路基宽度26米行车道宽4×3.75米公路一级四车道高速公路（说明书、土方计算表、30张CAD图）
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翻 译 原 文Low-temperature failure behavior of bituminous binders and mixesABSTRACTA research including a large experimental campaign on the thermo-mechanical behavior of different bituminous materials in the large strain amplitude domain is proposed. The primary goal of this paper is to identify and determine the links between the failure properties of bituminous binders and those of mixes at low temperatures.The thermo-mechanical behavior of bituminous binders was evaluated with the tensile strength at a constant strain rate and constant temperatures. The thermo-mechanical behavior of bituminous mixes has been studied byperforming measurements of the coefficient of thermal dilatation and contraction, tensile tests at constant temperatures and strain rates, and Thermal Stress Restrained Specimen Tests. Some pertinent links between fundamental properties of binders and mixes are established. Some characteristics which appear as pertinent and discriminating enough with regard to the low-temperature failure properties of bituminous mixes are presented.Keywords : bitumens, bituminous mixes, rheological behavior, thermo-mechanical properties, failure properties, tensile strength, TSRST, low temperature, brittle, ductile, brittle/ductile transition temperature.INTRODUCTIONThe different domains of bitumen behavior can be illustrated according to the strain amplitude (_) and the temperature (T), at a given strain rate. FIGURE 1 (drawn from (1) and (2) points out : the brittle and ductile domains, where the tensile strength p can be measured, the brittle failure, which could be characterized by the fracture toughness Kc (Linear Elastic FractureMechanics), the linear elastic behavior, characterized by the moduli E and G, the linear viscoelastic domain, characterized by the complex moduli E* and G*, the purely viscous (Newtonian) behavior, characterized by the viscosity , for strains of a few percent, the domain where the behavior is highly non-linear.A bituminous mix has also a complex temperature-sensitive behavior. Its response to a given loading is strongly dependent on temperature and loading path. In addition, at a given temperature and a given strain rate, four main typical behaviors can be identified according to the strain amplitude () and the number of applied cyclic loadings (N) (see FIGURE 2, from (3).This paper is aimed at providing an assessment of the work conducted to date within the framework of a partnership between the “Dpartement Gnie Civil et Btiment” of the Ecole Nationale des TPE, Appia and Eurovia. This study focused on the thermo-mechanical behavior of different bituminous materials in both the small strain domain and the large strain domain, at low and mid temperatures, when considering only a small number of loadings This paper only deals with the characterization of the failure properties (i.e. in the large strain amplitude domain) of bituminous materials, at low and mid temperatures. It may be underlined that this paper completes two previous papers which focused on the linear viscoelastic behavior of bituminous materials (i.e. in the small strain domain) at low and intermediate temperatures (2) and (4).MATERIALSFour very different bitumens have been tested : two pure bitumens (10/20 and 50/70 penetration grade), and two polymer modified bitumens with a high content of polymer, one with plastomer and one with elastomer. The polymer modified binders are named hereafter PMB1 and PMB2. TABLE 1 presents the results of the conventional tests (the Fraass brittle point, the Penetration at 25C and the Softening Point Ring and Ball) initially performed on the