Commission XII on Lightweight Concrete was installed at the Monaco Session of the C.E.B. in 1961, though the first meeting only took place on April 13, 1964, to orient and coordinate the program. With F.I.P. and R.I.L.E.M. represented at Delft, cooperation agreements were established.

It was decided that F.I.P. would handle prestressed lightweight concrete, while R.I.L.E.M. focuses on the technology, including aggregates, mixing, vibration, water-content, curing, and compacting. Cooperation includes exchanging reports and cross-member participation.

This distribution of tasks mirrors the satisfactory arrangement of the C.U.R. commissions in Holland. While defined, these roles are flexible; researchers working on structural lightweight concrete can seek mix-design information from R.I.L.E.M., with the goal that R.I.L.E.M.'s growing experience will improve its ability to provide necessary information.