Dr. Jayant D. Bapat - Durable and Sustainable Concrete with Mineral Admixtures, 3rd EACCES
1. DURABLE & SUSTAINABLE CONCRETE
WITH
MINERAL ADMIXTURES
by
Dr J D Bapat
http://www.drjdbapat.com
3rd EAST AFRICA CEMENT, CONCRETE
AND ENERGY SUMMIT
ADDIS ABABA
1-2 AUGUST 2018
2. ACKNOWLEDGEMENT
• WITH SINCERE THANKS TO THE PUBLISHER:
• I ACKNOWLEDGE THAT WHILE PREPARING THIS
PRESENTATION I HAVE USED INFORMATION GIVEN IN MY
BOOK:
“MINERAL ADMIXTURES IN CEMENT AND CONCRETE”
CRC PRESS – TAYLOR & FRANCIS GROUP
5. PULVERISED FUEL ASH
ENERGY & GHG
CEMENT TYPE THERMAL ENERGY ELECTRICAL ENERGY
PC 100 100
PPC (15%) 84 89
PSC (50%) 47 79
• IDEAL ENERGY CONSUMPTION FOR A NEW LARGE CAPACITY PLANT:
THERMAL: 680–720 kcal/kg & ELECTRICAL: 72–74 kwh/t
• CEMENT INDUSTRY CONTRIBUTES 5% OF TOTAL ANTHROPOGENIC CO2
EMISSIONS GLOBALLY
• WBCSD TARGET: REDUCTION IN CO2 EMISSION BY A FACTOR OF 2 BY 2050
FROM THEIR 1990 LEVELS
• TECHNOLOGICAL SHIFT: CHANGES IN CONCRETE RAW MATERIALS, MIX
DESIGN, NEW BUILDING TECHNIQUES & USING LESS MATERIALS
6. PULVERISED FUEL ASH (PFA)
PULVERISED FUEL ASH OR FLY ASH IS
INORGANIC MATTER LEFT AFTER COAL
COMBUSTION, WHICH GETS COLLECTED, IN FINE
FORM, IN ELECTROSTATIC PRECIPITATORS (ESP)
OF THERMAL POWER STATIONS
ADDITION OF PFA TO CEMENT OR CONCRETE
REDUCES CLINKER PRODUCTION & CONTRIBUTES
TO LONG TERM STRENGTH & DURABILITY OF
CONCRETE
7. PULVERISED FUEL ASH
PHYSICAL
ASTM C618 CLASSIFICATION:
CLASS F: OBTAINED BY BURNING ANTHRACITE COAL: POZZOLANIC
CLASS C: OBTAINED BY BURNING LIGNITE COAL: POZZOLANIC &
CEMENTITIOUS
PHYSICAL CHARACTERISTICS: NAMELY, SHAPE, SPECIFIC GRAVITY,
SIZE AND FINENESS, & UNBURNED CARBON CONTENT, AFFECT PFA
PERFORMANCE IN CONCRETE
POZZOLANIC REACTIVITY: AFFECTED BY FINENESS THAN GLASS
CONTENT (.) GRINDING OR SIZE REDUCTION OPERATION IMPROVES
POZZOLANIC ACTIVITY OF PFA
12. PULVERISED FUEL ASH
PHYSICAL
PARTICLE SIZE RANGE: 1 TO 100 MICRON
UNDER 10 MICRON: EARLY, 7 & 28 D, STRENGTH
10 TO 45 MICRON: REACT SLOWLY & CONTRIBUTE TOWARD LATE
STRENGTH , UP TO 1 YEAR
ABOVE 45 MICRON: INERT & ACT AS FINE SAND OR FILLER
UNBURNED CARBON (UBC) PARTICLES:
CONTRIBUTE MAX TO LOSS ON IGNITION
INFLUENCE CEMENT WATER DEMAND FOR STANDARD
CONSISTENCY
STRONG AFFINITY TOWARD ORGANIC CHEMICAL ADMIXTURES,
SUCH AS AIR-ENTRAINING AGENTS (AEA)
PFA WITH LESS THAN 3%–4% CARBON: SAFE TO USE
13. PULVERISED FUEL ASH
