BRITTLENESS OF ORGANIC BINDERS AFTER REPEATED TENSION AT NEGATIVE TEMPERATURES

Abstract

ABSTRACT Under real conditions of road pavement operation the films of organic binders are subjected to repeated tensile deformations, in particular, at negative temperatures. In the paper, an attempt to use Fraas apparatus not only for determining the brittleness temperature of binders but also for estimating their long-term strengths at negative temperatures under conditions of repeated tension at bending has been realized. One has investigated bitumens of BND 40/60; 60/90; 90/130 grades and polymer bitumen binders on their base with 2.0; 3.5; 5.0% of block copolymer of SBS type and of DST-30R-01 grade and 20% of plasticizer-industrial oil. For all specimens the Fraas brittleness temperature and also the temperature at which a binder layer on the metal plate cannot withstand 200 cycles of bending tension without developing a large crack have been determined. For bitumens this temperature is 5 to 7°C higher than the corresponding britteness temperature. A polymer bitumen layer withstands 200 cycles of bending tension at the temperature which is 1°C higher than the corresponding Fraas brittleness temperature. The Fraas temperature of the pre-loaded specimen decreases in specific cases by 20°C. It is shown that the crack resistance of polymer bitumen binders is significantly higher and that of bitumens is lower than it is expected according to the procedure of determining the Fraas brittleness temperature. The crack resistanse of the polymer-bitumen binder specimens in the process of loading at negative temperatures increases.