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Cement and Concrete: Promise of Fly Ash

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The presentation made by Dr J D Bapat illustrates the importance of fly ash utilisation. The slides depict how fly ash is used in cement and concrete to improve its strength and durability.

Published in: Engineering
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Cement and Concrete: Promise of Fly Ash

  1. 1. CEMENT & CONCRETE: PROMISE OF FLY ASH FLY ASH UTILISATION INTERACTIVE WORKSHOP 11 JULY 2014, MUMBAI MISSION ENERGY FOUNDATION, MUMBAI
  2. 2. FLY ASH RELEVANCE FOR INDIA IN INDIA 60% POWER FROM COAL COAL HAS LOW CALORIFIC VALUE & VERY HIGH ASH CONTENT ASH GENERATION: 175 MILLION t/a & CEMENT PRODUCTION CAPACITY: 350 MILLION t/a
  3. 3. FLY ASH ENERGY & GHG SAVER CEMENT TYPE THERMAL ENERGY ELECTRICAL ENERGY PC 100 100 PPC (15%) 84 89 PSC (50%) 47 79 • CEMENT INDUSTRY CONTRIBUTES 5% OF TOTAL ANTHROPOGENIC CO2 EMISSIONS GLOBALLY
  4. 4. FLY ASH ASTM CLASSIFICATION • ASTM C618 CLASSIFICATION: ASTM CLASS FAS DESCRIPTION N (>70%) RAW OR CALCINED NATURAL POZZOLAN, EXAMPLE: METAKAOLIN F (>70%) FA WITH POZZOLANIC PROPERTIES, PRODUCED FROM ANTHRACITE OR BITUMINOUS COAL C (>50%) FA WITH POZZOLANIC AND CEMENTITIOUS PROPERTIES, PRODUCED FROM LIGNITE SUBBITUMINOUS COAL, LIME CONTENT > 10% • FAS: Fe2O3 + Al2O3 + SiO2 • RETENTION ON 45 MICRON (325 MESH) SIEVE (%, MAX): 34%
  5. 5. FLY ASH ASTM CLASSIFICATION
  6. 6. FLY ASH INDIAN STANDARD IS 3812 REQUIREMENT • GRADE I, BITUMINOUS, SIMILAR TO ASTM TYPE F: Fe2O3 + Al2O3 + SiO2 = MIN 70% • GRADE II, LIGNITE, SIMILAR TO ASTM TYPE C: Fe2O3 + Al2O3 + SiO2 = MIN 50%
  7. 7. FLY ASH IN CONCRETE INDIAN STANDARD IS 456 REQUIREMENT FOR REINFORCED CONCRETE (i) MINERAL ADMIXTURES FA, GGBS, SF, RHA, MK (ii) ADDITION LIMITS (%) FA: 15-35, GGBS: 25-70 (iii) CONCRETE M 20-M 80 (iv) CEMENT CONTENT (kg/cu.m) EXCLUDING ADMIXTURE (MAX) 450 v) w/b RATIO(MAX) 0.4-0.55 (vi) CHLORIDE (MAX, kg/cu.m) 0.4-0.6 (vii) SULPHATE SO3 (% CEMENT m) 4
  8. 8. FLY ASH PARTICLE SHAPE SPHERICAL CENOSPHERES
  9. 9. FLY ASH PARTICLE SHAPE PLEROSPHERES: CRACKED SPHERES
  10. 10. FLY ASH IN CONCRETE: EFFECT OF PARTICLE SHAPE • SHAPE FA PARTICLES AFFECT WATER REQUIREMENT OF CONCRETE • SPHERICAL PARTICLES CREATE BALL BEARING EFFECT • THAT IMPROVES ITS FLOW PROPERTIES & REDUCE WATER REQUIREMENT
  11. 11. FLY ASH IN CONCRETE: EFFECT OF PARTICLE SIZE • POZZOLANIC REACTIVITY OF FA WAS MORE AFFECTED BY FINENESS THAN GLASS CONTENT • PARTICLES IN RAW FA RANGE MOSTLY FROM 1 TO 100 MICRON • PARTICLES UNDER 10 MICRON: EARLY (7 & 28 DAY) STRENGTH, 10-45 MICRON: LATE STRENGTH UP TO 1 YEAR ABOVE 45 MICRON: INERT & ACT AS FILLER
