Polyphosphric acid (PPA) modified asphalt binders were produced in the laboratory using one base asphalt and four levels of PPA contents (0.6%, 1.0%, 1.5% and 2.0% by weight of base asphalt). Penetration test, softening point test, rotation viscosity test, creep test with bending beam rheometer (BBR) and four components test were carried out to study the performance of PPA modified asphalt binders and possible modification mechanism. The results indicate that the high-temperature performance of PPA modified asphalt binders are obviously improved and temperature susceptibility are decreased, but the low-temperature performance slightly decline compared with base asphalt. The PPA content has a very significant effect on softening point whereas it has no significant influence on low-temperature performance according to variance analysis (ANOVA). Finally, four components test reveals that the primary modification mechanism of PPA is the change of chemical composition of asphalt binder.

The compactness is prone to markedly decreased after dampening in the subgrade filled by Ginger-stone soil. To solve this problem, a series of tests have been done on the conventional and improved Ginger-stone soil, such as granule analysis test, compaction test, CBR test and water stability test. The test results indicates that the CBR value of Ginger-stone soil is low and it has a strong capillary action, which make it cannot be directly used for roadbed filling of expressway and first class highway. By adding the lime(3%) and fly ash (9%) into the Ginger-stone soil, the CBR value and water stability of sample are obviously improved, and its control of construction becomes easy, so the improved Ginger-stone soil can be directly used as roadbed filling.

To solve the early destruction problems occurred when overlaying asphalt pavement structure containing semi-rigid base on broken cement concrete pavement, finite element software is used to compare the stress characters between the repaving pavement and ordinary pavement, and analyze the repaving structures under different loads and different road transverse grade. It shows that the value of compressive stress at the top of base of repaving pavement is significantly higher than that of ordinary pavement, meanwhile, its value of tensile stress of base bottom is lower; the asphalt surface and new base top of repaving pavement need to bare a high value of shear stress and compressive stress under overload, so it’s prone to splitting failure in the base. With the increase of transverse grade, both the shear stress difference of road surface and maximum vertical compressive at top of the base increase in a lower position, but the situation is opposite in the higher position.