This article reviews proposed technical approaches for the manufacture and use of alternatives to Portland Cement Clinker as the main reactive binder component for ordinary concrete construction in nonspecialty applications, while giving lower net global CO2 emissions in use. A critical analysis, taking into account a wide range of technical considerations, suggests that, with the exception of alkali-activated systems, (treated in a separate paper in this issue,) there are only four classes of alternative clinker system that deserve serious attention with respect to global reductions in concrete-related CO2 emissions: (A) Reactive Belite-rich Portland cement (RBPC) clinkers (B) Belite-Ye'elimite-Ferrite (BYF) clinkers (C) Carbonatable Calcium Silicate clinkers (CCSC) (D) Magnesium oxides derived from magnesium silicates (MOMS) A and B are "hydraulic" clinkers, (i.e. clinkers which harden by reaction with water,) C is a "carbonatable" clinker, (i.e. one which hardens by reaction with CO2 gas) and D can fall into both categories.

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For many microstructural studies it is necessary to ''stop'' cement hydration-to remove free water. This paper describes the results of a round robin test on the impact of hydration stoppage methods on the composition of hydrated cements. A regular and a fly ash blended Portland cement hydrated for 90 days were selected. Ten laboratories participated in the round robin test. Four common hydration stoppage methods were studied: (1) oven drying at 105 °C, (2) solvent exchange by isopropanol, (3) vacuum drying and (4) freeze drying. After the stoppage of hydration powder samples were studied by thermogravimetry (TG) and X-ray diffraction (XRD). Bound water and Ca(OH) 2 content were determined based on the TG data. Portlandite and ettringite content were quantified by Rietveld analysis of the XRD data. The goal was to establish interlaboratory reproducibility and to identify the best available protocols for research and standardization purposes. Based on the results of the round This report has been prepared by a working group within RILEM TC 238-SCM. The report has been reviewed and approved by all members of the TC.

The use of calcined clays as supplementary cementitious materials provides the opportunity to significantly reduce the cement industry’s carbon burden; however, use at a global scale requires a deep understanding of the extraction and processing of the clays to be used, which will uncover routes to optimise their reactivity. This will enable increased usage of calcined clays as cement replacements, further improving the sustainability of concretes produced with them. Existing technologies can be adopted to produce calcined clays at an industrial scale in many regions around the world. This paper, produced by RILEM TC 282-CCL on calcined clays as supplementary cementitious materials (working group 2), focuses on the production of calcined clays, presents an overview of clay mining, and assesses the current state of the art in clay calcination technology, covering the most relevant aspects from the clay deposit to the factory gate. The energetics and associated carbon footprint of the calcination process are also discussed, and an outlook on clay calcination is presented, discussing the technological advancements required to fulfil future global demand for this material in sustainable infrastructure development.

This recommendation is an outcome of the work carried out by a working group within the RILEM Technical Committee 238-SCM ''Supplementary Cementitious Materials''. The working group studied the effect of supplementary cementitious materials on the pore solution, the microstructure and the hydration product assemblage of hardened Portland cements blended with common supplementary cementitious materials. The recommendation reflects the results of a round robin test programme on common hydration stoppage methods in 10 participating laboratories. Among four different methods tested, solvent exchange by isopropyl alcohol (isopropanol) gave the best results in terms of preservation This recommendation has been prepared by a working group within RILEM TC 238-SCM. The recommendation has been reviewed and approved by all members of the TC.

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