  12. 12. FLY ASH IN CONCRETE: EFFECT OF UNBURNED CARBON MINIMISE UNBURNED CARBON • CARBON PARTICLES DO NOT TAKE PART IN CHEMICAL REACTIONS DURING CEMENT HYDRATION BUT INFLUENCE ITS WATER DEMAND FOR STANDARD CONSISTENCY • INCREASE REQUIREMENT OF AIR-ENTRAINING AGENTS (AEA) • FOAM INDEX (FI) IS IMPORTANT QUALITY CONTROL TEST TO DETERMINE EFFECT OF UBC IN FA • FA WITH < 3%–4% CARBON DOES NOT SERIOUSLY AFFECT PERFORMANCE OF ORGANIC CHEMICAL ADMIXTURES
  13. 13. FLY ASH IN CONCRETE: FLUIDISED BED FA  ASH PARTICLES FROM FB ARE LARGER & LESS SPHERICAL IN COMPARISON TO FA PRODUCED IN CONVENTIONAL PULVERIZED COAL FIRED SYSTEMS  IRREGULARITY OF SHAPE MAY NOT GIVE DESIRED RESULTS IN TERMS OF LOWERING WATER-TO-CEMENT RATIO  FLUIDISED BED FA IS MOSTLY NON- STANDARD
  14. 14. FLY ASH IN CONCRETE: PETCOKE CO-COMBUSTION FA  CO-FIRING OF COAL WITH PETCOKE ADDS MORE UBC & COARSENESS TO FA  ASH CONTENT JUST 0.5%  INCREASE IN CARBON CONTENT EXPECTED TO REDUCE EFFECTIVENESS OF AEA  HIGH VANADIUM CONTENT: GETS INCLUDED INTO SOLID CONCRETE STRUCTURE  USE OF PETCOKE PFA HAS NO DETRIMENTAL EFFECTS ON CONCRETE STRENGTH DEVELOPMENT
  15. 15. FLY ASH IN CONCRETE: QUALITY IMPROVEMENT  REMOVAL OF UBC PARTICLES, OBTAINING PROPER PARTICLE SIZE (< 10 MICRON) & SIZE DISTRIBUTION ARE PRINCIPAL TASKS OF FA PROCESSING  INCREASED STRENGTH, GREATER POZZOLANIC REACTIVITY & LOWER WATER DEMAND  IMPROVED CONSISTENCY FOR FA COMING FROM DIFFERENT SOURCES  TREATMENT INCLUDES SIZE REDUCTION &/OR CLASSIFICATION
  16. 16. FLY ASH IN CONCRETE: HYDRATION  IT BEGINS WITH ADDITION OF WATER TO CONCRETE & NEARLY 60%–65% HYDRATION IS COMPLETE IN 28 DAYS  MINERAL ADMIXTURES TAKE PART IN HYDRATION REACTIONS  AFFECT EARLY-AGE PROPERTIES: WORKABILITY, SETTING, SHRINKAGE, ETC., BESIDES STRENGTH & DURABILITY OF CONCRETE.
  17. 17. FLY ASH IN CONCRETE: SETTING & HARDENING • CALCIUM SILICATES FROM CEMENT REACT WITH WATER TO FORM C-S-H & CH • C-S-H IS PRINCIPAL STRENGTH GIVING COMPUND • C-S-H IN ACTS LIKE A “SPONGE,” ABSORBING VARIETY OF IONS • FULLY HYDRATED MASS OF CEMENT CONTAINS MORE THAN 70% C-S-H
  18. 18. FLY ASH IN CONCRETE: C-S-H
  19. 19. FLY ASH IN CONCRETE: ADDITIONAL STRENGTH WITH FLY ASH  (REACTIVE SILICA IN FA) + (CALCIUM HYDROXIDE) = ADDITIONAL C-S-H  ADDITIONAL C-S-H LEADS TO REDUCTION IN PERMEABILITY & IMPROVED DURABILITY  HYDRATION OF FA DOES NOT BEGIN UNTIL ABOUT 7 DAYS  LATE HYDRATION IMPORTANT FOR MASS CONCRETING  SETTING DELAYED WITH LEVEL OF REPLACEMENT  RATE OF STRENGTH DEVELOPMENT REMAINS APPROPRIATE UP TO A REPLACEMENT LEVEL OF 60%
  20. 20. FLY ASH IN CONCRETE: STRENGTH & DURABILITY  STRENGTH IS COMBINATION OF THREE FACTORS: STRENGTH = DILUTION + PHYSICAL + CHEMICAL  PHYSICAL EFFECT IS INCREASE IN STRENGTH DUE TO FILLER EFFECT  CHEMICAL EFFECT IS INCREASE IN STRENGTH DUE TO POZZOLANIC REACTION  IMPROVED INTERFACIAL TRANSITION ZONE (ITZ) MICROSTRUCTURE
