Praise be to Allah, the Lord of the Worlds.
The ruling on constructing pavements in a graveyard varies in accordance with the nature of the graveyard itself. If it is a private graveyard, then it is permissible to construct such pavements as the owner sees fit, and this isn`t considered disliked.
As for the public graveyard, that is for general use: if the will narrow the space of that graveyard and hinder the people from benefitting from it, then it is considered prohibited. However, if it doesn`t affect the nature of the area endowed as a graveyard and changes nothing in it, then constructing them is permissible.
Imam Zakaria Al-Ansari (May Allah have mercy on him) says, "An-Nawawi said in Al-Majmou` that it is prohibited to build any structure in a public graveyard………"{Asna Al-Matalib, 1/328}.
In conclusion, if the aforementioned pavements don`t narrow the space of that graveyard, don`t hinder the benefit received from it, and are useful, then constructing them is permissible. And Allah the Almighty knows best.