Rubber Modified Seal Coat Pilot Project on SBD-95-PM 57.2/64.5 Location 1 (EA 08-0Q4904) Vol 1: Construction Report, Part 2

Transcription

1 Rubber Modified Seal Coat Pilot Project on SBD-95-PM 57.2/64.5 Location 1 (EA 08-0Q4904) Vol 1: Construction Report, Part 2 Report Number: CP2C February 6, 2015 California Pavement Preservation Center Langdon Hall, Suite 203 California State University, Chico Chico, California (530)

2 PROJECT SUMMARY PAGE Tech Report: Title: Rubber Modified Seal Coat Pilot Project on SBD-95-PM 57.5/64.5, Location 1 (EA 08-0Q4904) Vol 1: Construction Report, Part 2 Authors: Lerose Lane, DingXin Cheng, and Brandon Fraser Prepared For: Caltrans Client Reference No.: 08-0Q4904 Prepared by: CP2 Center Date: February 6, 2015 Abstract: This report describes the rubber modified asphalt seal coat pilot project construction on SR 95 in San Bernardino County (near Needles) from PM 56.1 to PM The project includes an asphalt rubber seal coat using AR (Type I), AR (Type II) and a CRR18MB rubberized binder seal coat with 1/2 inch chips over existing asphalt concrete pavement with and without warm mix additive on various test sections. Within each seal coat test section, four Performance Evaluation Sections (PESs) were established for detailed performance monitoring and evaluation with the exception of the CRR18MB section within Location 1. These PESs are to be monitored to determine their performance. The overall purpose of this project is to compare the performance of different products in a desert environment with extreme heat during the summer temperatures. The project went down with a few material problems with the asphalt rubber viscosity, and the hot pre-coated chips during construction between September 30 and October 4, Caltrans District personnel followed the construction of the various products. The AR (Type II) and the AR (Type I) products had a heavier application rate than the CRR18MB product, and the AR (Type I) and (Type II) had a smoother appearance. The appendices of this report are included in the Part 2 of this report. The information on the pilot project can be found on the California Pavement Preservation Center s (CP 2 C) website: Keywords: Asphalt Rubber Seal Coat, Asphalt Rubber (Type I), Asphalt Rubber (Type II), CRR18MB, Warm Mix Additive, Performance Evaluation Section (PES) ii

3 Acknowledgements We appreciate the financial support of Caltrans for providing the funding for monitoring this important and meaningful project. We would like to extend our gratitude to Sri Balasubramanian, Haiping Zhou, and Mike Ristic, of Caltrans, who provided continuous support for this project. We would also appreciate the support from Caltrans District 08, Resident Engineer, Godwin Emuh, Mark Horn with Trinity Engineering Laboratories, Inc., the consultant testing firm, Felipe Castillo, Plant Manager, VSSI, Inc., and Superintendent, Leroy Gleaves, VSSI, Inc. The authors also appreciate the work by Gary Hicks of the CP2 Center for his review for both report content and consistency. The authors also thank the CP2 Center student research assistants, Brandon Fraser, Brennen Urbanek, Xai Lao, Andrew Montague, Nica Ceja, Victoria Goernert, Anthony Alfaro, Benito Sandoval, Jarvis Thor and Madelyn Giles, who provided support on field evaluation and laboratory testing. Disclaimer The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The content does not necessarily reflect the official views or policies of Caltrans and the State of California. iii

4 Table of Contents 1 APPENDIX A DISTRESS MAPPING APPENDIX B PRE-CONSTRUCTION DISTRESS PHOTOS APPENDIX C TESTING BY TRINITY ENGINEERING LABORATORIES, CP2 CENTER, ASPHALT PAVEMENT AND RECYCLING TECHNOLOGIES AND CALTRANS APPENDIX C-1 AGGREGATE SAMPLE GRADATIONS PERFORMED BY TRINITY ENGINEERING LABORATORIES, INC APPENDIX C-2 ASPHALT RUBBER DAILY VISCOSITY REPORT PERFORMED BY TRINITY ENGINEERING LABORATORIES, INC APPENDIX C-3 MODIFIED FIELD VIALIT TEST AND BINDER SPREAD RATES PERFORMED BY TRINITY ENGINEERING LABORATORIES, INC APPENDIX C-5 ASPHALT RUBBER DAILY BLENDING REPORT VSSI APPENDIX C-6---CP2 CENTER S TESTING RESULTS APPENDIX D POST CONSTRUCTION PHOTOS, OCTOBER 5, 2014, AND NOVEMBER 15, APPENDIX E EMISSIONS APPENDIX E-1 OPACITY CHART APPENDIX E-2 RINGLEMANN EMISSION STANDARD APPENDIX E-3 RINGLEMANN EMISSION SCALE iv

