NB/SH/T 0815-2010 Determination of burning behaviour of asphalt — Oxygen index method

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Card type: Test method

1. Method number / full title / English title / replacement relationship

• Standard number: NB/SH/T 0815-2010
• Chinese title: Determination of burning behaviour of asphalt — Oxygen index method
• English title: Asphalt—Determination of burning behaviour by oxygen index
• Adoption relationship: Modified adoption of ISO 4589-2:1996 "Plastics — Determination of burning behaviour by oxygen index (room temperature test)" (English version), MOD
• Replacement relationship: not provided in the available source (the foreword states "this standard is first published")
• Publication/implementation: published on 2010-05-01, implemented on 2010-10-01
• Issuing authority: National Energy Administration
• ICS 75.140; E 43

2. Scope of application and non-applicability

• Scope of application: no explicit "Scope" chapter text is provided in the available source (source-text extraction missing).
• Non-applicability: not provided in the available source.

3. Method principle

No independent "Principle" chapter is provided in the available source. From 8.1 to 8.6 and 9.1 it can be summarized: under specified conditions, an oxygen-nitrogen mixed gas is used to ignite a vertically mounted asphalt test specimen; by changing the oxygen concentration and recording the burning characteristics of the specimen ("O"/"X"), the oxygen index OI is calculated according to formula (1). No clause titled "Principle" is provided in the available source.

4. Reagents and materials (purity / preparation)

• 5.1.3 Gas sources: oxygen shall meet the requirements of GB (standard number requires confirmation against the source standard (source-text extraction)), and nitrogen shall meet the technical requirements of GB 3864.
• 5.2 Igniter fuel gas: propane, butane, liquefied petroleum gas, natural gas, etc.; for arbitration tests, propane not mixed with air shall be used as the ignition gas.
• 6.1 Glass fibre surface mat: glass fibre surface mat of specification 50 g/m².
• 6.2 Release agent: prepared by mass from glycerol and talc in the ratio 2:1.
• 6.3 Release paper: kraft paper of thickness 0.1 mm～0.2 mm (the original text "Imm ~0.2mm" is suspected to be 0.1 mm, requires confirmation against the source standard (source-text extraction)).

5. Apparatus and equipment

• 5.1.4 Gas measurement and control system: composed of a regulating valve, a rotameter with accuracy of ±0.5% (volume fraction), a pressure reducer, etc. The rotameter shall be calibrated at least once a year.
• 5.2 Igniter: a tube that can be inserted into the combustion column to ignite the specimen, with a nozzle diameter of 2 mm±1 mm; the flame shall point vertically downward, and the flame length shall be 16 mm±4 mm.
• 5.3 Timer: range at least 5 min, accuracy ±0.5 s.
• 5.4 Smoke exhaust system: capable of removing smoke and ash particles produced by combustion, but shall not affect the airflow velocity and temperature in the combustion column.
• 5.5 Mould frame: inner cavity 151 g mm (as in the original text, suspected to be 150 mm×150 mm, requires confirmation against the source standard (source-text extraction)).
• 5.6 Base plate: glass plate or ceramic plate of 250 mm×250 mm.
• 5.7 Scissors: for cutting glass fibre surface mat.
• 5.8 Knife: for cutting specimens.
• Figure 1 Schematic diagram of the oxygen index test apparatus (including igniter, combustion column, specimen, metal mesh, specimen holder, glass beads, oxygen regulating valve, base, oxygen pressure gauge, mixed gas regulating valve, mixed gas flowmeter, mixed gas pressure gauge, oxygen-nitrogen mixer, oxygen flowmeter, nitrogen flowmeter, nitrogen regulating valve, nitrogen pressure gauge, etc.).
• Figure 2 Specimen holder (unit: mm).

6. Recommended operating conditions

• Specimen drying: dry in an oven at 120 ℃±2 ℃ for 60 min～90 min (7.1).
• Preheating: preheat in an oven at 120 ℃±2 ℃ for 30 min～45 min (7.2).
• Asphalt heating: heat to a temperature at which it has good fluidity and can fully impregnate the glass fibre surface mat; the maximum heating temperature should not exceed 200 ℃ (7.3).
• The mixed gas in the combustion column shall flow for at least 30 s to remove air (8.2.2).
• The maximum flame application time is 30 s; remove the igniter every 5 s to observe once (8.2.3).
• The top of the specimen shall be at least 100 mm from the top of the combustion column (8.2.1).
• Oxygen concentration change d: 0.2% (volume fraction) (8.6.2, 8.6.3).

