1. Influence of the size and type of pores on brick resistance to freeze-thaw cyclesIvanka Netinger Grubeša, Martina Vračević, Vilma Ducman, Berislav Marković, Imre Szenti, Ákos Kukovecz, 2020, original scientific article Abstract: This paper estimates the frost resistance of bricks using the ratio of compressive strength before freezing to compressive strength after freezing to describe the damage degree of bricks being exposed to freeze-thaw cycles. In an effort to find the ratio that clearly distinguishes resistant bricks from non-resistant bricks, the authors attempted to establish the correlation between the ratio and Maage factor as a recognized model for assessing brick resistance. To clarify the degree of damage of individual bricks, the pore size distribution has been investigated by means of mercury porosimetry. Additionally, micro computed X-ray tomography (micro-CT) has been employed to define the influence of the type of pores (open or closed) and their connectivity on the frost resistance of bricks. According to the results, it can be concluded that there is a good correlation between the Maage factor and the ratio of pre- to post-freeze-thaw cycle compressive strengths, and that the latter ratio strongly correlates with the percentage of large pores (≥3 mm) in the brick. If such a correlation could be confirmed in a larger sample, then the ratio of pre- to post-freeze-thaw cycle compressive strengths could be used as a new method for assessing brick resistance to freeze-thaw cycles and it would be possible to determine the minimum percentage of large pores required to ensure the overall resistance of brick to freeze-thaw conditions. The complexity of the problem is, however, evidenced by the fact that no clear connection between the type (open versus closed) or connectivity of pores and the frost resistance of bricks could be revealed by micro-CT.
Keywords: clay masonry units, porosity, freeze-thaw resistance
Published in DiRROS: 17.08.2023; Views: 251; Downloads: 155
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2. RILEM TC 247-DTA round robin test : sulfate resistance, alkali-silica reaction and freeze-thaw resistance of alkali-activated concretesFrank Winnefeld, Gregor J. G. Gluth, Susana Bernal, Maria Chiara Bignozzi, Lorenza Carabba, Sundararaman Chithiraputhiran, Alireza Dehghan, Sabina Dolenec, Katja Dombrowski-Daube, Ashish Dubey, Vilma Ducman, Yu Jin, Karl Peterson, Stephen Dietmar, John L. Provis, 2020, original scientific article Abstract: The RILEM technical committee TC 247-DTA ‘Durability Testing of Alkali-Activated Materials’ conducted a round robin testing programme to determine the validity of various durability testing methods, originally developed for Portland cement based-concretes, for the assessment of the durability of alkali-activated concretes. The outcomes of the round robin tests evaluating sulfate resistance, alkali-silica reaction (ASR) and freeze–thaw resistance are presented in this contribution. Five different alkali-activated concretes, based on ground granulated blast furnace slag, fly ash, or metakaolin were investigated. The extent of sulfate damage to concretes based on slag or fly ash seems to be limited when exposed to an Na2SO4 solution. The mixture based on metakaolin showed an excessive, very early expansion, followed by a dimensionally stable period, which cannot be explained at present. In the slag-based concretes, MgSO4 caused more expansion and visual damage than Na2SO4; however, the expansion limits defined in the respective standards were not exceeded. Both the ASTM C1293 and RILEM AAR-3.1 test methods for the determination of ASR expansion appear to give essentially reliable identification of expansion caused by highly reactive aggregates. Alkali-activated materials in combination with an unreactive or potentially expansive aggregate were in no case seen to cause larger expansions; only the aggregates of known very high reactivity were seen to be problematic. The results of freeze–thaw testing (with/without deicing salts) of alkali-activated concretes suggest an important influence of the curing conditions and experimental conditions on the test outcomes, which need to be understood before the tests can be reliably applied and interpreted.
Keywords: alkali-activated materials/geopolymers, sulphate resistance, alkali silica reactivity, freeze-thaw resistance, Rilem TC
Published in DiRROS: 17.08.2023; Views: 226; Downloads: 163
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