This paper describes experimental investigations on corrosion-induced deterioration in reinforced cementitious materials and the subsequent development and implementation of a novel conceptual model. ...Reinforced mortar specimens of varying water-to-cement ratios were subjected to current-induced corrosion (10, 50, and 100μA/cm2). X-ray attenuation measurements and visual investigations provided both qualitative and quantitative information on the penetration of solid corrosion products into the surrounding cementitious matrix. X-ray attenuation measurements provided time- and location-dependent concentrations of corrosion products averaged through the specimen thickness. Digital image correlation (DIC) was used to measure corrosion-induced deformations including deformations between steel and cementitious matrix as well as formation and propagation of corrosion-induced cracks. Based on experimental observations, a conceptual model was developed to describe the penetration of solid corrosion products into capillary pores of the cementitious matrix. Only capillary pores within a corrosion accommodating region (CAR), i.e. in close proximity of the steel reinforcement, were considered accessible for corrosion products. The conceptual model was implemented into a FEM based cracking model and compared to experimental results provided in the literature and obtained from DIC measurements.
To test the applicability of the x-ray attenuation method to monitor corrosion products as well as the formation and propagation of cracks in cementitious materials, reinforced mortar samples were ...tested under accelerated corrosion conditions. Experimental results demonstrate x-ray attenuation measurements can track time-dependent development of corrosion products and the subsequent initiation and propagation of corrosion-induced cracks. Also, x-ray attenuation measurements allowed determination of the actual concentration of the corrosion products averaged through the specimen thickness. The total mass loss of steel, obtained by the x-ray attenuation method, was found to be in very good agreement with the mass loss obtained by gravimetric method as well as Faraday's law. Results of the presented experimental approach provide pertinent information for the further development and verification of numerical tools simulating corrosion-induced damage in reinforced concrete.
This paper presents a computational fluid dynamics model fit for multi-layer 3D Concrete Printing. The numerical model utilizes an elasto-visco-plastic constitutive model to mimic the flow behaviour ...of the cementitious material. To validate the model, simulation data is compared to experimental data from 3D printed walls. The obtained results show that the numerical model can reproduce the experimental results with high accuracy and quantify the extrusion load imposed upon the layers. Such load is found to exceed the material’s yields stress in certain regions of previously printed layers, leading to layer deformation/flow. The developed and validated numerical model can assist in identifying optimal printing strategies, reducing the number of costly experimental print failures and human-process interaction. By doing so, the findings of this paper helps 3D Concrete Printing move a step closer to a truly digital fabrication process.
► We model free surface flow of suspension of rigid particles in non-Newtonian fluid. ► We combine Lattice Boltzmann, Immersed Boundary Method and particle dynamics. ► The model is very efficient ...allowing simulations of tens of thousands of particles. ► The model is robust and accurate and easily extendable to a variety of problems.
A numerical framework capable of predicting the free surface flow of a suspension of rigid particles in a non-Newtonian fluid is described. The framework is a combination of the lattice Boltzmann method for fluid flow, the mass tracking algorithm for free surface representation, the immersed boundary method for two-way coupled interactions between fluid and rigid particles and an algorithm for the dynamics and mutual interactions of rigid particles. The framework is able to simulate the flow of suspensions at the level of the largest suspended particles and, at the same time, the model is very efficient, allowing simulations of tens of thousands of rigid particles within a reasonable computational time. Furthermore, the framework does not require any fitting constants or parameters devoid of a clear physical meaning and it is stable, robust and can be easily generalized to a variety of problems from many fields.