CHEMICAL & MINERALOGICAL
HETEROGENEOUS MIXTURE OF COMPLEX
ALUMINOSILICATE GLASSES & SOME CRYSTALLINE
CONSTITUENTS
OXIDE COMPOSITION OF PFA EXHIBITS SUBSTANTIAL
REGIONAL VARIATION
PFA COMING FROM SAME SOURCE (NAMELY, THERMAL
POWER STATION) MAY ALSO SHOW VARIATION IN
COMPOSITION
14. PULVERISED FUEL ASH
CHEMICAL & MINERALOGICAL
IN PORTLAND CEMENT THERE IS CLOSE RELATIONSHIP
BETWEEN CHEMICAL & MINERALOGICAL COMPOSITION
IN MINERAL ADMIXTURE THERE IS NO RELATIONSHIP
BETWEEN CHEMICAL & MINERALOGICAL COMPOSITION
15. PULVERISED FUEL ASH
FLUIDISED BED
LOW TEMP: IN COMPARISON TO CONVENTIONAL
PULVERIZED COAL FIRED SYSTEM, FLUIDISED BED SYSTEM
HAS A RELATIVELY LOW COMBUSTION TEMPERATURE,
TYPICALLY IN RANGE 800°C–900°C
NON-ASTM: PFA FROM FLUIDISED BED CANNOT BE
CLASSIFIED AS ASTM CLASS F OR C, IN MANY CASES,
BECAUSE OF LOW FAS (FERRIC OXIDE + ALUMINA + SILICA
CONTENT) & HIGH SO3 CONTENT
16. PULVERISED FUEL ASH
CO-COMBUSTION
PFA FROM CO-COMBUSTION OF BITUMINOUS COAL &
PETCOKE
ADDS MORE UBC & COARSENESS TO PFA
NO LEACHING OF NICKEL & VANADIUM IN ENVIRONMENT
USE OF PETCOKE PFA HAS NO DETRIMENTAL EFFECTS ON
EITHER STRENGTH DEVELOPMENT OR AIR ENTRAINMENT
COMPARED TO BITUMINOUS COAL PFA
17. PULVERISED FUEL ASH
ULTRA FINE FA OR UFFA
ULTRA-FINE FA
MEAN PARTICLE DIA OF CONVENTIONAL FA: 5-30 MICRONS
MEAN PARTICLE DIA OF ULTRA-FINE FA : 1-5 MICRONS
LOW UNBURNED CARBON
18. PULVERISED FUEL ASH
UFFA REMOVES FA LIMITATIONS
HIGHER EARLY STRENGTH & HIGHER HEAT OF HYDARTION
DUE TO FASTER & COMPLETE REACTION
LOW REPLACEMENT: 5-15% REPLACEMENT UFFA MAKES
SUBSTANTIAL CONTRIBUTION TO CONCRETE STRENGTH &
PERMEABILITY REDUCTION
BETTER DURABILITY: WITH LESS CARBON & FINER
PARTICLES REACTING COMPLETELY
CONCRETE DURABILITY PROPERTIES LIKE RESISTANCE TO
ALKALI-AGGREGATE REACTION, SULFATE ATTACK,
CORROSION ARE ENHANCED BY UFFA
19. PULVERISED FUEL ASH
SPECIFYING FOR CONCRETE
LARGER QUANTITIES OF FA (>25) DELAY SETTING & EARLY
STRENGTH, BUT CAN BE TACKLED EFFECTIVELY WITH SP
LOI: 2-4% DOES NOT ALWAYS ELIMINATE PROBLEM OF AIR
ENTRAINING AGENT, WHEN CARBON PARTICLES ARE FINE
WHERE POSSIBLE, SPECIFYING 56 DAY STRENGTH INSTEAD OF
28 DAY, CAN RESULT IN BETTER OPTIMISED MIXTURE
FOR REACTIVE AGGREGATES, BETTER TO PERFORM STANDARD
EXPANSION TESTS TO DETERMINE LIMIT OF FA ADDITION
TO CONTROL ASR, BETTER TO KEEP FA ALKALI < 5% Na2O eq.
