BS EN 14769-2012 pdf download.Bitumen and bituminous binders Accelerated long-term ageing conditioning by a Pressure Ageing Vessel (PAV).
6 Procedure
SAFETY PRECAUTIONS — Use laboratory safety procedures when handling the hot bituminous binders and preparing the specimens and when removing the residue from the pressure vessel Take particular care when lifting the lid of the pressure vessel.
Pre-heat the PAV vessel or forced draft oven to the ageing temperature. The binder is firstly pre-conditioned as necessary, prior to the long-term ageing procedure. The procedure used shall be stated in the report.
If it is necessary to prepare more than one set of samples in the short-term ageing/conditioning procedure (using either EN 12607 series or a stabilisation procedure) in order to obtain sufficient quantity for this procedure, sub-samples shall be combined and homogenised before the test. The stabilisation procedure shall be stated in the report.
NOTE 1 The hot residue may be poured immediately into the container or allowed to cool for PAV ageing later. If allowed to cool, the container with the binder should be covered and stored at ambient temperature. When it is to be used, the sample should be re-heated in accordance with EN 12594 for the miumum possible time and stirred prior to pouring into the container.
NOTE 2 Pre-healJng the vessel up to 15 C above the conditioning temperature may be used to reduce the drop in PAV temperature during the loading process and minimise the time required for stabilisation of the set temperature after loading. However, pressurising the vessel causes an increase in temperature and the vessel may cool slowly, making it difficult to achieve the specified temperature at the start of the test.
Pre-heat the container to the PAV conditioning temperature. Place the heated container on a balance and pour (50,0 ± 0.5) g into the container. Ensure that the binder Is distributed over the entire base of the container by tilting the filled container if necessary.
NOTE 3 The binder film thickness will be about 3.2 mm. The number of containers per binder will depend on the amount of binder required for subsequent testing. The heating of the container should be sufficient to enable the flow of the binder.
NOTE 4 (50,0 ± 0,5) g refers to containers conforming to EN 12607-2. When using containers of a different diameter, the requirement is that sufficient binder shall be poured such that the film thickness will be about 3,2 mm (see 5.5).
Place the pan holder inside the heated pressure vessel and set the ageing temperature to the specified temperature.
NOTE 5 Typical conditioning temperatures are 85 C, 90 °C, 100 °C and 110 C. Typical ageing times found to be suitable are 20 h ± 10 mm for the 90 °C. 100 °C and 110 °C temperature conditions, and 65 h ± 30 mm for the 85 °C temperature condition.
The chemistry of bituminous binder ageing is complex and the mechanism changes with increasing temperature. For this reason, the conditioning temperature should be kept as low as possible. High temperatures may make this ageing procedure unrepresentative of field ageing. The 110 °C condition should be limited to conditioning of binders for use in high ambient temperature (desert) areas.
NOTE 7 Containers containing binders from different sources may be used in the same ageing test. Less than the full set of 10 containers may also be used
NOTE 8 If desired, the change in mass after the long-term ageing may be determined by following the procedure given in EN 12607-2:2007, 6.2. the only difference being the heating period is that which is descnbed in this method.
The loading process into the pressure vessel shall be carried out as quickly as possible to minimise temperature loss.
WARNING: When the temperature within the vessel is 5 °C to 20 °C below the ageing temperature, apply an air pressure in accordance with the manufacturer’s instructions of (2,1 ± 0,1) MPa and commence the test. If the temperature within the PAV fails to reach the ageing temperature within two hours after application of pressure, the test shall be discontinued and the samples discarded.
Maintain the temperature and pressure for a specified ageing time.
If the PAV ageing vessel has reached the ageing temperature within the first two hours and the following conditions occur during the ageing procedure:
— the temperature indicated by the temperature recording device is above or below the set ageing temperature by more than 1.0 °C for more than 60 mm, and
– the pressure is higher than (2,1 + 0,2) MPa or lower than (2,1 – 0,2) MPa of the set pressure for more than 30 mm.
the test shall be terminated and the samples discarded.
At the completion of the ageing time, slowly release the internal pressure in the PAV using the air pressure bleed valve. Adjust the bleed valve as required so that the pressure Is reduced smoothly to atmospheric within a period of 8 mm to 15 mm. The pressure release time does not form part of the 20 h or 65 h ageing time.
NOTE 9 If the pressure is reduced too rapidly, the binder samples may foam.
Open the pressure vessel and carefully remove the pan holder complete with the containers. Place the filled containers in a pre-heated oven set to (170 ± 5) °C for (30 ± 1) mm. When fluid, stir each container to remove any air bubbles. If there is more than one container of any one binder, combine the contents of these containers and pour the hot residue into a suitable, larger, single container,
In some instances, air bubbles may still be entrapped within the binder. If this is the case, transfer the containers with the binder into a vacuum oven set at (170 ± 5) °C. Allow the containers to stand in the oven for (10 ± 1) mm without the vacuum applied. After 10 mm of equilibration, open the vacuum valve and rapidly reduce the pressure to (15 ± 2.5) kPa and maintain this pressure for (30± 1) mm. At the end of the 30 mm, release the vacuum and remove the container from the oven. If a vacuum oven is used, the fact shall be recorded.
NOTE 10 The specified heating times should not be exceeded.BS EN 14769-2012 pdf download.