Maturity and Maturity Testing - PDF Free Download

Session Overview Why Should We Use the Maturity Method? Introduction to the Maturity Method Concept Equipment Options Developing Strength-Maturity Curve Estimate In-Place Strength Case Study Highlights Copyright Post-Tensioning Institute all rights reserved. Page 2 of 45

Commercial Construction in Frisco, TX Courtesy: Tim Kaiser, Southern Star Concrete Saved several days per pour Maturity implementation showed the necessary strength to stress post-tensioned cables in 33 hours, much earlier than lab cured cylinders Copyright Post-Tensioning Institute all rights reserved. Page 3 of 45

How do we measure strength today? Current concrete strength specs are based on practices in place since the 1940s. Acceptance of concrete strength is currently based on: Sampling concrete as delivered to the job site Casting and curing of standard specimens Testing the specimens in a laboratory facility Copyright Post-Tensioning Institute all rights reserved. Page 4 of 45

What s wrong with conventional testing? Casting, transporting, storing, and testing specimens is a large and expensive effort Operator variability can influence strength Different temperatures from in-situ and lab Differences in lab cure versus field cure Copyright Post-Tensioning Institute all rights reserved. Page 6 of 45

Skyline Plaza Apartments, Fairfax County, VA 1973 Removed forms at 4 days Average air temperature of 7 C (45 F) 14 fatalities and 34 injured No method to accurately estimate in-place strength Copyright Post-Tensioning Institute all rights reserved. Page 8 of 45

Willow Island Cooling Tower, West Virginia, 1978 Previous day s lift unable to support construction loads Collapsed scaffolding and gantry 51 fatalities Average air temperature less than 10 C (50 F) Again, no method to accurately estimate in-place strength Copyright Post-Tensioning Institute all rights reserved. Page 10 of 45

In conclusion: We Know: Lab-cured Specimens do not account for Temperatures of in-place Concrete We Need Something Better. We Want: Estimate the in-place Concrete Strength without relying totally on Lab Specimens. Research Tells Us: Concrete Strength is a function of Time and Temperature. Copyright Post-Tensioning Institute all rights reserved. Page 13 of 45

Session Overview Why Should we Use the Maturity Method? Introduction to the Maturity Method Concept Equipment Options Developing Strength-Maturity Curve Estimate In-Place Strength Case Study Highlights Copyright Post-Tensioning Institute all rights reserved. Page 14 of 45

The Maturity Method Concept: The rate of cement hydration, and therefore the rate of strength gain, changes predictively with temperature. The strength of a given concrete mixture, which has been properly placed, consolidated, and cured, is a function of its age and temperature history. Nicholas J. Carino, NIST, 1993 Copyright Post-Tensioning Institute all rights reserved. Page 15 of 45

The Maturity Method Saul s Maturity Rule Concrete of the same mix at the same maturity has approximately the same strength whatever combination of temperature and time go to make up that maturity. A. G. A. Saul, 1951 Copyright Post-Tensioning Institute all rights reserved. Page 16 of 45

Concrete Strength is based on Time and Temperature The concept of maturity is actually pretty simple. More heat = more strength. More time = more strength. The Maturity Method simply combines both time and temperature into an index value: Ex: a specimen held at 90 degrees for 2 days = 90x2 = 180 degree-days. Or: a specimen held at 60 degrees for 3 days = 60x3 = 180 degree-days. Copyright Post-Tensioning Institute all rights reserved. Page 17 of 45

Concrete Strength is based on Time and Temperature Temperature T o Cold M1 Temperature T o Hot M2 Concrete Strength M1 = M2 = M Time Time Maturity Copyright Post-Tensioning Institute all rights reserved. Page 18 of 45

Calculating Maturity Calculate the Maturity using either: Nurse-Saul function Maturity = Temperature-Time Factor (TTF) Simple math Good enough for most jobs we do Arrhenius equation Maturity = Equivalent Age (t e ) More complex math Reportedly more accurate Copyright Post-Tensioning Institute all rights reserved. Page 19 of 45

Advantages of Maturity Provides instant predictions of in-place strength Reduces Cost and Time Not operator dependent Not specimen dependent Accurate, efficient, and consistent Simple Test Method Portable Equipment Ensures that strength of concrete meets specifications Copyright Post-Tensioning Institute all rights reserved. Page 22 of 45

Limitations of Maturity Maturity measures only time and temperature, so other factors that could affect strength are not considered. The concrete mixture proportions and materials being monitored shall not deviate from the ones used to develop the strength-maturity relationship, such as: Brand of cement Source and type of fly ash Source of aggregates Water to cement ratio Copyright Post-Tensioning Institute all rights reserved. Page 23 of 45

Limitations of Maturity Cannot account for humidity conditions during curing, therefore it is necessary to ensure that the concrete has enough moisture for hydration to occur Maturity does not measure concrete strength, it estimates it do not eliminate your breaks, but reduce them Copyright Post-Tensioning Institute all rights reserved. Page 24 of 45

