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The production of cement is responsible for about 8% of man-made CO2 emissions. CO2 fixation by mineral carbonation in Ca- and Mg-rich raw materials such as cement-based concrete in various stages of its lifetime and magnesium silicate-based rocks (e.g. olivine) can provide a significant and long-lasting sink of CO2. Carbonated material can be used in novel construction materials, which potentially could even be CO2 negative. Despite first applications beyond pilot stage, further research is needed to reach economically and environmentally friendly processes. The properties of the novel construction materials, their reaction mechanisms, suitable mix designs, mechanical properties, and durability need to be explored further., Current Opinion in Green and Sustainable Chemistry, 38

Carbonated wollastonite clinker (CS) may be suitable as supplementary cementitious material (SCM) for mortar and concrete. The microstructure of unground CS clinker, carbonated CS slurry and a mortar blended with carbonated CS are investigated by scanning electron microscopy. Additionally, a reference mortar with pure Portland cement and one with a cement replacement level of 30 mass-% by carbonated CS are produced to assess its contribution to compressive strength development. The calcium silicates are decalcified during carbonation resulting in CaCO3 and amorphous SiO2 . The latter reacts when used as SCM in mortar influencing the Ca/Si ratio of calcium-silicate-hydrate and contributing to compressive strength development.

The potential of ASR in concrete can be assessed by the concrete prism test. However, the transferability of the results obtained with accelerated tests to concrete behavior under field conditions has to be validated. Such a validation was performed ten years ago for concrete produced with Portland cement and various Swiss aggregates. In recent years, the use of supplementary cementitious materials (SCM) has increased. So far, no validation for such types of concrete has been conducted in Switzerland. The goal of the current project is to fill this gap and provide the missing validation. Eight structures where chosen for the investigation. In all of them concrete containing SCM was used and the results of the concrete prism test at time of construction were available. In general, the results of the concrete prism test correlate with the degree of damage in the structures assessed by the analysis of the microstructure., La reactividad potencial álcali-sílice (RAS) en el hormigón puede evaluarse mediante ensayos de prismas de hormigón. Sin embargo, debe validarse la transferencia de los resultados obtenidos mediante ensayos acelerados con el comportamiento del hormigón en condiciones reales. El ensayo acelerado de prismas de hormigón se realizó hace diez años para distintos hormigones fabricados con cemento Portland y diferentes áridos suizos. En los últimos años se ha incrementado el uso de adiciones. Hasta ahora, no se había realizado ninguna validación de estos hormigones en Suiza. El objetivo de este trabajo es llenar este vacío y proporcionar la validación que falta. Se eligieron ocho estructuras para la investigación. En todos los casos se había utilizado hormigón con adiciones y se disponía del ensayo de prismas de hormigón en el momento de la construcción. En general, los resultados de estos ensayos se correlacionan con el grado de daño en las estructuras, evaluándolas mediante análisis microestructural.

The formation of alkali-silica-reaction (ASR) products in concrete aggregates generates stress leading to the formation of cracks proceeding from the aggregates into the cement paste. However, there is little knowledge on the initial ASR products formed in aggregates before the cracking occurs, as their small volume considerably complicates analysis. In this study, a new approach for identification and visualisation of ASR product formation leading to concrete damage is presented. Caesium is added as a tracer during concrete production. Because it is mainly incorporated in ASR products, their backscattering contrast in the scanning electron microscope is considerably increased. This makes it possible for the first time to follow the temporal and spatial progression of ASR with resolution in the nanometre scale, thereby delivering a coherent reaction sequence.

The environmental impact of concrete production can be decreased by the use of cement with reduced clinker content or the reuse of concrete waste provided by the demolition of buildings in recycled aggregate concrete (RC). In this study, the carbonation resistance of RC is investigated in order to clarify the influence of recycled aggregate percentage, moisture state of the aggregates prior to concrete production and type of cement used. RC with two different replacement levels of natural aggregates is produced using three different blended cements and compared to reference concrete mixtures produced with natural aggregates. The carbonation resistance of RC can be decreased by particles of recycled aggregate that are either very porous or already carbonated before concrete production. There were no systematic differences in compressive strength and carbonation resistance between dry and pre-saturated aggregates. The carbonation resistance at a given compressive strength decreases with decreasing clinker content of the cement.

