SHM WITH NANO CEMENT BASED SENSORS

Transcription

1 SHM WITH NANO CEMENT BASED SENSORS GUILLAUME NOISEUX-LAUZÉ AND GEORGES AKHRAS ROYAL MILITARY COLLEGE OF CANADA 1

2 OUTLINE BACKGROUND STRUCTURAL HEALTH MONITORING OVERVIEW NANO CARBON COMPOSITE OVERVIEW OBJECTIVES EXPERIMENTAL TESTS SPECIMEN PREPARATION TEST SETUP RESULTS & DISCUSSION ONGOING & FUTURE WORK CONCLUSIONS QUESTIONS 2

3 BACKGROUND STRUCTURAL HEALTH MONITORING OVERVIEW Overarching research framework The main objective of SHM is to : Monitor the in-situ behaviour of a structure accurately and efficiently. Detect damage and determine the condition of the structure. The information can then be incorporated into management strategies. 3

4 BACKGROUND NANO CARBON REINFORCED COMPOSITE Carbon Nanotube (CNT) & Carbon Nanofiber (CNF) Reinforced Cement- Based Composite can potentially address two SHM challenges: Improve monitoring and sensing abilities by having the structural material itself act as a sensor. Improve material durability by inducing ductility, toughness and control crack growth. 4

5 HOW DOES IT WORK? BACKGROUND NANO CARBON REINFORCED COMPOSITE Self-sensing (piezoresistive) cement based material is made from cement mixed with electrically conductive fillers to increase it s ability to sense the strain, stress while maintaining good mechanical properties. 5

6 BACKGROUND NANO CARBON REINFORCED COMPOSITE HOW DOES IT WORK? (cont d) As the piezoresistive cement based material is deformed or stressed, the contact between the fillers and the cement matrix is changed, which affects its electrical resistance. Strain, stress, crack and damage can therefore be detected through measurement of the electrical resistance. 6

7 BACKGROUND APPLICATIONS Self-sensing pavement for traffic monitoring & vehicule loading measurements. Smart highways that will potentially track the location, weight and speed of traffic. In situ wireless and embedded sensors for damage detection in concrete structure. 7

8 OBJECTIVE & WORKPLAN The primary objective is to look into the piezorisitivity capability of carbon nanotubes (CNT) and carbon nanofiber (CNF) reinforced cement-based material. The secondary objective is to look at the effect of the Nano additive on compressive strength. 8

9 EXPERIMENTAL TEST CEMENT PASTE MIX PROPORTION Weight Cement Weight % Cement Kg/m 3 - Water Kg/m % Super Plast. 6.6 Kg/m 3 0.5% Silica Fume 65.7 Kg/m 3 5.0% CNT Kg/m % CNF Kg/m % CNT CNF Specimen (wt% Cement) (wt% Cement) #1 0.1% CNF 0 0,1 #2 0.2% CNF 0 0,2 #3 0.1% CNT 0,1 0 #4 0.2% CNT 0,2 0 #5 Control 0 0 #6 0.1% CNF /0.1% CNT 0,1 0,1 #7 0.2% CNF /0.2% CNT 0,2 0,2 9

10 EXPERIMENTAL TEST SPECIMEN PREPARATION Multi-walled Carbon Nanotube (MWNT), Nanocyl NC 7000l. PROPERTY UNIT VALUE Average diameter nm 9.5 Average length microns 1.5 Surface area m 2 /g Carbon purity % 90 Carbon nanofiber (CNF), Pyrograf -III PR 24 XT-LHT, PROPERTY UNIT VALUE Average diameter nm 100 Average length microns Surface area m 2 /g 43 10

11 EXPERIMENTAL TEST SPECIMEN PREPARATION Water+Superplasticizer+ CNT/CNF. Ultrasonic liquid processor (20 sec On 20 seconds Off) for 40 min. Processing capacity of 1L. 11

12 EXPERIMENTAL TEST SPECIMEN PREPARATION Effect of superplasticiser on hydrophobic property of CNT. 12

13 EXPERIMENTAL TEST SPECIMEN PREPARATION Cement & silica fume mix in the Hobart mixer for 5 min. The water/ CNT/ CNF solution was then added in the Hobart mixer and mixed for 5 min. Cement paste was then poured in the cylinder mould (D=75mm, H=150mm) and lightly vibrated. Strain gages were installed after approx. 30 days. 13