(IS 3812 SPECIFIES < 1.5%)
20. PULVERISED FUEL ASH
SPECIFYING FOR CONCRETE
CLORIDE RESISTANCE: PERFORM RCPT AS PER ASTM C1202 TO
FIND FA CONTENT FOR RCPT VALUE OF 1500-2000 COULOMBS (.) 56
DAY STRENGTH ADVISABLE
IS 456-2000: MAX ACID SOLUBLE Cl IN RCC = 0.6 Kg/M3
CONCRETE
SULPHATE RESISTANCE: IS 456 SPECIFIES MAX 4% BY MASS OF
CEMENT IN CONCRETE MIX
PERFORM TEST AS PER ASTM C1012 TO FIND OPTIMUM FA FOR
SULPHATE RESISTANCE (.) ONLY DISADVANTAGE IS TEST TAKES
LONG TIME: 6 MONTHS TO 1 YEAR
21. PULVERISED FUEL ASH
ADDITION TO CEMENT & CONCRETE
PFA IS ADDED DIRECTLY TO RMC AT BATCHING UNIT,
INTER-GROUND WITH CEMENT CLINKER, OR BLENDED WITH
PC AT CEMENT PLANT TO PRODUCE BLENDED CEMENT
BLENDED CEMENT: MOST NATIONAL STANDARDS ALLOW
ADDITION OF PFA TO CEMENT UP TO THE EXTENT OF 35%–
40%, TO MANUFACTURE BLENDED CEMENT
23. BLAST FURNACE SLAG (BFS)
GGBS
GROUND GRANULATED BFS OR GGBS
PRODUCED BY QUENCHING OF MOLTEN SLAG COMING FROM
BLAST FURNACE IN PARTICLE SIZE MOSTLY PASSING 4.75 mm
SIEVE & MAX UP TO 10 mm
1 t OF PIG IRON GENERATES 250–350 kg OF SLAG
BRITISH STANDARD SPECIFICATION FOR GGBS (BS 6699), FOR
USE WITH PORTLAND CEMENT, REQUIRES GLASS CONTENT >
67%
GRINDING OF GRANULATED BFS, LEADS TO PRODUCTION OF
GROUND GRANULATED BLAST FURNACE SLAG OR GGBS
24. BLAST FURNACE SLAG (BFS)
GGBS
LOWER SPECIFIC GRAVITY: IN RANGE OF 2.9–3.0, LOWER
IN COMPARISON WITH PC (3.0 - 3.2)
FINENESS & STRENGTH CHARACTERISTICS OF GGBS ARE
CONVENTIONALLY CORRELATED
ACTIVITY OF GGBS IS PROPORTIONAL TO THE GLASS
CONTENT
26. BLAST FURNACE SLAG (BFS)
QUALITY CONTROL
ASTM C-989-09: SPECIFIES THREE GRADES OF GGBS BY
STRENGTH: GRADE 80, 100 & 120
GRADE 120: REPRESENTS HIGHEST STRENGTH
GRADE IS DETERMINED BY STRENGTH OF MORTAR, WHEN GGBS
IS MIXED WITH EQUAL MASS OF PC
THREE GRADES: 80, 100 & 120 CLASSIFIED ACCORDING TO SLAG
ACTIVITY INDEX, BASED ON STRENGTH
SLAG ACTIVITY INDEX (%) = (STRENGTH OF
SLAG+CEMENT)/(STRENGTH OF CEMENT)X100 = (SP/P)100
27. BLAST FURNACE SLAG (BFS)
SPECIFYING FOR CONCRETE
TEMP INFLUENCES SETTING OF GGBS CONCRETE
MASS CONCRETING: TEMP RISE REDUCES WITH INCREASING
