maturity for opening pcc pavements: iowa...
TRANSCRIPT
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Maturity for Opening PCC Pavements: Iowa Experience
John Smythe, Construction Engineer
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Introduction
Maturity ConceptOpening SpecificationProceduresChallengesConclusions
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When Is It Okay to Drive On?What strength is needed?How do we measure?
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Beams/Cylinders
Specimen – not actual structureDifferent curing than pavement
Direct measurement of pavement concreteActual temperature in pavement
vs. Maturity
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Maturity Concept
Non-destructive testMeasures strength of in-place concreteEarly age testNot a 28-day strength test
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Maturity ConceptTime Temperature Factor: TTF
Relationship between thermal history and strength of a concrete
ASTM C 1074Nurse•Saul Equation
M (°C•hrs) =Σ[(T – T0)Δt] where T0 = (-10 °C)
Time × Temperature = Maturity (TTF)
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Time for Opening Standard Class C Concrete
5
7
500
500
>9
<9
Min. Time (Days)
Min. Flexural Strength,
(psi MOR-CPL)
PavementThickness
(in.)
Both strength and time conditions must be met.
At contractor’s option, maturity method to determine time for opening based on strength requirement only.
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Typical Opening Times Utilizing Maturity
Summer (>80 °F) 24-48 hoursFall/Spring (>55 °F) 36-72 hoursLate Fall (<50 °F) 48-144 hours
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Temperature Effect on Opening Time
40
50
60
70
80
90
100
5/1/01
5/8/01
5/22/0
15/2
9/01
6/4/01
6/12/0
16/1
9/01
6/25/0
16/2
7/01
7/10/0
17/1
6/01
7/23/0
1
8/1/01
8/6/01
8/14/0
1
Date
Tem
pera
ture
(deg
F)
30
35
40
45
50
55
60
65
70
75
Tim
e to
Ope
n (h
ours
)
HighLowHours
NHSX-218-2(57--3H-44
3 days
2 days
Seasonal Changes
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Advantages - ContractorUse as haul roadExpedite sub-drain & shoulderingAccelerate staged construction Reduced construction time & Costs
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Advantages – Public
Provide local access early
HomeownersBusinesses
Reduced Construction Time & Costs
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Maturity Procedure
Contractor develops strength-maturity curve for mix used
Determine required opening TTFContractor takes pavement temperature readings and calculates TTF
Submit data to EngineerEngineer responsible for opening section
Contractor performs monthly curve validation
Agency monitors testing at all steps
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Step 1- Develop Strength-Maturity Curve
Cast 12 beams
Thermocouple both ends of one beam
Test 3 beams at 4 different ages
Develop Strength vs. Maturity curve
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Equipment for Opening TTF
Beam MoldsMaturity MeterThermocouple WireTesting MachineComputer
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Maturity Meters
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MATURITY - STRENGTH DEVELOPMENTCOUNTY: PolkCURVE #: 1 MONITOR: INSPECTOR: PROJ. #: Im -35-5(109) REP/CONTRACTOR: C edar Valley DATE: 06/21/98
BEAM # LOAD AT TABLE BREAK W IDTH DEPTH FLEXURAL FLEXURAL AGE AT TTF TTF AVERAGE BEAMBREAK VALUE LOCATION COEFFICIENT STRENGTH BREAK CH 1 CH 2 TTF TEMP
(lbs) (lbs) (in) (in) (in) (psi) (days) (AVG)Enter Enter Enter Enter Enter Enter Enter Enter Enter
1 3000 3100 0.5 5.96 6.02 0.125004 388 1 650 650 650 24
2 3100 3250 0.5 6.00 6.01 0.124584 405 1 650 650 650 24
3 3050 3150 0.5 6.00 6.02 0.124171 391 1 650 650 650 24
4 3450 3400 0.5 5.98 6.00 0.125418 426 2 800 800 800 22
5 3550 3450 0.5 6.00 6.00 0.125000 431 2 800 800 800 22
6 3500 3425 0.5 6.00 6.00 0.125000 428 2 800 800 800 22
7 4000 4100 0.5 5.98 6.00 0.125418 514 3 1100 1100 1100 21
8 3990 4000 0.5 5.98 6.00 0.125418 502 3 1100 1100 1100 21
9 4000 4100 0.5 6.00 6.00 0.125000 513 3 1100 1100 1100 21
10 4600 4650 0.5 6.00 6.00 0.125000 581 4 1500 1500 1500 21
11 4700 4580 0.5 6.00 6.00 0.125000 573 4 1500 1500 1500 21
12 4750 4700 0.5 5.98 6.00 0.125418 589 4 1500 1500 1500 21
MIX INFORMATION EnterAIR: 7.8
SLUM P: 2 w /c: 0.42
M IX: C3W RC20FLY ASH SOURCE: Port Neal #4CEM ENT SOURCE: Ash G rov e
CO ARSE AGG REG ATE SOURCE: Duraham M ineFINE AGG REG ATE SOURCE: Vandalia
W ATER REDUCER BRAND: Daratard 17Add. Rate: 2 oz.
