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The increase in energy valorization of paper sludge and biomass waste through incineration results in a rise in waste paper fly ash (WPFA), often perceived as hazardous and requiring specific treatment. In this study, natural carbonation technology at a pilot scale was employed to mitigate the hazardous nature of WPFA by enhancing the stabilization of metal and metalloid trace elements (MMTE), particularly barium (Ba) and lead (Pb) leaching. Natural carbonation of WPFA was found to be optimal at a water/solid ratio of 0.3 L/kg under natural temperature and humidity conditions. Batch leaching tests based on thermodynamic equilibrium were used to assess MMTE solubility concerning pH in both non-carbonated and carbonated WPFA at natural pH. After 7 days of natural carbonation, the leaching concentration of Ba and Pb was below the legal limit in France. The concentration of Ba and Pb in carbonated samples decreased by 98.5% and 98%, respectively. Analyses using thermogravimetry, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy demonstrated the increased formation and quantity of calcite (CaCO3) with longer carbonation times, along with the formation of new minerals as BaCO3 and PbCO3, confirming the immobilization of these elements post-carbonation. The leaching behavior and release potential of carbonated WPFA were further evaluated using the four-stage sequential extraction procedure proposed by the European Commission's Bureau of Reference (BCR). The speciation of Ba and Pb shifted significantly from the soluble substance (F1) at 17.6% and 14.8%, respectively, to the carbonate fraction (F2) at 0.49% and 0.02% after 90 days of carbonation. The percolation water collected during the carbonation process adheres to discharge standards into the sea. [ABSTRACT FROM AUTHOR]

Flexible calcium carbonate (FCC) was developed as a functional papermaking filler for high loaded paper, which was a fiber-like shaped calcium carbonate produced from the in situ carbonation process on the cellulose micro-or nanofibril surface. Chitin is the second most abundant renewable material after cellulose. In this study, a chitin microfibril was utilized as the fibril core for making the FCC. Cellulose fibrils for the preparation of FCC were obtained by fibrillation of the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) treated wood fibers. The chitin fibril was obtained from the β-chitin from the born of squid fibrillated in water by grinding. Both fibrils were mixed with calcium oxide and underwent a carbonation process by the addition of carbon dioxide, thus the calcium carbonate attached on the fibrils to make FCC. When used in papermaking, both the FCC from chitin and cellulose gave a much higher bulk and tensile strength simultaneously than the conventional papermaking filler of ground calcium carbonate, while maintaining the other essential properties of paper. The FCC from chitin caused an even higher bulk and higher tensile strength than those of the FCC from cellulose in paper materials. Furthermore, the simple preparation method of the chitin FCC in comparison with the cellulose FCC may enable a reduction in the use of wood fibers, process energy, and the production cost of paper materials. [ABSTRACT FROM AUTHOR]

The influence of two polysaccharides, native corn starch and carboxymethyl cellulose (CMC), on the precipitation of calcium carbonate was examined by utilizing two different carbonation processes. In a batch process, carbon dioxide gas was fed through calcium hydroxide slurry at pH 11.5 to 12.0. The reaction was complete when the pH had been decreased to 7. In a fed-batch reaction, the carbon dioxide was dissolved in water while calcium hydroxide was pumped into the water, maintaining a constant pH of 6.0±0.5. Scanning electron microscopy, particle size analysis, and specific surface area analysis were used to characterize the structure of the precipitated calcium carbonate (PCC) pigments. In application testing, the impact of modified pigments on paper properties was examined. The results showed that carbohydrates can significantly affect the crystallization of calcium carbonate, but the influence depends on the precipitation conditions and the type and concentration of the carbohydrate added. The starch-modified PCC, produced by the fed-batch reaction, improved the mechanical properties of the paper, whereas CMCmodified PCC yielded paper with good surface and optical performance but weakened strength properties. [ABSTRACT FROM AUTHOR]

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Normally, the acidic impurities in hemihydrate phosphogypsum (HPG) must be neutralized when HPG is utilized, and a little amount of calcium hydroxide (CH) is the best choice. In this paper, the effects of excessive CH (5 wt.%, 10 wt.%, 15 wt.% and 20 wt.% of HPG) for carbonation curing on the performance of hardened HPG paste were studied. According to the results of macro tests and microanalyses of XRD, TG, SEM-EDS, MIP and N2 physisorption, it could be verified that CaF2, Ca3(PO4)2 and a large amount of nanoscale CaCO3 crystals were produced as a result of neutralization and carbonation, and the compressive strength and the water resistance of carbonated HPG + CH paste were significantly improved due to the effects of nanoscale CaCO3 crystals on pore refinement and the coverage on the surfaces of gypsum crystals of the hardened paste. Therefore, this study suggests a feasible and green method for recycling HPG/PG, with the collaborative effects of neutralization, performance enhancement and reductions in CO2 emissions. [ABSTRACT FROM AUTHOR]

This paper discusses the possibility of assessing the k-value of power plant fly ash using durability. Compressive strengths, activity indices, pressure water seepage depth and carbonation depth were determined for cement mortars with 10, 20 and 30% cement replacement by fly ash for ages of 7, 28 and 60 days. The k-values for each cement substitute were determined for each age using the relationship between water/cement ratio and compressive strength. Using the results of the depth of pressurized water seepage and depth of carbonation, the determined k-values were assessed and k-values that are safe for use of power plant fly ash in aggressive XC and XD environments were determined. [ABSTRACT FROM AUTHOR]

The current building industry is essentially changing due to implementation of new approach, which is predominantly motivated by the need to reduce its negative environmental impact. The paper is focused on the experimental evaluation of carbonation resistance in terms of accelerated tests performed on the concrete on the basis of blended binding system incorporating milled limestone. The used commercially produced cement was additionally modified by the limestone powder. The obtained results confirmed, that currently used design standards are convenient to real carbonation process, however further clinker replacement by the milled limestone causes significant loss of the durability of the hardened concrete. [ABSTRACT FROM AUTHOR]

The recycling process of concrete originates a byproduct, cement paste powder (CPP), which is a material composed mainly of hydrated cement. This cementitious material has demonstrated promising results when applied as a binder in new concrete batches, provided it has been subjected to a previous carbonation process. One of the obstacles to the industrial application of this strategy is the long duration of the typical carbonation process, which requires from 3 to 28 days. Recently, the authors have developed a short two-hour carbonation process and thoroughly analysed it over its entire extension. In this paper, a parametric analysis of the carbonation process is performed towards CO2 uptake maximization, aiming to increase the feasibility of its short duration. CO2 uptake is evaluated using the ignition by furnace method and thermogravimetric analysis. Among the parameters considered, the initial water content and the CPP thickness present the highest impact on CO2 uptake. The investigation of different CO2 concentrations inside the carbonation chamber showed that the maximum CO2 uptake does not occur for the highest concentration value. Moreover, a minimum resident time for the forced carbonation of CPP in industrial contexts is presented, and is found to be highly dependent on the CO2 concentration. The particle size and purity degree of CPP revealed a limited influence on the CO2 uptake achieved. Additionally, this paper provides further insight into the mechanisms involved in the carbonation of mature cement paste while increasing the feasibility of our recently proposed short duration carbonation process. [ABSTRACT FROM AUTHOR]

