Service Life Of RC Structures Research Articles

A comparison between uniform and galvanic corrosion rate in carbonation induced corrosion of reinforced concrete

Carbonation-induced corrosion is usually considered in uniform or generalized corrosion. This is true for small laboratory samples but not necessary the case for real reinforced concrete structures built with multilayers reinforcement. Multi-layers reinforcement could lead to a galvanic corrosion between first de-passivated layer closed to the concrete surface and deeper layers still passivated. The present paper compares the uniform corrosion density and the galvanic corrosion density for concrete samples made with two different type of cements. CEM III cement despite their higher susceptibility to carbonation show a significant lower galvanic corrosion density, which would lead to a significant increase in the service life of RC structures, exposed to carbonation.

Reliability estimation of corroded RC structures based on spatial variability using experimental evidence, probabilistic analysis and finite element method

Corrosion of steel reinforcement is spatially distributed over RC structures due to several factors such as different environmental exposure, concrete cover, and concrete quality, among others. Ignoring the effect of spatial variability is a drastic simplification for the prediction of the remaining service life of RC structures. Therefore, it is essential to identify the factors influencing the spatial steel corrosion and structural performance of corroded RC structures. In this paper, an experimental research is conducted to study the effects of main parameters (i.e. current density, concrete cover, rebar diameter, and fly ash) on the spatial variability associated with steel weight loss, corrosion crack, and structural behavior of accelerated-corrosion RC beams using X-ray radiography and digital image processing. The test results showed that low current density (Icorr ≤ 50 µA/cm2) induced highly non-uniform corrosion associated with few large pits and cracks at certain locations while higher current density produced more uniform corrosion and cracks over the beam length. Gumbel distribution parameters were derived from the steel weight loss data for modeling spatial steel corrosion. A novel approach was established to assess the reliability of RC structures using finite element (FE) analysis and probabilistic analysis considering the effects of modeled spatial variability of steel weight loss based on X-ray photographs. Using the Gumbel distribution parameters derived from the steel weight loss data associated with higher current density may underestimate the non-uniformity of corrosion distribution which can lead to an overestimation of the load capacity of corroded RC structures.

Feasibility of using seawater to produce ultra‐high ductile cementitious composite for construction without steel reinforcement

Using seawater as mixing water to produce concrete may lead to excessive chloride content inside cementitious paste. This dramatically increases the risk of steel corrosion in the service life of RC structures. To address this issue, the authors tried to develop cementitious composites with sufficient ductility and strength, making it a structural material free from steel reinforcement, so that seawater can be used freely in mixture. In this article, ultra‐high ductile cementitious composites (UHDCC) were fabricated using 100% natural seawater, sea‐fresh water (50 + 50%) and 100% freshwater, in which the water‐soluble chloride contents reached 0.288, 0.181, and 0.073%, respectively. Mechanical test results indicated that the presence of chloride ions has negligible influence on the strength of single polyethylene fiber and fracture toughness of UHDCC matrix. Also, no significant difference was found existing in tensile strength, tensile strain capacity, and composite bridging capacity of the UHDCCs mixed with seawater or freshwater. Four‐point bending test demonstrated that plain UHDCC beams mixed with seawater, sea‐fresh water or freshwater have the similar load bearing capacity to a reference RC beam having steel reinforcement of 0.57%. Generally, the present experimental study demonstrates that chloride content has negligible influence on the mechanical properties of UHDCC, thus providing a solution for concrete constructions located in coastal areas and isolated islands.

Chloride diffusivity and service life prediction of fatigue damaged RC beams under seawater wet-dry environment

The effects of low fatigue load level with lower limit of 0.1 Pu and upper limit of 0.2 Pu or 0.3 Pu on chloride diffusivity of RC beams were experimentally studied after 100 times of seawater wet-dry cycles, where Pu is the static ultimate strength of the RC beams and the cycles of fatigue loading was 200,000. Based on the test results, residual service life was also discussed here. Results show that, chloride diffusivity was accelerated as fatigue load level increased. When the load level was 0.2, based on Fick’s 2nd law, chloride diffusion coefficient of tensile concrete was higher than that of compressive concrete, but the result was reverse for the load level of 0.3. Furthermore, based on the Monte-Carlo Method, the predicted residual service life in one-dimensional state of chloride diffusion would be shortened by 85 percent when the fatigue load level was 0.2, and by 95 percent when fatigue load level was 0.3, compared with that of no fatigue damaged RC beam. The predicted service life in two-dimensional state was about half of that in one-dimensional state. It was concluded that fatigue damage has a more considerable effect on shortening service life of RC structures in chloride environment.

