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Only humans need shelter? Not really! Many fish rely, at least in part of their lives, on physical places where they rest, feed and find shelter.

Traditionally, harbors have been designed mainly for fisheries and for transport of goods and passengers. In recent years, water quality has improved in many harbors, and marine biodiversity is becoming increasingly important. In the present study, concrete elements - with complex surface designs - were deployed on harbor sea walls and at sites where coastal protection is needed. This was accomplished to improve the local marine biodiversity and fish abundance. Our study is conducted in the Vigo Harbor situated in northwestern Spain. A team of DTU researchers has just returned from a three weeks’ fieldtrip monitoring underwater biodiversity in the Spanish harbor. We investigate whether 1) concrete harbor walls with different structures, and 2) new concrete elements deployed for coastal protection may improve the local marine biodiversity and fish abundance. We measure biodiversity by analyzing underwater video footage. Harbors often have a central place in cities, and increased marine life may eventually turn harbors into exciting blue parks for people to enjoy. Although the project is conducted in Spain, the project results are also relevant for other European harbors where local marine biodiversity is growing in importance.

Der er stigende interesse for marine naturgenopretningsprojekter, som et redskab til at forbedre miljøtilstanden og biodiversiteten i danske havområder. Denne artikel beskriver nye projekter, som undersøger fordele og ulemper ved at anvende betonrev som et supplerende redskab til forbedring af havmiljøet i Køge Bugt., Der er stigende interesse for marine naturgenopretningsprojekter, som et redskab til at forbedre miljøtilstanden og biodiversiteten i danske havområder. Denne artikel beskriver nye projekter, som undersøger fordele og ulemper ved at anvende beton-rev som et supplerende redskab til forbedring af havmiljøet i Køge Bugt.

The use of calcined clays in construction materials has attracted significant attention in the last few years. Based on the continued need for sustainable construction to meet global development challenges, the green transition of the cement industry is an urgent necessity. The use of clay-blended cements will keep increasing to meet the need for mass quantities of materials and the prospect of reducing their embodied CO2, as traditional supplementary cementitious materials are expected to decline in availability. To enable the necessary rapid increase in the fraction of clays that can be used in cements, the use of modeling tools which provide insights into the clays and their reactivity in cementitious systems is of increased interest. The aim is to predict the properties of the calcined clays based on the original rock and calcination conditions, the phase evolution, material properties, and durability of construction materials. This is crucial to reduce the time needed for development and commercialisation, whereas extensive empirical work has been used in the past to achieve material transition in the construction sector, which can be extremely time consuming. This review article therefore aims to provide an overview of available thermodynamic data, issues with database integration, modelling of process parameters, and properties prediction for cementitious materials.

The durability performance of blended cementitious systems with calcined clays is reviewed in this paper by the RILEM TC 282-CCL on calcined clays as supplementary cementititous materials (SCMs) (working group on durability). The impact of metakaolin and other calcined clays on the porosity and pore structure of cementitious systems is discussed, followed by its impact on transport properties such as moisture ingress. The durability performance of binary and ternary cementitious systems with calcined clay is then reported with respect to chloride ingress, carbonation, sulphate attack, freeze–thaw and alkali-silica reaction. The role of unique microstructural alterations in concretes with calcined clay-limestone combinations due to the formation of CO3-AFm and their impact on different durability exposures is emphasised. While a large majority of studies agree that the chloride resistance of concretes with calcined clays is significantly improved, such concretes seem to be more susceptible to carbonation than those produced with plain Portland cement or other SCMs used at lower replacement levels. Also, several studies are focused on metakaolin and lower grade kaolinite clay, while there are limited studies on calcined smectite/illite or mixed clays, which could also play a crucial role to the improved adoption of large reserves of clay sources to produce sustainable binders.

Concretes, containing calcined clay and a calcium carbonate source, were submersed in Øresund strait (DK) and the chloride ingress and mineralogical changes were monitored. Half of the samples were mechanically treated to observe the settlement on undisturbed samples and under mechanically stressed conditions. The investigation showed that even cement replacements of more than 35% – the upper limit in EN 197-1 for composite cements, reduce the chloride binding significantly. Mechanical treatment, removed not only algae and microorganisms but also mineral layers otherwise observed in the reference samples. However, the calculated apparent diffusion rates did not differ significantly.

