AUSTROADS Modified Binder Test MBT 24:2001

Toughness of polymer modified binders

(ARRB Extensiometer)

PREFACE

This Modified Binder Test Method was prepared by an APRG Working Group on behalf of the
AUSTROADS. Representatives of AUSTROADS, ARRB Transport Research and the Australian
Asphalt Pavement Association have been involved in the development and review of this test method.

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FOREWORD

Polymer modified binders (PMBs) exhibit complex rheological behaviour and, consequently, simple
testing equipment will not provide a satisfactory measure of their characteristics. Toughness is a
property which is considered to be an important PMB performance characteristic and is an indication
of the cohesive strength of a PMB under strain and retention of that strength during extension.

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METHOD

1 SCOPE This test method sets out the procedures for the determination of toughness of
PMBs under specific conditions of deformation using the ARRB Extensiometer.

2 REFERENCED DOCUMENTS The following documents are referred to in

this test method:

AUSTROADS
MBT 01 Method of sampling polymer modified binders, polymers and scrap rubber
MBT 02 Protocol for handling polymer modified binders in the laboratory
MBT 21 Elastic Recovery, Consistency and Stiffness of polymer modified binders (ARRB
Elastometer)

3 PRINCIPLE The Extensiometer operates by straining, in tension, a sample of binder

between two parallel end plates, at a controlled elongation rate and to a desired preset elongation. The
resultant force is monitored along with the actual displacement. The normally specified test
temperature is 4°C.

4 APPARATUS
(a) ARRB Extensiometer - either the earlier, manually controlled version, or the later, PC-
controlled version. The Extensiometer is shown in Figure 1, and described in the Elastometer
User Manual (1996).

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(b) Recording device -

For manually controlled instrument: 2-pen Chart recorder, such as a Pantos Model U228-
2P-500, or alternatively a suitable PC based data acquisition system.

For PC controlled instrument: A PC with minimum requirements of a 486/33 with 8Mb

RAM, 540Mb hard disk and operating under Windows 3.1.

(c) Constant temperature bath - capable of maintaining a temperature of 0°C to 25°C to within
± 0.1°C, such as a LAUDA Model MS 20, or equivalent, coupled with an auxiliary cooling
unit, or equivalent device. The water bath must be of suitable dimensions to satisfactorily
accommodate the Extensiometer and provide a water depth of 350 mm for immersion of the
sample. The bath is fitted with a special overflow vessel to achieve this.

(d) Sample moulds - consisting of a silicone rubber mould for casting a square section specimen,
with the dimensions of 9 mm x 9 mm and 25 mm long, integral with two end plates and a
mould keeper.

(e) Forced convection oven - conforming to the requirements of MBT 02.

(f) Thermometer - calibrated for measuring the temperature in the overflow vessel of the water
bath to ± 0.1°C at the required test temperature.

(g) Pouring containers - 50 mL beakers, or small cans, with a pouring lip (other sizes may be
required).

5 CALIBRATION The operational dimensions and accuracy of the instrument must be

checked periodically. The procedure is similar to that for the ARRB elastometer (refer MBT 21),
except for the long travel displacement transducer, and is as follows:

5.1 General
(a) Sample moulds Regularly check the silicone rubber moulds and endplates for damage.

(b) Balance wheel Check the wheel for free movement, after removing the
counterweight cable. There should be negligible friction.

(c) Level Check the level of the instrument regularly to ensure that the pullrod hangs
centrally and clears the hole in the load cell.

5.2 Electronics
The instrument control unit, including chart recorder or PC, must be switched on at least half hour
before use to allow the electronics to stabilise. The instrument must be operated in a stable
temperature environment, as substantial temperature changes can influence the accuracy of the
system. The calibration procedures are as follows:

5.2.1 Manually controlled instruments:

(a) Force A 200 N load cell has been fitted to the Extensiometer. The accuracy of the
load cell can be checked regularly using the built in calibration function (cal). This simulates

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a load application and provides a calibrated reference output, which has been set to 190.00 N.
Firstly, zero the output with the load cell unloaded. Then press the cal button and check the
output as shown on the meter. If the reading is within 0.1% of the reference output, then the
functioning of the load cell can be regarded as correct.

At six monthly intervals, the load cell accuracy should be checked by applying a known load.
This is done by hanging an accurately known mass (5-10 kg) from the load cell and checking
the output, which should be within 0.1%. It may be convenient to remove the sample holder
assembly for this operation.

(b) Speed This should be checked on a regular basis by analysing the displacement versus
time chart during the loading phase. This will also provide a verification of the correct
function of the displacement transducer.

(c) Displacement The calibration of the displacement transducer (LVDT) is checked by

measuring the output for a given displacement of about 200 mm. Using the slow controls,
position the drive unit to the start position and zero the displacement transducer output. Then
move the unit up by about 200 mm and accurately measure the displacement and the
corresponding transducer output. The calibration should correspond to a value of 10 V for a
displacement of 250 mm. (ie. 0.04 V/mm)

5.2.2 PC controlled instruments:

The calibration of Force, Speed and Displacement is fully automated, with minimal actions required
by the operator. The procedures are self-contained, with full instructions on the PC screen via the
control software.

