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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]

This paper presents study results of the qualitative characteristics of coal deposit Kotezi. Regional geological researches were conducted from 1983 to 1987, and detailed from 2014 to the end of 2018. Tests were performed on the following coal quality parameters: average thickness of pure coal in coal layers, total moisture content, ash content, total sulfur content and lower heat value. Researches were conducted in the field, laboratory and cabinet. Subsequently, an analysis and interpretation of the obtained research results was carried out. Comparing the research geological results of all represented coal layers, deviations of the considered parameters were determined. Coals of the Bugojno basin belong to the younger coals, soft to medium hard, no luster (matt), brown to black colored, and have brown streak. Their fracture is plate-like and particleboard. They do not have a distinct lignite structure, except in the lower layers. With their general habitus, they resemble younger brown coals, and belong to humic coals which are relatively low in carbonation. In the vertical profile of coal layers, the highest quality components are from the upper part of the layer, while the slightly lower quality components are from the middle and lower parts of the layer. [ABSTRACT FROM AUTHOR]

The corrosion of rebars in concrete is a major cause of the falling bearing capacity of concrete structures. The durability of concrete could be effectively enhanced by adding mineral admixtures. Many studies have shown that rust inhibitors can effectively prevent rebar corrosion. Taking commonly used slag, fly ash, and silica fume as mineral admixtures, this paper explores how an alcohol-amine compound rust inhibitor affects the compressive strength, chloride penetration resistance, carbonation resistance, and rebar corrosion resistance of concrete with a large amount of mineral admixtures. The research results show that the addition of rust inhibitor hinders the early hydration of cementitious materials in concrete; the chloride diffusivity and carbonation depth of concrete were minimized, when the ratio of N,N-dimethylethanolamine (DMEA) to sodium monofluorophosphate (MFP) in the compound rust inhibitor stands at 15:1; the addition of rust inhibitor clearly suppressed the corrosion loss of the rebars in concrete, resulting in a low rebar corrosion rate. The research results provide experimental evidence for reducing rebar corrosion in reinforced concrete. [ABSTRACT FROM AUTHOR]

