The offer to the Office of Fair Trading follows fears that competition for the supply of secondary aggregates around the Gunheath quarry in Cornwall will be lessened by the AI takeover of Atlantic.
Amelia Fletcher, OFT Senior Director for Mergers said: "There is a growing demand for secondary aggregates because of their lower price compared to primary aggregates, as well as their environmental credentials.
"The OFT is looking for a remedy that will restore pre-merger competition for the supply of secondary aggregates in the areas of Cornwall and West Devon."
If the divestment is not accepted, then a referral to the Competition Commission is the next step.
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