Concrete Carbonation Process Research Articles

Concrete Carbonation of Deep Burial Storage Constructions under Model Aging Conditions

To ensure the safe operation of concrete structures of deep-burial storages, it is necessary to research the degradation mechanisms of such structures. Concrete carbonation is one of the key factors determining the service life of concrete structures. Existing methods for the concrete carbonation process research at various stages of the building structure life cycle make it possible to conduct model tests in the shortest possible time by simulating the operational factors influencing the corrosion process development. The authors carried out model tests of concrete of deep-burial storages using the method of accelerated concrete carbonation and by taking into account the effects of elevated temperatures. When exposed to elevated temperatures during carbonation, concrete samples exhibit a decrease in compressive strength in the first 56 days of testing by an average of 1.6 MPa. However, by the end of the tests (168 days), the strength of concrete samples at elevated temperatures is on average 4 MPa higher. The microstructure and carbonation dynamics were studied by XRD, TGA and SEM. The data obtained in the research can be used to develop models for predicting the service life of concrete structures of deep-burial storages.

Electrochemical realkalisation of carbonated cementitious matrix: characterization research to influence of time and current density

The depassivation of reinforcement caused by the reduction of concrete alkalinity due to the concrete carbonation process can induce the appearance of steel corrosion. The restoration of alkalinity can be done by chemical realkalinization (CRA) or electrochemical realkalinization (ERA) methods. In this context, the present work aims to evaluate the influence of the application time and the current density used in the electrochemical realkalinization process. For the development of the research, mortar samples were molded with a reinforced bar for electrical connection and remained for 24 months in a carbonation chamber. After this period, the carbonation depth that occurred was verified and then the specimens were submitted to the electrochemical realkalinization process using 3 different current values, 0.5, 1.0 and 1.5A/m2 and remained at different periods (7 , 14 and 21 days) in the recovery process. Additional tests of absorption, compressive strength, carbonation depth measurements, mercury intrusion porosimetry (MIP) and thermogravimetric analysis (TGA) were also carried out on reference, carbonated and realkalinized specimens. Based on the results of the tests, it was observed that the recovery process starts after 7 days with the lowest current density used. A better current density x application time ratio was also observed considering the results of the mercury intrusion porosimetry and thermogravimetric analysis tests in conjunction with the realkalinization process.

Feasibility of Application for the SHG Technology of Longitudinal Wave in Quantitatively Evaluating Carbonated Concrete

The ultrasonic transmission detection method is used to investigate the applicability for the second-harmonic generation (SHG) technology of longitudinal wave to quantitatively assess carbonated concrete. The principal of this method is to use the piezoelectric lead zirconate titanate (PZT) patch to detect the second-harmonic of longitudinal waves during the concrete carbonation process and extract non-linear parameters from observed signals. Non-linear parameters of concretes with two water–cement ratios (CI (w/c=0.47), CII (w/c=0.53)), two moisture contents (CI 0%, CI-W 100%), and three ultrasonic incident frequencies (50 kHz, 75 kHz, 100 kHz) were measured in this study. Results of the experiment demonstrate that non-linear ultrasonic parameters of longitudinal ultrasonic waves with high frequencies (75 kHz, 100 kHz) exhibit a better resolution regarding changes in concrete microstructure. Moisture (CI 0%, CI-W 100%) has little effect on the rate (CI: 62.73%, CI-W: 60.25, carbonation depth: 15 mm) for the change in relative non-linear parameters in the same concrete. The carbonation depth of concrete (CI (w/c=0.47), CI-W (w/c=0.47), CII (w/c=0.53)) can be well reflected by the change in relative non-linear parameters. Furthermore, there exists a good fit between the relative non-linear parameters of longitudinal waves and the concrete carbonation process. The relative non-linear parameters of longitudinal waves demonstrate feasibility in the quantitative assessment of concrete carbonation.

A predictive phase-field approach for cover cracking in corroded concrete elements

Steel bar corrosion is a crucial problem in reinforced concrete structures. Corrosion, being one of the most prevalent deterioration mechanism in concrete elements, has a significant impact on the structure's serviceability and durability, since the cross section of the steel reinforcement is reduced and the mechanical steel performances deteriorate. Additionally, residual material is created as a result of the steel oxidation process, and the volume occupied by the reinforcement grows, forcing the concrete cover to crack and spall. The carbonation-induced rebar corrosion and the subsequent cover cracking are simulated via the usage of a predictive model which combines the concrete carbonation process with the phase-field technique for brittle fractures. First, the carbon dioxide transport within the concrete is described using the Fick’s second diffusion law. Then, the corrosion process is estimated via the electrochemical kinetics equations providing the associated steel expansion. The steel deformation and strain are calculated with the Faraday Law. Finally, a phase field approach for brittle material is used to reproduce rupture in the concrete cover. The developed model is validated against examples available in literature and representative examples are illustrated, describing the capability of the proposed approach to replicate the cover cracking in concrete.