Mineral carbonation of alkaline earth metals is the conversion of carbon dioxide, in gaseous form or dissolved in water, to form solid inorganic carbonates. Alkaline earth metals can be derived from natural minerals, waste residues, or brines. Calcium and magnesium are the two most abundant of these metals, which when carbonated form a variety of calcium and magnesium carbonates of different mineral compositions and crystal structures. Determining inorganic carbon (IC) content of carbonation solid products with high precision is an essential requisite to quantify the amount of carbon dioxide sequestered by a given process at a given reaction time. It also enables understanding fundamental phenomena about the reactions, including the reaction rate, conversion limitations, and the mineral composition of carbonation products and by-products. The most conventional methods to determine IC content utilize destructive techniques based on acid decomposition (e.g. calcimeter) and thermal decomposition (e.g. thermogravimetric analyzer). The main disadvantage of these methods includes chemical usage, long measurement time, overestimation of IC, and limited ability to differentiate the various mineral forms of carbonates. In this regard, nondestructive techniques (NDT) constitute a valuable alternative to the conventional method for IC determination and carbonates characterization; these include spectroscopic methods (NIR, MIR), X-ray spectroscopy (XRD, XRF, XCT); and microscopic methods (SEM-EDS, TEM, RLM, EPMA). While infrared spectroscopy can be used to quantitatively identify carbonate spectral bands, X-ray diffraction quantitatively identifies the presence of specific crystalline carbonate phases. Elemental chemical information is provided by X-ray fluorescence, and microstructure analysis is done using electron probe microanalysis and micro-tomography. SEM provides visualization of crystal and particle size and morphology, while energy dispersive spectroscopy is used to inspect elemental composition of individual particles or intra-particle layers and grains. This paper presents a critical comparative analysis of the use of these NDT in determining IC content and carbonate composition. Improved understanding of the advantages, limitations, and applicability of each method can enable the development of standard protocols for characterization of carbonation products, which is especially required for carbon sequestration accounting in view of climate change mitigation. Unlabelled Image • Accurate, precise and efficient inorganic carbon determination need is discussed. • Techniques based on acid and thermal decomposition do not differentiate carbonates. • Non-destructive techniques evaluate mineralogy, micro-structure and speciation. • Complementary techniques provide mechanistic insights on enhanced weathering. • Learnings from slag carbonation research are informative for weathering research. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amines displayed dual functions as an alkaline reagent and the CaCO 3 regulator. • Remarkable CO 2 removal (>95 %) and CO 2 capacity (>340 g /kg) were obtained. • Promising gypsum conversion (>93 %) were obtained. • Primary/secondary amines postponed the formation of CaCO 3 and induced vaterite. • Amines were regenerated from their protonated forms by BMED. CO 2 mineralization of waste gypsum not only reduces the carbon emissions of power plants but also improves gypsum utilization by recovering high-value-added CaCO 3. However, the extensive consumption of various reagents limited its development. This paper proposed an amine-promoted waste gypsum carbonation process integrating with amine regeneration by bipolar membrane electrodialysis (BMED). The alkaline amine was expected to act as a multifunctional reagent for gypsum carbonation — alkaline reagent, CO 2 absorbent, gypsum dissolution promoter, and CaCO 3 crystal regulator. Seven typical amines with different amino types and p K a values were selected to investigate the feasibility of this process. Results show that promising CO 2 removal efficiency (>95 %) from an artificial exhausting gas, gypsum carbonation efficiency (>93 %), and CO 2 sequestration capacity (>340 g-CO 2 /kg-gypsum) can be achieved due to the additional alkalinity, fast CO 2 absorption, high CO 2 concentrations, and enhanced CaSO 4 dissolution in amine solutions. In addition, the interactions of amine-CO 2 -gypsum and the CaCO 3 growth mechanism in the gas–liquid-solid system were explored. Monoethanolamine (MEA), 3-amino-1-propanol (MPA), piperazine (PZ), and 1,3-Diaminopropane (DAP) could prolong the CaCO 3 precipitation due to their strong affinity for Ca2+ and CO 3 2−. In this case, CO 2 absorption by the liquid phase dominated the carbonation process in the initial 30 min for these four amines, while CaCO 3 precipitation mainly occurred within 30 ∼ 120 min. Amines' different affinities for Ca2+ and CO 3 2− provided an approach to selective synthesis of CaCO 3 polymorph: 100 % calcite by PZ, 100 % vaterite by DAP, a calcite-vaterite mixture by MEA, and a calcite-vaterite-aragonite mixture by MPA. After the carbonation process, amines were recycled from the liquid residue by BMED, which could provide OH− for amines regeneration from protonated amines, recovery of H 2 SO 4 , and decrease the solution salinity. [ABSTRACT FROM AUTHOR]

Large shrinkage and poor carbonation resistance are important reasons that limit the widespread use of alkali-activated slag. The expansion pressure of albite due to alkali-activated silica reaction in alkaline environments and the sequestration of CO 2 may solve the problems. In this paper, the effect of albite on shrinkage and carbonation resistance of alkali-activated slag were studied, and the mechanism of action between albite and alkali-activated slag was revealed. Firstly, alkali-activated slag slurry specimens with partial replacement of slag by albite were prepared with standard and carbonation curing. Then, the samples were tested for compressive and flexural strength as well as chemical shrinkage, autogenous shrinkage and drying shrinkage under standard and carbonation curing. Finally, the mechanism of interaction between albite and alkali-activated slag was analyzed by XRD, TG-DTG, FT-IR, SEM, MIP and 29Si MAS NMR. The results show that: 1) the influence of carbonation on the compressive strength and flexural strength of alkali-activated slag was reduced when mixed with albite. After carbonation curing for 28 days, the compressive strength of pure slag samples decreased by 50.67 %, while the strength of samples mixed with albite decreased by 34.51 %. 2) After adding albite, the chemical shrinkage, autogenous shrinkage and drying shrinkage of alkali-activated slag samples decreased by 33.33 %, 32.95 % and 46.76 %, respectively. 3) The amount of calcite due to carbonation curing was reduced. The content of calcite in the sample with albite was 65.49 % of that of pure slag sample under carbonation curing. 4) Albite can promote the degree of hydration and the generation of C-A-S-H gels of the alkali-activated slag. • Albite improves the hydration degree of alkali-activated slag. • Albite improves the carbonation resistance of alkali-activated slag. • Albite decreases the shrinkage of alkali-activated slag. [ABSTRACT FROM AUTHOR]

