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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.

After ten years of marine exposure, chloride and calcium profiles and petrographic data were obtained from the tidal and submerged zones of six concrete panels differing in binder composition. Moisture and portlandite profiles were also determined on the submerged concrete. The data enables us to improve our understanding of the impact of sea water exposure and can also be used for service life modeling. The depth of the maximum chloride content and the depth of the microstructurally changed zone were comparable. Both depths progressed over time and reached a depth of as much as 10 mm after ten years of exposure. When using these and other field data for testing of chloride ingress prediction models, we recommend excluding datapoints from the microstructurally changed zone, i.e., the outermost datapoints including the maximum chloride content, unless reactive transport models are used.

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.

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.

Magazine article on the preliminary results of a new composite cement within the framework of the EnDurCrete project.

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.

© Copyright SINTEF Building and Infrastructure 2014

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

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The static yield stress of fresh self-compacting concrete and its time dependency was measured in different materials and conditions/methods. First the BML ConTech4 was used at very slow rotation by analysis of the data logged in National Instruments lab View giving time dependent static yield stress in 5 different self-compacting mortars. The test cycle involved both static yield measurements starting from unconfined state as well as measurements in a confined state due to a residual stress after stop of the slow rotation. The confined yield stress increases with the same rate of change as the unconfined, though with an upwards parallel displacement due to the increased static yield stress under confined conditions. However, after removal of load and then applying new confinement the linear trend of increase of yield stress as function of time were independent of release/confinement repetition and the two lines (unconfined and confined) were parallel. We also observed linear increase of static shear moduli with time. Finally we investigated the static yield stress of the filler modified paste portion of the mortar in a Physica Paar parallel plate rheometer. First we observe the usual improved sensitivity of the static yield at very low increase of strain rate from zero, giving exponential increase of time dependant stress (gel strength test) compared to static yield in the constant strain rate test. A very clear linear time dependant increase of shear modulus with time was found, though with much lower absolute values than in mortar. The rate of change of static yield stress of SCC and mortar varied in the range 0.014 – 0.25 Pa/s in unconfined tests during the first 2,5 hours. In confined tests it is 0.2 – 0.41 P/s. The only values at t = 0 are by linear regression and extrapolation, often giving values less than zero indicating some kind of non-linearity at early age although the increase after app 30 minutes seems linear both for unconfined an confined tests. The test principles in the four tests were: coaxial viscometer for mortar, static plate with continuous development, inclined plane and parallel plate for paste or matrix. The differences between the measurements, briefly, concern both the type of materials that can be used (SCC vs matrix) and the test principles and stress conditions during testing. Our materials were mortar with w/b ≈ 0.50, 40 volume % matrix and 8 mm maximum aggregate size, as well as matrix with similar composition as in the mortar. Apparently, static yield is very sensitive to both test method and how it is calculated. Based on this limited experience it is hard to give a definite answer but the confinement in the ConTech viscometer is possibly a good thing for simulation of concrete confined in a narrow tall wall. This is the geometry where yield stress build-up is of interest for formwork pressure. The inclined plane showed some weaknesses with larger aggregate particles loosening from the surface but might relate to aggregate segregation. The plate test also has its weaknesses with small roughness on the surface and should perhaps have been exchanged for geometry with vanes of some kind normal to the plate to get similar “grip” as the vanes of the viscometer. More work is needed to obtain a test. Possibly different tests are needed for yield stress for different purposes: related to formwork pressure, to casting joints and to stability of aggregate particle sinking. Observations of difficulties in static yield stress measurements and discussion of the magnitudes of these variations in various types of measurements will hopefully lead to more knowledge in this field.

© Copyright SINTEF Building and Infrastructure 2012.

