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Lime is a product derived from the thermal decomposition of limestone (mainly calcium carbonate, CaCO3) into quicklime (CaO) and carbon dioxide (CO2), also called calcination. Controlled reaction with water is used to manufacture hydrated lime (Ca(OH)2) products. Lime is used in a wide variety of applications: metals industry, construction materials sector, civil engineering, environmental protection, agriculture, and chemical industry. Lime production is one of the sources of anthropogenic CO2 emissions resulting in global warming and ocean acidification. However, a proportion of the CO2 emitted during the calcination is reabsorbed by the lime during the product life within its different applications. This process called carbonation is thermodynamically favoured because it is exothermal. It allows permanent CO2 storage in a stable product since the lime combines with gaseous CO2 reforming CaCO3. This paper reports a comprehensive literature review on the carbonation potential of lime in different applications. The total carbonation potential is assessed as carbonation rate, i.e. the ratio between the CO2 reabsorbed through carbonation during the operational life of lime and the CO2 emitted during limestone calcination. This study provided preliminary evidence that, based on the current EU market, on average 23–33% of lime process emissions are carbonated during the use phase. Carbonation over time is also analysed for the lime applications where information is available. For three applications, namely water, flue gas cleaning and pulp and paper, the carbonation reaction is instantaneous. Up to 22% of the calcination emissions are absorbed within five years based on the current EU market. [ABSTRACT FROM AUTHOR]

In this paper, the promising way to utilize EAF (electric arc furnace) slag as a cementitious material has been studied by employing microbially accelerated carbonation technology. Under the conditions of cation supplementation and accelerated carbonation of bacteria, the highest compressive strength of the samples could achieve 18 MPa in this research. The changes in minerals and microstructures during the carbonation and microbial carbonation have been observed by X-ray diffraction (XRD), thermogravimetric analysis (TG), and mercury intrusion porosimetry (MIP). Carbonic anhydrase-producing microorganisms have obvious acceleration effects in the carbonation process, making the matrix compact and improving the mechanical properties. Besides, the treatment method of accelerating carbonation by microorganisms could effectively inhibit the leaching of heavy metals in the EAF slag. This paper provides a reference for the potential applications of EAF slag in engineering and reveals the mechanism of microbial acceleration. Industrial waste electric arc furnace (EAF) slag was used as a cementitious material and could fix carbon dioxide. Microbial technology promotes the deposition of calcium carbonate (1–5 μm) to fill pores over 1 μm. Microbial accelerated carbonated EAF bricks could reduce the leaching of heavy metals. [ABSTRACT FROM AUTHOR]

To understand the influence of slag chemistry on the carbonation resistance of slag-rich cement, this paper explored the carbonation characteristics of blended cement systems with different Al2O3 contents in slag through accelerated carbonation test. Irrespective of slag chemistry, three main CO2 binding phases were identified during accelerated carbonation test, i.e. carbonated Ca-Al AFm phases (amorphous or nano-crystalline), carbonated hydrotalcite-like phase, and calcium carbonate (amorphous calcium carbonate, vaterite, and calcite). Additionally, it was noted that the classification employed for slag reactivity (based on slag chemistry) cannot be extended to predict carbonation resistance of slag-rich cement directly. The main challenge occurred for slag with high alumina content. The experimental results showed that Al2O3-rich slag exhibited a high reactivity and can be considered as a reactive component in the blended mixture; however, it did not contribute to carbonation resistance of the mixture. Especially for CO2 binding capacity, it was similar for systems with varied alumina content in slag (from 3.69 to 18.19 wt.%) in the completely carbonated area. [ABSTRACT FROM AUTHOR]

The induction of accelerated carbonation curing (ACC) as carbon capture, utilization, and sequestration (CCUS) technique helps in achieving the net zero target. ACC is one of the potential techniques to sequester the CO2 in concrete. However, the usage of ACC in reinforced concrete is still debatable. This paper investigates the effect of ACC on mechanical, permeation, mineralogy, hydration and microstructural characteristics of concrete with the long-term performance of reinforced concrete using linear polarization resistance (LPR) and carbonation depth. In order to study the effect of ACC duration on the properties of concrete, the specimen was subjected to 6, 12, and 24 hours (h) of carbonation curing. The results were compared with conventional water-curing specimens. ACC at 12 h provided the best results for tested properties. The results were varied by statistical analysis using ANOVA and stoichiometry. Based on the best 12-h duration, 2.13 kg of CO2 can be sequestered in 1 m3 (0.89 kg/t) of concrete. [ABSTRACT FROM AUTHOR]

This study focused on the problem of recycling construction and demolition wastes as well as industrial waste by-products into sustainable concrete materials. By combining addition of three different industrial waste by-products, an environmentally friendly recycled aggregate self-compacting concrete (RA-SCC) mix was put forward. Carbonation resistance and microstructure of SCC incorporating high volumes of industry by-products and recycled aggregates were studied in this paper. A total of 9 RA-SCC with 50%, 75% supplementary cementitious materials (SCMs) and different SCM combinations were prepared, which consist of binary mix with fly ash (FA), ternary mix with FA and ground granulated blast-furnace slag (GGBS), and quaternary mix with FA, GGBS, and silica fume (SF). An exposure period of 3, 7, 14, and 28 days was adopted for accelerated carbonation tests. The test results indicate that, as RCAs content increased, RA-SCC carbonation depth increased. The carbonation depth of SCC with 100% RCAs increased by 49.35% compared to that of normal SCC. In addition, carbonation resistance of RA-SCC mixes with a given compressive strength decreased with increasing SCM content. However, the loss in carbonation resistance was greatly mitigated by the combined addition of different SCMs, on account of the substitution of cement with industrial by-products and natural aggregates with RCAs. The combined addition of different SCMs enhanced the carbonation resistance of RA-SCC mixes. The test results were validated through microstructural analysis using scanning electron microscopy (SEM), and X-ray diffraction (XRD). A comparison between predictions calculated using existing models and measured carbonation depth was implemented. By taking into account the effect of RCAs and SCMs, a modified carbonation model in conjunction with fib carbonation model was put forward. [ABSTRACT FROM AUTHOR]