different binders.Four different bituminous mixes, made from the 10/20, 50/70, PMB1 and PMB2 bitumens with one type of aggregate and grading, have been tested. The mixture samples had a continuous 0/10mm diorite grading, a 31% void content and a binder content of 6% by dry weight of aggregate.TESTS ON BINDERSSHRP Direct Tensile Tests (DTT)As described in AASHTO TP3 and (5), the SHRP Direct Tensile Test consists in elongating 27mm high bitumen samples at 1mm/min and at constant temperatures. The corresponding strain rate () equals 2.22m/m/h. At least six repeats at each temperature were realized on unaged samples. Apart from the determination of the conventional temperature leading to failure at 1% strain, T=1%, our analysis also consists in characterizing a threshold temperature separating the brittle behavior and the ductile one. Moreover, the tensile strength (maximum tensile stress) and thecorresponding strain for each temperature are considered and represented in FIGURE 3.In our opinion, the ranking of binders in function of their strain tolerance using the parameter T=1% does not seem to be really pertinent in the sense that this approach is rather empirical. This parameter will be hereafter compared with a new concept of brittle/ductile transition temperature of binders, which is introduced at the studied strain rate. The determination of this brittle/ductile transition temperature of binders is explained in the next paragraphs.Any isothermal direct tensile test yields much more data than just failure strain or stress values. In particular, the brittle-like or the ductile-like shape of the stress-strain curve can be examined at each temperature. Athigh temperatures, binders have a purely ductile behavior, whereas at very low temperatures their behavior is purely fragile. Following the considered temperature, the bitumen behavior sweeps from ductile (high temperature) to brittle (low temperature). Nevertheless, at intermediate temperatures, there is a slow evolution of the behavior from a ductile one to a brittle one when decreasing the temperature. Thus, practically, there is no determining an accuratetransition temperature directly from the examination of the shape of the stress-strain curve. In the best case, it is just possible to determine a more or less wide temperature range which corresponds to this slow transition of thephysical properties of binders.From our results, we introduce a brittle/ductile transition temperature of binders at the studied strain rate,Tbdb, which is the temperature at which the tensile strength peaks in the axes tensile strength-temperature (FIGURE3). This makes the determination of Tbdb easier and more accurate since the maximum of the tensile strength may be clearly identified. King et al. (5) have already noticed that when the temperature drops below about -15C, the tensile strength of bituminous mixtures decreases and the tensile specimen fractures at low strain as a brittle failure.The brittle/ductile transition temperature, hereafter named Tbdb (for a strain rate of 2.22m/m/h), can be considered as a pertinent, handy and alternative low-temperature parameter. Its physical meaning is directly linked to the type of fracture process of specimens, which influences the shape of the stress-strain curves.The values of Tbdb are presented in TABLE 1 along with the temperature corresponding to a strain of 1% at failure, T=1%. Tbdb and T=1% are highly correlated with each other (r2=0.977). Nevertheless, further investigations onother bituminous binders are still needed before any definitive conclusion can be drawn.As shown in FIGURE 3, the failure stress results are noticeably scattered at low temperatures, where the behavior is