The ASR products in concrete have various chemical compositions. It is yet unclear whether and how these products develop micro-expansion upon moisture ingress. This paper presents a 3D in-situ observation of the crystallography and volume change of an ASR-product-filled vein under varying relative-humidity (R.H.). The vein was observed to contain two layered nano-crystalline phases with distinct basal spacings, and was distributed heterogeneously in space. When R.H. changed from 10% to >38%, the basal spacing increased from 7.43 angstrom to 8.89 angstrom for one phase, whereas it remained constant (similar to 10.9 angstrom) for the other. This is the first time that an ASR product is observed in-situ to exhibit crystal structural expansion during wetting process. However, the product-filled vein exhibited no noticeable swelling when R.H. varied from 10% to 97%. Our findings provide the first direct evidence that the moisturization-induced crystal structural change of ASR product may not be a plausible explanation to the macroscale concrete expansion.

In this study, we propose a laboratory-scale methodology, based on X-ray micro-tomography and caesium (Cs) as a contrast agent, to advance the understanding of cracking due to alkali-silica reaction (ASR) in concrete. The methodology allows achieving a completely non-destructive and time-lapse characterization of the spatial-temporal patterns of both the cracks and the ASR products. While Cs addition slightly accelerated the ASR kinetics, the crack patterns, with and without Cs addition, were statistically equivalent. Cracks with ASR products appeared first in the aggregates, close to the interface with the cement paste. They propagated afterwards towards the aggregates interior. Some products were then extruded for several mm into air voids and cracks in the cement paste. This process suggests that, in the early stage, the ASR products may be a low-viscosity gel that can flow away from the source aggregate and may settle later elsewhere as a rigid phase, upon calcium uptake., Cement and Concrete Research, 150, ISSN:0008-8846

An indication about the expansion of the concrete can be derived from the crack-index [1]. The crack-index is determined by measuring the crack width along pre-drawn lines, Fig. 2.1 and is expressed as crack-width per measured length. However, it has to be kept in mind that the formation of the cracks may not be attributable solely to AAR. Still, the crack index indicates a concrete expansion at the studied location in mm/m.

Alkali-silica reaction (ASR) can cause expansion and cracking of concrete. Despite significant progress over the past 80 years, the molecular structures of the ASR products remain poorly understood. These reaction products are present in very small amounts within concrete aggregates, which severely limit their chemical and physical characterizations. In this study, synthesis of an ASR product structurally identical to that formed in field concrete is achieved in large quantities at 40 °C. The temperature is found to affect the formation of different types of crystalline ASR products: 12.0 Å (

Cement and concrete research 129, 105958 (2020). doi:10.1016/j.cemconres.2019.105958, The alkali-silica reaction (ASR) causes internal expansion that leads to severe concrete degradation. The structure of the ASR products remains largely unclear, due to the limitation of laboratory probes in micro-chemical-crystallographic study. We hereby performed synchrotron-radiation-based X-ray absorption spectroscopy and diffraction investigations to both ASR product samples collected from the field, and reference samples with known structure. Our results suggest that the field ASR crystals from distinct sources are nearly identical. They share a layer-silicate structure similar to the mineral shlykovite, whereas the stacking of the layers in field ASR crystals is altered in several ways, such as the variable basal spacing and significant glide of adjacent layers along the b-axis. We also demonstrate that the amorphous ASR product highly resembles C-S-H. Our study adds new insights to the atomistic structure of ASR products., Published by Elsevier, Oxford