• Nesquehonite was used as a new nucleation seeds for reactive magnesia cement, and its performance was compared with hydromagnesite. • The nucleation effect of nesquehonite seeds was demonstrated, resulting in increased nesquehonite formation and carbonation degree. • Nesquehonite seeds combined with hydration agent can further promote the compressive strength of RMC through forming more amounts of nesqeuhonite crystals and amorphous hydrated magnesium carbonates. • Compared with the hydromagnesite seeds, the nesquehonite seeds showed a more significant increase in the CO2 sequestration capacity of RMC. Among all carbonation products of reactive magnesia cement (RMC), nesquehonite exhibited the highest CO 2 amount of sequestration per molar. Inducing the nesquehonite formation may improve the CO 2 sequestration capacity of RMC. In this paper, nesquehonite seeds were introduced to promote the formation of nesquehonite in RMC. The performances of RMCs with 0%, 0.5%, 1%, 1.5% and 2% nesquehonite seeds were studied and compared with that of RMC mixed with hydromagnesite seeds. It was found that the hydration of RMC could be facilitated by nesquehonite seeds, resulting in reduced setting times. The nucleation effect of nesquehonite seeds was demonstrated, resulting in increased nesquehonite formation and carbonation degree. Nesquehonite seeds combined with hydration agent can further promote the compressive strength of RMC through forming more amounts of nesqeuhonite crystals and amorphous hydrated magnesium carbonates. Compared with the hydromagnesite seeds, the nesquehonite seeds showed a more significant increase in the CO 2 sequestration capacity of RMC. [ABSTRACT FROM AUTHOR]

[Display omitted] • The environmental impact of RACB under different curing scenarios was assessed. • The contribution distribution of each RACB production stage was subdivided. • The effect of curing time on the environmental sustainability of RACB was supplemented. • The environmental advantages of accelerated carbonization instead of traditional curing were determined. Accelerated carbonization curing has been a technically feasible alternative to the conventional curing method in the production of recycled aggregate concrete blocks (RACB). However, the environmental impacts of the curing scenarios on production have not yet been studied. Therefore, the paper evaluated the environmental feasibility of curing methods to produce RACB based on the LCA framework. The system boundary from the cradle to the door was selected to compare the overall influence of accelerated carbonation curing methods (pressurized carbonation curing, wet carbonation curing) and traditional curing methods (standard curing, autoclave curing) on the environmental impact. CO 2 absorption was calculated by the Kim and Chae carbonation model combined with experimental carbonation depth. Environmental emission calculated from the inventory database was distributed to ten midpoint indicators and three endpoint indicators by the CML 2016 baseline and ReCiPe endpoint method. The distribution of contributions to the environmental impacts of the four production stages (raw material processing stage, raw material transportation stage, block manufacture stage, and block curing stage) was subdivided to facilitate decision-making and improve the management of the block plant. A sensitivity analysis ultimately complements the effect of curing time on the environmental sustainability of RACB production. The results showed that the traditional curing method had a more significant environmental impact, while accelerated carbonization curing had a relatively lower environmental impact. Compared with standard curing, the GWP value of pressurized and wet carbonization curing decreased by 33.3% and 52.8%, respectively. The 1 m3 RACB showed the lowest GWP value of 254.7 kg CO 2 -eq under wet carbonization curing and the highest GWP value of 539.5 kg CO 2 -eq under standard curing. The CO 2 absorption capacity of −73.0 kg CO 2 -eq and −99.3 kg CO 2 -eq was demonstrated by pressurized and wet carbonization curing, respectively. The ranking from all midpoint and endpoint indicators is standard curing > autoclaved curing > pressurized carbonization curing > wet carbonization curing. Contribution analysis based on midpoint indicators showed that the raw material handling stage has the highest percentage contribution. Cement is still the most significant contributor to the environmental impact, followed by significant energy consumption, while water consumption hardly negatively impacts the environment. The results of sensitivity analysis indicate that accelerated carbonation curing (especially wet carbonation curing) is less relevant to the variation of curing time, while conventional curing methods are strongly influenced by curing time. [ABSTRACT FROM AUTHOR]

