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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

This test method covers the laboratory determination of the expansion rate of concrete cores (designated as “residual expansion potential” in the following context) extracted from structures affected by alkali silica reactions.

ASR in concrete typically follows a certain sequence. On the level of the structure, there is an initial period after construction where no expansion occurs. Then the concrete starts to expand and cracks develop, often in a linear way, and can eventually damage the structure (NB slight cracking and signs of AAR are usually insufficient to “damage” the serviceability or safety of a structure).

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.

The Swiss method to determine the residual expansion of concrete from structures is based on the storage of cores in a container at 38 °C and 100 % relative humidity for half a year. First, the cores are conditioned at 20 °C for a week to reach water saturation. Afterwards, they are moved to the container. Length changes are recorded regularly. At the end of the test, the cores are dried at 20 °C and low relative humidity until they reach their initial mass before the start of conditioning. The length change during the storage in the container and the irreversible length change (length difference before conditioning and after drying at the end of the test) are used to assess the expansion kinetics of the concrete.

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 (

Understanding reaction mechanisms of magnesium potassium phosphate (MKP) cement is of significant importance, as it is closely related to the optimum design of MKP cement-based materials. In this study, reaction mechanisms of MKP cements with a high magnesium-to-phosphate (Mg/PO4) molar ratio of 8 were investigated at two different water-to-solid (w/s) ratios of 0.5 and 5. The experimental findings show that the use of this high Mg/PO4 molar ratio suppresses the formation of potassium-free magnesium phosphate hydrates. K-struvite is mainly formed with probably more phosphate than the theoretical value. Moreover, the w/s ratio plays a crucial role on governing the reaction path of MKP cements. The lower w/s ratio (w/s = 0.5) leads to higher potassium concentration and pH value, thus suppressing the formation of intermediate product, Mg2KH(PO4)2·15H2O, which is formed at the higher w/s = 5. However, it causes the formation of minor amount of brucite at 28 d, which coexists with K-struvite in the paste.

Recently, the structure of the crystalline alkali-silica reaction (ASR) product formed in affected concrete has been identified based on μ-XRD measurements. However, the data were obtained from a single aggregate. In this study, Raman microscopy is applied on crystalline ASR products formed in several aggregates and concrete mixtures, enabling a comparison of their spectra and with it their structure. In a first step, samples from the same concrete used for μ-XRD measurements are analyzed and compared. In a second step, samples from a second structure and from a concrete prism test are measured. In addition to Raman microscopy, SEM with EDX is used to characterize the microstructure. The Raman spectra of the crystalline ASR product are practically identical in all studied aggregates and concrete mixtures, showing it is the same phase. This conclusion is further supported by the microstructural data.

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.

The carbonation of Portland cement, metakaolin and limestone mortars has been investigated after hydration for 91 days and exposure to 1% (v/v) CO2 at 20 °C/57% RH for 280 days. The carbonation depths have been measured by phenolphthalein whereas mercury intrusion porosimetry (MIP), TGA and thermodynamic modeling have been used to study pore structure, CO2 binding capacity and phase assemblages. The Portland cement has the highest resistance to carbonation due to its highest CO2 binding capacity. The limestone blend has higher CO2 binding capacity than the metakaolin blends, whereas the better carbonation resistance of the metakaolin blends is related to their finer pore structure and lower total porosity, since the finer pores favor capillary condensation. MIP shows a coarsening of the pore threshold upon carbonation for all mortars. Overall, the CO2 binding capacity, porosity and capillary condensation are found to be the decisive parameters governing the carbonation rate.

