1. Enhancing Homeland Security by Using Self-Sensing Concrete A contemporary topic

5. Tsunami

7. Tsunami

8. Hurricane Katrina

9. Levee breach

10. Homeland security National security against manmade and natural disasters

11. Technological approaches  Border monitoring  Building security enhancement  Building/city evacuation monitoring  Structural improvement  Chemical sensing  Disaster prediction

12. Self-sensing concrete Concrete that can sense its own condition

13. Self-sensing Ability of the structural material to sense itself without any embedded or attached sensor

14. Advantages of self-sensing  Low cost  High durability  Large sensing volume  Absence of mechanical property loss

15. Types of self-sensing  Strain/stress sensing  Damage sensing

16. Applications of strain/stress sensing  Traffic monitoring  Border security  Building facility management  Building security  Structural vibration control  Weighing  Earthquake prediction

17. Applications of damage sensing  Structural health monitoring  Hazard mitigation

18. Border security  Vehicle monitoring  Pedestrian monitoring

19. Building security Room occupancy monitoring Evacuation monitoring Intruder detection Damage monitoring

20. Self-sensing concrete material Cement-matrix composite containing discontinuous, randomly oriented and well-dispersed carbon fiber

21. Carbon fiber is not the sensor. The composite is the sensor.

22. Effects of fiber on concrete  Increase the flexural strength  Increase the flexural toughness  Decrease the drying shrinkage.  Increase the electrical conductivity  Render the self-sensing ability

23. Why not continuous fiber?  High cost  Cannot be incorporated in mix  Provides less effective self-sensing than discontinuous fiber

24. Carbon fiber  15 μm diameter  5 mm long  Amorphous (turbostratic)  Isotropic pitch based

25. Percolation threshold

26. Reasons for low fiber content  High conductivity is not required for self-sensing  Workability  Low cost  Compression strength

27. Below the percolation threshold Poor fiber dispersionGood fiber dispersion

28. Fiber dispersion techniques  Fine particulate admixture (silica fume, 0.1 μm)  Surfactant (methylcellulose)  Fiber surface treatment (ozone)  Rigorous premixing

29. Scientific origin of the self-sensing of strain Piezoresistivity (not piezoelectricity)

30. Piezoresistivity  Change of electrical resistivity due to strain  Gage factor = fractional change in resistance per unit strain (more than 2)  Gage factor up to 700 attained in carbon fiber reinforced cement

31. Crack Fiber

32. Method Measure the electrical resistance using a meter

33. Uniaxial tension

34. With carbon fiber Uniaxial tension   Longitudinal effect

35. With carbon fiber Uniaxial tension Transverse effect

36. Without carbon fiber Tension Longitudinal effect

37. Uniaxial compression

38. Stress Strain gage A B C D A B C D d d d k h d d h k Uniaxial compression d = 13, 25 and 51 mm Cured while the specimen is lying down Fiber length = 5 mm

39. d = 13 mm (small size) Longitudinal effect 0.95 vol.% fiber

40. d = 13 mm (small size) Transverse effect 0.95 vol.% fiber

41. Damage sensing Structural health monitoring

42. Stress Strain gage A B C D A B C D d d d k h d d h k Uniaxial compression

43. d = 25 mm (medium size) 0.48 vol.% fiber Longitudinal effect

44. Compressive testing up to failure Before loading After initial 3 cycles of loading Damage indeed occurred. Cubic specimens

45. Flexure 3-point bending

46. A1A1 A2A2 A3A3 A4A4 B4B4 B3B3 B2B2 B1B1 160 40 140 20 80 Flexure Dimensions in mm

47. With carbon fiber Flexure Surface resistance at compression side

48. Surface resistance at tension side With carbon fiber Flexure

49. Conventional concrete Self-sensing cement coating

50. Alternate scheme for flexural sensing  Coating the tension or compression side of a conventional concrete slab with self-sensing cement  Coating on the tension side gives higher sensitivity than coating on the compression side.

51. Self-sensing implementation in buildings Coat the ceiling with self-sensing cement.

52. Carbon fiber vs. carbon nanofiber  Nanofiber is less effective as a reinforcement.  Nanofiber fails to provide self-sensing.

53. Conclusion 1  Multifunctional cement-based materials have been attained without compromising the structural performance.

54. Conclusion 2  Carbon fiber cement is effect for the self-sensing of strain and damage, due to the reversible effect of strain on the electrical resistivity and the irreversible effect of damage on the resistivity.