The calibration routines are selected under Calibration in the ARRB PMB Test System main
menu. They are carried out quickly, and it is recommended that a check of the calibration be
performed at least at the beginning of each day of testing.

6 PREPARATION OF SAMPLES

6.1 General PMBs are complex mixtures of polymers and a variety of petroleum products.
If handled in accordance with the directions of the suppliers, there should be no significant risk. The
hazard of burns with PMBs is greater than with standard bitumens, due to the (normally) higher
handling temperatures. It is recommended that notices, describing the action to be taken in the event of
bitumen or PMB burns, should be displayed in the laboratory in the areas where bitumen and PMBs
are handled. A suitable warning could be as follows:

WARNING: HOT BITUMEN & PMBs CAN CAUSE BURNS

The following precautions should be taken when handling bitumen, or PMBs:

(a) Eye protection, such as safety glasses and/or face shields, shall be worn when handling hot
bitumen or PMBs.

(b) Heat-resistant gloves, with close-fitting cuffs, and other suitable protective clothing, shall be
worn when handling hot bitumen or PMBs.

(c) There shall be no smoking while handling hot bitumen or PMBs.

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(d) While the material is still cold, loosen the lid of the sample container (invert the can and warm
the lid, if necessary), or punch a hole in the lid.

(e) Examine the cold sample for the presence of water. If water is thought to be present, drain
most of it out, or blow with clean compressed air to evaporate the free water.

6.2 Sample preparation Samples for testing shall be provided in accordance with MBT
01 and MBT 02.

6.3 Pouring containers These are smaller containers, with a pouring lip to facilitate
pouring of the binder into the moulds. Small beakers (50 mL) are recommended. For higher
consistency binders, a larger number of smaller containers may be needed. For more fluid binders, a
larger container may be used to fill more moulds, before the material becomes too viscous to pour
easily.

Note : The temperatures and times for heating and stirring may need to be varied for certain materials
in accordance with recommendations from suppliers.

7 PROCEDURES

7.1 Chart recorder adjustments

(a) Displacement channel Set the recorder sensitivity to 10 V full scale. This
corresponds to a displacement of 250 mm and is used in conjunction with a break point of 250
mm (ie 100% full scale). For other displacements, when selecting a different break point, set
the sensitivity accordingly. For example, select 5 V for a 125 mm displacement (and break
point).

(b) Force channel Set the recorder sensitivity to 10 V full scale. This corresponds to a
force of 200 N for a full scale chart defle ction.

Note: For lower forces, other sensitivities may be used, eg select 2 V for a force of 20 N.

For repeat testing, where the expected force is known, select an appropriate sensitivity for
that channel. In other cases, initially use the high setting.

(c) Zero check Zero both channels by switching to check mode and using the position control.
Switch back to measure mode for testing. Generally, this operation only needs to be done at
the start of each day and requires occasional checking during testing.

(d) Chart speed Select a chart speed of 60 mm/(min). For the standard test speed of 0.7 mm/s
and displacement of 250 mm, a recorder trace of about 360 mm will be obtained. Use the
normal mode if the chart recorder has been modified.

7.21 Extensiometer adjustments (Manually controlled instruments only)

(a) Mode Switch over to Extensiometer mode, and select either return or stop. In the return
mode, the drive unit returns slowly to the starting position at the end of the test. This mode is
generally more convenient, but the elongated samples can move around and stick to the
instrument. In the stop mode, the drive unit stops at the end of the test. The sample can
then be removed, but the drive unit must be returned manually to the starting position.

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(b) Speed Select a speed of 0.70 mm/s and check the setting accuracy on the meter.
Use the low range of the speed dial (0-10 mm/s).

(c) Break Point Select a break point of 10.00 corresponding to 250 mm travel. Check the dial
setting accuracy on the meter.

(d) Zero Adjust the zero controls for both force and displacement until the red indicator lights
extinguish and the green light is on. This indicates that the zero is within the acceptable
preset limits and can be checked on the meter.

7.22 Extensiometer adjustments (PC controlled instruments only)

The system runs under Windows 3.1, and all operating adjustments are made using the PC.

(a) Select ARRB PMB Test System from the Program Manager to bring up the operations
main menu.

(b) Select the Extensiometer / Run Test function to bring up the Extensiometer Run
Parameters window.

(c) Enter all relevant details of the experiment as requested. The test cannot progress until all
required information has been supplied. The following information will be required:

(i) Run number, Date and Time (automatic).

(ii) Operator.
(iii) Sample mould. Select XA (only one choice at present)
(iv) Temperature.
(v) Speed (or strain rate)
(vi) Break Point (or strain).
(vii) Timer Select required time delay before test starts after pressing START.
(viii) Mode Select Return. (Hold is for future development)
(ix) Sample description. Two lines of text available. *
(x) Comments. (optional). Three lines of text available. *
* Do not use Enter key after the second (or third) line, as this will delete first line of text.