The paper reviewed the current perspectives on the development of carbon dioxide (CO2) sequestration through its process conversion into calcite. The process occurs in either geological or biological systems. However, geological sequestration is an expensive process, which is slow in comparison to bio-sequestration. Recently, the bio-sequestration of atmospheric CO2 into the soil using microorganisms such as algae has been investigated. However, the algae cannot be used in the bio-concrete due to their nature as phototrophic organisms. In contrast, bacteria are the most potent organisms in bio-concrete technology. The use of bacterial species in the bio-aerated concrete bricks (B-ACB) and its potential to bio-sequestrate CO2 represents a future strategy to reduce high CO2 pollution. Bacterial cells can capture CO2 by accelerating the carbonation processes, which convert CO2 into calcium carbonate (CaCO3) via carbon anhydrase and urease enzymes. The present paper aimed to highlight and discuss the applicability of bacteria in the B-ACB for capturing and storing CO2. It is evident from the literature that the new trends to use bio-concrete might contribute to the reduction of CO2 by accelerating the carbonation process and strengthening the B-ACB. [ABSTRACT FROM AUTHOR]

In this paper, early-age ambient pressure carbonation curing was successfully developed to lower the corrosion risk by avoiding deep CO2 penetration and preserving high pH around the steel surface. The effect of ambient pressure carbonation on the resistance of chloride-induced rebar corrosion was evaluated by applying an accelerated impressed current (IC) as a trigger. Due to improved physical properties, carbonation-cured concrete had a lowered current reading, a reduced rebar mass loss, a lessened total or free chloride content, and a decreased chloride diffusivity. Its time-to-corrosion-initiation and corrosion-propagation stages were also extended, which could strengthen the structural integrity and extend the residual service life of reinforced concrete components after corrosion initiation. Ambient pressure carbonation-cured concrete is corrosion resistant while still having the capacity to sequestrate carbon dioxide, which could contribute to the sustainability and circular carbon economy. [ABSTRACT FROM AUTHOR]

Characterising spatial variability, which is of utter importance in inspection and maintenance strategies, requires comprehensive spatially distributed databases. However, in real practice, spatially distributed inspection is costly and could damage the structure if a large number of destructive tests are carried out. Therefore, the first objective of this work is to propose a methodology to extract as much informations as possible from available spatially distributed databases, in order to characterise the spatial correlation. Moreover, a preventive maintenance strategy should be supported by deterioration models able to propagate uncertainty and spatial variability. Then, the second objective of the paper is to evaluate the ability of these models to propagate uncertainties and spatial variability. The methodology is illustrated with data collected through destructive tests in a concrete wall exposed to carbonation. The database encompasses information about the concrete porosity, saturation degree, density, and carbonation depth. Recommendations are hence provided in this work for the choice of input parameters that should be modelled as random fields. These recommendations were applied and then confirmed by comparing measured and modelled spatially distributed carbonation depths. The results highlight that uncertainties in measurements and statistical uncertainties have significant impact when dealing with spatial variability. [ABSTRACT FROM AUTHOR]

Chloride concentrations are often evaluated for concrete mixtures used in new construction for quantity control purposes. This paper reports on the reliability of results from ASTM C1152 (acid-soluble) and ASTM C1218 (water-soluble) tests commonly adopted for measuring chlorides in concrete. The effects of cementitious material type, water-binder ratio, admixed chloride level, and degree of carbonation on chloride concentrations of cementitious systems are evaluated. Results show that the release of bound chlorides due to carbonation could be represented by an increase in ASTM C1218 test value. Chloride concentrations measured using ASTM C1152 testing could be significantly lower than the actual chloride concentration for carbonated systems. This underestimation, as a percent of total chloride concentration, could be as high as 40% depending on the cementitious material type and chloride admixed level. Preliminary results indicate that ASTM C1218 could be more reliable when compared to ASTM C1152 for systems with admixed chlorides. [ABSTRACT FROM AUTHOR]

This paper proposes a method for the optimal design of concrete by incorporating fly ash. First, an optimal design with the aim of reducing the CO2 emissions was developed. Various constraints, such as the strength, slump, and carbonation with stress, were considered. Second, optimal mixtures were obtained using a genetic algorithm considering the aim functions and various constraints. The results obtained from the analysis demonstrate that, for low-strength concrete, carbonation dominates the mixtures, whereas for high-strength concrete, strength dominates the mixtures. Additionally, the stress types and levels affect the optimal mixtures. A rich mixture is crucial for structural elements with high-level stresses. Furthermore, compared with that of compressive stress, the effect of tensile stress on the mixtures is evident. Finally, optimal designs considering the material costs and embodied energy were performed. These optimal mixtures with low costs or low embodied energy are similar to those with low CO2 emissions. [ABSTRACT FROM AUTHOR]

The paper deals with the assessment of CO2 storage capacity in cement concrete using reactive transport modelling of the accelerated carbonation, i.e. 15 Vol % and experiments. To meet the most realistic geometry of concrete aggregates, the numerical solution is achieved using a homogeneous concrete without aggregates and two-phase concrete including aggregates. We utilise the reactive transport model to estimate molar concentration of cement components and porosity distribution during CO2 carbonation. The model also computes the hydration process before and during carbonation. The numerical solutions are obtained from an extremely nonlinear transient system of Partial Differential Equations (PDEs). The experiments of CO2 carbonation have been carried out using coarse concrete aggregates after 6 months of curing in water. Based on Thermal Gravimetric Analysis (TGA), CO2 uptake during carbonation is determined in weight percent. The numerical simulations fairly agree with the experiments. CO2 sequestration calculation via chemical reactions Single-Phase & 2-phase numerical concrete aggregate Accelerated carbonation modelling & experiments. [ABSTRACT FROM AUTHOR]