brittle. However, the performance of such a test at intermediate and high temperatures leads to a minor scatter of results. Therefore, from our results on four very different binders, the maximum tensile stress (tensilestrength) seems to be all the more repeatable than the temperature is high (FIGURE 3). As assumed by Largeaud et al. (7), the scattering at low temperature could be explained by the detrimental influence of occlusions of air bubbles in the small section of binder samples.TESTS ON MIXESDirect Tensile Tests (DTT)DTT results on mixesThese tests were performed at constant temperatures between 5C to -46C at constant strain rate. Two very different strain rates (300 and 45000m/m/h) were chosen so as to study the influence of strain rate upon the failure properties of bituminous mixtures. 220mm high cylindrical (diameter=80mm) samples were tested in tension using a servo-hydraulic press at the Eurovia laboratory. The strain in the sample was considered as the mean value of the measures given by three transducers placed at 120 around the sample. Two or three test replicates were performedat each temperature.On one hand, as previously shown by Di Benedetto et al. (8) (9), the experimental results on the four studied bituminous mixtures evidence that the stress at failure (viscoplastic flaw) is highly dependent on the strain rate in the ductile domain (high temperature). On the other hand, the obtained stress at failure only slightly depends upon the strain rate in the brittle domain (low temperature). So, as a first approximation, the tensile strength in the brittle domain can be considered as independent of the chosen strain rate. This point is of primary importance since a high strain rate can be used in the brittle domain in order to save time. Nevertheless, it is noteworthy that Stock and Arand (10) previously stated that in the brittle domain, at very low temperatures, the tensile strength slightly decreases while increasing the strain rate. This point needs to be deepened with further investigation.Furthermore, in reference to the transition temperature concept presented for binders, we introduced the brittle/ductile transition temperature of bituminous mixes, Tfdm, which depends on the applied strain rate (). The difference for the two considered strain rates (300 and 45000m/m/h) can reach 9C. This low-temperatureparameter is reported in TABLE 1 for the two considered strain rates.As illustrated in FIGURE 4 where all replicate results are plotted, the scatter of results is rather small whatever the strain rate and the temperature. The repeatability of such a test on mixes appears as especially good, as well in the fragile domain as in the ductile domain.FIGURE 5 sums up the influence of both the temperature and the strain rate on the brittle/ductile behavior for tensile tests at constant strain rate on binders and mixes.DTT on binders Vs DTT on mixesAs can be seen in FIGURE 6, the tensile strength of binders found with the SHRP Direct Tensile Tests at 1mm/min (2.22m/m/h) is quite close to the tensile strength of mixes at 300m/m/h. This point is noticeable and needs furtherinvestigation. Indeed, as testing bituminous mixtures is very expensive and time-consuming, one of the current great issues is to determine methods in which the properties of mixes could be evaluated with enough accuracy from the properties of the binder and from the mix composition. To confirm these results, next steps could consist in testing another strain rate for binders (150mm/min, i.e. 333m/m/h, if possible) and also different mix compositions. In addition, in the brittle domain at very low temperatures, and only as a first approximation (lack of repeatability), the previous observations (cf. FIGURE 6) allow to consider that the tensile strength of binders equals the tensile strength of mixes which does not depend on the strain rate (FIGURE 4). To our knowledge, this statement which is sometimes supposed to be valid has been but little experimentally checked. Moreover, this statement is of the utmost importance since the failure in mixes could be predicted, as a first approximation, from the failure in binders. For instance, as regards the current revision of the AASHTO low temperature specification MP1 (MP1A), the failure stress from DTT on binders is incorporated in a comprehensive model to calculate and predict the socalled critical cracking temperature of pavement (11) (12).Coefficient of thermal dilatation/contraction of bituminous mixesThe linear coefficient of thermal dilatation/contraction “” depends on the thermal characteristics of the components of the bituminous mixture (binder, aggregate and air). It especially highly depends on the binder content since thecoefficient of linear thermal dilatation/contraction of bitumen is some 30 times greater than that of the mineral aggregate (13) (14) (15). In our study, as only one mix design is considered, the influence of the amount of binder and aggregate can not be evaluated.Parallelepipedic asphalt samples (L*W*H = 16*4*4 cm3) of the four types of investigated mixes were laid on their length on a layer of small glass marbles coated with a silicone spray. This base provides nearly frictionless movement. Each sample was submitted to different plateaus of temperature in the range of +24 to 26C. Thetemperature was held constant for about three-hour periods after each increment of around three degrees Celsius.Two identical strain gages are used for each test : the first one is glued on the upper part of the asphalt beam, the second one on the lower part, for not taking into account the flexion of the beam during the test. The average value is considered. A third strain gage was glued on a reference titanium silicate beam, of known -value(0.03m/m/C), in order to account for and correct the effect of temperature. In addition, a temperature probe was used to measure the temperature at the surface of asphalt samples.The thermal strain can be written as follows :=T 1where : linear coefficient of thermal dilatation/contraction (m/m/C)T : change in temperature (C)Thermal equilibriumAfter each temperature change, the temperature is held constant during 3 hours so as to allow the specimen, the titanium silicate beam and the three strain gages to equilibrate at the considered temperature. At the onset of this plateau of temperature, a transitional period is first observed, in which each element is contracting (or dilating) until thermal equilibrium. The transitional period of each element depends i)on its dimensions (the strain gage reaches more quickly the thermal equilibrium than the mix sample), ii)on its thermo-physical coefficients, iii)on the temperature change amplitude, iv)etc. From our results, this transitional period lasts about 1 hour.Experimental coefficientsFIGURE 7 shows that the thermal dilatation coefficient of mixes and their thermal contraction coefficient are really close (see also (16). The two coefficients are hereafter considered as equal. Moreover, FIGURE 7 highlights that the four different mixes have very close thermal contraction coefficients over the considered range of temperature (from -26 to +24C). As Di Benedetto and Neifar (16), using a specially designed test method, and Serfass et al. (17) have already shown, a linear relationship between the thermal contraction coefficient and the temperature can beconsidered, as a first approximation, below 5C. These coefficients vary slowly