7.3 Preparation of moulds

(a) Assemble the silicone rubber mould with the two end plates in the support keeper.
(b) Heat the assembly to 180°C in the sample preparation oven.
(c) Using a 50 mL beaker, pour the sample slowly into the mould and avoid trapping air. Overfill
to 0.5 mm of the top of the silicone rubber mould.
Be careful not to pour binder on the mould surrounds as the sample cannot be satisfactorily
trimmed afterwards. If trimming is required, this should be carried out by levelling the sample
with a hot blade.

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(d) Allow the specimens to cool at room temperature for 60 minutes, then place in the water bath
for a further 15 minutes before testing. Avoid rapid cooling since rapid contraction can
distort the sample and lead to adhesion failure at the face of the end plate(s).
(e) Trim the surface of the sample if required.

7.4 Loading the sample into Extensiometer

(a) Maintain the overflow vessel of the waterbath at the test temperature, within ± 0.1°C. Due
to thermal losses the waterbath temperature has to be maintained slightly lower than the
overflow vessel.

Note: The normally specified test temperature is 4°C.

(b) Before loading the sample mould into the instrument, ensure that the drive unit is correctly
positioned.

Normally the drive unit is automatically positioned correctly after a test run. If this is not the
case, then position it as follows:

(i) Manually controlled instrument: Switch to run, and using the slow controls, move
the drive unit up about 1 mm and then down until it stops automatically in the correct
starting position. Switch back to standby until ready to test.

(ii) PC-controlled instrument: Using the up/down switch on the motor controller,
move the drive unit up about 1 mm and then down until it automatically stops in the
correct starting position, which is indicated by the illumination of the ready light on the
motor controller module.

(c) Immediately prior to testing, remove the keeper from the mould.

(d) Assemble the sample into the Extensiometer, keeping the silicone rubber mould as support.
Fit the sample so that the shaft of the upper plate locates fully in the pullrod, and secure with
the two grub screws.

(e) Lower the pull rod and sample so that it hangs freely from the load cell, and the shaft of the
lower end plate fits loosely into the base plate. Secure the lower end plate with the two
grubscrews. The silicone rubber mould can now be removed carefully.

(f) Lower the Extensiometer into the overflow vessel.

(g) Leave the sample for 15 minutes to achieve temperature equilibrium before starting the test.

7.5 Testing (Manually controlled instruments only)

(a) Switch to run on the motor drive (red flashing light will extinguish).

(b) Lower both pens of chart recorder. Select normal for the chart drive (if modified).

(c) Recheck zero for force and displacement on the Extensiometer.

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(d) Press the start button to commence the test. Simultaneously (or just before) switch on the
chart drive of the recorder. This will happen automatically if the recorder has been modified.
The Extensiometer will begin straining the sample and will automatically stop when the break
point is reached.

(e) At the end of the test, switch off the chart drive, either directly or using the stop / reset
button, if automatic.

(f) Raise the Extensiometer out of the waterbath. Inspect the sample for any signs of
imperfection in straining, such as uneven cross-section or trapped air bubbles.

(g) Record all test conditions on the chart such as:

(i) Sample description.

(ii) Sample mould.

(iii) Temperature.

(iv) Speed.

(v) Break Point.

(vi) Recorder voltage settings and chart speeds used.

(vii) Comments.

(viii) Operator.

7.6 Testing (PC-controlled instruments only) The Extensiometer can be

started in two modes, either directly, or via a timer delay function. The delay mode has been provided
to allow a 15 minute period for temperature equilibration of the sample, after which the test is
automatically started. (Other times are available if required).

(a) Direct mode Set timer for 0 min. in Run parameters. Leave the sample for 15 minutes to
achieve temperature equilibrium, then click START to start the test.

(b) Timer mode Set timer for 15 min. in Run parameters. Click START as soon as the run
parameters have been entered and the sample has been lowered into the bath. The timer will
then count down for 15 minutes and start the test automatically after this period. The test
sequence and data acquisition will progress fully automatically. While the test is running
progress is displayed on the screen as elapsed displacement.

8 CALCULATIONS

8.1 Manually controlled instrument

Measure the first peak force from the chart and record the displacement at which the maximum force
occurred. Record the displacement at which the sample failed (characterised by a rapid drop in
recorded load) and the load at this point, if it is not the maximum. Record the load at the point of
maximum extension, if the sample did not go to failure.

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Calculate the area under the force-displacement curve to the specified level of displacement for both of
the duplicate tests. Calculate the toughness as the mean of the two tests.

Note 9 Commonly specified displacement levels are 100 mm, 150 mm and 250 mm.

8.2 PC controlled instrument

All calculations are performed within the software with outputs displayed in summary form on the
screen and available in hard copy form.

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9 REPORT
Toughness, in Nm, and the corresponding displacement, in mm.

Force (in N) of the first peak, and the corresponding displacement (in mm) at which it occurred.

10 PRECISION
No inter-laboratory testing has been conducted for the range of PMBs currently available.

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Displacement Transducer
(Elastometer function)

Drive Motor
Counterweight
(Elastometer function)

Load Cell

Lift Rod
Upper End Plate
coupled to drive
Sample assembly

Lower End Plate

attached to
instrument chassis

Figure 1. The Elastometer is shown schematically in Extensiometer mode.

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