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.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.