Evaluation of interlayer shear bond devices for asphalt pavements/Asfaltbetonio dangos sluoksniu sukibimo bandymo metodu ir prietaisu vertinimas/Asfalta segas slanu bides pretestibas noteiksanas iekartu novertejums/Asfaltkatete kihtidevahelise nihkesideme katseseadmete hindamine.

Raab, Christiane ; Partl, Manfred Norbert ; Halim, Abd El Halim Omar Abd El 等

1. Introduction

Due to the increasing demands of the road users as well as increasing rehabilitation costs and decreasing budgets the design and construction of long lasting asphalt pavements is becoming more and more important. Extensive research efforts are still under way world-wide, focusing on the optimisation of the mechanical properties of mixes in the individual layers. However, it was often neglected that not only the material properties of the individual layers but also the interlayer bond play an important role in achieving optimal long-term structural performance of a pavement (Raab, Partl 2004).

As shown in Fig. 1 the bond between asphalt layers is extremely important for the bearing capacity and the long term performance of pavements, a fact that has become more widely accepted during recent years and led to adhesion testing as a subject of study and a development of many different test methods and procedures to evaluate the bond between pavement layers over the last decades.

The reason why it has taken long to formulate qualitative requirements for the bond between the layers of an asphalt pavement may certainly have to do with the great number of parameters influencing this bond as well as their interactions. The complexity of these interactions is also the reason for the difficulties to quantify the single parameters. Fig. 2 names some of the most important parameters for a durable bond between the layers. By listing the different parameters separately it becomes clear that there are many interactions between them. For example mineral aggregate size, binder properties and mixture composition are influenced by the chosen pavement type, while they are responsible of the friction and the interlock properties.

[FIGURE 1 OMITTED]

Consequently it is not surprising that a lot of different methods have been proposed to determine the bond between pavement systems. The following figure (Fig. 3) gives a schematic overview of possible test methods and their application ranges.

The choice of a certain test methods depends on the assumed loading mode and the type of application (e.g. insitu, laboratory), the problem area (e.g. bond failure due to tensile stresses, such blisters or failure due to shear stresses) as well as the accuracy and repeatability of a certain test method.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

During recent years many European countries as well as the United States and Canada have established methods and equipment for testing the interlayer bond. On the one hand, there are methods commonly used in different countries, such as the Leutner shear test (Leutner 1979) which was taken into the national test specifications in Germany shortly after its standardisation in Switzerland and Austria. On the other hand specific solutions such as the wedge splitting test (Tschegg et al. 2007) or the torsion test British Board of Agreement (BBA). Guideline document for the assessment and certification of thin surfacing systems for highways, 2004, Choi et al. 2005) were proposed. In Italy the ASTRA shear apparatus (Canestrari, Santagata 2005) was developed and will shortly become a national specification. In the USA interlayer bond testing has become a serious issue. As a potential option for testing the bond between asphalt layers, (Mohammad et al. 2002) designed a custom made shearing apparatus for use in the Superpave Shear Tester. In Canada, Carleton University, has also been working for many years on the development of an in-situ shear tester (Abd El Halim 2004).

The different test methods, including the various equipment, have been presented in numerous publications (Canestrari et al. 2005; Kruntcheva et al. 2006; Raab, Partl 1999; Stockert 2001; West et al. 2005) in such a way that photographs of the various devices are depicted. But often from these photographs the functioning of the devices is not too clear and detailed information regarding test devices (e.g. gap width) and test conditions (e.g. loading function, normal force) are difficult to obtain.

The following paper tries to give a more complete overall overview of the most important test method for interlayer bond testing, the shear testing, highlighting the differences in terms of test devices, testing specifications and test results for the different devices and countries. The concentration on shear testing was chosen since that test method has been by far the most common method to determine the bond between asphalt pavements. Although, there are many different devices, some of them have already been standardised and common test specifications (deformation rate, test temperature) have already existed in a few countries for some time.