The heterogenous mineralogy of ultramafic deposits hosting mining operations makes it challenging to accurately determine the waste rock's mineral carbonation potential (MCP). Additionally, the significantly higher carbonation capabilities of olivine than serpentine add to the difficulty. To address this issue, in this work, a new and unique tool called the MCP calculator was developed as a Microsoft ExcelTM spreadsheet to accurately determine the amount of anthropogenic CO2 that a given rock mass can sequester through mineral carbonation. The program estimates the modal mineral abundance of ultramafic rocks to aid in MCP estimation. This tool is designed to be cost-effective and tailored for use by the mining industry, utilising abundant lithogeochemical data to evaluate their deposit as a potential substrate for industrial mineral carbonation operations. The paper introduces the MCP calculator, outlines a framework for developing the MCP parameter, and presents an example of its application. The calculator is specific to the mineral assemblage investigated at the Turnagain ultramafic complex in northern British Columbia but can be adjusted to study comparable deposits. The paper acknowledges that using waste rock in a mineral carbonation operation requires economic and practical decisions beyond the scope of the research. [ABSTRACT FROM AUTHOR]

Mineral carbonation is a technology for capturing and storing CO2 in solid minerals. When mineral carbonation is used to produce construction materials, the quantification of the CO2 uptake of these products is of the utmost importance, as it is used to calculate the CO2 footprint of the product and/or carbon offset. The CO2 uptake is generally determined by measuring the CO2 content of a material before and after accelerated carbonation. This approach, however, does not take hydration and dehydroxylation reactions into account that may occur during carbonation, and it can therefore under- or overestimate the CO2 uptake. Thus, a more accurate and practical method to determine CO2 uptake, which also accounts for hydration and dehydroxylation reactions, is proposed in this paper. This method is based on analytical methods to determine the dry mass and the CO2 content of the solid products before and after carbonation, and on the calculation of the CO2 uptake by the following equation: CO2 uptake (wt.%) = CO2 carbonated (wt.%) × (weight after carbonation (g)/weight before carbonation (g) − CO2 initial (wt.%), with CO2 carbonated being the CO2 content in g/100 g dried carbonated material, and CO2 initial being the CO2 content in g/100 g dried initial material, i.e., before carbonation. The "weight before carbonation" is the dry weight of the initial material, and the "weight after carbonation" is the product's dry weight after carbonation. In this paper, we show that up to 44% under- or overestimation of CO2 uptake can occur when hydration and dehydroxylation reactions are not taken into account during mineral carbonation. [ABSTRACT FROM AUTHOR]

The wet carbonation process of steel slag (SS) is envisaged to be an effective way to sequestrate CO2 and improve the properties of SS as a supplementary cementitious material. However, the carbonation process still struggles with having a low carbonation efficiency. This paper studied the effect of glycine on the accelerated carbonation of SS. The phase composition change of carbonated SS was analyzed via XRD, FT-IR, and TG–DTG. The carbonation process of SS is facilitated by the assistance of glycine, with which the carbonation degree is increased. After 60 min of carbonation, SS with glycine obtained a CO2 sequestration rate of 9.42%. Meanwhile, the carbonation reaction could decrease the content of free calcium oxide in SS. This significantly improves the soundness of SS–cement cementitious material, and the compressive strength of cementitious materials that contain carbonated SS with glycine is improved. Additionally, the cycling performance of glycine in the successive wet carbonation process of SS was investigated. Multicycle experiments via solvent recovery demonstrated that although the promotion effect of glycine was reduced after each cycle, compared with the SS–water system, the carbonation process could still be facilitated, demonstrating that successive wet carbonation via solvent recovery has considerable potential. Herein, we provide a new idea to facilitate the wet carbonation process of SS and improve the properties of SS–cement cementitious material. [ABSTRACT FROM AUTHOR]

The Intergovernmental Panel on Climate Change (IPCC), which is the United Nations body for assessing the science related to climate change, has recently recognized the natural carbonation process as a way of carbon offsetting with mortar and concrete. Accordingly, this activity could be recognized as a carbon removal process for which certification should be granted. The aim of the certification of carbon removal is to promote the development of adequate and efficient new carbon removal processes. Therefore, the main objective of this study is to provide reliable results on carbon dioxide uptake by cement-based materials in Spain. Yearly, greenhouse gas emissions are reported to the United Nations Framework Convention on Climate Change (UNFCCC) by each country, and the natural carbonation should be added up to the carbon accounting. Therefore, natural carbonation should be included in the IPCC Guidelines for National Greenhouse Gas Inventories, and such accounting information should be made available promptly to the national regulatory authorities. This paper provides the results of carbon dioxide uptake by Spanish cement-based materials from 1990 to 2020 by using an easy method of estimating the net carbon dioxide emissions (simplified method) considering the carbon dioxide released by the calcination during clinker production (process emissions). The outcome of this study reveals that there was 93,556,000 tons of carbon dioxide uptake by the mortar and concrete manufactured in Spain from 1990 to 2020. [ABSTRACT FROM AUTHOR]

The carbonation of concrete greatly affects its service life. In this paper, fiber Bragg grating (FBG) sensors were used to investigate the relationship between concrete carbonation and its mechanical properties. A T130 High Sensitivity Strain Cable Sensor with a good linearity was used to monitor the internal strain in concrete, to investigate the variation in the elastic modulus of concrete with carbonation time. A mathematical model of elastic modulus and carbonation time of concrete based on FBG was established. At the same time, the authors explored the relationship between the carbonation depth and compressive strength of concrete and the carbonation time using a phenolphthalein solution test and a compressive strength test, respectively. The experimental results indicate that the carbonation depth, compressive strength, and elastic modulus of concrete increase with carbonation time. In the early stage of carbonation, these three parameters increase rapidly, while they grow slowly in the later stage of carbonation. The varying trend of the elastic modulus of concrete is consistent with the compressive strength, which shows a binomial relationship. Therefore, the elastic modulus, measured using FBG sensors, is used as an indicator of the characterization of the carbonation resistance of concrete. This work provides a new approach for concrete carbonation detection and assessment. [ABSTRACT FROM AUTHOR]

