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Use of Concrete Maturity For Measuring In-Place Strength of
Concrete
Use of Concrete Maturity For Measuring In-Place Strength of
Concrete
Prasad Rangaraju, Ph.D., P.E.Assistant Professor
Department of Civil EngineeringClemson University
OverviewOverview
• Need for measuring in-place strength of concrete
• Existing techniques to measure strength
• Concrete Maturity
• What, How, Why and When
• Applications and Limitations
• State-of-Practice
Need for Estimating In-Place StrengthNeed for Estimating In-Place Strength
Pavements• QA/QC Operations• Saw cutting operations• Opening to traffic
Structural Applications• Form removal• Application of Post-tensioning• Shore removal• Rapid Scheduling and Safety
ESPECIALLY IN COLD WEATHER
In-Place Strength Evaluation for New ConstructionIn-Place Strength Evaluation for New Construction
• Field-Cured Specimens• Cast-In-Place Specimens• Cores• Ultrasonic Pulse Velocity• Penetration Resistance• Rebound Hammer• Break-Off• Pullout• MATURITY
Cast-In-Place Specimens (CIPPOC) (Cast-in-Place-Punch-Out-Cylinder)Cast-In-Place Specimens (CIPPOC) (Cast-in-Place-Punch-Out-Cylinder)
Field Cured SamplesField Cured Samples
The deck is hot
The cylinders are not
Facts about “Field Cured Concrete”Test SamplesFacts about “Field Cured Concrete”Test Samples
• Test samples do not reflect the influence of several factors on strength:
• Temperature fluctuations within mass of concrete• Weather conditions• Critical curing conditions • Other actual job site conditions
• Improper sample preparation and testing
• Limited information from selected locations
that brings us to …..Concrete Maturity Testing
that brings us to …..Concrete Maturity TestingConcrete Maturity Testing
Concrete Maturity TestingConcrete Maturity Testing
• WHAT is it? – Basics
• HOW does it work? – Theory
• WHY do we need it? – Benefits
• WHEN do we use it? – Applications &
– Limitations
Concrete MaturityConcrete Maturity
• ASTM C1074, “Standard Practice for Estimating Concrete Strength by the Maturity Method.”
• SHRP C 376 “Manual on Maturity and Pullout for Highway Structures”
Maturity MethodMaturity Method
ASTM C 1074
3.1.6 Maturity Method – a technique for estimating concrete strength that is
based on the assumption that samples of a given concrete mixture attain equal strengths if they attain equal
values of maturity index.
Maturity IndexMaturity Index
ASTM C 1074
3.1.5 Maturity Index – is an indicator of Maturity that is calculated from the
temperature history of the cementitious mixture by using a
maturity function.
Time
Tem
per
atu
re
M
t1
…..in other words Maturity Index (M)…..in other words
Maturity Index (M)
Maturity Concept
If M1 = M2 = M = Maturity Index
Tem
per
atu
reTime
M2
t2
Tem
per
atu
re
Time
M1
t1
Maturity Index – Strength RelationMaturity Index – Strength Relation
Co
ncre
te S
tren
gth
(Maturity Index)M1 = M2 = M
Tem
per
atu
re
Time
M1
t1
Tem
per
atu
re
Time
M2
t2
How do we calculate Maturity Index?How do we calculate Maturity Index?
• Maturity Index:
• Temperature-Time Factor (TTF)
• Equivalent Age at a Specified Temp.
Temperature-Time Factor (TTF)Temperature-Time Factor (TTF)
• TTF is calculated based on Nurse-Saul Function
METHOD - I
M(t) = Σ (Ta – To) Δt
Where:M(t) = Temperature-Time Factor at age t, degree-days,
degree-hoursTa = Average concrete temp during time interval Δt, ºCTo = Datum temp, ºCΔt, = Time interval, days or hours
Nurse-Saul Function(Temperature-Time Factor)
Nurse-Saul Function(Temperature-Time Factor)
To
Datum Temp.
t
Time, Hr.