Carbonation Model and Prediction of Polyvinyl Alcohol Fiber Concrete with Fiber Length and Content Effects

Durability is an important aspect of reliability of concrete structures. In order to establish the carbonation model of polyvinyl alcohol (PVA) fiber concrete including the influences of PVA fiber length and volume content, a series of accelerated carbonation experiments were carried out on the normal concrete specimens and PVA fiber concrete specimens with fiber lengths of 3 mm, 6 mm, 12 mm and 18 mm and fiber volume contents of 0.1%, 0.3%, 0.5%, 0.75%, 1.0% and 1.5%, respectively. The experimental conditions remained at temperature of 20 ℃, humidity of 70%, and carbon dioxide concentration of 20%. It was found that the addition of PVA fibers could improve the carbonation resistance of concrete considerably. Within the investigated range of fiber length and content, the carbonation resistance of concrete is first strengthened and then weakened with increasing PVA fiber length or content. The quadratic carbonation depth prediction model could characterize the influences of PVA fiber length and content better than the linear model. The carbon dioxide diffusion equation was established by introducing a PVA fiber influence factor and its parameters were determined from the carbonation depth prediction model. The carbonation process of PVA fiber concrete under the accelerated carbonation experiment condition was simulated. Both the model and the numerical method were validated by comparison between the experimental and numerical results. Finally, the influences of added PVA fibers on the carbonation life and durability of reinforced concrete components were further studied numerically. The results showed that compared with the normal concrete component, the durability of PVA fiber concrete components is significantly improved.

Description of the concrete carbonation process with adjusted depth-resolved thermogravimetric analysis

AbstractThe thermal gravimetric analysis (TG) is a common method for the examination of the carbonation progress of cement-based materials. Unfortunately, the thermal properties of some components complicate the evaluation of TG results. Various hydrate phases, such as ettringite (AFt), C–S–H and AFm, decompose almost simultaneously in the temperature range up to 200 °C. Additionally, physically bound water is released in the same temperature range. In the temperature range between 450 °C and 600 °C, the decomposition of calcium hydroxide and amorphous or weakly bound carbonates takes place simultaneously. Carbonates, like calcite, from limestone powder or other additives may be already contained in the noncarbonated sample material. For this research, an attempt was made to minimise the influence of these effects. Therefore, differential curves from DTG results of noncarbonated areas and areas with various states of carbonation of the same sample material were calculated and evaluated. Concretes based on three different types of cement were produced and stored under accelerated carbonation conditions (1% CO2 in air). The required sample material was obtained by cutting slices from various depths of previously CO2-treated specimen and subsequent grinding. During the sample preparation, a special attention was paid that no additional carbonation processes took place. As reference method for the determination of the carbonation depth, the sprayed application of phenolphthalein solution was carried out. Microscopic analysis was examined to confirm the assumptions made previously. Furthermore, the observed effect of encapsulation of calcium hydroxide by carbonates caused by the accelerated carbonation conditions was examined more closely.

Two-Dimensional Mathematical Model of Carbon Dioxide (CO2) Transport in Concrete Carbonation Proses

A new two-dimensional mathematical model was developed to describe the transport phenomena of carbon dioxide in concrete structures. By treating transport phenomena as a concrete carbonation process, a two-dimensional linear partial differential equation was derived based on the principle of mass balance and convective-dispersive Equation. It was found the analytical solution by the separation of variables method combined with some substitution approaches. The numerical results are presented to illustrate the practical application of this model.

CO2 uptake model of limestone-powder-blended concrete due to carbonation

In this study, a model for evaluating the CO2 uptake rate of plain concrete and limestone-powder-blended concrete in both the service and recycling phases was proposed. First, a blended cement hydration model was proposed to evaluate the content of carbonatable substances, porosity and carbon dioxide diffusivity. In the service phase, a one-dimensional carbonation model was proposed to evaluate the carbonation depth. In the recycling stage, an unreacted core model was proposed to evaluate the carbonation process of spherical recycled concrete. Secondly, considering the concrete materials, structural elements and environmental exposure, a CO2 uptake model at the service stage and recycling stage was proposed. The total CO2 uptake rate is the sum of the CO2 uptake rates in the service stage and the recycling stage. The analysis results showed (1) as the limestone replacement rate increased from 0% to 20% (water–binder ratio is 0.3), the CO2 uptake rate in the service phase increased from 3.12% to 3.84%, and the total CO2 uptake rate increased from 22.82% to 26.11%. (2) Given a certain concrete mixture, as the surface area to volume ratio of structural units increased, or the amount of recycled concrete decreased, the CO2 uptake rate increased, but the total CO2 uptake rate did not change. (3) Given a certain limestone powder replacement ratio, as the water/binder ratio increased, the total CO2 uptake ratio increased. The contributions of this study are 1) propose an integrated hydration-carbonation-CO2 uptake model for limestone blended concrete, 2) clarify the differences of carbonation equations between service stage and recycling stage, and 3) determine the effects of concrete mixtures, structural element sizes and types, life cycle stages, and recycled concrete sizes on CO2 uptake.

