new way to aging of bitumen in the laboratory.
This article describes the process of developing procedures for aging a thin (300 microns) film for short and long periods of time.The new procedure is being developed as an alternative to the test methods used: rolling thin film oven (RTFO) and aging of pressure (PAV).The new technique, called simple aging procedure (simple aging test, SAT), can be applied to pure and modified bitumen emulsion and residue.Prior to the implementation of the strategic program of road studies there was a significant interest in the aging of the thin film under static conditions.However, for short-term aging technique was adopted RTFO, since tests with the bending beam rheometer required a large number of aged asphalt.Since the adoption of the standard as a method RTFO identified some problems when you try to apply it for the aging of highly modified binders.With reference to the warm mixture RTFO method at lower temperatures (low temperature simulation of manufacture) may impose certain restrictions on the rolled film material for uniform aging.Designed recently rheometer operating on the principle of dynamic shear (DSR) with a 4-mm parallel plates allows testing at temperatures down to -40 ° C, requires only 25 mg binder and allows to evaluate the m-value displacement and stiffness to the bending beam rheometer.Using this technique in conjunction with the SAT to determine the rheology of bitumen, aged short and long term, with low and medium temperature.In addition, there is sufficient material for the aged type DSR rheometer with 25mm plates.SAT The technique eliminates the problem of "rolling" sample of polymer-modified asphalts and warm.In testing several types of bitumen by the procedure SAT been marked time and temperature aging equivalent to these parameters using techniques RTFO and PAV.
Introduction
Solidification on aging under the influence of oxidation - a process that takes place when laying the hot mix, as well as during the life cycle of the pavement.It greatly affects the performance of the coating such as rutting, cracking and separation and, as a result, durability.Modelling of the solidification of aging in laboratory conditions is extremely important for the development of specifications based on performance.This study describes a new method for testing thin-film samples by oxidation, which gives results equivalent to standard procedures rolling thin film oven (RTFO, method ASTM D2872) and aging in a pressure chamber (PAV, the method ASTM D6521) for pure bitumen.The achievement will ensure the effectiveness of the test thin film (several hundred nanometers) - a technique recently developed on the principle of dynamic rheometer shear, which enables testing of samples at temperatures down to -40 ° C, it requires only 25 mg of sample, and includes any adjustment to the strain on the device [1].
Test procedure a thin film of bitumen in the furnace was developed in the early 60s Hveem [2] was adopted in 1970 by ASTM.During the Strategic Programme Road Research it was chosen as the standard for modeling short curing aging which occurs when paving.Currently, a technique used in the specification Superpave bitumen.
main advantage test method of fine bitumen film in an oven of rotation (RTFOT) prior to testing of the thin film in an oven in a static (TFOT, method ASTM D1754) is in the fact that during the rotation of glass vessels aging undergoes large surface area of the sample.However, the number of rotations and the effect on fresh sample surface varies depending on the viscosity of bitumen before testing and viscosity changes during testing.The process of movement and mixing of bitumen in the flasks is further complicated by polymer modification of bitumen.Lowering the temperature tests to simulate RTFO oxidation occurring in the production of warm mix, it causes similar difficulties.
Reduction of rotation or eliminate rotation when tested by the method RTFO for highly modified bitumen - the problem has been known for several years [3].Bahia [3] proposed to solve it by dipping a steel rod in the flask and thus ensure the distribution of the film.Experiments conducted by Federal Highway Administration and the Southeast group asphalt producers showed that steel rods reduce the level of bitumen aging (both modified and unmodified) and contribute to leakage of bitumen (both types) from the flasks. [4]Although steel rod really contributes to the leakage of bitumen from the flask, the polymer-modified bitumens often spill over the edge of the flask, even if there is no shaft.The reason for that - Weissenberg effect (the rise of a viscoelastic fluid on a rotating rod) [5].It is assumed that elastic force (stretching of the polymer chains), caused by the rotation of the glass bulbs, results in a positive vertical direction of force, which causes rise in bitumen on the inner walls of the flask.
Solution of these issues formed the basis for the work of the Western Research Institute (WRI) on a new procedure short and long aging, which was named the simple aging procedure (SAT).She is devoted to this article.
A Method SAT, as an alternative to the standard and RTFO RTFO / PAV, presented the following requirements:
1) The degree of aging should be equivalent to that of the method RTFOT.Up until the Superpave specifications based on tests RTFOT, any new technique must comply with the process of aging RTFOT for pure bitumen.