This paper presents the performance of a multifunctional generic compound, 4-Aminobenzoic acid (4ABA) as migratory inhibitor applied on hardened concrete surface to curb corrosion due to combined chloride and carbonated environment. Electrochemical techniques (LPR and EIS), gravimetric analysis were applied to evaluate the corrosion performance and the inhibition mechanism of 4ABA. Chloride and carbonation profiles were developed to investigate the dominant cause of corrosion during the exposure. Visual and microscopic analysis of concrete surface and rebar surface was also done. Compressive strength test was performed to study the effect of corrosion inhibitor on strength property of hardened concrete. Results confirm that 4ABA prolonged the passive state of rebar when used as preventive measure and restrained the on-going corrosion process when employed as repair strategy. Combined exposure by chlorides and CO2 leads to redistribution of chloride ions in concrete matrix. The results also conclude that during the combined exposure, chloride ions initiate the corrosion process and carbonation aggravates this process. Application of 4ABA does not influence the strength properties of concrete. ABA has performed the inhibition by protective layer development and shield formation against the negatively charged corrosive ions. Blended cement concrete system which was observed to be more vulnerable to corrosion was seen to attain similar corrosion resistance as OPC concrete after inhibitor application. [ABSTRACT FROM AUTHOR]

The addition of Electric Arc Furnace Dust (EAFD) in concrete is a good solution to encapsulate its potential toxic elements and to contribute to the valorisation of industrial wastes. This paper investigates the feasibility of using EAFD as an addition to concrete production. Four experimental mixes have been produced (one of traditional concrete and three introducing a 5, 10 and 15% of EAFD per cement weight without replacing any material). The mechanical properties of the resultant concrete mixtures (compressive strength, elastic modulus and density) were evaluated. In addition, the natural carbonation of EAFD concrete mixtures was studied. Finally, a microstructural campaign was carried out to study the morphology and microstructure of the considered concrete mixtures. Results showed that concrete with an addition of 15% of EAFD per cement weight had a higher compressive strength and elastic modulus and a lower carbonation depth in comparison with traditional concrete. [ABSTRACT FROM AUTHOR]

This paper presents an investigation into the behaviour of a clay soil stabilised with MgO under forced carbonation and comparison with conventional chemical stabilisation methods. The tests were conducted in two groups. In the first group the soil was mixed with 5, 10, 15 and 20% MgO or cement. Unconfined compressive strength (UCS) tests were performed on compacted samples from these mixtures at curing times of 7, 14 and 28 days. In the second group, samples prepared with different percents of MgO were subjected to CO2 under pressures of 0.5, 1.0 and 1.5 bar for periods of 4, 8, 12 and 24 h. The results showed that adding MgO increases the strength of the soil and, like other binders, the amount of increase in strength depends on the percent of MgO and curing time. It is also resulted that the effect of MgO is less than cement in increasing the strength. It was revealed that forced carbonation can facilitate the stabilisation of MgO-stabilised soil in a few hours compared with usual process that takes several days. XRD and SEM results showed that the gained strength is resulted from the interaction between the soil and the agents. [ABSTRACT FROM AUTHOR]

This study investigates the causal relationship between hydroelectricity consumption (HC), economic growth (GDP), and carbon dioxide (CO2) emission in Malaysia by applying the time-series techniques. The major findings for this paper are as follows: (1) long-run relationship exists between HC, GDP, and CO2emissions. (2) We found a unidirectional causality relationship from HC to CO2emissions in the short-run while in the long-run causality runs from GDP and HC toward CO2emissions. (3) The results of the variance decompositions suggest that the impact of HC and CO2toward GDP becomes noticeable only over the long-run, providing an important policy route map for Malaysia. A step-wise (e.g. combined-use) shift from fossil fuels to Renewable Energy Sources (RESs) seems to be the viable alternative for Malaysia. In this manner, the potential of hydropower for electrification would be the way forward but with caution as the social implication should also be hand in hand with this massive development plan. [ABSTRACT FROM PUBLISHER]

Physical models for carbonation-induced reinforcement corrosion and concrete cracking have been proposed mainly based on accelerated carbonation tests. However, it has been criticised for not being representable of the natural corrosion process, and may not be applicable to real structures, so it is meaningful to calibrate and modify these models with in-situ inspection data of reinforced concrete (RC) structures in actual carbonation environment. The available in-situ data with the current inspection technologies (non-destructive) include concrete cover thickness, concrete strength, carbonation depth, reinforcement corrosion proportion, cracking proportion, etc. Based on Bayesian updating theorem, the paper proposes an integrated procedure for the updating of carbonation-induced deterioration models with inspection data, and then the durability assessment of existing RC structures in remaining service lives. In the procedure, the carbonation depth model and the probability of reinforcement corrosion are firstly updated with the inspected data, and then the un-carbonated depth model, the cracking probability and the critical corrosion depth model for cracking are updated subsequently. The methodology is illustrated using a case study of a RC industrial building with an age of 33 years. The influences of prior distribution and inspection data amount on the updating effect are discussed. Especially, the uncertainty associated with the number of corroded samples due to the error in corrosion inspection is discussed, and its effect on updated corrosion probability is investigated. [ABSTRACT FROM AUTHOR]

