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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]

The increase of energy valorization of paper sludge waste and biomass due to their high calorific value by incineration leads to an increase of waste paper fly ash (WPFA) quantities, which are in most cases considered as hazardous, and must be dealt with accordingly. The Alternative options for the management of WPFA, such as stabilization/solidification, vitrification or sintering, are not fully developed or either costly. In the present study, accelerated carbonation technology was used to reduce the hazardous nature of WPFA by improving the stabilization of metallic and metalloids trace elements (MMTE), especially Barium (Ba) and Lead (Pb) leaching. The accelerated carbonation of WPFA was found to be optimal at a water/solid ratio of 0.3 L/kg under controlled temperature and humidity conditions. The use of water saturated with 25% sodium bicarbonate (NaHCO 3) improved the carbonation of WPFA and the stabilization of Ba and Pb. Batch leaching tests based on thermodynamic equilibrium was used to evaluate the solubility of the MMTE as a function of pH and at the natural pH of non‑carbonated and carbonated WPFA. Thermogravimetry, X-ray diffraction, scanning electron microscopes and energy dispersive spectroscopy analyses were performed to investigate the evolution of carbonation over time and its effect on the chemical and mineralogical properties of WPFA. After 30 days of accelerated carbonation, the leaching concentration of Ba and Pb was below the French legal limit. The leaching concentration of Ba and Pb from carbonated samples decreased 99% and 99.5% respectively. The leaching and release potential behavior of carbonated WPFA were further evaluated using the four-step sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR). The speciation of MMTE underwent significant transformation, shifting predominantly from the soluble fraction to the carbonated fraction as a result of the carbonation reaction. [Display omitted] • Accelerated carbonation with NaHCO 3 of WPFA has been performed. • Ba, Pb and Cl leaching concentration decreased effectively after carbonation. • After 15 days of accelerated carbonation, the WPFA becomes inert. • Parameters L/S = 0.3 l/kg, 20 °C/65 °C with NaHCO 3 improves carbonation. • Ba and Pb was precipitated as carbonate BaCO 3 and PbCO 3 [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]

Climate change induced partly by emissions of carbon dioxide (CO2) is an urgent issue worldwide, calling for advanced methods of carbon sequestration. Since CO2-emitting industries often generate alkaline waste, sequestrating CO2 by mineral carbonation of alkaline waste is promising both for carbon capture and utilization, and for preventing waste disposal. Here we review the principles of mineral carbonation and we discuss mineral carbonation of alkaline waste and byproducts in Taiwan. We focus on wastes such as iron and steel slag, cement and concrete waste, incineration ash, coal combustion ash, and paper waste. We evaluate the CO2 reduction potential to reveal promising materials and industries. We found that 4.2 Mt CO2 can be directly sequestered annually. Moreover, the use of alternative materials in the cement and concrete industries can indirectly facilitate CO2 sequestration. [ABSTRACT FROM AUTHOR]

Ex-situ mineral carbonation, a CCU process, is one possible approach for the decarbonisation of emission-intensive industry with hard-to-abate process emissions like the cement industry. The chemical reaction ensures long-term binding of carbon dioxide in minerals with the effect of storing otherwise emitted CO 2 long term. As a major hurdle for CCU processes is often their economic viability, to create incentives for the usage of this process, these carbonated mineral products must become marketable. A separation approach for the reaction products of this process and possible utilization paths are presented. The separation results in three different fractions, each enriched in either the reaction products amorphous silica or magnesium/calcium silicate or unreacted peridotite. The fractions enriched with reaction products are tested as supplementary cementitious material in cement or as a filler in rubber and paper. The application tests show promising results, comparable or even better than the conventional product. Additionally, based on the laboratory explorations, we present initial economic and environmental investigations showing potential carbon footprint reductions of up to 27% for blended cement with a total global reduction potential of 681 Mt CO2e /a. Also, potential carbon footprint reductions of 52% can be achieved by using carbonation products as fillers in rubber and 197% in paper, respectively. While the costs for the utilization of carbonated minerals have been calculated to be higher than for the conventional products, CO 2 emission certificates could ensure the same price for cement and even lower costs for the substitution of fillers in paper and rubber. [Display omitted] • The technical feasibility of the separation of the carbonation products by centrifugal classification has been proven. • Yield of the separation process can be optimized by better liberation of the particles. • Application tests for cement, paper or rubber show the potential of the carbonated and separated products as a (partial) substitute. • The modeled industrial process – in this case a cement plant with carbonation products as clinker substitute – is ecological and economical feasible. [ABSTRACT FROM AUTHOR]

