Asphalt ductility, penetration and softening point are the main parts of asphalt penetration classification system. Often referred to as asphalt three indicators. The accuracy of the test results is directly related to the use of asphalt.

There are three kinds of asphalt grading system: needle penetration grading system, viscosity grading system and Superpave asphalt performance grading system.

(1) Needle penetration grading system, according to the size of the asphalt needle penetration to determine the climate conditions and load conditions adapted to the asphalt. The main parts of the grading system are ductility, penetration and softening point. The grading system is formed by the safety index flash point of asphalt, the purity index solubility of asphalt, the anti-aging property index of asphalt, the film oven test and the constraint index wax content of crude oil used in the production of asphalt.

(2) Viscosity classification system, according to the asphalt or film oven after the asphalt viscosity value at 60℃ to determine the use of asphalt environment and conditions. The viscosity of 60℃ indicates the high temperature performance of asphalt. Other test requirements are also given in the system, such as the penetration of the needle at 25℃, the viscosity at 135℃, the viscosity of the residue after TFOT at 60℃, the ductility at 25℃ and the flash point.

Analysis of influencing factors of three indexes of asphalt (penetration, softening point, elongation)

(3) Superpave asphalt performance grading system, using the dynamic shear mold scale at the highest design temperature of the pavement to characterize the high temperature performance of the asphalt, using the stiffness and stiffness change rate with deformation at the lowest design temperature of the pavement to characterize the low temperature performance of the asphalt, using the dynamic shear mold scale at fatigue temperature to characterize the fatigue performance of the asphalt, The short-term and long-term aging properties of asphalt were characterized by rotary film oven test and pressure aging tank test, respectively.

Asphalt ductility, penetration and softening point are the main parts of asphalt penetration classification system.

Asphalt ductility refers to a specified form of asphalt sample, at a specified temperature at a certain speed to be stretched to break the length, measured in cm. Ductility reflects the extensibility of asphalt material and is an important index to evaluate the plasticity of asphalt. The larger the ductility, the better the plasticity of asphalt. Asphalt ductility, especially low temperature ductility, can reflect the cracking resistance of asphalt, so it is also directly related to the cracking resistance of asphalt mixture.

Needle penetration refers to the depth of vertical penetration of a standard needle with a certain quality into the asphalt sample at a specified temperature and time, measured in 0.1mm. The standard test conditions are temperature 25℃, load 100g and penetration time 5s. The degree of penetration is an index that indicates the hardness and consistency of asphalt, the ability to resist shear damage, and reflects the relative viscosity of asphalt under certain conditions. The penetration index reflects the temperature sensitivity of asphalt and is directly related to the shear resistance and high temperature performance of asphalt mixture.

Needle penetration index is the temperature sensitivity index of asphalt binder, reflecting the degree of needle penetration with the temperature change, the standard stipulates that it should be measured at 15℃, 25℃, 30℃ and 3 or more temperature conditions, and calculated according to the specified method, if the needle penetration value at 30℃ is too large, 5℃ can be used instead.

Analysis of influencing factors of three indexes of asphalt (penetration, softening point, elongation)

At the asphalt softening point, the sample is placed in the metal ring of the specified size, and the steel ball of the specified size and quality is placed in water or glycerin, and heated at the specified speed until the steel ball sinks to the specified distance at the temperature measured in ° C. Softening point reflects asphalt viscosity, high temperature stability and temperature sensitivity.

The equivalent softening point T800 is equivalent to the temperature when the asphalt penetration is 800, which is used to evaluate the high temperature stability of asphalt.

The softening point is also directly related to the high temperature stability of asphalt mixture.

Detection is actually a series of specified operations carried out by the detection equipment on the detection object under specified conditions. Therefore, the six aspects of human, machine, material, method, environment and measurement involved in the whole testing process directly affect the accuracy and effectiveness of the test results. For example, whether the sample extraction is representative, whether the sample processing causes sample deterioration and aging; Whether the equipment has been verified or calibrated, and whether the accuracy can meet the requirements of the method standard; Test whether the environment is effectively controlled and whether the temperature meets the standard requirements; Whether the method standard is selected correctly and whether it can be tested according to the standard process; Whether the parallel test is carried out, whether the test error meets the standard requirements, and whether the data processing is correct. In particular, these aspects are operated by people, and people are the biggest influencing factor in the detection process.