This report gives the findings from a collaboration project between the Norwegian Public Roads Administration (NPRA) and the COIN FA 2.1 project managed by SINTEF Building and Infrastructure which was start in spring 2010. The COIN FA 2.1 project "Robust and highly flowable concrete with controlled surface quality" is a sub-project of the COncrete INnovation centre (www.coinweb.no) running from 2007-2014. One of the objectives of the COIN FA 2.1 project is to develop an objective classification tool for concrete surfaces cast against smooth formwork. The classification tool should assess pores, grey level and grey level variations. The state of the concrete surface is documented using photographic equipment. The images are analysed using Matlab based image analysis software called BetongGUI. The image taking procedure and image analysis tool were under development during the collaboration project. The NPRA's project "Askimporten tunnel – Field test of surface treatment of wall segments" started in 2010, aims to document the long-term effects of different surface treatment with respect to maintaining a light grey surface colour and reducing the environmental impacts on the concrete elements. In total 9 different surface treatment products were tested. The NPRA has invited the COIN FA 2.1 project into this collaboration project to document the wall segments with regards to grey level as a case study for implementation of their classification tool. Regarding the surface treatment products it could be concluded that products 4, 5a and 7 seemed to perform best over time. Product 1a also maintains a lighter visual appearance than the reference before washing, but has similar reflection values as the reference after washing. All these products contain white pigments. None of the colourless surface treatments maintain a lighter appearance than the reference fields over time. During the collaboration project several improvements were made to the classification tool: • flash settings are to be kept constant • a pop-up white calibration object was used during the last site visit instead of white cardboard to prevent folds and hence erroneous reflections • the grey scale calibration object appeared to be too glossy and therefore only the lightest field of the calibration object is used for greyscale calibration in combination with linearized images • robustness problems with the white calibration software and image analysis software were dealt with.

Three full scale wall elements were cast with three different concretes: an unstable SCC, one stabilized by adding filler, and one stabilized by adding chemical stabilizer. The aim of this study was to investigate the effect of the stabilization on the rheology of the SCC and on the final surface quality. All delivered SCC's were rather stone rich and unstable, even the stabilized ones. This was most likely caused by a change in the fines and water content of the sand for which the concrete recipe was not corrected. Even though the SCC's were not as expected certain conclusions could be drawn. All three mixes had a low viscosity and relatively high yield stress indicating segregation. The questionable stability was confirmed by the sieve segregation test, but not by the visual segregation index on the flow board. Stability assed on a hardened concrete cylinder indicated good stability for the unstable and filler stabilized SCC. However, the chemically stabilized concrete showed clear signs of bleeding. Regarding the surface quality of the wall elements, it can be concluded that all surfaces had a similar grey level independent of the type of SCC used or whether or not formwork agent was applied. It is not possible to come to clear conclusions as to how the SCC type or the surface treatment affects the amount of pores. However, there is an indication that the chemical stabilizers can lead to large bleeding pores in the lower part of the surface of the concrete wall, whereas filler stabilization can gives rise to the formation of very fine pores. The fact that all SCC's were on the verge of instability, did not allow for clear rheological differences nor clear differences in final surface quality. 3D005940

During cement production large amounts of CO2 are emitted, about 1 tonne CO2 per tonne clinker, if no measures are taken. About 40% originates from fuel combustion, grinding and other operations, and 60% from the de-carbonation of limestone to form the clinker phases. One way to reduce these emissions on the short term is by replacing part of the clinker with other materials such as slag, limestone powder, fly ash, silica fume and natural pozzolans. The type of replacement materials used depends on their availability (e.g. amount available, price and transportation) and is therefore dependent on the geographical location of the cement plant. The aim of this study is to contribute to the development of a novel all-round Portland composite cement for the Norwegian market. When this study was started, the cements produced at the Norwegian cement plants were: CEM I Portland cements containing up to 5% limestone powder and CEM II/A-V Portland fly ash cements containing up to 18% fly ash but no limestone powder. In this study, the effect of increasing the replacement levels of the ordinary Portland cement (OPC) (up to 35% replacement), and combining siliceous fly ash (FA) and limestone powder (L) to replace OPC are investigated. Using a combination of fly ash and limestone to replace OPC seems to be better than using only one of them. Limestone powder accelerates the early hydration more than fly ash, but fly ash contributes to strength development at later ages due to its pozzolanic reaction. Additionally a chemical interaction between fly ash and limestone has been observed, first in simplified cementitious system and later also in Portland composite cement. Limestone powder interacts with the AFm and AFt phases formed during the hydration of OPC. At first, ettringite forms during the hydration of OPC. When all gypsum is consumed, ettringite will react with the remaining aluminates and form monosulphate. In the presence of limestone, hemi- and monocarboaluminate are formed instead of monosulphate. The ettringite does, therefore, not decompose. This leads to higher volume of the hydrates, which on its turn might reduce the porosity and enhance the compressive strength. The effect of limestone powder on OPC is limited due to its low aluminate content. However, when part of the OPC is replaced by fly ash, the fly ash will introduce additional aluminates to the system as it reacts. This will lower the SO3/Al2O3 and increase the AFm/AFt ratio and thereby amplify the impact of limestone powder. These changes in the AFm and AFt phases have been experimentally observed by TGA, XRD and EDX, and predicted using thermodynamic modelling. Only a few percent of limestone powder are required to prevent ettringite from decomposing to monosulphate. The changes in hydration products resulting from these small limestone powder contents coincides with an increase in compressive strength. Replacement of 5% fly ash with 5% limestone powder in a 65%OPC+35%FA cement resulted in a compressive strength increase ranging between 8 and 13% after 28 days of curing. At higher limestone contents the compressive strength decreases again as the additional limestone mainly serves as an inert filler. Replacing 5% of OPC with limestone powder resulted, on the other hand, in a strength reduction or a slight increase up to 4% after 28 days of curing. The beneficial effect of limestone is maximal at 28 days, and reduces slightly upon further curing. It is furthermore valid at 5, 20 and 40°C. However, at 40°C the fly ash reaction is accelerated and over time the fly ash content is more important than the synergetic effect. The observed increase in compressive strength has to be partly due to the chemical interaction described above as an inert filler (crystalline quartz) with a similar psd does not have the same beneficial impact on strength as limestone. Additionally, the presence of limestone powder does not seem to affect the reactivity of OPC and fly ash significantly. The observed effect between fly ash and limestone enables higher replacement levels than when only one of them is used. The applicability of the study is demonstrated by the fact that cement with the optimal composition found in this study (65%OPC+30%FA+5%L) has recently been used in the construction of the Meteorological Centre in Oslo and the Science Centre in the county of Ostfold PhD i konstruksjonsteknikk PhD in Structural Engineering