2) Easy, no need to clean flasks.The test procedure is to allow short-term space aged sample directly into the oven for long-term aging.
3) The amount of bitumen will be sufficient to determine the grade of penetration index (SHRP PG) and the description of the chemical composition.
4) When placing or removing the samples do not have to use a solvent that is particularly important for polymer-modified bitumen.
5) The thickness of the film should be low enough to eliminate the problem of oxygen diffusion is present in the test sample is stationary (TFOT).
6) The methodology should allow to reduce the temperature to simulate the conditions of manufacture of the warm mixture.
7) the test shall be less than the test RTFO or RTFO / PAV.
8) Cost method should be low.
9) The methodology should allow aging of the films from the emulsion residue.
oxidative aging of the film (film thickness of several hundred microns) able to fulfill all the above requirements, but for subsequent tests on asphalt SHRP take a very large surface area of the sample.In particular, the problems become test with the bending beam rheometer, since for each sample sticks take 15 grams of bitumen and need a few such specimens.SHRP Test on medium and high temperatures are carried out on the dynamic shear rheometer (DSR), which requires only a few grams of bitumen.
It has been said that the invention with a dynamic shear rheometer (DSR) with a 4-mm parallel plates allows testing at temperatures down to -40 ° C, requires only 25 mg binder and allows to evaluate the m-value and stiffness displacement [6] for a rheometerwith the bending beam.Next will be given a more detailed description of this technology.Its combination with the method of aging the film - an alternative method RTFOF.Moreover, after the test is enough bitumen for SHRP testing at low, medium and high temperature.
Research and development of new tests in the last decade, mainly have the following objectives:
a) Prepare the test after a few grams of bitumen for the subsequent test with the bending beam rheometer;
b) To solve the problem outflow of bitumen from the flask during the test RTFO;
c) To solve the problem of rolling a polymer-modified bitumen test RTFOT.
Examples include the following methods: test aging of a rotating cylinder (RCAT) [7], a modified German spinner flask (MGRFT) [4], the test with forced ventilation (SAFT) [8].
Experimental part Materials
rheometer is a dynamic shift into 4-mm parallel plates
disagreements regarding the module of glycerol in the glassy state (Gg) made Schröter [9] develop a method of adjusting for the error of dynamic shear rheometer, ittooling and plates.Sui [1] applied to this adjustment measurements of dynamic shear bitumen at low temperatures (~ 5 ° C ... -40 ° C) for a 4-mm parallel plates with a gap of 1.7 mm (in the article, this method is referred to as 4-mm dynamic shear rheometer).
At low frequency (high temperature) bitumen malleable, and error correction tool negligible.At high frequency (low temperature) yielding varies, and in order to obtain the true value of the modulus of brittle fracture bitumen for measuring shear rheometer applied correction.
To test requires only 25 mg of material (in practice - around 150 mg for the manufacture of the sample pattern), which is several orders of magnitude smaller than is necessary for the manufacture of the bar for testing with the bending beam rheometer.
preconditioning of samples is required.Bookmark in rheometer is carried out at a relatively low temperature (60-70 ° C).
In this study, the study of the rheological properties is conducted using 4-mm dynamic shear rheometer.M-unit and the shear stiffness S (t) estimated by correlation with the 4-mm dynamic shear rheometer designed Sui [6].The method Sui base curve angle and the modulus relaxation shear stress G (t) for 2 hours correlated with corresponding values of S (t) and m for 60 seconds at a temperature of 10 ° C above the true low temperature for a given grade, obtainedresulting measurements with a bending beam rheometer.Method Sui changed by measuring the angle and the magnitude of G (t) for 60 seconds at a temperature of 10 ° C above the temperature at SP grade.Rheology at medium and low temperatures measured on the plates of a diameter of 8 mm and 25 mm.
Mutual conversion of the storage modulus G '(ω) in the relaxation modulus is satisfied by the equation approximation derived Christensen [10]:
G (t) ~ G' (ω) | ω = 2 / πt
module measurement of dynamic shearIt was performed on rotating dynamic shear rheometers Malvern Kinexus and TA ARES.Reading frequency sweep was conducted at intervals of 15 ° C in the range from -30 to + 45 ° C with an angular frequency range of 0.1 to 100 rad / sec.At low temperatures, the high-frequency limit of the sweep was reduced to 50 rad / s.
technology use 4-mm dynamic shear rheometer can be used "in the field" for the analysis of micro samples in the evaluation of the performance properties of the coating and analysis of materials, to describe the rheological properties of bitumen and regenerated binding at medium and low temperatures, to describe the rheology of the emulsion sludge and materialfilling cracks, as well as for the development of a test method of a thin film - the object of this article.