The utilization of recycled aggregates (RA) for concrete production has the potential to offer substantial environmental and economic advantages. However, RA concrete is plagued with considerable durability concerns, particularly carbonation. To advance the application of RA concrete, the establishment of a reliable model for predicting the carbonation is needed. On the one hand, concrete carbonation is a long and slow process and thus consumes a lot of time and energy to monitor. On the other hand, carbonation is influenced by many factors and is hard to predict. Regarding this, this paper proposes the use of machine learning techniques to establish accurate prediction models for the carbonation depth (CD) of RA concrete. Three types of regression techniques and meta-heuristic algorithms were employed to provide more alternative predictive tools. It was found that the best prediction performance was obtained from extreme gradient boosting-multi-universe optimizer (XGB-MVO) with R2 value of 0.9949 and 0.9398 for training and testing sets, respectively. XGB-MVO was used for evaluating physical laws of carbonation and it was found that the developed XGB-MVO model could provide reasonable predictions when new data were investigated. It also showed better generalization capabilities when compared with different models in the literature. Overall, this paper emphasizes the need for sustainable solutions in the construction industry to reduce its environmental impact and contribute to sustainable and low-carbon economies. [ABSTRACT FROM AUTHOR]

This paper presents a literature review on the effects of accelerated carbonation on alkali-activated materials. It attempts to provide a greater understanding of the influence of CO2 curing on the chemical and physical properties of various types of alkali-activated binders used in pastes, mortars, and concrete. Several aspects related to changes in chemistry and mineralogy have been carefully identified and discussed, including depth of CO2 interaction, sequestration, reactions with calcium-based phases (e.g., calcium hydroxide and calcium silicate hydrates and calcium aluminosilicate hydrates), as well as other aspects related to the chemical composition of alkali-activated materials. Emphasis has also been given to physical alterations such as volumetric changes, density, porosity, and other microstructural properties caused by induced carbonation. Moreover, this paper reviews the influence of the accelerated carbonation curing method on the strength development of alkali-activated materials, which has been awarded little attention considering its potential. This curing technique was found to contribute to the strength development mainly through decalcification of the Ca phases existing in the alkali-activated precursor, leading to the formation of CaCO3, which leads to microstructural densification. Interestingly, this curing method seems to have much to offer in terms of mechanical performance, making it an attractive curing solution that can compensate for the loss in performance caused by less efficient alkali-activated binders replacing Portland cement. Optimising the application of such CO2-based curing methods for each of the potential alkali-activated binders is recommended for future studies for maximum microstructural improvement, and thus mechanical enhancement, to make some of the "low-performing binders" adequate Portland cement substitutes. [ABSTRACT FROM AUTHOR]

The construction industry is essential to the development and economy, but is also the largest generator of construction and demolition waste (CDW). While efforts are made to minimize such generation, the construction industry has been developing applications for it in the form of aggregates to replace the commonly used natural aggregates. However, in structural applications, it is necessary to ensure that the properties of concrete produced with CDW, as recycled aggregates (CDW-concrete), guarantee adequate performance and do not put the structure at risk. For this, one of the alternatives is improving the properties of CDW aggregates through carbonation, a process called carbonate curing or accelerated carbonation. In this sense, this paper aims to investigate the carbonation of CDW aggregates, clarifying how this process occurs, the existing carbonation methods, the main properties that affect this process, and their influence on the properties of recycled aggregates and the CDW-concrete. To this end, the SREE (systematic review for engineering and experiments) method was used to search and analyze scientific manuscripts published without a time limit. The results revealed that the most widely used method for carbonate curing is recommended by Chinese standard GB50082, and highlighted the need for further research to investigate the CDW-concrete, focusing on its eco-friendly potential to capture CO2 from the atmosphere. [ABSTRACT FROM AUTHOR]

This paper is the second output of a project that examines the embodied greenhouse gas emissions ('embodied carbon') from the use of concrete in buildings. In the current absence of either regulation or widespread industry practice in quantified carbon assessment, it seems likely that messaging will play a powerful role in influencing designers' perceptions and decisions. Using the UK as a case study, this paper considers the current messages about the carbon implications of concrete in buildings from professional institutions and the cement and concrete trade body. Three mechanisms through which it is claimed carbon emissions are significantly reduced are identified: thermal mass, durability, and carbonation. By assessing each of these in turn against the available scientific literature, it is shown that they are likely to have a far more limited effect on the total impacts than suggested. More accuracy is needed from trade organisations if real carbon reductions are to be achieved. [ABSTRACT FROM AUTHOR]

This paper presents comprehensive research of the advantages and applicability of various concrete carbonation detection methods. Employing a combination of Phenolphthalein indicator (PI), Thermogravimetric analysis (TGA), X-ray phase analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and Quantitative calcium carbonate analysis (CA), a detailed comparison to determine the carbonation depth in the partial carbonation zone of concrete specimens is conducted. Among the quantitative analysis methods, CA measures CaCO3 content based on chemical reactions, while TGA obtains the concentration distribution of Ca(OH)2 and CaCO3. Among qualitative analysis methods, XRD tested the intensity distribution of Ca(OH)2 and CaCO3, while FTIR traced the characteristic peaks of C-O functional groups in a specific spectral range to determine the depth of carbonation of concrete. Results indicate that the depth of carbonation values measured by CA, TGA, XRDA, and FTIR are 2–3 times higher than those measured by PI. This research may provide valuable insights for the design of carbonation detection in concrete. [ABSTRACT FROM AUTHOR]

Magnesium silicate hydrate (MSH) cement has the advantages of low energy consumption, minimal environmental pollution, carbon negativity, and reduced alkalinity, but excessive drying shrinkage inhibits its application. This paper analyzed the influence of steel slag (SS) dosage, carbon dioxide partial pressure, and carbonation curing time on the compressive strength, shrinkage rate, and phase composition of MSH cement. Various analysis methods, including X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP), were used to study the hydration products and microstructure. The results showed that under normal curing conditions, MSH cement mixed with different steel slag contents experienced a decline in strength at all ages. However, the greater the amount of SS incorporated, the lesser the degree of drying shrinkage. The compressive strength of all groups was improved, and the drying shrinkage was reduced by carbonation treatment. The samples with 5%, 10%, and 15% SS content exhibited shrinkage rates of 2.19%, 1.74%, and 1.60%, respectively, after 28 days of curing. The reason was that after carbonation treatment, hydrated magnesium carbonates (HMCs) were generated in the SS–MSH cement, and a Ca–Mg–C amorphous substance formed by hydration and carbonation of C2S in steel slag filled in the pores, which enhanced the density of the matrix, improved the compressive strength of the specimen, and reduced the shrinkage rate. [ABSTRACT FROM AUTHOR]