5 Table of Figures Figure B-1. AR (Type II) PES 1 (Left), PES 2 (Right) in Good Condition Figure B-2. AR (Type II) PES 2 in Good Condition (Left), PES 3 in Poor Condition (Right) Figure B-3. (Type II) PES 3 in Poor Condition Figure B-4. AR (Type II) PES 4 (Left), and Looking North from PM at PES 3 and PES Figure B-5. AR (Type II) PES 4 Typical Transverse Cracking (Left), AR (Type II) with WMA PES 3, Severe Fatigue Cracking, PM 59.0 (Right) Figure B-6. AR (Type II) with WMA, End PES 3 (Left), and Beginning PES 4, Looking SE at PM (Right) Figure B-7. AR (Type II) with WMA PES 4 (Left), Looking North from Beg. PES 4, PM Figure B-8. AR (Type II) PES 5, Looking North from PM Figure B-9. AR (Type II) PES 5 Fatigue Cracking, PM Figure B-10. AR (Type II) PES 6 Looking North from PM (Left), Beginning PES 6 (Right) Figure B-11. AR (Type II) PES 6 Cracking Figure B-12. AR (Type II), PES 7 in Good Condition Looking South (Left), PM Figure B-13. AR (Type II), PES 7 Minor Cracking (Left), PES 8 (Right), PM Figure B-14. AR (Type I) with WMA, PES 1, Looking North from PM (Left), Typical Distress (Right) Figure B-15. AR (Type I) with WMA, PES 2 Typical Severe Fatigue Distress Figure B-16. AR (Type I) with WMA, PES 3 Looking North near PM , Severe Fatigue Failure Typical Condition Figure B-17. AR (Type I) with WMA PES 4, Severe Fatigue Failure Typical Condition 35 Figure B-18. AR (Type I), PES 1 Looking North near PM (Left), Beginning of PES Figure B-19. AR (Type I), PES 1, Severe Fatigue Cracking (Left & Center), and AR (Type I) PES 2 Similar Pavement Condition Figure B-20. Pothole Patch AR(Type I), PES 2 (Left), Beginning PES 2 PM Figure B-21. AR (Type I), PES 3, Looking North near PM (Left), Typical Pavement Condition (Right) Figure B-22. AR (Type I), PES 4, Looking South near PM (Left), Typical Pavement Condition (Right) Figure B-23. CRR18MB, End PES 3 with Corrected PM (only 2 PES Sections for CRR18 MB, PES 3 and PES 4 Due to Repairs) Typical Severe Fatigue Failures Figure B-24. CRR18MB PES 3, Beginning near PM (Left), Looking North at PES 3 and PES v

6 Figure B-25. CRR18MB, PES Figure B-26. CRR18MB with WMA PES 1 and PES 2 Looking North from PM (Left), Typical Condition (Right)PES 1 and PES 2 are only 474 feet long Figure B-27. CRR18MB with WMA PES 3 near PM (Left), and Typical Pavement Condition (Right) Figure B-28. CRR18MB with WMA Looking South from PM (Left), and Typical Pavement Condition (Right) vi

