Loss onheating test
bitumen Loss onheating test
Bitumens are manufactured to meet certain specifications on delivery to the customer. Their performance, however, depends on their properties after processing and application which the user must take into account when selecting the grade for this process. For example, it is well known that in the asphalt manufacturing process, where the binder is exposed to massive contact with air, a penetration bitumen hardens by about 30 per cent of its penetration value. To avoid excessive hardening and increased brittleness, it is necessary to control the ageing properties of the bitumen as well as the properties on delivery.
The loss on heating test controls the volatility of a bitumen and determines the degree to which it may have been ‘cut’ by a low molecular weight flux. In addition, it was an early attempt to simulate the change in properties of a bitumen in an asphalt plant.
A fifty-gram sample of bitumen in a film approximately 5 mm deep is heated in moving air for five hours at 163°C and the loss in weight is determined.
In an attempt to assess the susceptibility to hardening as well as loss of volatiles, the Thin Film Oven Test, TFOT, (ASTM D1754) was devised. In this test a three-millimeter bitumen film is heated in a similar oven at 163°C for five hours.
A third test has recently been introduced to assess the effect of heat and air on a moving film of bitumen (ASTM D2872), the Rolling Thin Film Oven Test, RTFOT. A sample of bitumen is placed into a glass container fitted with an internal rim. The container is placed on its side and rotated in an oven at 163°C for 75 minutes. An air blast is directed over the sample film once per revolution.
In all these tests the properties of the resultant bitumen compared with those of the original give a measure of the effect of the treatment. Penetration or viscosity changes can be measured. Of the three tests the first is used widely for specification purposes. The TFOT is popular on mainland Europe, whereas RTFOT is used in the UK, to assess the effects of the manufacturing process for road materials on penetration grade bitumens.
For oxidised bitumen no tests have been shown to adequately predict the effects of hardening. This is possibly due to the low temperatures of the tests and/or because of skin formation on the samples.