GGBS
CARBONISATION: INCREASES WITH GGBS CONTENT BUT
DEPENDS UPON TEMP & RH (.) EFFECTIVELY CONTROLLED
WITH CURING
HIGH RESISTANCE TOWARDS Cl ION PENETRATION DUE TO
ION BINDING CAPACITY
SULPHATE RESISTANCE: INCREASES WITH GGBS > 50%
BETTER RESISTANCE TOWARDS ACID ATTACK
28. BLAST FURNACE SLAG (BFS)
ADDITION TO CEMENT & CONCRETE
PARTIAL REPLACEMENT FOR CEMENT IN FOLLOWING TWO WAYS:
CEMENT MANUFACTURING UNIT:
SEPARATE GRINDING OF BFS & CLINKER & MIXING ALONG
WITH GYPSUM IN A MECHANICAL BLENDING UNIT
INTERGRINDING OF BFS, CLINKER & GYPSUM
CONCRETE MAKING SITE: GGBS OF DESIRED FINENESS
ADDED TO CONCRETE, TO REPLACE CEMENT PARTIALLY
MOST WORLD STANDARDS LIMIT THE ADDITION OF BFS IN SLAG
CEMENT UP TO 70%
HIGHER REPLACEMENTS ADVANTAGEOUS FOR CERTAIN
APPLICATIONS
30. HYDRATION
HYDRATION: COMBINATION OF ALL CHEMICAL & PHYSICAL PROCESSES
OCCURING, AFTER CONTACT OF ANHYDROUS SOLID WITH WATER
HYDRATION PERIODS:
WORKABILITY PERIOD: 1–3 h: VERY LOW RATE (DORMANT) HYDRATION:
WETTING, MIXING, TRANSPORTING, AGITATING, PLACING & FINISHING OF
CONCRETE
SETTING PERIOD: MIN IST > 60 min & MAX. FST RANGE 3–5 h: ACTIVE
REACTION: CUIRING CAN START AFTER FST
HARDENING PERIOD: ABOUT 28 DAY: DECELERATION & SLOW REACTION:
CURING TO CONTINUE FOR 7 TO 14 DAYS
31. HYDRATION
WITH MINERAL ADMIXTURES
FIVE PRINCIPAL MINERAL ADMIXTURES: PFA, BFS, SF, RHA, & MK,
ARE EITHER POZZOLANIC OR CEMENTITIOUS
CH REACTS WITH BOTH POZZOLANIC & CEMENTITIOUS
ADMIXTURES TO FORM ADDITIONAL CEMENTITIOUS PRODUCTS
ADMIXTURE HYDRATION PRODUCES MORE C-S-H, WHICH LEADS
TO HIGHER STRENGTH
HYDRATION DOES NOT BEGIN UNTIL AMORPHOUS MINERALS
(GLASS) DISSOLVES & REACTS WITH CH
PFA ADDITION: WORKABILITY IMPROVES OR WATER
REQUIREMENT DECREASES, FOR GIVEN WORKABILITY
IST & FST INCREASE: WITH REPLACEMENT BUT STRENGTH
DEVELOPMENT REMAINS APPROPRIATE
CURING: PROVIDE PROPER CURING TEMPERATURE & MOISTURE
FOR UP TO A WEEK
32. STRENGTH & DURABILITY
DURABILITY: ABILITY OF STRUCTURE TO RESIST WEATHERING
ACTION, CHEMICAL ATTACK & ABRASION, MAINTAINING MIN
STRENGTH & OTHER DESIRED ENGINEERING PROPERTIES