7 Figure D-1. North End of Project at PES 8. PM , Southbound (November 13, 2014)93 Figure D-2. AR (Type II) or AR (Type I) PES 8 (November 13, 2014) Figure D-3. Near PM 64.04, After RXR, Southbound Figure D-4. South of RxR AR (Type II) PESs 5 and 6, Southbound Figure D-5. North of CRR18 MB PESs 3 and 4, Southbound Figure D-6. At CRR18MB, PES 3 and PES 4, Southbound Near PM Figure D-7. CRR18MB near PM 63.0, Southbound Figure D-8. CRR18MB, near PES 3 and PES 4, Southbound Figure D-9. CRR18MB with WMA, Southbound near PM Figure D-10. CRR18MB with WMA, PES 2 (Left), PES 4 (Right) (October 5, 2014) Figure D-11. CRR18MB with WMA, Southbound (November 14, 2014) Figure D-12. AR (Type I) PES 3, Looking South near PM 61.2 (October 5, 2014) Figure D-13. AR (Type I) (October 5, 2014) Figure D-14. AR (Type I) with WMA, End PES 1 and 2, Southbound, PM (Area of Uncoated aggregate on Left, PES 1) (Nov. 14, 2014) Figure D-15. AR (Type I) with WMA, PES 1, Area of Uncoated Aggregate (Left), PES 3 Burnt Aggregate (Right) (October 5, 2014) Figure D-16. AR (Type I) with WMA near PM 60.0, Southbound (November 14, 2014) Figure D-17. AR (Type II) with WMA near PM 59.7, Southbound (November 14, 2014) 101 Figure D-18. AR (Type II) with WMA (October 5, 2014) Figure D-19. AR (Type II) with WMA, Southbound (November 15, 2014) Figure D-20. AR (Type II) with WMA near PM 59.3, Southbound (November 14, 2014) 103 Figure D-21. AR (Type II) with WMA, Example of Poor Joint near PM 59.0 (October 5, 2014) Figure D-22. AR (Type II) with WMA near PM 59.00, Southbound (November 14, 2014) Figure D-23. AR (Type II) with WMA near PM 59.00, Northbound (October 5, 2014) Figure D-24. AR (Type II) with WMA Near PES 1 and PES 2, Southbound (November 14, 2014) Figure D-25. AR (Type II) with WMA, PES 4 (October 5, 2014) Figure D-26. AR (Type II) Near PM 58.6, Southbound (November 14, 2014) Figure D-27. AR (Type II) Near PM 58.6, Southbound (October 5, 2014) Figure D-28. AR (Type II) PES 4, PM (October 5, 2014) Figure D-29. AR (Type II) PES 3, PM , Looking North (October 5, 2014) Figure D-30. AR (Type II) End PES 1, PM (October 5, 2014) Figure D-31. AR (Type II), PES 1 and PES 2, Southbound (November 14, 2014) Figure D-32. AR (Type II) Near PESs 1 and 2, Looking South, near PM 58.00, Toward Interchange with Highway 40 (November 14, 2014) Figure D-33. AR (Type II) PES 1 (October 5, 2014) vii

8 1 APPENDIX A DISTRESS MAPPING On Wednesday, July 16, 2014 through Friday, July 18, 2014, and on Wednesday, September 24, 2014, CP2 Center staff, Lerose Lane, Brandon Fraser, and Xai Lao, with Caltrans traffic control, mapped the distress on all of the test sections. The total length of each distress that was measured is summarized in Table 1. PES Cracking Condition Summary in Part 1 of this report. The following figures show the detailed field crack mapping for each test section. 1

9 2

10 3

11 4

12 5

13 6

14 7

15 8

16 9

17 10

18 11

19 12

20 13

21 14

22 15

23 16

24 17

25 18

26 19

27 20

28 21

29 22

30 23

31 24

32 25

33 26

34 27

35 28

36 2 APPENDIX B PRE-CONSTRUCTION DISTRESS PHOTOS Most PES s were severely distressed. The AR (Type II) PESs 1, 2, 7, and 8 were the only sections in good condition. Figure B-1. AR (Type II) PES 1 (Left), PES 2 (Right) in Good Condition Figure B-2. AR (Type II) PES 2 in Good Condition (Left), PES 3 in Poor Condition (Right) Figure B-3. (Type II) PES 3 in Poor Condition 29

37 Figure B-4. AR (Type II) PES 4 (Left), and Looking North from PM at PES 3 and PES 4 Figure B-5. AR (Type II) PES 4 Typical Transverse Cracking (Left), AR (Type II) with WMA PES 3, Severe Fatigue Cracking, PM 59.0 (Right) 30

38 Figure B-6. AR (Type II) with WMA, End PES 3 (Left), and Beginning PES 4, Looking SE at PM (Right) Figure B-7. AR (Type II) with WMA PES 4 (Left), Looking North from Beg. PES 4, PM Figure B-8. AR (Type II) PES 5, Looking North from PM

39 Figure B-9. AR (Type II) PES 5 Fatigue Cracking, PM Figure B-10. AR (Type II) PES 6 Looking North from PM (Left), Beginning PES 6 (Right) Figure B-11. AR (Type II) PES 6 Cracking 32

