By Bethany Wales London-listed raw materials group Sigmaroc said it has “forged an alliance” worth more than £100m with quarrying specialist Duo Group to produce sustainable limestone. The ten year agreement between the two companies will see Exeter-headquartered Duo Group establish state-of-the-art processing plants at up to seven SigmaRoc limestone quarries to reprocess quarry tip waste into a “premium construction material”. On top of generating an estimated £150m in revenue over the decade SigmaRoc said it would “significantly reduce” its environmental impact and extend the operational lif…