Subject matter

This TC is tasked with a review of the state of the scientific understanding of calcium sulfoaluminate (CSA)-containing cements. CSA cements were developed in the late 50’s following the work by Alexander Klein at UC Berkeley. They differ from Portland cement in that the main reactive compound in these cements is Ye’elimite, a fast-hydrating compound. As such, these binders can be considered a separate class of cements. They exhibit a diverse range of characteristics, from rapid strength to low shrinkage and reduced carbon footprint. The literature reports a reduction in Global Warming Potential of up to 30% compared to Portland cement. Several types of ye’elimite-contaning clinkers and cements are manufactured and available commercially worldwide. Sustained commercial production is decades old in North America, Europe, and China. The clinkers, or the finished CSA cements may or may not be blended with Portland cements, but in general the mineralogy of these materials deviates significantly from that of Portland cement. Despite commercial success, classification, standards and specifications are in their infancy and when they do exist, are usually ad hoc. Part of the difficulty in the acceptance of CSA cements is that they are considered alternative cements that do not fit established standards. Therefore, despite their attractiveness as a low-carbon alternatives to Portland cement, agency and industry specifications and understanding lag behind commercial use.
The main incentive for the use of CSAs is the decrease in time of construction time, compared to Portland cement. They are frequently used for rapid construction or repair of pavements, or as accelerating additives in dry mix mortars. This is a unique economic opportunity for a low-carbon binder. The scope of the TC will include a review of the mineralogy and performance of all types of CSA-containing cements in fresh and hardened states (blended or unblended with OPC and/or SCMs). The TC will review the knowledge base on the mineralogy of the CSA clinkers and cements, summarize hydration mechanisms, assess what is known of the durability of CSA mortars and concrete, review field applications, and identify knowledge and research gaps.

Terms of reference

The timeframe of this new TC is five (5) years, starting in Fall 2024 with a kick-off meeting. There, the TC will be structured into 5 workgroups, and their scope will be defined in detail during the first year of the TC. The working groups will work in the years 2-4 of the TC mainly on bibliographic reviews to be published in a topical collection of Materials and Structures. Interlaboratory testing is considered as an option. In the final year, the dissemination of the TC work will be completed by a final TC meeting during a RILEM conference or convention.
It is expected that approximately 30 members will contribute actively. The participation of young researchers (PhD students / PostDocs) will be encouraged. The stimulation of the dialogue between experts from academia and industry is one of the important missions of our TC.

Detailed working programme

The TC will be composed of 5 working groups (WG):

• WG1: Clinkering and characterization, including thermodynamics of clinkering.
• WG2: Hydration mechanisms, which will include blends with PC, SCMs and admixtures (excluding fresh mortar/concrete properties), and thermodynamics of hydration.
• WG3: Physical properties of CSA-based construction materials, including fresh mortar/concrete properties.
• WG4: Durability and applications.
• WG5: Nomenclature, standardization, and testing.

The board of the TC will be composed of the Chair, the Deputy Chair and the WG leaders (2 per WG). The board will meet regularly, at least twice a year, mainly to coordinate the activities between the WG and to plan the full TC meetings.

The proposed timeline of the TC activities is:
Year 1: Kick-off meeting including an internal workshop: Recruiting new active members, defining WG leaders, allocation of members to the working groups, definition of topics for first review papers in separate meetings of the individual WGs (at least 1 per WG). Start of comprehensive literature review of CSA cements. WG leaders work on the publication of the first RILEM Technical Letter paper justifying the work of the TC and defining its precise scope of work.
Year 2-4: Work on the articles to be published in a dedicated topical collection of Materials and Structures. Planning and organization of a research symposium on CSA cements connected to RILEM and ACI meetings. RILEM recommendation related to the nomenclature of CSA cements. Interlaboratory testing including exchange of samples, data and testing procedures may be included in the TC work if appropriate.
Year 5: Finalization of topical collection. Publication of the second RILEM Technical Letter summarizing the work of the TC. Identification of specific topics for follow-up TC(s). Final dissemination of the TC work at the RILEM week by means of a dedicated session.