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Thermal Monitoring of ConcreteThermal Monitoring of ConcreteThermal Monitoring of ConcreteThermal Monitoring of ConcreteTechnology Overview and ApplicationsTechnology Overview and ApplicationsTechnology Overview and ApplicationsTechnology Overview and Applications
Presented by: Jason Sander, PE
Matthew Lehmenkuler, EI
Terracon Consultants, Inc.
Wednesday, October 11, 2017
Technological Advances in Concrete Over Technological Advances in Concrete Over Technological Advances in Concrete Over Technological Advances in Concrete Over TimeTimeTimeTime
1824 – Portland Cement Invented
1836 – 1st compressive strength test of concrete
1889 – 1st concrete bridge was constructed (San Francisco, CA)
1891 – 1st concrete pavements constructed (Bellafontaine, OH)
1903 – 1st concrete high rise was constructed (Cincinnati, OH)
1913 – 1st load of ready mix concrete was delivered
1930 – Air entrainment was first used for F/T protection
1938 – 1st concrete overlay
1970’s – Fiber reinforcement for concrete was developed
Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete TestingTestingTestingTesting
ASTM C143
adopted in 1939
Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete TestingTestingTestingTesting
ASTM C231
tentative
standard in 1949
Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete TestingTestingTestingTesting
ASTM C1064
established in
1986
Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete TestingTestingTestingTesting
Mercury thermometer invented in Mercury thermometer invented in Mercury thermometer invented in Mercury thermometer invented in
1714 by:1714 by:1714 by:1714 by:
Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete Testing Testing Testing Testing
The ‘MODERN’ ERA of concrete
thermal measurement should
not limit us on progress.
Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete Technological Advances in Concrete TestingTestingTestingTesting
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– ApplicationsApplicationsApplicationsApplications
Maturity Testing
Concrete Curing
Weather Protection
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– ApplicationsApplicationsApplicationsApplications
• ASTM C 1074 – Standard Practice for Estimating Concrete
Strength by the Maturity Method
• ODOT Supplement 1098 – Procedure for Estimating Concrete
Strength by the Maturity Method
• Basically, any case where the in-place strength of the concrete and thermal curing history is to be known or monitored
• Applications include:
Maturity Testing Maturity Testing Maturity Testing Maturity Testing ----
Post tensioned concrete stressing
Maturity results from thermal monitoring can be used to determine appropriate time for tendon stressing.
Photo Credit:
https://www.youtube.com/watch?v=PDgfnGqPj1c
Early form/shoring removal
Maturity results from thermal monitoring can be used to determine the appropriate time to strip concrete forms.
Early loading
Maturity results from thermal monitoring to allow for early loading when strength results meet specification.
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Maturity Method Maturity Method Maturity Method Maturity Method
Application includes:
Benefit for both Engineer and Contractor
Saves construction schedule time
Saves construction dollars
• Maturity - principle that concrete strength is directly related to both age and its temperature history, as the cement hydrates and releases heat
• Measured maturity of in-place concrete is used to estimate its strength development based on a pre-determined ‘calibration’ of the time-temperature strength relationship developed in a laboratory
“Maturity-Strength Correlation Curve”
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Maturity Method Maturity Method Maturity Method Maturity Method
• Rate of strength gain at early ages is related to rate of cement hydration and heat generation (temperature rise in the concrete)
• Heat generation takes into account environmental factors influencing temperature and mass of concrete (dimensions of element)
• Maturity uses actual temperature profile of concrete in structure to estimate strength
• Traditional field cured cylinders do not replicate the same temperature profile of the concrete in-place, and thus may not truly reflect in-place strength
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Maturity Method Maturity Method Maturity Method Maturity Method
Cooler at
exterior/skin
Hotter in Core
Concrete typically heats to 110-180 deg. F internally after
placement, depending on curing and protection.
