DURABILITY of CONCRETE STRUCTURES. 3 PART Prof. Dr. Halit YAZICI

Transcription

1 DURABILITY of CONCRETE STRUCTURES 3 PART Prof. Dr. Halit YAZICI 1

2 CARBONATION & CORROSION 2

3 PROTECTION of STEEL FROM CORROSION BY CONCRETE PHYSICAL PROTECTION PREVENTION of PENETRATION of WATER & HARMFUL MATERIALS to STEEL (DEPENDENT on IMPERMEABILITY & THICKNESS OF CONCRETE COVER) CHEMICAL PROTECTION PROVIDING A HIGH ALKALI ENVIRONMENT for STEEL (PASSIVIZATION EFFECT - ph ) Concrete Reinforcement steel ph 12.5 MICROSCOBIC OXIDE LAYER (PASSIVE OUTER LAYER) REINFORCEMENT CAN NOT CORRODE (IF PASSIVE LAYER IS STABLE) 3

4 PROTECTION of STEEL FROM CORROSION BY CONCRETE Steel Reinforcment Concrete CARBONATION ph < CHLORIDES Cl - > CRITICAL VALUE ACIDIC WATERS Depassivation of Passive Layer End of Chemical Protection POSSIBILITY of CORROSION (In Presence of Oxygen & Water) PERMEABLE & THIN CONCRETE COVERS ARE INADEQUATE INSUFFICIENT CHEMICAL & PHYSICAL PROTECTION LEADS TO CORROSION of REINFORCEMENT 4

5 SOURCES OF ALKALINITY HYDRATION PRODUCTS of C 3 S & C 2 S Ca(OH) 2 FREE CaO + H 2 O Ca(OH) 2 (ALKALI OXIDE) K 2 O, Na 2 O + H 2 O KOH, NaOH ph Production of Concrete Beginning of Alkalinity Protection Beginning of Carbonation End of Chemical Protection Time 5 Beginning of Electrolytic Corrosion 2 5

6 CO 2 + H 2 O SO 2 + H 2 O Ca(OH) 2 CO 2 CARBONATION PENETRATION of GASES to THE PORES of CONCRETE & REACTION with PORE WATER H 2 CO 3 H 2 SO 3 (CARBONIC ACID) (SULFUROUS ACID) NEUTRALIZATION of HYDRATED COMPOUNDS of CEMENT by ACID ATTACK ACID + ALKALI SALT + WATER 3Ca(OH) 2 +CO 2 ph 12.6 CaCO 3 +H 2 O ph 8.3 ph< Initiation of Corrosion (In Presence of O 2 & H 2 O) 6

7 CARBONATION CHANGES in CONCRETE INNER STRUCTURE CARBONATION of HYDRATED COMPOUNDS of CEMENTS Ca(OH) 2, CSH, ETTRINGITE, FRIEDEL S SALT DROP of ph VALUE SHRINKAGE FORMATION CORROSION of STEEL (In presence O 2 ve H 2 O ) MICROCRACKS on CONCRETE SURFACE 7

8 FACTORS INFLUENCING CARBONATION CARBONATION RATE; ALL FACTORS INFLUENCING THE POROUS STRUCTURE OF CONCRETE (W/C, CURING CONDITIONS, CEMENT DOSAGE, etc.) QUALITY & THICKNESS OF CONCRETE COVER (IMPERMEABILITY) HUMIDITY (50-70% max:) CO 2 CONTENT (CLEAN AIR 0.03% - POLLUTED 0.3%) CHEMICAL COMPOSITION OF CEMENT (ALKALI & CaO CONTENT%) TEMPERATURE & etc. 8

9 EFFECT OF HUMIDITY TO CARBONATION & RUSTING DRY HUMID %50 Carbonation %85 Corrosion IMMERSED CARBONATION RUSTING Corrosion Risk Relative Humidity (%) 9

10 FACTOR FACTORS INFLUENCING CARBONATION CARBONATION RATE W/C RATIO CURING PERIOD CEMENT DOSAGE DRYNESS OF CONCRETE WATER SATURATION HUMIDITY % MAX. CO 2 CONCENTRATION ALKALI CONTENT COMPRESSIVE STRENGTH TEMPERATURE (NORMAL) 10