Analysis of influencing factors of three indexes of asphalt (penetration, softening point, elongation)

Environmental control

1. Ventilation and smoke exhaust

2. Test room temperature: 15° C ~30 ° C

3. Temperature of the water bath

Elongation :5 ° C, 10 ° C, 15 ° C, 25 ° C

Penetration :5℃, 15℃, 25℃, 30℃

Softening point: 5℃±0.5℃, 32℃±1.0℃

4. Test water and replacement:

Distilled or purified water should be used for softening points

The water in the densimeter should be alcohol or table salt adjuster with a density similar to that of asphalt

The test water should be replaced when the water is polluted by the spacer or asphalt

The need for ventilation to exhaust smoke in the detection environment is for the consideration of detection safety and personnel health, and is also a basic requirement for the environment.

Room temperature, the standard requirements of the pattern after casting mold should be 15 ° C ~30 ° C, generally speaking, the temperature can be controlled within this range, but it should be noted that the greater the difference between the room temperature and the required temperature of the test, the sample needs longer maintenance at the sample temperature in order to make the internal temperature of the sample consistent with the test temperature. Therefore, controlling the room temperature close to the test temperature is more conducive to obtaining accurate test results. For example, if the room temperature is too high, the sample will not be sufficiently cooled, and the internal temperature of the sample is too high, the test results of penetration and ductility will be too large.

The temperature of the water bath is the biggest factor affecting the test results, and the precision of temperature control is required to reach 0.1℃ for the penetration and elongation of the needle

Softening point Although the required temperature control accuracy is slightly lower, it does not exceed 1 ° C. The water bath must have corresponding heating and cooling functions, and the temperature control accuracy must meet the above requirements. If the water temperature is too high, the penetration and elongation results will be larger, and the softening point results will be smaller. Especially for the ductility test, the change of temperature at low temperature has more influence on the result than that at high temperature.

As for the test water, the softening point should be distilled water or pure water, mainly to avoid bubbles in the heating process affecting the accuracy of the test results, because bubbles will have a flotation effect on the sample, resulting in large test results.

The density of the water in the ductility meter is similar to that of the asphalt, which is mainly to prevent the sample from floating or sinking during the tensile process. Generally, floating will cause high results, and sinking will cause low results.

The replacement of test water mainly considers the turbidity of the water caused by the spacer and asphalt, which will especially affect the observation of the contact point between the test needle and the asphalt during the needle penetration test. If the water is not changed for a long time, it may also produce odor. It is recommended to change the water once a week or so, and shorten the water change time when the water is used frequently.

Sample handling

1, sample validity: variety, specifications, status, quantity (T 0601-2011 asphalt sampling method)
(1) The sample quantity of viscous asphalt (solid asphalt) is not less than 4.0kg. (2) Sampling without stirring equipment in the oil storage tank: the upper, middle and lower positions are taken 1-4L and fully mixed; There is mixing equipment: after mixing, take from the middle.
(3) Sampling valve of tank truck, tank truck and wine distributor: sampling after 4kg outflow; From the discharge adjustment: release all asphalt half sampling; From item cover: Sampler samples from the middle.
(4) Sampling during loading or unloading, sampling from asphalt storage pools, sampling from asphalt carriers to evenly take at least 3 specified quantities of samples at time intervals, and then thoroughly mix these samples before sampling.
(5) The asphalt sample must be stored in a sealed metal container with a lid, and it is strictly prohibited to put it into a paper bag or plastic bag for storage. The sample should be stored in a cool and clean place to prevent sample contamination.
(6) Proper anti-freezing measures should be taken for emulsified asphalt samples in winter.

The validity of the sample is mainly concerned with the representativeness of the sample and the deterioration of the sample (contamination and aging). T0601 of the E20 standard specifies the requirements for sample extraction and storage. Since most testing institutions are commissioned to accept samples, the sampling requirements are not detailed here, but it is necessary to pay attention to whether the number of samples meets the testing requirements, viscous asphalt (solid asphalt) is not less than 4.0kg, and whether the sample is contaminated. The storage of samples must be stored in a sealed metal container with a lid. It is strictly prohibited to put them into paper or plastic bags. The sample should be stored in a cool and clean place to prevent sample contamination. Proper anti-freezing measures should be taken for emulsified asphalt samples in winter.

