w/b=.3) (w/b=.4) (w/b=.5) (w/b=.3) (w/b=.4) (w/b=.5) (c) r = 6% Distance from open surface (cm) (w/b=.3 (w/b=.4 (w/b=.5 (w/b=. (w/b=. (w/b=. Relative water content in in mortars after drying for for days days

33 2) Diffusion of CO 2 (i) (i) formulation -- After the the migration of of moisture out out of of concrete, CO CO 2 2 starts diffusing into into concrete according to to its its concentration gradient. water CO 2 x Fick s Law F c (x,t) = D c C(x, t) x

34 (ii) Diffusion coefficient of of CO 2 Parameters affecting Dc 1. Pore characteristic of concrete 2. Water content in concrete 3. Aggregate content 4. Boundary condition 5. Relative humidity in pores Low porosity High porosity CO 2 CO 2 Concrete to concrete Water Concrete to environment CO 2 High degree of saturation in pore Water CO 2 Low degree of saturation in pore CO 2 Water CO 2

35 (ii) Diffusion coefficient of of CO 2 Parameters affecting DH 1. Pore characteristic of concrete 2. Water content in concrete 3. Aggregate content 4. Boundary condition 5. RH in pores of concrete D D co ci ( 1,t) = (x,t) = d(t) n RH(x,t) 7 (t) η d(t) n (t) η 1 RH(x,t) 2 2 Cw (x,t) 1 Cw (x,t) 1 High relative humidity in pore Water Low relative humidity in pore Water CO 2 CO 2

36 Pore Structures Average pore diameter and Total porosity)

37 Average Pore Diameter of Paste Effect of water to cement ratio d ave (t), nm data: w/c=.3 data: w/c=.4 model: w/c=.3 model: w/c=.4 Effect of type of cement d ave (t), nm 5 4 α ave (t), % data: type I data: type III data: type V model: type I model: type III model: type V α ave (t), %

38 Average Pore Diameter of Paste (continued) Effect of fly ash d ave (t), nm 5 of average pore diameter, d ave (t) d ave () t = e ( 8.2 ( w / b.19) ) ( w / b.19) data: f/b= data: f/b=.3 data: f/b=.5 data: f/b=.7 model: f/b= model: f/b=.3 model: f/b=.5 model: f/b= αave ( ) ( t ) f f α ave (t) b b Fc α ave (t), % C3A

39 Effect of water to cement ratio Total Porosity of Paste n(t), % data: w/c=.3 data: w/c=.4 model: w/c=.3 model: w/c= Effect of type of cement α ave (t), % n(t), % data: type I data: type III data: type V model: type I model: type III model: type V α ave (t), %

40 Total Porosity of Paste (continued) Effect of fly ash n(t), % data: f/b= data: f/b=.3 data: f/b=.5 data: f/b=.7 model: f/b= model: f/b=.3 model: f/b=.5 model: f/b= α ave (t), % of total porosity, n(t) w n() t = 23.9 ln b C3A e f b 1.43 αave ( ( ) ) () t.86 w / b Fc

41 3) ) Calculation of CH content and ph H t (x, t) = CH gh (x, t) CH cp (x, t) CH cc (x, t) Generated by hydration of cement Consumed in pozzolanic reaction Consumed in carbonation reaction

42 (i) CH generated by by Hydration of of Cement -CH released from hydration reaction (C (C 2 2 S and and C 3 3 S) S) is is the the main main component generating alkalinity in in concrete. 3C 3 S + 6H (1) 2C 2 S + 4H CSH + 3CH CSH + CH Amount of CH generated by hydration reaction (kg) Reacted mass of C 3 S (49) (1) (22) Reacted mass of C 2 S %C3S %C2S CHgh (x,t) = αc3s(t) Wc.49 + αc2s(t) Wc.22 A x 1 1 Degree of hydration of C 3 S Degree of hydration of C 2 S

