Use of Concrete Maturity For Measuring In-Place...

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)

Penetration ResistancePenetration Resistance

Break-Off TestBreak-Off Test

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

( NRMCA Circular 132, 1991)

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

Average Maturity

Average Strength

• 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 3: Read the MetersStep 3: Read the Meters

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

Go Tigers !!Go Tigers !!

If you don’t want to…..If you don’t want to…..