The behavior upon exposure to CO 2 of novel cementitious materials prepared with a low clinker cement CEM II/C-M (S-LL) is investigated in this paper. A simplified carbonation model considering the dissolution of a combined Ca-containing hydrate phase (CH, C-S-H, ettringite, monocarbonate, and Si-hydrogarnet) and the precipitation of calcite according to the evolution of phase assemblages calculated with thermodynamic modeling is applied to simulate accelerated carbonation tests in the laboratory. The dissolution rate of the Ca-containing hydrate phase is assumed to be determined by the water saturation degree, the partial pressure of CO 2 , and the fraction of its remaining volume compared to the initial one, which provides a way to predict the precipitation rate of calcite. Two mass conservation equations are considered in the model: water migration through the connected pores and diffusion of carbon dioxide in gaseous phases. Selected physical variables representative of the reactive transport properties are quantified from experimental measurements, including dynamic vapor sorption tests and drying experiments. The model response is compared to experimental data in terms of portlandite profiles from thermogravimetric analysis, and carbonation depth measurements using a pH indicator after specific times of accelerated carbonation. These experiments were also performed on a reference mortar prepared with the CEM II/A-S cement. All experimental results were simulated with the simplified carbonation model and the results compared to the response of the novel material. • Carbonation response of a novel low clinker CEM II/C-M (S-LL) cement is studied. • A simplified carbonation — drying model is coupled with thermodynamic calculations. • Transport properties are identified via DVS tests and drying experiments. • Model is validated against experimental portlandite profiles and carbonation depth. • Performance of the novel CEM II/C-M (S-LL) is compared to existing CEM II/A-S. [ABSTRACT FROM AUTHOR]

This paper describes a multi-scale approach for the modelling of the degradation of model cement pastes using reactive transport. It specifically aims at incorporating chemistry-transport feedback results from a pore-scale approach into a continuum description. Starting from a numerical representative elementary volume of the model cement paste, which was built according to extensive experimental dedicated chacarterizations, this paper provides three separate descriptions of two different degradations: leaching and carbonation. First, 2D pore-scale simulations are performed and predict degradation depths in very good agreement with experiments. Second, 3D pore scale descriptions of how the microstructre evolves provides accurate description of the evolution of transport properties through degradation. Finally, those latter results are incorporated as a feedback law between porosity and effective diffusion coefficient into a 1D continuum approach of reactive transport. This paper provides pore-scale explanations of why reactive transport modelling has encountered mitigated success when applied to cementitious materials, especially during carbonation or degradations consisting of precipitation reactions. In addition to that, different degradation modellings are in very good agreement with experimental observations. [ABSTRACT FROM AUTHOR]

ABSTRACT In Part II of this two-part series of papers, optimization of carbonation reaction with sodium metaborate and kinetics of the reaction are studied and compared to the structural properties, which were reported in Part I. This paper presents a comprehensive study on the optimization of reaction conditions and determination of reaction parameters of sodium metaborate (NaBO2) and carbon dioxide (CO2). Both hydrated and dehydrated forms of NaBO2 have high sorption capacities of CO2 up to 400°C. Decomposition of the products starts beyond 400°C and completes at 600°C. The shrinking core model is used to explain the kinetics of the noncatalytic heterogeneous reaction. The reaction progresses in two stages: one is surface reaction controlled and the other is diffusion controlled. The apparent activation energy and preexponential factor for reaction-controlled and diffusion-controlled regions are calculated as 11.8 kJ/mol and 3.5 × 106 cm2/min and 18.2 kJ/mol and 6.5 × 10−5 cm2/min, respectively. [ABSTRACT FROM AUTHOR]