  21. 21. FLY ASH IN CONCRETE: IMPORTANCE OF CURING  IMPORTANT FOR DEVELOPMENT OF STRENGTH & DURABILITY PROPERTIES  EARLY & LONG TERM CURING IS BENEFICIAL  PREVENTION OF MOISTURE LOSS IMPORTANT: (a) WHEN W/C RATIO IS LOW, (b) WHEN CEMENT HAS A HIGH RATE OF STRENGTH DEVELOPMENT & (c) WHEN CONCRETE CONTAINS MINERAL ADMIXTURES  MOISTURE LOSS FROM CONCRETE SURFACE SPECIALLY FOR THIN ELEMENTS, RELATIVELY HIGH IN HOT, DRY CLIMATE
  22. 22. FLY ASH IN CONCRETE: DURABILITY AGAINST CARBONATION • CARBONATION REFERS TO PRECIPITATION OF CALCITE (CaCO3) THRU REACTION OF PENETRATING ATMOSPHERIC CO2, WITH CALCIUM HYDROXIDE IN PORE SOLUTION • MAIN CONSEQUENCE OF CARBONATION IS DROP OF pH OF PORE SOLUTION OF CONCRETE FROM STANDARD VALUES OF 12.5–13.5, TO A VALUE OF ABOUT 8.3, SO THAT PASSIVE LAYER THAT USUALLY COVERS & PROTECTS REINFORCING STEEL AGAINST CORROSION BECOMES UNSTABLE • EARLY & LONGER CURING PRODUCES BETTER CARBONATION RESISTANCE, ESPECIALLY IN CONCRETE WITH MINERAL ADMIXTURES
  23. 23. FLY ASH IN CONCRETE: CARBONATION LEADS TO CORROSION CARBONATION & SUBSEQUENT CORROSION OF REINFORCEMENT
  24. 24. FLY ASH IN CONCRETE DURABILITY AGAINST AAR • AGGREGATES CONTAINING REACTIVE MINERALS REACT WITH SOLUBLE ALKALIES IN CONCRETE & SOMETIMES RESULT IN EXPANSION, CRACKING OF CONCRETE STRUCTURES • STRUCTURES IN DIRECT CONTACT WITH WATER, SUCH AS DAMS AND BRIDGES, ARE MORE SUSCEPTIBLE TO AAR • CONDITIONS TO INITIATE & PROPAGATE AAR: (A) CRITICAL QUANTITY OF REACTIVE AGGREGATE, (B) SUFFICIENT ALKALI IN CONCRETE & (C) SUFFICIENT MOISTURE (.) ALL THREE CONDITIONS MUST PREVAIL TOGETHER • MINERAL ADMIXTURES REPLACING CEMENT, SUCH AS BFS, FA & NATURAL POZZOLANS, MITIGATE OR ELIMINATE AAR IN CONCRETE • TOTAL ALKALI CONTENT OF CONCRETE & LEVEL OF CEMENT REPLACEMENT BY MINERAL ADMIXTURES ARE KEY FACTORS GOVERNING EXPANSION OF CONCRETE
  25. 25. FLY ASH IN CONCRETE CRACKING DUE TO AAR CONCRETE PAVEMENT CRACKED DUE TO AAR
  26. 26. FLY ASH IN CONCRETE DURABILITY AGAINST CORROSION • REINFORCING STEEL, SURROUNDED BY ALKALINE ENVIRONMENT IN CONCRETE STRUCTURE, IS PROTECTED FROM ATTACK OF AGGRESSIVE AGENTS BY THE PASSIVE IRON OXIDE FILM FORMED ON ITS SURFACE • WHEN CHLORIDE IONS PENETRATE THROUGH POROUS CONCRETE & BUILD UP AROUND REINFORCEMENT & ALKALINITY (pH) OF SURROUNDING PORE SOLUTION FALLS SUBSTANTIALLY & PROTECTIVE IRON OXIDE FILM DEPASSIVATES & CRACKS, EXPOSING STEEL • EXPOSED STEEL GETS CORRODED IN PRESENCE OF WATER & OXYGEN, RESULTING IN FORMATION OF EXPANSIVE CORROSION PRODUCTS (RUST) THAT OCCUPY SEVERAL TIMES THE VOLUME OF ORIGINAL STEEL CONSUMED • EXPANSIVE CORROSION LEADS TO CRACKING & SPALLING OF CONCRETE COVER • MINERAL ADMIXTURES IMPART ENHANCED RESISTANCE TO CORROSION: REDUCE DIFFUSION OF CHLORIDE IONS & OTHER DETERIORATING AGENTS, ON ACCOUNT OF THE REFINEMENT OF PORE STRUCTURE