40 Figure B-12. AR (Type II), PES 7 in Good Condition Looking South (Left), PM Figure B-13. AR (Type II), PES 7 Minor Cracking (Left), PES 8 (Right), PM Figure B-14. AR (Type I) with WMA, PES 1, Looking North from PM (Left), Typical Distress (Right) 33

41 Figure B-15. AR (Type I) with WMA, PES 2 Typical Severe Fatigue Distress Figure B-16. AR (Type I) with WMA, PES 3 Looking North near PM , Severe Fatigue Failure Typical Condition 34

42 Figure B-17. AR (Type I) with WMA PES 4, Severe Fatigue Failure Typical Condition Figure B-18. AR (Type I), PES 1 Looking North near PM (Left), Beginning of PES 1 35

43 Figure B-19. AR (Type I), PES 1, Severe Fatigue Cracking (Left & Center), and AR (Type I) PES 2 Similar Pavement Condition Figure B-20. Pothole Patch AR(Type I), PES 2 (Left), Beginning PES 2 PM

44 Figure B-21. AR (Type I), PES 3, Looking North near PM (Left), Typical Pavement Condition (Right) Figure B-22. AR (Type I), PES 4, Looking South near PM (Left), Typical Pavement Condition (Right) 37

45 Figure B-23. CRR18MB, End PES 3 with Corrected PM (only 2 PES Sections for CRR18 MB, PES 3 and PES 4 Due to Repairs) Typical Severe Fatigue Failures Figure B-24. CRR18MB PES 3, Beginning near PM (Left), Looking North at PES 3 and PES 4 Figure B-25. CRR18MB, PES 4 38

46 Figure B-26. CRR18MB with WMA PES 1 and PES 2 Looking North from PM (Left), Typical Condition (Right)PES 1 and PES 2 are only 474 feet long. Figure B-27. CRR18MB with WMA PES 3 near PM (Left), and Typical Pavement Condition (Right) 39

47 Figure B-28. CRR18MB with WMA Looking South from PM (Left), and Typical Pavement Condition (Right) 3 APPENDIX C TESTING BY TRINITY ENGINEERING LABORATORIES, CP2 CENTER, ASPHALT PAVEMENT AND RECYCLING TECHNOLOGIES AND CALTRANS This appendix contains several sub sections. Each is identified below: APPENDIX C-1 AGGREGATE SAMPLE GRADATIONS PERFORMED BY CALTRANS APPENDIX C-2 ASPHALT RUBBER DAILY VISCOSITY REPORT BY TRINITY ENGINEERING LABORATORIES, INC. APPENDIX C-3 MODIFIED FIELD VIALIT TESTS AND BINDER SPREAD RATES APPENDIX C-4 BINDER TESTING BY ASPHALT PAVEMENT AND RECYCLING TECHNOLOGIES, INC. APPENDIX C-5 ASPHALT RUBBER DAILY VISCOSITY BLENDING REPORT VSSI APPENDIX C-6 CP2 CENTER LABORATORY TESTING 40

48 3.1 APPENDIX C-1 AGGREGATE SAMPLE GRADATIONS PERFORMED BY TRINITY ENGINEERING LABORATORIES, INC. FROM REPORT DATED : 41

49 FROM SAMPLE TAKEN , AM: 42

50 FROM SAMPLE TAKEN , AM: 43

51 FROM SAMPLE TAKEN , PM: 44

52 FROM SAMPLE TAKEN , AM: 45

53 3.2 APPENDIX C-2 ASPHALT RUBBER DAILY VISCOSITY REPORT PERFORMED BY TRINITY ENGINEERING LABORATORIES, INC. 46

54 47

55 48

56 49

57 50

58 3.3 APPENDIX C-3 MODIFIED FIELD VIALIT TEST AND BINDER SPREAD RATES PERFORMED BY TRINITY ENGINEERING LABORATORIES, INC. The spread rate tests did not match those of the contractor s distributor trucks, or as shown by the shipment weigh slips. The CP2 Center is not sure why the test results didn t agree with the actual application rates as verified from the contractor s records. The spread rate tests, performed by Trinity Engineering Laboratories, Inc., showed consistently lighter application rates, with individual test plates showing over a 0.1 gal/yd 2 variation. The target for the spread rate testing was +/ gal/yd 2, and there were to be 2 tests performed daily. Table 10, in Part 1 of this report shows a summary of the field Vialit test results reported by Trinity Engineering Laboratories, Inc. The modified field Vialit tests showed that the AR binders had a higher percentage of aggregate retention than the CRR18MB. For this project, the retention was Report Only per Section D(4)(d)(v) of the special provisions. 51