In practice, assessing the mechanical behavior of seawater sea sand concrete under severe environmental conditions is urgently needed to evaluate the service life of the prepared concrete. In this paper, the influence of carbonation on the mechanical properties, especially the stress–strain relationship of seawater and sea sand concrete (SSC), sea sand concrete (SC), and ordinary concrete (OC), were investigated by experimental and theoretical means. The microstructural analysis revealed that SSC and SC have higher CO2 sequestration than OC. Although the compressive strength of all concrete specimens increased during the carbonation time, the net increase of compressive strength (excluding cement hydration) contributed by the carbonation of SSC and SC was less than that of OC. The stress–strain curves' ascending branches of the three types were roughly similar; for the descending branch, the slope of SSC and SC became steeper compared with OC after carbonation. The results also revealed that the brittleness of SSC and SC increased orderly with the extension of carbonation time. Finally, an empirical expression for the stress–strain relationship of SSC and SC considering the effect of carbonation was proposed, which provides an analytical base for concrete structure design and practical application for marine infrastructures. [ABSTRACT FROM AUTHOR]

Basic oxygen furnace (BOF) slag is an industrial waste produced from steel-making. It can be utilized as building material, but its high content of free CaO (f-CaO) causes volume expansion of materials and limits its utilization. However, carbonation of BOF slag can decrease the f-CaO content, improve stability, and reduce carbon emissions. This study investigated the influence of temperature, pressure, liquid to solid, reaction time, and stirring pattern on f-CaO consumption and CO2 sequestration, which reached a maximum f-CaO consumption and CO2 sequestration of 99.58% and 5.12% (51.2 g CO2/Kg BOF slag), respectively, under optimum conditions. According to the results of the XRD patterns of carbonated slag, no peaks of CaO were detected, the peaks of Ca2Fe2O5 and Ca2SiO4 were slightly reduced, and new peaks of CaCO3 were detected. The reaction process has been described by a shrinking core model revealing that the diffusion of reactants through the product layer was the rate-limiting step for carbonation. The kinetic equation for CO2 sequestration was derived as: InK = − 2132.83·T−1–9.1543. This approach presents a green, cost-effective, and rapid method for enhancing steel slag utilization while capturing and storing CO2. The method proposed in this paper holds significant potential for wider adoption. [ABSTRACT FROM AUTHOR]

Applications related to alkali-activated materials (AAMs) have received much attention due to their excellent mechanical properties and low-energy production. Although much research has focused on developing AAMs, their application is still limited. One of the primary reasons is the efflorescence. Not only does efflorescence affect the material aesthetics, but it also affects the mechanical performance, leading to a decrease in material quality. This paper first summarizes the current research on AAMs efflorescence. The formation process of efflorescence is divided into three parts: alkaline cation leaching, air carbonation, and efflorescence formation. Furthermore, the influences caused by different factors, including raw materials, curing conditions, AAMs modalities, etc., on the efflorescence are proposed. This paper highlights the solutions for efflorescence by avoiding free alkaline cation leaching and preventing air carbonation. The advantages and disadvantages of efflorescence are discussed in-depth, showing that it can be exploited under certain conditions, such as in wastewater treatment. This paper has important implications for the practical preparation and application of AAMs. [ABSTRACT FROM AUTHOR]

Steel slag is a solid waste product generated during the carbonation stage of steelmaking. It has high levels of heavy metals and substantial amounts of free calcium and magnesium oxide, making it unsuitable for use as a cement material. Furthermore, the disposal of steel slag in landfills requires many resources and can seriously contaminate the surrounding environment. One method of reducing its negative environmental impact is carbonation, which involves reacting steel slag with carbon dioxide to form stable minerals. However, many parameters influence the carbonation efficiency of steelmaking slag, including temperature, time, particle size, pressure, CO2 concentration, liquid-to-solid ratio, moisture content, humidity, additives, etc. To this end, this paper comprehensively reviews the most important steel slag carbonation-influencing factors. Moreover, it compares the characteristics from two perspectives based on their causes and effects on carbonation. Finally, this article reviews earlier studies to identify the factors that affect steel slag carbonation and the potential of carbonated steel slag as a sustainable construction material. Based on previous research, it systematically examines all the elements for future work that need to be improved. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete (RAC) includes recycled concrete aggregates (coarse and/or fine) as substitutes for natural aggregates as an approach to achieving a circular economy. Some concerns remain about its performance, including the carbonation resistance. The higher porosity of recycled concrete aggregates is logically a disadvantage, but the analysis must address many other factors. This paper provides an in-depth examination of recent advances in the carbonation performance of RAC. The emphasis is on factors that influence CO2 diffusion and the carbonation rate, e.g., the replacement ratio, source concrete quality, interfacial transition zone features, residual portlandite content, and porosity. The influences of previous treatments, combined action with supplementary cementitious materials, and loading conditions are also discussed. The replacement ratio has a significant impact on the carbonation performance of concrete, but it is also dependent on other factors. During carbonation, the physical effects of the porosity of the aggregate and the physical–chemical effects of the portlandite content in the adhered mortar are particularly important. The residual portlandite is especially significant because it is the primary hydration product responsible for the alkaline reserve for carbonation and the potential pozzolanic reaction, which are per se competing factors that determine the carbonation rate. [ABSTRACT FROM AUTHOR]

Ca-looping is an effective way to capture CO2 from coal-fired power plants. However, there are still issues that require further study. One of these issues is the effect of steam on the Ca-looping process. In this paper, a self-madethermogravimetric analyzer that can achieve rapid heating and cooling is used to measure the change of sample weight under constant temperature conditions. The parameters of the Ca-looping are studied in detail, including the addition of water vapor alone in the calcination or carbonation stage and the calcination/carbonation reaction temperatures for both calcination and carbonation stages with water vapor. Steam has a positive overall effect on CO2 capture in the Ca-looping process. When steam is present in both calcination and carbonation processes, it increases the decomposition rate of CaCO3 and enhances the subsequent carbonation conversion of CaO. However, when steam was present only in the calcination process, there was lower CaO carbonation conversion in the following carbonation process. In contrast, when steam was present in the carbonation stage, CO2 capture was improved. Sample characterizations after the reaction showed that although water vapor had a negative effect on the pore structure, adding water vapor increased the diffusion coefficient of CO2 and the carbonation conversion rate of CaO. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) has been commonly used as a construction material for decades due to its high compressive strength and moderate tensile strength. However, these two properties of RC are frequently hampered by degradation. The main degradation processes in RC structures are carbonation and the corrosion of rebars. The scientific community is divided regarding the process by which carbonation causes structural damage. Some researchers suggest that carbonation weakens a structure and makes it prone to rebar corrosion, while others suggest that carbonation does not damage structures enough to cause rebar corrosion. This paper is a review of the research work carried out by different researchers on the carbonation and corrosion of RC structures. The process of carbonation and the factors that contribute to this process will be discussed, alongside recommendations for improving structures to decrease the carbonation process. The corrosion of rebars, damage to passive layers, volume expansion due to steel oxidation, and crack growth will also be discussed. Available protection methods for reducing carbonation, such as rebar structure coating, cathodic protection, and modifier implementation, will also be reviewed. The paper concludes by describing the most significant types of damage caused by carbonation, testing protocols, and mitigation against corrosion damage. [ABSTRACT FROM AUTHOR]