2. Shear testing

The construction of shear testing devices for asphalt pavements originally was derived from shear testing in soil mechanics and already in the late 1970ies different equipments such as the Leutner test (Leutner 1979) in Germany or similar tests in the US were developed (Uzan et al. 1978). There are two fundamentally different systems: the direct and the simple shear test.

The direct shear test, in general, is a guillotine type test where the shear force is induced directly at one side part and not at the front surface of the specimen (Fig. 4). The direct shear testing devices, as depicted in Tables 1 and 2, can be divided in devices which use a clamping or fitting system to hold the test specimen (Partl, Raab 1999; Romanoschi, Metcalf 2002; Sholar et al. 2004; West et al. 2005; Zeng et al. 2008) and devices which utilize a bending mechanism (3 or 4 point shear tests) to apply the shearing (De Bondt 1999; Miro Recasens et al. 2003).

[FIGURE 4 OMITTED]

In the simple shear tests (Table 3) the upper part of the test specimen is sheared against the bottom part of the test specimen and the shear force is induced at the specimen front surface of the specimen. In the case of a three layered specimens (De La Roche 1996; Milien et al. 1996) the middle part is sheared against both outer parts. For the simple shear test, as depicted in Table 3 the mechanism of the different devices is similar, differing mainly in the way the shear forces are applied and how both parts of the test specimen are moved against each other (Canestrari et al. 2005; Sanders et al. 1999).

As opposed to the direct shear tests, where the test specimens can either be clamped or fitted into steel moulds, the test specimens in the simple shear test are always fitted into the shear mould by glue or tight fixtures. Therefore, here the application of a normal force vertical to the shear plane is always an option. Whereas in shear test devices using clamping mechanisms, normal forces are often not taken into consideration. Another possibility to include a normal force was developed by Romanoschi whose testing device allowed for the longitudinal axis of the test specimen being at a 25.5[degrees] angle with the vertical (Romanoschi, Metcalf 2001).

While some shear tests, mainly the ones used of quality assessment, only allow for static testing, others can be used either in a static or a dynamic mode (Ascher, Wellner 2007; Crispino et al. 1997; Romanoschi, Metcalf 2002; Sanders et al. 1999).

Since in Europe most direct shear devices where designed to be mounted in a servo-hydraulic Marshall testing machine, the tests were normally conducted deformation controlled at a rate of 50 mm/min.

Mostly, cylindrical test specimens of 100 mm (Austria) or 150 mm (Germany, Switzerland) taken either directly from the road or laboratory specimens were tested (Stockert 2001). Some devices, such as the modified Empa direct shear device LPDS, could also be used to measure the bonding of rectangular test specimens (Raab, Partl 2007). Normally the specimens were conditioned at test temperatures between 20[degrees]C and 25[degrees]C. Only in the case of research projects have other temperatures of between 10[degrees]C and 40[degrees]C been looked at (Partl, Raab 1999). However, they were found inappropriate for quality assessment, since the higher the temperature, the more difficult to find distinct differences between the different asphalt pavements. Furthermore, specimens may already be damaged during conditioning or during testing (clamping of the specimen).

Most European countries (besides Germany, Austria, Switzerland and the UK) adopted the Leutner equipment, modifying it slightly, for quality assurance of construction sites (Austrian Standard RVS 8S.04.11: 2004) Bending type test set ups where developed for research purposes in Spain and the Netherlands (De Bondt 1999). The Spanish device known as the LCB shear test was developed at the Technical University of Catalonia, Spain (Miro Recasens et al. 2003). Here, cylindrical test specimens were tested at a deformation rate of only 1.27 mm/min. At Delft University in the Netherlands de Bondt (De Bondt 1999) developed a four point shear test where bending effects were minimized through special arrangement of loading and supporting points.

At the Technical University of Dresden the development of a dynamic version of the Leutner shear test, is under way. This dynamic device was constructed by Ascher and also allows for a normal force (Ascher, Wellner 2007). In the dynamic testing of the bond different parameters such as temperature (-10[degrees]C, + 10[degrees]C and + 30[degrees]C), normal load (0 to 1.11 N/[mm.sup.2]) and the loading function (sinusoidal function with amplitudes from 0.005 to 0.1 mm and a frequency from 1 to 15 Hz) were included. The purpose of the project was to find a "bonding factor" which can be used for pavement design in BISAR or in finite element programs.

