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The Need for Compaction Improvement
Compaction of an asphalt mix has been a standard in the building and functioning of the pavements for a long period. It has commonly been assumed that the results of compaction lie in the ensuing density and air voids,and are not due to construction techniques. It has also been considered that the cracks induced by construction only appear unattractive and do not actually affect the physical performance of the surfacing.
Extensive research has been conducted to establish the real cause and effect of the construction cracks. It was established that compaction by steel roller is responsible for construction-induced cracks due to the geometric unsuitability between the roller and the base. Damage and cracks in roads are not only due to cold weather because these issues have also been observed on roads in countries with warm weather.
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Design of the Asphalt Multi Integrated Roller (AMIR)
The AMIR has a belt with multiple layers that are made of specific rubber compounds.The belt and rollers create plate-like contact surface of approximately three square meters to use for compaction. The rubber belt, being elastic, provides a surface that is similar in stiffness to the asphalt surface. Since the contact area available is large due to the flat plate, the applied stress at the asphalt is insignificant compared to that applied by conventional steel rollers. Furthermore, if the rolling speed is same, the load duration by AMIR is thirty times greater than normal steel rollers. The huge contact area reduces horizontal forces applied to the asphalt and ensures confinement during the compaction. Thus, the roller induced cracking is eliminated, permeability is reduced, and resistance to fatigue damage and tensile strength are increased.
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Test Results of Asphalt Multi Integrated Roller
AMIR has overcome compaction problems and produces a smooth surface that does not have cracks. Numerous fatigue tests were performed on different mixes. Comparison was carried out of the compaction produced by the normal rollers and the Asphalt Multi Integrated Roller. The contributing factors like direction and kind of mix were varied to obtain results under different test conditions. The test results demonstrated that compaction by the Asphalt Multi Integrated Roller, using either form of mix, produced approximately twice the compaction fatigue life. It was also observed that the rolling direction had an insignificant effect on the fatigue life of the mix produced by Asphalt Multi Integrated Roller. However, the fatigue resistance to transverse cracking was low for the mix produced by steel rollers. The research has concluded that the cracks produced by steel rollers can decrease the fatigue life considerably, and these problems can be overcome by the use of Asphalt Multi Integrated Roller. Furthermore, the mechanical properties like density, fatigue life, tensile strength and moisture resistance are improved considerably.
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Problems Conventional Steel Drum Rollers
Cracks produced during compaction by normal steel rollers are due to the non harmony of the rigid circular steel drum with the gentle, even asphalt pavement. Since the shape of the steel drums is circular, only a small contact area is accessible to the asphalt for compacting. With the movement of the roller, the asphalt at the roller front is pushed forward, producing a dragging force in the asphalt at the rear. This action of pushing and dragging produces cracks in the asphalt. The rollers with rubber tires were introduced to press the asphalt and seal the cracks. However, such rollers have not been successful to prevent the development of cracks. Furthermore, these rollers use water to avoid picking asphalt during the compaction. This lowers the temperature of the asphalt and avoids the crack closing.