DESIGNING FOR STRENGTH & DURABILITY SYNONYMOUS TO
DESIGNING FOR SUSTAINABILITY
NATIONAL STANDARDS MOSTLY PRESCRIPTIVE , DEFINING
EXPOSURE CONDITIONS, DESIGN PROCEDURE, BUILDING
MATERIALS & THEIR APPLICATION, NOT ASSURING MIN SERVICE
LIFE OF STRUCTURE, WHEN SPECIFICATIONS ARE FOLLOWED
DURABILITY DEPENDS UPON BOTH EXPOSURE ENVIRONMENT &
QUALITY OF CONCRETE
33. STRENGTH & DURABILITY
DESIGNING FOR DURABILITY
PERMEABILITY IS THE SINGLE MOST IMPORTANT CRITERION FOR
DURABILITY
TWO MAJOR FAULTS IN CONCRETE CONSTRUCTION THAT CAN
LEAD TO THE LOSS OF DURABILITY: INADEQUATE COVER TO
REINFORCEMENT & INADEQUATE COMPACTION OF COVER
CONCRETE
QUALITY CONTROL NORMS FOR CONSTRUCTION MATERIALS
WELL ESTABLISHED, BUT PRACTICALLY NONEXISTENT FOR
CONSTRUCTION PROCESS
34. STRENGTH & DURABILITY
CONCRETE STRENGTH
STRENGTH OF CONCRETE CONTAINING MINERAL ADMIXTURES,
f(ADMIXTURE)
f(ADMIXTURE) = f(DILUTION) + f(PHYSICAL) + f(CHEMICAL)
f(DILUTION) = REDUCED STRENGTH PROPORTIONAL TO
AMOUNT OF CEMENT IN MIXTURE
f(PHYSICAL) = INCREASE IN STRENGTH DUE TO PHYSICAL
EFFECT OR HETEROGENEOUS NUCLEATION & FILLER EFFECT
DUE TO MINERAL ADMIXTURE
f(CHEMICAL): INCREASE IN STRENGTH RELATED TO
POZZOLANIC REACTION
35. STRENGTH & DURABILITY
INTERFACIAL TRANSITION ZONE
(ITZ)
0% SF 10% SF
SEM IMAGES OF CONCRETE ITZ MICROSTRUCTURE AT 28 DAYS WITH 0%
& 10% BY MASS OF SF. 7.6
38. STRENGTH & DURABILITY
IMPORTANCE OF CURING
CURING: IS A PROCESS OF PREVENTING LOSS OF MOISTURE FROM
CONCRETE, WHILE MAINTAINING SATISFACTORY TEMPERATURE REGIME
EARLY & LONG TERM CURING IS BENEFICIAL FOR DEVELOPMENT OF
CONCRETE PROPERTIES
MOISTURE LOSS PREVENTION IMPORTANT WHEN w/c RATIO IS LOW,
WHEN CEMENT HAS A HIGH RATE OF STRENGTH DEVELOPMENT & WHEN
CONCRETE CONTAINS MINERAL ADMIXTURES
ADEQUATE & CONTINUOUS SUPPLY OF WATER IS NECESSARY FOR
LONG-TERM STRENGTH DEVELOPMENT & IMPROVED DURABILITY
PERFORMANCE OF CONCRETE WITH MINERAL ADMIXTURES
40. STRENGTH & DURABILITY
ROLE OF MINERAL ADMIXTURE
REDUCE CONCRETE DETERIORATION BY: (A) CARBONATION, (B) ASR, (C)
