MATERIALS AND STRUCTURES (International Union of Laboratories and Experts in Construction Materials, Systems and Structures (RILEM))
Effect of alkali activators on diffusivity of metakaolin-based geopolymers
Kurumisawa, K., Omatu, H., Yamashina, Y.
MATERIALS AND STRUCTURES, Vol.54, 2021, AUG.
(https://doi.org/10.1617/s11527-021-01758-y)
Abstract
A basic investigation into whether a geopolymer can be utilized as a part of an artificial barrier during radioactive waste disposal was conducted in this study. Geopolymers are comprised primarily alumina and silica, and they exhibit negligible leaching owing to the absence of calcium. Studies on geopolymers are limited compared to those on other cementitious materials because the physical characteristics of geopolymers vary with the production conditions. In this work, metakaolin based geopolymers were prepared, and their diffusion performance was analyzed. The results indicate that the diffusivity of cesium in a geopolymer is affected by the type of alkali activator. Sodium-activated geopolymers had higher cesium adsorption capacity than potassium-activated geopolymers. The cesium adsorption capacity also had a significant effect on the diffusivity of cesium in the geopolymers. It was shown that, in addition to the pore structure and surface area, the mobility of water affects the diffusion performance of the geopolymer.
Effect of surface moisture on air-permeability kT and its correction
Bueno, V; Nakarai, K; Nguyen, MH; Torrent, RJ; Ujike, I
MATERIALS AND STRUCTURES, Vol.54, 2021, APR.
(https://doi.org/10.1617/s11527-021-01666-1)
Abstract
It is a well-known fact that moisture in the pores hinders the flow of gas through them, thus having a strong effect on the gas-permeability of concrete. Contrary to laboratory tests, where specimens can be preconditioned by drying, site air-permeability tests are normally conducted under the natural moisture conditions prevailing at the moment of the measurement. Swiss Standard SIA262/1-E: 2019 prescribes that the site air-permeability test (double vacuum cell or Torrent method) is applicable to measure the air-permeability coefficient, kT, only when the surface moisture content m does not exceed 5.5%, m measured with an electrical impedance-based instrument. This paper analyses 50 sets of parallel data of kT and m, recorded during different drying processes, originated from five independent investigations. The analysis confirms that a relation of the type kT=kT0e-delta m can be fitted to the large majority of the cases (R=0.95), with delta falling within 1.0-2.0 in 84% of the 50 cases analysed, with a median value of 1.45. This analysis allows the authors to propose a practical method to correct the effect of m on kT, the robustness of which is verified by a sensitive analysis. The correction is of little practical relevance for surface moistures between 4.5% and 5.5%. It is expected that this correction may be included in future versions of standards.
Application of super absorbent polymers (SAP) in concrete construction-update of RILEM state-of-the-art report
Mechtcherine, V; Wyrzykowski, M; Schrofl, C; Snoeck, D; Lura, P; De Belie, N; Mignon, A; Van Vlierberghe, S; Klemm, AJ; Almeida, FCR; Tenorio, JR; Boshoff, WP; Reinhardt, HW; Igarashi, SI
MATERIALS AND STRUCTURES, Vol.54, 2021, MAR 25.
(https://doi.org/10.1617/s11527-021-01668-z)
Abstract
Superabsorbent polymers (SAP) are a new, promising class of chemical admixtures which offer new possibilities in respect of influencing the properties of cement-based materials in the fresh, hardening, and hardened states. Much research work has been done in the last two decades to set the stage for introducing this truly multipurpose agent into the practice of construction. In particular, three RILEM Technical Committees: 196-ICC, 225-SAP and 260-RSC contributed considerably to the related progress by coordinating and combining the efforts of international experts in the field. The major product of the RILEM TC 225-SAP work was the State-of-the-Art Report published in 2012. This comprehensive document covered all topics relevant to the application of SAP as a concrete admixture. Since then further important progress has been made in understanding the working mechanisms of SAP in concrete and the effects of SAP-addition on various concrete properties. The article at hand presents an update on the state-of-the-art and is the concluding document delivered by the RILEM TC 260-RSC.