Earth construction: Field variabilities and laboratory reproducibility

Building construction is a major polluting sector. As a result, there is increasing global interest in the development of sustainable building materials with low environmental impact. Earth-based materials are among the materials of interest and building with earth-based materials has thus received a particular renewal of attention. Previous research has focused on the physical characteristics and durability of these materials. The aim of this study is to assess the variability of materials made in-situ and their reproducibility in the laboratory using an automatic normal Proctor machine with different compaction energies. Both cob and light earth were investigated. Cylindrical and prismatic specimens were produced on-site and in the laboratory: cob was made of silt, silty clay, sandy silt, and flax straw; and a separate layer of light earth was made of elastic silt and reed fibres. An experimental program was designed to evaluate the properties of the materials in terms of their water content, density, porosity, compressive strength, and thermal conductivity. The results revealed that the in-situ densities could be reproduced in the laboratory with compaction energies of 0.6 MJ/m3 and 0.2 MJ/m3 for cob and light earth, respectively. These compaction energies will allow the research to produce laboratory specimens that were representative of the materials implemented on-site. Regarding the compressive strength, the values obtained in the laboratory were higher than those of the in-situ specimens. Correction factors of 0.88 and 0.67 for cob and light earth. These values should be applied to calibrate the laboratory results in relation to in-situ. Concerning the thermal conductivity, the values obtained in the laboratory were similar for cob and higher for light earth. A correction factor of 0.87 should be applied to calibrate the laboratory results to those obtained in-situ

Artificial reefs built by 3D printing: Systematisation in the design, material selection and fabrication

The recovery of degraded marine coasts and the improvement of natural habitats are current issues of vital importance for the development of life, both marine and terrestrial. In this sense, the immersion of artificial reefs (ARs) in the marine environment is a way to stimulate the recovery of these damaged ecosystems. But it is necessary to have a multidisciplinary approach that analyses the materials, designs and construction process of artificial reefs in order to understand their true impact on the environment. For this reason, this paper presents the manufacture of artificial reefs by 3D printing, proposing designs with a combination of prismatic and random shapes, with different external overhangs as well as inner holes. For the definition of the artificial reef designs, criteria provided by marine biologists and the results obtained from a numerical simulation with ANSYS were taken into account, with which the stability of the artificial reefs on the seabed was analysed. Three dosages of cement mortars and three dosages of geopolymer mortars were studied as impression materials. The studies included determination of the rheological properties of the mortars, to define the printability, determination of the cost of the materials used, and determination of the mechanical strength and biological receptivity in prismatic specimens that were immersed in the sea for 3 months. To evaluate the environmental impact of the materials used in the production of the mortars, a Life Cycle Assessment (LCA) was carried out. In order to choose the mortars that encompassed the best properties studied, Multi-Criteria Decision Making (MCDM) was applied and the two best mortars were used for the manufacture of the artificial reefs. Finally, the advantages and disadvantages of the 3D printing process used were analysed. The results of the studies carried out in this research show that cement mortars have better characteristics for artificial reef applications using 3D printing, and that the technique applied for the manufacture of the artificial reefs allowed the digital models to be faithfully reproduced

Construction field monitoring of a cob prototype building

International audienceCob is an earthen building material made by soil, fibres and water used for millennia. However, cobconstruction disappeared out during the nineteenth century. These last years, it is experiencing arenaissance in Northwestern France and Southern England. Due to a limited technical knowledge, theinvestigation of engineering properties is important for modern design practice and code requirements.Moreover, to ensure building properties, it is necessary to have same quality mix along the buildingphases.The aim of this study is to determine material variation during the monitoring of a cob prototype buildingin Normandy (France). This study investigated structural cob mix composition, water content, density,mechanical properties and thermal conductivity. Specimens shape used were cylindrical 110 x H220mm and prismatic 300 x 300 x 70 mm.Results indicated a variation in cob mix (water content, materials proportions) between three differentlifts. These variations lead to different densities and, consequently, to variables compressive strengths:0.99 to 1.38 MPa and thermal conductivities from 0.610 - 0.816 W.m-1∙K-1