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Maturity Method Maturity Method Maturity Method Maturity Method
50
60
70
80
90
100
110
120
130
140
150
0 12 24 36 48 60 72 84 96
Te
mp
era
ture
(D
eg
. F
)
Time (Hours)
Concrete Temperature vs. Time
6” x 12” Cylinder
3’ x 3’ x 2’ Test Blocks
43º F
• Maturity, in addition with other non-destructive tests, is used to facilitate decision making for construction operations to proceed more quickly, safely, and economically
• Designed to account for environmental and design factors that will affect the in-place concrete strength compared to field cured cylinders, thus providing more accurate information about actual concrete strength
• Not intended to replace laboratory cured cylinders
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Maturity Method Maturity Method Maturity Method Maturity Method
Old Way vs. New WayOld Way vs. New WayOld Way vs. New WayOld Way vs. New Way
Heat GainHeat GainHeat GainHeat GainExample…Depending on the calibration, concrete cured at a
temperature of 50º F for 7 days may have the same
maturity, and thus strength, as the same mix cured at 80º F
for 3 days
• ‘Correlation Study’
• Cylinder fabrication and testing at specified ages
• Typically 12 hours, 24 hours, 36 hours, 3, 5, 7, 14 and 28 days
• Three cylinders tested at each age and strength is averaged (for 4” x 8”)
• Or Two 6” x 12”
• Thermocouples are embedded into two cylinders and activated
• Maturity index is read at each time cylinders are tested in laboratory
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Maturity Method Maturity Method Maturity Method Maturity Method
“Calibration Curve”
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Maturity Method Maturity Method Maturity Method Maturity Method
“Calibration Curve”
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Maturity Method Maturity Method Maturity Method Maturity Method
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
0 5,000 10,000 15,000 20,000 25,000
Maturity (ºC-Hours)
Com
pre
ssiv
e S
treng
th (
psi)
Day 1Average
Day 3Average
Day 5Average
Day 7Average
Day 14Average
Average
Maturity TestingMaturity TestingMaturity TestingMaturity Testing
Strength-Maturity Relationship
ASTM C1074
ODOT Supplement 1098
+10.0 %
-10.0 %
0
1000
2000
3000
4000
5000
6000
7000
8000
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000
Co
mp
ressiv
e (
psi)
Maturity (°C-Hrs.)
StrengthStrengthStrengthStrength----Maturity Correlation CurveMaturity Correlation CurveMaturity Correlation CurveMaturity Correlation Curve
Concrete Strength
is 5120 psi
Cold Weather Concrete Photo
Cold Weather Concerns
• Concrete work can be accomplished during even the coldest weather as long as the appropriate precautions are taken.
• The objectives are to prevent damage from early-age freezing (when the concrete is still saturated), to make sure the concrete develops the needed strength, and to limit rapid temperature changes or large temperature differentials that cause cracking.
• Concrete generates its own heat during hydration--over the first one to three days, and how long it lasts depends of the mass and level of protection.
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Cold Weather ConcreteCold Weather ConcreteCold Weather ConcreteCold Weather Concrete
“Cold weather exists when the air
temperature has fallen to, or is expected to
fall below 40° F during the protection
period. The protection period is defined as
the time required to prevent concrete from
being affected by exposure to cold
weather.”
ACI 306ACI 306ACI 306ACI 306----10101010
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Cold Weather ConcreteCold Weather ConcreteCold Weather ConcreteCold Weather Concrete
“If placing concrete when the atmospheric
temperature is 32° F or less, or if the
weather forecasts predicts these
temperatures during the curing period,
follow the procedures of this subsection.”
ODOT Item 511.12ODOT Item 511.12ODOT Item 511.12ODOT Item 511.12
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Cold Weather ConcreteCold Weather ConcreteCold Weather ConcreteCold Weather Concrete
ODOT Specification 511.12
• Maintain the concrete surface temperature between 50 ° F and 100° F for a period of not less than 5 days, except as modified in 511.12.C (Flooding with Water).
• After the minimum cure period of 5 days, reduce the concrete surface temperature at a rate not to exceed 20 ° F in 24 hours until the concrete surface temperature is within 20 ° F of atmospheric temperature.
• Install sufficient high-low thermometers to readily determine
the concrete surface temperature. For deck slabs, install high-low thermometers to measure deck bottom surface, deck fascia surfaces, and deck top surfaces.
• How often can high-low thermometers be checked? What happens if the tolerances are exceeded?
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Cold Weather ConcreteCold Weather ConcreteCold Weather ConcreteCold Weather Concrete
• The basic idea is to not shock the concrete—
concrete should feel warm and welcome when it
goes into place.