For the simple shear test deformation rates between 1.5 mm/min in the UK (Sanders et al. 1999), and 2.5 mm/min in Italy (Canestrari, Santagata 2005) were used. In the UK the direct shear test was normally conducted in the dynamic mode, where the specimens were tested under a sinusoidal shear stress with a frequency of 2 Hz. While the vertical stress was kept constant at 200 kN/[m.sup.2], the shear stress was increased in 5 levels (50, 100, 200 and 250 kN/[m.sup.2]) until the specimen failed. If the specimen did not fail during dynamic testing, a static test was performed using the above mentioned deformation rate of 1.5 mm/min. In Italy shear tests were conducted in a static mode using different normal loads (0, 0.2 and 0.4 MPa).

The specimens in the simple shear test, were found to be either prismatic (320x200 mm) (Sanders et al. 1999) or rectangular (max cross section of 100x100 mm) and cylindrical with a diameter between 95 mm and 99 mm (Canestrari et al. 2005).

A simple dynamic shear test for glued three layered specimens, known the Modified Compact Shearing (MCS) test (Millien et al. 1996; Diakhate et al. 2006) was developed at the Laboratory "Mechanic and Modelling of Materials and Structures in Civil Engineering (3MsCE) of the University of Limoges in France. The device allowed conducting static or dynamic tests on glued three layered specimens test specimens with the dimension of 70x100x30 mm. The specimen was placed in a metal frame where the side parts of the sample are fixed while its central part was subjected to a sinusoidal displacement, causing a shear force at both interfaces. The aim of the test program was the investigation of shear fatigue tests of asphalt concrete layer interfaces with emulsions at a constant temperature of 5[degrees]C and a frequency of 1 Hz.

In the US direct shear testing was generally used in quality assessments and research projects, where the main focus was on the evaluation of bonding properties of different tack coat types and tack coat application rates. Different DOTs, asphalt pavement institutes or universities evaluated or modified various guillotine type shear test devices using different clamping and fixing mechanism (Leng et al. 2008; Sholar et al. 2004; West et al. 2005). As depicted in Table 1 the device differed in the fixing mechanism of the specimen as well as in the specimen diameter and the deformation rate of the testing machine. The Iowa Department of Transportation shearing device, a modification of the shearing device for Portland Cement Concrete (PCC) (Test Method No. IOWA 406-B Method of Test for Determining the Shearing Strength of Bonded Concrete by Iowa Department of Transportation Highway Division), was built for 100 mm diameter cylindrical specimens (either roadway cores or laboratory specimens) and with a gap width of 3.175 mm between its steel shearing platens. Further modifications used aluminium rings of 150 mm and a width of 4.8 mm between them to hold the specimen (Sholar et al. 2004).

Some devices, such as the so called NCAT bond strength device (West et al. 2005), where the specimen was held in a metal half cups, also allowed the application of normal forces, which were chosen between 0 and 550 kPa (80 psi). For direct shear testing, specimen diameter generally varied between 95 mm and 150 mm and the deformation rate between 2.5 mm/min, 12 mm/min and 50 mm/min, often depending on the available testing machine.

In the course of another research project Romanoschi (Romanoschi, Metcalf 2002) used a direct shear test device with normal load. The cores ([empty set] 95 mm) were first fixed in a steel split ring, with the interface positioned at the end of the ring. The half outside the steel ring was then placed and fixed in a steel cup positioned vertically and welded to a vertical supporting plate. The position of the interface was adjusted at the rim of the cup using a screwing piston placed inside the cup. To generate the shear at the interface, the vertical actuator pushed on top of the steel split ring with the constant displacement (12 mm/min) until a shear displacement of 12 mm was reached. To this day in the United States different modified Leutner type shear test devices such as (Leng et al. 2008) have been developed and various research projects are still underway. For his research Al-Qadi (Leng et al. 2008) developed a fixture where the test specimens were housed in a special steel camber with a diameter of about 100 mm. The device was designed to apply shear force in the vertical direction and normal force in the horizontal.