Reactive transport models are useful tools in the development of cement-based materials. The output of cement-related reactive transport models is primarily regarded as qualitative and not quantitative, mainly due to limited or missing experimental validation. This paper presents an approach to optimize the calibration process of reactive transport models for cement-based materials, using the results of several short-term experiments. A quantitative comparison of changes in the hydrate phases (measured using TGA and XRD) and exposure solution (measured using ICP-OES) was used to (1) establish a representative chemical model, limiting the number of hydrate phases and dissolved species, and (2) calibrate the transport processes by only modeling the initial tortuosity. A case study comprising the early age carbonation of cement is presented to demonstrate the approach. The results demonstrate that the inclusion of a microstructure model in our framework minimizes the impact of the initial tortuosity factor as a fitting parameter for the transport processes. The proposed approach increases the accuracy of reactive transport models and, thus, allowing for more realistic modeling of long-term exposure.

The increased focus on innovation, development and active learning at DTU has lead to an increase of laboratory facilities and an increased use of experimental activities in courses and projects. This paper presents experiences in six concepts successfully tested at DTU’s civil engineering department DTU Byg, describing how the experimental activities in courses and projects can best be organized and used with a low resource consumption for educators, students and the university.

This paper investigates how the composition of Portland composite cements affects their chloride-binding properties. Hydrated cement pastes prepared with a reference Portland cement and composite Portland cements containing metakaolin and/or silica fume were exposed to NaCl or CaCl2 solutions. Chloride-binding isotherms were determined and the hydrate assemblage was investigated using TGA, XRD, 27Al NMR, 29Si NMR and thermodynamic modelling. Compared to the reference Portland cement paste, silica fume replacement did not alter the chloride-binding capacity. The metakaolin replacement resulted in the highest chloride-binding capacity. When combining silica fume with metakaolin, the chloride binding is similar to the reference Portland cement. In this study the differences in chloride binding were linked not only to changes in the AFm content, but also to alterations in the Al-uptake and chain length of the C(-A)-S-H.

Zur Beurteilung des externen Sulfatwiderstands von zementbasierten Bindemitteln werden Prüfverfahren verwendet, welche meistens als Testkriterium die freie Dehnung eines Probekörpers verwenden. Die Ergebnisse dieser Arbeit zeigen, dass bei praxisnahen Sulfatkonzentrationen der Betrag der freien Dehnung nicht zwingend mit der schädigenden Expansionsspannung korreliert, da unterschiedliche Bildungsmechanismen von Ettringit und Gips unterschiedlich große Kristallisationsdrücke ausüben können., In order to assess the resistance of cementitious binders against external sulfate attack, current testing procedures usually utilise the length change of samples as a testing criterion. The results of this thesis show that the amounts of free expansion and expansion stress do not necessarily correlate in the case of sulfate concentrations encountered in the field, because different mechanisms of ettringite and gypsum formation can lead to different amounts of crystallisation pressure.

This study evaluates the sulphate resistance of blended cement derived from the addition of thermally activated coal waste as pozzolan, at replacement levels of 0%, 20% (CMW20) and 50% (CMW50) with a multi-method approach. The pastes were prepared at a w/b ratio of 0.5, using a water-reducing admixture in the blended pastes to compensate for their high water demand. Sulphate resistance is reduced in CMW20 pastes, while longterm benefits are observed for CMW50 pastes, although moderate signs of deterioration are observed at the beginning of the exposure. The initial damage in CMW50 pastes is attributable to the precipitation of products (mainly ettringite and monosulphoaluminate) in the small capillary pores (<0.01 ¿m). This is prevented in OPC and CMW20 pastes since their microstructure allow the precipitation in the macropores (>0.05 ¿m). The greater long-term resistance of CMW50 pastes was explained by thermodynamic calculations, which suggests that the lower calcium leachability of these cements prevented gypsum formation. This, together with the higher content of carboaluminate phases, leads to lower supersaturation levels in the pore solution with respect to ettringite, reducing stresses derived from sulphate exposure.

Mortars prepared with a CEM I and a CEM III/B binder were investigated in different magnesium sulfate solutions. The main deterioration mechanism for the CEM I was expansion, while surface erosion was dominant for CEM III/B. The presence of sodium, potassium and calcium in a magnesium sulfate solution led to less expansion and less surface deterioration for both, CEM I and CEM III/B, than which was observed in solutions containing only sodium or magnesium sulfate. The presence of a mixture of different cations seems to lower both the surface deterioration and the expansion and might explain why sulfate attack damages are not as frequent in the field as in laboratory tests. Sulfate binding before cracking/expansion is similar in the presence of all different solutions investigated, indicating that the speed of sulfate ingress and the amount of bound sulphate depends during the first months mainly on the binder