Blended cements, where Portland cement clinker is partially replaced by supplementary cementitious materials (SCMs), provide the most feasible route for reducing carbon dioxide emissions associated with concrete production. However, lowering the clinker content can lead to an increasing risk of neutralisation of the concrete pore solution and potential reinforcement corrosion due to carbonation. carbonation of concrete with SCMs differs from carbonation of concrete solely based on Portland cement (PC). This is a consequence of the differences in the hydrate phase assemblage and pore solution chemistry, as well as the pore structure and transport properties, when varying the binder composition, age and curing conditions of the concretes. The carbonation mechanism and kinetics also depend on the saturation degree of the concrete and CO2 partial pressure which in turn depends on exposure conditions (e.g. relative humidity, volume, and duration of water in contact with the concrete surface and temperature conditions). This in turn influence the microstructural changes identified upon carbonation. This literature review, prepared by members of RILEM technical committee 281-CCC carbonation of concrete with supplementary cementitious materials, working groups 1 and 2, elucidates the effect of numerous SCM characteristics, exposure environments and curing conditions on the carbonation mechanism, kinetics and structural alterations in cementitious systems containing SCMs.

FOREWORDAn extensive Round Robin test programme on compressive softening was carried out by the RILEM Technical Committee 148-SSC "Test methods for the Strain Softening response of Concrete". The goal was to develop a reliable standard test method for measuring strain softening of concrete under uniaxiat compression. The main variables in the test programme were the specimen slenderness hid and the boundary restraint caused by the loading platen used in the experiments. Both high friction and low friction loading systems were applied. Besides these main variables, which are both related to the experimental environment under which softening is measured, two different concretes were tested: a normal strength concrete of approximately 45 MPa and a higher strength concrete of approximately 75MPa. In addition to the prescribed test variables, due to individual initiatives, the Round Robin also provided information on the effect of specimen shape and size. The experiments revealed that under low boundary friction a constant compressive strength is measured irrespective of the specimen slenderness. For high friction loading systems (plain steel loading platen), an increase of specimen strength is found with decreasing slenderness. However, for slenderness greater than 2 (and up to 4), a constant strength was measured. The shape of the stress-strain curves was very consistent, in spite of the fact that each labora-tory cast its own specimens following a prescribed recipe. The pre-peak behaviour was found to be independent of specimen slenderness when low friction loading platens were used. However, for all loading systems a strong increase of (post-peak) ductility was found with decreasing specimen slenderness. Analysis of the results, and comparison with data from literature, showed that irrespective of the loading system used, a perfeet localization of deformations occured in the post-peak regime, which was first recognised by Van Mier in a series of uniaxial compression tests on concrete between brushes in 1984.Based on the results of the Round Robin, a draft recommendation will be made for a test procedure to measure strain softening of concrete under uniaxial compression. Although the post-peak stress-strain behaviour seems to be a mixture of material and structural behaviour, it appears that a test on either prismatic or cylindrical specimens of slenderness hid = 2, loaded between low friction boundaries (for example by inserting sheets of teflon between the steel loading platen and the specimen), yield.; reproducible results with relatively low scatter. For normal strength concrete, the closed-loop test can be controlled by using I the axial platen-to-platen deformation as a feed-back signal, ] whereas for high-strength concrete either a combination of axial] and lateral deformation should be used, or a combination of] axial deformation and axial load.

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.

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