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Pyrrhotite is an iron sulfide which when present in concrete aggregate may lead to expansive reactions, cracks and finally disintegration of the concrete. This potential risk when using aggregates containing sulfides in concrete production has been known for several decades, and international concrete standards take this into account. Though, recent examples of deterioration of concrete structures in Canada and USA, and the rejection of tunnel masses for application as concrete aggregates for the construction of the Follo line tunnel in Norway, have raised questions regarding the test methods and regulations for sulfides and pyrrhotite in concrete aggregates. A Norwegian R&D project led by NTNU is currently looking into the characterization and quantification of sulfide minerals in aggregates (WP1) and working with the development of test methods for documentation of the damage potential in concrete (WP2). There is a close collaboration between the Norwegian research team and researchers from the university of Laval in Canada which have been working with pyrrhotite in concrete for over a decade. This paper introduces the basic chemistry of the reactions of pyrrhotite in concrete, presents examples of deterioration caused by pyrrhotite and lists the relevant regulations currently in place in Norway and North America. Eventually, the challenges and research questions raised will be discussed and how we are planning to tackle these will be presented.

It is now more than 80 years since Alkali Aggregate Reactions (AAR) first were reported as a deleterious deterioration mechanism in concrete. In Norway, AAR was recognised in the late nineteeneighties. Norwegian experience and expertise have increased significantly since then and entered the international stage, with connections to leading research parties worldwide. Several Norwegian master’s degrees, PhD theses and major R&D projects have been carried out, focused on test methods and corresponding criteria for the prediction of AAR as observed on Norwegian concrete structures. Reliable Norwegian test methods and guidelines have been developed, through the Norwegian Concrete Association, and linked to the European concrete standard, enabling use of local reactive aggregates, in a sustainable way, by documenting and producing non-reactive and durable concrete. Norwegian researchers have participated actively in the various Technical Committees (TC’s) on AAR in RILEM and have been in the leadership of the two most recent TC’s since 2014. This work has recently achieved some significant progress regarding recommendations, and performance-based testing concept, to prevent damage by AAR in new concrete structures. This paper is a review of the research carried out in Norway during more than 3 decades, parties involved, and the results and conclusions achieved. Eventually, this paper presents a summary of where we are today in international AAR research, identifies key milestones and addresses some specific topics for future research.

Mortar samples were exposed to two NaCl solutions with different pH, to investigate the impact of leaching on total chloride profiles. One set of samples was exposed to a NaCl solution, and a set of twin samples was exposed to a NaCl solution additionally containing KOH, to limit leaching. A clear correlation between the leaching depth and the chloride ingress depth was observed. We investigated the changes in the C-S-H composition as a function of the depth from the exposed surface in the two sets of samples with SEM-EDS after 180 days of exposure. The results showed that the Ca/Si ratio of the C-S-H changed only in the outermost 0.7 mm. The Cl/Si ratio of the C-S-H followed the trend observed in the total chloride profiles. The adsorption of sodium and potassium on the C-S-H was also found to be depending on the leaching conditions during the exposure.

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The behaviour of novel cementitious materials (low clinker cement CEM II/C and CEM VI) exposed to CO2 is simulated and investigated with a simplified model in this paper. Based on studies of the evolution of the phase assemblage obtained from GEMS, the carbonation process is simplified into the dissolution of one combined Cacontaining phase and the precipitation of calcite phase. The purpose is to quantify some physical variables representative of the reactive transport properties: saturation degree for drying, porosity, calcite and Ca-containing phase content for carbonation. The dissolution rate of the Ca-containing phase and corresponding precipitation of calcite are assumed to be determined by the saturation degree, the partial pressure of CO2, and the concentration of calcium in solid phases. The carbonation process is assumed to be ruled by two phenomena: the water migration through the connected porosity and the diffusion of carbon dioxide in the gaseous phase, which are governed by two mass conservation equations. This model is solved by the finite element code Cast3M, and is verified using experimental data from carbonation depth measurements using a pH indicator, portlandite and carbonate profiles from thermogravimetric analysis and drying experiments on mortar and concrete.

Portland cements were made by mixing 4 different clinkers with 2 gypsum levels and 0-5% limestone powder. The compressive strength after 28 days of curing varied from 40 (5802) to 70 MPa (9718 psi) for mortar with equal w/c. Some of the clinkers were replaced with 4 different fly ashes and the response on strength differed. To explain the relatively large differences in strength evolution, the clinker and fly ash composition was investigated by SEM-BSE/EDS, the oxide compositions were determined by XRF and differences in clinker mineralogy determined by XRD Rietveld analysis. The microstructure of hydrated cement pastes of clinker/fly ash was investigated by SEM/EDS. The highest strength was achieved with the white clinker containing no C4AF, produced using CaSO4/CaF2 flux, and therefore contained a higher total calcium sulphate content. The white cement also seemed to contain two calcium aluminate phases with potentially some fluoride in one of them, one probably glassy as Rietveld analysis underestimated C3A. The C4AF content of the other clinkers have low reactivity within the 28 days explaining some of the difference. One “fly ash” was actually a fluidized bed ash with higher calcium and sulphate content and different morphology explaining the different behavior from the other fly ashes

Concrete elements exposed for 26 years to seawater spray and deicing salts along a road close to Sandnessjøen in Norway were investigated. Concrete cores from 4 elements with different binder compositions (A: 100 % Portland cement (PC), B: 96 % PC and 4 % silica fume (SF), D: 93 % OPC and 7 % SF, and E: 77 % OPC, 20 % fly ash (FA) and 3 % SF) were analysed. Chloride ingress and alkali leaching were qualitatively assessed with µ-XRF elemental mapping. Cold Water Extraction (CWE) was performed to determine the amount of free alkali (Na and K) both on the inner part of the concrete cores which was not affected by leaching, and on the pure aggregate. The potential alkali release from the aggregates was determined using the newly developed RILEM AAR-8 method. This method showed that the used aggregate released less alkalis than the limit for being classified as a low-releaser. Small amounts of alkali (especially Na) were released from the aggregate even by applying the more "gentle" CWE method on milled powder from the aggregates. Hence, care should be taken to check that potential alkali release from aggregates during field exposure is not partly masked by alkalis released during application of CWE in the lab. As the amount of potentially bound alkali in the different hydrated binders is not known, the uncertainty in the share of alkali coming from cement free available in the pore solution complicates potential verification of alkali release further. For future investigations, reference samples with different binders combined with various types of aggregates (non- reactive & non releasing, reactive & non-releasing, high releaser, ...) are planned to better estimate the share of alkali from the binder available in the pore solution as well as the alkali released from aggregates.

Engineers specializing in civil engineering must integrate into their design measures to protect marine biodiversity, which authorizes the concept of eco-design of marine infrastructure that respects the environment. The cementitious materials are preferred to design marine infrastructure and interact with the marine environment. These structures will be colonized by marine microorganisms and macroorganisms. Initially, the organisms form a biofilm on the concrete surface according to environmental factors and the physicochemical properties of the material. In this study, it was shown that the pre-carbonation of cementitious materials accelerates the growth of microorganisms forming a biofilm by lowering the pH of the surface. It was shown using a laboratory test that colonization of the surface by microorganisms also increases the hydrophobicity of the surface and could thus improve the durability of the material by reducing the absorption of seawater containing aggressive ions.