14 EXPERIMENTAL TEST EXPERIMENT SET-UP Resistivity measurement Metal disks. Carbon conductive grease. 14

15 EXPERIMENTAL TEST EXPERIMENT SET-UP Resistivity meter. 500 kn Test Frame. HBM Data Acquisition. 15

16 EXPERIMENTAL TEST EXPERIMENTS Cyclic compressing test with amplitude ranging from 1-20 kn with a loading rate of 0.2 kn/sec was conducted. Standard Test for Compressive Strength of Cylindrical Concrete Specimens were completed. Specimens resistivity were recorded throughout the experiments. 16

17 EXPERIMENTAL TEST EXPERIMENTS 17

18 Stress (MPa) FCR (%) EXPERIMENTAL TEST RESULTS - CYCLIC COMPRESSING TEST % CNF Time (sec) Stress Fractional Change in Resistivity

19 Stress (MPa) FCR (%) EXPERIMENTAL TEST RESULTS - CYCLIC COMPRESSING TEST % CNT / 0.1% CNF Time (sec) Stress (Mpa) FCR (%)

20 Fractional Change in Resistivity (FCR) EXPERIMENTAL TEST RESULTS - CYCLIC COMPRESSING TEST FCR /Strain 1.00 Avg Strain (µm/m) kN loading 0-20 kn loading FCR = Ɛ

21 Resistivity (Ohm*m) EXPERIMENTAL TEST 400 Specimens Resistivity Control 0.1% CNF 0.2% CNF 0.1% CNT 0.2% CNT 0.1% CNF /0.1% CNT 0.2% CNF /0.2% CNT

22 Stress (MPa) FCR (%) Stress (MPa) FCR (%) EXPERIMENTAL TEST RESULTS - STANDARD COMPRESSIVE STRENGTH TEST % CNT Control Time (sec) Time (sec) Stress FCR Stress FCR

23 Compressive Strength (MPa) EXPERIMENTAL TEST 70 Compressive Strength of Cylindrical Cement Paste Specimens Control, Cement Paste (CP) 0.1% CNF (CP) 0.2% CNF (CP) 0.1% CNT (CP) 0.2% CNT (CP) 0.1% CNF 0.2% CNF /0.1% CNT (CP)/0.2% CNT (CP) 23

24 EXPERIMENTAL TEST CHALLENGES FOR DEVELOPMENT Repeatable, large-scale and low energy method for distributing CNTs in cement-based materials. Current fabrication procedures require a controlled environment only available in a lab. Cost of CNTs & CNF (has fallen 100-fold since 1990 but still ). Unknown long term durability and effect of environment. 24

25 ONGOING AND FUTURE WORK The specimen in the second phase of testing contains aggregates with various concentrations of CNT and CNF. These tests will help determine if the combination of CNT and CNF effectively overcomes challenges associated with the formation of conductive network in cement composite containing aggregates. 25

26 CONCLUSION Results obtained during the first testing phase are coherent with other studies such as; Azhari et al. (2012) Tyson et al. (2011) and Han et al. (2010). CNF/CNT-cement significantly increase the electrical conductivity vs CNT-cement or CNF-cement alone. The electrical resistance of the specimen changed in tandem with the strain levels and could be use as a sensor. A lot more test needs to be conducted to created reliable & accurate models (Strain/FCR). 26

27 ACKNOWLEDGMENTS The authors would like to thank NSERC for its financial support. 27

28 QUESTIONS? 28

29 SHM OVERVIEW SHM is typically achieved by the continuous and autonomous monitoring of key structural parameters by embedding, in strategic positions, sensors such as: Electric-resistance strain gauges Optic sensors Piezoelectric ceramic. Most of these sensors have considerable shortcomings such as: Low sensitivity High cost Poor durability Unfavourable compatibility with concrete structures. (i.e. loss of structural mechanical properties)

30 CARBON NANOTUBE REINFORCED COMPOSITE CNT STRUCRURE / PROPERTIES Structurally rolled-up & twisted sheets of graphite nm (hair is 25 μm bigger) Really high aspect ration (L/ ) > 1000 up to 1M (50 m hair) Modulus of Elasticity can reach 1000 GPa (5 x steel) The tensile strength up to 63 GPa (+50 x steel) (highest tensile strength of any material yet measured) Large surface area (typically m 2 /g)