2, sample melting: heating method, heating temperature, heating time (1) When there is no moisture in the petroleum asphalt, the oven temperature should be 90℃ above the softening point temperature, usually about 135℃. The asphalt sample obtained shall not be heated directly by the open flame of electric furnace or gas furnace. (2) When the sample contains water, it should be heated in the oven at about 80 ° C until the asphalt is all melted for dehydration.
(3) The dehydration of the sample should be heated and dehydrated in a controlled temperature sand bath, oil bath, and electric heating jacket, and asbestos pads must be added when electric furnaces and gas furnaces are forced to be heated and dehydrated. Heat for no more than 30min. Stir gently with glass rod. Under the condition of not more than 100 ° C, careful dehydration until no foam, the final heating temperature should not exceed the softening point of 100 ° C (petroleum asphalt) or 50 ° C (coal asphalt)
(4) The bitumen in the sample holder is filtered through a 0.6mm filter, and is immediately injected into the molds of various tests without equal cooling. If the temperature drops, it can be properly heated in the oven.
(5) The number of repeated heating of the sample after cooling shall not exceed two times to prevent the aging of the asphalt from affecting the test results. In order to avoid mixing air bubbles, the asphalt should not be stirred repeatedly during the asphalt filling mold.

When the sample is heated, the sample should first be uniformly heated as far as possible, and the asphalt aging caused by excessive local or overall temperature and repeated heating should be avoided. After the asphalt aging, the test results of the penetration degree and softening point will be high, and the test results of the ductility will be low. Therefore, the heating should be heated by the oven, and the temperature should be about 90 ° C above the softening point, and the open fire heating of the electric furnace or gas furnace should not be directly used, which may cause the aging of the asphalt.

The dewatering of the sample should be heated and dehydrated on the sand bath, oil bath and electric heating jacket at controlled temperature. When the electric furnace and gas furnace are forced to be heated and dehydrated, asbestos pads must be added. Heating time should not exceed 30min and stir gently with glass rod. Under the condition of not exceeding 100 ° C, carefully dehydrate until there is no foam, and the final heating temperature should not exceed 100 ° C (petroleum asphalt) or 50 ° C (coal asphalt) above the softening point.

In addition, the heated asphalt should be filtered through a 0.6mm filter, which can eliminate the influence of impurities on the one hand, and increase the uniformity of asphalt and exhaust gas on the other hand.

The heated sample is immediately injected into the mold of each test without cooling.

Analysis of influencing factors of three indexes of asphalt (penetration, softening point, elongation)

The following points should be noted in the production of specimens:

(1) Spacer: It is appropriate to apply with a brush, and the spacer can be coated with a thin layer. Too thick will occupy the asphalt space in the mold, resulting in small ductility and softening point results. For the ductility test die, only the inner surface of the bottom plate and side die can be coated, and the end die can not be coated, otherwise the sample will fall off directly and the test will fail. For the mold test of softening point, only the bottom plate can be coated, and the test ring can not be coated, otherwise it will cause the whole asphalt circle to drop and the test will fail.

(2) Casting mold: the asphalt sample of the casting mold should not have bubbles, and the casting mold process should not bring bubbles into the test piece. If there are bubbles, the sample will change from a dense structure to a spongy structure, the density will become smaller, the test result of needle penetration will be larger, and the results of ductility and softening point will be smaller. And the discreteness of each test is increased.

In addition to preventing bubbles from entering, the standard requires that the sample height should exceed the expected needle penetration value by 10mm, and it should generally be installed to be basically the same as the mouth of the sample dish, so as to facilitate the observation of the contact between the test needle and the sample.

Extensibility casting mold, should be from one end to the other end several times, slightly higher than the test mold, shall not mix bubbles. When cooling down, due to thermal expansion and cold contraction, the volume will be reduced, and the casting mold is only poured when it is equal to the saliva of the test mold, the concave height is easy to be lower than the height of the test mold, resulting in the waste of the specimen.

Softening point casting mold: slightly higher than the ring surface can be, too high will flow out of the sample ring stick to the outer wall, resulting in the positioning ring sleeve, heating will also flow, affecting the result.

Analysis of influencing factors of three indexes of asphalt (penetration, softening point, elongation)

(3) Cooling

Injection degree: small cup: not less than 1.5h (15-30℃ room temperature), large cup: not less than 2h (15-30℃ room temperature), special cup: not less than 3h (15-30℃ room temperature)

Ductility: The specimen is cooled at room temperature for not less than 1.5h (15-30℃ room temperature).

Softening point: The sample is cooled at room temperature for 30min (15-30℃ room temperature).

A dust cover is recommended during cooling.

If the cooling time is too long and the sample is cooled sufficiently, the penetration value will be low.

(4) Scraping die

Needle penetration test specimen: do not scrape mold.

Elongation specimen: Use a hot scraper to scrape from the middle to both ends, and the temperature of the scraper should be controlled at about 150℃. If the scraping temperature is too high, it is easy to concave the asphalt surface, resulting in small results, and the scraping temperature is too low, which is easy to make the surface uneven, and the mold should be re-filled.

Analysis of influencing factors of three indexes of asphalt (penetration, softening point, elongation)

Softening point specimen: the requirements are basically the same as the scraping die of the ductility specimen.

