1 23 Materials and Structures ISSN 1359-5997 Volume 44 Number 9 Mater Struct (2011) 44:1641-1653 DOI 10.1617/s11527-011-9724-y Optimising an expansion test for the assessment of alkali-silica reaction in concrete structures Xiao Xiao Gao, Stéphane Multon, Martin Cyr & Alain Sellier