This paper presents a study on the effects of accelerated carbonation curing (ACC) on performance of self-compacting concrete (SCC) mixtures prepared using limestone powder (LSP) alone and blend of limestone powder and silica fume (SF) as mineral fillers. Specimens cast using both SCC mixtures were subjected to ACC that consisted of exposing specimens to CO2 for 10 hours under a constant pressure of 414 kPa. ACC-treated specimens were tested for evaluating effects of ACC on properties of SCC mixtures in terms of CO2 uptake, mechanical and durability properties, morphology, and mineralogy. Test results indicate that the ACC-treatment substantially enhanced the properties of both SCC mixtures. Strength of ACC-treated concrete specimens can be improved further by exposing them to air for a period of first 7 days of the ACC-treatment. ACC-treatment of LSP-SF-C was more effective than that for LSP-C. Properties of ACC-treated SCC mixtures were comparable with that of the same mixtures subjected to moist-curing for 7 days except drying shrinkage, which was higher for ACC-treated specimens than the moist-cured specimens. However, shrinkage of ACC-treated specimens after 7 days was within the permissible limit in case of LSP-C whereas 7-day shrinkage for LSP-SF-C exceeded the permissible limit of 500 µm. [ABSTRACT FROM AUTHOR]

In this paper, the effects of carbonation and moisture on chloride and ionic transport into concrete are studied. Based on the concrete composition and porosity as well as the physicochemical equilibrium, a comprehensive macroscopic model is proposed for this problem. The model features the chemical activity of ions, the interactions between chloride ions and concrete; and the ion–ion interactions in the solution. The governing equations of moisture and ionic transport into nonsaturated concrete are thoroughly described and solved numerically by the finite difference method in time and in space. Applications of the numerical model are demonstrated by predicting the evolution of the porosity and the service-life of a concrete specimen exposed to an aggressive environment containing chloride, carbon dioxide and moisture. A comparison of the model with a set of experimental data is finally proposed. [ABSTRACT FROM AUTHOR]

This paper presents the results of investigations on reinforced concrete structures present in the former Auschwitz I and Auschwitz II-Birkenau concentration and extermination camp. Field inspection employing the non-destructive method of reinforcement potential measurement according to the ASTM-C 876-15 standard, followed by laboratory investigations performed on genuine historic reinforced concrete samples collected from the former Auschwitz camp, allowed assessment of the actual condition of this 70-year-old construction material. Electrochemical potential measurements allowed mapping of the regions characterized by enhanced reinforcement corrosion risk and the regions of its immunity. The composition of concrete, water absorbency, content of detrimental salts, and degree and profile of carbonation as well as mechanical properties were evaluated. Results revealed the most common and probable mechanism responsible for degradation of the reinforced concrete structures in the former Auschwitz camp. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of the coupling between cement hydration and drying of concretes with high amount of fly ash or blast-furnace slag and concretes with Portland cement or blended cements. The study, conducted with the MLS by FEMMASSE® code, aims at assessing the influence of drying on concrete properties governing carbonation kinetics, i.e. porosity, Portlandite content and liquid water saturation degree. These properties were found not uniform according to the depth within the concrete material. In the cover zone, high substitution concrete should have a higher carbonation risk than Portland cement concrete because of the slow hydration kinetics combined with the suspending effects of drying on hydration. Therefore, high substitution concrete should require a longer period of curing than Portland cement-based concretes. [ABSTRACT FROM AUTHOR]

The paper presents the results of carbonation resistance of Self-Compacting Concrete (SCC) made with coarse recycled concrete aggregates and fine recycled concrete aggregates. To evaluate the carbonation resistance of SCC mixes, two different groups consisting of nine SCC mixes were prepared. The impact of coarse recycled concrete aggregates and fine recycled concrete aggregates has been quantified based on the observed performance of SCC mixes of Group-I whereas, the influence of Silica Fume (SF) has been observed on the SCC mixes of Group-II. The incorporation of SF in various SCC mixes not only improves the compressive strength, the carbonation resistance is significantly increased. It has also been observed with the scanning electron microscopy analysis that the incorporation of SF in SCC mixes containing different contents of recycled concrete aggregates, resulted in the production of SCC mixes, with higher/comparable performance to that of control SCC mix. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The paper considers two deterioration mechanisms of concrete, frost-induced damage and carbonation. The objective of experimental study is to investigate how the microstructure degradation of cement-based materials caused by the cyclic water freezing affects the carbonation rate. Influence of water to cement ratio and addition of air-entraining admixture was analysed. The change of cement mortar pore structure due to frost damage was investigated by multi-cycle mercury intrusion porosimetry and capillary absorption test. The carbonation depth was examined using phenolphthalein indication and pH microelectrodes. The experimental results indicate that the ice-induced damage noticeably enhances the carbonation of concrete. Addition of AEA reduces considerably changes of the pore size distribution caused by the frost damage. [ABSTRACT FROM PUBLISHER]

This study centers on a novel approach of high flexural strength rankinite (3CaO·2SiO2, abbreviated as C3S2) cement benefiting from in-situ formation of aragonite whisker (AW) during carbonation curing. The manufacturing parameters including MgCl2 concentration and reaction temperature play key influence on formation of AW. The results showed that high temperature favored AW formation and AW with length-diameter ratio of 15 ∼ 30 could be generated with concentration of Mg2+/Ca2+ molar ratio of 0.1 at 70 °C. Under this condition, the flexural strength of the C3S2 cement reached 7.5, and 15.6 MPa after 3d and 28d and the corresponding compressive strengths were 30.2 and 71.1 MPa, respectively. The results also showed that 40.9% of CO2 by mass was consolidated in rankinite paste after 48 h, suggesting a promising prospect for calcium silicate-containing waste residue and cement to capture CO2 and simultaneously manufacturing high-performance materia. [ABSTRACT FROM AUTHOR]