Calcium looping is a Carbon Capture and Storage (CCS) technology which has the potential to be applied to both power generation plants and some industrial emission sources. The main problem with the use of calcium oxide-based sorbents is their characteristic decay in carrying capacity. This is caused by sintering and is made worse during multiple cycles of CO 2 absorption (carbonation) and release (calcination). This paper provides an investigation into the degradation of a novel type of sorbent that is able to regenerate porosity during the temperature cycling of calcium looping. The porosity regeneration of this sorbent is a result of a dicalcium silicate additive undergoing a reliable phase change (α′ ↔ β), which consequently has a useful volume change associated with it. The sorbent here, has been tested for the first time under reasonably realistic conditions within a TGA for multiple cycles. The results demonstrated that the sorbent displays the characteristic decline in carrying capacity when calcined in the presence of CO 2 , but not when calcined in the absence of CO 2 in the fluidising gas. This paper also presents an improved method to conduct TGA carrying capacity measurements of CO 2 sorbents which minimises the over carbonation between cycles. [ABSTRACT FROM AUTHOR]

Some jointed plain concrete pavements in the midwestern region of the United States of America have exhibited damage at the joints. This damage manifests itself in cracking and spalling in a small section (approximately 100 mm wide) along joints. These cracks may be due to either freeze-thaw cycling of concrete with a high degree of saturation or chemical reactions that occur between the deicing salt and the cementitious matrix. For example, deicing salts (e.g., CaCl 2 MgCl 2 ) may react with the cementitious matrix leading to the formation of calcium oxychloride. The formation of calcium oxychloride leads to matrix damage that results in the cracking and spalling of the concrete. The objective of this paper is to document the effect of carbonation on the potential for calcium oxychloride formation in a cementitious matrix. This paper examines ground hydrated cement paste powder made of different ordinary portland cements and portland cement containing fly ash, slag or silica fume. Each of these materials are tested for their potential to react with CaCl 2 after exposure to different levels of carbonation. The results indicate that the potential of calcium oxychloride formation decreases with the increase in the degree of carbonation. For long carbonation durations or higher degree of carbonations, there is no calcium oxychloride formation even if the calcium hydroxide is not totally carbonated. It appears that this is due to the fact that carbonation reaction creates a calcite barrier around the remaining calcium hydroxide. The calcite barrier reduces the potential for reaction between calcium hydroxide with the deicing salt. This work indicates that in addition to previous work that has shown that calcium oxychloride formation can be reduced with the use of supplementary cementitious materials and topical treatments (sealers), carbonation is a factor that should be considered in determining the amount of calcium oxychloride that can form in a cementitious matrix. [ABSTRACT FROM AUTHOR]

Highlights • Aerated steel slag blocks are prepared by accelerated carbonation. • C 4 AČH 11 formed during the hydration process of steel slag-aluminum system. • C 4 AČH 11 converted to aragonite, vaterite, calcite, and amorphous aluminum hydroxide by carbonation. • The formation and carbonation reactions of C 4 AČH 11 can be produced thermodynamically. Abstract The present paper discusses investigated the foaming behaviors and microstructure of three aerated steel slag block (ASSB) samples prepared with three different foaming agents (namely animal protein, hydrogen peroxide, aluminum powder) and by accelerated carbonation. The composition and microstructure of the ASSB samples before and after accelerated carbonation were characterized using X-ray diffraction (XRD), Rietveld method, thermogravimetric analysis (TGA), fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscopy (FE-SEM). It is an advisable method for foamed steel slag products to use the aluminum powder and accelerated carbonation technology. The aluminum powder favored a good foaming behavior for steel slag owing to (i) a high porosity and low dry density, (ii) a high hydration degree of minerals in steel slag, including brownmillerite, larnite, and lime, which was confirmed by the analysis of mineral compositions using Rietveld method, and (iii) the interlaced lamellas of monocarboaluminate and calcium silicate hydrate (C-S-H) gel strengthen the bubbles wall, which was confirmed by morphology analysis using FE-SEM. After accelerated carbonation, the monocarboaluminate shifted to aragonite, vaterite, calcite and amorphous aluminum hydroxide (Al(OH) 3), which was confirmed by XRD, TGA and FT-IR. The network skeleton formed by aragonite crystals improved the compressive strength of ASSB prepared by aluminum powder. In addition, the reactions of the formation and carbonation of monocarboaluminate phase were proved to be thermodynamically possible in this work. [ABSTRACT FROM AUTHOR]