11 C = K t LOW STRENGTH CONCRETE W/C>0.6 FACTORS INFLUENCING CARBONATION C : CARBONATION DEPTH (mm) K : COEFFICIENT of CARBONATION (mm/year 0.5 t : TIME (year) K >3-4 4 mm/year mm OF CARBONATION DEPTH CAN BE REACHED IN 15 YEARS! CONCRETE COVERS (2-3 3 cm) MIGHT NOT PROVIDE THE NECESSARY PROTECTION DURING SERVICE LIFE Depth of carbonation front of concrete specimens after 30 years ( specimens are kept in open air unexposed to rain in England) 28 days comp. strength Carbonation depths 28 g ün lü k b asın ç da ya nım ı (M pa) K arb o natlaş m a D erin liği (m m )

12 CARBONATION of OTHER HYDRATED COMPOUNDS of CEMENT BESIDES Ca(OH) 2 CARBONATION CSH REACTION PRODUCT CaCO 3, AMORF SILICATE GEL, H 2 O ETTRINGITE FRIEDEL S S SALT CaCO 3, CaSO 4.2H 2 O, ALUMINIUM GEL, H 2 O FORMATION of FREE ALUMINIUM GEL CHLORIDES 12

13 CARBONATION FRONT Carbonated concrete Carbonation Front Uncarbonated concrete SPRAY OF INDICATOR LIQUID ON CORE SPECIMEN CO 2 NORMAL CONCRETE with HIGH ph VALUE REVEALS COLOR ph < 9.3 ph > 9.3 THIS METHOD INDICATES THE DEPTH OF CARBONATION FRONT PHENOLPTHALEIN (%0.1 ) ph > 8.3 PINK, RED COLOR THYMOLPTHALEIN (%0.1 ) ph > 9.3 BLUE, PURPLE PURPLE COLOR 13

14 CARBONATION FRONT 14

15 CARBONATION OF CEMENT WITH POZZOLANIC ADDITIVES REPLACEMENT OF CEMENT WITH LARGE AMOUNTS OF POZZOLANIC MATERIALS STABILIZATION OF Ca(OH) 2 BY POZZOLANIC REACTION DECREASE IN AMOUNT OF CEMENT SHARP DECREASES IN AMOUNT OF Ca(OH) 2 INSUFFICIENT CURING RAPID CARBONATION 15

16 SCHMIDT HAMMER TEST ON CARBONATED SURFACES CARBONATION SURFACE HARDENING BIG ERRORS ON OLD STRUCTURES!!! EXAMPLE: TEST RESULTS OF TWO BUILDINGS (a. 25 YEARS OLD b. 50 DAYS OLD) AGE OF CONCRETE 25 YEARS AGE OF CONCRETE 50 DAYS HAMMER RESULTS : fck = 16.9 MPa! CORE RESULTS : fck = 4.8 MPa HAMMER RESULTS : fck = 25.1 MPa! CORE RESULTS : fck = 18.0 MPa 16

17 REALKANIZATION ACTIVE METHODS PLACEMENT of TITANIUM ANOD ON CONCRETE SURFACE PENETRATION of Na + & (OH) - IONS BY APPLICATION of DIRECT CURRENT NOT PRACTICAL + SIDE EFFECTS; RISK OF HYDROGEN BRITTLENESS of R.F., ASR, LOSS OF BOND APPLICATION of LIME BASED PLASTER LOW W/C, min. 20 mm THICKNESS, HIGH LIME CONTENT ALKALINITY of PORE WATER INCREASES by PENETRATION OF Ca ++ ve (OH) - IONS in WATER LOSS OF EFFECTIVENESS DURING DRYING!! CARBONATED SURFACES SHOULD BE SCRAPED OFF IF POSSIBLE. SURFACES SHOULD BE REPAIRED by SPECIAL MORTARS. IMPERMEABILITY SHOULD BE PROVIDED PASSIVE METHODS 17

18 DEVELOPMENT of CORROSION Corrosion Service life Acceptable level PENETRATION of CHLORIDES, CARBONATION FRONT, WATER, OXYGEN to INNER LAYERS of RFC must be PREVENTED Initial stage Active corrosion IMPERMEABLE CONCRETE COVER with SUFFICIENT THICKNESS is NECESSARY EXTRA EXPENSIVE PRECAUTIONS MIGHT BE REQUIRED (VERY SELDOM) 18

