Breedon Aggregates is set to buy Cumnock-based Barr Quarries for £20.8M.
Breedon, which operates across the UK, said the acquisition demonstrated its commitment to Scotland.
Barr Quarries employs about 130 people and operates 11 quarries, five asphalt plants and six ready-mixed concrete plants north of the border. It had turnover of £25.5M last year.
Breedon chairman Peter Tom said: “Scotland has played a vital part in Breedon’s success and we have made significant investments there over the past four years.
“With the uncertainties surrounding the independence issue now behind us, we believe our prospects north of the border have never been brighter and we can look ahead with renewed confidence.
“Our acquisition of Barr Quarries is a clear demonstration of our long-term commitment to this important market.”
The acquisition, which will include Barr Surfacing & Civil Engineering, remains subject to TUPE consultations and final due diligence.
Barr Environmental and Barr Construction will remain part of Barr Holdings.