Amorphous and crystalline alkali silica reaction (ASR) products formed in aggregates of two different concrete mixtures exposed to the concrete prim test both at 38 °C and 60 °C have been analysed by scanning electron microscope with energy dispersive X-ray spectroscopy and by Raman microscopy. Additionally, amorphous ASR products were synthesized and analysed with Raman microscopy and 29Si nuclear magnetic resonance. Amorphous ASR products display a higher Na/K-ratio than crystalline ones. Both types of products display a structure dominated by Q3-sites (Si-tetrahedra with three bridging oxygen atoms typical for a layer structure) with a secondary amount of Q2-sites (Si-tetrahedra with two bridging oxygen atoms typical for a chain structure). Temperature in the CPT alters the structure of the crystalline ASR. While the Raman spectra of the product formed at 38 °C is identical to the one formed in concrete structures, the one of the 60 °C product corresponds to K-shlykovite.

Alkali-silica reaction (ASR) causes severe degradation of concrete. The mechanical property of the ASR product is fundamental to the multiscale modeling of concrete behavior over the long term. Despite years of study, there is a lack of consensus regarding the structure and elastic modulus of the ASR product. Here, ASR products from both degraded field infrastructures and laboratory synthesis were investigated using high-pressure X-ray diffraction. The results unveiled the multiphase and metastable nature of ASR products from the field. The dominant phase undergoes permanent phase change via collapsing of the interlayer region and in-planar glide of the main layer, under pressure >2 GPa. The bulk moduli of the low- and high-pressure polymorphs are 27±3 and 46±3 GPa, respectively. The laboratory-synthesized sample and the minor phase in the field samples undergo no changes of phase during compression. Their bulk moduli are 35±2 and 76±4 GPa, respectively. The results provide the first atomistic-scale measurement of the mechanical property of crystalline ASR products.

When shotcrete is in contact with sulfate containing ground water, there is a risk of a drastically reduced service life. In this case, the use of sulfate-resisting cement is recommended. Since physical characteristics of the cement matrix of shotcrete differ from conventional concrete, sulfate-resisting cements do not always guarantee sufficient shotcrete durability. Thus, testing of the sulfate resistance in accelerated tests is necessary. Providing test samples from on-site (real) shotcrete is time consuming and demanding. In this study, the sulfate resistance and physical properties such as compressive strength and transport properties of samples produced in the laboratory without spraying are compared to the properties of field samples. A new compaction method is proposed, which is apt to allow high accelerator dosages. For different alkali-free set-accelerators and cement types, the laboratory-produced samples not only reveal similar sulfate resistance test results as on-site shotcrete, but also exhibit comparable porosity, transport properties and chemical phase assemblage.

Shotcrete is often in direct contact with groundwater containing sulfate. The resistance to sulfate attack of modern sprayed concretes produced with non-alkali aluminate-based accelerators in combination with different cement types is related to their microstructure, transport properties, porosity and phase composition. A characterization of these properties allows a comprehensive assessment of the sulfate resistance of shotcrete with the identification of the relevant physical and chemical influencing factors. As with conventional concrete, the cement type and the water to binder ratio are also decisive for the sulfate resistance in shotcrete. On the one hand, capillary porosity and diffusion coefficient show cement-specific differences, and accordingly the sulfate solution uptake and the sulfur profile in the test specimen with cement type and w/b also are different. On the other hand, the type of cement defines the potential for ettringite formation and thus for damage to the concrete. Sulfate expansion is caused by the conversion of monocarbonate/hemicarbonate/monosulfate (AFm phases) to ettringite. The application of sulfate-resistant cements does not guarantee the sulfate resistance of sprayed concretes in each case. Their use, however, minimizes the damage potential. In the sulfate resistance tests, damage in shotcrete causing a drop in the dynamic modulus of elasticity occurs at a higher sulfate expansion compared to conventional concrete due to the higher volume of hardened cement paste and the smaller maximum aggregate size. The studied alkali-free accelerators, currently used in practice, are found to have no direct adverse effect on the sulfate resistance in the dosage investigated and behave more favorably than the aluminate based alkali-containing accelerators. However, the accelerators influence the sulfate resistance indirectly by causing higher porosity and permeability and thus by an increased sulfate solution uptake of the shotcrete.