19 CORROSION QUALITY of CONCRETE COVER is the MAIN FACTOR of DURABILITY APPLICATION MISTAKES FORMATION of CRACKS over TOP SURFACES BLEEDING & PLASTIC SETTLEMENT EXCESS WATER on top SURFACES (HIGH W/C RATIO) RAPID EVAPORATION PLASTIC SHRINKAGE CRACKS POOR CURING RETARDATION of HYDRATION RATE LOW MECHANICAL PROPERTIES CRACKS MORE PERMEABLE CONCRETE COVER THAN THE CONCRETE CORE 19

20 CORROSION OF STEEL BASICALLY IS A RETURNING TO ORIGINAL FORM TYPES OF CORROSION ATMOSPHERIC CORROSION Fe + ½O 2 +H 2 O Fe (OH) 2 - ATMOSPHERIC - ELECTROLYTIC - CHLORIDE - CONTACT - HYDROGEN BRITTLENESS Fe(OH) 2 FeO + H 2 O RUST CORROSION RATE (DEPENDS ON HUMIDITY) Clear Atmospheric (climatic) Conditions 4-6 µm/ m/year Polluted Atmospheric conditions µm/ m/year IF RUST LAYER IS STABLE IF NOT STABLE MEASUREMENT OF NOT DANGEROUS DIAMETER, TENSILE STRENGTH TEST, 20 CLEANING IS NECESSARY

21 ELECTRO-CHEMICAL CHEMICAL CORROSION of METALS TWO SIMULTANEOUS REACTIONS THAT COMPLIES EACH OTHER OXIDATION (ANODIC PROCESS) DISSOLUTION of IRON IONIZATION of STEEL by LOSS OF ELECTRONS Fe Fe e - LOSS of MASS COMBINATION of SURPLUS ELECTRONS in STEEL + H 2 O + O 2 FORMS 2(OH) - 2e - + ½O 2 + H 2 O 2(OH) - PROTECTED TRANSFER OF e - TO CATHODE TRANSFER OF (OH) - TO ANODE REDUCTION (CATHODIC PROCESS) ANODIC & CATHODIC AREAS MAY BE VERY CLOSE TO EACH OTHER (MICROELEMENT) OR MAY BE FAR AWAY (MACROELEMENT) IN THE SAME STEEL. 21

22 ELECTRO-CHEMICAL CHEMICAL CORROSION of METALS CONCRETE PORE WATER: PROVIDES AN ELECTROLYTE MEDIA (THAT ENABLES THE TRANSFER OF ELECTRONS) CATHODIC & ANODIC PROCESSES BEGINS FACTORS BATTERY FORMATION HUMIDITY, O 2 CONCENTRATION, SALT CONCENTRATION, THICKNESS & IMPERMEABILITY of CONCRETE DIFFERENT ANODIC & CATHODIC AREAS 22

23 CORROSION OF STEEL Concrete Pore water (Electrolythic) Fe +2 2e - Anodic O 2 2(OH) - H 2 O ½O 2 Steel Cathodic Oxygen diffusion through concrete cover ANODIC PROCESS Fe Fe e - CATHODIC PROCESS H 2 O +1/2O 2 + 2e - 2(OH) - Fe (OH) - Fe(OH) 2 + H 2 O+ + 1/2O 2 Fe(OH) 2 Fe(OH) 3 23

24 CHLORIDE CORROSION CHLORIDE IONS: MOST HAZARDOUS CHEMICAL FOR REINFORCEMENT DISSOLUTION OF PASSIVE LAYER INCREASE OF ELECTROLYTE, DECREASE ELECTRICAL RESISTANCE, EASE OF ION FLOW REDUCTION OF ph value CHLORIDE SOURCES CONCRETE MATERIALS (CEMENT, WATER, ADDITIVES, AGGREGATE) INTRUSION of EXTERIOR CHLORIDES (SEA WATER,, DE-ICING SALTS, ETC.) 24

25 CHLORIDE SOURCES SALT PLANTS USAGE OF SEA WATER FOR CONCRETE MIXING AND/OR CURING WATER CONTACT WITH SEA WATER & WETTING DRYING CYCLES SALTY AGGREGATES (SAND PROCURED FROM SEA) DE-ICING AGENTS SALTY UNDERGROUND WATER ACCELERATORS WITH CaCl 2 WINDS BLOWING FROM SEA 25