Phase-field simulations of cover cracking in corroded RC beams

Corrosion of steel reinforcement bars is a crucial issue for the reinforced concrete structures. Being one of the most common deterioration mechanisms, corrosion severely affects the serviceability and durability of the structure as the steel reinforcement suffers from a reduction of the cross section and deterioration of the mechanical properties. Additionally, due to the steel oxidation process, residual material is formed, and the volume occupied by the reinforcement increases, leading to cracking and spalling of the concrete cover. A predictive model coupling concrete carbonation process and phase-field approach for brittle fractures is proposed to simulate the carbonation induced corrosion of rebar and the subsequent cracking phenomenon. First, a Fick diffusion law is used to describe the carbon dioxide (CO2) diffusion within the concrete which leads to a generalized corrosion process. As the corrosion evolves, the steel mass loss is converted into expansion strain due to the formation of residual material, and the damage evolution within the concrete cover is determined. After validation against examples from the literature, numerical simulations are performed, presenting a phase-field strategy capable to describe the cover cracking of corroded RC beams.

Fib models for modeling of chloride ion ingress and concrete carbonation: Levels of assessment of input parameters

AbstractDegradation processes affecting structural materials, such as chloride ion ingress, concrete carbonation, and the subsequent corrosion of reinforcement, are limiting factors for the service life of reinforced concrete structures and/or structural elements. The objective of a structural condition assessment is to determine the current state and estimate the future performance of a structure with a maximum degree of accuracy and a minimum of effort. There is therefore a need for advanced methodologies and predictive deterioration models for the assessment of structures/structural elements over time. In the paper, the focus is on the widely accepted models for modeling of chloride ion ingress into concrete and concrete carbonation process incorporated in the fib Model Code 2010. Three levels of assessment of input parameters are presented, starting with simple quantification based on codes/literature recommendations and progressing to higher levels of assessment using design documentation and visual inspection data, additional on‐site measurements, and/or laboratory tests.

Extreme solutions in control of moisture transport in concrete carbonation

This paper is concerned with a control system modeling concrete carbonation process when underlying hysteresis effects are taken into account. The system consists of a diffusion equation for moisture and an ordinary differential equation accounting for the hysteresis. We obtain the bang–bang principle for this system asserting the proximity of all attainable states to the so-called bang–bang states. The later are the states reached by controls valued in the extreme points of the control constraint. In our study we are able to dispense with the monotonicity of the right-hand side in the hysteresis equation. This assumption has repeatedly appeared in previous analysis of control systems with hysteresis.

Mathematical Modeling of Transport Phenomena of Carbon Dioxide in Concrete Structures

Concrete has a reputation as a “low tech” material, but it is actually very complex and worthy of study. It’s the most widely used construction material in the world. Carbonation process in concrete regularly involves a chemical reaction between carbon dioxide ( CO2) and the products of cement hydration. By treating transport phenomena as a concrete carbonation process, this study presented a two-dimensional linear partial differential equation derived based on the principle of mass balance and convective-dispersive equation incorporating rate constant for zero-order production. We assume the diffusion coefficient of CO2 in any direction of concrete is all the same. The analytical solution of the model is achieved by the eigenfunctions expansion technique. The results obtained are presented graphically and discussed. It is revealed that the relationships among CO2 concentration, carbonation depth and time that can be used to state a carbonation transport phenomena in concrete structures are influenced by the diffusion coefficient.

On the Existence of Weak Solutions for a 1-D Free-Boundary Concrete Carbonation Problem

In this paper we deal with a one-dimensional free-boundary problem arising in the modeling of concrete carbonation process. More precisely, we investigate global existence, uniqueness and large-time behavior of weak solutions for the problem under consideration. We also obtain the existence of a weak solution when the measure of the initial domain vanishes.