Three types of alkali-silica reaction (ASR) products, i.e., crystalline K-shlykovite, Na-shlykovite and nano-crystalline ASR-P1, have recently been synthesized at 80 °C. It is critical to verify the formation of these ASR products in concrete in order to transfer the knowledge of ASR gained from the synthesized products to the ones formed in field concrete. Therefore, ASR products formed in concrete exposed to KOH, NaOH or mixture of KOH/NaOH solution at 60 and 80 °C are analyzed using Raman spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy. The results show that at temperature between 60 and 80 °C K-shlykovite and ASR-P1 are formed in concrete exposed to KOH or a mixture of KOH/NaOH solution, whereas Na-shlykovite is formed in concrete exposed to NaOH solution. Moreover, K-shlykovite and Na-shlykovite do not co-precipitate in the same concrete, not even in the concrete exposed to the mixture of KOH/NaOH solution.

A new experimental methodology for studying ASR expansions at the level of a single aggregate-cementitious matrix interface is proposed. For this methodology, small sandwich-like specimens, with cement paste or mortar on top and bottom of a disc of soda-lime (SL) glass in the middle, are used. These specimens are placed in airtight containers with an alkaline solution and heated in an oven at 60 °C. In these conditions, ASR products are formed rapidly at the interface of the disc and the cementitious matrix, inducing length changes in the specimen which are measured regularly. The morphology and composition of the ASR products are studied by means of SEM/EDS analyses. This inexpensive and very easy to replicate methodology may provide valuable information about the ASR expansion mechanisms. The specimens developed expansions of about 30 µm before the SL glass got detached from the cement paste matrix. SEM/EDS analyses of the reaction products formed in between the SL glass and the cement paste matrix indicate calcium-to-silica molar ratios ranging between 1.0 and 1.5. Finally, based on the experimental results presented in this paper, as well as on other experimental and theoretical results found in the literature, a reaction-expansion mechanism for ASR in SL glass concrete is proposed.

Several aspects of alkali-silica reaction (ASR) are still poorly understood, for example the formation of ASR products occurring before significant aggregate cracking. This study focuses on the analysis of these products and the comparison with the products formed after crack formation. A novel approach for the characterisation of ASR products was used combining different electron microscopy techniques. This combination allows analysis of the ASR products present in small gaps and cracks with a width below 1 μm present between adjacent mineral grains of aggregates. In the three samples studied, the products in thin grain boundaries show no distinct morphology and they are amorphous. They were defined as untextured ASR products. The products present in larger veins form fibrils and platelets, called platey products, and are mainly crystalline. In spite of the differences in morphology, untextured and platey ASR products are of similar composition.

The sulfate resistance of concrete was tested using drying-immersion cycles of varying duration in different sulfate solutions. The measured expansion in the different protocols showed a correlation to the sulfate profiles in the test specimens determined by EDX. Based on the magnitude of expansion and the test duration, a suitable protocol for testing job-site concrete was identified. A matrix of 20 concrete mixtures was tested with this protocol. The test permitted to distinguish the effect of cement type, w/c and paste volume on expansion. Measurements of the dynamic E-modulus made it possible to link expansion and mechanical damage and to define a limit value for expansion. As this test appears to be suitable to determine the potential of concrete for expansion induced by ettringite formation due to sulfate ingress, it was introduced into the Swiss norms.

