Thermal Monitoring of Concrete

Transcription

1 Thermal Monitoring of Concrete Technology Overview and Applications Presented by: Jason Sander, PE Matthew Lehmenkuler, EI Terracon Consultants, Inc. Wednesday, October 11, 2017

2 Technological Advances in Concrete Over Time 1824 Portland Cement Invented st compressive strength test of concrete st concrete bridge was constructed (San Francisco, CA) st concrete pavements constructed (Bellafontaine, OH) st concrete high rise was constructed (Cincinnati, OH) st load of ready mix concrete was delivered 1930 Air entrainment was first used for F/T protection st concrete overlay 1970 s Fiber reinforcement for concrete was developed

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5 Technological Advances in Concrete Testing ASTM C143 adopted in 1939

6 Technological Advances in Concrete Testing ASTM C231 tentative standard in 1949

7 Technological Advances in Concrete Testing ASTM C1064 established in 1986

8 Technological Advances in Concrete Mercury thermometer invented in Testing 1714 by:

9 Technological Advances in Concrete Testing The MODERN ERA of concrete thermal measurement should not limit us on progress.

10 Technological Advances in Concrete Testing

11 Thermal Monitoring Applications Maturity Testing Concrete Curing Weather Protection

12 Thermal Monitoring Applications Maturity Testing - 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:

13 Post tensioned concrete stressing Maturity results from thermal monitoring can be used to determine appropriate time for tendon stressing. Photo Credit:

14 Early form/shoring removal Maturity results from thermal monitoring can be used to determine the appropriate time to strip concrete forms.

15 Early loading Maturity results from thermal monitoring to allow for early loading when strength results meet specification.

16 Thermal Monitoring Maturity Method Application includes: Benefit for both Engineer and Contractor Saves construction schedule time Saves construction dollars

17 Thermal Monitoring Maturity Method 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

18 Thermal Monitoring 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

19 Thermal Monitoring Maturity Method Cooler at exterior/skin Hotter in Core Concrete typically heats to deg. F internally after placement, depending on curing and protection.

20 Concrete Temperature vs. Time x 3 x 2 Test Blocks Temperature (Deg. F) º F 6 x 12 Cylinder Time (Hours)

21 Thermal Monitoring Maturity Method 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

22 Old Way vs. New Way Heat Gain Example 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

23 Thermal Monitoring Maturity Method 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

24 Thermal Monitoring Maturity Method Calibration Curve

25 Thermal Monitoring Maturity Method Calibration Curve

26 Maturity Testing Strength-Maturity Relationship ASTM C1074 ODOT Supplement 1098 Compressive Strength (psi) 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1, Day 5 Average Day 1 Average Day 3 Average Day 7 Average 0 0 5,000 10,000 15,000 20,000 25,000 Maturity (ºC-Hours) Average Day 14 Average

27 Strength-Maturity Correlation Curve Concrete Strength is 5120 psi % % Compressive (psi) ,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 Maturity ( C-Hrs.)

28 Cold Weather Concrete Photo Cold Weather Concerns

29 Thermal Monitoring Cold Weather Concrete 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.

30 Thermal Monitoring Cold Weather Concrete ACI 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.

31 Thermal Monitoring Cold Weather Concrete ODOT Item 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.

32 Thermal Monitoring Cold Weather Concrete ODOT Specification Maintain the concrete surface temperature between 50 F and 100 F for a period of not less than 5 days, except as modified in 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 highlow 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?

33 Thermal Monitoring Cold 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.

34 Thermal Monitoring Cold 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.

35 Thermal Monitoring Cold Weather Concrete Crows Feet, or ice crystal casts that occur during freezing in plastic state

36 Thermal Monitoring Cold 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

37 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.

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42 Thermal Monitoring Execution

43 Equipment Con Con-Cure 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

44 Field 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

45 Field Installation & Evaluation

46 Field Installation & Evaluation

47 Field 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

48 Con-Cure Cure NEX The Cloud 2. 4G Network Sends 3. Data to Cloud Storage 1. Node Connects to 4G Network 4. Data on the Cloud can be accessed anywhere by a device with access to Cloud. (Internet Access)

49 Technological way of viewing Temperature and Maturity Results

50 Cloud Dashboard

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53 Example Maturity Strength Relationship What s happening behind the scenes Compressive (psi) Compressive Strength In-place = 3750 psi M=1150 deg. C-hr ,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 Maturity ( C-Hrs.)

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55 NEX Alerts Temperature High/Low Alerts via SMS and/or Current Maturity Strength Alerts via SMS and/or

56 Thank you for your time. Questions?