  27. 27. FLY ASH IN CONCRETE: DURABILITY AGAINST CORROSION FLY ASH CONCRETE IS USED UNDER SEVERE EXPOSURE CONDITION SUCH AS IN DECKS & PIERS OF SUNSHINE SKYWAY BRIDGE, TAMPA BAY, FLORIDA
  28. 28. FLY ASH IN CONCRETE: DURABILITY AGAINST EXTERNAL SULFATE ATTACK • COMMONLY OBSERVED PHENOMENON, WHEN STRUCTURES ARE EXPOSED TO SULFATE SOLUTIONS OR BUILT IN SULFATE BEARING SOIL AND/OR GROUND WATER • ALL COMMONLY OBTAINED WATER SOLUBLE SULFATES ARE DELETERIOUS (Mg > Na > Ca) TO CONCRETE, BUT EFFECT IS SEVERE WHEN IASSOCIATED WITH Mg CATIONS • SULFATE IONS REACT WITH IONIC SPECIES OF PORE SOLUTION TO PRECIPITATE GYPSUM, ETTRINGITE OR THAUMASITE OR A MIXTURE OF THESE PHASES, DEPENDING UPON TEMPERATURE & OTHER FAVORABLE CONDITIONS • PRECIPITATION OF THESE SOLID PHASES LEADS TO STRESS WITHIN CONCRETE INDUCING EXPANSION, STRENGTH LOSS, SPALLING & SEVERE DEGRADATION • APPLICATION OF PROTECTIVE COATING, LIKE EPOXY-BASED COATING, IS ALSO RECOMMENDED ON CONCRETE SURFACE EXPOSED TO MgSO4 ENVIRONMENT
  29. 29. FLY ASH IN CONCRETE: DURABILITY AGAINST INTERNAL SULFATE ATTACK • INTERNAL SULFATE ATTACK (ISA) OR DELAYED ETTRINGITE FORMATION (DEF) • FORMATION OF EXPANSIVE ETTRINGITE IN HYDRATED CONCRETE AFTER HARDENING IS SUBSTANTIALLY COMPLETE • OCCURS WHEN ETTRINGITE, FORMED DURING HYDRATION, IS DECOMPOSED & SUBSEQUENTLY FORMED AGAIN IN HARDENED CONCRETE • MOSTLY OBSERVED IN PRECAST CONCRETE PRODUCTS, CURED AT ELEVATED TEMPERATURE • TWO CONDITIONS PROMOTING DEF: (A) INTERNAL TEMPERATURE ABOVE 70°C, TO DECOMPOSE ETTRINGITE FORMED DURING INITIAL HYDRATION, (B) AFTER RETURNING TO NORMAL TEMPERATURE, CONCRETE IS EXPOSED TO MOIST OR WET SURROUNDINGS • ADDITION OF MINERAL ADMIXTURES TO CONCRETE REDUCES DEF • FA AT HIGHER REPLACEMENT LEVELS FOUND EFFECTIVE IN CONTROLLING DEF
  30. 30. FLY ASH IN CONCRETE HIGH VOLUME FLY ASH CONCRETE (HVFAC) • TERM COINED BY MALHOTRA et.al. in 1980 • CEMENT CONTENT < 200 kg / cu. M • WATER CONTENT < 130 kg / cu. M • FA CONTENT > 50% CEMENT REPLACEMENT BY MASS • HRWRA REQUIRED FOR HIGH SLUMP (150-200 mm) & HIGH EARLY STRENGTH (>30 MPa) & w/b RATIO: O.3 • HRWRA NOT REQUIRED FOR LOWER SLUMP, LOWER STRENGTH & w/b RATIO: 0.4 • AEA REQUIRED UNDER FREEZE-THAW CONDITIONS TO MAINTAIN AIR-VOID RATIO
  31. 31. HVFAC ROAD: FATEHPUR BERI MUNICIPAL CORPORATION N DELHI (MCD) (100 m LONG – 7 m WIDE)
  32. 32. HVFAC UNDERGROUND CONSTRUCTION S-E ENTRANCE SUBWAY, RAJIV CHOWK , N DELHI DELHI METRO RAIL CORPORATION (DMRC)