The diffusion coefficient $$D_{{{\text{O}}_{2} }}$$ , the porosity and the pore structure of mortars produced with a Portland cement and a range of blended cements containing limestone powder, microsilica, portlandite or slag were measured in the non-carbonated and the carbonated state. Additionally, the setup for measuring O2 diffusion was adapted to measure also the CO2 diffusion of the carbonated mortars. The diffusion coefficient $$D_{{{\text{O}}_{2} }}$$ and the total porosity were increased in the mortars containing microsilica and slag, while they were decreased in the other mortars due to carbonation. Invariably, the pore structure became coarser in all samples. The relationship between diffusion coefficients $$D_{{{\text{O}}_{2} }}$$ and $$D_{{{\text{CO}}_{2} }}$$ in the carbonated mortars was always linear, with $$D_{{{\text{O}}_{2} }}$$ systematically higher by factor of 1.37. As this factor broadly agrees with what was found in the scant literature about CO2 diffusion, it could be used for estimating $$D_{{{\text{CO}}_{2} }}$$ of carbonated mortar and concrete based on measurements of O2 diffusion.

In high-performance concrete (HPC) subjected to high temperature during tunnel fires, the build-up of vapor pressure due to dehydration of the cement hydration products cannot be relieved due to the very low porosity and permeability of this type of concrete, often resulting in explosive spalling. Explosive spalling may cause devastating damage of the tunnel structure, which threatens both, civilians and emergency response units. This work suggests a potential application of silica aerogel in the protection of concrete linings, which consists in decorating the surface of HPC structures with a highly-insulating aerogel-cement mortar layer, with the aim of delaying the heating of the HPC and extending the performance of the main concrete structure of the tunnel under fire. The main aim of this study is investigating the impact of the microstructure, with special focus on the pore structure, on the thermal conductivity and the mechanical properties of the aerogel mortars. In particular, the integrity of the aerogels in the mortars, both in the mixing process and the possible long-term chemical degradation, was a main concern. Finally, a preliminary test of the performance against fire spalling was performed. While aerogel-containing mortars were able to protect HPC cubes from fire spalling under a specific thermal loading protocol, the thermal conductivity and the mechanical properties obtained were similar to those of cellular concrete in the same range of total porosity. A possible explanation of the lower-than-expected insulation performance is the partial degradation of the aerogel filler by reaction with the alkaline pore solution of the mortars. Implications of these new findings on aerogel-cement mixtures are also discussed.

In this study, the effect of CO2 concentration and ambient relative humidity (RH) on accelerated and natural carbonation of 18 concrete mixtures produced with nine different cement types is investigated. Increasing the CO2 concentration from 0.045 to 1 and 4 % at 57 % RH does not alter the relative carbonation resistance between the concrete mixtures. The increase of RH from 57 to 70 and 80 % RH at 4 % CO2 shows a water-to-cement ratio and cement-specific effect that affects the relative carbonation resistance between the concrete mixtures. The carbonation resistance at 4 % CO2 and 57 % RH allows assessing the carbonation resistance of concrete in sheltered and with restrictions in unsheltered outdoor exposure. The carbonation resistance below 70 % RH is mainly governed by the CO2 buffer capacity. However, in the accelerated tests at 80 % RH and in the unsheltered outdoor exposure capillary condensation is of increased importance.

The recycling of demolition rubble and its reuse in building materials is desired, but the question rises how reinforced concrete members made with recycled aggregate concrete has to be designed. Since a similar flexural behavior of recycled aggregate concrete and natural aggregate concrete was shown in several studies, this paper focuses on the shear resistance of slabs without shear reinforcement. The slabs were made of concrete using different types of aggregates: (a) 100% wt recycled concrete aggregate, (b) 50% wt mixed rubble aggregates and 50% wt natural aggregates, (c) 100% wt mixed rubble aggregates as well as (d) natural aggregates. The latter was used as a reference concrete. In order to determine the shear resistance, slabs were loaded until shear failure occurred in a four-point-bending test. The slabs made of recycled aggregate concrete showed similar crack distributions as the slabs made of natural aggregate concrete. Predictions for the shear resistance were obtained using the critical shear crack theory of Muttoni as well as the Swiss and the European standards (SN 505 262 and Eurocode 2). The predictions by the critical shear crack theory and the European standard showed good correlation with the experimental results (mean ratio between experimental and predicted value: 1.00 ± 0.05 and 0.99 ± 0.04, respectively). But the predictions by the critical shear crack theory and the European standard overestimated the shear resistance of the slabs made of concrete with 100% wt mixed rubble aggregate. Especially for these slabs the Swiss standard predicted 8–11% lower shear resistances than the critical shear crack theory and the European standard.

