Superpave grading for high traffic volumetric criteria
The Superpave mix design system is a comprehensive method of designing paving mixes determined by the traffic, climate, and structural section of a particular pavement site. The first project of the Superpave mix design in Malaysia was in 1996. The application was in the technical specifications for runway and taxiway pavement for Kuala Lumpur International Airport (KLIA) project. In the meantime, research work carried out by the Public Works Department (PWD) showed that distresses happened usually on heavily trafficked roads and becomes a major problem as axle loading increased. It is clearly shown that there are inabilities of conventional mix design methods to control the performance of materials. In conjunction with that, the Superpave has been proven in western countries as the best mix design method because it offers performance-based specification for asphalt pavement mixtures. For this reason, this method is selected for the laboratory mix design. After all, the aim of this research is to evaluate the properties of the Superpave mixture design using Malaysian materials. The properties of the mixture design intended to satisfy for heavy duty roadways. As a summary, several trial aggregate gradations were developed and initial trial asphalt content has been calculated for four categories; CLV, CHV, FLV, and FHV. And finally, three design aggregate structures are selected and it's has proven suits for heavy duty roadways volumetric criteria.
BITUMINOUS ROAD SURFACING IN HIGH STRESS AREAS : MALAYSIAN EXPERIENCE
Past experience with conventional asphaltic concrete in high stress areas whereby the surfacing material is constantly subjected to extremely long loading times of the slow moving heavy commercial vehicles at high surfacing temperatures has indicated shortcomings. This is evident by excessive rutting and shoving that occurs within a short period of time after laying. Under such conditions, conventional bitumen behaves in a viscous manner thus allowing the bituminous material to flow under the high stresses. Consequent reduction in air voids decreases resistance to deformation as the fine aggregates occupy more of the voids thus reducing contact area between the coarse aggregates. This eventually results in structural instability and the surfacing material shears under the traffic loads. This paper highlights past experience by Public Works Department of Malaysia (JKR) in evaluating various methods in mitigating permanent deformation of bituminous road surfacing in high stress areas since 1989. Several types of bitumen modifier and innovative bituminous mix have been tried in the past and they were shown to exhibit mixed performances. The techniques which are proven or widely known to be effective in mitigating surface distress induced by slow moving heavy vehicles in high stress areas are herein recommended.
Ignition and burning rates of segregated waste combustion in packed beds.
Recent developments in national recycling and re-use programmes for municipal waste have led to segregation of an increasing proportion of waste to enhance material recovery. Several of the segregated streams contain materials that can not viably be re-used or recycled but can be used for energy recovery. In this study, the combustion of cardboard and waste wood was investigated in a small-scale packed bed reactor in order to provide fundamental data for the design/operation of moving bed furnaces. Key parameters of combustion including the ignition and burning rates were evaluated for various air flowrates and compared to the modelling results. Two successive stages of combustion were identified for both samples: the propagation of ignition front into the bed and combustion of the fuel above the ignition front. The burning rate of cardboard reached a peak of about 300 kg/m(2)h at the air flowrate of 936 kg/m(2)h and decreased at higher air flowrates. For waste wood, both the ignition and burning rates increased in the tested range of the air flowrate up to 702 kg/m(2)h, of which the values were very close to those for the cardboard. The model prediction was in good agreement with the test results for waste wood. However, the burning rate for cardboard was under-predicted due to strongly irregular shapes of the fuel.