  33. 33. HVFAC MCD & DMRC CONSTRUCTIONS EXPERIENCE • USING ONLY HALF OF THE CONVENTIONAL OPC , SAVED GHG EMISSIONS, NEARLY 200 Kg PER M3 OF CONCRETE USED • LOWER EARLY COMPRESSIVE STRENGTH BUT VERY GOOD LATER-AGE STRENGTH WHICH CONTINUES TO INCREASE OVER SEVERAL MONTHS • PRACTICAL EXAMPLE FOR INCREASING ACCEPTANCE CRITERION TO 60-90 D, WHEREVER STRUCTURE IS LOADED AT LATER AGE • BETTER IN TERMS OF ELASTIC MODULUS, FLEXURAL, TENSILE & ABRASION • LOWER PERMEABILITY & HENCE BETTER DURABILITY • SETTING TIME AT DMRC PROJECT WAS UNDULY LONG, WHILE AT MCD IT WAS QUITE LIKE PLAIN CONCRETE, SUGGESTING IMPORTANCE OF CHOOSING CORRECT SUPERPLASTICIZER • QUALITY CONTROL IMPORTANT IN HVFAC AS IN CONVENTIONAL CONCRETE
  34. 34. FLY ASH IN CONCRETE FINE FA OR FFA • ALSO TERMED AS ULTRA-FINE FA • MEAN PARTICLE DIA OF CONVENTIONAL FA: 20-30 MICRONS • MEAN PARTICLE DIA OF FINE FA : 1-5 MICRONS • LOW UNBURNED CARBON • OBTAINED BY GRINDING &/OR AIR SEPARATION
  35. 35. MICROSTRUCTURE: TRADITIONAL VERSUS HPC C3A + GYPSUM + WATER = ETTRINGITE = 3CaO.Al2O3.3CaSO4.32H2O
  36. 36. FLY ASH IN CONCRETE HPC WITH FFA • HIGH STRENGTH: 70-140 MPa @ 28-91 D • HIGH EARLY STRENGTH: 20-30 MPa @ 3-12 h OR 1-3 D • HIGH EARLY FLEXURAL STRENGTH: 2-4 MPa @ 3-12 h OR 1-3 D • HIGH MODULUS OF ELASTICITY > 40 GPa • ABRASION RESISTANCE: 0-1 mm DEPTH OF WEAR • LOW PERMEABILITY: 500-2000 COULOMBS • CHLORIDE PENETRATION < 0.07% Cl AT 6 MONTHS • LOW WATER ABSORPTION: 3-5%
  37. 37. FLY ASH IN CONCRETE SF & FFA COMPARED • CONCRETE CONTAINING FFA COULD BE PRODUCED WITH ONLY 50% OF HIGH-RANGE WATER REDUCER (HRWR) DOSAGE IN COMPARISON TO SILICA FUME (SF) CONCRETE
  38. 38. TRAINING COURSE
  39. 39. TRAINING COURSE TWO DAY TRAINING COURSE ON DURABLE, HIGH PERFORMANCE CEMENT & CONCRETE WITH MINERAL & CHEMICAL ADMIXTURES
  40. 40. TRAINING COURSE CONTENTS  APPLICATION OF MINERAL ADMIXTURES: FA, BFS, SF, MK RHA  APPLICATION OF CHEMICAL ADMIXTURES & SUPER PLASTICISERS  HIGH PERFROMANCE CONCRETE: HIGH STRENGTH, SCC, RCC, LIGHTWEIGHT, PERVIOUS, HVFAC  GROUP DISCUSSIONS, CASE STUDIES & VIDEOS  DETAILS: http://www.drjdbapat.com
  41. 41. TRAINING COURSE WHO SHOULD ATTEND  ENGINEERS WORKING AT CONSTRUCTION SITE  ENGINEERS WORKING WITH CEMENT, CONCRETE INDUSTRY  ENGINEERS WORKING WTH MANUFACTURERS AND SUPPLIERS OF CHEMICAL ADMIXTURES AND MINERAL ADMIXTURES  ENGINEERS WORKING ON PRODUCT DEVELOPMENT  STUDENTS/RESEARCHERS  DETAILS: http://www.drjdbapat.com
  42. 42. TRAINING COURSE FLEXIBILITY CONTENTS: CHOOSE AS PER YOUR REQUIREMENT DURATION: 1-2 DAYS VENUE: PUNE OR YOUR HEAD OFFICE, PLANT OR CONSTRUCTION SITE DETAILS: http://www.drjdbapat.com
  43. 43. FLY ASH IN CONCRETE: ACKNOWLEDGEMENT • I THANKFULLY ACKNOWLEDGE THAT WHILE MAKING THIS PRESENTATION, I HAVE FREELY DRAWN UPON THE INFORMATION PUBLISHED IN THE FOLLOWING BOOK: MINERAL ADMIXTURES IN CEMENT AND CONCRETE AUTHOR: JAYANT D. BAPAT PUBLISHER: CRC PRESS, TAYLOR & FRANCIS GROUP, USA

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