Rate of Hydration is Exponentially Sensitive to Temperature. NPCA Precast Show Focus on Concrete Temperature. March 2, 2019

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1 FOCUSING ON CONCRETE TEMPERATURE: WHY HIGH EARLY TEMPERATURE HELPS AND HURTS Ken Hover, Ph.D., P.E., Professor of Civil & Environmental Engineering, Cornell University FOCUSING ON CONCRETE TEMPERATURE General Effects of Temperature Hydration Heat of hydration Top Temp Limit: Sulfate Reactions (D.E.F.) Maturity precast.org/education precast.org/education Growth Rate Hydration Conc. Temperature - Rate of Hydration is Exponentially Sensitive to Temperature Cornell University, Ithaca, New York

2 - - Field development slower than lab cure Field development faster than lab cure % % 5 % C C 6C 5 F 7 F 96 F Risk of Freezing Cornell University, Ithaca, New York

3 Temperature and Compressive Strength: A bit more complicated! Concrete Temperature: Sub-Microscopic Perspective Rate of Hydration Rate of Heat- Release Concrete Temperature Hydration Concrete Temperature: Sub-Microscopic Perspective 6 Curing Temperature ( C) 9 Rate of Hydration Quality of Hydration Compressive Strength (psi) 5 8 day strength day strength Compressive Strength (MPa) Concrete Temperature Hydration Curing Temperature ( F) Cornell University, Ithaca, New York

4 Effect of Concrete Temperature on Strength Effect of Low Temperature on Strength Kosmatka: Design & Control Kosmatka: Design & Control Basis for C Spec. Requirements Constructability Problems! Cylinder Testing 7C 95-% RH Not Optimum Not Field Simulation Just standard Cornell University, Ithaca, New York

5 6-8F 68-78F for f c 6 psi ASTM C Making Cylinders.. Initial Curing Immediately after molding and finishing, the specimens shall be stored for a period up to 8 h in a temperature range from 6 and 8 F [6 and 7 C] and in an environment preventing moisture loss from the specimens. For concrete mixtures with a specified strength of 6 psi [ MPa] or greater, the initial curing temperature shall be between 68 and 78 F [ and 6 C]. Cornell University, Ithaca, New York 5

6 6F (6C) < T cylinder < 8F (7C) Peak Cylinder Temp F (5C) Avg. Cylinder Temp 7F (C) Strength-Loss at 8 days (5- psi).5-7 MPa ASTM C Making Cylinders Shield all specimens from the direct sunlight and, if used, radiant heating devices. The storage temperature shall be controlled by use of heating and cooling devices, as necessary. Record the temperature using a maximumminimum thermometer. FOCUSING ON CONCRETE TEMPERATURE General Effects of Temperature Hydration Heat of hydration Top Temp Limit: Sulfate Reactions (D.E.F.) Maturity precast.org/education Cornell University, Ithaca, New York 6

7 Transitions in Concrete Behavior Heat Released Concrete is Warm-blooded! Heat of Hydration Time (hours to days) Cement Manufacture Energy In Energy Out Energy Consumption in the Manufacture.6 million BTU/ Ton Cement.9 million BTU/ Ton Steam.8 million kj/ Tonne Cement. million kj/ Tonne Steam of Cement to % Thermal Efficiency to % Thermal Efficiency.5 million BTU/ Ton Cement 5. million BTU/ Ton Steam 5. million kj/ Tonne Cement 6.5 million kj/ Tonne Steam Heat of Hydration Heat of Hydration About 9, BTU per Ton Cement Slightly Less than % of Heat Energy input at Cement Plant returned to Precaster (at no extra charge) About 9 BTU per lb Cement Slightly Less than % of Heat Energy input at Cement Plant returned to Precaster (at no extra charge) Cornell University, Ithaca, New York 7

8 Heat of Hydration 6 Sack Mix = 56 lb x 9 BTU = 7, BTU / CY 5 W lamps 85F / 9C 56 lb Cement / CY 6 Watts / CY F / 8C, BTU / HR,5 BTU / HR Isothermal Calorimetry 56 lb Cement / CY BTU per hour / CY Cornell University, Ithaca, New York 8

9 Field Calorimeter FOCUSING ON CONCRETE TEMPERATURE General Effects of Temperature Hydration Heat of hydration Top Temp Limit: Sulfate Reactions (D.E.F.) Maturity precast.org/education Type of portland cement Potential compound composition,% C S C S C A C AF Blaine fineness m /kg Type of portland cement Chemical composition, % SiO Al O Fe O CaO MgO SO Na O eq I (mean) II (mean) III (mean) IV (mean) 5 V (mean) Portland, Blended, 5 7 and Other Hydraulic White (mean) 6 Cements 8 8 I (mean) II (mean) III (mean) IV (mean) V (mean).9 Portland, Blended, and Other Hydraulic Cements White (mean) Reactivity of Cement Compounds. Burning changes raw mix chemically into cement clinker. PCA PCA Cornell University, Ithaca, New York 9