43 (ii) CH consumed by by Pozzolanic Reaction of of Fly Ash -CH liberated from the the hydration reaction becomes available for for pozzolanic reaction. 3CH + 2SiO 2 CSH (252-1) (252) (1) - Amount of siliceous component in FA %SiO2 CHcp(x,t) = α poz(t) φ f Wf A x Effectiveness ratio, which is the weight fraction of the amorphous phase of SiO 2 to the total weight of SiO 2 in fly ash * Amount of of CH in in non-carbonated concrete CH t (x, t) = CH gh (x, t) CH cp (x, t)

44 (iii) Carbonation reaction and its reaction rate -CO 2 2 and and CH CH dissolve and and enter the the reaction process. - Concentration of CH in pore water (solubility of CH) CH t (x, t) 1 Cw (x, t) [ CH](x, t) = ; Vw (x, t) = V (x, t) 74 1 w n(t) 1 A x Volume of pore water Molecular weight of CH However, the the solubility of of CH CH in in water is is very very low. low. The The saturated molar concentration of of CH CH in in water is is and and 1 1 mol/m 3 3 at at C C and and 1 C, respectively. Therefore, [CH] is is limited by by its its concentration at at saturated state.

45 Concentration of CO 2 in in pore water Assumption :: Rate of of dissolution of of gas gas in in the the pore pore water follows the the Henry s law law and and ideal gas gas law. law. Henry s constant [CO P x = 2 ] n V = H P RT = x CRT Gas pressure in pores [ CO 2 ](x, t) = HRTC(x, t) * Rate of of CH reduction Rate of carbonation reaction rc (x,t) = kc [CH](x,t) [CO2](x,t) Rate of reduction of dissolved CH in the considered element x

46 - Rate of Carbonation Reaction Rate of of reaction was formulated based on on Arrhenious' law. = βexp E RT kc β = mol/m 3 /day, E = 4 j/mol * Amount of of dissolved CHin in pores of of carbonated concrete CH = t t (x,t) CH t (x, t) 74 W e (x, t) r c (x, t) dt

47 (iv) ph in in pore solution --The The soluble part part of of CH CH in in water is is completely ionized because CH CH is is categorized as as a strong base. CH Ca OH - - Concentration of OH - in pore solution [ OH](x,t) = 2 [CH ](x,t) * ph in in pore solution of of concrete ph (x, t) = 14 + log( [OH](x, t) )

48 4) Verifications (i) (i) Verification of of CH CH H in in mortar specimens (Papadakis s ( data) data) : w/b w/b =.5.5 and and A/B A/B = CH (kg/m 3 of mortar) (r=%) (r=2%) (r=3%) (r=%) (r=2%) (r=3%) Ages (day) CH (kg/m 3 of mortar) (a) w/b = Replcement percentage (%) CH (kg/m 3 of mortar) (b) w/b = Replcement percentage (%) CH CH in in mortar specimens (Author s s data) at at days days

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51 (ii) Verification of of carbonation depth (natural environment) - Carbonation depth was was the the distance from concrete surface to to center of f the the innermost concrete element that that has has the the ph ph value less less than than (a) (a) 6 6 months months (w/b=.4) (w/b=.4) (w/b=.5) (w/b=.5) (w/b=.6) (w/b=.6) 8 8 (w/b=.4) (w/b=.4) (w/b=.5) (w/b=.5) 4 4 (w/b=.6) (w/b=.6) Replacement Replacement of of fly fly ash ash (%) (%) ity-sheltered verage verage CO CO 2 2 concentration = ppm. ppm. verage verage relative humidity = 72.5% 72.5% verage verage temperature = C C Carbonation Carbonation depth depth (mm) (mm) Carbonation Carbonation depth depth (mm) (mm) (b) (b) months months Replacement Replacement of of fly fly ash ash (%) (%) (d) (d) months months (w/b=.4) (w/b=.4 (w/b=.5) (w/b=.5 (w/b=.6) (w/b=.6 (w/b=.4 (w/b= (w/b=.5 (w/b= (w/b=.6 (w/b= (w/b=.4) (w/b=.4 (w/b=.5) (w/b=.5 (w/b=.6) (w/b=.6 (w/b=.4 (w/b= (w/b=.5 (w/b= (w/b=.6 (w/b=