AIR ADM IXT URE BRAND: Darav air 1400Add. Rate: 6 oz.
M ETHOD O F DEVELO PM ENT: M aturity M eterDesired Flexural Strength (M O R): 500 psi
REQUIRED TTF: 1058
Certified M aturity Contractor Representative - Com ments:Signature
M aturity Curve Reviewed - Testing Engineer
M aturity Curveof A ll F lexural S trengths
300
400
500
600
700
2.000 3.000 4.000Log of TTF (C-hours)
Flex
ural
Stre
ngth
(psi
)
RegressionStrengths
Iowa DOT Spreadsheet
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Step 2- Pavement Temperature Measurement
Insert thermocouple in pavement
18” from edgeMid depth
Minimum of 2 locations per day’s paving
Read morning and evening minimumCalculate pavement TTFWhen pavement TTF > required opening TTF OK to open
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Equipment for Measuring Pavement TTF
Thermal Meter or dataloggerThermocouple wire
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Maturity - Field Data
Project : Maturity Curve #: 1 Probe # : 1
County : Date Placed: 9/11/99
Contractor: Mix: C3W RC20
TTF Required to Open : 1058
Section of Pavement for Opening by MaturityFrom Location: 104+00 To Probe Location: 121+50
Age Temp TTF Sum Air TempDate Time (hours) (deg C) at age TTF (deg C)
(deg C-hr) (deg C-hr)
09/11/99 10:00 AM 0.00 28 003:00 PM 5.00 30 195 19507:00 PM 9.00 29 158 353
09/12/99 07:00 AM 21.00 21 420 77306:00 PM 32.00 20 335.5 1108.5
0 00 00 00 0
TTF: 1108.5Value in box should be equal to or greater thanrequired TTF.
Contractor Representativecc: RCE, Central Materials, Contractor
Field Data
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Step 3- Monthly Curve Validation
Cast & Cure 3 BeamsMonitor Maturity until approximate required opening TTF is reachedTest all 3 beams and averageAverage Strength should be within ±50 psi of opening strength at TTF
>50 psi okay, more conservative<50 psi must develop new curve
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Monthly Curve ValidationAssured same basic mix being placed
Weather conditions did not affect TTF, only time of opening
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Factors Affecting TTFCementFly AshAdmixturesw/c ratioMix TypeAggregates
A curve validation can be used to allow some changes without establishing a new curve
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Challenges to ImplementationContractor casting test specimens for acceptance based on strengthRequire new curve for minor mix changesRequire more expensive field maturity devices
Some cost $10 – 25 each
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Keys to Implementation
Contractor flexibilityAllow minor mix changes – fly ash, etc.Allow curve validation instead of requiring new curve to be developed
Utilize thermocouple wire and thermometer or datalogger
Minor cost for few inches of thermocouple wireBuild in Factors of Safety
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Factors of Safety
Iowa uses 500 psi opening Only 300 psi needed (Table previous slide)
Curve established on concrete with higher air content Require curve development at highest w/c ratio expected
Iowa allows w/c to change 0.02 higher Field maturity tested near edge
Temperature lower than at mid slab
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ConclusionsReliable method of opening PCC pavementsMany factors affect strength maturity relationshipMay use validations to allow mix changes Monthly curve validations give a measure of reliabilityContractor’s option since 1997 – zero instances of cracking from opening early
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Any Questions
About Maturity ?