Construction field monitoring of a cob prototype building

International audienceCob is an earthen building material made by soil, fibres and water used for millennia. However, cobconstruction disappeared out during the nineteenth century. These last years, it is experiencing arenaissance in Northwestern France and Southern England. Due to a limited technical knowledge, theinvestigation of engineering properties is important for modern design practice and code requirements.Moreover, to ensure building properties, it is necessary to have same quality mix along the buildingphases.The aim of this study is to determine material variation during the monitoring of a cob prototype buildingin Normandy (France). This study investigated structural cob mix composition, water content, density,mechanical properties and thermal conductivity. Specimens shape used were cylindrical 110 x H220mm and prismatic 300 x 300 x 70 mm.Results indicated a variation in cob mix (water content, materials proportions) between three differentlifts. These variations lead to different densities and, consequently, to variables compressive strengths:0.99 to 1.38 MPa and thermal conductivities from 0.610 - 0.816 W.m-1∙K-1

Optimisation of 3D printed concrete for artificial reefs: Biofouling and mechanical analysis

Protection, restoration, and regeneration of aquatic habitats are an increasingly important issue and are requiring intensive research. In the marine environment, artificial reefs may be deployed to help offset habitat loss, increase local biodiversity and stimulate the recovery of ecosystems. This study aimed at the fabrication of artificial reefs by 3D printing. In the framework of the European INTERREG Atlantic Area collaborative project “3DPARE”, six printed concrete formulations with limited environmental impact, based on geopolymer or cement CEM III binders and recycled sands, were immersed in the Atlantic along British, French, Portuguese and Spanish coasts. The colonisation of the concrete samples by micro- and macroorganisms and their durability were assessed after 1, 3 and 6 months of immersion. Results showed that both parameters were better with CEM III compared to geopolymer-based formulations. Therefore the use of CEM III should be prioritised over these geopolymer binders in 3D printed concrete for artificial reef applications

Artificial reefs in the North –East Atlantic area: Present situation, knowledge gaps and future perspectives

Artificial reefs have been deployed in multiple regions of the world for different purposes including habitat restoration and protection, biodiversity and fish stock enhancement, fisheries management and recreation. Artificial reefs can be a valuable tool for ecosystem protection and rehabilitation, helping mitigate the effects of anthropogenic impacts that we face today. However, knowledge on artificial reefs is unevenly distributed worldwide, with some regions having much more quality information available and published (e.g. European Mediterranean Sea area), while others, for instance the North-East Atlantic area, do not. Here, we provide a characterization of purposely built artificial reefs in North-East Atlantic area based on all available literature (i.e. research papers and reports), highlighting the needs and gaps that are vital for establishing future perspectives for artificial reef deployment and research. In the North-East Atlantic area, sixty-one purposely built artificial reefs have been deployed since 1970, mostly between the years 1990–2009, with Spain being the country with the highest number of artificial reefs. The most reported purpose for their deployment is fisheries productivity and habitat/species protection, although, most artificial reefs are multipurpose in order to maximise the benefits of a given financial investment. The majority of artificial reefs were submerged at < 50 m, mainly between 10 and 20 m of depth. The most used designs were cubic blocks and complex designs made by an array of combined shapes, which mostly consist of concrete (79%). From all the analysed data on artificial reefs, 67% of the cases reported surveys to assess biodiversity after the deployment. However, in 26% of those cases, data was not available. When data was available, only 31% of cases reported long-term biomonitoring surveys (3 years or more). Based upon these findings, we noticed a general lack of scientifically robust data, including records of species and abundance of both fish and invertebrates, as well as macroalgae, preventing an adequate determination of the best balance between shape, construction material and bio-colonization. Critiques and suggestions are discussed in the light of currently available data in order to perform more efficient research, evaluation and functioning of future artificial reefs