7. Sampling and specimen preparation

• 7.1 Take a square piece of glass fibre surface mat with side length 150 mm±1 mm, dry it in an oven at 120 ℃±2 ℃ for 60 min～90 min, then immediately place it in a desiccator to cool to room temperature. At the same time, cut more than 15 sheets of kraft paper of 50 mm×60 mm as release paper for later use.
• 7.2 After weighing the dried glass fibre surface mat (accurate to 0.1 g), place it together with the mould frame and base plate in an oven at 120 ℃±2 ℃ and preheat for 30 min～45 min.
• 7.3 Take an asphalt sample according to GB/T 11147, heat it to a temperature at which it has good fluidity and can fully impregnate the glass fibre surface mat, stir evenly, then weigh an amount of asphalt equal to 25 times the mass of the glass fibre surface mat (accurate to ±1 g). The maximum heating temperature of the asphalt sample should not exceed 200 ℃.
• 7.4 Remove the glass fibre surface mat, mould frame and base plate from the oven, quickly apply the release agent evenly on the base plate, place the mould frame horizontally on the base plate, place three pieces of glass fibre surface mat overlapping into the mould frame, pour the hot asphalt evenly over them to impregnate them, after cooling to room temperature wipe off the release agent with a dry cloth or soft paper, trim off 15 mm±1 mm from each of the four edges, then cut into specimens of length 110 mm～120 mm and width 6.5 mm±0.5 mm; each group shall have at least 15 specimens.
• 7.5 As shown in Figure 3, roll up the above cut asphalt specimens from one end with release paper for later use.

8. Analytical procedure

• 8.1 Determination of the starting oxygen concentration at the beginning of the test: ignite one specimen in air and observe the burning behaviour. Rapid burning → initial oxygen concentration about 18%; slow or unstable burning → about 21%; cannot sustain burning → at least 25%. The formula for calculating oxygen concentration is given in Annex A.
• 8.2 Specimen mounting and ignition:
  • 8.2.1 Clamp the specimen in the holder and mount it vertically in the centre of the combustion column; the top of the specimen shall be at least 100 mm from the top of the combustion column.
  • 8.2.2 After determining the oxygen concentration according to 8.1, look up the corresponding oxygen and nitrogen flow rates from Annex B, adjust the flow rates, and let the oxygen-nitrogen mixed gas flow in the combustion column for at least 30 s to remove air. This process shall be repeated before each specimen test. The airflow velocity and oxygen concentration shall not be changed during ignition and burning.
  • 8.2.3 Ignite the igniter, adjust the flame to the specified length, insert the nozzle into the combustion column, and let the flame fully contact the top surface of the specimen but not contact the side surfaces. The maximum flame application time is 30 s; remove the igniter every 5 s to observe once. If it cannot be ignited within 30 s, increase the oxygen concentration and continue ignition until it is ignited within 30 s. When the entire top surface of the specimen burns, it is considered ignited; immediately start timing and measure the burning length.
• 8.3 Evaluation of burning characteristics:
  • 8.3.1 If the burning time is less than 180 s or the flame self-extinguishes before burning 50 mm, record the characteristic "O", and record the burning time and burning length.
  • 8.3.2 If the burning time exceeds 180 s or the burning exceeds 50 mm, record the characteristic "X", and extinguish the specimen.
• 8.4 Principle for selecting the next oxygen concentration: if "O" is obtained, increase the oxygen concentration; if "X" is obtained, decrease the oxygen concentration.
• 8.5 Determination of the initial oxygen concentration: change the oxygen concentration in appropriate steps and repeat 8.2～8.4 until the difference between two oxygen concentrations (volume percentage) is not greater than 1.0% and one is "O" and one is "X". Record the oxygen concentration of the specimen with characteristic "O" among these two specimens as the initial oxygen concentration C₀.
• 8.6 Change of oxygen concentration:
  • 8.6.1 Using the initial oxygen concentration C₀, repeat 8.2～8.4, record the "O" or "X" characteristic corresponding to C₀ as the first value of the N_T and N_L series.
  • 8.6.2 Using 0.2% (volume fraction) of the total mixed gas as the oxygen concentration change d, repeat 8.2～8.4, measure a set of oxygen concentration values and corresponding characteristics until a characteristic different from 8.6.1 is obtained. The results obtained from 8.6.2 plus the same characteristic obtained from 8.6.1 constitute the results of the N_T series (see the example in part 2 of Annex C).
  • 8.6.3 Keep d=0.2%, repeat 8.2～8.4, continue testing 4 specimens, record the oxygen concentration and corresponding characteristic of each specimen, and denote the oxygen concentration of the last specimen by C_f. These 4 test results together with the last test result in 8.6.2 constitute the remaining part of the N_L series, N_L=N_T+5 (see the example in part 2 of Annex C).