Concrete carbonation is known as a stochastic process. Its uncertainties mainly result from parameters that are not considered in prediction models. Parameter selection, therefore, is important. In this paper, based on 8204 sets of data, statistical methods and machine learning techniques were applied to choose appropriate influence factors in terms of three aspects: (1) the correlation between factors and concrete carbonation; (2) factors' influence on the uncertainties of carbonation depth; and (3) the correlation between factors. Both single parameters and parameter groups were evaluated quantitatively. The results showed that compressive strength had the highest correlation with carbonation depth and that using the aggregate–cement ratio as the parameter significantly reduced the dispersion of carbonation depth to a low level. Machine learning models manifested that selected parameter groups had a large potential in improving the performance of models with fewer parameters. This paper also developed machine learning carbonation models and simplified them to propose a practical model. The results showed that this concise model had a high accuracy on both accelerated and natural carbonation test datasets. For natural carbonation datasets, the mean absolute error of the practical model was 1.56 mm. [ABSTRACT FROM AUTHOR]

In order to quantitatively analyze the factors affecting the carbonation of reinforced concrete structures, the carbonation coefficient model is established based on 1834 groups of test data from natural carbonation and indoor accelerated tests in this paper. The main factors considered in the statistical model are the environmental temperature, the concentration of carbon dioxide, relative humidity, water–cement ratio, fly ash replacement, compressive strength of 28 days, curing time, compaction type, exposure to a salt environment, and environmental exposure classes. Based on the multiple nonlinear regression method, the carbonation coefficient model is fitted in two sections according to the different environmental exposures of the concrete structure. To analyze the applicability of the formula, the statistical formulas of relative humidity less than 70% and relative humidity higher than 70% are verified by the test data, and satisfactory results are obtained. Based on the quantitative analysis of the statistical model, the specific effects of relative humidity, strength, carbon dioxide content, fly ash, and curing time on concrete carbonation are clarified. The results show that the factors affecting carbonation are also different with different humidity values in the exposed environment of the concrete structure. When the relative humidity of the exposed environment is less than 70%, the parameters that have a great impact on concrete carbonation are fly ash replacement, compressive strength of 28 days, relative humidity, and the concentration of carbon dioxide. Among them, fly ash replacement, relative humidity, and the concentration of carbon dioxide can promote the carbonation of concrete. When the relative humidity of the exposed environment is higher than 70%, the parameters that have a great impact on concrete carbonation are the concentration of carbon dioxide, relative humidity, compressive strength of 28 days, curing time, and exposure classes. Only the concentration of carbon dioxide is conducive to the carbonation of concrete, and relative humidity has a very significant effect on concrete carbonation. [ABSTRACT FROM AUTHOR]

Carbonation curing on steel slag is one of the most promising technologies for the iron and steel industry to manage its solid waste and carbon emissions. However, the technology is still in its demonstration stage. This paper investigates the market stakeholders of carbonation curing on steel slag for construction materials for its effective application by taking China as a case study. A holistic analysis of the competition, market size, and stakeholders of carbonation curing on steel slag was carried out through a literature review, a survey, a questionnaire, and interviews. The results showed that carbonation curing on steel slag had the advantages of high quality, high efficiency, low cost, and carbon reduction compared with other technologies. Shandong province was the most suitable province for the large-scale primary application of the technology. Stakeholder involvement to establish information platforms, enhance economic incentives, and promote adequate R&D activities would promote carbonation curing of steel slag into practice. This paper provides a reference for the commercialization of carbonation curing on similar calcium- and magnesium-based solid waste materials. [ABSTRACT FROM AUTHOR]

The durability of concrete structures, which are designed for long- -term use is predominantly determined by the resistance to chemical influences, i.e., the concrete's ability to protect the reinforcement steel. The carbonation and the chloride ingress into concrete are the most significant causes of steel corrosion and the potential failure of the structure. The primary goal is to ensure that any significant damage does not occur during the structure's service life, primarily achieved by selecting an adequate thickness of the concrete cover. The issue is approached through calculations based on performance analyses, and the use of appropriate models for these chemical phenomena. The paper provides a brief overview and the methodology for analysing the impact on the durability of concrete structures in accordance with the leading international normative documents. The emphasis is on the recent changes introduced in second generation of European Eurocode standards. The consequences of the analysed phenomena are presented through the results of field tests conducted at salt factories, coke industries, and thermal power plants, and through laboratory tests. The tests were performed in order to develop a rapid prediction method for the measure of chloride ingress into concrete without the stimulating chloride ion migration by electricity, as an alternative to standardized tests. [ABSTRACT FROM AUTHOR]

Steel fiber reinforced geopolymer concrete (SFRGC) shows excellent mechanical properties comparable to steel fiber reinforced concrete. However, research on the durability of SFRGC is scarce. This paper presents the carbonation performances of SFRGC, including the carbonation depth and strength variation during carbonation. The results show that the permeability and carbonation depth of SFRGC are close to those of plain geopolymer concrete (GC). Their carbonation depths are much deeper than those of cement concrete because of the lower alkali content of the geopolymer matrix. Carbonation hardly influences the final flexural strength of plain GC, but the flexural strength of SFRGC declines significantly during carbonation because of the decrease in steel fiber-geopolymer matrix bond strength. The scanning electron microscope results show that the failure mode in uncarbonated SFRGC specimens is fiber rupture, while in carbonated SFRGC specimens, fiber pullout is the failure mode. These findings suggest that using SFRGC in the atmosphere is not recommended. [ABSTRACT FROM AUTHOR]