Fibre-reinforced polymer (FRP) systems have recently become popular in repairing concrete or masonry structures because of their inherent advantages. In spite of these benefits, FRPs have drawbacks ...having low fire resistance, poor environmental sustainability and incompatibilty with the substrate concrete. The effort to address these issues has led to the development of an emerging strain hardening cementitious (SHC) material using an inorganic polymer known as hybrid fibre-reinforced geopolymer (HFRG) composites. Compared with cement-based SHC composites, HFRG has better bond performance to concrete substrates, higher fire resistance, greater corrosion durability and helps to reduce CO
2
emissions. This paper reviews the recent development of HFRG composites as an emerging repair material. Literature reveals that flowability of a fresh HFRG mixture decreases with increasing fibre content though still workable up to 2% fibre volume. Fibre synergy could result in 10–181% higher flexural toughness of geopolymer composites than when just using mono fibres. The application of HFRG composites to RC beams increased displacement ductility by to 263%. To date, there has been no reported field application of HFRG as a repair material though mono-fibre FRG has been field-applied as a strengthening material in large-diameter sewer RC pipes, RC culverts, RC sewerage manholes and dam surface improvement.
This paper discusses the need for reliable and valid multi-scale and multi-physics prediction models to support the design of new as well as the assessment, maintenance, and repair of existing ...reinforced concrete structures.
A multi-physics and multi-scale deterioration model for chloride-induced corrosion of reinforced concrete has been established. Ongoing work includes extension of the model to 3D as well as modelling of the impact of the steel-concrete interface characteristics and electrochemical potential on chloride thresholds.
Identified challenges include, among others, the improved understanding and modelling of single- and multi-deterioration mechanisms, environmental exposure, and data for validation.
We envision that next generation maintenance and management of reinforced concrete infrastructure will combine numerical simulations based on multi-scale and multi-physics principles and extensive in-situ monitoring, allowing continuous Bayesian updating of 4D simulations of functional performance.
The design, construction, and operation of civil infrastructure that is more environmentally, socially, and economically responsible over its life cycle from extraction of raw materials to end of ...life is increasingly desirable worldwide. This paper presents a probabilistic framework for the design of civil infrastructure that achieves targeted improvements in quantitative sustainability indicators. The framework consists of two models: (i) probabilistic service life prediction models for determining the time to repair, and (ii) probabilistic life cycle assessment (LCA) models for measuring the impact of a repair. Specifically, this paper introduces a new mathematical approach, SIPmathTM, to simplify this design framework and potentially accelerate adoption by civil infrastructure designers. A reinforced concrete bridge repair in Norway is used as a case study to demonstrate SIPmath implementation. The case study shows that SIPmath allows designers to engage in sustainable design using probabilistic methods using the native, user-friendly Microsoft Excel interface. Methods are developed through this case study to determine the probability of failure of a more sustainable design compared to a baseline design, and these methods are then verified using alternative software and approach.
This study established a reactive transport model (RTM) for saturated cement-based materials based on multi-ionic transport through an uncharged, ‘free water’ and charged, ‘the electrical double ...layer’ coupled with a chemical equilibrium model for interaction between pore solution and solid phase. A set of modified Poisson-Nernst-Planck equations, including the effect of temperature, pore solution property, and pore structure changes, have been introduced for multi-ionic transport. A comprehensive method has been illustrated for determining the diffusion coefficient at infinite dilution of the aqueous species present in the pore solution in a cementitious material. Numerical predictions were compared to experimental data to demonstrate the applicability of the RTM. For mortar specimens exposed to NaCl solution and seawater, numerical predictions agree well with experimentally determined Portlandite and carbonate in the phase assemblage, elemental distribution such as chloride, sodium, potassium, magnesium, and sulfur adjusting the initial tortuosity factor.
Viscoelastic behavior of early-age normal and high-strength concrete has been investigated. The study shows that concrete exhibits high tensile creep strain if loaded at an age less than or equal to ...1 day. The investigations furthermore show that the creep strain is not proportional to the stress level in the specimen when loading occurs at 1 day. Creep experiments were also carried out on concretes with different w/c ratios and some qualitative comments are made. Finally, an approach for mathematical modeling of early-age creep for normal concrete was explored.
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