The influence of additive MgO and its content on both the compressive strength and carbonation depth of alkali-activated slag concrete (AASC) was investigated under an accelerated carbonation environment. Furthermore, the modification mechanism of MgO on the carbonation resistance of AASC was explored by multiple analytical techniques. Results showed that the incorporation of MgO effectively enhanced the post-carbonation compressive strength and diminished the carbonation depth of concrete. As the MgO content increased, there was a gradual reduction in carbonation depth. The incorporation of MgO promotes the hydration of slag, altering the Al environment, and promoting the formation of C-S-H and Mg-Al hydrotalcite phases. Moreover, the addition of MgO resulted in the emergence of magnesium carbonate and calcium magnesium carbonate in the carbonation products, which filled the pores and prevented the further diffusion of CO2 into the interior. In addition, the improvement effects are more pronounced in the water glass system compared to the NaOH system. [ABSTRACT FROM AUTHOR]

This paper presents the results of an investigation on the influence of a replacement of limestone powder (LSP) by silica sand (SS) on properties of engineered cementitious composites (ECC). For this purpose, five different ECC mixtures were adopted: ECC mixture with only SS (M1) for control purposes and four ECC mixtures in which SS is partially replaced by four levels of replacements (25, 50, 75 and 100% by weight of total SS) of LSP. The mechanical properties of ECC were investigated for 3, 28 and 90 days, while the durability tests were performed for 90 days. It was concluded that increase in LSP content resulted in a decrease in fluidity of ECC mixtures indicating longer flow times. Increase in the LSP content had a positive effect on the performance of the compressive strength, fracture toughness and flexural strength at the ages of 3 and 28 days, while this was not valid at the age of 90 days when compared to the reference mixture M1. Moreover, it can be said that the use of LSP instead of SS in ECC mixtures had the positive effect on ductility and good dispersion of fibres due to its fine particle structure compared to SS. On the other hand, the mass loss due to acid attack and the sorptivity coefficient of ECC specimens decreased, while the carbonation resistance increased in all ECC mixes compared to the reference mixture M1 with only SS when LSP content in ECC mixtures increased. [ABSTRACT FROM PUBLISHER]

The carbonaceous nanofillers such as graphene and graphene oxide play competent role due to fine structural and functional properties having wide range of technical applications. This paper reviews structure and flame-retardant properties of graphene and graphene oxide. These nanofillers form promising nanomaterials for next generation high-performance structural and multifunctional composite structures. One of the major difficulties to produce strong and thermally conductive graphene/graphene oxide composites is fine dispersion of carbon nanomaterials. Consequently main focus of review is on flame retardancy of organic filler-based nanocomposite. To the end, techniques for nonflammability property measurement of polymer/graphene and polymer/graphene oxide have been discussed. [ABSTRACT FROM AUTHOR]

Autoclaved aerated concrete (AAC) is widely used for its lightweight, high thermal insulation, and superior machinability. However, its loose and porous microstructure can cause a significant decrease in compressive strength after carbonation and the mechanism of the deterioration remains uncertain. This study delved into the alteration trends of AAC's compressive strength and dry density within carbonation environments. Additionally, a variety of testing techniques were employed to elucidate the microscopic mechanisms. The results showed that when the calcium/silicon ratio (Ca/Si ratio) stood at 0.75, AAC exhibited its highest degree of resistance against carbonation. Microscopic analysis revealed a progression in hydration product characteristics as the Ca/Si ratio increased. The transformation journey encompassed a shift from the initial structure to a needle-like tobermorite configuration and, subsequently, to a flaky structure. The study offers invaluable insights that furnish guidance for enhancing the durability of AAC and broaden the horizons of its potential applications. [ABSTRACT FROM AUTHOR]

The paper presents experimental research on the durability of a non-conventional technique for the repair of reinforced concrete damaged by carbonation-induced corrosion of steel reinforcement. The technique is called electrochemical re-alkalization and is often considered as an option for the repair of buildings, structures, and other artefacts made of reinforced concrete, for which conservation requirements are becoming increasingly important, in spite of their relatively young age. Absorption of a sodium carbonate solution is one of the processes that lead to concrete re-alkalization. The aim of the work is to investigate the contribution of this process to preventing future carbonation of re-alkalized concrete. Concrete specimens with six different compositions were initially carbonated, then re-alkalized through absorption of a sodium carbonate solution, and then exposed again to carbonation (re-carbonation). The results showed that the pH of concrete after re-carbonation was only slightly lower compared to that of re-alkalized concrete, highlighting a contribution of the treatment in preventing future pH reduction. [ABSTRACT FROM PUBLISHER]

Concrete strength evaluatedin situby means of the conventional SonReb method can be highly overestimated in presence of carbonation. This latter, in fact, is responsible for the physical and chemical alteration of the outer layer of concrete. As most of the existing concrete structures are subjected to carbonation, it is of high importance to overcome this problem. In this paper, an Improved SonReb method (I-SonReb) for carbonated concretes is proposed. It relies on the definition of a correction coefficient of the measured Rebound index as a function of the carbonated concrete cover thickness, an additional parameter to be measured duringin situtesting campaigns. The usefulness of the method has been validated showing the improvement in the accuracy of concrete strength estimation from two sets of NDT experimental data collected from investigations on real structures. [ABSTRACT FROM PUBLISHER]

Accelerated carbonation can promote the application of steel slag in construction materials. This method can not only resolve the fatal volume expansion of steel slag, but also sequestrate CO2. The carbonation thermodynamics, carbonation degree, carbonation methods and influencing factors of steel slag were reviewed. The theoretical CO2 uptake of steel slag is between 25% to 50%. However, the actual CO2 uptake distribution curve obeys normal distribution with a median value of 15%, which affected by carbonation methods, different influencing factors such as curing temperature, CO2 concentration and pressure, particle size of steel slag, liquid to solid ratio, and extraction agents. The improvement mechanism of accelerated carbonation on mechanical properties and stability of steel slag-based building materials was analyzed. Besides, different accelerated carbonated steel slag-based products with enhanced properties were summarized. Finally, some valuable suggestions concerning accelerated carbonation of steel slag were presented for further research and industrial application. [ABSTRACT FROM AUTHOR]

