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OCEAN POWER INNOVATION NETWORK COLLABORATIVE INNOVATION GROUP (CIG) REPORT Corrosion in reinforced concrete structures used for offshore renewables CIG CORROSION IN REINFORCED CONCRETE STRUCTURES REPORT -PUBLIC VERSION
Abstract
The main objective of this Collaborative Innovation Group (CIG) of the Ocean Power Innovation Network (OPIN) project,was to identify one or several future R&D collaboration opportunities within the CIG members (all or a subset) and start preparing the basis for associated grant applications. A state-of-the-art report has been prepared to support this final goal, collecting inputs from all CIG members on the activities identified in Table 1.
The present report is not a comprehensive, international state-of-the-art study. The aim was to share knowledge, information and ideas amongst the CIG members. This information was collected by means of written contributions, online workshops, surveys, etc.
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Coastal marine ecosystems provide essential benefits and services to humanity, but many are rapidly degrading. Human activities are leading to significant land take along coastlines and to major changes in ecosystems. Ecological engineering tools capable of promoting large-scale restoration of coastal ecosystems are needed today in the face of intensifying climatic stress and human activities. Concrete is one of the materials most commonly used in the construction of coastal and marine infrastructure. Immersed in seawater, concretes are rapidly colonized by microorganisms and macroorganisms. Surface colonization and subsequent biofilm and biofouling formation provide numerous advantages to these organisms and support critical ecological and biogeochemical functions in the changing marine environment. The new challenge of the 21st century is to develop innovative concretes that, in addition to their usual properties, provide improved bioreceptivity in order to enhance marine biodiversity. The aim of this study is to master and clarify the intrinsic parameters that influence the bioreceptivity (biocolonization) of cementitious materials in the marine environment. By coupling biofilm (culture-based methods) and biofouling (image-analysis-based method and wet-/dry-weight biomass measurement) quantification techniques, this study showed that the application of a curing compound to the concrete surface reduced the biocolonization of cementitious materials in seawater, whereas green formwork oil had the opposite effect. This study also found that certain surface conditions (faceted and patterned surface, rough surface) promote the bacterial and macroorganism colonization of cementitious materials. Among the parameters examined, surface roughness proved to be the factor that promotes biocolonization most effectively. These results could be taken up in future recommendations to enable engineers to eco-design more eco-friendly marine infrastructure and develop green-engineering projects.
The study reports properties of a stable and high strength ternary binder matrix using Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBS), and Metakaolin (MK). The bulk of the binder system is composed of Fly Ash and Ground Granulated Blast Furnace Slag (GGBS), while Metakaolin is added in three levels of 20%, 10%, 5% by weight, as suggested by the design of experiments. Alkali solution consisting of sodium hydroxide flakes and sodium silicate solution was used as the alkali activator. Fresh properties of all the Alkali Activated binder Pastes were studied to understand the Setting time and Mini-Slump. Mechanical properties of the hardened fly ash based ternary binder mortar were tested for compressive strength and ultrasonic pulse velocity (UPV) after 3, 7,28, and 56 days of curing. X-Ray Diffraction (XRD), Field-Emission-Scanning-Electron-Microscope (FESEM), Energy-Dispersive-Spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR) were conducted in order to study the microstructural properties fly ash based ternary paste cured for 7 days. The compressive strength of hardened fly ash based ternary samples varied between 57.14 and 102.04 MPa. Ternary mixtures were observed to have a homogeneous and denser microstructure, with the development of various gels like CSH, CASH, NASH, and (N, C)-ASH.
The present paper deals with the stochastic modeling of bio-colonization for the computation of stochastic hydrodynamic loading on jacket-type offshore structures. It relies on a multidisciplinary study gathering biological and physical research fields that accounts for uncertainties at all the levels. Indeed, bio-colonization of offshore structures is a complex phenomenon with two major but distinct domains: (i) marine biology, whose processes are modeled with biomathematics methods, and (ii) hydrodynamic processes. This paper aims to connect these two domains. It proposes a stochastic model for the marine organism’s growth and then continues with transfers for the assessment of drag coefficient and forces probability density functions that account for marine growth evolution. A case study relies on the characteristics (growth and shape) of the blue mussel (Mytilus edulis) in the northeastern Atlantic.
