The decrease of penetration and the increase of softening point of modified bitumen are due to the change of physical properties of bitumen caused by the addition of modifier. The modifier can be compatible with the gum in bitumen, absorb the saturation and aromatic content in bitumen, and thus change the component content and molecular structure of bitumen. The compatibility effect reduces the gum content in modified bitumen, and the bitumen with less bitumenene content has better compatibility with the modifier.

The modifier absorbs part of the oil and produces swelling effect. The swelling modifier can improve the pavement performance of the base bitumen. Needle penetration is an index to measure the viscosity and fluidity of bitumen. The decrease of needle penetration means that the viscosity of modified bitumen increases and the fluidity decreases.

The softening point refers to the temperature at which the bitumen begins to soften during heating, and the increase of the softening point indicates the enhanced thermal stability of the modified bitumen. The lower penetration and the higher softening point of the modified bitumen will make the modified bitumen have better anti-deformation and anti-aging properties, and improve the road performance and durability of the bitumen.

In short, the decrease of penetration and the increase of softening point of modified bitumen are due to the change of physical properties of bitumen caused by the addition of modifier, which has a positive impact on the performance of bitumen and improves the anti-deformation and anti-aging properties of bitumen.