• Warm up formwork and any embeds, including
the reinforcement, and remove snow, ice, and
water from the forms.
• Make sure the ground isn’t frozen.
• This can be accomplished with enclosures,
heating blankets, or hydronic heaters.
• Surfaces should be no more than 15° F colder
than the concrete—but also no more than 10° F
hotter than the concrete.
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Cold Weather ConcreteCold Weather ConcreteCold Weather ConcreteCold Weather Concrete
• Concrete must be protected from freezing until it has reached a minimum strength of 500 pounds per square inch (psi), which typically happens within the first 24 hours.
• Early freezing can result in a reduction of up to 50 percent in the ultimate strength.
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Cold Weather ConcreteCold Weather ConcreteCold Weather ConcreteCold Weather Concrete
“Crows Feet”, or ice
crystal casts that occur
during freezing in
plastic state
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Cold Weather ConcreteCold Weather ConcreteCold Weather ConcreteCold Weather Concrete
• It is also important to prevent rapid cooling of the concrete upon termination of the heating period. Sudden cooling of the concrete surface while the interior is warm may cause thermal cracking.
• Loosen the forms while maintaining cover with plastic sheeting or insulation, gradual decrease in heating inside an enclosure
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– Cold Weather ConcreteCold Weather ConcreteCold Weather ConcreteCold Weather Concrete
How does technology help us?How does technology help us?How does technology help us?How does technology help us?
Analog and hand used devices have to be accessed and
visually read creating challenges.
Digital systems record an actual temperature and can
provide a detailed log over time. These systems are now
wireless and operate over the cloud, and thus able to
accessed anytime from anywhere.
Thermal Monitoring Thermal Monitoring Thermal Monitoring Thermal Monitoring –––– ExecutionExecutionExecutionExecution
Equipment Equipment Equipment Equipment –––– ConConConCon----Cure NEX Cure NEX Cure NEX Cure NEX
• NEX Wireless System
• Reusable system
• Nodes transmit thermal information wirelessly to cloud via 4GLTE cell network
• Cloud dashboard calculates strength
• Thermocouple data probes
• Record temperature and loads data to cloud every 10 minutes
• Internal back-up if cell network or cloud is not available
Field Installation & EvaluationField Installation & EvaluationField Installation & EvaluationField Installation & Evaluation
• Probes typically installed in critical areas of the structure being poured
• Able to place wires through holes or openings in the formwork
• Installed at same frequency in which test cylinders are to be fabricated
• Activate prior to being surrounded by concrete
Field Installation & EvaluationField Installation & EvaluationField Installation & EvaluationField Installation & Evaluation
Field Installation & EvaluationField Installation & EvaluationField Installation & EvaluationField Installation & Evaluation
• Wirelessly read thermocouple probes embedded in concrete
• View maturity index (M) directly from screen at any desired time
• Refer to Maturity-Strength Curve to estimate in-place compressive strength
Field Installation & EvaluationField Installation & EvaluationField Installation & EvaluationField Installation & Evaluation
ConConConCon----Cure NEX Cure NEX Cure NEX Cure NEX –––– “The Cloud”“The Cloud”“The Cloud”“The Cloud”
Node Connects to
4G Network
Data on the Cloud can be
accessed anywhere by a device
with access to Cloud.
(Internet Access)
4G Network Sends
Data to Cloud
Storage
1.
2. 3.
4.
Technological way of
viewing Temperature
and Maturity Results
Cloud Dashboard Cloud Dashboard Cloud Dashboard Cloud Dashboard
Example Example Example Example –––– Maturity Strength RelationshipMaturity Strength RelationshipMaturity Strength RelationshipMaturity Strength Relationship
0
1000
2000
3000
4000
5000
6000
7000
8000
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000
Co
mp
res
siv
e (
ps
i)
Maturity (°C-Hrs.)
M=1150 deg. C-hr.
Compressive Strength In-place = 3750 psi
What’s happening behind the scenes…
NEX Alerts NEX Alerts NEX Alerts NEX Alerts
Temperature High/Low Alerts
via SMS and/or Email
Current Maturity Strength Alerts
via SMS and/or Email
Questions?Questions?
Thank you for your time.