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

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

Abstract This paper presents the results of a study about the mechanical behaviour, before and after aging, of two cement-based composites reinforced with long sisal fibres cured at early age in a CO 2 environment. After curing, samples of both composite systems were submitted to wetting and drying cycles to accelerate the aging of the materials allowing the evaluating of the efficiency of the CO 2 treatment. Besides promoting CO 2 capture, the used cure also allowed the increase in the durability of the sisal fibre-cement based composites by the Calcium Hydroxide (CH) consumption and pH decrease promoted by the carbonation reactions. The lime-pozzolanic material composite was also treated with CO 2 at early stages of formation, with the carbonation and pozzolanic reactions acting simultaneously to deplete the Ca(OH) 2 thus improving its durability. Four-point bending test, thermogravimetry analysis of the matrix and SEM analysis of the fibres were done before and after aging to study the durability mechanisms of the composites. The obtained results showed that the CH free cement-based composite containing metakaolin and fly ash presented the best mechanical behaviour before and after accelerated aging. The early age carbonation of the lime-pozolan composites improved its mechanical response, before and after accelerated aging, when compared with the non-carbonated samples. The thermogravimetry test showed that the increase of the carbonation time of the reference Portland cement-based composite consumed the C S H, compromising the ductility and strain capacity of this composite family after aging. The SEM pictures showed petrified fibre effect by the migration of hydrated products after 10 and 20 cycles of ageing for this composite system. [ABSTRACT FROM AUTHOR]

Abstract Understanding the changes in the pore solution upon carbonation is crucial with respect to comprehending the mechanisms of reinforcement corrosion in carbonated mortar or concrete. In this paper we used Cold Water Extraction (CWE), a rapid leaching method, on profile ground powder from partially carbonated Portland cement and Portland-fly ash cement mortars to study changes in the pore solution composition. Carbonation decreased the free alkali metal content measured with CWE, which matched with the portlandite profiles determined by thermogravimetry and the carbonation depth detected with pH indicator. The alkali metal uptake by carbonation products was confirmed by SEM-EDS and thermodynamic modelling. Besides the decrease in the alkali metal concentration in the pore solution upon carbonation, we observed for both binders a considerable increase in chlorine and sulphur concentrations. This can further accelerate corrosion in carbonated concrete. [ABSTRACT FROM AUTHOR]

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

Highlights • The impact of atmospheric marine environments on concrete is studied numerically. • A multi-species transportation model is developed for marine aerosol ingress. • Chemical interactions are modelled by a hybrid thermodynamic modelling method. • The importance of modelling the carbonation-induced water release is discussed. • The degradation mechanisms behind the marine aerosol attack are revealed. Abstract This paper presents a novel and comprehensive numerical method to study the impact of the atmospheric marine environment on cementitious materials. The transportations of moisture, aqueous and gaseous substances are modelled by a multi-species transportation model. A hybrid thermodynamic modelling method is developed to consider the chemical interactions, including carbonation, chloride binding, and other simultaneous chemical reactions. The proposed method is implemented to model the reported experiments, and the detailed degradation mechanisms are revealed. Furthermore, the significances of modelling the carbonation-induced water release and the mutual influences between carbonation and chloride aerosol attack are demonstrated. [ABSTRACT FROM AUTHOR]

