The effect of the penetration tester is closely related to the following aspects

1、 Instrument parameters and structural design

1. Geometric features of needle body

-The taper of the needle tip must strictly comply with the standard (usually 90 °± 1 °). If the taper is too large, it will increase the penetration resistance, while if it is too small, it is easy to cause the phenomenon of 'sliding needle'

-The diameter error of the needle rod should be controlled within ± 0.01mm, otherwise it will change the pressure distribution

-The needle material must have a hardness of HRC62 or higher and a surface roughness Ra ≤ 0.2 μ m

2. Accuracy of load system

-The loading weight error should be less than ± 0.1g (standard 100g ± 0.1g)

-The release mechanism must ensure free fall motion with a kinetic energy conversion efficiency of ≥ 98%

-The accuracy of the contact load sensor needs to reach a resolution of 0.1N

3. Displacement measurement system

-The precision requirement for a dial gauge is 0.01mm scale, and regular calibration is required for measurement

-The resolution of the optical encoder system should be ≥ 0.005mm

-The flatness error of the measuring reference surface shall not exceed 0.02mm/m

2、 Sample state control

1. Temperature control

-The temperature control accuracy should reach ± 0.2 ℃ (± 0.5 ℃ near the softening point of asphalt)

-Constant temperature holding time: Petroleum asphalt ≥ 1.5h, modified asphalt ≥ 3h

-Temperature gradient control: temperature difference in the thickness direction of the sample ≤ 0.3 ℃

2. Sample preparation

-The pouring height needs to be precisely controlled (standard 50mm ± 1mm)

-Cooling rate affects structure formation: the difference between natural cooling and forced cooling can reach 0.3mm penetration

-Surface treatment requirements: The angle between the scraping plane and the standard horizontal plane should be ≤ 30 °, and the residual layer thickness should be ≤ 0.5mm

3. Homogeneity of the sample

-The rotational viscosity needs to be controlled within the range of 1.5-3.5 Pa · s

-The bubble content should be less than 0.5vol% (5mm level bubbles affect the measurement)

-Aging samples need to simulate actual aging conditions (such as a needle penetration change rate of>40% after RTFOT)

3、 Environmental impact factors

1. Atmospheric pressure correction

-Correction of+0.3mm penetration required for every 1kPa decrease

-High altitude areas need to be equipped with pressure compensation devices (error<5hPa)

2. Humidity control

-When RH>65%, a dehumidification device needs to be configured

-Condensation on the surface of the sample can cause a virtual increase in penetration of 0.5-1.2mm

3. Vibration isolation

-Need to set a rubber isolation layer>5mm

-Laboratory background vibration acceleration<0.05g (10-50Hz frequency band)

4、 Operational standardization

1. Accuracy of alignment

-The deviation between the needle tip and the center of the sample should be less than 1mm

-The verticality error should be less than 0.5 ° (tilting 1 ° will result in a 0.8mm error)

2. Loading program

-During the preloading phase, a contact pressure of 5N ± 1N should be maintained

-The main loading time is controlled to be completed within 2.5 ± 0.5s

-The holding time should be accurate to ± 0.1s (if exceeded by 0.5s, the needle penetration will increase by 2% -5%)

3. Timing of Reading

-Start timing at the end of loading

-For every 1-second increase in reading delay, the average penetration rate increases by 0.15mm

5、 Data processing methods

1. Revise the calculation

-Conversion formula for non-standard temperature: P=P '+Δ T × (T-T0) × K

(K value taken as 0.04mm/℃ for petroleum asphalt)

-Need to deduct the surface settlement of the sample (usually 0.1-0.3mm)

2. Abnormal value discrimination

-Exclude abnormal data based on the principle of 3 times standard deviation

-Allowable range for parallel experiments:<mean 15%

3. Characterization of Results

-Complete testing conditions (including temperature, loading rate, etc.) need to be reported

-Multi point data should be subjected to spatial interpolation analysis (Kriging method is recommended)

6、 Intrinsic properties of materials

1. Colloidal structure influence

-For every 1% increase in asphaltene content, the penetration decreases by approximately 8-12 dmm

-When the colloid index CI>2, the structural recovery effect is significant

2. Modification agent effect

-SBS modified asphalt has a 'phase separation temperature window' (10-25 ℃)

-Nano modified materials reduce the slope of the needle penetration temperature curve by 30% -40%

3. Aging gradient effect

-After aging in the film oven, the needle penetration attenuation rate reaches 30% -60%

-UV aging causes a sudden drop in penetration of the surface layer while maintaining a high internal retention rate