59 52

60 53

61 54

62 55

63 APPENDIX C-4 BINDER TESTING 56

64 57

65 58

66 59

67 60

68 61

69 62

70 63

71 64

72 3.4 APPENDIX C-5 ASPHALT RUBBER DAILY BLENDING REPORT VSSI These plant records were furnished by Felipe Castillo, Plant Manager for VSSI. They show the viscosity prior to shipping the product to the job site. The distance between the blending plant at the job site on SBD 95 to the construction site was 0.0 to 7.3 miles. The plant for both the hot pre-coated chips and the asphalt rubber was set up in the interchange loop with Route 40. The materials viscosity at 375 F was between 2,000 to 2,500 cp. The specified viscosity at the job site prior to placement was 1,500 to 2,500 cp at 375 F per ASTM D 7741 for AR. The viscosity was tested at the job site prior to application by Trinity Engineering Laboratories, with only VSSI performing viscosity readings at the plant site during production. 65

73 66

74 67

75 68

76 69

77 70

78 71

79 72

80 73

81 74

82 75

83 3.5 APPENDIX C-6---CP2 CENTER S TESTING RESULTS 76

84 77

85 78

86 79

87 80

88 81

89 82

90 83

91 84

92 Cone Penetration 85

93 Resilience 86

94 CT 202, CT 226 Sieve Analysis (Not performed by CP 2 Center) 87

95 Mass Loss Tests 88

96 Softening Point Summary of Test Results 89

97 Aggregate Gradation Test Results 9/29/2014 Uncoated Chips 9:50am Plant Hwy 95 Split Sample WT = 3614 grams Sieve # Seive Wt (g) Sieve + Mtrl Mtrl % Retained % Passing Spec 1" /4" /2" /8" # # # # # # # /2/2014 SET #1 Split Sample WT = 2577 grams Sieve # Seive Wt (g) Sieve + Mtrl Mtrl % Retained % Passing Spec 1" /4" /2" /8" # # # # # # #

98 10/04/2014 Uncoated Chips 12:30pm Plant Hwy 95 Split Sample WT = 2561 grams Sieve # Seive Wt (g) Sieve + Mtrl % Retained % Passing Spec 1" /4" /2" /8" # # # # # # #

99 10/2/14 Uncoated SET #2 Split Sample WT = 2572 grams Sieve # Seive Wt (g) Sieve + Mtrl Mtrl % Retained % Passing Spec 1" /4" /2" /8" # # # # # # #

100 4 APPENDIX D POST CONSTRUCTION PHOTOS, OCTOBER 5, 2014, AND NOVEMBER 15, 2014 AR (Type II) PES 8 may actually be AR (Type I), or a mixture of AR (Type II) and AR (Type I). The blend sheets only showed 159 tons of AR (Type II) being produced, and the Progress Payment for December, 2014, showed approximately 169 tons of AR (Type II) being paid which agrees with the planned quantity. Also, there was more AR (Type I) produced than was needed or used. With Trinity s and APART s testing records, CP2 Center staff has not been able to determine from the viscosity tests which tests on October 4, 2014, were for AR (Type II) and which were for AR (Type I). Location 1 for this project was reviewed by Lerose Lane, CP2 Center staff, on November 15, This was about 5 weeks after the seal coat was placed, and all of the different materials for this pilot project appeared to be performing well. Figure D-1. North End of Project at PES 8. PM , Southbound (November 13, 2014) 93

101 Figure D-2. AR (Type II) or AR (Type I) PES 8 (November 13, 2014) Figure D-3. Near PM 64.04, After RXR, Southbound 94

102 Figure D-4. South of RxR AR (Type II) PESs 5 and 6, Southbound Figure D-5. North of CRR18 MB PESs 3 and 4, Southbound 95

103 Figure D-6. At CRR18MB, PES 3 and PES 4, Southbound Near PM 62.7 Figure D-7. CRR18MB near PM 63.0, Southbound 96

104 Figure D-8. CRR18MB, near PES 3 and PES 4, Southbound Figure D-9. CRR18MB with WMA, Southbound near PM

105 Figure D-10. CRR18MB with WMA, PES 2 (Left), PES 4 (Right) (October 5, 2014) Figure D-11. CRR18MB with WMA, Southbound (November 14, 2014) 98