The geological storage of nuclear waste includes multibarrier engineered systems where a large amount of cement-based material is used. Predicting the long term behaviour of cement is approached by reactive transport modelling, where some of the boundary conditions can be defined through studying natural cement analogues (e.g. at the Maqarin natural analogue site). At Maqarin, pyrometamorphism of clay biomicrites and siliceous chalks, caused by the in-situ combustion of organic matter, produced various clinker minerals. The interaction of infiltrating groundwater with these clinker phases resulted in a portlandite-buffered hyperalkaline leachate plume, which migrated into the adjacent biomicrite host rock, resulting in the precipitation of hydrated cement minerals. In this study, rock samples with different degrees of interaction with the hyperalkaline plume were investigated by various methods (mostly SEM-EDS). The observations have identified a paragenetic sequence of hydrous cement minerals, and reveal how the fractures and porosity in the biomicrite have become sequentially filled. In the alkaline disturbed zone, C-A-S-H (an unstoichiometric gel of Ca, Al, Si and OH) is observed to fill the pores of the biomicrite wallrock, as a consequence of reaction with a high pH Ca-rich fluid circulating in fractures. Porosity profiles indicate that in some cases the pores of the rock adjacent to the fractures became tightly sealed, whereas in the veins some porosity is preserved. Later pulses of sulphate-rich groundwater precipitated ettringite and occasionally thaumasite in the veins, whereas downstream in the lower pH distal regions of the hyperalkaline plume, zeolite was precipitated. Comparing our observations with the reactive transport modelling results reveals two major discrepancies: firstly, the models predict that ettringite is precipitated before C-A-S-H, whereas the C-A-S-H is observed as the earlier phase in Maqarin; and, secondly, the models predict that ettringite acts as the principal pore-filling phase in contrast to the C-A-S-H observed in the natural system. These discrepancies are related to the fact that our data were not available at the time the modelling studies were performed. However, all models succeeded in reproducing the porosity reduction observed at the fracture–rock interface in the natural analogue system.

The alkali–aggregate reaction comprises the alkali–silica reaction (ASR) and the alkali–carbonate reaction (ACR). Reaction kinetics of the ASR depends on the grain size and crystalline structure of the reactive silicon dioxide. The reaction starts in the aggregates along the particle periphery and progresses inward. After cracking of the particle, larger amounts of reaction products are formed and are eventually extruded in the cement paste, where they fill cracks and voids. ASR products within aggregates predominantly consist of (hydrated) silicon, alkalis and calcium with characteristic atomic ratios of (Na + K)/Si ∼ 0·25 and Ca/Si ∼ 0·25. They take up additional calcium while releasing alkalis when extruded. Amorphous and crystalline reaction products occur and coexist. Expansion is the result of water adsorption by the reaction products. In ACR, harmless dedolomitisation is distinguished from deleterious reaction of fine-grained silica disseminated throughout the carbonate matrix. Further research is needed to gain more in-depth knowledge about the thermodynamics and kinetics of ASR products and the mechanisms of expansion. This should allow the establishment of a better link between concrete structures and both accelerated testing and models.

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 use of alternative cements with lower CO2 emissions during production compared to ordinary Portland cement (PC) is only sustainable, if the durability and with it the service life of components and structures produced with them are not compromised. In this project, the carbonation resistance of mortars produced with calcium sulfoaluminate cement (CSA) and three different slag-based cements is studied in accelerated conditions and natural exposure. Additionally, the diffusion coefficients of oxygen ($$D_{{{\text{O}}_{2} }}$$) and carbon dioxide ($$D_{{{\text{CO}}_{2} }}$$) are measured (the latter one only on carbonated mortars) and the change in mortar porosity due to carbonation is determined. Mortar PC used as reference and mortar CSA display the lowest carbonation coefficients, both in accelerated conditions and natural exposure. The three systems based on slag display higher carbonation coefficients. After carbonation, the diffusion coefficient $$D_{{{\text{O}}_{2} }}$$ is increased for all mortars except for mortar PC, whose total porosity is decreased as well, in contrast to all other mortars. The diffusion coefficients $$D_{{{\text{O}}_{2} }}$$ and $$D_{{{\text{CO}}_{2} }}$$ show a linear relationship in the carbonated mortars.

Alkali-silica reaction (ASR) is one of the most important deterioration mechanisms in concrete leading to substantial damages of structures worldwide. Synchrotron-based micro-X-ray diffraction (micro-XRD) was employed to characterize the mineral phases formed in micro-cracks of concrete aggregates as a consequence of ASR. This high spatial resolution technique enables to directly gain structural information on ASR products formed in a 40-year old motorway bridge damaged due to ASR. Micro-X-ray-fluorescence was applied on thin sections to locate the reaction products formed in veins within concrete aggregates. Micro-XRD pattern were collected at selected points of interest along a vein by rotating the sample. Rietveld refinement determined the structure of the ASR product consisting of a new layered framework similar to mountainite and rhodesite. It is conceivable that understanding the structure of the ASR product may help developing new technical treatments inhibiting ASR. (C) 2015 Elsevier Ltd. All rights reserved.

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.

