The binder predominantly governs cracking in bituminous pavements. Hardening occurs during production and afterwards during use. Filler in the pavement contributes most to the surfaces of the mineral aggregates and is potentially catalytically active. Thus, the filler can influence the properties of the binder in the pavement and therefore also the tendency for cracking.
During previous research, catalytic activity of the filler on bituminous binders could be clearly proven. A marked change in binder properties suggests that fillers may play a role in ageing of binder during use and consequently may also enhance cracking.
In the project, Swiss fillers and binders commonly used in Switzerland were investigated to characterize fillers, binders or combinations of them being especially prone to ageing and consequently to cracking of roads in which they are used.
Main result of the project is to determine the catalytic activities of different fillers, to classify them according the properties of the fillers. To determine the ability of binder to withstand such catalytic oxidation. To evaluate the need of appropriate standardization.
The need for standardization will be discussed and, if the need is given, drafts for appropriate standards will be included in the final report. Test methods will be described to evaluate the risk of cracking for a given combination of filler and binder in roads.
Aging can be defined as the change of the properties of a bituminous binder as function of time. This change is generally connected with a loss of performance and functionality of the binder. The most obvious aspect of aging is the hardening and embrittlement of the binder. In addition, the adhesion between binder and aggregates can be reduced too. As a consequence this leads to a degradation of the pavement. Thus aging of the binder affects the performance of the road. The resistance against fatigue decreases, as proved clearly by crack formation in older bituminous pavements.
Earlier research proved that fillers show a catalytically accelerating aging. This allows the definition of an aging index describing the influence of the present filler on aging process. Using a test method to determine this aging index, a number of fillers and binders frequently used in Switzerland were investigated.
Marked differences between fillers were found, not all producing the same additional hardening. In addition, binders too did not show the same susceptibility to the catalytic activity of the fillers.
In contrast to the earlier research including binders and fillers originating from USA, less extreme hardening was observed. A high aging index was found only for a few combinations.
This final research report describes the further development of the method compared to. Variations in the test methods are discussed. The method was assessed by comparing the aging index with the fatigue behavior of selected mastics. The relevance of the aging index for practical applications is discussed.