The carbonation action in concrete, in which carbonation reactions transform calcium hydroxide into calcium carbonate, is considered as a multi-phase physico-chemical process. Generally, carbonation in the cementitious composites has negative effects on the protection of reinforced bars due to the accelerated corrosion problem. The investigation of the carbonation degree is, therefore, necessary to evaluate the carbonation influence on the reinforced cementitious composites. In the present paper, experimental techniques to measure the carbonation degree in concrete are reviewed, including both qualitative and quantitative methods. It should be noted that, while qualitative technique focuses on the alterations in the concrete pore solution alkalinity which reflects the carbonation depth through the pH indicator, most quantitative methods could provide accurate determination of the CO2 penetration capacity during the carbonation process. The method used, for the practical phase, depends on the purpose of the carbonation degree measurement. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the effect of internal and external humidity differences on the distribution characteristics of the carbonated zone of cement-based materials. Carbonation tests with ambient humidity and pore water saturation as the influencing factors were implemented. The calcite content of the mortar along the depth of carbonation was presented. The rationality of the carbonation model was verified by the calcite test results, and the effect of internal and external humidity differences on the carbonation zone distribution of cement-based materials was analyzed by the model. The results showed that the test results of calcium carbonate and the simulation results can clearly distinguish the completely and partly carbonated zones of cement-based materials. The effect of pore water saturation on the distribution of the carbonated area was conspicuous, but the difference in pore water saturation cannot change the variation of the extent of the carbonated zone with ambient humidity. The change regularities of fully and partly carbonated zones with humidity differences were obtained. [ABSTRACT FROM AUTHOR]

Application of high volume fly ash concrete is still not advocated by construction fraternity due to lack of standardisation. In India, fly ash as a pozzolanic material can be used in manufacturing of Portland Pozzolana cement and composite cement with a maximum limit of 35%. Present study had been carried out at various percentages of fly ash and a detailed mechanical and durability study was conducted. In this paper, concrete mixes were designed at two water binder ratio with 30%, 35%, 40% and 50% fly ash content. Mechanical behaviour of concrete was studied through tests like compressive strength (at age of 1, 3, 7, 28, 56 and 90 days) and flexure strength (at an age of 7, 28 and 90 days). Durability aspect of high volume fly ash concrete mixes were determined through various test like RCPT, non-steady state chloride migration, bulk conductivity, accelerated carbonation etc. and comparison is made with control mixes (i.e. concrete made with OPC). Alkali silica reactivity (ASR) study was also carried out at 30%, 35%, 40% and 50% fly ash content using reactive aggregates. It was quite evident from test results that strength characteristics of high volume flyash concrete mix made with 50% flyash content was remarkably lower than that of all other concrete mixtures. High volume flyash concrete mix designed at 40% flyash content had shown exemplarily performance in comparison to other high volume flyash concrete mixes as well as control mixes. Flyash content was found to most significant parameter influencing rate of carbonation. [ABSTRACT FROM AUTHOR]

With steadily rising CO2 concentrations in the ambient air and fast-changing concrete compositions with reduced clinker contents, the availability of reliable and accelerated concrete carbonation tests is of crucial importance to design durable structures. This paper focuses on the effects of moisture under accelerated conditions and the effects of different CO2 exposure conditions. Mortar prisms incorporating three different cement types were cured and stored at either 50% or 65% relative humidity (RH). Afterwards, the prisms were carbonated at different ambient humidities (50, 57 and 65%), different CO2 concentrations (0.04, 1 and 3 vol.%) and complemented by a series of tests at increased gas pressure (2 barg). High-resolution test methods were used to explain the underlying carbonation mechanisms. The results show that pre-conditioning for two weeks—as currently suggested by the European Standard—seems to be too short because the initial inner moisture content severely affects the carbonation rate. Relative humidity during carbonation of 57% led to higher carbonation rates compared to 50% and 65%. In addition, climate data needs to be periodically (preferably permanently) recorded in research experiments and in laboratory testing to ensure fair interpretation of experimental results. [ABSTRACT FROM AUTHOR]

The use of tricyclic copolymer latex (AMPS) can effectively improve the carbonation resistance of sulphoaluminate cement. This paper investigated polymer AMPS and polycarboxylic acid to modify sulphoaluminate cement materials by exploring the carbonation level of sulphoaluminate cement paste and mortar and the strength before and after carbonation. Then, the optimal dosage of polymer and polycarboxylic acid was obtained so that the carbonation resistance of sulphoaluminate cement reached the best state. The compressive strength was significantly improved by adding AMPS for sulphoaluminate cement paste and mortar. After carbonation, the strength decreased and combined with the carbonation level; it was concluded that the carbonation resistance of sulphoaluminate cement materials was the best when the optimal dosage of AMPS and polycarboxylic acid was 5% and 1.8%, respectively. Due to the addition of AMPS, the hydrated calcium aluminosilicate (C-A-S-H) and hydrated calcium silicate (C-S-H) gels, generated by the hydration of sulphoaluminate cement and the surface of unreacted cement particles, are wrapped by AMPS particles. The water is discharged through cement hydration. The polymer particles on the surface of the hydration product merge into a continuous film, which binds the cement hydration product together to form an overall network structure, penetrating the entire cement hydration phase and forming a polymer cement mortar with excellent structural sealing performance. To prevent the entry of CO2 and achieve the effect of anti-carbonation, adding polycarboxylic acid mainly improves the sample's internal density to achieve the anti-carbonation purpose. [ABSTRACT FROM AUTHOR]

Pore structure and composition of cement paste are the main two factors in controlling the sulfate attack on concrete, but the influence of carbonization on pore structure and composition is often ignored in sulfate attack. Therefore, will the damage performance of concrete partially exposed to sulfate solution be different avoiding the alterations of pore structure and composition due to carbonation? In this paper, the cement pastes were partially immersed in 5 wt. % sodium sulfate solution, with N2 as protective gas to avoid carbonation (20 ± 1°C, RH 65 ± 5%). Pore structures of cements were changed by introducing different contents of limestone powders (0 wt. %, 10 wt. %, 20 wt. %, and 30 wt. %) into cement pastes. The damage performance of the specimens was studied by 1H NMR, XRD and SEM. The results showed that the immersion zone of pure cement paste under N2 atmosphere remained intact while serious damage occurred in the evaporation zone. However, the damage of cement + limestone powders pastes appeared in the immersion zone rather than in the evaporation zone and cement pastes containing more limestone were more severely damaged. Compositional analysis suggested that the damage of the evaporation zone or the immersion zone was solely caused by chemical attack where substantial amount of gypsums and ettringites were filled in the pore volumes. Introduction of limestone powders led to the increase of the pore sizes and porosity of cement pastes, causing the damage occurred in the immersion zone not in the evaporation zone. [ABSTRACT FROM AUTHOR]