CORROSION OF REINFORCEMENT, (D) SULFATE ACTION, (E) DECALCIFICATION OR
LEACHING & (F) FROST ACTION
WHEN MINERAL ADMIXTURE IS USED:
(A) FIXES ALKALI: ABOUT 95% ALKALIS FIXED THROUGH ADSORPTION OR SOLID
SOLUTION
(B) SECONDARY C-S-H: FORMED BY SECONDARY HYDRATION, FILLS UP PORES
IN HARDENED CEMENT PASTE, MAKING PORE STRUCTURE FINER & DENSER
(C) REDUCES C3A: PREVENTS SULFATE ATTACK
(D) CH REDUCTION: LEADS TO REDUCTION IN CaSO4 GENERATION & HELPS
MITIGATE SULFATE ATTACK
(E) PERMEABILITY REDUCTION THRU PACKING EFFECT OF UNREACTED
PARTICLES
(F) CHLORIDE BINDING: SOME MINERAL ADMIXTURES HAVE GREATER CHLORIDE-
BINDING CAPACITY IN COMPARISON TO PC
41. STRENGTH & DURABILITY
CARBONATION
CARBONATION: PRECIPITATION OF CALCITE (CaCO3) & OTHER
CO2-BASED SOLID COMPUNDS, THROUGH REACTION OF
PENETRATING ATMOSPHERIC CO2 WITH Ca IONS IN PORE
SOLUTION
pH DROP: DROP OF pH OF PORE SOLUTION OF CONCRETE
FROM 12.5–13.5 TO ABOUT 8.3, SO THAT PASSIVE IRON OXIDE
LAYER THAT USUALLY COVERS & PROTECTS REINFORCING STEEL
AGAINST CORROSION, BECOMES UNSTABLE
C-S-H LOSS: WITH CONSTANT CO2 DIFFUSION, CH GETS
FURTHER DEPLETED & CALCIUM FROM C-S-H ALSO REACTS,
LEADING TO LOSS OF STRENGTH, VOLUMETRIC DECREASE
(SHRINKAGE) & CRACKING & INCREASE IN CONCRETE POROSITY
43. STRENGTH & DURABILITY
CARBONATION
INCREASES WITH CO2 CONCENTRATION IN SURROUNDINGS
NORMAL ATMOSPHERIC CONDITIONS & RH OF 50%–80%
OPTIMUM
JAN BIJEN et.al.: LARGE SCALE STUDY ON DURABILITY OF
STRUCTURES BUILT ALONG DUTCH COAST, WITH BFS CONCRETE (.)
STRUCTURES INCLUDED SLUICES, PIERS & QUAYS, RANGING IN
AGE FROM 3 TO 63 YRS (.) IN 48 OUT OF 51 STRUCTURES,
CARBONATION DEPTH WAS < 5 mm
EARLY & LONGER CURING GIVES BETTER CARBONATION
RESISTANCE, ESPECIALLY IN CONCRETE WITH MINERAL
ADMIXTURES
44. STRENGTH & DURABILITY
ALKALI-AGGREGATE REACTIONS
(AAR)
AAR: WHEN AGGREGATES CONTAINING CERTAIN DOLOMITIC (Ca +
Mg) OR SILICEOUS MINERALS REACT WITH SOLUBLE ALKALIES IN
CONCRETE
SOMETIMES RESULT IN DETRIMENTAL EXPANSION, CRACKING &
PREMATURE LOSS OF SERVICEABILITY OF CONCRETE
STRUCTURES AFFECTED
ALL KINDS OF CONCRETE STRUCTURES MAY BE AFFECTED (.)