from around 30 to 15m/m/C while decreasing temperature from 5 to 26C. The thermal contraction coefficient appears as nearly constant at temperatures above 5C, but the excessive creep of the sample makes the measurements inaccurate.The environmental chamber did not allow to investigate temperatures lower than 26C so that no glass transition point (change in the slope of -T curve) could have been identified from our results. It is noteworthy that Di Benedetto & Neifar (16) previously pointed out the anisotropic behavior of mixes.They measured on cylindrical samples the coefficients of both radial and axial thermal contraction. These latter were found to be different (30 to 50%).Thermal Stress Restrained Specimen Tests (TSRST)Typically, restrained cooling tests (or TSRST) are considered as an accelerated performance test to predict lowtemperature cracking of bituminous mixtures. These tests were carried out at a cooling rate of 10C/h from an initial temperature of 5C using a servo-hydraulic press at the Eurovia laboratory and were run in duplicate or triplicate on 250mm high samples (diameter=60mm). A temperature probe was used to measure the temperature at the surface of asphalt samples. The thermal regulation is directly realized from the measured surface temperature. The air in theenvironmental chamber is circulated with a fan so that the temperature distribution is uniform. The strain in the sample was considered as the mean value of the values given by three transducers placed at 120 around the sample.This strain is kept equal to zero during the whole test. As the material is restrained, its tendency to shorten results in the development of a tensile stress that produces failure. The strain can be modeled as the sum of a “thermal” strain and a “mechanical” strain :with: mechanical strain, described by the DBN viscoplastic model (24-25) (not developed in this paper);: thermal strain which is equal to . (cf. equation 1).Moreover, as the coefficients of thermal contraction of the four mixes vary from 30 to 15m/m/C when the temperature drops from 5 to -30C (FIGURE 8), the equivalent mechanical strain rate () ranges from300 to 150m/m/h during the restrained cooling tests (since =0). It is noteworthy that aluminum caps were used tofix samples to the MTS hydraulic press in order to avoid excessive shear stresses at the top and at the bottom of samples. The standard value of the coefficient of thermal contraction of aluminum is around 23m/m/C, which is close to that of mixes over the considered range of temperatures.From our results, failure occurs in the brittle domain when the induced thermal stress equals the tensile strength obtained at 300m/m/h (FIGURE 8). This means that the strength of the bituminous mixes seems to be a function of the temperature (18) and the strain rate only, and does not depend upon the previous followed stress and temperature paths. Moreover, to the extent that the tensile strength only slightly depends on the strain rate in the fragile domain (FIGURE 4), it seems possible to forecast the thermal cracking in the brittle domain by means of the tensile strength curve obtained at any strain rate. The temperature which corresponds to failure, the so-called fracture temperature TTSRST, is given in TABLE 1.For equivalent changes in temperature, the lower the thermally induced tensile stress, the better the mix behavior. Likewise, the colder the TSRST fracture temperature, the greater the mix resistance to low-temperature cracking. Therefore, among the four considered bituminous mixes, the two polymer modified mixtures are the bestregarding their resistance to low-temperature cracking.Moreover, the performance ranking of the four considered mixtures