In atmospheric or chlorine environment, the rebar corrosion process can be initiated by concrete carbonation or chloride penetration, respectively. Along with the rebar corrosion, tensile stress will occur in concrete around rebars, and cracks will be formed when the stress reaches the tensile strength of concrete. This paper mainly studies the uniform and pitting rebar corrosion processes by lattice model at meso-scale. Firstly, the models of uniform and pitting rebar corrosions are developed. Secondly, an integrated procedure based on the lattice model is proposed to identify the crack pattern in the concrete. Published experimental results are adopted to validate the proposed models and method. Thirdly, some typical cases such as the corrosion process of a single rebar and multi-rebars, rebar corrosion process in the corner and pitting corrosion processes are simulated. Finally, the damage of the rebar corrosion to the concrete cover is studied. The results show that the rebar corrosion in the corner and the pitting corrosion can result in a severer damage to the concrete cover compared with the ordinary uniform rebar corrosion. Furthermore, the corrosion of multi-rebar can result in a larger scale of concrete cover spalling due to the firstly formed transverse crack. [ABSTRACT FROM PUBLISHER]

Based on generalized linear models and gamma degradation processes, two models predicting the natural carbonation of reinforced concrete (R.C) structures are proposed. They include the main factors influencing the carbonation process (material, environmental and curing factors) and their effects are evaluated from a large sample of natural carbonation depths measured experimentally worldwide. Then, predicted carbonation values are obtained using both the proposed models and the fib model for sheltered R.C structures exposed in the field. It is revealed that the proposed models have a rather high level of accuracy compared to the fib model and may be proposed as valuable alternatives. [ABSTRACT FROM AUTHOR]

In this study, it is aimed to investigate the influence of axial compressive stress on the carbonation resistance of recycled coarse aggregate concrete (RAC). The test variables are compressive stress ratios and carbonization ages. The compressive stress ratios of RAC are 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and the carbonization ages are 3, 7, 14, 28 days, respectively. The test results show that the carbonation depth of RAC decreases first and then increases with the increase of the compressive stress ratio, and the carbonation depth increases with the increase of the carbonization age. The prediction model of carbonation depth of RAC under axial compressive stress is established based on theoretical analysis and experimental results. [ABSTRACT FROM AUTHOR]

The present study focused on the characteristics of lime-based mortars with egg white addition prepared according to a historic Chinese recipe. Results suggested that under dry curing condition, the addition of egg white into mortars could decrease water absorption and increase surface hardness and compressive strength. Hardness and strength values of mortars cured under humid condition, however, were compromised by the egg white addition. Analyses results showed that under dry curing, egg white could inhibit carbonation and form amorphous calcium carbonate in the specimens, while under humid curing, egg white would impede hydration reactions and increase mortar pore size. [ABSTRACT FROM AUTHOR]

This study investigates the carbonation behaviour of alkali-activated fly ash-based (AFA) concretes. AFA contains 20.67% of unburned carbon. GBFS and OPC were used as sources of calcium (20%). A mixture of NaOH and Na2SiO3 was used as activator. OPC concrete was used as reference material. AFA/GBFS, AFA/OPC and OPC concretes, with and without reinforcing steel, were exposed to accelerated carbonation in a chamber under controlled conditions (25 °C, 65% RH, 1% CO2). In the non-reinforced concrete, the carbonation depth and compressive strength were evaluated up to 360 days. FTIR and SEM were used as complementary tests. Given that carbonation is one of the causes of corrosion in reinforcing steel, the electrochemical behaviour of steels embedded in alkali-activated concrete was evaluated using half-cell potential test, polarization curves and linear polarization resistance techniques. According to the obtained results, AFA/GBFS and AFA/OPC concretes are more susceptible to carbonation than OPC with compressive strength losses of up to 40%. Regarding the corrosion behaviour of the reinforcing steel, the AFA/GBFS concrete showed very negative potentials and high corrosion densities; however, at the end of the exposure period (20 months), the reinforcing steel showed no signs of deterioration, unlike the steel embedded in the OPC concrete. [ABSTRACT FROM AUTHOR]

Practical observations demonstrate that the corrosion deterioration of numerous reinforced concrete structures is due to the combination of carbonation and chloride ingress. However, the comprehensive combined model developed directly based on the coupling mechanism of them is very complicated. This article presents a simplified model to describe the transport of chloride ions with carbonation by introducing the Stefan condition, which is mainly used for the mathematical modelling of boundary movement caused by phase transformation in thermodynamics. Meanwhile, the influence function of carbonation on the diffusion coefficient of chloride ion is also re-discussed. An empirical formula is fitted directly according to the mix proportions of concrete, which can greatly reduce the computational cost. Then, an intuitively expressed formula of chloride concentration distribution under the influence of carbonation can be solved. Ultimately, its prediction accuracy is verified by two experiments. [ABSTRACT FROM AUTHOR]

The heterogenous mineralogy of ultramafic mine waste rocks make their carbonation rate hard to evaluate. This study investigated the effect of mineral composition on direct aqueous carbonation, through quantitative X-ray diffraction. The results show that magnesite was the main carbonated product, which was a stoichiometric conversion of forsterite. Diopside acted as a seed for quick crystallisation of magnesite. Lizardite could enhance the carbonation conversion, which reaches the optimum value when the weight ratio of lizardite to forsterite is 0.3–0.4. Sulphide in the reactant samples has a positive influence on carbonation. Brucite, magnetite and maghemite show little influence on carbonated products. [ABSTRACT FROM AUTHOR]