An imaging concept is proposed for the phase identification and segmentation of elemental map images from energy dispersive spectroscopy. The procedure starts with presegmentation using common clustering algorithms, continues with automated identification of the chemical compositions, followed by their screening by professional expertise. The ultimate phases are finally clustered by applying a minimum Euclidean distance classifier. The potential, performance and limitations of the approach are presented on energy dispersive spectroscopy maps acquired by a scanning electron microscope and conducted on samples produced from cement clinker, natural rock and hydrated cement mortar. Nevertheless, the technique is suitable for arbitrary types of materials and general devices for energy dispersive spectroscopy acquisition. It is an approach for extending common energy dispersive spectroscopy analysis by means of visual examination and ratio plots towards quantitative rating.

When cement with mineral additions is employed, the carbonation resistance of mortar and concrete may be decreased. In this study, mortars containing mineral additions are exposed both to accelerated carbonation (1% and 4% CO2) and to natural carbonation. Additionally, concrete mixtures produced with different cements, water-to-cement ratios and paste volumes are exposed to natural carbonation. The comparison of the carbonation coefficients determined in the different exposure conditions indicates that mortar and concrete containing slag and microsilica underperform in the accelerated carbonation test compared to field conditions. The carbonation resistance in mortar and concrete is mainly governed by the CO2 buffer capacity per volume of cement paste. It can be expressed by the ratio between water added during production and the amount of reactive CaO present in the binder (w/CaOreactive) resulting in a novel parameter to assess carbonation resistance of mortar and concrete containing mineral additions.

In this study, the potential of time-of-flight secondary ion mass spectrometry (ToF-SIMS) for the application in cement-based materials is assessed in combination and comparison with scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). Mortar, concrete and samples from model systems providing products formed by the alkali–silica reaction (ASR) were studied. ToF-SIMS provides qualitative data on alkalis in cases where EDX reaches its limits in regard to detectable concentration, lateral resolution and atomic number of the elements. Due to its high in-depth resolution of a few atomic monolayers, thin layers of reaction products can be detected on the surfaces and chemically analyzed with ToF-SIMS. Additionally, it delivers information on the molecular conformation within the ASR product, its hydrogen content and its isotope ratios, information not provided by EDX. Provided the samples are carefully prepared, ToF-SIMS opens up new possibilities in the analysis of cement-based materials.

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 the first half of the twentieth century, a variety of dry-mix renders with different trade marks spread across Europe. Their stated performance made them attractive for buildings where the overhanging eave was absent, hence they found broad application in rationalist buildings and districts. However, their composition and properties are barely known. In this paper, the Terranova render of the Engineering Faculty in Bologna was characterised, to investigate the reasons for its outstanding durability. Unexpectedly, the render was found to be constituted by dolomitic lime and only a small amount of white cement and exhibited a remarkable strength. The presence of air voids seems due the use of air entraining agents and may have contributed to the frost resistance of this render during 80 years. The results are expected to contribute not only to the knowledge of Terranova render, but also to a better understanding of durability issues for new renders.

The influence of the LiNO3 on the ASR product was studied both in a model system and in mortars. In the model system, the addition of LiNO3 decreases the dissolution rate and the solubility of silica. Lithium changes the 2-dimensional cross-linked (Q3 dominated) network of the ASR product into a less structured, Q2 dominated product, likely by adopting the role of calcium. In the mortar samples the addition of LiNO3 decreases expansion and significantly influences the chemical composition and the morphology of the reaction product. Lithium decreases the calcium, sodium and potassium content and changes the relatively porous plate-like reaction product into a dense one without texture. The findings in the mortars indicate that the ASR-suppressing effect of lithium is caused by the lower potential of the reaction product to swell. Furthermore, it forms a protective barrier after an initial reaction slowing down ASR.

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.

Cracks accelerate the ingress of harmful fluids, impairing the durability of reinforced concrete structures. Plastic shrinkage cracking poses a problem in particular for concrete components such as slabs, in which a high percentage of the surface area is exposed to drying. In this study, the impact of different admixtures on the occurrence and on the extent of plastic shrinkage cracking of SCC was investigated. Plastic shrinkage cracking was measured according to ASTM C1579-06 in a climate chamber at a temperature of 30 °C and relative humidity of 60%. Starting directly after casting, the settlement, the capillary pressure and the mass loss were recorded. At the end of the test, the crack-width distribution was analyzed. A shrinkage reducing admixture and a paraffin-based curing compound were effective in preventing cracking. Based on the observed evaporation, settlement, capillary pressure and cracking behavior, the mechanisms for crack prevention were identified.