which were made from the same mixdesign and four different binders is very discriminating. Thus, for the considered mix design, this confirms that thebitumen property appears as a key factor regarding the resistance to low-temperature cracking of bituminous mixes.The influence of the cooling rate has not been studied during this laboratory work. Mixtures resistance tothermal cracking has been measured under very severe conditions (-10C/h). It is of particular interest to note thatmore realistic pavement surface cooling rates are generally in the range from about 0.5 to 2C/h (19) (20). Amid theresults drawn from the literature, Fabb (21) previously showed that the cooling rate has little effect on the fracturetemperature and the fracture strength when the rate was greater than 5C/h. From the results of Jung and Vinson (22)(23), when considering cooling rates of 1C/h and 10C/h, the relative difference between the amplitudes of inducedthermal stresses can reach 100% near the fracture temperature. Typically, TTSRST is coldest at 1C/h, which can beeasily simulated by the “DBN” law (27). Notwithstanding this fact, the ranking of bituminous materials does notseem to be influenced by the chosen cooling rate. Therefore, the TSRST with a cooling rate of 10C/h can stillprovide rather quickly pertinent information regarding to the low-temperature cracking properties of bituminousmixtures.Eventually, the thermally induced stress of the given mixes may also have been predicted using the lawdescribed by Di Benedetto et al. (24-26) and Neifar et al. (27-28). The prediction is given by the general viscoplastic“DBN law” (Di Benedetto and Neifar) using the results of i)complex modulus tests, ii)the tensile strength of mixesand iii)the knowledge of the thermal contraction coefficient. This procedure consists in a very effective alternative tothe widespread procedures which are based only on the linear viscoelastic properties of these materials. Theinfluence of non linearities for the prediction of the TSRST has been previously evidenced with the DBN law (25)(28). Then, the cracking temperature can be determined from the intersection of the cooling and tensile strengthcurves (27-28). For more details, the reader is referred to the following references (24-28).The mixtures resistance to thermal cycles remains to be tested soon in a complementary study or,alternatively, can be theoretically predicted by means of the “DBN law” for instance. Finding that the rankings ofmixtures regarding to either low-temperature cracking or cyclic thermal resistance are similar could be in particularof great interest.ANALYSIS DISCUSSIONThe parameters T=1%, Tbdb, Tbdm(300m/m/h), Tbdm(45000m/m/h) and the failure temperature at the TSRST,named TTSRST, are presented in TABLE 1 for the four studied bituminous materials. TABLE 2 gathers the correlationcoefficients between all the previously introduced parameters.First, Tbdb and T=1% are highly correlated with each other (r2=0.977). One must bear in mind that thephysical meaning of the introduced Tbdb is directly linked to the type of fracture process of specimens, whichinfluences the shape of the stress-strain curves. That is why this pertinent parameter could be associated to thecurrent low-temperature specification for asphalt binders based up to now on T=1%.Second, for the considered mix design, Tbdm(300m/m/h) and Tbdm(45000m/m/h) exhibit pretty goodcorrelation with Tbdb (resp. r2=0.936 and 0.908) and T=1% (resp. r2=0.929 and 0.925). Moreover, the correlationbetween Tbdb and TTSRST is r2=0.992. This evidences that, at low temperatures, the failure properties of bituminousmixtures can be predicted from those of bitumens.These correlation coefficients between mixes