This research work aims at studying the influence of fermented organic additive on strength and carbonation of air lime mortar for the conservation of heritage structures. Binder to aggregate ratio of 1:3 by weight and water to binder ratio of 0.7 were considered. Red grape (Vitis vinifera) as an organic additive with 2, 4, 6, 8 and 10 percentages were accounted for fermentation of 0, 1, 2 and 3 days and were added with lime mortar. Experimental investigations were conducted on mechanical and mineralogical properties. 6% of organic addition with 3 days of fermentation resulted in a 49% increase in the mechanical resistance compared to the reference mortar on 90th-day test. XRD records an increased calcite formation due to accelerated carbonation. FTIR indicates the presence of polysaccharides that have helped in accelerating carbonation. TGA-DTA supports XRD and FTIR results in confirming the strength gain through the formation of calcium carbonate. Hence, the results are explicit, revealing that the fermented organic addition in air lime mortar has increased the carbonation rate, as the polysaccharides present in organic played a crucial role in accelerating the transformation of calcium hydroxide to forms of calcium carbonate and thereby enhancing the strength significantly. [ABSTRACT FROM AUTHOR]

Biochar is a promising material for environmental amendment. However, the adsorption mechanism of nitrogen-based ionic species, particularly the pH dependence, is still under debate because of its high susceptibility to experimental conditions. In this study, the adsorption of ammonium sulfate by rice-husk biochar produced by low-temperature carbonation as an eco-friendly approach was studied using Fourier-transform infrared (FT-IR) spectroscopy, 13C magic-angle spinning (MAS) nuclear magnetic resonance (NMR), and open-space analysis using positrons coupled with molecular simulations. In the aqueous solution with pH of 5.38, graphenes are isolated exposing fresh surfaces, which physisorb N H 4 + via interaction with π electrons rather than surface functional groups. Furthermore, the low-temperature carbonation leads to a lower degree of graphitization with grain boundary defects in graphene, triggering the fracture of graphene during the shaking process in an aqueous solution. S O 4 2 − physisorption occurs as an outer-sphere surface complex on the positive charge caused by a charge transfer of ∼2.5% from the terminal hydrogen at the graphene edge. A decrease in aqueous pH by ∼0.7% significantly changes the above adsorption properties both on the surfaces and at the edges: diminishment of physisorption and transition to chemisorption by the formation of an inner-sphere surface complex. [ABSTRACT FROM AUTHOR]

Accelerated carbonation curing (ACC) is one of the emerging techniques to sequester CO2 in concrete. The present study focuses on assessing the near surface properties of concrete subjected to ACC. Freshly cast concrete was subjected to ACC for a period of 6 hours after an initial preconditioning of 2 hours and was followed by water spray till 3 days. Thermogravimetric analysis (TGA) and X-Ray Diffraction (XRD) analysis revealed presence of CaCO3 and increased quantity of CSH gel in near surface of ACC concrete. The findings of XRD and TGA were also confirmed by Scanning Electron Microscopy which exhibited a densification of microstructure due to precipitation of CaCO3 in voids. Mechanical properties and permeation properties of both bulk concrete and near surface concrete were assessed and results were compared with traditional water curing. Compressive strength and abrasion resistance of concrete was found to increase by 30% at the age of 3 days in ACC concrete. Water absorption, sorptivity, chloride permeability and carbonation depth decreased in case of carbonation cured concrete, showing a reduction in permeability of concrete surface. The effect of ACC was more prominent on near surface properties than on bulk properties at later ages and the same were confirmed by performing analysis of variance. [ABSTRACT FROM AUTHOR]

Significant research efforts have been recently invested towards the evaluation of chloride-induced deterioration effects on the seismic vulnerability of aging highway bridges. Furthermore, when located in coastal cities with increased urbanisation or near shipyards, bridge structures may also be subjected to potentially high levels of carbon dioxide emissions. Consequently, the physicochemical process resulting from simultaneous ingress of chlorides and concrete carbonation may lead to accelerated corrosion deterioration of reinforced concrete components, as evidenced in past experimental tests. Nevertheless, little attention has been paid towards modelling this joint influence of chloride and carbonation-induced corrosion deterioration on strength degradation of bridge components. The present study proposes a numerical iterative scheme to evaluate the simultaneous impact of these deterioration mechanisms on the seismic response and bridge fragility. The proposed framework is demonstrated on a case-study multi-span continuous steel girder bridge in Central and Southeastern United States. Results reveal a considerable influence on the corrosion initiation time and seismic vulnerability under the concurrent carbonation and chloride ingress. Furthermore, this study also conducts a systematic exploration of uncertainty at different stages of the deterioration process. This exercise helps provide recommendations on balancing between computational complexity and accuracy of seismic fragility predictions. [ABSTRACT FROM AUTHOR]

The carbonation characteristics of marine biological attachment on concrete of offshore artificial islands were studied. The finite element analysis method is adopted to build a finite element analysis model for the carbonation characteristics of the marine organism attachment to the marine artificial island concrete under different temperature environments. By the analysis of the plastic displacement of the carbonation characteristics of the marine artificial island concrete caused by the lateral displacement before yielding and the marine organism attachment. The hysteretic curves of the carbonation characteristics of the marine organism adhesion to the concrete of the offshore artificial island at 0 degrees, 10 degrees, 20 degrees and 30 degrees and the degradation curves of the carbonation characteristics of the marine organism adhesion to the concrete of the offshore artificial island are compared respectively. The test results show that the marine organism adhesion at different temperatures shows different characteristics to the carbonation characteristics of the concrete of the offshore artificial island. The degradation curve of the carbonation characteristics of the marine artificial island concrete due to the attachment of marine organisms is stable, the curve will eventually stabilise at the corresponding degradation value in the descending process, indicating the stable point of performance. [ABSTRACT FROM AUTHOR]

