Use of Concrete Maturity For Use of Concrete Maturity For Measuring - - PowerPoint PPT Presentation

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 Engineering Clemson University

Overview Overview

• 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 Strength Need 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 Construction In-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 Resistance Penetration Resistance

Break-Off Test Break-Off Test

Field Cured Samples Field Cured Samples

The deck is hot The cylinders are not

Facts about “Field Cured Concrete” Test Samples Facts 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 Testing Concrete Maturity Testing

Concrete Maturity Testing Concrete 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 Maturity Concrete 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 Method Maturity Method

ASTM C 1074 3.1.6 Maturity Method – a technique for estimating concrete strength that is based on the assumption that samples

• f a given concrete mixture attain

equal strengths if they attain equal values of maturity index.

Maturity Index Maturity 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 Temperature M

t1

…..in other words Maturity Index (M) …..in other words Maturity Index (M)

Maturity Concept

If M1 = M2 = M = Maturity Index

Temperature Time M2

t2

Temperature Time M1

t1

Maturity Index – Strength Relation Maturity Index – Strength Relation

Concrete Strength (Maturity Index) M1 = M2 = M

Temperature Time M1 t1 Temperature 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-hours Ta = Average concrete temp during time interval Δt, ºC To = Datum temp, ºC Δt, = Time interval, days or hours

Nurse-Saul Function (Temperature-Time Factor) Nurse-Saul Function (Temperature-Time Factor)

To Datum Temp. t

Time, Hr. Temperature, 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

• f 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 Age Equivalent Age

ASTM C 1074 3.1.2 Equivalent Age – the number of days

• r 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

• n 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

• r 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 Meters Maturity 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 Testing Steps 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 Relationship Step 1: Develop the Strength- Maturity Relationship

• Prepare a minimum of 20 cylinders or beams

using 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 Relationship Step 1: Develop the Strength- Maturity Relationship

Step 1: Develop the Strength- Maturity Relationship Step 1: Develop the Strength- Maturity Relationship

• Perform compression or flexural tests at ages
• f 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 Relationship Step 1: Develop the Strength- Maturity Relationship

y = 112.40Ln(x) - 407.42 R2 = 0.96 100 200 300 400 500 600 700 800 2000 4000 6000 8000 10000 12000 14000 16000 MATURITY INDEX, TTF (ºC·HR) FLEXURAL STRENGTH (PSI) 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 Field Step 2: Embed Sensors in Field

Step 2: Embed Sensors in Field Step 2: Embed Sensors in Field

Step 2: Embed Sensors in Field Step 2: Embed Sensors in Field

Step 3: Read the Meters Step 3: Read the Meters

Step 4: Interpret the Data Step 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 Relationship Verification 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 Relationship Verification 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 Method Advantages 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 Method Advantages 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 Maturity Advantages 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 Maturity Limitations of Maturity

• Requires establishment of strength-maturity

relationship in the laboratory prior to any field measurements

Limitations of Maturity Limitations of Maturity

• The concrete mixture proportions and

materials being monitored must not deviate 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 Maturity Limitations 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 Maturity Limitations 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 Testing State-of-Practice in Maturity Testing

• Several states have now established

protocols for the method.

• Two state DOTs that have pioneered the use
• f maturity testing in highway construction

are:

• Iowa DOT (Materials I.M. 383)
• Texas DOT (Tex-426-A)

Guidelines for Thermocouple Use Guidelines for Thermocouple Use

State Item Quantity Frequency Texas 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

Acknowledgements Acknowledgements

• 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…..