BS EN 14771:2012 pdf download – Bitumen and bituminous binders — Determination of the flexural creep stiffness — Bending Beam Rheometer (BBR)
5 Apparatus
5.1 Bending Beam Rheometer (BBR), consisting of a loading frame with test specimen supports,acontrolled temperature liquid bath and a data acquisition system.
5.1.1 The loading frame, consisting of a set of sample supports, a blunt-nosed shaft to apply the load tothe mid-point of the test specimen, a load cell mounted in line with the loading shaft, a means for zeroing theload applied to the specimen, a means for applying a constant load to the test specimen and a deflectionmeasuring transducer attached to the loading shaft. A schematic picture of the device is shown in Figure 1. The loading system, which shall be capable of applying a contact load of 25 mN to 45 mN to thetest specimen and maintaining a test load of 930 mN to 1030 mN within ±10 mN.The rise time from thecontact load to the test load shall be less than 0,5 s. Details of the loading pattern are shown in Figure 2. The loading shaft,which shall be continuous and in line with the load cell and deflectionmeasuring transducer with a spherically shaped end (6,3±0,3) mm in radius. The load cell, which shall have a minimum capacity of no less than 2,0 N and a resolution of atleast 2,5 mN. The LVD-transducer, or other suitable device to measure the deflection of the test specimen thatshall have a linear range of at least 6 mm, and be capable of resolving linear movement of 2,5 um. The sample supports, which shall consist of two non-corrosive metal supports with a (3,0±0,3)mm contact radius and spaced 101 mm to 103 mm apart. The spacing of the supports shall be measured to0,3 mm (see Figure 3).
5.1.2 A temperature measurement device,used as a calibrated temperature transducer that shall becapable of measuring the temperature with an accuracy of ± 0,1 °C over the range of – 36 °C to 0 °℃.Themeasuring head shall be mounted within 50 mm of the mid-point of the test specimen.
5.1.3 A liquid bath,capable of maintaining the desired test temperature near the test sample within±0,2 °C during isothermal conditioning and during the test procedure in the range of – 36 °C to 0 °℃.Bathliquid shall not affect the properties of the bituminous binder being tested. The density of the liquid shall notexceed 1050 kg/m3 at the test temperature.
NOTE 95 % (volume fraction) ethanol has been found to be suitable as a bath liquid. A bath agitator, which shall be used for maintaining the required temperature homogeneity withagitation intensity so that the fluid currents do not disturb the testing process. circulating bath, an optional separate bath unit, cooling the test bath liquid.
5.1.4 A data acquisition and control system, which resolves loads to at least 2,5 mN, test specimendeflection to at least 2,5 um, and bath liquid temperature to the nearest 0,1 ‘C.The software shall control themeasuring system and record time, load deflection and temperature during the test. All the load and deflectionreadings shall be an average of at least five points within±0,2 s of the reporting time.
5.2 Test specimen moulds, with the interior dimensions (6,4 ± 0,1) mm wide, (12,7 ± 0,1) mm deep and (127 ± 5) mm long, fabricated from a suitable metal as shown in Figure 4. The thickness of the two end pieces used for each mould shall not vary from each other in thickness by more than 0,1 mm.
NOTE Small errors in thickness of the test specimen can have a large effect on the calculated modulus because the calculated modulus is a function of the thickness raised to the third power.
6 Preparation of test samples
6.1 General The laboratory sample shall be taken in accordance with EN 58 and prepared in accordance with EN 12594.
6.2 Preparation of moulds Spread a very thin layer of petroleum-based grease onto the interior faces of the dry and clean metal mould sections. Press the plastic strips against the metal faces to force out any air bubbles. Cover the inside faces of the two end pieces with a thin film of de-moulding agent to prevent bituminous binder from sticking to the metal end pieces. Assemble the mould as shown in Figure 4 using O-rings to hold the pieces of the mould together. Ensure plastic sheeting fits so that no raised edges occur on the cast beam.