Probabilistic service life of RC structures under carbonation

The service life of reinforced concrete structures is assessed for carbonation environments using mathematical models based on different tests: carbonation test-based modelling and air permeability test-based modelling. The study includes experimental testing of five concrete mixes with respect to compressive strength, accelerated carbonation and air permeability with different types of cement, in order to assess the models using probabilistic calculus. Both mathematical models are part of the Portuguese National Annex to the European standard EN 206 for the estimation of design service life. Engineers have the option of choosing which of the two models to use, which means that using either model should produce similar results. The design service life results show that the two models do not converge. The different principle of each test – accelerated carbonation and air permeability – and their different characteristics regarding the various parameters of the modelling equations are some of the aspects discussed.

Evaluating the effect of corrosion on service life prediction of RC structures – A parametric study

Abstract The structural degradation of concrete structures due to reinforcement corrosion is major durability issue all over the world, primarily when the rebar in the concrete is exposed to the marine or aggressive environment. In the present work, an attempt has been made in predicting the service life of RC structures taking into account well known corrosion models. Parametric studies are completed on Bazant’s model, Morinaga’s model, Wang and Zhao’s model and IRC model to study the impact of cover thickness, corrosion rate, increase in diameter of the bar, perimeter of the bar, etc. This paper shows the consequences of the parametric investigation of the input parameters for four chosen consumption corrosion damage models. The adequacy of the models in predicting the service life is shown through four functional contextual analysis illustrations.

Corrosion inhibitors’ effect on design service life of RC structures

The implementation of new data regarding the performance of corrosion inhibitors is applied through a performance-based method approved by recent European standards for the probabilistic calculus of service life of reinforced concrete structures. A set of concrete compositions was mixed in order to experimentally obtain strength – compressive – and durability properties – carbonation and chloride diffusion and together with the available results concerning the performance of two types of corrosion inhibitors three scenarios were defined for each concrete composition: (i) plain concrete; (ii) concrete with added admixture inhibitor and (iii) concrete with surface applied migration inhibitor. The probabilistic calculus of service life for each scenario was carried out using modeling equations in which the concrete properties were changed in view of the inhibitors’ performance characteristics. The results show that there is a significant improvement in the design service life when this is modeled considering the effect of corrosion inhibitors.

Seismic Capacity Design of RC frames and environment-induced degradation of materials: Any concern?

The Capacity Design approach emerged in the second half of the last century and is currently adopted by all the modern codes of practice for construction in seismic areas. It is based on the fundamental concept that the structure under consideration should not exhibit brittle failure modes, as brittle members or mechanisms are designed to be stronger than the maximum expected stresses they possibly get from the adjacent ductile members or mechanisms. This condition is generally imposed at the design stage without considering any degradation in material properties possibly due to the environmental agents. Although structural codes for RC structures usually provide practitioners with sound criteria intended at limiting the development of detrimental degradation phenomena, they have been never assessed against the possible loss in over-strength of brittle failure modes due to environment-induced degradation phenomena possibly occurring during the service life of the structure.This study aims to answer the question stated in the title and, in the authors’ knowledge, is one of the first attempts to embrace two traditionally distant research fields, such as Earthquake Engineering and Material Science. Thus, the paper investigates the time evolution of the possible failure modes in beams due to the premature degradation of steel stirrups and longitudinal reinforcement during the service life of RC structures. Both material properties and environmental conditions are taken into account to assess durability and structural safety in seismically designed RC beams and the possible consequences of material degradation on their expected failure modes under seismic actions.