There is a rising interest in the production of composite cements due to mounting environmental awareness and the diminishing natural resources. In composite cements considerable parts of the clinker is replaced by supplementary cementitious materials. Within two STAR’s we will focus on the fly ash and limestone as replacements for part of the clinker. This first part will mainly focus on the reactivity, activation and reaction products of fly ash. Fly ash is a relatively slow reacting pozzolan. Its reactivity depends on the alkalinity of the cement, the curing temperature, the replacement level and the water-binder ratio. The reactivity of fly ash can be improved by thermal, chemical or mechanical activation. Thermal activation is based on the fact that higher curing temperature leads a faster increase of the pH, and an increased solubility of the glassy silicate phase of fly ash. Although it might be of interest for prefabrication industry, it is not really an option for every day use on the construction side. When discussing chemical activation, it is clear that alkalinity place a major role. At room temperature fly ash only starts to react noticeable at a pH higher than 13.3. This level of alkalinity is only reached after one or more days in ordinary Portland cement. By increasing the alkalinity of the cement, the early stage reactivity of fly ash could be boosted. Though care should be taken with regard to the alkali reactivity of the aggregates and the user-friendliness of such high alkaline cement. The third activation technique, mechanical activation, appears to be one of the more promising technique. One possibility is the extraction of the finer, more reactive particles from the bulk fly ash by air classification. Another method is based on intensive grinding of the fly ash. Cements prepared with a clinker replacement levels up to 25% have shown an improved strength development compared to reference cement. Oppdragsgivere: Aker Kværner Engineering and Technology, Borregaard LignoTech, maxitGroup, Norcem A.S, Norwegian Public Roads Administration, Rescon Mapei AS, Spenncon AS, Unicon AS, Veidekke ASA and The Research Council of Norway 3D006010

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 limitleaching. 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 theleaching conditions during the exposure. &nbsp

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., The paper was presented at ERICA - CASH II Final Conference, 25 - 27 January 2021 in section: 'Transport of water and small ion through agglomerates of hydrates'.