In this study, the effect of different concentrations of calcium hydroxide (Ca(OH)2) was evaluated as a pre-treatment for accelerated carbonation and its influence on the fibrillation of cellulosic pulps to obtain nanofibrils, and its application as a coating agent for papers. Eucalyptus (EUC) and Pine (PIN) unbleached cellulosic fibers were submitted to pre-treatment with Ca(OH)2 at concentrations of 5 and 10% and subjected to accelerated carbonation, being subsequently mechanically fibrillated to produce cellulose nanofibrils (CNF). Pretreatment with calcium hydroxide followed by accelerated carbonation provided a 35% reduction in energy consumption. Cellulosic pulps EUC and PIN pretreated with calcium hydroxide showed higher fibrillation efficiency. There was a reduction in the cobb test values for papers coated with CNF in PIN. The WVP was lower for papers coated with CNF of EUC and control PIN. The CNF coating of EUC and PIN provided an oil barrier for the kit 11 solution. The CNF coating improved the dispersion of PVA and PVOH. The papers coated in this work have the potential to be used as packaging for fatty and oily foods or as a spreading agent for other industrial coatings. [ABSTRACT FROM AUTHOR]

This paper is a reply to the discussion by S.A. Walling and J.L. Provis on our papers “Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements” and “Enhancing the carbonation of MgO cement porous blocks through improved curing conditions”. Walling and Provis discuss the assignment of X-ray diffraction patterns, the use of acid digestion to quantify the degree of carbonation, the interpretation of thermal analysis data, and the stability of hydrated magnesium carbonates. In this reply, we confirm the conclusions made in the two papers based on the combined evidence of microstructural and mechanical performance results. [ABSTRACT FROM AUTHOR]

The paper presents processing techniques of waste newsprint paper. Wastepaper was soaked in a soda or a hydrochloric solution and heated in a reactor with limited air access or in an autoclave. In the first stage, at 300°C, we obtained brittle carbonated coal with particle sizes of 10-50 µm, which can be used after milling as an additive in poor coals in the production of a coal-water slurry fuel. At the second stage, at 500-600°C, we obtained an amorphous carbon containing of up to 91.2% of C, which is widely used in the tire, rubber, and paint and varnish industries. [ABSTRACT FROM AUTHOR]

This paper is a discussion of two recent papers by Unluer & Al-Tabbaa which analysed accelerated carbonation of reactive MgO blocks. We suggest that the authors have incorrectly analysed key data, leading to overstated claims of MgO carbonation. Based on the reassignment of their X-ray diffraction data, it is proposed that little MgO carbonation occurred in the samples discussed in those papers, with CaCO 3 instead forming during accelerated carbonation. We also draw attention to the thermodynamic instability of nesquehonite under ambient conditions, which calls into question the long-term stability of these binders. [ABSTRACT FROM AUTHOR]

This study aimed to maximise the amount of CO2 storage by indirect carbonation using paper sludge ash (PSA), which is an alkaline industrial waste. The properties of the following three types of solvents were considered: acids (acetic acid and hydrochloric acid), ammonium salts (ammonium chloride and ammonium acetate) and others (sodium citrate and water). When carbon dioxide was injected into calcium leachates prepared from PSA using acids, carbonation did not occur, and using ammonium salts as solvent, the carbonation efficiency was low. However, after pH swing of the leachates using sodium hydroxide and ammonia solution for acid and ammonium salt solvents, up to 324 kg CO2/(ton PSA) and 175 kg CO2/(ton PSA) were stored, respectively. When carbon dioxide was injected into calcium leachates prepared from PSA using sodium citrate or water, solid was initially generated which later dissolved. In order to solve this problem, CO2 injection was stopped just before the pH of the solution reached 10.5 for sodium citrate and 8.3 for water, resulting in the storage of 136 kg CO2/(ton PSA) and 29 kg CO2/(ton PSA), respectively. Solids obtained through carbonation were pure calcium carbonate. [ABSTRACT FROM AUTHOR]

• Evolution of linear attenuation coefficient (LAC) regarding carbonation may vary via different CT. • X-ray energy level used for CT scan can reverse the LAC relationship between calcium carbonate and calcium hydroxide. • Hygral equilibrium and polymorphs of carbonation product can also affect the LAC of carbonated areas. A discussion on a recently published article authored by Kim et al. [Effect of carbonation on cement paste microstructure characterized by micro-computed tomography. Constr. Build. Mater. 263 (2020) 120079] is presented. [ABSTRACT FROM AUTHOR]

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]

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]

Copyright of Environmental & Social Management Journal / Revista de Gestão Social e Ambiental is the property of Environmental & Social Management Journal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Copyright of EMERG: Energy. Environment. Efficiency. Resources. Globalization is the property of Romanian National Committee of World Energy Council and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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 article announces that T. A. Harrison and his colleagues have received the MCR Award from the "Magazine of Concrete Research" for their paper "Experience of using the prTS 12390-12 accelerated carbonation test to assess the relative performance of concrete."

