Comparison of material properties of SCC concrete with steel fibres related to ingress of chlorides

The paper focuses on the evaluation of chloride ion diffusion coefficient of self-compacting concrete with steel fibre reinforcement. The reference concrete from Ordinary Portland Cement (OPC) and Self-Compacting Concrete (SCC) with several values of added steel fibres-0%, 1% and 2% of weight-were cast in order to investigate the effect of fibres. The three procedures of diffusion coefficient calculation are presented-rapid chloride penetration test, accelerated penetration tests with chloride as well as the surface measurement of electrical resistivity using Wenner probe. The resulting diffusion coefficients obtained by all methods are compared and evaluated regarding the basic mechanical properties of concrete mixtures.Web of Science103art. no. 22

Probabilistic modeling of chloride penetration with respect to concrete heterogeneity and epoxy-coating on the reinforcement

The presented article demonstrates the probabilistic method based modeling of the 2D chloride ingress into reinforced concrete structures with respect to concrete heterogeneity and epoxy-coated steel reinforcement. Spatial change of concrete diffusion is assessed through the investigation of random variation of the ability of concrete to resist chloride ingress. Time-dependent chloride concentration at the reinforcement level in both homogeneous and heterogeneous models is comparatively considered taking into account of the influence of reinforcement protection as well as the defects and holidays of the coating. Expansion optimal linear estimation method is exploited to generate a random field for the structure at the mesoscale and correlation length is employed to simplify the modeling process. Preliminary analyses of the built model are conducted in both deterministic and probabilistic solutions under the scheme of the finite element method. Thus, possibility of such analyses is exploited.Web of Science1224art. no. 406

Effect of cracking and randomness of inputs on corrosion initiation of reinforced concrete bridge decks exposed to chlorides

The paper is aimed at the indicative evaluation of the effect of random scatter of input parameters in case of durability of reinforced concrete bridge deck. The time to onset of corrosion of steel reinforcement of concrete bridge deck exposed to chloride is evaluated. The effect of cracking in concrete onto chloride ingress is considered. The selected steel reinforcement protection strategies are: unprotected steel reinforcement, epoxy-coated steel reinforcement and water-proof barrier bellow asphalt overlay. The preliminary model for damage effect on chloride ion ingress through water proof membrane under penetrable asphalt overlay is used. 2-D finite element chloride ingress model is combined with Monte Carlo simulation technique. The innovative crack effect modeling via highly penetrable elements is applied. Deterministic and probabilistic calculations are compared.Web of Science39372

Durability Analysis of Concrete Bridge Deck Exposed to the Chloride Ions Using Direct Optimized Probabilistic Calculation

Durability of reinforced concrete structures is a deeply discussed problem recently. Concrete structures in the external environment are very often affected by chloride ions from de-icing salt or sea water. Chloride ions penetrate through the concrete cover layer of the reinforcement and can cause eventually the corrosion of the steel. However, when estimating the durability of the structure, it is not sometimes possible to express the parameters by constant values; therefore, the probabilistic methods come in handy. Then, the variability of inputs and outputs can be expressed by histograms. Two probabilistic approaches were applied in this task – Monte Carlo simulation with Simulation-Based Reliability Assessment method, which is widely used for such type of problems, and the Direct Optimized Probabilistic Calculation, which is still relatively new type of approach. The result is a comparison of mentioned methods in terms of accuracy on the model of one-dimensional chloride penetration with time independent diffusion coefficient by using the Fick’s Second Law of Diffusion

Reinforced Concrete Bridge Deck Model Considering Delayed Exposure to Chlorides

The paper is focused on the model of the effect of delayed chloride exposure on the chloride induced corrosion initiation on ideal reinforced concrete bridge. The Finite Element-based numerical model is applied. The effect of concrete quality is expressed in the form of time dependent diffusion coefficient in order to evaluate the effect of concrete type as well as the effect of aging. The influence of extended chloride exposure on the corrosion initiation is introduced

Numerical solution of 2-D chloride diffusion problem using FEA

Import 03/08/2012U železobetonových mostů existuje několik faktorů ovlivňujících jejich životnost. Jedním z kritických problémů je koroze výztuže způsobená pronikáním posypových solí. Modelování degradace železobetonu je aktuální úkol s mnoha náhodnými vstupními parametry. Při pravděpodobnostním posudku metodou Monte Carlo je však použito velké množství simulačních kroků. To vede i při dnešní úrovni výpočetní techniky k časově náročným výpočtům. Cílem práce v této oblasti je naprogramování nástroje, který bude v konečném důsledku schopný urychlit celý proces výpočtu. Prvním krokem je příprava a implementace algoritmu v prostředí programu MatLab, který při výpočtu sice nemá požadovanou rychlost, ale zdá se být vhodným nástrojem pro pochopení daného problému. Práce pojednává o postupu vytvoření modelu nestacionární difuze chloridů a výpočtu chloridové koncentrace a obsahuje také ověření výsledků porovnáním s dostupným řešením.Concrete bridges life time affecting several factors. Corrosion of reinforcement caused by deicing salts penetration through the concrete bridges is one of the critical. Modeling of concrete degradation is the current task with a lot of random input parameters. There is needed large number of simulation steps in the probabilistic assessment using Monte Carlo. That leads to time-consuming calculations even in current level of computerization. Programming algorithm to accelerate the process of calculation is the aim of the research. The first step is the preparation and implementation of the algorithm in MatLab software. It is not fast, but it seems to be a useful tool for understanding the problem. The work discusses preparation of a model of transient diffusion of chloride, calculation of the chloride concentration and the example shows the functionality of the program.Prezenční228 - Katedra stavební mechanikyvýborn