26 INTRUSION OF CHLORIDE IONS TO CONCRETE Cracks WETTING -DRYING PENETRATION of Cl - Penetretion depth from surface (mm) Content (%) CAPILLARY SUCTION OF SALINE WATER, DIFFUSION PERIODS, WETTING-DRYING CYCLES INCREASE Cl - CONCENTRATION & Cl - PENETRATION DEPTH 26

27 CHLORIDE CORROSION Passive Layer ( 50 µm) ph>12.5 Cl - Electrolyte (OH) - Cl - Fe +3 ph 5 Steel Electrolyte Fe Cl - FeCl 3 + 3(OH) Electrolyte - FeCl 3 Fe Fe(OH) 3 + 3Cl - Cathode Anode REGENERATION of CL - CONTINUOUS CONTINUOUS REACTION 27

28 CRITICAL CHLORIDE CONTENDS OF CONCRETE Critical Values of Chloride Content of Concrete ( % of Cement Weigth) 0.4 Bad Quality Concrete 50 Low Corrosion Risk (Electrolythic Process Stops) Non-carbonated Concrete Good Quality Concrete High Corrosion Risk Relative Humidity (%) Carbonated Concrete Low Corrosion Risk (No Oxygen) 28

29 CHLORIDE CONTENTS OF CONCRETE ACI 222R BY WEIGHT of CEMENT Acid Soluble Chloride (%) Water Soluble Chloride (%) Prestressed Concrete Reinforced Concrete (Humid environment) Reinforced Concrete (Dry environment) TS EN206-1 Max. Cl content by weight of cement Chloride Content (%) Concrete Reinforced Concrete Prestressed Concrete

30 RELATIONSHIP BETWEEN CONCRETE COVER & CHLORIDE INGRESS Concrete Cover (mm) W/C=0.6 W/C=0.5 W/C=0.4 NECESSARY COVER THICKNESS FOR CHLORIDE CONTENT <%0.2 AFTER 800 CYCLES W/C =0.4; c 40 mm W/C =0.5; c 70 mm W/C =0.6; c 90 mm 0 ACI 222R Number of Wetting&Drying Cycle in Saline Media W/C =0.4; c 50 mm W/C =0.45; c 65 mm 30

31 CONTACT CORROSION METALS AT UPPER LEVELS OF ELECTROMOTIVE SERIES ARE MORE STABLE (DO NOT OXIDE) COMPARED TO THE METALS AT LOWER LEVELS TWO DIFFERENT METALS (IN IN CONTACT) + H 2 O + O 2 GALVANIC BATTERY ANODIC METAL ELECTRON LOSS (MASS LOSS) CATHODIC METAL IS STABLE CORROSION RARE IN CONVENTIONAL R.F.C. STRUCTURES (EPOXY BONDED R.F. + STEEL,, AL. + St, etc.) 31

32 REINFORCEMENT CORROSION in CRACKED CROSS-SECTIONS Anodic Reaction at cracked region O 2 O 2 (OH) - Fe +2 Fe +2 (OH) - MACRO ELEMENT LARGE AREA : CATHODE SMALL AREA : ANODE Uncracked Large area cathode W O 2 (OH) - Fe +2 c MICRO ELEMENT ANODIC & CATHODIC AREAS ARE VERY CLOSE TO EACH OTHER IN CRACK MAXIMUM ALLOWABLE CRACK WIDTH W < mm 32

33 PERMEABILITY CORROSION RELATIONS CARBONATION MATERIALS Mix Proportions, Cement type & Aggregate properties, Admixtures, etc. PRODUCTION METHODS Mixing, Transportation, Casting, Vibration, Finishing PROCESSES AFTER CASTING Curing, Concrete strength at loading, service conditions CO 2 Penetration PERMEABILITY DECREASE OF ph value Cl - PENETRATION WATER PENETRATION (Splashing, Hydraulic pressure, Immersion, Capillary suction, O 2 PENETRATION WASHING OUT OF Ca(OH) 2 CRACKS, POP-OUTS & SPALLING OF CONCRETE CORROSION 33

