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

Use of Concrete Maturity For Use of Concrete Maturity For Measuring In-Place Strength of Measuring In-Place Strength of Concrete 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 Need for Estimating In-Place Strength 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 In-Place Strength Evaluation for New Construction 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 Specimens (CIPPOC) (Cast-in-Place-Punch-Out-Cylinder) (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” Facts about “Field Cured Concrete” Test Samples 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 ….. that brings us to ….. Concrete Maturity Testing 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 of 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.

…..in other words …..in other words Maturity Index (M) Maturity Index (M) Temperature M t 1 Time

Maturity Concept Temperature Temperature M2 M1 t 1 t 2 Time Time If M1 = M2 = M = Maturity Index

Maturity Index – Strength Relation Maturity Index – Strength Relation Temperature Concrete Strength M1 Time t 1 Temperature M2 M1 = M2 = M (Maturity Index) t 2 Time

How do we calculate Maturity Index? How do we calculate Maturity Index? • Maturity Index: • Temperature-Time Factor (TTF) • Equivalent Age at a Specified Temp.

METHOD - I Temperature-Time Factor (TTF) Temperature-Time Factor (TTF) • TTF is calculated based on Nurse- Saul Function M( t ) = Σ (Ta – To) Δ t Where: M( t ) = Temperature-Time Factor at age t , degree-days, degree-hours Ta = Average concrete temp during time interval Δ t, ºC To = Datum temp, ºC Δ t, = Time interval, days or hours

Nurse-Saul Function Nurse-Saul Function (Temperature-Time Factor) (Temperature-Time Factor) M( t ) = Σ (T a – T o ) Δ t Temperature, ºC  t T T a To T o Datum Temp. Time, Hr.

Datum Temperature (T o ) Datum Temperature (T o ) • 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 (T o ) Datum Temperature (T o ) • 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 Strength-Maturity Relation (Temperature-Time Factor Method) (Temperature-Time Factor Method)

METHOD - II Equivalent Age Equivalent 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

Equivalent Age ( t e ) Equivalent Age ( t e ) Based on Arrhenius Equation for describing the Rate of chemical reactions and its dependence on temperature Material Properties (determined in lab)

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

Maturity Meters • 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 • Sensors • Permanent embedded • Size: 1.5” x 1” diameter • Data collectors • Hand-held • Wireless • Temperature/Maturity NOMADICS • Software • Nurse-Saul function ( Intellirock System)

Maturity Meters • Laptop or Pocket PC • User defined • Sensors Size: • ¼” x ¾” diameter • Data Storage: • 2048 Readings • Sensor Life: COMMAND Center • 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

Maturity Meters • PC Data Collector • Sensors: • Thermistor • Thermocouple • Meter Size: JAMES M-Meter • 2.5”x2.75”x0.5” • Weight: 6 oz. • Battery Life: 1 year • Arrhenius equation

Maturity Meters • 4 Thermocouples • Connected to PC • Memory: 10 months • Battery Life: 3 weeks • Meter Dimensions: • 8”x4.8”x3” • Meter Weight: • 8 lbs GILSON • 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- Step 1: Develop the Strength- Maturity Relationship 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- Step 1: Develop the Strength- Maturity Relationship Maturity Relationship

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

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

800 STRENGTH-MATURITY RELATIONSHIP 700 FLEXURAL STRENGTH (PSI) 600 500 400 y = 112.40Ln(x) - 407.42 R 2 = 0.96 300 If the design strength is 555 psi, 200 the required maturity, (TTF req ), that corresponds to that strength is 100 5,232ºC·Hr Mix 383, Class C 0 0 2000 4000 6000 8000 10000 12000 14000 16000 MATURITY INDEX, TTF (ºC·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