Tem
per
atu
re,
ºC
T
Ta
To
M(t) = Σ (Ta – To) Δt
Datum Temperature (To)Datum Temperature (To)
• Datum Temperature represents a temperature below which no active hydration of cement is considered to take place that contributes towards the development of strength
• Datum temperature for a given concrete depends on:
• Type of Cement
• Type and Dosage of Admixtures
• Temperature of Concrete at the Time of Hardening
Datum Temperature (To)Datum Temperature (To)
• ASTM C 1074 recommends assuming datum temperature to be 0°C, if ASTM Type I cement is used without admixtures
• Expected curing temperature is within 0 °C and 40 °C.
• If more accurate datum temperatures are desired, it can be experimentally determined in lab using the same materials.
Strength-Maturity Relation(Temperature-Time Factor Method)
Strength-Maturity Relation(Temperature-Time Factor Method)
Equivalent AgeEquivalent Age
ASTM C 1074
3.1.2 Equivalent Age – the number of days or hours at a specified temperature
required to produce a maturity equal to the maturity achieved by a curing period at
temperatures different from the specified temperature
METHOD - II
Equivalent Age (te)Equivalent Age (te)
Material Properties (determined in lab)
Based on Arrhenius Equation for describing the Rate of chemical reactions and its dependence on temperature
Equivalent Age at a Specified Temp Equivalent Age at a Specified Temp
How do we monitor temperature?How do we monitor temperature?
• Temperature can be monitored using thermocouple or thermistor embedded in concrete, and the data can be logged using data acquisition systems.
OR
• Standalone maturity meters that record temperature and time using a thermocouple or a thermistor embedded in concrete
• Manual readings with thermocouple probe
• Chart recorder with thermocouple probe
• Conventional maturity meter system with thermocouple probe
• Conventional maturity meter system with thermistor probe
• Embedded microprocessor maturity system with thermistor
Maturity Meters
Maturity MetersMaturity Meters
NOMADICS
(Intellirock System)
• Sensors
• Permanent embedded
• Size: 1.5” x 1” diameter
• Data collectors
• Hand-held
• Wireless
• Temperature/Maturity
• Software
• Nurse-Saul function
Maturity Meters
COMMAND Center
• Laptop or Pocket PC
• User defined
• Sensors Size:
• ¼” x ¾” diameter
• Data Storage:
• 2048 Readings
• Sensor Life:
• Up to 10 years
• Nurse-Saul function
Maturity Meters
• Maturity Meter• Size: 2” x 4” x ½”• Weight: 2 oz.• Battery Life: 4 yrs.
• Thermistor Sensor• Pre-calibrated• Epoxy-Tipped• Reusable
• CMT Software• Nurse-Saul function
CON-CURE
• PC Data Collector
• Sensors:
• Thermistor
• Thermocouple
• Meter Size:
• 2.5”x2.75”x0.5”
• Weight: 6 oz.
• Battery Life: 1 year
• Arrhenius equation
JAMES M-Meter
Maturity Meters
Maturity Meters
GILSON
• 4 Thermocouples• Connected to PC• Memory: 10 months• Battery Life: 3 weeks• Meter Dimensions:
• 8”x4.8”x3”• Meter Weight:
• 8 lbs• Nurse-Saul function
Steps of Maturity TestingSteps of Maturity Testing
1. Establish Strength-Maturity Relationship (Lab)
2. Embed Maturity Sensors in Field Concrete (Field)
3. Read Maturity Values from Sensors (Field)
4. Interpret the Data
Step 1: Develop the Strength-Maturity RelationshipStep 1: Develop the Strength-Maturity Relationship
• Prepare a minimum of 20 cylinders or beamsusing the same size of specimen which will be used later in the project for verification
• The concrete mixture proportions and constituents shall be the same as those of the job concrete whose strength will be estimated using this practice
Step 1: Develop the Strength-Maturity RelationshipStep 1: Develop the Strength-Maturity Relationship
Step 1: Develop the Strength-Maturity RelationshipStep 1: Develop the Strength-Maturity Relationship
• Perform compression or flexural tests at ages of 1, 3, 5, 7, 14, and 28 days
• Test three specimens at each age and compute the average strength
• The Maturity Index from specimens with thermocouples should be recorded at each age
• Determine the best-fit curve through the data
• The resulting curve is the strength-maturity relationship to be used for estimating the in-place strength of the concrete
Step 1: Develop the Strength-Maturity RelationshipStep 1: Develop the Strength-Maturity Relationship