A fixed link is about to be built across the Fehmarn Belt between Denmark and Germany. The main structure of the link is a submerged reinforced concrete tunnel with a design service life of 120 years considering corrosion initiation as limit state. With the aim of supporting the design and operation of the reinforced concrete structures for the fixed link, Femern A/S in 2010 established the Fehmarn Belt Exposure Site in Rødbyhavn, Denmark, where 15 concretes differing in binder composition are exposed. Chloride-induced corrosion of embedded reinforcement steel is an important deterioration mechanism in marine exposed reinforced concrete structures. Concrete acts as a protective layer for the steel, both physically by impairing chloride ingress and chemically by passivating the steel due to the high pH of concrete. However, when a sufficiently high content of chlorides has penetrated through the concrete and reached the embedded steel reinforcement, steel corrosion is initiated. The focus of this study was to test and further develop the basis for application of chloride ingress models for service life design and reassessment of marine exposed reinforced concrete structures. The topic was approached by conducting an evaluation of which chloride data to use and how to use them for chloride ingress predictions by analyzing a) microstructural changes in the concretes and their impact and b) the assumptions made if correcting for paste fraction. By comparing chloride profiles combined with petrographic analysis of tidal and submerged concrete after ten years of marine exposure, supplemented with moisture and portlandite profiles of the submerged exposed concrete and earlier data on microstructure and chloride ingress, the relationship between chloride profiles and microstructural changes was investigated. Because of stochastic variation in the paste fraction and systematic variations due to geometrical restraints at cast surfaces, data for total chloride content are occasionally calibrated using parallelly measured calcium content as a measure of the actual paste fraction assuming non-calcareous aggregates and no calcium leaching. The assumption of no calcium leaching was investigated by comparing calcium profiles measured after a half, two, five and ten years from the same concrete panels exposed at the Fehmarn Belt Exposure Site and by analyzing the impact of calibration on chloride profiles. The earlier made square root observation of a linear relationship between the penetration depth of 0.05% chloride by wt. of concrete versus square root of time was generalized. The applicability and limitations were assessed, and the scope of validity widened with the aim of proposing it as a method (the square root method). Field data from marine submerged, tidal, splash, atmospheric and from inland deicing salt exposure at various Northern European locations was analyzed for a range of reference chloride contents. The square root method was compared to selected engineering models by evaluating the ability to predict data achieved after ten years of submerged exposure at the Fehmarn Belt Exposure Site based on data achieved up to five years of exposure. The tested models were (i) the fib Model Code, which include a time-dependent apparent diffusion coefficient (Da); (ii) the HETEK model, which include both time-dependent Da and surface chloride content (Cs) and (iii) the ClinConc model, which include time-dependent Da and indirectly time-dependent Cs (through time dependent chloride binding). The results showed a microstructurally changed zone extending up to ten millimeters from the exposed surface was a general feature for all concretes exposed for ten years at the Fehmarn Belt Exposure Site. When comparing to previous results from the same panels, it was noted that the depth of the microstructurally changed zone progressed inwards over time. A correlation was observed between chloride profiles and microstructural changes. The depth of the maximum chloride content (xCmax) was found to almost coincide with the depth of the microscopically changed zone (xMCZ). A steady increase was observed in xCmax from 0.6-2.5 mm after six months to 4.5-10 mm after ten years and in xMCZ from 1-2.5 mm after six months to 4-10 mm after ten years depending on binder type with least progression for a concrete containing 67% ground granulated blast-furnace slag. Calcium calibration of chloride profiles is sometimes used to account for the higher paste fraction in the surface near region due to the wall effect and for stochastic variations in the paste content in concrete in general. However, calcium leaching can introduce errors to the calibrated chloride contents in the leached part of the profile. It was found that the calcium content in the surface near region (up to 10 mm) decreased systematically over the period of 10 years. This results in the calcium content no longer being a suitable measure of the paste fraction up to this depth. As a result of the decreasing calcium content to a depth typically extending beyond that of the maximum chloride content (“chloride peak”), it was found that the calibrated maximum chloride content in several cases was higher than the uncalibrated. Based on the findings, it is recommended to exclude datapoints from the microstructurally changed zone, i.e., the outermost datapoints including the maximum chloride content, when using field data for testing of chloride ingress prediction models, unless reactive transport models are used. Analyses of chloride profiles with 237 combinations of concrete, exposure and reference contents showed that chloride ingress of a reference content followed a linear relationship with an average R2 of 0.96, when the penetration depth of the reference content was plotted against the square root of exposure time. This square root observation appeared valid for the studied Portland cement based concretes with fly ash, silica fume and ground granulated blast furnace slag exposed in submerged and tidal exposure zones, when applying reference contents of 0.1-1.8 % chloride by wt. of binder, and in atmospheric zone when applying reference contents of 0.1-0.5 % chloride by wt. of binder. It was found that the parameters describing the straight line depended on the chosen reference content. Faster ingress was seen for low compared to high contents. Further the slope of the straight line (ingress parameter) depended on the exposure with faster ingress for tidal than for submerged exposure. It was concluded that the square root method appears to be a promising method for reassessment of chloride ingress, among others because it does not rely on data affected by the microstructurally changed zone or calcium leaching. When comparing the square root method to other ingress models for reassessment, the square root method predicted with the lowest residual standard error (best), but currently it is only applicable for reassessment and not yet for design.