The scraping die shall be flush with the test die surface of the specimen, and the specimen surface shall be smooth and shall not be uneven. If the sample is higher than the test mode, the result will be larger, if it is lower than the test mode, the result will be lower, and the uneven surface will increase the dispersion of the result.

04

Equipment control

1, equipment accuracy elongation meter: temperature, speed, length; The water circulation should be interrupted during the drawing process, the drawing speed is 5cm/min 0.25cm/ min, and the drawing degree is 1cm/min 0.5cm /min at low temperature. Softening point instrument: temperature, time, quality, length; An electric furnace with an oscillating agitator should be used, the oscillator is placed at the bottom of the beaker, and the water temperature can be adjusted to rise 5° C/minute within 3 minutes to 0.5° C needle insertion meter: temperature, length, time, quality, whether the equipment is level, the quality of the needle rod and the freedom of sliding, the shape and size of the standard needle are crucial.
2, the equipment pre-remote rotation: the equipment is normal, the temperature is satisfied
3, temperature double control

Equipment accuracy control, temperature control is the key, first of all, the equipment heating and cooling function (softening point instrument generally only heating function), temperature parameter calibration results should meet the standard requirements, the needle penetration and elongation, requiring temperature control accuracy of 0.1 ° C, softening point although the required temperature control accuracy is slightly lower, it does not exceed 0.5 ° C or 1 ° C. In addition, the equipment should have a water circulation device, general ductility meter and needle penetration water bath with a circulating pump, softening point meter with oscillating agitator electric furnace. When there is no stirring device at the softening point, the water in the test cup will form a temperature gradient, affecting the test result. Generally, the temperature under low temperature agitation is lower than that without agitation, and the temperature under high temperature agitation is higher than that without agitation.

Analysis of influencing factors of three indexes of asphalt (penetration, softening point, elongation)

At present, asphalt testing mostly uses testing equipment with a high degree of automation. Attention should be paid to the accuracy of control of other parameters in addition to temperature, such as whether the length measurement of the ductility meter is accurate and whether the drawing speed meets the standard requirements. If the drawing speed of the instrument is too fast, the result will be smaller, and the impact will be greater at low temperature. Softening point meter steel ball diameter and mass (diameter 9.53mm, mass 3.5g±0.05g), if the automatic timing and identification of steel ball drop height (25.4mm), should also calibrate the time and length. Sinking depth, sinking time, quality of needle connecting rod, size and shape of test needle. In particular, if the needle tip is bent and deformed, bending and deformation will lead to small results, and the mass of the needle connecting rod (the total mass of the needle and the pin connecting rod assembly is 50g±0.05g, with a 50g±0.05g weight, the total mass of the test is 100g±0.05g) will be smaller if it becomes lighter, and vice versa. For the needle penetration meter, attention should also be paid to the sliding freedom of the needle connecting rod and the perpendicularity of the test needle and the specimen surface. Large friction resistance or non-vertical test needle will lead to small test results.

In addition, whether the equipment is level will affect the drop of the steel ball during the softening point test, the sinking of the test needle during the penetration test, and the tilt of the equipment will cause the softening point result to be larger and the penetration result to be smaller.

The pre-operation of the equipment is mainly a function of two aspects, one is to see whether the equipment operates normally, and the other is to make the test water temperature meet the test requirements. Most of the current equipment has weak cooling capacity and strong heating function. When the test water temperature is higher than the test requirements, the cooling process is slower, and the equipment should be run in advance. In addition, when the room temperature is relatively different from the test temperature, the equipment should also be run in advance.

Because the temperature is the biggest factor affecting the asphalt test, the temperature should be double controlled in the test, and the temperature of the test water should be measured by the thermometer at any time.

Analysis of influencing factors of three indexes of asphalt (penetration, softening point, elongation)

Test control

1. Specimen maintenance
Needle penetration: small sample 4: not less than 1.5h (15~30° C room temperature) +1.5h (constant temperature tank)
Large sample blood: not less than 2h (15~30° C room temperature) +2h (constant temperature tank)
Special sample dish: not less than 3h (15~30° C room temperature) +2.5h (constant temperature tank)
Ductility: the specimen shall be cooled at room temperature for no less than 1.5h. The test mold together with the bottom plate shall be kept in the water tank at the specified test temperature for 1.5h.
Softening point: After the sample is cooled at room temperature for 30min, it is placed in a constant temperature tank with water of 5° C and 0.5° C for at least 15min; Or at least 15min in a constant temperature bath filled with glycerin at 32 ° C and 1 ° C. At the same time, the metal bracket is also placed in the same sink.