52 (ii) Verification of of carbonation depth (natural environment) - Carbonation depth was was the the distance from concrete surface to to center of f the the innermost concrete element that that has has the the ph ph value less less than than (a) (a) 6 6 months months (w/b=.5) (w/b=.5) 9 9 (w/b=.6) (w/b=.6) 6 6 (w/b=.5) (w/b=.5) 3 3 (w/b=.6) (w/b=.6) Replacement Replacement of of fly fly ash ash (%) (%) Carbonation Carbonation depth depth (mm) (mm) (b) (b) months months (w/b=.5) (w/b=.5) 9 9 (w/b=.6) (w/b=.6) 6 6 (w/b=.5) (w/b= (w/b=.6) (w/b= Replacement Replacement of of fly fly ash ash (%) (%) ity-non-sheltered verage verage CO CO 2 2 concentration = ppm. ppm. verage verage relative humidity = 83% 83% verage verage temperature = C C Carbonation Carbonation depth depth (mm) (mm) (d) (d) months months Replacement of fly ash (%) (w/b=.5) (w/b=.5) (w/b=.6) (w/b=.6) (w/b=.5) (w/b=.5 (w/b=.6) (w/b=.6

53 (ii) Verification of of carbonation depth (natural environment) - Carbonation depth was was the the distance from concrete surface to to center of f the the innermost concrete element that that has has the the ph ph value less less than than (a) (a) 6 6 months months Replacement Replacement of of fly fly ash ash (%) (%) (w/b=.5) (w/b=.5) (w/b=.6) (w/b=.6) (w/b=.5) (w/b=.5) (w/b=.6) (w/b=.6) Carbonation Carbonation depth depth (mm) (mm) (b) (b) months months Replacement Replacement of of fly fly ash ash (%) (%) (w/b=.5) (w/b=.5) (w/b=.6) (w/b=.6) (w/b=.5) (w/b=.5 (w/b=.6) (w/b=.6 ral-sheltered verage CO CO 2 2 concentration = 3 3 ppm. ppm. verage relative humidity = 8% 8% verage temperature = C C Carbonation Carbonation depth depth (mm) (mm) (d) (d) months months (w/b=.5) (w/b=.5) (w/b=.6) (w/b=.6) (w/b=.5) (w/b=.5 (w/b=.6) (w/b=.6

54 (ii) Verification of of carbonation depth (natural environment) - Carbonation depth was was the the distance from concrete surface to to center of f the the innermost concrete element that that has has the the ph ph value less less than than (a) 6 months (a) 6 months Replacement of fly ash (%) Replacement of fly ash (%) (w/b=.5) (w/b=.5) (w/b=.5) (w/b=.5) Carbonation depth (mm) Carbonation depth (mm) (b) 12 months (b) 12 months Replacement of fly ash (%) Replacement of fly ash (%) (w/b=.5) (w/b=.5) (w/b=.5) (w/b=.5) easide-sheltered verage verage CO CO 2 2 concentration = ppm. ppm. verage verage relative humidity = 72% 72% verage verage temperature = C C Carbonation Carbonation depth depth (mm) (mm) (d) (d) months months Replacement of fly ash (%) (w/b=.5) (w/b=.5) (w/b=.5) (w/b=.5)

55 ii) i) Verification of of carbonation depth (accelerated environment) Carbonation depth (mm) b) 2 months exposure (w/b=.5) (w/b=.6) M odel (w/b=.5) M odel (w/b=.6) CO CO 2 2 concentration = 4% 4% Relative humidity = 55% 55% Temperature = 4 4 C C Replacement of fly ash (%) CO CO 2 2 concentration = 6.5% 6.5% Relative humidity = 65% 65% Temperature = 3 3 C C Carbonation Carbonation depth depth (mm) (mm) Exposure Exposure period period (day) (day) (w/b=.4) (w/b=.4) (w/b=.5) (w/b=.5) (w/b=.6) (w/b=.6) M odel odel (w/b=.4) (w/b=.4 M odel odel (w/b=.5) (w/b=.5 M odel odel (w/b=.6) (w/b=.6