Infrared spectroscopy
IR analysis was carried out in a mode of "transmission" in the chamber of 1.0 mm with a sample of 50 mg of bitumen per 1 ml of carbon disulfide.It was carried out 32 cycles of scanning equipment: Perkin Elmer Spectrum 100, the resolution of 4 cm-1.
Materials
Table 1 describes the studied types of bitumen.Samples were taken from the tank during road construction.Three of the four binders prepared test site in Rochester, Minnesota, United States (built in 2006).Bitumen "MV" (Manitoba) received a testing ground for warm mix in Manitoba, Canada, was built in 2010.
Results and discussion
Development methodology SAT, compared with its RTFO and RTFO / PAV
It should be remembered that the idea is not new SAT.Aging thin bitumen films to simulate short and long term oxidative aging, which occurs in an actual operation, widely studied for the past 70 years.The analysis of sources held Airey [11].Development of the method
SAT is to adapt and deepen existing research on the aging of the thin film, in particular, research Glover [8, 12] and Petersen [13].Complement is the use of 4-mm dynamic shear rheometer, which allows us to consider this technique as an alternative to RTFOT.
In developing a SAT problems was to provide the minimum film thickness and thereby reduce the effect of diffusion.By trial and error, it has been picked up the thickness of 300 nm, allowing to provide a thin film without using a solvent.The sample volume for the rheological and chemical research was another limiting factor.
SAT test protocols are given in Table 2: The short-term test for warm asphalt mix at 130 ° C for 50 minutes in an oven with forced blowing.A preliminary protocol, as currently we have just started work on comparison of aging, performed by this protocol and aging, which is actually happening on the road, which laid the warm mixture.
Fig.2 shows the latest designed device for short- and long-term aging of a thin film by the method of SAT.The plate has 3 slots for aging 3 different films, each of them require 1.00 g of bitumen that gives a film thickness of approx.300 nm.
Preparation of thin films of bitumen test is performed as follows.The pressurized working box filled with nitrogen, placed heated (about 120 ° C) the stand, and put it on a plate for testing SAT (bitumen).When heated to 120 ° C spreads the bitumen for about 2/3 of the surface area of the plate.Spatula bitumen is spread over the rest of the plate, and then leave it in the box for a few minutes there was an alignment surface to bitumen film.The plate is then removed from heating and allowed to stand in a chamber filled with nitrogen to cool to room temperature (23 ° C).
The end plate was drilled a hole to insert a thermocouple with which the temperature was recorded in the oven with forced blowing.The plate is placed in a preheated aluminum block which provides rapid heating of the test plate in the furnace.Fig.3A shows data on the temperature in the furnace (a thermocouple in the data plate).Registration was performed for 50 minutes, the furnace temperature - 150 ° C.Plate temperature increases rapidly from ambient to about 140 ° C or reaches 146 ° C after 50 minutes.
scheme of short-term and long-term aging is shown in Fig.3B.Dimensions of the plate are chosen so that the plate can be inserted into a standard tray aging vessel under pressure.
established that the test film thickness of 300 nm for about 40 hours in an oven with forced blowing at a temperature of 100 ° C and a pressure of 0.74 atm give results that conform PAV (ASTM D6521) test film with a thickness of 3.2 mm20 bar in a standard tray.The duration of 40 hours is an approximation, since there is a difference in pressure in the aging of bitumen [14].Aging of the film thickness of 300 nm in a vessel under a pressure of 20 atm for 8 hours to give the level of aging in standard tests with the tray and the film thickness according to the specifications.
To determine the approximate time and temperature at which the simulated aging, comparable to those standards and RTFO RTFO / PAV, used IR spectroscopy.Initial projections were then compared with the testimony of rheological analysis.Thus, in Fig.4A shows the relative IR spectra (SAT, RTFO, RTFO / PAV) bitumen "MV" on the protocols listed in Table 2. Figure.4B shows the corresponding data rheological analysis - complex shear modulus G * (ω).It can be seen that the spectra are very similar.