In this study, the stress–strain-behaviour of self-compacting concrete (SCC) and conventionally vibrated concrete (CVC) is compared. The influence of the paste volume and the cement type on E-modulus, flexural and compressive strengths, drying shrinkage, creep and stress development under restrained conditions is investigated on three SCC mixtures and three mixtures of CVC with identical water-to-cement-ratio. SCC reaches lower values for E-modulus, compressive and flexural strengths but higher values for shrinkage, creep and strain under restrained conditions. Besides the paste volume, the cement type plays a fundamental role regarding creep. Composite models were applied for comparisons and were able to predict the differences in E-modulus and shrinkage between CVC and SCC.

Petanque is a game originating in Provence, France, which has become common in many European countries. It is played using balls with a diameter of 70–80 mm and a weight of 650–800 g. The weight can either be adjusted by the thickness of the metallic shell or, mainly in case of cheap balls, by a filling. Petanque balls are commonly available at supermarkets. After an explosion of a petanque ball stored in a cupboard, thousands of balls sets had to be recollected in Switzerland under strong safety measures. Several balls, including the remains of the exploded one, where subsequently investigated. The balls were made of a metallic shell, completely filled with a sand-like material. Up to 1 l of a gas, mainly composed of hydrogen, was found within intact balls, compressed in the pore space of the sand. This indicated a systematic cause of the explosion. To elucidate the mechanisms leading to the explosion of the ball, the materials of the shell and the filling were characterised (composition, porosity, moisture content, strength, etc.). Furthermore, the fracture surface and the welding of the two shell halves were analyzed. Based on these results, the pressure in the ball was calculated and compared to the theoretical resistance of the shell. Due to a high moisture content, small metallic particles in the filling corroded under anaerobic conditions in the completely sealed ball, leading to a formation of hydrogen gas. The resistance of the shell was considerably reduced in the region of the weld due to notch effects. The explosion could be reasonably explained by comparing the stresses due to internal pressure with the reduced resistance of the shell.

In a model system for alkali―silica reaction consisting of microsilica, portlandite (0-40 mass%), and 1M alkaline solutions (NaOH, KOH), the influence of calcium on silica dissolution and on the formation of reaction products is investigated. The reaction and its products are characterized using calorimetry, X-ray diffraction, thermogravimetric analysis, nuclear magnetic resonance, desorption experiments, and pore solution analysis in combination with thermodynamic modeling. Silica dissolution proceeds until portlandite is consumed due to the formation of C-S-H, and subsequently, saturation of dissolved silica in the alkaline solution is reached. As a result, the amount of dissolved silica increases with the increasing portlandite content. Depending on the amount of portlandite added, the reaction products show differences in the relative amounts of Q 1 , Q 2 , and Q 3 sites formed and in their average Ca/Si ratio. The ability of the reactions products to chemically bind water decreases with the decreasing relative amount of Q 3 sites and with the increasing Ca/Si ratio. However, the amount of physically bound water in the reaction products reaches a maximum value at a Ca/Si ratio between 0.20 and 0.30.

In aeration tanks of wastewater treatment plants (WWTP), biodeterioration can lead to a partial dissolution and ensuing erosion of the concrete due to an acid attack caused by the nitrifying biofilm covering the tank surface. In this study, concrete samples were exposed in four different WWTP. The CaO content of the cement used, the water-to-cement ratio, and curing affect the resistance of the concrete to acid attack. However, both experimental data and thermodynamic modeling show that water hardness is the dominating parameter for surface erosion. In the presence of high water hardness, the protons produced by the nitrifiers are buffered and the calcite precipitation occurring in all concrete samples is increased. This results in a decrease of porosity near the surface and higher mass transfer resistance against carbon dioxide and therefore in lower deterioration rates of the concrete.