and binders properties still need to be confirmed byadditional tests with other binders and especially other mix compositions.For the considered set of binders, the Softening Point Ring and Ball and the Fraass Brittle Point are notgood indicators of the low-temperature cracking properties of bituminous mixtures. Indeed, the correlationcoefficients of these two traditional parameters with T=1%, Tbdb, Tbdm(300m/m/h), Tbdm(45000m/m/h) and TTSRST are not good. Eventually, the correlation coefficients of the Penetration at 25C with T=1%, Tbdb, Tbdm(300m/m/h), Tbdm(45000m/m/h) and TTSRST appear as not so good. Indeed, as far as the authors know, in the literature, except the results of Jung and Vinson (23) (29) that evidenced pretty good correlation between TTSRST and the Penetration at15C, poor correlation is usually emphasized (5).Finally, as the Penetration at 25C, the Softening Point Ring and Ball and the Fraass Brittle Point are concerned, these conventional tests do not bring relevant information nor do they provide a very accurate ranking regarding to the failure behavior of the bituminous materials at low temperatures. Lets add that the Penetration at 25C and the Softening Point Ring and Ball are not well correlated with the low-temperature criterions since, obviously, they are not associated with the same domain of temperature.CONCLUSIONSA rational approach which consists in comparing the properties of binders and mixes only in the same domain of behavior (the large strain domain up to failure) has been considered in this paper. From our results, the following conclusions can be drawn : A new way of determining the brittle/ductile transition temperature related to the peak of the tensile strength/temperature response curve (at a given strain rate) is proposed. This makes the determination of such a transitional temperature easier and more accurate. For the considered set of binders, the tensile tests on binders and mixes rank the materials in the same manner regarding the rate-dependent brittle/ductile transition temperatures of binders and mixes. As a first approximation, the tensile strength of mixes can be considered as independent of the strain rate in the brittle domain (at very low temperatures). This point is of primary importance since a high strain rate can be used in the brittle domain so as to save time. Only as a rough approximation, in the brittle domain (at very low temperatures), the tensile strength of binders and mixes can be considered as close. This point needs further investigation. An expanded laboratory testing program is recommended to further explore the effects of strain rate and mixdesign on the tensile strength of bituminous binders and mixes. Parameters such as i)the temperature leading to failure at 1% strain at the SHRP tensile tests on binders, ii) and iii)the fragile/ductile transition temperatures of binders and mixes (for given strain rates) and iv)the failure temperature obtained at the TSRST tests have been determined for each material. It has been shown that theselow-temperature parameters well correlate with each other. This series of parameters ranks in the same manner the bituminous materials regarding to their low-temperature properties. That means that these four parameters can be good surrogates to each other. Concerning the relevancy of the traditional parameters (the Penetration at 25C, the Softening Point Ring and Ball and the Fraass Brittle Point), as many other authors have previously stated, bad correlation between the latter parameters and more rational characteristics have been found herein.沥青和沥青混合料的低温破坏性能摘要本文是对含有不同添加剂材料的沥青热力行为在大应变情况下的对比实验进行研究。实验目的是弄清低温和沥青混合料的低温破坏性能之间的关系并且通过测试沥青混合料的在常温.常应变率下的应力来评价它的热力行为。 