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]

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 objective of this paper is to present the methodology used to validate the threshold levels of durability indicators from data acquired from existing reinforced concrete structures that may present corrosion problems resulting from carbonation or chloride ingress. This study was conducted in the framework of the French National Project PERFDUB in close collaboration with the MODEVIE ANR project. Durability tests form the basis of a performance‐based approach for the durability of concrete structures, and in order to set the threshold level for each of these durability indicators, it is important to take into account the experience feedback that can be obtained from the actual behavior of existing structures. This paper presents the investigations carried out on eight reinforced concrete structures, all of them having an age well in excess of 50 years, and the main data gathered on some relevant durability and lifetime indicators. Based on all these data, predictive models of carbonation and chloride penetration are applied in order to validate the threshold levels to be adopted for the durability indicators, and several other conclusions are drawn. [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]

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 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]

The performance of existing materials such as concrete has been improved significantly by blending it with specific property enhancement materials especially nanomaterials like nanosilica. Utilization of nanosilica has been proved to be beneficial because of its indispensable qualities, which helps in creating concrete with improved strength and durability. In this paper, the impact of nanosilica on toughness of cement has been researched. For this purpose, 3% of ideal measurement of nanosilica has been added to solid combinations of M40, M50, M60 grades of concrete. Additionally, the admixture Conplast SP 430 is utilized to build workability. For the experimental studies, M40, M50, M60 evaluations of cement with water concrete proportion of 0.48, 0.45, and 0.40 is used. Durability has been investigated through sorptivity, freeze & thaw, carbonation, rapid chloride porousness tests. Results of this current examination study indicated that nanosilica can be successful in improving the sturdiness of cement. [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]

The C02 emission of iron and steel industry is large, and the urination of metallurgical solid waste such as steel slag is difficult. Steel sag carbonation material has good stability and durability, but its low tenia strength and easy cracking limit the application in the construction field. In this paper, still lag is used as carbonization raw material, polypropyiene fiber is used as reinforcement material, and carbonization curing is used to develop and prepare fiber reinforced steel lag carbonization material. Based on the compressive strength, flexural strength and carbonation degree of steel lag carbonation materials, the influence of polypropylene fiber content on the mechanical properties and carbonation consolidation properties of still lag carbonation materials were studied by means of micro-analysis methods including thermogravimetric and mercury intron method. [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]

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]

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]

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 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]

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]

The article offers information on International Conference on Accelerated Carbonation for Environmental and Material Engineering (ACEME) conference held in Newcastle over March 12-14, 2018 arranged by Center for Energy Initiatives (CEI) to research and development activities on accelerated carbonation. It is noted that "CO2 Capture and Storage by Mineral Carbonation" and “Pilot and Full-Scale Applications, Utilization of the Carbonated Materials & Other" are other themes addressed in the event.

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]

Carbonation curing cement-based materials can improve the properties of cement products while permanently sequestering CO2, which is considered to be a very promising carbon reduction technology. In this paper, cement pastes with different pore structures were prepared by changing the water-cement ratio (w/c =0. 35, w/c =0. 4, w/c =0. 45) and pre-conditioning time (2, 4, 6, 8, 16, 24, 48 and 72 h), and the influences of pore structure and water content on the carbonation reaction of cement paste were studied. The results show that the carbon sequestration rate of cement paste with different water-cement ratios reaches the maximum when the pre-conditioning time is 8 h, and the carbon sequestration rate increases with the increase of water-cement ratio. At the same time, for cement paste with early hydration (24 h standard curing +8 h pre-conditioning), the influence of water-cement ratio on the pore structure is much greater than the degree of hydration. The cement paste with initial water-cement ratio of 0. 45 undergoes 8 h pre-conditioning and then undergoes 8 h carbonization curing. Its carbon sequestration rate, carbonation depth and compressive strength reach 20. 35% (mass fraction), 12. 49 mm and 61. 99 MPa, respectively, which increases the compressive strength by 14. 27% compared with the strength of the 28 d standard curing test block (54. 25 MPa). The main products of carbonation reaction are CaCO3 and silica gel. The filling of CaCO3 optimizes the pore structure of cement paste, significantly reduces the pores larger than 50 nm, and the main crystal forms of CaCO3 are calcite and aragonite. [ABSTRACT FROM AUTHOR]

Existing structures often no longer meet the demands formulated in contemporary design codes with respect to structural safety and serviceability. This occurs, for instance, if the loads on existing structures, like traffic loads on bridges, are larger than assumed in the original design. A second potential reason is that structures are subject to deterioration, like alkali–silica reaction within the concrete or corrosion of the reinforcement due to chloride attack or carbonation. A third possible reason is that in recent codes, additional criteria have been introduced based on new theories and/or negative experiences with older structures. The new fib Model Code for Concrete Structures 2020 will be valid both for the design of new structures and the assessment of existing structures. This paper shows how the design and assessment of concrete structures are integrated into this new code concept. [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]

From first principles, criteria for the EN 12390-10 outside protected test have been developed and compared with existing practice. These criteria align well with the UK recommendations but are more conservative than the current French and Spanish requirements. The EN 12390-10 outside protected test is unsuitable for classification as this would require anybody using the procedure with identical concrete to get the same result. Unfortunately, current tests that are suitable for classification, whilst safe, do not reflect the real performance of slowly reacting cements. Improving the test for classification purposes will take time and meantime the use of the EN 12390-10 outside protected test and the criteria given in this paper provides a procedure by which both sustainability and durability may be achieved. The downside of this test is its slowness and, therefore, it is only suitable for type testing or the determination of limiting values and other criteria to be used in specifications or production. [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]