Influence of surface seal variables on bitumen bond strength properties

[摘要] ENGLISH ABSTRACT: Surface seals are widely used in South Africa. There are a number of reasons which includeaffordability, versatility and durability. There are, however, in some cases problems with stoneloss that can lead to a shortened lifespan of the pavement. The loss of aggregate chippings insurface seals poses a major problem in the seal pavement industry. This study aims to identifythe influencing factors that lead to these adhesive failures as well as to find optimumcombinations of binders and aggregates at various conditions.Various binders commonly used in South African surface seal construction will be tested usingthe Bitumen Bond Strength (BBS) test method. The binders used in the study include 80/100penetration grade bitumen, elastomer modified bitumen, bitumen rubber, elastomer modifiedemulsion and cationic rapid setting emulsion. Aggregates used in the study include dolerite,granite and quartzite. The test samples were cured and tested at two temperatures, 15 °C and35 °C. The samples were also cured for 2, 6 and 24 hours respectively.The study tackles a wide range of variables in order to obtain a good understanding of adhesionproperties of surface seals used in South Africa. Tests were repeated at least once to ensurerepeatability and in some cases up to four repeats were performed. The loading rate at whichthe tests were performed had a significant influence on the BBS results. This rate varied whichcomplicated the process of comparing the results. It was therefore decided to unify the loadingrates.The BBS results exposed the difference between hot applied binders and emulsions. Theformer having significant stronger adhesion properties. It was also confirmed by the results thattemperature plays a key role in the BBS results due to the visco-elastic properties of bitumen.These influences will be discussed along with others such as aggregate types and curing times.The type of failure is also discussed. Failure can either be adhesive or cohesive, the formerbeing a failure between the aggregate and the binder while the later refers to a failure in thebinder itself.The results of other students will also be discussed and compared to the results of this study.These include results of predecessors that tested emulsions as well as results from tests doneon fractured aggregate surfaces and precoated aggregates. This study showed very similarresults as these from other students, except for tests done with emulsions. It was discovered that the method of curing of the emulsions must be adapted to ensure proper curing of theemulsions.It was found that aggregates did not influence the BBS properties to the same extent astemperature and binder application type. The BBS results of hot applied binders also did notsignificantly increase as the curing time increased, but the results of emulsions showed someincrease. However, the emulsions needed more time to cure properly.

[发布机构] Stellenbosch University