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6/23/2021
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Introduction to Concrete Maturity and Temperature profiling.
TODAY’S AGENDA
• Maturity Testing: Why, What and
How.
• Q&A
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WHAT’S WRONG WITH TRADITIONAL TESTING
METHODS?
CURRENT METHODS ARE INACCURATE
• Geometric differences
• Cylinders have small volumes but large
surface areas, so they retain less heat.
• Environmental differences
• Temperature history for cylinders may differ
due to curing conditions causing a different
rate of strength gain.
• Handling differences
• Cylinders can be improperly prepared,
handled, and/or tested causing low breaks.
Cylinder strengths do not reflect early placement strengths
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WHY USE MATURITY?BECAUSE IT IS MORE REPRESENTATIVE
The ‘Dog Chasing Its Tail’
Contractor
Producer Testing Agency
The ‘Low Break’ Problem
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CONCRETE CURING CYCLE
Mass Traps Heat
Mass Traps Heat
Heat Cures Concrete
Heat Cures Concrete
Curing Creates
Heat
Curing Creates
Heat
WHY USE MATURITY?
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WHY USE MATURITY?
WHY USE MATURITY?
“Of all the test methods studied, the maturity method exhibited
the lowest variability and most consistent agreement with the
generally-accepted standards for concrete testing. Of all the test
methods evaluated, the maturity method was found to be the
only one that provided reliable data comparable in variability and
consistency to those obtained from standard quality control.”
Center for Transportation Research
University of Texas at Austin
Research Report 1198-1F
BECAUSE IT IS MORE ACCURATE
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WHY USE MATURITY?
On March 2, 1973, portions of a multi-story apartment building, under construction in Fairfax County, Va., suffered a progressive collapse. Fourteen workers were killed and 34 were injured in the accident. The National Bureau of Standards concluded that the most probable cause of the failure was premature removal of formwork. At the time of the failure, the concrete was only four days old. During that period, the average had averaged about 7 degrees Celsius. The NBS investigators determined
that traditional test methods did not provide a reliable estimate of the in-place
concrete strength at the time of the failure. This triggered an interest in the maturity method for estimating in-place strength development under variable temperature conditions.
WHY USE MATURITY?
• Concrete is a Major Cost
Multiple Millions of Dollars on Most Projects
• Concrete Strength is in the Critical Path
Important Operations Are Dependent Upon Concrete Strength
• Common Testing Methods Dated
Projects Rely on 100-Year-Old Methods
• Methods Are Flawed
Even When Performed Perfectly They Are Inaccurate
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WHAT IS MATURITY?
• Maturity is a proven, non-destructive, strength estimation
technique that uses time and temperature measurements to
determine the real-time strength gain of in-place concrete.
• Originally developed in the late 1940’s & early 50’s
• Accidents in the 1970’s led to further maturity research
• Interest increased in the 1980’s as companies looked for ways to
accelerate construction
• Widespread adoption in the U.S. over the last 25 years
WHAT IS MATURITY?
• ASTM C 1074 – Standard Practice for Estimating Concrete Strength by the
Maturity Method
• ASTM C 918 – Measuring Early Age Compressive Strength & Projecting
Later Age Strength
• ACI Committee 318, Par 6.2 – Building Code Requirements for Structural
Concrete
• ACI Committee 228, Par 2.7 – Nondestructive Committee
• ACI Committee 306, Par 6.4 – Cold Weather Committee
• OSHA Section 1926.752 & 1926.703
• FHWA SA-97-105
THE MATURITY METHOD IS AN INDUSTRY STANDARD
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HOW DOES MATURITY WORK?
• Concrete Mix + Temperature + Time -> Strength
• Concrete Mix = Constant
• Maturity = Time * Temperature
• Concrete Mix + Maturity -> Strength
HOW DOES MATURITY WORK?
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MATURITY TESTINGASTM C1074
CREATING A CALIBRATION CURVE
Cast 17 cylinders from the mix design that will be used in the field.
5 sets of 3 will be used for destructive testing.
Place InSite loggers in the remaining two at the geometric center of each sample.
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CREATING A CALIBRATION CURVE
Cure all cylinders in the same environment in accordance with an approved ACI method.