The adoption of any binder system for structural concrete depends on the performance characteristics desired for addressing the long-term deformation and durability concerns. The major properties influencing the performance includes the shrinkage characteristics governing the long-term deformation, and durability characteristics related to various transport mechanisms, governing the performance in different service conditions. This paper describes the potential of Limestone Calcined Clay Cement (LC3) for use in structural concrete in comparison with Ordinary Portland Cement (OPC) and fly ash based blended cement (FA30). Three types of concrete mixtures were designed for the study, two based on achieving an equivalent strength grade (M30 and M50 concrete grade) with each binder, and the third with equal binder content and w/b ratio. Mechanical properties such as compressive strength and elastic modulus, and autogenous and drying shrinkage, along with various durability parameters of the different concretes were assessed. Oxygen permeability, rapid chloride penetration, chloride migration, resistivity development and water sorptivity were the various parameters considered for evaluation of durability performance. The results indicate the superiority of LC3 binder over other binders in producing durable concrete, especially in a chloride laden environment. The major reason for the better performance was attributed to the more compact and dense microstructure of the system with the LC3 binder against OPC and FA30. The drying shrinkage performance was seen to be similar for concrete with all three binders.
This study aims to use NASH (sodium alumina silicate hydrate) gel and CASH (calcium alumina silicate hydrate) gel to overcome the negative effects of incorporating microencapsulated phase change materials (MPCM) on the mechanical strength and thermal conductivity of blast furnace slag-based geopolymer mortars. The coexistence of CASH and NASH gels was obtained by using an inclusion of a small amount of metakaolin (MK) in a geopolymer matrix based on blast furnace slag (GBFS); this results in a geopolymer with high mechanical strength. Several tests were performed to characterize different mortars (with and without MK) such as workability, microstructural properties, water porosity, mechanical properties (compressive strength, dynamic Young modulus) and thermal properties (thermal conductivity, the specific heat capacity). The results obtained showed that the coexistence of NASH and CASH gel brought improvements in terms of mechanical properties and thermal conductivity compared to GBFS-based geopolymer-MPCM only. Indeed, the addition of 10 and 20% of MK was sufficient to obtain this coexistence. With a concentration of MPCM up to 10% in the geopolymer mortars, the compressive strength was increased by about 10 MPA and the thermal conductivity was increased by about 31%, which led to an improvement in the specific heat capacity of up to 1280 J/Kg.K. These improvements were due to the high reactivity of MK under the activation conditions used. This favored the good dissolution of silica and aluminum in the MK, which participated well with the calcium in the GBFS to create the NASH and CASH gels. In fact, it was felt that these two gels filled the small pores caused by the MPCM and that this compensated well for their negative effects on the geopolymer matrix.
Geopolymer-MPCM based mortars after their optimizations with NASH and CASH gel coexistence showed good workability, compressive strength, and thermal performance. On the other hand, a reduced water porosity compared to Portland cement-MPCM based mortars.
This paper aims to find the optimum formulation among 24 geopolymer mortars (GMs) based on granulated blast furnace slag (GBFS), metakaolin (MK) and alkaline solution which is characterized by its molar ratio SiO2/Na2O (MR) and its Activator representing the dry extract. (GBFS + MK)/Activator, GBFS/MK, and MR are the variables used to evaluate the GMs performances. Their effect on the rheology, setting time, porosity, mechanical properties and stability to efflorescence was investigated and the results were compared with those of Portland cement mortar (PCM). The outcomes show that GMs and PCM exhibit a Binghamian behavior where the rheological parameters depend on the MK/GBFS ratio and the MR. The relationship between compressive and flexural strengths is independent of the raw materials while it is not the case for the relationship relating dynamic modulus with the compressive strength. The optimal performances are achieved with: GBFS/MK = 1, GBFS + MK/Activator = 3 and MR between 1.6 and 1.8. The optimum GMs have shown better or comparable properties than those of PCM.