To simulate the repetitive load of moving vehicles, in another study Romanoschi and Metcalf (2002) proposed a test configuration to conduct shear fatigue tests on asphalt concrete layer interfaces. The longitudinal axis of the specimen was tilted 25.5[degrees] to the vertical. A vertical load was applied with 10% of the max load and with a frequency of 5 Hz. So, the total period was 0.2 s and the length of the pulse was 0.05 s, simulating the pass of a vehicle at 50 km/h. The corresponding normal stresses at the interface, 0.5, 0.75, 1.0 and 1.25 MPa were within the range of normal stress values for interfaces of road and airfield pavements.

The elastic and permanent displacements at the interface in normal and tangential directions were recorded for each cycle and the dynamic tests were stopped when the permanent shear displacement (PSD) at the interface reached 6 mm or when it was considered that the number of cycles corresponding to a PSD of 6 mm could be extrapolated.

In the course of the American research program SHRP (Sousa et al. 1994) a relatively complicated test device for performing simple shear tests, the so called Superpave shear tester (SST) was developed. Originally the device was not used to evaluate the interlayer shear properties between pavement layers, but to determine permanent deformation and the modulus of asphalt layers.

The SST consisted of shear and axial actuators, load cells and deformation measurement systems, computer control and data acquisition systems, a temperature control and a hydraulic pump. This machine uses closed-loop computer driven control hydraulic pistons connected to vertically and horizontally operating platens. The specimen was normally glued onto aluminum "caps" which were hydraulically clamped to platens inside the temperature control chamber.

Mohammad et al. (2002) performed simple direct shear tests on various types of tack coat materials at several spread rates using laboratory fabricated asphalt specimens. A custom made shearing apparatus was designed and fabricated for use in the SST. Specimens were fabricated in the gyratory compactor in two lifts with a tack coat applied prior to compaction of the second lift. The apparatus was mounted inside the SST and the tests were conducted in constant load mode (222.4 N/min). No normal load was applied to the specimens. The tests were conducted at 25[degrees]C and 55[degrees]C.

As opposed to bond testing using pull-off or torque devices, shear testing is generally performed in the laboratory. In the early 1980s Empa developed a method for shear testing in situ. The shear test with a truck tire was used to test the adhesion between bituminous surface courses and cement concrete layers. Additional to the horizontal shear force a vertical force induced by a single truck tire was applied during the test and the caused deformations were measured (Empa report 1985, not for public use).

In some European countries bond testing was standardised during the 1990s. Although the requirements often stayed below the limits shown in different research projects, standardisation was a first step using shear bond testing on a regular bases in quality control. Research by Raab and Partl (1999; 2008) for example showed that for pavements with stone mastic asphalt (SMA) and asphalt concrete surface courses, a max shear force of 21 kN or 18 kN for the adhesion between the base courses could easily be obtained for 150 mm cores. Nevertheless, Swiss specification only required a max shear force of 15 kN between surface and binder course and 12 kN between a binder and a base course or between two base courses. Theses values correspond to 1.3 N/[mm.sup.2] for the adhesion between surface and base course and 1.1 N/[mm.sup.2] between two base courses when using the shear strength the values. In Germany a research project launched by the German Road Authorities in 2001 (Stockert 2001) and based on approx 500 cores with SMA or AC surface course delivered similar results and proposed the following requirements for the adhesion between the layers:

25 kN for the adhesion surface course/binder course;

20 kN for the adhesion binder course/base course;

16 kN for the adhesion surface course/base course.

In Austria the adhesion testing according to Leutner was conducted on 100 mm specimens and a test temperature of 20[degrees]C [+ or -] 1[degrees]C. According to the RVS 8S.04.11: 2004 for SMA and AC surface and the binder course a min shear strength of 0.8 N/[mm.sup.2] was required when using a non modified binder and 1.2 N/[mm.sup.2] when using a modified binder tack coat. For binder and base courses or two base course layers the requirements were 0.5 N/[mm.sup.2] for non modified and 1.0 N/[mm.sup.2] for polymer modified tack coats. The shear strength in Austria had to be measured parallel to the direction of the traffic.