The determination of the residual expansion potential can provide important information on the prognosis of AAR in concrete structures. However, there are still uncertainties about the test protocol and data analysis. In this study, residual expansion of cores from several concrete structures damaged by AAR was measured. The expansion during the test can be divided into different phases with different expansion rates. The results indicate that the expansion in the first phase, that takes place after sample conditioning but before a linear expansion rate is reached, is specific for each concrete and proportional to the further expansion of the cores during the test. Therefore, it can be used to distinguish concrete with different residual expansion potentials. The residual expansion correlates both with the expansion rates on the investigated structures and the expansion of lab concrete, having a similar composition as the on-site concrete, determined with a concrete performance test.

There is little knowledge about the relation between AAR-induced damage observed in structures and the expansion potential obtained with accelerated tests. In this study, aggregates used in structures damaged by AAR were tested with the microbar test (MBT/AFNOR XP 18-594) and the concrete performance test (CPT/AFNOR P18-454). After the tests, the samples were examined using optical and scanning electron microscopy. Based on the results, the significance of the microbar test has to be examined very critically. The agreement of measured expansion, reacted rock types and the composition of the reaction products between the on-site concrete and the reproduced concrete subjected to the CPT clearly indicates that the reaction mechanisms in the structure and in the concrete performance test are comparable. As such, the concrete performance test seems to be an appropriate tool to test the potential reactivity of specific concrete mixtures.

The effects of expansion on concrete structures induced by alkali–silica reaction (ASR) are complex. Numerous attempts have been made to model them. Some of these models assume an E -modulus for the ASR product, as no experimental data exist up to now. In this study, Vickers hardness, indentation and E -modulus are determined by micro-indentation tests on undried, polished concrete samples taken from a structure damaged by ASR. Both the indentation tests and the chemical analysis by EDX performed on the ASR product in different aggregates indicate that it is relatively homogenous. Vickers hardness ranges between 10 and 19 and E -modulus between 7 and 9 GPa. Towards the edge of the aggregates the ASR product takes up calcium and the values for Vickers hardness and E -modulus increase.

Ethyl silicate (tetraethylorthosilicate, TEOS) is one of the most used consolidants for natural stones in the restoration of architectural and cultural heritage and the literature concerning its performance in this application is quite abundant. In this paper, the need, and sometimes urgency, of preserving ancient fired-clay elements (bricks and terracotta decorations) is highlighted as well, and the effects of ethyl silicate consolidation (75 wt% TEOS in white spirit) are investigated from a microstructural, physical–mechanical and aesthetic point of view. Fired-clay brick samples (open porosity ≈45 %; compressive strength ≈14 N/mm2) were treated and then characterized by mercury intrusion porosimetry, scanning electron microscopy, water absorption, compressive strength test and spectrophotometry, to assess the effects of the treatment. The TEOS treatment gave encouraging results: a good penetration depth (about 10 mm), a limited reduction in porosity, a large decrease in water absorption, a significant improvement in compressive strength and a positive aesthetic outcome. The results obtained pointed out TEOS treatment as a promising solution for fired-clay bricks consolidation.

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 concrete, bricks and masonry rubble as concrete aggregates is an important way to contribute to a sustainable material flow. However, there are still various uncertainties limiting the widespread use of recycled concrete (RC). The fluctuations in the composition of commercial grade recycled aggregates (RAs) and their influence on the properties of fresh and hardened concrete are of particular concern regarding the use of RC. In this project, variations in the composition of RA were studied over a period of several weeks. Concrete mixtures were then produced with these aggregates in order to evaluate the resulting variations in concrete properties. Using two of them, consisting a high content of RA, the principal applicability of RC-mixtures for structural use in comparison to conventional concrete (CC) was shown in web shear and flexural reinforced beams, which were tested to their ultimate shear force resistance. Evaluating experimental and analytical results based on the modified truss methodology, no significant drop for beams made of RA in their shear force resistance was observed. Although the high variability in aggregate composition causes corresponding variations in concrete properties, the results obtained demonstrate that RA is suited for a wide variety of applications in the building industry.

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.