10 HYDRATION OF PORTLAND CEMENT Primary Minerals: Tri-calcium silicate(c S) (CaO SiO ) +6H O. Clinker with gypsum is ground into portland cement and shipped. CaSO [CaO SiO H O] + [Ca(OH) ] Di-calcium silicate(c S) (CaO SiO ) + H O [CaO SiO H O] + [Ca(OH) ] PCA The Sulfate Reaction C S + [M]SO + xh O C A CaSO H O Calcium Magnesium Sodium etc. Ettringite Portland, Blended, and Other Hydraulic Cements Cornell University, Ithaca, New York

11 Steam Curing Delayed Ettringite Formation PCA Warm concrete accelerates hydration That raises the temperature That accelerates hydration - That raises the temperature FOCUSING ON CONCRETE TEMPERATURE General Effects of Temperature Hydration Heat of hydration Top Temp Limit: Sulfate Reactions (D.E.F.) Maturity 6 8 precast.org/education Calculating the Influence of Concrete Temperature Cornell University, Ithaca, New York

12 - Hydration How long will it take the corn to grow from this height. to this height (Full Maturity), ready to harvest? - Answer depends on growth rate. Growth rate depends on temperature For this season, how long until harvest at full yield? And for this specific hybrid? Average Daily Temperature (F) Continuous Temperature Record 6 9 Days after Germination of Corn Cornell University, Ithaca, New York

13 Growing Degree Day (GDD) Day x (Average Daily Temp minus 5F ) Average Daily Temperature (F) Varies with Growing Degrees specific crop 6 9 Days after Germination of temperature Corn & hybrid Continuous Temperature Record Assume no significant growth below datum Average Daily Temperature (F) Count only the degrees above 5F! 6 9 Days after Germination of Corn Growing Degree-Days = Area under Time-Temp Graph, down to 5 F Limit Average Daily Temperature (F) 6 5 And then add-up (accumulate) degree days Average Daily Temperature (F) 6 5 And then add-up (accumulate) growing degree days 6 9 Days after Germination of Corn 6 9 Days after Germination of Corn Each Growth Stage Associated with a specific number of GDD 5 to GDD to Full Maturity Depending on Hybrid Realized Growth Potential Realized Growth Potential Cornell University, Ithaca, New York

14 How long will it take the concrete to reach target strength for removal? - Answer depends on growth rate. Growth rate depends on temperature The Corn Analogy (Imaginary Corn) Warmer Concrete Temp. Cooler Rate of Development of Concrete Properties Degree of Hydration Hydration is a Growth process! Compressive Strength (psi) Step : Perform tests at various constant temperatures Step : Assume or compute a Datum Temperature (F) Step : Compute Curing Degree Days to psi. Curing Degree Days to psi: (7 - )x(.5 days) = 89 Deg-Days (55 - )x(7.6 days) = 8 Deg-Days ( - )x(. days) = 8 Deg-Days Need about 9 Curing Degree-Days to reach psi Age Days Record of In-Place Concrete Temperature Temperature (F) Concrete Surface Ambient Air inches deep 5 inches deep Time after Batching (hours) Cornell University, Ithaca, New York

15 Temperature (F) inches deep Accumulate (Degree ) hours/ = Maturity Time after Batching (hours) Maturity Measure temperature in place Collect time-temperature data Do lab work to get best datum temperature for your mix Convert temp data to maturity data Do lab work to correlate strength with maturity Real-Crete must match Lab-Crete Predict strength from maturity Perform periodic strength verifications Works better for cool concrete than for hot concrete Effect of Concrete Temperature on Strength Effect of Low Temperature on Strength Kosmatka: Design & Control Kosmatka: Design & Control FOCUSING ON CONCRETE TEMPERATURE General Effects of Temperature Hydration Heat of hydration Top Temp Limit: Sulfate Reactions (D.E.F.) Maturity Calibrating the mix and temperature range - Curve is unique to particular cement and blend of cementitious materials Curve Defined by Activation Energy E a 6 8 precast.org/education Cornell University, Ithaca, New York 5

16 Let s Assume we know:. Exactly what cm we got, and. Exactly how those cm behave Datum Temp. = F Datum Temp. = F 6 8 Datum Temp. = 65F Datum Temp. = F 6 8 Adjust the constants used in your maturity calculations to give best results for YOUR materials Cornell University, Ithaca, New York 6