Concrete mix design for service life of RC structures exposed to chloride attack

The purpose of this research is to propose a design technique of concrete mix proportions satisfying service life through genetic algorithm (GA) and neural network (NN). For this, thirty mix proportions and the related diffusion coefficients in high performance concrete are analyzed and fitness function for diffusion coefficient is obtained considering mix components like w/b (water to binder ratio), cement content, mineral admixture (slag, flay ash and silica fume) content, sand and coarse aggregate content. Through averaging the results of 10 times GA simulations, relative errors to the previous data decrease lower than 5.0% and the simulated mix proportions are verified with the experimental results. Assuming the durability design parameters, intended diffusion coefficient for intended service life is derived and mix proportions satisfying the service life are obtained. Among the mix proportions, the most optimized case which satisfies required concrete strength and the lowest cost is selected through GA algorithm. The proposed technique would be improved with the enhancement of comprehensive data set including wider the range of diffusion coefficients.

Numerical Simulation Method for Predicting Chloride Concentration Distributing around Reinforcement in Concrete

The reinforcement in concrete alters the pathway for chloride transporting and in turn causes the chloride concentration to accumulate faster near the reinforcement closest to the exposed surface. A mass conservation matrix equation under the non-stable diffusion based on the Fick’s second law was derived. Hereby, a numerical simulation method for predicting chloride concentration in concrete was established utilizing the compiled module based on FEA. The validity of the method was verified by the comparison with the analytical results. The proposed method has a wider applicability for predicting the service life of RC structures. And it can be applied flexibly to any complicated section shape of RC members with multi-boundary attacked by chloride and the reinforcement considered simultaneously.

Modelling corrosion propagation in reinforced concrete structures – A critical review

Abstract The adoption of corrosion initiation as a limit state to define service life of RC structures has been challenged by researchers and engineers alike in light of the advancements in the concrete construction industry: improved reliability and safety, reduction in costs, and conservation of both materials and energy, which contribute towards sustainable concrete construction. The corrosion propagation phase is now appreciated as a significant component in the service life of RC structures and a good understanding of the propagation process is paramount. Various models have been developed to simulate and/or predict the propagation phase. This paper presents a critical review of some of the available models for corrosion propagation, and proposes ways forward to overcome some of these problems. Salient issues including the modelling techniques, input parameters and limit states are covered. Emphasis is also placed on the usefulness of the propagation models as tools to aid in the repair and maintenance of corrosion-damaged RC structures.

Service life of RC structures: Carbonation induced corrosion. Prescriptive vs. performance-based methodologies

For the last 30 years research projects have been carried out to estimate the service life of RC structures subjected to environmental aggression, based on time-dependent models. These research efforts resulted in the implementation of performance-based methodologies in guide documents [1] and European and national standards. However, the prescriptive methodologies are currently used in most cases. This paper aims to study the convergence of prescriptive- and performance-based methodologies as regards carbonation induced corrosion. An experimental work was carried out to determine the performance properties of prescribed concrete compositions, whose test results were included in the mathematical models of the performance-based specifications. Both safety factor and probabilistic approaches were used to estimate the service life periods of each composition being compared to the target periods defined in the prescriptive specification. The results show that the convergence between the two methodologies still needs to be improved.

How Reliable is the Durability of RC Structures?

The goal of this paper is to show some trends and time profiles of the reliability index relevant to the Serviceability Limit State considering the design service life of RC structures. The interactive web page “RC_LifeTime” – originated by the authors – is used (see http://www.stm.fce.vutbr.cz/). The depassivation of reinforcing steel due to carbonation is considered conservatively as a limiting condition. It is based on model concrete carbonation with 12 random input variables; the Latin Hypercube Sampling simulation method is used. RC_LifeTime offers the following options: Service Life Assessment – a statistical evaluation of service life, where optionally the target value of reliability index ß may be an additional input value and then the corresponding service life is the output value; Concrete Cover Assessment – a statistical evaluation of concrete cover value for the target service life, where optionally the required concrete cover value may be input in this case and the relevant reliability index ß describes the reliability of reinforcement depassivation.