It is a pleasure to contribute an editorial introduction to this Thematic Issue of Materials and Structures dedicated to the analysis of geopolymers and other alkali-activated materials. This is a topical collection of articles related to a class of materials which are attracting a high degree of attention worldwide at present, for their environmental and technical properties. The subjects of these articles include fundamental studies of binder structure at the nanoscale, the validation of new precursors (both aluminosilicate solids and activators) for alkali-activated binder production, the study of the durability of alkali-activated binders and concretes, and industrial-scale application of alkali-activation technology.

This Thematic Issue is therefore intended to span the full range from basic chemistry to real-world application, and features contributions from leading researchers and practitioners from Europe, Asia, and the Americas. Among the authors of these articles are several key members of the RILEM Technical Committee 247-DTA, which is dedicated to the durability testing of alkali-activated binders, and which is currently conducting a round-robin testing programme intended to assess the validity of standard durability tests when applied to this particular class of materials. This has been identified through the work of a previous RILEM Technical Committee (TC 224-AAM) as being a key area requiring attention to enable the standardisation and further deployment of alkali-activated materials, and so features prominently in several of the articles published in this Thematic Issue.

The field of alkali-activation is a highly active area of research in the international community at present, and the articles collected in this Thematic Issue represent key outputs from some of the global leaders in this field. We trust that the articles collected here will be interesting and enlightening to the reading audience of Materials and Structures, as they represent an advancement in the state of the art of this key area of activity of RILEM, and of the broader construction materials community, at present.