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Modified bituminous materials can be used to advantage on roads that are subject to high stress, such as on heavily trafficked sections, sharp bends, and bridge decks, or to wide variations of temperatures. Addition of polymer to bitumen improves the visco-elastic properties by increasing the resistance to permanent deformation at high stresses and temperatures. To encourage more accurate road surfacing design in New Zealand, accurate reproducible measurements of the mechanical properties of both unmodified and polymer-modified bitumens are needed.

Test methods to obtain these data are generally expensive. A low cost analysis technique that has potential for both quality control and performance specification in testing laboratories is torsional braid analysis.

An investigation to test the torsional braid analysis technique was commenced in 1991 using samples of unmodified and polymer-modified bitumens that are used on New Zealand roads. The technique was tested in the frequency range 0.1–0.01 Hz, and in the temperature range 5–60°C. However, the quantitative results for the shear moduli of the bitumens tested were difficult both to interpret and to compare with other results because of the high experimental error, especially in these low frequencies and in this temperature range.

The method without refinements, such as automated data collection, was not entirely satisfactory for the intended application of characterising polymer-modified materials to be used in high temperature and high stress sections of New Zealand roads.

Keywords: Bitumen, pavements, polymer-modified bitumens, rheometry, roads, shear moduli, torsional pendulum, torsional braid analysis