In Tables 1 to 3 schematic drawings of the different direct and simple shear devices are presented. Since the shear equipment was often not included in standards and testing specifications, the main test parameters such as specimen dimension (core diameter), deformation rate (test speed), test mode (static, dynamic), normal force, temperature, and others parameters such as the gap width between the shear plates according to special are also given.

3. Discussion

As Tables 1 to 3 depict there is a great variety of test devices to test the shear bond of asphalt pavements. The shear tests are inspired by shear testing in soil mechanics and application with or without normal force are used. The application and influence of normal force is one of the issues which have been under debate for quite some time. Many researchers argue that the normal force, representing the wheel load on the road, has to be included in interlayer bond testing. Regarding its influence (e.g. the magnitude of normal force) different opinions and findings are being discussed (Romanoschi, Metcalf 2002; Uzan et al. 1978).

Furthermore, when looking at the presentation and interpretation, as well as the comparison of the test results from different shear devices, no uniform opinion is available. Although some common statements such as the dependency of adhesion tests on temperature or deformation rate are not debated among researchers, there are many divergent results regarding the influence of normal stress, tack coat and surface roughness on the adhesion properties (Raab, Partl 2004; Romanoschi, Metcalf 2002; Uzan et al. 1978; Ziari, Khabiri 2007).

Especially for quality assurance, standards and testing specification only require the interlayer bond values in form of forces since test specifications prescribe specific test specimen diameters. This method is easy for comparison of specimens of equal size, but has a disadvantage for the comparison with other results.

Another distinction between different test devices is their workability and the simplicity of performing a test. Here, devices using clamping mechanisms are preferable over devices where the test specimens have to be glued into moulds. The more time is needed for specimen preparation, and the more cumbersome a test set up becomes (e.g. the MCS device), the greater the influence of unknown variables on the test results and test devices are not likely to be used for daily quality assurance. Looking at the guillotine devices, the different clamping mechanisms play an important role for the workability but they are also important for a defined pressure with which specimens are held during the test (e.g. as in the Empa test device). Furthermore, devices using prismatic specimens are more practical especially for quality assurance since field specimens are mostly drilled cores and even a lot of laboratory specimens such as Marshall and gyratory specimens are prismatic. Some devices are flexible in a way that they allow for the testing of either prismatic or rectangular specimens (e.g. Empa test device, ASTRA test device). Another advantage of the guillotine (Leutner) type devices is that they are very flexible since they can be installed in a common universal testing machine requiring no special test set ups and constructions.

That the comparison of different test devices as well as their results and outcome becomes a more and more important issue shows the inter-laboratory test program initiated by RILEM. Here, research and materials testing institutions from Europe and North America were asked to perform shear tests on pre-selected and defined material under certain test conditions using their specific shear test equipment (Piber et al. 2009). First investigations show that a comparison of results in case of the Leutner device (or some of its modified versions) leads to similar findings and tests using 100 mm or 150 mm specimens provide similar results.

4. Conclusions

The paper presents an extended overview on the existing test shear test devices and gives detailed information on the functioning mechanisms (device figures) and test specifications.

Looking at the different publications and devices the following statements and conclusions can be drawn.

Shear testing seems to be a good and effective method for testing the interlayer bond of asphalt pavements.

In many publications some of these test methods and devices are described by presenting photographs and sketches. Often photographs show the functioning of the devices only insufficiently and detailed information regarding the test devices (e.g. gap width) and test conditions (e.g. loading function, normal force) are difficult to retrieve. Therefore, detailed drawings showing the mechanism of a device as depicted in this paper are preferable.

For the construction of test devices it is important that the test set up is not complicated and the installation of test specimens is simple. Clamping mechanisms are often preferable over set ups where specimens have to be glued or fixed into special moulds. When clamping the specimen, care has to be taken that this procedure does not damage the specimen and does not influence the test results. Therefore, it is important that a defined pressure is used and that the specimen is not tilted during the test.