Reinforcement corrosion is the risk most frequently cited to justify concrete durability research, especially where it is induced by chlorides. Surface-applied corrosion inhibitors are widely used to mitigate the corrosion process both for carbonation and chlorides of steel reinforcement in concrete. They are applied onto the surface of hardened concrete and penetrate towards steel reinforcement. This paper discusses the corrosion inhibition performance of a new generation of a dual-phase surface-applied corrosion inhibitor (DP-SACI), and its efficiency in corrosion induced by chlorides over 3% referred to cement mass, and also in pre- and post-cracked structures. This corrosion mitigation activity was evaluated onsite for almost four years, in a sea wall exposed to XS1 ambiance. The electrochemical techniques used were based on the determination of the electrical resistivity of concrete, the half-cell corrosion potential and the steel corrosion rate (from linear polarization resistance measurements). All of these electrochemical parameters provide accurate information for on-site structures about the efficiency over the time of surface-applied corrosion inhibitors. The effectiveness of the dual-phase surface-applied corrosion inhibitor proved to be up to 99%, even with ongoing corrosion and 0.3 mm cracks near the rebar. The use of DP-SACI provides a non-destructive repair method that inhibits the corrosion process and increases the service life of the element. [ABSTRACT FROM AUTHOR]

Engineered cementitious composites (ECCs) belong to a broad class of fibre-reinforced concrete. They incorporate synthetic polyvinyl alcohol (PVA) fibres, cement, fly ash and fine aggregates, and are designed to have a tensile strain capacity typically beyond 3%. This paper presents an investigation on the carbonation behaviour of engineered cementitious composites (ECCs) under coupled sustained flexural load and accelerated carbonation. The carbonation depth under a sustained stress level of 0, 0.075, 0.15, 0.3 and 0.6 relative to flexural strength was measured after 7, 14 and 28 days of accelerated carbonation. Thermogravimetric analysis, mercury intrusion porosimetry and microhardness measurements were carried out to show the coupled influence of sustained flexural load and accelerated carbonation on the changes of the mineral phases, porosity, pore size distribution and microhardness along the carbonation profile. A modified carbonation depth model that can be used to consider the coupled effect of flexural tensile stress and carbonation time was proposed. The results show that an exponential relationship can be observed between stress influence coefficient and flexural tensile stress level in the carbonation depth model of ECC, which is different when using plain concrete. Areas with a higher carbonation degree have greater microhardness, even under a large sustained load level, as the carbonation process refines the pore structure and the fibre bridges the crack effectively. [ABSTRACT FROM AUTHOR]

Reactive transport models are useful tools in the development of cement-based materials. The output of cement-related reactive transport models is primarily regarded as qualitative and not quantitative, mainly due to limited or missing experimental validation. This paper presents an approach to optimize the calibration process of reactive transport models for cement-based materials, using the results of several short-term experiments. A quantitative comparison of changes in the hydrate phases (measured using TGA and XRD) and exposure solution (measured using ICP-OES) was used to (1) establish a representative chemical model, limiting the number of hydrate phases and dissolved species, and (2) calibrate the transport processes by only modeling the initial tortuosity. A case study comprising the early age carbonation of cement is presented to demonstrate the approach. The results demonstrate that the inclusion of a microstructure model in our framework minimizes the impact of the initial tortuosity factor as a fitting parameter for the transport processes. The proposed approach increases the accuracy of reactive transport models and, thus, allowing for more realistic modeling of long-term exposure. [ABSTRACT FROM AUTHOR]

The corrosive water environment has a decisive influence on the durability of a diversion tunnel lining. In this paper, the effects of carbonation on cement-based materials in water-immersion and saturated-humidity environments were studied by increasing the CO2 concentration. The results show that under conditions of water-immersion and saturated humidity, the color of the non-carbonation region is dark, while the carbonation region is gray, and the color boundary is obvious. However, in an atmospheric environment, there is no zone with a dark color and the color boundary is not obvious. In a saturated-humidity environment, the carbonation depth increases over time and changes greatly, and its value is about 16.71 mm at 200 days. While in a water-immersion environment, the carbonation depth varies little with time and the value is only 2.31 mm. The carbonation depths of cement mortar samples in different environments generally follow a linear relationship with the square root of time. The carbonation coefficient in a saturated-humidity environment is more than nine times that in the water-immersion environment. In a water-immersion environment, the carbonation causes a large loss of calcium in cement-based materials, and their Ca/Si ratio obviously decreases. The calcium silicon ratio (Ca/Si) of cement-based materials in a water-immersion environment is 0.11, which is much less than 1.51 in a water-saturated environment and 1.49 in an atmospheric environment. In a saturated-humidity environment, the carbonation only reduces the pH of the pore solution in the carbonation region, and the structural stability of cement-based materials is not degraded. The number of pores of all radii after carbonation in a water-immersion environment exceeds that in a saturated-humidity environment, and the total pore volume and average pore radius in a water-immersion environment are also larger than in a saturated-humidity environment, so the water-immersion environment accelerates the development and expansion of pores. The research results can provide some theoretical and technical support for the design, construction, and safe operation of diversion tunnel linings. [ABSTRACT FROM AUTHOR]

A calcium carbonate (CaCO3)-based coating with gamma-C2S (γ-C2S) as the main carbonatable binder is proposed to protect the metal substrate against corrosion in this paper. Here, the morphology and phase assemblage of the coatings are studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the corrosion resistance of the coating is evaluated by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). Results show that the carbonated coating has excellent properties in terms of ultraviolet (UV) aging resistance, salt fog resistance, and electrochemical corrosion resistance. The porosity of deposited coating on steel substrates decreases by 47.1% after carbonation due to the compacted calcium carbonate formation, which is recognized as a self-compacting process during carbonation. The coating also exhibits rapid strength development within the first 2 h of carbonation; both the CO2 uptake efficiency and degree of carbonation (DOC) can reach more than 95% of the total CO2 uptake efficiency and final DOC values. This study provides a novel insight to extend the category of inorganic coating with additional benefits of CO2 solidification. [ABSTRACT FROM AUTHOR]

