Measuring and Modeling of Formwork Pressure of Self-Consolidating Concrete

Transcription

1 Measuring and Modeling of Formwork Pressure of Self-Consolidating Concrete Prof. David Lange and Jacob Henschen University of Illinois at Urbana-Champaign Regensburg, Germany March 12, 2014

2 Greetings from the University of Illinois

3 Self-consolidating concrete (SCC) Continuous casting Higher casting rates No vibration necessary Casting in dense reinforcement

4 Formwork Pressure Higher fluidity leads to higher lateral pressures on the formwork

5 Over 40ft tall wall Nominal strength 1600 pcf One pour. How fast?

6 Formwork standards ACI 347 Forms for highly fluid concrete must withstand full hydrostatic pressure DIN 18218: Recently revised to account for fluidity of SCC

7 Measured pressures Maximum pressures typically lower than hydrostatic

8 Field measurements have shown that h Maximum Pressure Envelope h Maximum Pressure Envelope

9 Field measurements have shown that h Maximum Pressure Envelope h Maximum Pressure Envelope

10 Field measurements have shown that h Maximum Pressure Envelope h Maximum Pressure Envelope

11 Field measurements have shown that h Maximum Pressure Envelope h Maximum Pressure Envelope

12 Field measurements have shown that h Maximum Pressure Envelope h Maximum Pressure Envelope

13 Field measurements have shown that h Maximum Pressure Envelope h Maximum Pressure Envelope

14 Field measurements have shown that Fast Pour h Maximum Pressure Envelope Slow Pour h Maximum Pressure Envelope

15 Mechanisms of form pressure decay The main factors: Internal friction Aggregate contact and tendency to settle/consolidate Skeleton structure Higher agg content leads to rapid pressure decay Thixotropy Tendency of concrete to gel when at rest Shear strength increases even before set occurs Greater thixotropy leads to rapid pressure decay

16 Can we accurately model formwork pressure? Minimize testing Accurate and robust Field deployment

17 First step, measuring formwork pressure Honeywell full bridge pressure transducer Sensor brackets hold sensor face flush to formwork surface

18 Lab testing Pressure decay rate consistent at varying depths Vibration and admixtures alter pressure decay

19 Our approach Step 1: Characterize the characteristic pressure decay of the material Measure decay curve from a column Calculate pressure as a function of height of concrete over time, C(t) Step 2: Impose variable pressure head on the material that is undergoing gelation, stiffening Generate filling rate curve Multiply filling rate curve by C(t) from column to generate predicted pressure over time

20 Step 1 1m Filled quickly to generate maximum pressure Pressure measured while material is at rest

21 decay signature Normalize pressure Apply numerical approximation of curve C (t ) mo d = ( at C0 2 ) +1 α

22 Step 2 Apply overburden pressure head Use unit weight of concrete P (t ) = C (t ) γ h(t ) Pressure = Model x Unit weight x Casting rate

23 Field Validations Illinois DOT I-74 retaining walls OSF Hospital Milestone Project Stockholm Round Robin Tests

24 Field Validation #1 Illinois DOT I-74 retaining walls

25 I-74 Retaining wall SCC used for aesthetics Slump flow: 71 cm Wall height: ~7 m Placed with tremie or pump

26 Wall 8511 Panel 9-10 Height 6.0 m 2 sensors at 5.6 m from top 1 at bulkhead 2 under drop chute

27 Wall 81 Panel R Height: 2 m 2 sensors at 1.7 m 1 under drop chute 2 at bulkhead

28 Field Validation #2 OSF Hospital Milestone Project

29 OSF Hospital Milestone Project Foundation wall construction Continuous placement Slump flow: cm Height: m

30 Wall #1

31 Wall #2

32 Plan View Drop chutes Wall #3

33 Field Trial Summary

34 IlliForm: Model implemented in Excel

35 Field Validation #3 Stockholm Round Robin Tests

36 Round robin tests in Stockholm for 10 different form pressure models Height: 6.6 m RILEM TC 233-FPC Stockholm, June 2012 Comparison of 10 models Height: 4.2 m Theoretical Lab tests Field tests 8 wall sections tested over Reference: Billberg, P et. al, Field validation of models for predicting lateral 4 days form pressure exerted by SCC, Cement and Concrete Composites, accepted 2014.

37 Reference: Billberg, P et. al, Field validation of models for predicting lateral form pressure exerted by SCC, Cement and Concrete Composites, accepted Corresponding author: Peter H. Billberga Nicolas Rousselb, Sofiane Amzianec, Marc Beitzeld, George Charitoue,Björn Freundf, John N. Gardnerg, Guillaume Grampeixh, Carl-Alexander Graubneri, Lloyd Kellerj, Kamal H. Khayatk, David A. Langel, Ahmed F. Omranm, Arnaud Perrotn, Tilo Proskeo, Robert Quattrociocchip, Yannic Vanhoveq 37

38 Round Robin Results Walls filled step-wise Pauses can cause deviation

39 Round Robin Results Decay curves Maximum pressure

40 What parameters do other models use to characterize change in SCC with time? pressure decay by column test structural buildup by concrete rheometer slump-loss by slump tests setting time by vicat test pore pressure by pressure sensor on form