Mechanical and Durability Parameters of the Concrete Bridges under Service in the Czech Republic

RC bridges are the typical structures exposed to the combined effect of carbonation, chloride ingress, and mechanical load. Due to this, the structures are susceptible to corrosion, which influences the load-carrying capacity and safety. An important part of the preparation for performance-based design is an analysis of the durability of existing structures to improve the reliability of available numerical tools. In this study, the correlations between compressive strength, chloride content, pH, exposure time, and risk factor were analysed. All were evaluated based on the in-situ measurements performed on regular inspections of 14 motorway bridges under service in the Czech Republic.Ostrav

Variation of durability and strength parameters of pumice based mixtures

The numerical modelling of chloride penetration into concrete is very sensitive to the correct description of the input data. In the recent era, high-performance concrete (HPC), which combines Portland cement and other supplementary cementitious materials, has been gaining attraction due to their desirable material properties and durability. The presented results show the application of the modified approach for the evaluation of the suitability of the time-dependent model for the variation of the diffusion coefficient. The 26 various binary and ternary-based concrete mixtures blended with volcanic pumice pozzolan (VPP) as a major supplementary cementitious material (SCM) are compared with the reference Ordinary Portland Cement mixture. Other SCMs namely fly ash, slag, silica fume, and metakaolin were also utilized in ternary-based concrete mixtures. In-depth statistical analysis was carried out to show the variability and effects of the amount of the volcanic pumice as an SCM on the diffusion coefficient. The mean value and regression via linear approximation of the time-dependent coefficient of variation of the diffusion coefficients were used as well as the Root of Mean Squared Error approach. The presented results are suitable as the component of the input parameters for the durability-related probabilistic assessment of the reinforced concrete structures exposed to chlorides. In addition, the time-dependent ultimate limit state-related data was presented.Web of Science1413art. no. 367

Inverse analysis of straw bale mechanical parameters in load-bearing structures based on a finite element model

Scientific and practical research into alternative building materials is of high importance in terms of sustainability and ecology. Many variables have to be taken into account when using straw bales as load-bearing structures in residential buildings. The main problems are the lack of information on the mechanical properties of this material and its potential high variability. The development of numerical FEM models based on accurate experiments can help to better understand the behaviour of this material. The main objective of this paper is to present a simplified isotropic model of straw bales based on measured data from a laboratory experiment, which will facilitate the preparation and evaluation of further future experiments. Already partially published data of compression tests of load-bearing straw bales were analysed. Using an automated algorithm, an estimate of the elastic modulus of the bale was determined, and inverse analyses were performed using accurate FEM numerical models based on similarity to the force-deformation diagram. In all experiments, it was found that the ideal combination is elastic modulus at 20% load and Poisson's constant of 0.2. From the results, further experimental directions can be determined, mainly considering a larger number of specimens with different properties. These and other findings provide the basis for the ever-expanding field of research on load-bearing straw bales in construction.Web of Science1212art. no. 215

Relationship of different properties from non-destructive testing of heavy concrete from magnetite and serpentinite

Radiation-shielding concrete has been analyzed by several methods of destructive and non-destructive testing (NDT). Concretes made of crushed basalt, magnetite, serpentinite, and two different types of cement (Portland cement CEM I and slag cement CEM III/A) were studied. In this study, we analyzed concrete columns with a height of 1200 mm and a cross-section of 200 x 200 mm(2). The top and bottom of the column were analyzed using data from compressive strength, dynamic modulus of elasticity, water penetration, and diffusion coefficients derived from the electrical resistivity test. This article presents the properties of fresh concrete and concrete after two years of setting. It was determined how the different ratios of basalt, magnetite, and serpentinite affect the individual measured parameters. Furthermore, correlation relations between individual resulting values were analyzed. It was observed that compressive strength generally does not correlate with other results. The diffusion coefficient correlated well with density and water penetration. Little or no correlation was observed in the diffusion coefficient with compressive strength and modulus of elasticity. The results of the study make it possible to refine the testing of heavy concretes in terms of electrical resistivity, and point to the possible use of NDT methods. The results also show which composition of heavy concrete is better in terms of effective diffusivity.Web of Science1415art. no. 428