STRUCTURES IN DIRECT CONTACT WITH WATER, SUCH AS DAMS &
BRIDGES, ARE PARTICULARLY SUSCEPTIBLE TO AAR
TWO TYPES OF AAR: (A) ALKALI–CARBONATE REACTION (ACR) &
(B) ALKALI–SILICA REACTION (ASR)
45. STRENGTH & DURABILITY
ALKALI-AGGREGATE REACTIONS
(ACR & ASR)
ALKALI-CARBONATE REACTION (ACR)
PROCESS OF DEGRADATION OF CONCRETE CONTAINING
DOLOMITIC (DOLOMITE: CaCO3.MgCO3 ) AGGREGATE
SEPARATION OF CALCIUM & MAGNESIUM COMPOUNDS TAKES
PLACE
ALKALI-SILICA REACTION (ASR)
INCREASED REACTIVITY OR INSTABILITY OF AMORPHOUS,
SILICA FOUND IN AGGREGATE ROCKS
ASR MAY BE OBSERVED AFTER 5–25 YEARS OF CONSTRUCTION &
MAY AFFECT ANY CONCRETE STRUCTURE
47. STRENGTH & DURABILITY
ALKALI-AGGREGATE REACTIONS
INITIATION & PROPAGATION: THREE NECESSARY CONDITION: (A)
CRITICAL QUANTITY OF REACTIVE AGGREGATE, (B) SUFFICIENT ALKALI IN
CONCRETE & (C) SUFFICIENT MOISTURE
ALKALI CONTENT IN CEMENT EXPRESSED AS “SODIUM OXIDE
EQUIVALENT”
(MASS PERCENT) Na2Oeq = Na2O + 0.658 K2O
HARMLESS ALKALI CONTENT: < 0.6% Na2Oeq IN CEMENT OR < 1.8 Kg/m3
IN CONCRETE
ASTM C1260, ACCELERATED MORTAR BAR TEST (AMBT), IS MOST WIDELY
USED TEST METHOD
MINERAL ADMIXTURES REPLACING CEMENT, SUCH AS BFS, PFA &
NATURAL POZZOLANS, MITIGATE OR ELIMINATE AAR IN CONCRETE
HIGHER REPLACEMENTS GOOD: SIGNIFICANT REDUCTION IN AAR
EXPANSION ACHIEVED FOR PFA (>25%) OR BFS (>40%) OR COMBINATION OF
BOTH
49. STRENGTH & DURABILITY
CORROSION
CHLORIDE ATTACK & CORROSION OF REINFORCEMENT
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 VOLUME OF
ORIGINAL STEEL CONSUMED
EXPANSIVE CORROSION PRODUCTS CREATE TENSILE STRESS IN
CONCRETE SURROUNDING CORRODING STEEL REBAR, LEADING
TO CRACKING & SPALLING OF CONCRETE COVER
50. STRENGTH & DURABILITY
CORROSION
AASHTO T259: 90-DAY SALT-PONDING TEST TO EVALUATE CHLORIDE
DIFFUSION COEFFICIENT, REQUIRES LONG-TERM PONDING (IN YEARS) TO
OBTAIN RELIABLE ESTIMATES OF CHLORIDE DIFFUSION COEFFICIENT
RAPID CHLORIDE PERMEABILITY TEST (RCPT), ASTM C1202: DEVELOPED
TO NON-DESTRUCTIVELY OBTAIN INDICATION ON CHLORIDE PERMEABILITY
OF CONCRETE, IN A SHORT TIME PERIOD
RCPT CORRELATES CONCRETE RESISTIVITY WITH PERMEABILITY
MINERAL ADMIXTURES IMPART ENHANCED RESISTANCE TO DIFFUSION
OF CHLORIDE IONS & OTHER DETERIORATING AGENTS, ON ACCOUNT OF
REFINEMENT OF PORE STRUCTURE
CORROSION INITIATION DELAYED & PROPAGATION EXTENDED
AASHTO: American Association of State Highway and Transport Officials
52. STRENGTH & DURABILITY
CORROSION
FLY ASH CONCRETE IS USED UNDER SEVERE EXPOSURE CONDITION SUCH AS
