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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.

This study investigates whether chloride ingress testing can be done using NaCl solution instead of seawater when assessing the performance of concrete in marine conditions. Seawater contains besides sodium and chlorine additional elements such as sulfur and magnesium, which can change the phase assemblage in the concrete and thereby affect chloride ingress. Mortar samples prepared with Portland cement were exposed to seawater or NaCl solution with a similar chloride concentration. After 180 days of exposure to seawater, only the outer 1 mm was enriched in sulfur and magnesium, which had only a limited impact on the chloride ingress. Leaching, observed in the outer 10–20 mm both for NaCl and for seawater exposure had a much stronger influence on the chloride ingress. Hence, chloride ingress in marine exposed concrete can be assessed using NaCl solutions. To mirror the leaching in field exposure, the volume of exposure solution needs to be high.

The formation of potentially deleterious reaction products from the reaction of dolomite fines in Portland cement pastes was investigated. It was shown that the reaction of dolomite fines did not follow the commonly accepted dedolomitization reaction. Instead, similar hydration phases as reported for the Portland cement containing limestone are observed, with the exception that also hydrotalcite is formed. It was shown with SEM-EDS and XRD that hydrotalcite is the only magnesium containing hydration product of the dolomite reaction, as no brucite or M-S-H were detected. In the next step of this study this reaction will be investigated in Al-rich systems. This is the accepted version of the article.

Carbonation resistance of concrete is usually tested under accelerated conditions, i.e. by elevating the CO2 concentration compared to natural conditions and keeping the RH close to 60%. However, it is not clear if these conditions mirror the natural process. Using SEM-EDS we investigated the composition of the reaction products of carbonated and non-carbonated concrete containing 0, 18 and 30% fly ash exposed to three different carbonation conditions. In noncarbonated concrete the reaction products depended on the binder. However, in carbonated concrete the reaction products were similar in composition in all the concretes and exposure conditions tested. This is the published version, available from https://nordicconcrete.net/wp-content/uploads/2017/08/XXIII-NCR-Symposium-DEL-2-A4-A6-proceedings.pdf

In this paper we illustrate the applicability of µ-XRF for investigations of chloride ingress and self-healing in cracked concrete. A cracked and an uncracked concrete core exposed to seawater for more than 30 years were investigated with µ-XRF. The cracked sample had higher chloride ingress in the outer part of the concrete core (first 20 mm). Parts of the investigated crack were self-healed with calcium and magnesium rich phases. It was concluded that µ-XRF is a powerful tool for fast and detailed characterization of elemental distribution; e.g. chloride ingress, as it is able to detect spatial irregularities caused by for example cracks. This is the authors' submitted version of the manuscript.

SINTEF and NTNU organized a WORKSHOP on moisture in concrete, 6th-7th February 2012 in Trondheim. The workshop was related to and supported by the COIN Focus Areas 3.1 “Crack free concrete structures” and 3.2 “Service life”. The purpose of the workshop was to share information on • available methods of measuring and modeling moisture in concrete and discuss pros and cons • moisture induced volume changes. The present report gives a brief overview over most of the methods presented and discussed at the workshop. A list of participants is given in Appendix 1; the programme is given in Appendix 2. The moisture state of concrete may be characterized either by moisture content or by relative humidity (RH) exerted by the moisture. The two are related via the sorption isotherm (moisture content vs. RH), which is not a given relationship, but which for a given concrete depends on a large number of factors. The most important are degree of hydration, temperature history, moisture history (drying/wetting), carbonation and whether the present moisture state is one of adsorption or desorption. The choice of RH or moisture content to characterize the moisture state in a given case depends on the purpose. For example, moisture content or degree of capillary saturation (as degree of filled pores) is obviously most relevant if the problem at hand is frost damage. For chemical reactivity of various kinds RH may be most relevant, since the RH, and not the amount, is a direct measure of the activity of the pore water. The methods discussed are divided into two categories: 1. measuring the relative humidity (RH) 2. measuring the moisture content, and the degree of capillary, vacuum and pressure saturation (DCS, DVS and DPS) Based on the discussions, literature and procedures earlier used at SINTEF and NTNU for measurement relative humidity, and measurement of moisture content and degree of saturation are proposed. Table 2 and Table 5 provide an overview of respectively relative humidity sensors and methods for measurements of moisture content and degree of saturation. © Copyright SINTEF Building and Infrastructure 2016 The material in this publication is covered by the provisions of the Norwegian Copyright Act. Without any special agreement with SINTEF Building and Infrastructure, any copying and making available of the material is only allowed to the extent that this is permitted by law or allowed through an agreement with Kopinor, the Reproduction Rights Organisation for Norway. Any use contrary to legislation or an agreement may lead to a liability for damages and confiscation, and may be punished by fines or imprisonment.

