The 60-tonne beams, which are box-section girders, were delivered for the project two weeks ago.
They were transported to the site in six sections, four to Grandholm Village on the north side of the River Don on 18 June, with the remaining two to Tillydrone on the south side in the following days.
Preparation works have been on-going since then and the southern beams are due to be lifted in place on 8 July.
The northern beams will be installed the following week.
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A 1,000 tonne crane will lift the beams, securing them into place to the already constructed abutments.
The project requires the development of two major bridges, with the first being a 26m skew span reinforced concrete bridge over the Mill Lade at Grandholm Village.
The second involves a 90 metre span steel box girder bridge over the River Don.
Contractor Balfour Beatty is developing the main viewing area on the south side of the river at Gordon Mills Road.
Councillor Ross Thomson said: "This viewing area has been constructed to allow the public the opportunity to witness an important and significant step in the construction of a major piece of infrastructure for Aberdeen.
"It will be a fantastic place for people to see what's happening at the site next week, and I'm looking forward myself to watching those huge steel beams being lifted into place."
Ken Brown, Balfour Beatty Project Manager for the Third Don Crossing, said: "The new viewing area will provide a great advantage point for local people to see the steel beams being lifted in to place."
(LM)
