4. ConclusionsThe slope of densification curve cannot be used as the only criterion for judging whether compaction is difficult or easy; otherwise, the inaccurate conclusion that more coarse aggregates make compaction easier may be drawn. The mixture having more of asphalt has a faster density-increasing speed; it is more easy to compact and has a smaller air void when their gradations are the same. Test schemes (1), (2), (3), and (4) have the same amount of asphalt and mineral powder, but the content of coarse aggregates increases gradually and that of fine aggregates decreases gradually; the variety rule of compaction characteristic with the content of fine aggregates is depicted in Figure 4. It can be seen from Figure 4 that when the content of fine aggregates is small and that of coarse aggregates is large the mixture is difficult to compact; with the gradual increase of fine aggregates compaction performance of mixtures improves gradually; but with the continual increase of fine aggregates compaction performance of mixtures starts to fall. So there is an optimal amount of fine aggregates.When the contents of coarse aggregates, mineral powder, and asphalt are all kept constant, the thicker ones in fine aggregates has a prominent effect on compaction performance; more of thicker ones will make compaction more difficult. When the contents of fine aggregates, mineral powder, and asphalt are all kept constant, the proportion of each size section among coarse aggregates above 4.75mm has no obvious influence on compaction characteristic; maybe more of thicker coarse aggregates will contribute to compaction; this is probably because there are less of contact points between coarse aggregate particles. When the contents of coarse aggregates and asphalt are kept fixed, the air void of the mixture with more mineral powder is smaller and more easy to compact, which shows that an appropriate amount of mineral powder will improve workability of mixtures and contribute to field compaction.Mineral powder continuing to add after it has added to a certain amount will not do good to compaction any longer; this is because overmuch mineral powder will make mixtures dry and hard and do harm to field construction compaction. When the content of coarse aggregates is kept constant, the mixture having more of mineral powder and asphalt has a smaller air void and its density-increasing speed is faster. The mixture having more of coarse aggregates and mineral powder but less of fine aggregates has a smaller final air void, and its density-increasing speed is fast; although it is more easy to compact, its final air void will be too small. The mixture having overmany fine aggregates but lacking enough mineral powder is more difficult to compact and the final air void is usually large.