• Curing tank or moisture room
• Place one cylinder with an embedded sensor at the center and the other at the edge of the sample grouping.
CREATING A CALIBRATION CURVE
Conduct destructive tests and record the date and time of each test
• Break 3 samples at specified intervals
• ASTM C1074 recommends breaks at 1,3,7,14 and 28 days
• More than 17 samples can be created for more granularity
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CREATING A CALIBRATION CURVE
• Enter the compressive break data into InSite
• Either import or input the corresponding maturity data
• Repeat this process for each subsequent break point
Place sensors in critical locations.
Place Sensors in the field
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Use the established maturity curve.
4. Validate the curve.
• Early-age compressive strength tests of standard cured specimens of concrete as-delivered, subjected to accelerated curing, or field-molded cylinders instrumented with maturity sensors. (C918, C684, C31)
Measured strengths of cylinders are compared with maturity-estimated
strengths to validate the curve. If deviation of > 10% is consistently
exceeded, a new curve should be developed.
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MASS CONCRETE MONITORING
WHAT IS MASS CONCRETE?
“any volume of concrete in which a combination of dimensions of the
member being cast, the boundary conditions, the characteristics of
the concrete mixture, and the ambient conditions can lead to
undesirable thermal stresses, cracking, deleterious chemical
reactions, or reduction in the long-term strength as a result of
elevated concrete temperature due to heat from hydration” –
American Concrete Institute (ACI), 2010
ACCORDING TO THE AMERICAN CONCRETE INSTITUTE
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WHAT IS MASS CONCRETE?
CONTROLLING THE DIFFERENTIALTHE CORE TO SURFACE MUST NOT EXCEED SPECIFICATION
35°
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“any volume of concrete in which a combination of dimensions of the member being cast, the
boundary conditions, the characteristics of the concrete mixture, and the ambient conditions
can lead to undesirable thermal stresses, cracking, deleterious chemical reactions, or
reduction in the long-term strength as a result of elevated concrete temperature due to heat
from hydration” – American Concrete Institute (ACI), 2010
ACI Definition of Mass Concrete?
ACI 207 2r A Report on the Effects of Thermal and Volume Change on Mass Concrete Elements
WHAT IS MASS CONCRETE?THE MORE CEMENT BY VOLUME, THE MORE YOU SHOULD WORRY ABOUT THE EFFECTS OF CONCRETE TEMPERATURE
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Controlling Temperature Differential -
Core to Surface
Engineered Differential Temperature Limit
0
10
20
30
40
50
60
70
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0 1000 2000 3000 4000 5000 6000 7000In-Place Compressive Strength, psi
All
ow
ab
le T
em
p.
Dif
f.,
°F
Calculated (Example)
Specified 35°F
Advantages:
Reduce Monitoring Time
Element In Service Sooner
Utilize In-Place Strength
Disadvantage:
Requires Advance Planning
Up-Front Mix Testing
WHAT ARE THE OPTIONS?
THERMOCOUPLE BASED COMBINATION SYSTEMS COMPLETELY WIRELESS
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WHAT ARE THE OPTIONS?
• Thermocouples are inexpensive
• Thermocouples are less accurate
• No data if disconnected
• Susceptible to theft and damage
• Difficult to work with
THERMOCOUPLE BASED
WHAT ARE THE OPTIONS?
• You don’t have to deal with wires
• Very high logger cost
• Easily lost in concrete
• Short transmission distances
• Limited deep depth options
COMPLETELY WIRELESS
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WIRED & WIRELESS COMBINATIONS
WHAT ARE THE OPTIONS?
WIRED WIRELESS COMBO
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How do I pick?
Budget
FeaturesEnvironment
Conclusions• Maturity is a relationship between time and temperature and strength.
• Maturity bridges the gap between break tests and in-place concrete and
can reduce the number of break tests required in the field.
• Maturity implementation requires some up front testing and decision
making.
• Maturity is now an integral part of any mass concrete thermal control
plan.
• There are a number of options when it comes to maturity systems; do
some homework and be an informed consumer.
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Questions?
Thank you very much for your time!
Mark ChaseRPX Technologies, [email protected]
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