RILEM TC 247-DTA round robin test: sulfate resistance, alkali-silica reaction and freeze–thaw resistance of alkali-activated concretes

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

RECYCLING WASTE FOR THE PRODUCTION OF SUSTAINABLE MORTARS FOR BRICK MASONRY

For many years bedding mortars have been considered a secondary component in structural brick masonry walls and they were classified only on the base of their binder (see, e.g., the Italian law DM 20/11/1987 concerning the Regulation for designing, building, testing and strengthening masonry) rather than characterized for their actual mechanical performance. This approach has recently changed and joint mortars have gained higher and higher attention, as they substantially influence the final mechanical performance of masonry. At the same time, a growing awareness of the sustainability issue has been registered in the field of building materials (Bignozzi, 2011), given the extremely high environmental impact of the construction sector (Franzoni, 2011) and its expected increase due to the global population growth (estimated to pass from 6.5 billion in 2005 to about 9.0 billion in 2035 (Dixit and Fernandez-Solis, 2010)). In this scenario, mitigating the consumption of raw materials and energy the manufacturing of building materials is of paramount importance and recycling waste and by-products appears as a feasible route toward this goal. Nevertheless, while recycling waste in concrete was widely investigated and has now entered the building practice, even if with some limitations and die-hard prejudices, the use of not hazardous waste and by-products for masonry (and in particular for mortar joints) is much less considered, despite the widespread presence of structural masonry and wall plug all over the word. In this paper, different mortars with improved sustainability were prepared, partially or totally substituting the fine aggregate with recycled fractions (sand from grounding demolished concrete or end-use tyre rubber) or replacing the cement with a low-carbon binder (alkali-activated binder). After a first characterization of the mortars in terms of strength and microstructure, some brick masonry triplets were built and characterized to assess their properties, with particular reference to their shear behaviour, in view of their possible use in masonry buildings in seismic zones of the world

Assessing the suitability of fly ash geopolymer for strengthening existing reinforced concrete structure

Abstract from the Young Researchers’ Forum, XIII AIMAT Congress and SIB Congress - Ischia, Italy, July 2016. Fiber-reinforced cementitious matrix (FRCM) composites have gained increasing interest as newly developed system for strengthening reinforced concrete structures. FRCM system provides for the embedding of high-strength fibers into an inorganic matrix. The possibility of using geopolymers instead of cementitious matrix is very attractive since this new class of inorganic material, synthetized through the alkali activation of an aluminosilicate precursor, showed competitive features when compared to cement based materials in both terms of performances and sustainability. However, research dealing with the use of geopolymer for strengthening and rehabilitation of reinforced concrete structures with externally-bonded composite materials are limited