Billionaire Gautam Adani-led Adani Group on Tuesday said it will acquire CK Birla group firm Orient Cement at a valuation of Rs 8,100 crore as part of its expansion drive.Ambuja Cements, the cement and building material company of Adani Cement and part of the diversified Adani Group, has signed a binding agreement for the acquisition of Orient Cement Ltd (OCL) at an equity value of Rs. 8,100 crore.