Highlights • Time to carbonation-induced steel corrosion cover cracking is investigated. • Steel mass loss to initiate surface cracking increases with increase in cover depth. • Blended cement concretes required higher steel mass loss to cause cover cracking. • Higher w/b ratio concretes required longer times to cover cracking. • An empirical relationship for time to cover cracking is proposed. Abstract This paper reports on a study that was aimed at developing a coherent empirical relationship for the time to cracking of the cover concrete in a reinforced concrete structure, subjected to reinforcing steel corrosion that is induced by carbonation in an inland, urban environment in South Africa. In particular, the study considered the influence of cover depth and the quality of concrete in the cover zone on the extent of corrosion at the time of cover concrete cracking. The results of the study were then used to develop an empirical relationship to estimate the time to cover cracking and the associated extent of reinforcing steel corrosion. Test concretes were prepared using three binder types: plain Portland cement (PC – CEM I 52.5N), 70/30 PC/FA (fly ash) and 50/50 PC/GGBS (ground granulated blastfurnace slag) at relatively high w/b ratios of 0.60 and 0.95. 13.2 mm crushed granite stone and granite crusher sand were used as aggregates. RC prism specimens were prepared using 20 mm diameter high yield deformed steel bars placed at cover depths of 12 mm, 20 mm or 30 mm. Sufficient 100 mm companion concrete cube specimens were prepared for permeability, porosity tests and carbonation depth measurement. The results indicate that, as the cover depth increases, a higher extent of corrosion is required to initiate cracking at the concrete surface. Also, at the same cover depth, the higher w/b ratio concrete, which was more porous, more permeable and had lower tensile strengths, required more steel corrosion to initiate surface cracking. Blended cement concretes required a higher extent of steel corrosion to initiate cover cracking than the PC concretes. [ABSTRACT FROM AUTHOR]

Abstract Despite the importance of carbonation in many processes, still the reaction needs investigation. The reaction is essential for the effectiveness of consolidants, based on CaCO 3 forming products, used in stone conservation. Research on carbonation of two calcium alkoxides products, developed during the Nanomatch project, is presented in this paper and the results discussed and compared with those reported with the most used nanolimes. Calcium tetrahydrofurfuryloxide (Ca(OTHF) 2), dissolved in four different solvents, and calcium ethoxide (Ca(OEt) 2), diluted in ethanol, were applied on glass slides and their carbonation kinetics investigated together with their coatings after being kept in uncontrolled and controlled RH conditions (50% and 90%). This allowed to understand the evolution and the phases formed along the process. Carbonation follows the two pathways already reported for alkoxides; it is a quick process and eventually leads to the formation of the most stable crystalline phase (calcite), with high humidity favouring this final step. Alkoxides resulted thus to be suitable compounds for stone conservation, where full carbonation and formation of calcite needs to be obtained for the effectiveness of consolidation. Graphical abstract Unlabelled Image Highlights • Carbonation of new stone consolidants, calcium alkoxides products, was studied. • Carbonation follows two ways already reported for alkoxides and is a quick process. • The process ends with the formation of the most stable crystalline phase (calcite). • High humidity favours the conversion to calcite. • Alkoxides resulted suitable compounds for stone conservation. [ABSTRACT FROM AUTHOR]

Highlights • New ecological concretes made with carbonated aggregates. • Measurement of mechanical and thermal properties of eco-concretes studied. • Prediction and validation of thermal conductivity with HAC model. Abstract This paper presents a study on the effect of carbonated-aggregates on mechanical properties and thermal conductivity of eco-concretes. These carbon negative eco-aggregates are produced by accelerated carbonation where industrial by-products or incinerators' waste are combined with carbon dioxide (CO 2). These manufactured aggregates have particular characteristics giving them a certain interest in the field of civil engineering such as in replacement of natural aggregates in concrete. Morphological, physical, mechanical and thermal characterizations were performed on eco-aggregates in order to use them in the production of concrete. Then, concretes based on these carbonated-aggregates were formulated. In the experimental program, different mixtures were prepared by partially replacing natural aggregates by carbonated ones resulting in concretes with unit weights varying between 1750 and 2290 kg/m3. For all produced concrete mixes, the water to cement (w/c) ratio was kept constant. Compressive strength, modulus of elasticity, thermal conductivity, water absorption and sorptivity were measured. Results have been compared to control concrete mixes produced using ordinary aggregates and expanded clay. The results show that the tested eco-concretes have sufficient mechanical strength and interesting thermal conductivity. Therefore, they could be used for construction projects. [ABSTRACT FROM AUTHOR]

