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The stability of fresh cement paste can be described as its ability to remain homogeneous over time. Instability in the form of sedimentation and bleeding occurs for various reasons related to the material composition. In this study, the relevant mechanisms for quantifying stability are reviewed, and a conceptual model is proposed describing the sedimentation progress in terms of bleeding (supernatant), the homogeneous zone, the variable concentration zone, and the compressible sediment zone. A sensitive hydrostatic pressure test (HYSPT) with good repeatability and without influence from evaporation was developed to describe the sedimentation process of fresh cement paste. HYSPT relies on the fact that the mainly restricted Stokesian settlement of particles causes changes in the solid fraction and the fresh density at a given height and time. The influence of the pressure detection direction and position were investigated by changing the inlet design of glass pipes. The pressure drop due to cement dissolution, chemical shrinkage, and paste structural buildup also was investigated but was found to be negligible compared to the effect of density variation due to sedimentation before setting. The sedimentation rates obtained from HYSPT measurements were found to coincide with the volume fraction variation detected via in situ measurements. The solid fraction and bleeding results were in alignment with the conceptual model.

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The RILEM AAR-13 test procedure is not a test method by itself; rather it is a procedure applying alkali wrapping to concrete prisms during test exposure to assess the expansion potential of alkali-silica reaction. When combined with procedures of other test methods, for example AAR-10 or AAR-11, it becomes a full test procedure. The wrapping procedure described was originally proposed by a technical committee of the Japan Concrete Institute ''Technical Committee on Performance Based Design and Maintenance Scenario with Controlling ASR Deterioration''. The procedure includes a detailed description of the materials to be used for wrapping, procedures for calculation of alkalinity of the solution that aims to simulate the pore solution of the concrete prism depending on the alkali content of the concrete, and finally specific procedures for storage and measurements of the prisms. The procedure of calculating the alkalinity of the solution to be applied for the wrapping is assumed to be conservative because no This recommendation has been prepared by a working group within RILEM TC 258-AAA. The recommendation has been reviewed and approved by all members of the TC.

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