IN DECKS & PIERS OF SUNSHINE SKYWAY BRIDGE, TAMPA BAY, FLORIDA
53. STRENGTH & DURABILITY
CORROSION
HUNGRY HORSE DAM, ON MONTANA’S FLATHEAD RIVER (.) ONE
OF THE LARGEST CONCRETE-ARCH DAMS IN USA,
COMPLETED IN 1953, WAS BUILT WITH 120,000 T OF FLY ASH
54. STRENGTH & DURABILITY
EXTERNAL SULFATE ATTACK
HIGH C3S & C3A CONTENT IN PC REDUCES RESISTANCE TO
SULFATE ATTACK
PARTIAL REPLACEMENT OF PC WITH MINERAL ADMIXTURES
REDUCES C3S & C3A IN BLEND
Na2SO4: CONCRETE WITH MINERAL ADMIXTURES SHOWS
LOWER EXPANSION
MgSO4: CONCRETE WITH MINERAL ADMIXTURES SHOWS HIGHER
STRENGTH REDUCTION, IN COMPARISON TO THAT WITH PC
NEGATIVE EFFECT OF MINERAL ADMIXTURES, DURING MgSO4
ATTACK OFTEN OFFSET BY REDUCED PERMEABILITY &
DENSIFICATION CAUSED BY THEIR USE
APPLICATION OF PROTECTIVE COATING LIKE EPOXY
RECOMMENDED ON CONCRETE SURFACE EXPOSED TO MgSO4
ENVIRONMENT
7.29
55. STRENGTH & DURABILITY
EXTERNAL SULFATE ATTACK
Al2O3 (ALUMINA) CONTENT OF BFS IS SAID TO LOWER ITS
SULFATE RESISTANCE (.) HOWEVER THERE IS NO DIRECT
RELATIONSHIP, AS A PART OF Al2O3 IS TAKEN UP IN C-S-H
STRUCTURE, WHERE IT IS LESS PRONE TO SULFATE ATTACK
BLENDED CEMENT WITH > 60% BFS, SHOWS MODERATE
TO GOOD SULFATE RESISTANCE, IRRESPECTIVE OF Al2O3
CONTENT OF SLAG
WITH REGARD TO PFA, REPLACEMENT LEVEL OF 25%–30%
OF CEMENT INCREASES SULFATE RESISTANCE OF
CONCRETE
56. STRENGTH & DURABILITY
FREEZE-THAW ACTION
DETERIORATION OF CRITICALLY SATURATED CONCRETE DUE TO FREEZING OF
WATER
TYPICAL SIGNS OF FREEZE–THAW DETERIORATION: SPALLING & SCALING, LARGE
CHUNKS OF CONCRETE (cm SIZE) BREAKING OFF, EXPOSED AGGREGATE & SURFACE
PARALLEL CRACKING
AIR VOIDS WITHIN CONCRETE PROVIDE GOOD FROST RESISTANCE
PORE SYSTEM IN SOME AGGREGATES SHOW SUSCEPTIBILITY TO DAMAGE FROM
FREEZE–THAW (.) HENCE EFFORTS ARE ALSO FOCUSED ON IDENTIFYING DAMAGE-
RESISTANT AGGREGATES
CONCRETE WITH HIGH WATER CONTENT & HIGH W/C RATIO IS LESS FROST
RESISTANT THAN CONCRETE WITH LOWER WATER CONTENT
FREEZE–THAW RESISTANCE OF CONCRETE CONTAINING 30%–50% PFA REPLACING
CEMENT, SHOWED EXCELLENT RESULTS
D-CRACKING: CRACKING OF CONCRETE, MOSTLY IN PAVEMENTS, CAUSED BY
FREEZE–THAW DETERIORATION OF COARSE AGGREGATE WITHIN CONCRETE
TO PREVENT D-CRACKING: SELECT DURABLE MATERIALS
58. DISCUSSION
DISCUSSION MAY CONTINUE ON THE FOLLOWING
WHATSAPP GROUP:
MODERN CONCRETE
SEND: YOUR NAME, DESIGNATION, COMPANY
TO Dr J D BAPAT MOBILE: 9422517402
60. DISCUSSION
DISCUSSION MAY CONTINUE ON THE FOLLOWING
WHATSAPP GROUP:
MODERN CONCRETE
SEND: YOUR NAME, DESIGNATION, COMPANY
TO Dr J D BAPAT MOBILE: 9422517402