The durability of a concrete bridge structure is a systematic problem composed of material, structure, natural environment, and service environment. Various factors are coupled, which affect each other, and single-factor research cannot fundamentally solve this problem. In this paper, the carbonation characteristics of RC beams with different loading states under the coupling action of carbonation and chloride erosion are studied. Through the experiment, the author tries to find the influence of stress state and chloride ion erosion on the carbonation of concrete and analyze the failure mode and the attenuation rules of the flexural and shearing capacity of the corroded RC beams under the coupling action. For this purpose, five groups of experiments under different working conditions were designed, including chloride ion erosion and carbonation experiments without external load of the cubic blocks, and chloride erosion and carbonation coupling experiments of RC beams under different stress states and stress levels. The carbonation rate of concrete can be reduced by 56%∼60% under the coupling action of chloride salt. Different loading states and stress levels have an obvious influence on carbonation and chloride ion corrosion, which further affects the corrosion rate of steel bars. Under a low corrosion rate, the bending and shear failure modes of the corroded beams are similar to those of the noncorroded beams, and the section strain distribution still approximately conforms to the plane section assumption. The relationship between the relative ultimate shear strength or the relative ultimate flexural strength and the average section-corrosion rate of the reinforcement is approximately linear. [ABSTRACT FROM AUTHOR]

The crack and carbonation of concrete pose a great challenge to its durability. Therefore, this paper studies the effect of cracks on the carbonation depth of cement paste under different factors. The relationship between carbonation and cracks was determined, and the carbonation mechanism of cement paste with cracks was clarified. The results show that a small water–binder ratio can effectively inhibit the carbonation process. The bidirectional carbonation enlarged the carbonation area around the crack. Within 21 days of the carbonation, the carbonation depth increased with carbonation time, and the Ca(OH)2 on the surface of the specimen was sufficient, allowing for a convenient chemical reaction with CO2. The influence of crack width on the carbonation process at the crack was greater than the influence of the crack depth. Carbonation influenced the hydration of cement-based materials, altering the types and quantities of hydration products. In conclusion, accurately predicting the regularity of carbonation in cracked structures is critical for improving the durability of concrete. [ABSTRACT FROM AUTHOR]

Recycled coarse aggregates (RCAs) are widely used as a sustainable material in the construction sector. However, the variability of the material is the main factor that limits its use in practice. This paper investigates the effectiveness of RCA selection by an air jigging process in concrete. The performance was assessed with compressive strength and durability indicators from natural and accelerated carbonation tests. The RCA used was provided by two recycling plants. Air jigging technology reduced the mortar and ceramic content in RCA; hence, it increased the strength of the jigged material relative to concrete without air jigged RCA. However, jigging RCA resulted in natural and accelerated carbonation coefficients up to 2.5 times higher than concrete made with natural coarse aggregate. The treatment of RCA by air jigging technology enhanced the properties of concrete, achieving additional benefits compared with nontreated material. Furthermore, the existing models that provide a correlation between accelerated and natural results of carbonation depth and current international standards do not apply to RCA. Therefore, modifications of these models were carried out to enhance the service life prediction of RCA concrete. [ABSTRACT FROM AUTHOR]

Accelerated carbonation of recycled concrete aggregates (RCA) could be an efficient way to reduce the carbon footprint. High CO2-concentration under optimal relative humidity could accelerate the CO2 binding capacity of the hydrated cement paste in the RCA. The latter is the topic of this paper. The study looks into the forced carbonation of crushed cement pastes as a basis to understand the CO2 uptake in relation to various binders containing supplementary cementitious materials (SCM) such as fly ash (FA) and ground granulated blast furnace slag (GGBS). Samples include three cement pastes: ordinary Portland cement, substitution rate of 30 % FA and 50 % GGBS respectively at a water/binder ratio of 0.45. All binders were graded to 0/2, 2/4 and 4/8 mm fraction sizes and preconditioned before exposed to CO2 concentration of 10 % under controlled temperature at 20 °C and 65 % RH. All tested binders presented a high CO2 uptake within the first hours of exposure with clear differences concerning the fraction sizes and the composition. The phase content before and after carbonation was observed by X-ray diffraction and the portlandite and calcite were quantified by thermogravimetric analyses and their derivative curves for fraction size 4/8 mm. [ABSTRACT FROM AUTHOR]

The construction sector is responsible for a great environmental impact. The cement industry, which is included in this sector, emits about 650 to 800 kg of CO2 per each tonne of cement produced, being one of the most polluting industries in terms of greenhouse gas emissions. The cement manufacturing process releases about 7% of the total worldwide CO2 emissions. However, concrete and cement-based materials present CO2 uptake potential during their service life and post-demolition through carbonation processes. The carbonation reactions rate depends on several factors, namely type and content of cement, porosity of concrete, temperature, relative humidity and exposure conditions area. Therefore, to estimate the CO2 capture of concrete during its life cycle is not a straightforward calculation. Some studies have been developed using different methodologies in order to evaluate the CO2 potential of cementitious elements in service and post-demolition. This paper reviews the documented approaches that quantify the CO2 uptake of concrete over time, summarizing the assumptions adopted for each previous work. Overall, it was concluded that part of the CO2 emissions released during cement production are reabsorbed by concrete products during their life cycle, which partially offsets the environmental impact and reduces the CO2 footprint of the cement industry. [ABSTRACT FROM AUTHOR]

Recycled aggregate produced from crushed waste concrete is suitable for use in structural concrete. It reduces the demand for non-renewable resources and also for energy in general. However, RA is more porous than most natural aggregates. The porosity of the concrete cover defines the corrosion resistance of reinforced concrete, and it is therefore disputed how the use of recycled aggregate may affect the durability of reinforced concrete. This paper describes the corrosion-related performance of reinforced concrete with recycled aggregates in the initiation stage (determined by the carbonation and chloride ingress) and propagation stage (determined by the electrical resistivity and cracking) of corrosion. The aspects of interest are not only the porosity of RA but also its effects on the chloride binding, carbonation, electrochemical properties and corrosion cracking development. [ABSTRACT FROM AUTHOR]

In industrialized countries, most of the reinforced concrete (RC) structures and infrastructures have more than 40 years, since they were built around 1960 − 1980, and were designed for a service life of 50 years. Consequently, in the next years, the number of structures and infrastructures that will need to be repaired will steeply increase. Several techniques, characterized by a different durability, environmental impact and economic impact, are available for the repair of a reinforced concrete structure damaged by the corrosion of reinforcement. To help the designers in the choice of the most suitable one, a preliminary assessment of the condition of the structure is essential, aimed at diagnosing the causes of deterioration, the extent of damage, i.e. the extent of corroding reinforcement, and its evolution in time. An approach, with a wide consensus, for the evaluation of the extent of corroding reinforcement is available for carbonation-induced corrosion, whilst it is still lacking for chloride-induced corrosion. In this paper two approaches for the evaluation of the extent of corroding reinforcement for a RC structure subject to chloride-induced corrosion are presented and compared, showing similar results. These approaches can be useful to properly plan a restoration intervention as well as to assess the reliability of the recently proposed model for service life design. [ABSTRACT FROM AUTHOR]