Contractors seeking an urgent solution when large voids were found within the structure of a landmark railway viaduct turned to Leca® LWA as the lightweight solution. The unexpected voids were discovered behind the abutments of a Victorian bridge during a major £8 million replacement project at Harthope Viaduct on the West Coast Main Line near Moffat, Dumfries & Galloway. With only five days remaining before possession, contractors Skanska UK Civil Engineering, of Doncaster, working on behalf of Network Rail West Coast Main Line, had to source and install a lightweight product capable of filling the voids without imposing undue loadings on the existing bridge abutments in just 2 days. It was also essential that the material could be easily positioned at a vertical height of 12 metres and placed directly into the voids which had been caused by the gradual collapse of stone arch covers constructed behind the abutments of the original 1848 structure. Leca® LWA lightweight aggregate met the criteria and at a unit weight of 5 kN/m3 fell within the requirement specified by the client's consulting engineers, Scott Wilson Rail, of Glasgow, for a material of less than 12 kN/m3. It also provided a number of additional benefits.