Influence of loading and cracks on carbonation of RC elements made of different concrete types

Accurate prediction of concrete carbonation is important for the correct assessment of both durability and environmental impact of reinforced concrete (RC) structures. Loading applied to a RC structure and concrete cracking caused by this loading may significantly affect the concrete carbonation process. However, so far these factors have received little attention of researchers, especially this concerns ‘green’ concretes, i.e. concretes in which Portland cement (PC) is partially replaced by supplementary cementitious materials such as fly ash (FA) and ground granulated blast-furnace slag (GGBS). Thus, the aim of the study presented in the paper was to experimentally investigate the influence of static loading and associated concrete cracking on carbonation of RC elements made of PC concretes and ‘green’ concretes containing significant amounts FA and GGBS. For this purpose, six concrete mixes with two water/binder (w/b) ratios (0.40 and 0.55) and different proportions of PC, FA and GGBS were prepared. The mixes were used to cast twelve RC beams (100 × 120 × 900-mm) and a larger number of 100-mm concrete cubes. The beam specimens were loaded in four-point bending to produce flexural cracks of maximum width of either 0.1 mm or 0.3 mm. The loaded beam specimens along with unloaded cube specimens were then placed into a carbonation chamber and subject to accelerated carbonation for 120 days. After that the carbonation depths in the beams and cubes were measured. Results of the tests show a significant effect of load induced stresses (both tensile and compressive) on the carbonation resistance of the concretes, especially of ‘green’ concretes. The influence of cracking on concrete carbonation was also observed and discussed in the paper.

Multiscale model for moisture transport with adsorption phenomenon in concrete materials

We consider a new two-scale problem which is given as a mathematical model for moisture transport arising in a concrete carbonation process. In research for moisture transport, it is a crucial step how to describe the relationship between the relative humidity and the degree of saturation, mathematically. Here, we have proposed the two-scale model consisting of the diffusion equation for the relative humidity in a macro domain and the free boundary problems describing the relationship in infinitely micro domains. Accordingly, the structures of the micro domains are unknown in our model. This is a significant feature of our new model to emphasize. The aim of this paper is to establish local existence in time and uniqueness of a solution to the model.

Existence and uniqueness for a concrete carbonation process with hysteresis

A partial differential system arising in the moisture transport in concrete carbonation modeling is considered. The system consists of a diffusion equation for moisture and an ordinary differential equation accounting for the hysteresis effect appearing in the process. The existence of solutions for this system supplied with suitable initial boundary conditions and having fairly general nonlinear right-hand sides is established. When the dimension of the space domain is one, the uniqueness of a solution is also provided.

Carbonation Reaction and Microstructural Changes of Metro-Tunnel Segment Concrete Coupled with Static and Fatigue Load

AbstractCarbonation problems relating to concrete durability cannot correspond to the real engineering service environment, because the degradation of concrete properties is actually affected by load and multiple environment factors for a coupling effect. This paper studies the chemical reaction mechanism, carbonation depth, pH values, and pore-structure changes under a load and carbonation coupling effect. The authors study the time-dependent evolution of carbonation depth under different levels of tensile and compressive loads. The authors then further study the time-dependent evolution of concrete carbonation depth under fatigue bending loads at different stresses levels and cycles. While taking advantage of the microstructure characterization methods, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and a pH-value meter were used to analyze the chemical reaction mechanism of the concrete carbonation process, undertake a quantitative analysis of the solid phase composition, and examine the ...

Test method to simulate the influence of the interface on the concrete carbonation process

A trial test method is introduced to form and magnify regular interface. Through researching on the carbonation of the magnifying interfacial transition zone (ITZ), the practical carbonation of the concrete can be simulated. Because the diffusion rate of CO2 in the ITZ is several times greater than that in the bulk paste, the diffusion rate and direction of CO2 will change and form a new carbonation front line. An interfacial effect zone caused by the ITZ will change the distribution of the complete carbonation zone and the partial carbonation zone. One of the important reasons for the formation of the partial carbonation zone was the existence of the interfacial effect zone. Consequently, the method mentioned in this paper provides a new way for researching on the microstructure of the cement based materials during the carbonation process.

Modelling of concrete carbonation; is it a process unlimited in time and restricted in space?

Abstract The aim of the article is mathematical modelling of the carbonation process that has been based on results of research conducted both in accelerated and natural conditions. The article covers short characteristic of carbonation, its processes and effects. Also critical review of articles that concern carbonation mathematical models was included in the paper. Assuming the self-terminating nature of carbonation the hyperbolic model of carbonation was formulated. Such a model describes the carbonation progress as the process unlimited in time but with the restricted range in concrete depth that is limited by the value of a model asymptote. Presented results cover research on carbonation of concrete with a different water-cement ratio and different types of binders and duration times of early curing. Investigations have been conducted as accelerated (1% concentration of CO2) as well as in long-term exposures in natural conditions. The obtained results confirmed statistically that hyperbolic model is a well-founded approach when the modelling concrete carbonation process is concerned

Large time behavior of a solution of carbon dioxide transport model in concrete carbonation process

In [7] we show the global existence and uniqueness of a solution of carbon dioxide transport model in concrete carbonation process. This model is governed by a parabolic-type equation which has a non-local term depending on the unknown function itself. In this paper, we show the large time behavior of that solution.