Pilot Project for Maximum Heat of Mass Concrete - Research Highlights

Transcription

1 2013 FTBA Construction Conference Pilot Project for Maximum Heat of Mass Concrete - Research Highlights Adrian M. Lawrence, Ph.D., P.E. UF/FDOT-SMO 1

2 Background The FDOT currently defines mass concrete as: Minimum dimension 3 Ratio of concrete volume to the surface area >1 Requires a temperature differential control plan Model procedure outlined in ACI 207, also known as the Schmidt Method. 2

3 Scope of Research Use finite element modeling (FEM) to predict the temperature differentials and peak temperatures in massive concrete structures. Determine/Suggest the size of the element that does not need a mass concrete plan Determine the R values for soil 3

4 Finite Element Modeling (FEM) TNO Diana FEM program Adiabatic* temperature rise based on the ratio of cementitious components in a mix design Determined from Isothermal Calorimetry Testing *temperature rise without the loss or gain of heat to/from external sources 4

5 Finite Element Modeling (FEM) To construct the model, the hydrating concrete, as well as the formwork and insulating materials are taken into consideration. Concrete Bottom Insulation Top Insulation Plywood Panels 5

6 Laboratory Testing Hydration Energy curve obtained from Isothermal Calorimetry Testing 6

7 300 Laboratory Testing Hydration Energy curve obtained from Isothermal Calorimetry Testing Cummulative Energy ( J/g) No Admixture With Admixture Time (hours) Type D Water Reducer Retarder Type F high range water reducer Air Entraining 7

8 Laboratory Testing Adiabatic Temperature Rise curve obtained from the Hydration Energy Curve Temperature ( o C) Hydration Time (hour) 8

9 Field Work Two bridge elements constructed in the field in Florida were monitored for temperature developments Footing at a project in Miami Footing at a project in Orlando 9

10 Miami, Florida Field Work Concrete Mix Design: Portland Cement - Type I/II Fly Ash Class F 10

11 Miami, Florida Field Work Contractor opted to place concrete directly on top of the 11 soil

12 Field Work Installation of temperature sensors into the footing cage Temperature sensor 12

13 Field Work Location of temperature sensors in pier footing Sensor 10 Sensor 9 Sensor 8 Sensor 7 Sensor 6 Sensor 5 Sensor 4 Sensor 3 Sensor 2 Sensor 1 Sensor 20 Sensor 19 Sensor 18 Sensor 17 Sensor 16 Sensor 15 Sensor 14 Sensor 13 Sensor 12 Sensor 11 13

14 Footing, Miami, FL Field Work Temperature ( Sensor 1 Sensor 2 Sensor 3 Sensor 4 Sensor Time (hours) Measured temperatures along vertical centerline of footing 14

15 Finite element mesh Modeling Top Insulation Concrete Footing Underlying soil layer 15

16 Modeling Predicted temperature distribution 167 hours (7 days) after concrete placement 16

17 Footing, Miami, FL Comparisons Temperatures ( C) Sensor 1 86 Sensor 2 77 Schmidt Model at Sensor 1 Schmidt Model at Sensor 2 68 FE Model at Sensor 1 FE Model at Sensor Time (hours) Temperatures ( F) 17

18 Comparisons Temperature ( C) Sensor 3 86 Schmidt Model at Sensor 3 68 FE Model at Sensor Time (hours) Temperature ( F) Temperature ( C) Sensor 4 86 Schmidt Model at Sensor 4 68 FE Model at Sensor Time (hours) Temperature ( F) Temperature ( C) Sensor 5 86 Schmidt Model at Sensor 5 68 FE Model at Sensor Time (hours) Temperature ( F) 18

19 Comparisons Temperature ( C) Temperature ( C) Sensor 6 Sensor 7 77 FE Model at Sensor 6 68 FE Model at Sensor Time (hours) Sensor 11 sensor 12 FE Model at Sensor 11 FE Model at Sensor Time (hours) Temperature ( F) Temperature ( C) Temperature ( F) Temperature ( C) Sensor 8 95 Sensor 9 FE Model at Sensor 8 86 FE Model at Sensor Time (hours) Sensor Sensor 14 Sensor FE Model at Sensor 13 FE Model at Sensor FE Model at Sensor Time (hours) Temperature ( F) Temperature ( F)

20 Orlando, Florida Field Work Temperature sensor wires 20

21 Field Work Concrete Mix Design: Portland Cement Type I/II Fly Ash Class F Ultra-Fine Fly Ash* *- Used for Strength Only. Not as a requirement for Durability. 21

22 Field Work Two methods of insulating the elements were employed: Placing 2 thick Styrofoam (R-5/inch) on the outside of the plywood formwork Placing 2 thick Styrofoam (R-5/inch) on the inside of the plywood formwork 22

23 Temperature ( C) Bottom Sensor 68 Middle Sensor Top Sensor Time (Hours) 80 Insulation Placed on the Inside of Formwork Comparisons Temperature ( C) Temperature ( F) Insulation Placed on the Outside of Formwork Bottom Sensor Middle Sensor Top Sensor Time (Hours) Temperature ( F)

24 Segmental Bridge Pier Segment High-strength concrete: 80 psi Volume to Surface Area ratio: 0.97 ft. Was not deemed Mass Concrete CRACKED core of the segment was used to calculate the volume to surface area ratio 24

25 Segmental Bridge Pier Segment Should the V/A threshold of 1.0 be reduced when high strength mixes are used? What should that threshold be? 25

26 Segmental Bridge Pier Segment Core length: 18 ft Core height: 6 ft Two core thicknesses were considered: 5 ft volume to surface area ratio = 0.97 ft 4 ft volume to surface area ratio = 0.89 ft Hydration data from a normal strength concrete mix design used. 26

27 Segmental Bridge Pier Segment Temperature distribution at 7 days V/A 0.97: maximum temperature differential = 28.4 o C (51 o F) V/A 0.89: maximum temperature differential = 26.2 o C (47 o F) 27

28 Summary of Findings At locations with a high water table (above the footer bottom) soil should not be relied on as a good insulator, it is therefore highly recommended to place a layer of insulating material between the concrete and the soil. Placing insulation on the inside of the formwork improves the performance of mass concrete placements in terms of maintaining low delta temperatures. 28

29 Summary of Findings Preliminary data suggests that the volume to surface area requirements should be reduced when high strength concrete is used for segmental bridge pier structures. Structures with least dimension of 6 ft and smaller, concrete with up 48% of the Portland cement replaced with Class F Fly Ash, insulation with R-values 2.5 or greater, consistently maintained delta temperatures below the 35 F. 29

30 Thanks- Any Questions? 30