Fly ash containing high alkaline metal oxides has been an attractive material for CO2 sequestration in a form of stable mineral carbonate. This study revealed the potential of Turkish fly ashes in terms of CO2 using a gas-solid carbonation process that was performed under different CO2 pressures at ambient temperature. Five fly ashes were collected from thermal power stations (Elbistan [EFA], Yatağan [YFA], Seyitömer [SEFA], Orhaneli [OFA], and Soma [SFA]). The ratio of FA:H2O was kept as 1:1, which promoted the carbonation reaction. The properties of fresh and carbonated fly ashes were determined using XRD, SEM, and TG analyses. TG analyses show that the CO2 storage capacity of fly ashes using the gas-solid carbonation under CO2 pressure of 3 bar for 2 h was found to be 1.14 g CO2/100 g-EFA, 2.63 g CO2/100 g-YFA, 0.17 g CO2/100 g-SEFA, 0.12 g CO2/100 g-OFA, and 7.28 g CO2/100 g- SFA, respectively. The amount of CO2 sequestrated in carbonated SFA increased within increasing CO2 pressure and carbonation time. Experimental findings reveal that 14.25 g CO2 was captured per 100 g-SFA in the form of cubic calcite crystals with a maximum carbonation efficiency of 43.41% under CO2 pressure of 5 bar for 15 h. However, there was no significant change determined in terms of the carbonation efficiency comparing with that of 6.5 h. This study shows a good alternative for the use of Turkish fly ash to capture CO2 as solid mineral carbonates under low CO2 pressure at ambient temperature. [ABSTRACT FROM AUTHOR]

An iron-rich siltation pond waste from a nickel mining site was used as the starting material for indirect carbonation. Iron-leaching experiments were conducted on the mining waste, using HCl as the leaching agent at varying HCl concentrations, reaction times, and reaction temperatures. It was found that the extraction efficiency of iron (EEI) increased when a more concentrated HCl solution was used and at higher temperatures. Based on the EEI trend over time, a layer of silica gel layer forms around the sample, hindering further iron extraction. A maximum EEI of 93.79% was observed. [ABSTRACT FROM AUTHOR]

Presented is a series of estimating methods for the parameters in a comprehensive combined model which is developed recently. The calculation of numerous intermediate-process parameters is optimised or combined to simplify the expression. The effect of carbonation on the change of apparent diffusion coefficient of chloride is expressed by three polynomial functions. Furthermore, a new simplified analytical method is proposed for the approximate study of this combined action. With the assumption of linear diffusion, the analytical results for the carbonation depth and concentration of free chloride ions can be obtained from a function of exposure time and mix proportions of concretes; the coupling effect is included by introducing an empirical factor. Several sets of experimental data are used for the verification of our equations. [ABSTRACT FROM AUTHOR]

Additivating mortars with crystallization modifiers is a novel approach to mitigate salt crystallization damage in historic masonry. Once verified the effectiveness of crystallization modifiers in bulk solution, the next step consists in verifying whether: (i) modifiers are still effective when mixed in mortar and going through the carbonation process and (ii) modifiers alter any mortar properties which might limit their application. This research addresses these issues for sodium ferrocyanide and borax, modifiers for sodium chloride, and sodium sulfate, respectively. Several experimental techniques have been applied to elucidate these questions. The results show that the selected modifiers are still able to alter the salt crystallization after going through the carbonation process of the mortar. Besides, no major effects of the modifiers on the fresh and hardened mortar properties were observed. It can therefore be concluded that there are no restraints for the future use of these crystallization modifiers in restoration mortars. [ABSTRACT FROM AUTHOR]

Assessment of the reinforced concrete shells of a sewer after two decades of service is presented. The methods used to investigate the sewer structure are described and the criteria for evaluating its safety are given. As part of the assessment and analysis laboratory tests of the concrete were carried on core samples taken from the shells. Concrete strength, carbonation, water permeability and leaching depth were checked. The degree of corrosion of the reinforcing steel and loss of reinforcement cover were also examined. The material tests’ results were then used in a numerical analysis of the stress in the shells that checked level of the structural safety. Based on the experimental and numerical results the approximate life cycle was estimated at another 55 years. [ABSTRACT FROM AUTHOR]

Steelmaking slag is a good alternative material for the fixation of CO2 gas as precipitated calcium carbonate (PCC) that are of used in many industrial applications such as paint, plastic, medical and so on. Therefore, the experimental conditions for production of PCC from steelmaking slag produced in Iskenderun Steelmaking Industry were determined via indirect carbonation process. At first, the influences of acid concentration, liquid-to-solid (L/S) ratio, particle size, reaction time and temperature on the dissolution of Ca from steelmaking slag were investigated, respectively. We determined that all parameters had strong effects on the dissolution of Ca from steelmaking slag except for the reaction time. Also, the effects of Na/CH3COO ratio, CO2 flow rate, reaction temperature and time on the precipitation of Ca ions as PCC particles were investigated. The properties of PCC were determined using chemical, SEM, XRD and particle size analyses. Furthermore, non-reacted CO2 left from the carbonation reactor was stored in the lab-scale gasometer tank for the re-use in that process. [ABSTRACT FROM AUTHOR]

As the main greenhouse gas, CO2is considered as a threat in the context of global warming. Many available technologies to reduce CO2emission was about CO2separation from coal combustion and geological sequestration. However, how to deal with the cost-effective storage of CO2has become a new challenge. Moreover, chromium pollution, the treatment of which requires huge energy consumption, has attracted people’s widespread attention. This study is aimed to develop the sequestration of CO2via chromium slag. A dynamic leaching experiment of chromium slag was designed to testify the ability of CO2adsorption onto chromium slag and to release Cr(VI) for stabilization. The results showed that the accumulative amounts of Cr(VI) were ca. 2.6 mg/g released from the chromium slag after 24 h of leaching. In addition, ca. 89 mg/g CO2was adsorbed by using pure CO2in the experiment at 12 h. Calcite is the only carbonate species in the post-carbonated slag analyzed by powder X-ray diffraction and thermal analysis. The approach provides the feasibility of the utilization of chromium slag and sequestration of the carbon dioxide at the same time at ordinary temperatures and pressures. [ABSTRACT FROM AUTHOR]