The first objective was to find out why a white clinker from previous studies has a higher strength potential than the other 3 clinkers tested in the same study, as well as finding out whether or not it contains other aluminate compounds than C3A. Clinker δ gives higher early strength than the other clinkers because it contains anhydrite as flux and therefore has a total higher calcium sulphate content than the other cements when the same amount of gypsum is added to the clinkers. Clinker δ also has a higher C3A content (≈ 6%) than predicted from the Rietveld analysis and part of it probably as a glassy XRD amorphous phase with some fluorine. Clinker δ only has a marginally higher surface than the other clinkers, but substantially higher C3S content that will add to the higher early strength together with excess calcium sulphate not bound early by C3A being able to help accelerate C3S hydration. The other clinkers also contained substantially amounts of C4AF that has a slow hydration with large amounts remaining unhydrated at 28 days. The second objective was to find out why one particular ash out of 4 tested gave much higher strength than the others when replacing cement (clinker with gypsum) in mortars. Fly ash D is not a real fly ash, but a fluidized bed ash that consist of a much more open structure than the closed glassy, spherical particles of the other fly ashes. It also contains a lot more calcium oxide (17.9% CaO) than the other fly ashes (Fly ash B is the second highest with 7.1% CaO). Hence it is assumed to be more reactive than the other ashes. Fly ash D also contains considerable more sulphate (6.6% as SO3) than the other fly ashes (fly ash B is the second highest with 0.5% SO3) which would lead to more ettringite formed on the expense of AFm resulting in more water bound and hence higher strength. The higher sulphate content (and partly less aluminate) for fly ash D compared to the other fly ashes also leads to a less response of this fly ash to the synergy effect with limestone, since AFt is stabilized on the expense of AFm. 102000442-1

Many of the suggested methods for testing of SCC stability are quite demanding in execution and therefore seldom used in field. Furthermore, questions have been raised about how well they represent the stability problems in situ. The aim of the present investigation was therefore to find a method to assess stability of SCC which is practical, reliable and representative for in situ stability problems. This was done by a large scale test where the stability assessed according to four selected methods was compared with the stability assessed in low wall elements (10 m long) where the SCC was cast from one end, by measuring the distribution of the coarse aggregate content. Two mixes of the same concrete were tested in order to see the comparison for both stable and unstable concretes. The one was known to give sufficient stability for wall casting, and the other one added more water reducing admixture to give rather poor stability. The results showed a good agreement between three of the methods and between these methods and the stability assessed by measuring the coarse aggregate distribution in the walls. One of these methods is a simple visual based assessment of the residue after the slump flow test.

The objective is to study the parameters of cements and fly ashes in combination with limestone that would optimize the synergistic chemical reaction between fly ash and limestone that leads to more bound water and thereby less porosity and higher compressive strength. Most notably this will be the reactive aluminate content of cements and fly ashes and how these will be able to combine with limestone to calcium carboaluminate hydrate at a given point in time. Four cement clinkers with two gypsum levels were combined with four different fly ashes and one limestone powder (the type used for raw meal in cement production). The study was carried out in two steps: 1) Combination of clinkers with two levels of gypsum (1.5% and 3.0% replacing clinker) and 0 and 5% limestone powder replacing clinker + gypsum. 2) Clinkers, each with 3 % gypsum, replaced with 35% fly ash and where 0 or 5% fly ash was replaced with limestone. The cement clinkers are usually believed to contain so little aluminate in the form of the mineral C3A that the limestone has so little to react with in order to form calcium carboaluminate hydrate and stabilize ettringite (i.e. the synergic reaction) that the influence of limestone on the 28 days strength would be negligible. The 28 d strength was mostly unchanged when 5% limestone replaced cement (i.e. clinker + gypsum) which means that limestone actually has the same efficiency factor as cement with respect to 28 d strength, so it is likely that some reaction has happened. However, there was a huge difference in 28 days strength between the clinkers, ranging from 44.6 MPa to 67.1 MPa when combined with for instance 3% gypsum. The reason for this is discussed, but it was not obvious from the clinker characteristics. Nevertheless, the clinker achieving the highest strength had the highest alite (C3S) content and either an aluminiumrich alite or an x-ray amorphous aluminium containing phase. This clinker was also the only clinker showing a significant strength increase when replaced with 5% limestone, indicating an aluminate interaction in spite of having lower C3A content than other clinkers. Limestone replacing cement gave also the same 1 day strength as pure cement, indicating the same efficiency factor as cement. Among the fly ashes in step 2, there were 3 ordinary fly ashes and 1 rich in anhydrite (12% calcium sulphate). The latter fly ash gave always the highest 28 days strength when 35% was replacing the four different clinkers with 3% gypsum. It raises the question whether or not one just as well could add more gypsum rather than limestone in combination with the fly ashes. Replacing 5% of the other 3 fly ashes with limestone gave always a strength increase, meaning the efficiency factor of limestone is higher than the fly ash, presumably due to the synergic reaction. The strength gain by limestone replacing fly ash combined with the different clinkers gave a good linear correlation with the amount of glass in the fly ash multiplied by the alumina content in that glass. This "multiplication factor" probably corresponds to the amount of alumina "easily" available by the fly ash to the system in the pozzolanic reaction and that the degree of reaction for the 3 fly ashes in the regression was about equal at 28 days. Finally, mortars where 35% calcined marl replacing the clinkers with 3% gypsum were made in order to compare with the fly ash performance. Calcined marl gave higher strength than any of the fly ashes and even led to higher strength than mortars based on 100% clinker + gypsum for 3 out of 4 clinkers (even for the one with highest strength; 67.1 vs. 75.5 MPa). 102000442-1