Segregation Of Asphalt Mixture And Its Influence On Homogeneity Of Pavement Structure

Segregation in the Hot-Mixed Asphalt (HMA) causes inferior homogeneity of pavement structure which is a key contributor to the early pavement damage. It has very obvious theoretical sense and engineering value in aspects of improving pavement quality, bettering pavement homogeneity and duribility, lasting pavement service life and minimizing the life cycle cost. This dissertation has made a thorough study in fields of causes and mechanism of segregation, impact of segregation on pavement homogeneity and its countermeasures. The main contents and achievements are as follows:(1) This paper pioneered the introduction of systematic and management methods to identify main contributive factors to segregation. It is proven by the research that in the complicated system of construction process, the obvious causes of segregation are inclusive of large verity of aggregate mass and insufficient precision of loading and quantitifying in mixture batching, unsophisticated paver operator and rolling equipment not well matched, comparatively low rolling temperature and unreasonable rolling time etc.( 2 ) Based on the analysis of aggregate movement and its structural characteristics in variant work stage, this paper analysized the aggregate's movement and structural status and studied further the segregation mechanism. The research reveals that during pavement construction and in the loading, transporting and transferring and spirally distributing process, the coarse aggregate has larger horizontal inertia force, centrifugal force and gravity and consequently it has larger momentum, while the fine aggregate has much smaller above said mechanical indexes, this difference leads to segregation.(3) The indoor test has shown the graduation segregation impact on the pavement characteristics. A criterion of segregation control based on the current specification and related to the Marshall Test is proposed. The Marshall Test has revealed the variation of oil-aggregate ratio induced by the segregation and its impact on Marshall Index. The research has indicated that the saturation is very sensitive to the segregation variation and secondly to the air-void ratio, this means that segregation is the fundamental source of pavement water damage.(4)The indoor test has studied the temperature segregation impact on the pavement on the pavement homogeneity. Via corelationship of temperature with various Marshall Indices, this paper posed the temperature segregation allowance responding to the current specification. It proves that the higher the formation temperature, the easier it meets various requirements of the specification. Or it will be more difficult otherwise. So, in controlling the temperature segregation , this paper proposed that both lowest temperature and its variation must be concerned.(5) A test device for evaluating graduation segregation was developed. The indoor model test simulated the graduation segregation, using the difference of accumulative passing percentage between the front and rear aggregate bin to define the segregation level defined as"segregation possibility". It is also a very meaningful index of HMA to figure out its possibility of segregation before its paving.(6) After knowing the main causes of segregation and the corresponding countermeasures, a conclusion can be made as"a combination of controlling maximum size of the aggregate, adopting suitable asphalt–aggregate ratio, managing stone refinery strictly, quantifying the aggregate, using material transfer vehicle and live bottom truck is the effective way to deal with the segregation."By dynamic management and countermeasures set against the outstanding factors, segregation can be effectively mitigated.