The pore systems of cement-based materials are studied by N(2) sorption and mercury intrusion porosimetry (MIP). Pore size distributions and internal surfaces are derived. Especially in materials with a broad pore size distribution, these (and other) methods generally do not lead to coincident results. It is shown here, how the interpretation of the experimental data of the two methods may be modified in order to obtain coincident pore size distributions from both methods. The studied pore systems are described as array of chambers which are connected by smaller throats. N(2) adsorption is used to calculate the size of the pores, whereby no distinction between throat or chamber type is possible with this method. Assuming mercury entrapping in ink-bottle type pores (pores that are connected to an external surface through smaller pores only) being the dominant process for mercury snap-off during extrusion and applying multi-cycle MIP, the calculation of the size of the entrances of these ink-bottles is possible. It is shown that similar results also may be derived from mercury extrusion data by applying a contact angle correction for the retracting mercury meniscus. A good agreement of the pore size distribution of the connected, non-ink-bottle type pores derived from either N(2) sorption or mercury intrusion is obtained. Samples of cement paste and mortar are analysed. A significant difference between cement paste and mortar regarding the neck entrances of ink-bottle type pores is found and attributed to the coarse pore space around the aggregates, the interfacial transition zone.

Currently the work for two new railway tunnels through the Swiss Alps with a length of 35 and 57 km respectively is in progress. Prepared aggregates quarried from the tunnels are reused for the concrete. About 50% of these aggregates are classified as reactive in regard to alkali-aggregate reaction (AAR) according to the AFNOR P 18-588 microbar test. In order to obtain information about AAR in concrete exposed to underground conditions, eight existing tunnels are investigated in this study. The concrete and shotcrete of the 16 coring sites studied is between 19 and 44 years old. The visual inspection of the tunnels and the physical properties of the concrete and shorcrete indicate no substantial damage although signs for AAR are present in the majority of the samples. Furthermore, the aggregates of seven coring sites are classified as reactive, but they obviously do not reach their reaction potential. A possible reason might be the minor climatic fluctuations in the tunnels. The results of this study indicate that reactive aggregates might be used for concrete in tunnels without causing damage due to AAR.

The reaction mechanism of alkali-silica reaction (ASR) is poorly understood due to the difficulties to directly characterize ASR products in concrete. In this study, ASR products with initial Ca/Si of 0.25 and (K + Na)/Si ratio 0.5 with different K/Na ratios are synthesized at 80 °C. The synthesized ASR products are characterized by different techniques, also the solution chemistry is analyzed and saturation indices are calculated. The results show that crystalline and nano-crystalline phases are formed in the presence of both alkalis and calcium. No ASR product is present in the absence of calcium. All synthesized crystalline ASR products highly resembles the crystal structure of shlykovite, indicating that a substitution of K in shlykovite by Na can occur. Its silicate sheet structure has strong similarity to the ASR products formed in concrete according to Raman spectra, while some differences are observed in their morphologies and basal peak of the XRD patterns.

Alkali silica reaction (ASR) can significantly affect the service life of concrete. The dissolution of aggregates has a direct impact on gel formation and thus on the macroscopic expansion. The conventional expansion tests and other investigations confirmed ASR reactivity of three aggregates from different locations in Switzerland. The reactive minerals within alpine and composite aggregates were identified using an innovative scratch-tracking method. This method helps to study aggregate dissolution if measuring the amount of released Si is not enough, because: several minerals release Si or Al and/or new phases are probable to form during dissolution experiment. The scratch-tracking method on theses alpine aggregates showed faster dissolution of feldspars and quartz while muscovite was hardly affected. The dissolution of the aggregates in solution confirmed these differences between minerals., Cement and Concrete Composites, 124, ISSN:0958-9465, ISSN:1873-393X