Typical Applications of Maturity Facilitates Quality Control / Quality Assurance Promotes fast-track applications Aids in cold-weather paving Tracks early-age strength gain of concrete Optimize Form Removal Optimize Prestressing / Post-tensioning Optimize Traffic Opening or Form Shoring Optimize Sawcut Timing Copyright Post-Tensioning Institute all rights reserved. Page 25 of 45

Maturity Specs and Guidelines ASTM C1074 Standard Practice for Estimating Concrete Strength by the Maturity Method ACPA IS257P Maturity Testing of Concrete Pavements: Applications and Benefits ACI 228.1 In-Place Methods to Estimate Concrete Strength Iowa DOT (I.M.383) Method of Testing the Strength of Portland Cement Concrete using the maturity Method Copyright Post-Tensioning Institute all rights reserved. Page 26 of 45

Conventional Maturity Meters Typical features: External Data Logger Embedded Thermocouple or Thermistor Must Be Connected to Function Check Batteries Prior to Use Vulnerable to Theft and Weather Copyright Post-Tensioning Institute all rights reserved. Page 28 of 45

State-of-the-Art Maturity Meters Typical features: Sensors and Loggers combined No External Box Needed to Function Direct Connect or Wireless Read by Laptop PC, Pocket PC, or Proprietary Readers Copyright Post-Tensioning Institute all rights reserved. Page 29 of 45

State-of-the-Art Maturity Meters Engius IntelliRock (reader and sensor) Con-Cure Maturity System COMMAND Center Software (reader and sensor) Copyright Post-Tensioning Institute all rights reserved. Page 30 of 45

How to Measure Maturity Two Step Process: 1. Develop Laboratory Maturity-Strength Curve 2. Measure Time & Temperature (Maturity) in the Field and Estimate Strength Copyright Post-Tensioning Institute all rights reserved. Page 32 of 45

Strength-Maturity Relationship Cast 15 (Minimum) cylinders In the Laboratory Minimum Batch of 3 m 3 (4 yd 3 ) Measure Slump and Air Content Embed Maturity Sensors in 2 or More Specimens Moist Cure Monitor Maturity (Temperature and Time) Copyright Post-Tensioning Institute all rights reserved. Page 33 of 45

Strength-Maturity Relationship Break Specimens at 1, 3, 7, 14, and 28 days Calculate Average from 2 or More Tests Calculate Maturity at Time of each Break In the Laboratory Plot Average Strength vs. Average Maturity Calculate a Best-Fit Logarithmic Curve Copyright Post-Tensioning Institute all rights reserved. Page 34 of 45

Strength-Maturity Relationship In the Laboratory COMPRESSIVE STRENGTH (PSI) 6000 5000 4000 3000 2000 1000 0 3day 1day 7day 14day 0 2000 4000 6000 8000 10000 12000 14000 16000 MATURITY INDEX, TTF ( C-HR) 28day y = 893 ln(x) - 3516 R 2 = 0.99 Copyright Post-Tensioning Institute all rights reserved. Page 35 of 45

Strength-Maturity Relationship In the Laboratory COMPRESSIVE STRENGTH (PSI) 6000 5000 4000 3000 2000 1000 0 3500 psi 2580 C-HR 0 2000 4000 6000 8000 10000 12000 14000 16000 MATURITY INDEX, TTF ( C-HR) Copyright Post-Tensioning Institute all rights reserved. Page 36 of 45

How to Use the Maturity Method Second, in the Field Embed temperature sensors into fresh concrete in field Connect sensors to logger or reader Read the maturity value as desired When we hit our target maturity, we have met our strength Copyright Post-Tensioning Institute all rights reserved. Page 38 of 45

Palisades West Office Park - Austin, TX Courtesy: Tobe Evans, Austin Commercial $68 Million 360k Sq. Ft. Two office buildings (7-story and a 5-story) Seven level parking garage Total cost of maturity equipment was < $9000 Saved 18-24 hours per pour, nearly 2 months total Copyright Post-Tensioning Institute all rights reserved. Page 41 of 45

Palisades West Office Park - Austin, TX Courtesy: Tobe Evans, Austin Commercial 37k CY of Concrete 64 pours, 3-4 sensors per pour Achieving design strength goal in 18 hours Sensors read 30 hours after placement to make sure design strength was reached for posttension stressing operations Early form stripping Eliminated some breaks Copyright Post-Tensioning Institute all rights reserved. Page 42 of 45

442k Sq. Ft. 21-story office tower with garage and condominiums Reduced structure duration by four months Reduced project budget by $3 million 2000 McKinney - Dallas, TX Courtesy: John Boehm, The Beck Group Copyright Post-Tensioning Institute all rights reserved. Page 43 of 45

2000 McKinney - Dallas, TX Courtesy: John Boehm, The Beck Group 43k CY of concrete Placed avg of 120 yards per work day 3-5 sensors per pour Saved two days per floor Stressing post-tension the day after placement, which allowed columns to be started and decks to be flown to the next level only 2 days after placement. Copyright Post-Tensioning Institute all rights reserved. Page 44 of 45