ABSTRACT
The requirements imposed on road pavements are ever increasing nowadays, necessitating the improvement of the properties of paving materials. The most commonly used paving materials include bituminous mixtures that are composed of aggregate grains bound by a bituminous binder. The properties of bitumens can be improved by modification with polymers. Among the copolymers used for modifying bitumens, styrene-butadiene-styrene, a thermoplastic elastomer, is the most commonly used. This article presents the results of tests conducted on bitumens modified with two types of styrene-butadiene-styrene copolymer (linear and radial). Two bitumen types of different penetration grades (35/50 and 160/220) were used in the experiments. The content of styrene-butadiene-styrene added to the bitumen varied between 1% and 6%. The results of the force ductility test showed that cohesion energy can be used for qualitative evaluation of the efficiency of modification of bitumen with styrene-butadiene-styrene copolymer. The determined values of the cohesion energy were subjected to the original analysis taking into account the three characteristic elongation zones of the tested binders. The performed analyses made it possible to find a parameter whose values correlate significantly with the content of styrene-butadiene-styrene copolymer in the modified bitumen. With smaller amounts of added modifier (approximately 2%), slightly better effects were obtained in the case of linear copolymer styrene-butadiene-styrene and for larger amounts of modifier (5-6%) radial copolymer styrene-butadiene-styrene was found to be more effective. This is confirmed by the changes in the binder structure, as indicated by the penetration index (PI).
ABSTRACT
Compaction of Hot Mix Asphalt (HMA) is a process aimed at obtaining the desired performance properties. Attainment of the required compaction can be hampered by external factors, which includes the presence of water. Water is known to cause quick lowering of the HMA temperature. The bottom face of the asphalt layers of a pavement is a sensitive point from the fatigue life point of view. In the site conditions, it is often difficult to obtain the required air void content at the bottom of an asphalt layer and excessive moisture content in the base course lying beneath the asphalt layer can be one of the causes. This article presents the results of tests carried out on a test section on which HMA was placed on an unbound aggregate base layer of varying moisture content. The material used for the binder course was asphalt concrete mixture composed of aggregate of minus 16 mm grading and 35/50 bitumen. Being relatively hard it is the most often specified bitumen for binder courses and also base courses. One of its characteristics is a considerable increase of viscosity with decreasing temperature, which hampers the process of compaction. The bulk specific gravity was measured to determine the variations in the air void content through the specimens. The complex modulus of elasticity and fatigue life were the other parameters which were determined on the specimens with different air void contents. The test results show worsening of the properties which have a decisive bearing on the service life of pavement.