y = 112.40Ln(x) - 407.42
R2 = 0.96
0
100
200
300
400
500
600
700
800
0 2000 4000 6000 8000 10000 12000 14000 16000
MATURITY INDEX, TTF (ºC·HR)
FL
EX
UR
AL
ST
RE
NG
TH
(P
SI)
STRENGTH-MATURITY RELATIONSHIP
Mix 383, Class C
If the design strength is 555 psi, the required maturity, (TTFreq), that corresponds to that strength is
5,232ºC·Hr
Step 2: Embed Sensors in FieldStep 2: Embed Sensors in Field
Step 2: Embed Sensors in FieldStep 2: Embed Sensors in Field
Step 2: Embed Sensors in FieldStep 2: Embed Sensors in Field
Step 4: Interpret the DataStep 4: Interpret the Data
• When the maturity reaches a value that is equal to or greater than that required value:
• Record the maturity value,
• If required, verify the adequacy of any supplemental specimen strength data
• Cut the thermocouple wires at the concrete surface
Verification of Strength-Maturity RelationshipVerification of Strength-Maturity Relationship
• Cast verification test specimens from field concrete
• Instrument at least two of the specimens using two different maturity meters
• Cure verification specimens in the laboratory and test when these achieve a given maturity
Verification of Strength-Maturity RelationshipVerification of Strength-Maturity Relationship
• Calculate the predicted strength based on the Strength-Maturity relationship corresponding to the maturity at which the verification specimens were tested
• Compare measured vs. predicted strengths
Advantages of Maturity MethodAdvantages of Maturity Method
• Field implementation of the maturity concept and procedures is simple
• Insures that strength of concrete meets specifications, if the procedure is followed correctly
• Provides instant predictions of in-place strength
• Maturity probes are relatively cheap, which enables strength measurement more representatively
Advantages of Maturity MethodAdvantages of Maturity Method
• The probes can be placed at critical locations to precisely determine the strength at a given location
• Provides a continuous measure of strength gain
• Strength estimation not affected by external factors such as improper sample preparation, capping procedures, or loading rates on the sample, etc.
Advantages of MaturityAdvantages of Maturity
• Significant time and money savings can be achieved in construction through:
• Removal of shoring, formwork, etc at appropriate time based on maturity.
• Cold weather protection.
• Determination of proper time for loading, saw cutting, or opening for service.
• Acceptance of the concrete (QA/QC).
Limitations of MaturityLimitations of Maturity
• Requires establishment of strength-maturity relationship in the laboratory prior to any field measurements
Limitations of MaturityLimitations of Maturity
• The concrete mixture proportions and materials being monitored must notdeviate from the ones used to develop the strength-maturity relationship, i.e.:
• Brand of cement
• Source and Class of fly ash
• Source of aggregates
• Water to cement ratio
Limitations of MaturityLimitations of Maturity
• Cannot account for humidity conditions during curing (maturity method assumes adequate curing is provided)
• Cannot account for influence of early-age concrete temperature on long-term strength properties
• It is necessary to ensure that the concrete has enough moisture for hydration to occur
Limitations of MaturityLimitations of Maturity
• Cannot account for inadequate concreting practices in the field:
• Consolidation• Placement• Curing• Protection during early ages• Variations in W/C ratio• Fluctuations in air content
State-of-Practice in Maturity TestingState-of-Practice in Maturity Testing
• Several states have now established protocols for the method.
• Two state DOTs that have pioneered the use of maturity testing in highway construction are:
• Iowa DOT (Materials I.M. 383)• Texas DOT (Tex-426-A)
Guidelines for Thermocouple UseGuidelines for Thermocouple Use
State Item Quantity FrequencyTexas Pavements 2 2510 m2 (3,000 yd2) or fraction (Pavement) Texas Structures 46 m3 (60 yd3) or fraction (Structural Concrete)
386 m3 (50 yd3) cumulative basis (Misc. Concrete) Iowa Pavements 2 Per Day of Paving
2
AcknowledgementsAcknowledgements
• SCDOT
• FHWA
• Gerald D. Lankes, P.E., Construction Division, TxDOT
• John Gnaedinger, Con-Cure Corporation