34 PRODUCTS of CORROSION Steel Cracks Fe FeO Fe 3 O 4 Fe 2 O 3 Fe(OH) 4 Fe(OH) 3Fe(OH)3. 3H 2 O Steel Pop-outs Volume (cm 3 ) RUST PRODUCTS VOLUME INCREASE UP TO 6 6 TIMES LATERAL CRACKS BETWEEN COVER & REINFORCEMENT CRACKS DUE TO SWELLING 34

35 CORROSION HAZARDS RUSTING OF REINFORCEMENT LOSS OF X-SECTION CHANGE IN DEFORMATION PROPERTIES & TENSILE STRESS LOSS OF BOND BETWEEN CONCRETE & REINFORCEMENT CRACK OF CONCRETE COVER BEGINNING OF ATMOSPHERIC TYPES OF CORROSION DUE TO AIR EXPOSURE 35

36 REINFORCEMENT CORROSION The effect of reinforcement cross-sectional area loss of on moment carrying capacity x70 cm N=100 ton Moment Moment Taşıma carrying Kapasitesinde capacity Kayıp loss (%) % Donatıda RF area Kesit loss Kaybı (%) % Transition from ductile to brittle behaviour without warning sign! 36

37 HAZARDS of CORROSION 37

38 HAZARDS of CORROSION 38

39 HAZARDS of CORROSION

40 HAZARDS of CORROSION

41 HAZARDS of CORROSION

42 HAZARDS of CORROSION 42

43 HAZARDS of CORROSION

44 HAZARDS of CORROSION

45 HAZARDS of CORROSION

46 HAZARDS of CORROSION 46

47 HAZARDS of CORROSION 47

48 HAZARDS of CORROSION 48

49 HAZARDS of CORROSION 49

50 HAZARDS of CORROSION 50

51 HAZARDS of CORROSION 51

52 HAZARDS of CORROSION 52

53 HAZARDS of CORROSION 53

54 HAZARDS of CORROSION 54

55 HAZARDS of CORROSION DATÇA A PORT 55

56 HAZARDS of CORROSION 56

57 HAZARDS of CORROSION DATÇA A PORT 57

58 HAZARDS of CORROSION 58

59 HAZARDS of CORROSION 59

60 HAZARDS of CORROSION 60

61 HAZARDS of CORROSION 61

62 HAZARDS of CORROSION CORROSION DETERIORATION OF COLUMNS UNDER THE ATATURK S S MAUSOLEUM 62

63 HAZARDS of CORROSION 63

64 HAZARDS of CORROSION 64

65 HAZARDS of CORROSION 65

66 HAZARDS of CORROSION 66

67 67

68 Corrosion rate of reinforcement Electrochemical measurements φ12, φ16, φ20 60 mm 75 mm 160 mm 20 mm Gamry PCI4/300 Potentiometer 68

69 Reinforced concrete Plain reinforcement 69

70 CLASSIFICATION OF ENVIRONMENTAL EXPOSURE TS EN206 Max. W/C Min. STRENGTH NO RISK OF CORROSION OR DETERIORATION X C14 CORROSION RISK DUE TO CARBONATION XC1 XC2 XC3 XC C20 C25 C30 C30 Min. CEMENT DOSAGE (kg/m 3 ) X0 : VERY DRY (Very low humidity, interior of buildings) XC1 : DRY (Low humidity, interior of buildings) XC2 : HUMID ENVIRONMENT (Components exposed to water, Foundations) XC3 : MODERATE HUMIDITY (not exposed to rain, int./ext. components) XC4 : CONTINOUSLY DRY-WET ENVIRONMENT (one face exposed to water) 70

71 CLASSIFICATION OF ENVIRONMENTAL EXPOSURE TS EN206 Max. W/C PRECAUTIONS DUE TO CHLORIDE CORROSION (EXCEPT SEA WATER) XD1 XD2 XD Min. STRENGTH C30 C30 C35 Min. CEMENT DOSAGE (kg/m 3 ) XD1 : HUMID, RARELY DRY (Splashing of water containing Chloride ions) XD2 : MODERATE HUMIDITY (Swimming pools, industrial water) XD3 : CONTINUOUSLY DRY-WET ENVIRONMENT (Bridges, Floors, car parking structures) 71