9. Qualitative and quantitative determination and calculation formulas

• 9.1 Oxygen index calculation: OI = C_f + kd …… (1)
  • OI: oxygen index expressed as volume percentage; when calculating the standard deviation, take two decimal places; when reporting the oxygen index, take one decimal place;
  • C_f: the last oxygen concentration in the N_L series, taken to one decimal place, %;
  • k: the coefficient obtained by the 9.2 method from Table 1;
  • d: the change in oxygen concentration used in 8.6, taken to one decimal place.
• 9.2 Determination of the k value: the k value and its sign depend on the characteristics of the test specimen tested according to 8.6, and are determined from Table 1.
  • 9.2.1 If the characteristic of the specimen tested in 8.6.1 is "O", then the first opposite characteristic (8.6.2) is "X". From the first column of Table 1, select the row corresponding to the last four characteristics in 8.6.3. The value and sign of k in that row are determined according to the number of "O" characteristics in the N_T series in 8.6.1 and 8.6.2, as the 2, 3, 4, or 5 column. The intersection of the row and column is the required k value.
  • 9.2.2 If the characteristic of the specimen tested in 8.6.1 is "X", then the first opposite characteristic (8.6.2) should be "O"; from the sixth column of Table 1, select the row corresponding to the last four characteristics in 8.6.3. The value and sign of k in that row are determined according to the number of "X" characteristics in the N_T series in 8.6.1 and 8.6.2, as the 2, 3, 4, or 5 column. The intersection of the row and column is the required k value. However, when calculating OI, the sign of the k value should be changed (a positive value becomes negative, and vice versa).
  • Table 1 Determination table for the k value: the source text contains two parts, a (the number of "O" characteristics in the N_T series) and b (the number of "X" characteristics in the N_T series); for the specific values, see Table 1 in the source text (some values in the source-text extraction part are suspected to contain noise and require confirmation against the source standard (source-text extraction)).
• 9.3 Verification of the d value: calculate, according to formula (2), the standard deviation σ of the oxygen concentrations used for the last 6 specimens in N_L (including C_f).
  • σ = [Σ(C_i − OI)² / (n−1)]^(1/2) …… (2)
  • σ: standard deviation of the oxygen concentration;
  • C_i: the oxygen concentration values corresponding to the last 6 specimens in the N_L series;
  • OI: the oxygen index calculated according to 9.1;
  • n: the number of oxygen concentration tests included in Σ(C_i − OI)²; for this method, n=6.
  • When d satisfies (the source text here is incomplete in source-text extraction, requires confirmation against the source standard (source-text extraction)) or d=0.2, then the oxygen index calculated according to 9.1 is valid.
  • If d < (the source text is incomplete, requires confirmation against the source standard (source-text extraction)), then increase d and repeat the 8.6 operation until the condition is satisfied;
  • If d > (the source text is incomplete, requires confirmation against the source standard (source-text extraction)), then repeat the 8.6 operation until the condition is satisfied.
• Appendix A (normative appendix) Calculation of oxygen concentration: C₀ = 100 V₀ / (V₀ + V_N) (the formula source-text extraction in the source text is incomplete, requires confirmation against the source standard (source-text extraction)).
• Appendix B (informative appendix) Comparison table of oxygen concentration and flow rate B.1 (including comparison of C₀/% with V₀/(L/min), V_N/(L/min); for the specific values, see Table B.1 in the source text).
• Appendix C (informative appendix) Examples of test result calculation (including Table C.1, Table C.2, Table C.3).

10. Precision

• Chapter 10 of the source text, "Precision": for materials with stable combustion, this method has the precision shown in Table 2 (Table 2 source-text extraction in the source text is incomplete, requires confirmation against the source standard (source-text extraction)).
• 95% confidence level: repeatability r, reproducibility R (specific values not provided in the available source / requires confirmation against the source standard (source-text extraction)).
• Foreword note: the standard deviation in the precision of ISO 4589-2:1996 was deleted, while repeatability and reproducibility were retained.

11. Report

The test report shall include:

• a. sample name;
• b. type of fuel gas;
• c. test environment temperature and humidity;
• d. oxygen index, %.

12. Referenced documents

• GB/T 11147 (asphalt sampling, referenced by 7.3)
• GB 3864 (technical requirements for nitrogen, referenced by 5.1.3)
• GB (standard number requires confirmation against the source standard (source-text extraction), technical requirements for oxygen, referenced by 5.1.3)
• ISO 4589-2:1996 (modified adoption)

13. Source and verification

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14. Quick Q&A Reference