沥青混合料的热力行为通过量测样品常温常应力下的热稳定系数和热膨胀力被研究。从而建立起基本成分性状和混合物的特性间的关系以得出沥青混合料低温破坏的一些明显的特征。关键字:沥青，含掺合剂的沥青混合料， 流动行为，热力学特性，破坏，拉应力， TSRST ，低温, 脆性，延性，脆、延性随温度的改变。绪论不同的沥青行为能用给定的应变率下广义应变(_)对应的温度（T)来描述 。从图 1(从（1）和（2）得出)可以看出：知道了拉伸应力p时，就能分辨脆性和延性破坏；脆性破坏时, 可以用线弹性系数Kc来表示；线弹性的破坏性质,用模量E 和 G 来表示；线性兼具黏弹性的破坏性质,用复杂模量E* 和 G*,来表示；纯黏性(牛顿体)的破坏性质, 用黏着系数来表示；对于高度非线性的一些张力行为.沥青混合料也表现出对温度复杂的敏感性。 给定的荷载的反应与温度和加载过程有关。 除此之外,对给定的温度和给定的应变率,四种主要的典型破坏行为都能用广义应变()和重复加载次数来表示。(见到图 2, 表(3)本文旨在为“Dpartement Gnie Civil et Batiment” of the Ecole Nationale des TPE, Appia and Eurovia的合作任务提供数据.这项研究同时还关注：当仅仅考虑小的荷载循环次数时，小应变和大应变，较低温度和正常温度条件下含不同掺合剂的沥青材料的热力学行为。本文只讨论广义大应变下的在较低温度和正常温度间变化的沥青混合料的破坏性能。 在早先的两篇论文中我们讨论了（2）号和（4）号试件在小应变条件下从较低温度向中间温度变化时的线黏弹性破坏。实验材料现在四种有显著差别的沥青已经被测试 :二种纯沥青 (针入度分别为10/20 和 50/70), 和二种被称为 PMB1 和PMB2的改性沥青混合料（一种添加的是塑性高聚物，一种加的是弹性高聚物） 表 1 列出了不同的沥青混合料常规试验的结果（弗拉斯脆点，25C的针入度，软化点）测试了四种不同等级的含掺合剂的沥青混合料试件（10/20 ,50/70, PMB1 ，PMB2 ），它们包含有0/10 毫米米间的连续级配的闪绿岩，31%的空隙率，6%的添加剂。结合料测试 SHRP 直接拉伸测试 (DTT)按照AASHTO TP3 和TP(5)的试验规程, 做了SHRP 直接拉伸测试 (DTT),在恒定温度下以1 毫米/ 分钟的速度将沥青混合料试件拉长27毫米，对应的应变率是 2.22 m/m/h 。每个未老化的试件在一个温度点上至少重复测试六次，除了传统试验中在1%的应变时由温度导致的破坏,我们的分析还表明存在一个区分脆性破坏和延性破坏的临界温度,而且, 在每一个温度点上拉伸应力( 最大的张应力) 和它对应的应变也表现在了图3中。我们看来，因为传统方法有相当大的经验成分在其中,T =1% 的容许应变和混合料的功能间似乎并不相关,与含掺合料的沥青混合料在计划研究的应变率下的脆延临界温度的新观点的比较，将在下一段中说明任何的等温直接拉伸试验跟仅用失效应变或应力比起来产生更多数据和更大的价值。在个别试验中，能得到每个温度下脆性或者延性破坏的应力应变曲线。在高温情况下，含掺合料的沥青混合料表现出纯粹的延性行为，但在非常低的温度下又是纯粹的脆性行为。 在他们之间的过渡温度, 沥青的行为从延性 (高的温度) 到脆性 (低的温度)转变。然而，在中间的温度，当温度减退的时候，有由脆到延的缓慢变化趋势。因此，实际地，不能从应力应变曲线上直接得到一个确定的临界温度， 在最好的情形中，也只是可能确定符合混合料物理性质缓慢变化的一个或大或小的温度范围从试验结果中得出：我们得到了在确定应变率下的脆延性转变的临界温度-Tbdb，在应力温度曲线上（图3）对应着拉伸应力的峰值。 因此我们可以更容易更准确的确定Tbdb。 King et al.先前已经发现当温度降到-15C以下时，含掺合剂的沥青的拉伸应力减少并且小应变水平下样品也呈脆性破坏。脆延性转变的临界温度, 由此被命名为 Tbdb(相应于 2.22 m/m/h 的应变率),它是一个相关，便利和可供选择的低温参数它的物理意义直接地和样品的破坏类型相关，影响着应力-应变曲线的形状。从表 1可以看出1Tbdb 和1% 的应变率失效时对应的温度彼此是高度相关的(r2=0.977)。然而, 需要对其他含掺合剂的进一步的研究,才能得出确定的结论。如图 3 所示, 脆性破坏时的失效应力具有明显的散布性。然而, 在中高温度时，相同测试的表现得到了不那么散布的结果因此,从对四种非常不同沥青混合料的上的试验结果来看, 最大的张应力 (抗拉强度）的可重现性似乎比温度的高得多。混合料测试直接拉伸测试 (DTT)混合料直接拉伸测试结果这些测试是在恒定的应变率从 5C 到-46个 C 之间进行的 。 选择了两种非常不同的应变率（300m/m/h和45000m/m/h）来研究它对含掺合剂的沥青混合料的失效特性的影响。我们在 Eurovia 实验室利用液压-伺服压力系统对高为 220 毫米圆柱体试件 (直径80 毫米) 样品的进行了应力测试。样品的应变取试件上呈120放置的应变片的结果的平均值，并且在每个温度点上重复两三次。一方面, 像 Di Benedetto et al(8)(9)先前指出的那样，对四种试件的研究结果证明，在延性破坏领域下（高温条件）的失效应力（黏塑性破坏）和应变率高度相关。另一方面，脆性破坏领域下（低温条件）的失效应力仅仅些微地依赖于应变率。因此, 作为第一近似值,拉伸强度在脆性破坏领域被认为独立于所选择的应变率。这一点很重要，因为在研究脆性破坏领域时我们能用高的应变率来节省时间。然而,值得注意的是Stock和Arand (10)以前发表过在脆性破坏领域，当温度非常低时加大应变率，拉伸强度会稍微的降低。这点需要用进一步的实验研究来深化。此外,关于结合料的转变温度的观念, 我们推荐含掺合剂的脆延性转变温度（Tfdm），它依赖于采用的应变率(?)，对我们采用的两种应变率（300m/m/h和45000m/m/h）Tfdm相差达到9C（如表1所示）。图 4列出了所有的统计实验结果，不同的应变率和温度的结果散布性相当的小对混合料的这种测试在脆性和延性破坏领域都具有很好的可重复性。图 5 总计出了含掺合剂的混合料在恒定应变率下的应力测试中（脆性和延性）的温度和应变率的影响。结合料的 DTT Vs 混合剂的 DTT像能在图 6 中见到的那样,结合料的按SHRP直接拉伸试验在1毫米/分钟(2.22m/m/h)时的拉伸强度和混合料在300m/m/h时的拉伸强度相当接近。这点是引人注目的,并且需要更进一步的研究。的确, 因为含掺合剂的沥青试验费用昂贵和耗费时间,现在的大课题之一是决定哪一种方法，能足够精确的从结合剂和混合料组成成分的性质来评价它的性质。为了证明这些结果，下一个步骤可以在于测试其他的应变率（如果可能150 在毫米/分钟,也就是 333m/m/h, )下的结合料和不同组成成分的混合剂。我们知道,这一观点尽管缺少试验的佐证但还是被认为是有效的，而且，这个观点是极为重要的，因为从结合剂的失效就可以预测混合料的失效。举例来说, 按照 AASHTO 重新校订的低温规格 MP1(MP1A),很多的结合剂试件的 DTT 的失效应力被用来计算和预测 材料的破坏温度(11) (12)。沥青混合料的热膨胀收缩系数线形热膨胀收缩系数 仰赖于沥青混合料组成成分（结合剂，骨料，空气）的热特性。尤其是高度地仰赖结合剂成分，因为沥青的线形热膨胀收缩系数比骨料的要大30倍(13) (14) (15)。在我们的研究中,因为只考虑一种混合料,结合料和骨料的数量的影响没办法估计。把四种长方体(L*W* H=16*4*4 cm3)的柏油样品的长向放置在涂满矽树脂水磨大理石面上，他们的摩擦力可以忽略不计。每个样品在 +24 到 26 C之间试验，温度的每阶增量为3摄氏度，并维持3小时不变。 每个测试中使用两个相同的应变片:第一个贴在沥青梁的上表面，另一个贴在下表面，取它们的平均值来消除测试期间梁弯曲的影响。第三个应变片贴在参考的钛矽酸盐梁（为0.03m/m/C）上来补偿环境温度的影响。 除此之外，用一个温度探头来测量沥青样品的表面温度。热应变可以写成下面的表达式： = T 1其中 是线热膨胀系数 T是温度改变量热的平衡在温度变化之后, 在 3 小时期间内保持为常数,以便让钛矽酸盐梁和三个应变片在这个温度下达到热平衡。在每一个温度下达到热平衡之前，观察各个部分是缩短还是变长，每个部分的变化时期长短依赖 i) 它的尺寸上 ( 应变片对热平衡的反应比混合料的快多了），ii)它的thermo-physical系数,iii)温度的变化范围，iv)等等。从我们得到的结果来看，变化时期要持续一个小时。从图 7来看， 混合料的热膨
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