Engineering firm Keller said expectations for its full year remain unchanged and within the current range of market expectations."Most of the geographical markets in which we operate remain challenging," the group warned in Thursday's trading update."Whilst in most of our regions public infrastructure spending remains robust,privately-financed construction generally is still extremely weak."As a result revenues and margins since the first half have continued to weaker than the same period in 2008 as difficult market conditions continue.Order intake, which in the first half of the year was down 22% on a like-for-like basis compared with the preceding first half, has since remained reasonably steady, the group added.