Marshall Stability and Flow of Lime-modified Asphalt Concrete

The purpose of highway pavement is to provide smooth surface over which vehicles can move safely from one place to another. The two major types of pavement (flexible and rigid) have been mostly selected for the highway pavement to fulfil this function and they must be capable of transferring the wheel load to the subgrade such that its bearing capacity is not exceeded. However, the flexible pavements normally show defects like rutting, fatigue failure, low skid resistance and so on, causing the pavement to fail before its design life. Therefore, it is important to modify the asphalt concrete to make it more resistant to rutting and fatigue failure. Lime-modified asphalt has been observed to have better resistance to rutting, cracking and stripping, as well as having improved aging behavior. Therefore, this study looks at the Marshall properties of hydrated lime-modified asphalt mixture and the conventional asphalt. The conventional asphalt mixture was made using 10% mineral filler while for the lime-modified asphalt, the mineral filler was replaced with hydrated lime. The bitumen with penetration grade 60/70 was used and the content varied from 5.0 to 7.5%. Marshall stability and flow tests were carried out on the samples. The results show that the Marshall stability for the asphalt concrete with mineral filler ranges from 5.89 – 7.90 kN while that with hydrated lime ranges from 5.9 to 8.2 kN. The flow values for the asphalt concrete with mineral filler range from 2.3 mm – 3.3 mm, while that with hydrated lime range from 2.4 – 3.4 mm. The optimum bitumen content for both mixtures was found to be 6.5%. The stability and flow for the mixture with mineral filler were 7.9 kN and 3.3 mm, respectively, while for the mixtures with hydrated lime they were 8.2 kN and 3.4 mm, respectively. This indicates the replacement of the mineral filler with lime improves the stability of the mixtures, while there was slight increase in the flow of the mixture with hydrated lime. The slight increase in stability and flow values may be attributed to the complete replacement of the mineral filler with lime and the high lime content used in the study. More studies are being carried out to evaluate the Marshall properties for mixture with the mineral filler partially replaced with lime and for varying proportions of the lime content in the asphalt mixture.