Here we present a geopolymer as a sustainable alternative for cements. The geopolymer binder is presented in a dry form (dry mixing method). The geopolymer has demonstrated to be ideal candidate to mitigate the typical carbon footprint emissions of cements, such as Portland. The potential global benefits include a reduction of up to 1480 million tons of CO2 per year when compare with Portland cement. In this design, it is proposed an alkali-activated cementitious material that is made out of a mix of silica-rich sand and sodium carbonate. Such sand has 80-85 wt% SiO2 and 15-20 wt% mixed rock grain. This composition is processed at temperatures around 850 °C that is 650 °C less than that for Portland cements. One of the benefits is that the use of limestone is eliminated resulting in such reductions in CO2 emissions. The emission analysis is carried during a calcination process used to analyze the decarbonation or CO2 emission step. This work presents a complementary characterization of the products including an infrared spectroscopy analysis and thermogravimetry.
Underwater inspections stand to gain from using stereo imaging systems to collect three-dimensional measurements. Although many stereo-matching algorithms have been devised to solve the correspondence problem, that is, find the same points in multiple images, these algorithms often perform poorly when applied to images of underwater scenes due to the poor visibility and the complex underwater light field. This article presents a new stereo-matching algorithm, called PaLPaBEL (Pyramidal Loopy Propagated BELief) that is designed to operate on challenging imagery. At its core, PaLPaBEL is a semiglobal method based on a loopy belief propagation message passing algorithm applied on a Markov random field. A pyramidal scheme is adopted that enables wide disparity ranges and high-resolution images to be handled efficiently. For performance evaluation, PaLPaBEL is applied to underwater stereo images captured under various visibility conditions in a laboratory setting, and to synthetic imagery created in a virtual underwater environment. The technique is also demonstrated on stereo images obtained from a real-world inspection. The successful results indicate that PaLPaBEL is well suited for underwater application and has value as a tool for the cost-effective inspection of marine structures.
Alkaline activated concretes based on a mixture of fly ash (FA) and blast furnace slag (GBFS), as well as FA and Portland cement (OPC), both at a ratio of 80:20, were exposed to temperatures between 25 °C and 1100 °C. Then, the physicochemical and mechanical changes were evaluated. The results indicate that the activated concretes have better performance than the reference ones (100% OPC). At temperatures of 1100 °C, the residual strengths of the FA/GBFS and FA/OPC concretes are 15 and 5.5 MPa, respectively, unlike the OPC concrete that lost 100% of its strength. At temperatures above 900 °C, the activated matrix densified, and the crystalline phases, such as sodalite, nepheline, albite and akermanite, are identified.
Image processing-based methods, capable of detecting and quantifying cracks, surface defects or recovering 3D shape information are increasingly being recognised as a valuable tool for inspecting underwater structures. It is of great practical importance for inspectors to know the effectiveness of such techniques when applied in conditions. This paper considers an underwater environment characterised by poor visibility chiefly governed by the lighting and turbidity levels, along with a range of geometry and damage conditions of calibrated specimens. The paper addresses the relationship between underwater visibility and the performance of image-based methods through the development and calibration of a first open-source underwater lighting and turbidity image repository (ULTIR). ULTIR contains a large collection of images of submerged specimens that have been photographed under controlled lighting and turbidity levels featuring various forms of geometry and damage. ULTIR aims to facilitate inspectors when rationalising the use of image processing methods as part of an underwater inspection campaign and to enable researchers to efficiently evaluate the performance of image-based methods under realistic operating conditions. Stakeholders in underwater infrastructure can benefit through this first large, standardised, well-annotated, and freely available database of images and associated metadata.