106 Figure D-12. AR (Type I) PES 3, Looking South near PM 61.2 (October 5, 2014) Figure D-13. AR (Type I) (October 5, 2014) 99

107 Figure D-14. AR (Type I) with WMA, End PES 1 and 2, Southbound, PM (Area of Uncoated aggregate on Left, PES 1) (Nov. 14, 2014) Figure D-15. AR (Type I) with WMA, PES 1, Area of Uncoated Aggregate (Left), PES 3 Burnt Aggregate (Right) (October 5, 2014) 100

108 Figure D-16. AR (Type I) with WMA near PM 60.0, Southbound (November 14, 2014) Figure D-17. AR (Type II) with WMA near PM 59.7, Southbound (November 14, 2014) 101

109 Figure D-18. AR (Type II) with WMA (October 5, 2014) Figure D-19. AR (Type II) with WMA, Southbound (November 15, 2014) 102

110 Figure D-20. AR (Type II) with WMA near PM 59.3, Southbound (November 14, 2014) Figure D-21. AR (Type II) with WMA, Example of Poor Joint near PM 59.0 (October 5, 2014) 103

111 Figure D-22. AR (Type II) with WMA near PM 59.00, Southbound (November 14, 2014) Figure D-23. AR (Type II) with WMA near PM 59.00, Northbound (October 5, 2014) 104

112 Figure D-24. AR (Type II) with WMA Near PES 1 and PES 2, Southbound (November 14, 2014) Figure D-25. AR (Type II) with WMA, PES 4 (October 5, 2014) 105

113 Figure D-26. AR (Type II) Near PM 58.6, Southbound (November 14, 2014) Figure D-27. AR (Type II) Near PM 58.6, Southbound (October 5, 2014) 106

114 Figure D-28. AR (Type II) PES 4, PM (October 5, 2014) Figure D-29. AR (Type II) PES 3, PM , Looking North (October 5, 2014) 107

115 Figure D-30. AR (Type II) End PES 1, PM (October 5, 2014) Figure D-31. AR (Type II), PES 1 and PES 2, Southbound (November 14, 2014) 108

116 Figure D-32. AR (Type II) Near PESs 1 and 2, Looking South, near PM 58.00, Toward Interchange with Highway 40 (November 14, 2014) Figure D-33. AR (Type II) PES 1 (October 5, 2014) 109

117 5 APPENDIX E EMISSIONS No air quality testing was performed on this project. Some air quality estimates may be done from construction photographs. The CP2 Center has not attempted to perform any air quality estimates at this time. 5.1 APPENDIX E-1 OPACITY CHART Figure E-1 shows an opacity chart used by the ARB for emissions. The percent opacity is matched to the pocket smoke chart as shown below. This scale was used to judge the % opacity on the job Figure E-1 Opacity Chart from Whitlow Enterprises 110

118 5.2 APPENDIX E-2 RINGLEMANN EMISSION STANDARD 5.3 APPENDIX E-3 RINGLEMANN EMISSION SCALE The Ringelmann scale is a scale for measuring the apparent density of Smoke. It was developed by Maximilien Ringelmann of La Station d'essais de Machines in Paris in It has a 5 levels of density inferred from a grid of black lines on a white surface which, if viewed from a distance, merge into known shades of grey. There is no definitive chart, rather, Prof. Ringelmann provides a specification; where smoke level '0' is represented by white, levels '1' to '4' by 10mm square grids drawn with 1mm, 2.3mm, 3.7mm and 5.5 mm wide lines and level '5' by all black. A popular version is that published by the U.S. Bureau of Mines in circular 8333 of The British Standard version (BS2742:1969) alters Ringelmann's specification to give a chart similar, on modern paper with modern ink, to the probable appearance of charts produced on earlier, possibly darker, paper, with paler ink. The data obtained has definite limitations. The apparent darkness of a smoke depends upon the concentration of the particulate matter in the effluent, the size of the particulate, the depth of the smoke column being viewed, and natural lighting conditions such as the direction of the sun relative to the observer while the accuracy of the chart itself depends on the whiteness of the paper and blackness of the ink used. In use, the observer glances from the smoke, as it issues from the stack, to the chart and notes the number most nearly corresponding with the shade of the smoke. A clear stack is recorded as No. 0, and 100 percent black smoke as No