Like changes round pub — they work on the surface (10)

'they work on the surface' is the definition.
(people who apply asphalt to road surfaces)

'like changes round pub' is the wordplay.
'like' becomes 'as'.
'changes' becomes 'alters' ('alter' can be a synonym of 'change').
'round' indicates putting letters inside.
'pub' becomes 'ph' (public house).
'as'+'alters'='asalters'
'asalters' enclosing 'ph' is 'ASPHALTERS'.