72 PRECAUTIONS FOR CORROSION PRECAUTIONS OF STANDARDS FOR CONCRETE DESIGN & COVER TO SUSTAIN DURABILITY Are GENERALLY BASED ON 2 APPROVALS YEARS SERVICE LIFE 2. MAX. AGGREGATE SIZE IS mm FOR MORE SERVICE LIFE INCREASE THE COVER EX: FOR 100 YEARS ADD 10 mm CEMENT DOSAGE and etc. HAS TO BE TAKEN INTO CONSIDERATION COVER DETAILED INTHE PROJECT: C nom C nom = C min + c c: THE COVER DEPENDENT ON PROJECT TOLERANCES, QUALITY CONTROL and ETC. (GENERALLY 5 mm) 72

73 Concrete cover Corrosion Risk Corrosion Risk Factor Related to Concrete Cover Existance of Chloride ions Normal environment Average Relative Humidity of Concrete (%) DEPTH OF COVER SHOULD BE INCREASED BASED ON RISK FACTOR 73

74 CONCRETE COVER TS500 (2000) MINIMUM THICKNESS ELEMENT in CONTACT with SOIL COLUMNS & BEAMS EXPOSED to ATMOSPHERIC CONDITIONS COLUMNS & BEAMS INDOORS SHEAR WALLS, CURTAINS, PLATES FOLDED PLATES & MEMBRANES 50 mm 25 mm 20 mm 15 mm 15 mm 74

75 CONCRETE COVER pren NO RISK CORROSION DUE TO CARBONATION CORROSION DUE TO CHLORIDES CORROSION DUE TO SEA WATER X0 XC1 XC2/XC3 XC4 XD1/XD2/XD3 XS1/XS2/XS3 REINFORCED CONCRETE C min (mm) PRESTRESSED CONCRETE C min (mm)

76 CONCRETE COVER(mm) I II III IV V MAX W/C CONCRETE STRENGTH MIN CEMENT DOSAGE I : PROTECTED SURFACES AGAINST AGGRESSIVE ENVIRONMENT II : PROTECTED SURFACES EXCESSIVE RAIN & FROST DAMAGE, EXISTANCE OF CONDENSATION III : EXPOSED TO EXCESSIVE RAIN, DRYING & WETTING IV : SEA WATER, DE-ICING AGENT, FREEZE-THAWING V : ACIDIC WATER (ph 4.5), WEARING, EROSION

77 SPECIAL METHODS & MATERIALS STAINLESS STEEL EXPENSIVE & POOR BOND EPOXY PAINTING GOOD CHEMICAL RESISTANCE, BRITTLENESS, MAY CRACKS DURING STEEL WORKS (BENDING ETC.), HIGH COST, POOR BOND, LONG TERM PERFORMANCE IS NOT KNOWN GALVANIZING WITH ZINC LONG TERM PERFORMANCE IS NOT CLEAR, LOSS OF BOND, CRACK DEVELOPMENT DURING STEEL WORKS, WELDING IS NOT POSSIBLE 77

78 SPECIAL METHODS & MATERIALS GLASS FIBER REINFORCEMENT FOREGOING RESEARCH NOT COMPLETED, BRITTLENESS, NOT WORKABLE, MAY CAUSE ASR, ASR RESISTANT TYPE IS VERY EXPENSIVE CHEMICAL ADMIXTURE (CORROSION INHIBITATORS) SUCCESSFUL RESULTS WITH CALCIUM NITRATE, LONG TERM PERFORMANCE IS NOT CLEAR, RETARDING EFFECT, MAY CAUSE ASR, LOSS OF COMPRESSIVE STRENGTH, EFFLORESENCE 78

79 SPECIAL METHODS & MATERIALS CATHODIC PROTECTION USING EXPANDABLE RECHANGEABLE METAL SUCH AS ZINC & MAGNESIUM THEY CORRODE INSTEAD OF STEEL, APPLICATION DIFFICULTY IN REINFORCED CONCRETE CATHODIC PROTECTION BY AC CURRENT CORROSION IS PREVENTED BY REVERSING ELECTRO-POTENTIAL OF STEEL, HARDNESS OF APPLICATION UNIFORM DIRECT CURRENT, RISK OF HYDROGEN BRITTLENESS 79

80 DURABILITY of CONCRETE STRUCTURES 3 PART Prof. Dr. Halit YAZICI 80