Cooling and insulation of the test specimen. Cooling in the air is to reduce the temperature of the test specimen to room temperature, and insulation in the water bath is to ensure that the internal and external temperatures of the test specimen are the same as the temperature of the test water. Because asphalt is a material with poor thermal conductivity (thermal conductivity 0.6-0.7W/ m2.℃), the specimen must be cooled in the air and kept warm in water for a long enough time, and must be maintained according to the standard requirements. If the curing time is insufficient, the internal temperature of the specimen is higher than the required temperature of the test, which will make the test result of the needle penetration ductness test larger and the softening point test result lower. For the needle penetration specimen, the longer the cooling time is, the better. If the cooling time is too long, the needle penetration value will be low.

2. Control key points

Elongation: Record the breakpoint in the case of low elongation

Penetration: The point of the needle in contact with the asphalt

Softening point: starting temperature and heating rate

Test control key points:

1, ductility test: if the front control point is done well, the most critical thing in the test process is to record the fracture position. Especially for the sample with large elongation, it is possible to pull it very thin and not break (of course, the standard stipulates that if the three test results are greater than 100cm, the test results are recorded as “> 100cm “, special needs can also be recorded separately measured values). The specimen should be cone-pointed when extended, and the actual section is close to zero when pulled apart. If such a result is not available, it should be noted in the report.

2. Needle penetration test: whether the tip of the needle is in contact with the asphalt is the key, and the test can only be started after the tip of the needle is just in contact with the sample surface. The error caused by this factor is a human error, which should be eliminated through repeated practice and experience. The distance between the three measuring points and the edge of the test mold should not be less than 10mm, and the center of the sample plate should be evenly distributed as the center of the circle. If the distance is too small, the structure of the asphalt sample will be damaged, resulting in a larger result.

Analysis of influencing factors of three indexes of asphalt (penetration, softening point, elongation)

3, softening point test: the key is to control the initial temperature and heating speed. The initial temperature should be controlled within the range of 5±0.5℃. If the water temperature does not drop to 5℃, the results will not only be too large, but also increase the dispersion of the results. The heating speed is required to be controlled within the range of 5±0.5℃ per minute. Too fast heating speed will cause the sample and the medium to have no time to heat up simultaneously, and the result will be larger, and the reverse will be smaller.

Data processing

1. Needle penetration: When the difference between the maximum and minimum values of the results of 3 parallel tests of the same sample is within the following allowable error range, the average value of the 3 test results is calculated, and an integer is taken as the result of the needle penetration test, which is 0.1mmit.

2, ductility: when more than one of the 3 measurement results is less than 100cm, if the difference between the maximum or minimum value and the average value meets the requirements of repeatability test, the integer of the average value of the 3 measurement results is taken as the ductility test result, if the average value is greater than 100cm, it is recorded as “> 100cm” ; If the difference between the maximum or minimum value and the mean value does not meet the requirements of the repeatability test, the test should be repeated. When the test result is less than 100cm, the allowable error of repeatability test is 20% of the average value
3. Softening point:
Two parallel tests were conducted, and the average value was taken when the difference met the repeatability error, and the accuracy was 0.5° C, the softening point was below 80° C, the repeatability tolerance was 1 ° C, and the reproducibility tolerance was 4 ° C. The softening point is above 80℃, the repeatability tolerance is 2℃, and the reproducibility tolerance is 8C.

Analysis of influencing factors of three indexes of asphalt (penetration, softening point, elongation)

Needle penetration: When the difference between the maximum value and the minimum value of the results of 3 parallel tests of the same sample is within the allowable error range (the allowable error is 2 when the penetration degree is 0-49, the allowable error is 4 when the penetration degree is 50-149), the average value of the 3 test results is calculated, and the integer is taken as the needle penetration test result, measured by 0.1mm.

Ductility: When more than one of the three test results is less than 100cm, if the difference between the maximum or minimum value and the average value meets the requirements of the repeatability test (when the test result is less than 100cm, the allowable error of the repeatability test is 20% of the average value), The integer of the average value of the three test results is taken as the ductility test result. If the average value is greater than 100cm, it is denoted as “> 100cm “; If the difference between the maximum or minimum value and the mean value does not meet the requirements of the repeatability test, the test should be repeated.

Softening point: two parallel tests, the difference in line with repeatability error (softening point below 80℃, repeatability tolerance is 1℃, reproducibility tolerance is 4℃; When the softening point is above 80 ° C, the repeatability tolerance is 2 ° C, and the reproducibility tolerance is 8 ° C), the average value is taken, accurate to 0.5 ° C.