The gap between upper and lower part of the shear moulds has to be small enough not to induce a bending moment. The device itself has to be sufficiently stiff to enable the occurring forces to be accommodated.

Although shear failure normally occurs in warm climate, moderate test temperatures (around 20[degrees]C) seem to be preferable, as compared to testing at hot temperature the danger of damaging the specimen during testing is smaller.

For the comparison of different test devices, it is important that test parameters such as normal force and deformation rate are comparable. The application of normal forces has an influence on test results and more research is necessary to clearly work out in which way.

Regarding the results from interlayer shear bond testing it is important to compare the outcome of different devices and methods in a detailed way. The above mentioned Rilem interlaboratory test provides a first step in this direction, but here definitely more research is needed.

DOI: 10.3846/1822-427X.2009.4.186-195

Received 30 January 2009; accepted 11 November 2009

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Christiane Raab (1), Manfred Norbert Partl (2), Abd El Halim Omar Abd El Halim (3)

(1,2) EMPA Swiss Federal Laboratories for Materials Testing and Research, CH-8600 Dubendorf, Switzerland E-mails: (1) christiane.Raab@empa.ch, (2) Manfred.Partl@empa.ch (3) Dept of Civil and Environmental Engineering Carleton University CA-K1S 5B6 Ottawa, ON, Canada

E-mail: a.halim@carleton.ca

Table 1. Direct shear test devices (1)

Device Characteristics

Leutner Specimens: cylinders 150 mm or 100 mm
device (Austria), specimens are mechanically
 clamped with a latch fastener

 Gap width: 1 mm

 Testing: static

 Normal force: none

 Method for quality control in different
 European countries (e.g. Austria,
 Germany and Switzerland)

 Deformation rate: 50 mm/min

 Temperature: 20[degrees]C (standard),
 for research 10[degrees]C to 40[degrees]C

 Result: force/deformation diagram, max
 force (stress)

Modified Specimens: grinders 150 mm (standard),
device, others: 148 mm to 155 mm, and
Empa rectangular specimens 150 x 130 mm,
 specimens are hold by defined pneumatic
 pressure using a semicircular damp

 Gap width: 2 mm

 Testing: static

 Deformation rate: 50 mm/min

 Normal force: none

 Temperature: 20[degrees]C (standard),
 other for research 40[degrees]C

 Result: force deformation diagram, max
 force (stress), stiffness (max force/max
 slop of the force/deformation curve) in
 kN/mm

Iowa device Specimens: cylinders 150 mm, specimens
 are fixed in aluminium rings with pipe
 clamps

 Gap width: 4.8 mm

 Testing: static

 Normal force: none

 Deformation rate: 50 mm/min

 Temperature: 25[degrees]C

 Result: force deformation diagram, max
 force (stress)

NCAT device Specimens: cylinders 150 mm, specimens
 are cut and placed in steel cups

 Gap width: 4.8 mm

 Testing: static

 Normal force: 0 to 550 kPa, applied by
 screwing the front pressure plate to the
 steel cups using a latch fastener

 Defomation rate: 50 mm/min

 Temperature: 10[degrees]C,
 25[degrees]C, 60[degrees]C

 Result: force deformation diagram, max
 force (stress)

Romanoshi Specimens: cylinders 95 mm, specimens
device are cut and placed in steel cups
 Gap width: 5 mm

 Testing: static

 Normal force: 0 to 550 kPa

 Defomation rate: 12 mm/min

 Temperature: 15[degrees]C, 25[degrees]C,
 35[degrees]C

 Result: force deformation diagram, max
 force (stress)

Table 2. Direct shear test devices (2)

Device Characteristics

Al-Qadi Specimens: cylinders 100 mm, specimens
device are cut and placed in steel cups

 Testing: static

 Normal force: possible

 Deformation rate: 12 mm/min

 Temperature: 10[degrees]C, 20[degrees]C,
 30[degrees]C

 Result: force deformation diagram, max
 force (stress)