56 Mix Design of Concrete Subjecting to Carbonation

57 (iii) Design charts for depassivation time City area (indoor), Covering = 2 cm City area (indoor), Covering = 3 cm FA A 2ก ก Maintance free period (yrs) Water to binder ratio r = % r = 1% r = 2% r = 3% r = 4% r = 5% Maintance free period (yrs) Water to binder ratio r = % r = 1% r = 2% r = 3% r = 4% r = 5% City area (indoor), Covering = 2 cm City area (indoor), Covering = 3 cm FA A 2ข ข Maintance free period (yrs) r = % r = 1% r = 2% r = 3% r = 4% r = 5% Maintance free period (yrs) r = % r = 1% r = 2% r = 3% r = 4% r = 5% Water to binder ratio Water to binder ratio

58 (ii) Workability prediction model (Khunhongkeaw 22, Wangchuk 23) -It was verified that free water content has linear relationship with deformability of of ordinary concrete Slump (cm) W Free water content, (kg / m 3 ) γ =1.1 γ =1.2 γ =1.3 γ =1.4 SL = α ( W fr fr -W )

59 (iv) Design charts for slump FM M 2.75 Slump (cm) r = % γ=1.15 γ=1.2 γ=1.25 γ=1.3 γ=1.4 Slump (cm) r = 3% γ=1.15 γ=1.2 γ=1.25 γ=1.3 γ= Water to binder ratio Water to binder ratio 25 r = % 25 r = 3% FM M 3.25 Slump (cm) γ=1.15 γ=1.2 γ=1.25 γ=1.3 γ=1.4 Slump (cm) γ=1.15 γ=1.2 γ=1.25 γ=1.3 γ= Water to binder ratio Water to binder ratio

60 (i) (i) Strength prediction model (Kaewklurb( 22) -It was empirically formulated to to have relationship mainly with CaO content in in concrete. fc'( 28 days), MPa w/b =.3 w/b =.4 w/b = log (CaOeff) - The 28-day compressive strength is is given by, f c c (28) = [ α 11 log(c) + λ f f α 2 ] χ γγ χ l l χ w χ aa

61 FA 2a, 7 days FA 2b, 28 days r = % r = % 5 6 fc' at 7 days (ksc) γ=1.15 γ=1.2 γ=1.25 γ=1.3 γ=1.4 fc' at 28 days (ksc) γ=1.15 γ=1.2 γ=1.25 γ=1.3 γ= Water to binder ratio Water to binder ratio r = 3% r = 3% 4 5 fc' at 7 days (ksc) γ=1.15 γ=1.2 γ=1.25 γ=1.3 γ=1.4 fc' at 28 days (ksc) γ=1.15 γ=1.2 γ=1.25 γ=1.3 γ= Water to binder ratio Water to binder ratio

62 Proposed Design Guideline for Thailand

63 Proposed Three Zones based on Severity of Environment 1 CO2 Concentration (ppm) Severe Moderate Low Relative humidity (%)

64 Cement only 3 years 5 years 75 years 1 years Design Chart for Severe Environment water to binder ratio Cover thickness (mm) % FA (2a) 3 years 5 years 75 years 1 year water to binder ratio

65 21 EGAT and SIIT For workability and strength design

66 The END

67 3.2 Design charts (i) Limitations - This method is is appropriate for conventional fly ash concrete that has f c c (28) not over 6 6 Mpa and slump between 1 to to cm. -The standard Portland cement type I complied with the requirement of of TIS-15 is is recommended. - The method is is suitable for unprocessed FA that are classified as as type 2a 2a and 2b 2bby by EIT-114 and have fineness not over than 32 m 2 /kg and water requirement between %. %. - Fine and coarse aggregates must be be river sand and limestone, respectively. The aggregates must satisfy the industrial standard (TIS-566).

68 (ii) Design charts for compressive strength - The design charts for compressive strength are constructed at at age of of concrete of of 7, 7, 28, days and separated into two sets for fly ash type 2a 2a and 2b. - Compressive strength is is designed by by assuming the value of of γ equal to to 1.2. Then the value of of water to to binder ratio is is selected from the design charts from the required compressive strength. -It is is noted that if if the compressive strengths at at more than one specific age is is required, the minimum water to to binder ratio that satisfies all all strength requirements is is selected.