Balfour Beatty, Galliford Try and Carillion issued separate stock market announcements yesterday to confirm they would each invest up to £20 million as part of their commitment to the deal.
They will then share one-third of the construction revenue from the project.
The work involves building 46 kilometres of dual carriageway between Stonehaven and Blackdog.
A further 12 kilometres of existing dual carriageway is to be upgraded with 40 new kilometres of side roads and 72 structures, including bridges, also on the plan.
Work is expected to start later this year.
Once the project, which is the largest procured through the Scottish Government's non-profit distributing model to date, is completed in the spring of 2018 the consortium will then go on to manage the roads for a further 30 years.