LBC device Specimens: cylinders 100 mm, specimens
 are placed in steel cup

 Testing: static

 Normal force: none

 Deformation rate: 1.27 mm/min

 Temperature: 5[degrees]C to 45[degrees]C

 Result: force deformation diagram, max
 force (stress)

De Bondt Specimens: prismatic specimens
device 450 x 100 x 125 mm Testing: static and
 dynamic

 Normal force: none (possible)

 Loading function: [tau]/[[tau].sub.f] = 0.25,8 Hz

 V Result: force along contact plane-slip
 along contact plane

Asher Specimens: cylinders 100 mm, specimenare
device glued into two steel semicircles Gap
 width: 0 to 15 mm

 Testing: dynamic

 Normal force: 0-1.11 N/[mm.sup.2]

 Loading function: sinusoidal with
 amplitudes of 0.005 to 0.1 mm and
 frequency of 1-15 Hz

 Temperature: -10[degrees]C to 30[degrees]C

 Result: force time diagram and
 deformation time diagram, AK = relative
 deformation between layers/shear stress
 between layers in [m.sup.3]/N

Romanoshi Specimens: cylinders 100 mm, specimen
dynamic are fixed into steel cups, longitudinal
device xis of the specimen is at 25.5[degrees]
 with the vertical axis Testing: dynamic

 Normal force: 0.5, 0.75, 1.0 and 1.25
 MPa

 Loading conditions: vertical load 10% of
 max load, frequency of 5 Hz, total
 period of 0.2 s, length of pulse of 0.05
 s (simulating a vehicle pass at 50 km/h)

 Temperature: 25[degrees]C

 Result: elastic and permanent
 displacements at the interface in normal
 and tangential directions for each
 cycle; dynamic tests were stopped when
 the permanent shear displacement (PSD)
 at the interlace reached 6 mm or when it
 was considered that the number of cycles
 corresponding to a PSD of 6 mm could be
 extrapolated.

Table 3. Simple shear test devices

Device Characteristics

Shear box Specimens: prismatic (320 x 200 mm),
 specimens are in the mould fixed using
 an epoxy glue

 Gap width: approx 10-20 times the mean
 particle diameter of the test specimen

 Testing: dynamic and static, if dynamic
 test does not result in failure
 Deformation rate: 1.5 mm/min

 Normal force: applied servo
 hydraulically, 0, 50, 100, 200 and 250
 kN/[m.sub.2]

 Loading function: sinusoidal shear
 stress with frequency of 2 Hz, vertical
 load 200 kN/[m.sub.2]. While vertical
 stress was kept constant, shear stress
 was increased in 5 levels until the
 specimen fails; if the specimen did not
 fail during dynamic testing, a static
 test was performed with constant
 deformation rate.

 Result: dynamic shear stress-relative
 displacement diagram

ASTRA device Specimens: rectangular, ma x cross
 section of 100 x 100 mm and cylindrical
 with diameters 95 to 99 mm, specimen are
 fix ed in two steel cups

 Gap width: diameter of particle diameter
 of the test speciment

 Testing: static

 Normal force: 0, 0.2 and 0.4 MPa,
 applied by a lever and weight system

 Deformation rate: 2.5 mm/min

 Temperature: variable in climatic
 chamber

 Result:data-file with shear force T,
 horizontal [xi] and vertical [eta]
 displacement related to time

SHRP shear Specimens: cylindrical with 0150 mm,
test device specimen are glued onto aluminum "caps"

SST Testing: static or dynamic

 Loading function: constant load mode
 (222.4 N/min)

 Normal force: none, possible

 Temperature: 25[degrees]C and 55[degrees]C

 Result: shear stress-deformation diagram

MCS device Specimens: three layered specimens test
 sp ecirnens with the dimension of 70 x
 100 x 30 mm, specimen are placed in a
 metal feme where the side parts of the
 sample are fixed while the central part
 is subjected to a sinusoidal
 displacement

 Testing: dynamic

 Loading function: sinusoidal
 displacement, 1 Hz

 Normal force: none

 Temperature: 5[degrees]C

 Result: shear force time and deformation
 time diagrams