41 Do these 10 models work? 140 y =1,22x 1,23x 1,37x 1,16x 1,20x 1,30x 1,42x 1,09x 1,40x R² =0,77 0,82 0,85 0,81 0,86 0,79 0,80 0, N= Wall 1 Wall 2 Wall 3 Wall 4 Wall 5 Wall 6 Wall 7 Wall 8 1:1 ) a P (k u s tp ic d re Wall 2 Wall Wall 3 4 Wall 5 Wall 6 Wall Wall 7 8 1: Measured Measuredpressure pressure(kp (kpa) Measured a)

42 Comparison of Models Model Khayat/Omran Ovarlez/Roussel Lange/Tejeda-Dominguez Perrot et al Gardner et al Beitzel Proske mean Proske design DIN mean DIN design Average Slope R

43 Summary Formwork pressure of SCC is difficult to characterize with a single parameter i.e. filling rate or slump flow Pressure decay signature approach provides reasonable prediction of formwork pressure Several modeling approaches have been developed based, giving industry a choice of tools to use for pressure prediction

44 Acknowledgements Our projects: Stockholm Round Robin: Swedish Cement and Concrete Research Institute (CBI) Development Fund of the Swedish Construction Industry (SBUF)

45

46

47 Self-consolidating concrete (SCC) Continuous casting Higher casting rates No vibration necessary Casting in dense reinforcement

48 Formwork Pressure Higher fluidity leads to higher lateral pressures on the formwork

49 Over 40ft tall wall Nominal strength 1600 pcf One pour. How fast? 5

50 Formwork standards ACI 347 Forms for highly fluid concrete must withstand full hydrostatic pressure DIN 18218: Recently revised to account for fluidity of SCC

51 Measured pressures Maximum pressures typically lower than hydrostatic

52

53

54

55

56

57

58

59

60 Can we accurately model formwork pressure? Minimize testing Accurate and robust Field deployment

61 First step, measuring formwork pressure Honeywell full bridge pressure transducer Sensor brackets hold sensor face flush to formwork surface

62

63

64

65

66

67 Field Validations Illinois DOT I-74 retaining walls OSF Hospital Milestone Project Stockholm Round Robin Tests

68 Field Validation #1 Illinois DOT I-74 retaining walls

69 I-74 Retaining wall SCC used for aesthetics Slump flow: 71 cm Wall height: ~7 m Placed with tremie or pump

70

71

72 Field Validation #2 OSF Hospital Milestone Project

73 OSF Hospital Milestone Project Foundation wall construction Continuous placement Slump flow: cm Height: m

74

75

76 Plan View Drop chutes Wall #3

77 Field Trial Summary

78 IlliForm: Model implemented in Excel

79 Field Validation #3 Stockholm Round Robin Tests

80 Round robin tests in Stockholm for 10 different form pressure models Height: 6.6 m RILEM TC 233-FPC Stockholm, June 2012 Comparison of 10 models Height: 4.2 m Theoretical Lab tests Field tests 8 wall sections tested over 4 days Billberg, P et. al, Field validation of models for predicting lateral Reference: form pressure exerted by SCC, Cement and Concrete Composites, accepted 2014.

81 Reference: Billberg, P et. al, Field validation of models for predicting lateral form pressure exerted by SCC, Cement and Concrete Composites, accepted Corresponding author: Peter H. Billberga Nicolas Rousselb, Sofiane Amzianec, Marc Beitzeld, George Charitoue,Björn Freundf, John N. Gardnerg, Guillaume Grampeixh, Carl-Alexander Graubneri, Lloyd Kellerj, Kamal H. Khayatk, David A. Langel, Ahmed F. Omranm, Arnaud Perrotn, Tilo Proskeo, Robert Quattrociocchip, Yannic Vanhoveq 37

82 Round Robin Results Walls filled step-wise Pauses can cause deviation

83 Round Robin Results Decay curves Maximum pressure

84 What parameters do other models use to characterize change in SCC with time? pressure decay by column test structural buildup by concrete rheometer slump-loss by slump tests setting time by vicat test pore pressure by pressure sensor on form

85 Do these 10 models work? y =1,22x 1,16x 1,20x 1,30x 1,42x 1,23x 1,37x 1,09x 1,40x R² R² =0,77 0,79 0,81 0,86 0,85 0,82 0,80 0, N= ) a P (k u s tp ic d re Wall Wall 1 W 2 Wall Wall all 3 W all 4 Wall Wall 5 6 Wall Wall 7 Wall 8 1: Wall 2 Wall 3 Wall 4 Wall 5 Wall 6 7 Wall 8 1: Measured Measuredpressure pressure(kp (kpa) a)

86 Comparison of Models Model Khayat/Omran Ovarlez/Roussel Lange/Tejeda-Dominguez Perrot et al Gardner et al Beitzel Proske mean Proske design DIN mean DIN design Average Slope R

87 Summary Formwork pressure of SCC is difficult to characterize with a single parameter i.e. filling rate or slump flow Pressure decay signature approach provides reasonable prediction of formwork pressure Several modeling approaches have been developed based, giving industry a choice of tools to use for pressure prediction

88 Acknowledgements Our projects: Stockholm Round Robin: Swedish Cement and Concrete Research Institute (CBI) Development Fund of the Swedish Construction Industry (SBUF) 44