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

Abstract The in-situ carbonation of basaltic rocks could provide a long-term carbon storage solution. To investigate the viability of this carbon storage solution, 175 tonnes of pure CO 2 and 73 tonnes of a 75% CO 2 -24% H 2 S-1% H 2 -gas mixture were sequentially injected into basaltic rocks as a dissolved aqueous fluid at the CarbFix site at Hellisheidi, SW-Iceland. This paper reports the Mg stable isotope compositions of sub-surface fluids sampled prior to, during, and after the CO 2 injections. These Mg isotopic compositions are used to trace the fate of this element during the subsurface carbonation of basalts. The measured Mg isotopic compositions of the monitoring well fluids are isotopically lighter than the dissolving basalts and continue to become increasingly lighter for at least two years after the gas-charged water injection was stopped. The results indicate that the formation of isotopically heavy Mg-clays rather than Mg-carbonates are the predominant Mg secondary phases precipitating from the sampled fluids. Isotope mass balance calculations suggest that more than 70% of the Mg liberated from the basalt by the injected gas charged water was precipitated as Mg-clays, with this percentage increasing with time after the injection, consistent with the continued precipitation of Mg clays over the whole of the study period. The formation of Mg clays in response to the injection of CO 2 into basalts, as indicated in this study, could be detrimental to carbon storage efforts because the formation of these minerals consume divalent Mg that could otherwise be used for the formation of carbonate minerals and because such clays could decrease host rock permeability. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the evolution of mechanical and chemical properties of sodium silicate activated fly ash and metakaolin geopolymers in one year time scale. The initial curing protocols are considered, which were chosen based on the isothermal heat release properties of both reaction systems. Increasing initial temperature contributes to the cumulative heat release, strength development and zeolite formation of both geopolymers, especially the fly ash based, but results in slightly worse pore characteristics. The formation of zeolite is rapid, indicating a simultaneous process with geopolymerisation. During sample handling and aging, natural carbonation took place. Two kinds of carbonation processes are detected: reaction of CO 2 with mobile alkalis on the one hand and with framework oxygen atoms of the alunimosilicate gels on the other hand. [ABSTRACT FROM AUTHOR]

Blended cements are preferred to Ordinary Portland Cement (OPC) in construction industry due to costs and technological and environmental benefits associated with them. Prevalence of significant quantities of carbon dioxide (CO2) in the atmosphere due to increased industrial emission is deleterious to hydrated cement materials due to carbonation. Recent research has shown that blended cements are more susceptible to degradation due to carbonation than OPC. The ingress of CO2 within the porous mortar matrix is a diffusion controlled process. Subsequent chemical reaction between CO2 and cement hydration products (mostly calcium hydroxide [CH] and calcium silicate hydrate [CSH]) results in degradation of cement based materials. CH offers the buffering capacity against carbonation in hydrated cements. Partial substitution of OPC with pozzolanic materials however decreases the amount of CH in hydrated blended cements. Therefore, low amounts of CH in hydrated blended cements make them more susceptible to degradation as a result of carbonation compared to OPC. The magnitude of carbonation affects the service life of cement based structures significantly. It is therefore apparent that sufficient attention is given to carbonation process in order to ensure resilient cementitious structures. In this paper, an indepth review of the recent advances on carbonation process, factors affecting carbonation resistance, and the effects of carbonation on hardened cement materials have been discussed. In conclusion, carbonation process is influenced by internal and external factors, and it has also been found to have both beneficial and deleterious effects on hardened cement matrix. [ABSTRACT FROM AUTHOR]

Highlights • The detrimental effect of carbonation on the physical sulfate attack on concrete is disclosed. • A larger carbonation depth leads to greater concrete scaling by Na 2 SO 4 crystallization. • The negative effect of concrete carbonation on the concrete durability is extended. Abstract Concrete carbonation is regarded as a significant cause of reinforcement corrosion in buildings. This research paper will present another detrimental effect of concrete carbonation on the concrete durability. Concrete cylinders placed in an accelerating carbonation chamber for 10 and 20d were partially immersed in a 10% Na 2 SO 4 solution. After 28, 60, 120, and 240d exposure, the mass loss of the concrete specimens was measured, and the damage mechanism checked by means of XRD analysis, NMR, ESEM and EDS. The results showed that a larger carbonation depth in the concrete caused more concrete scaling, and that sulfate crystals were also identified in the carbonated concrete. Due to their susceptibility to carbonation, blended concretes containing fly ash and slag showed more scaling than Portland concrete. Therefore, the "physical sulfate attack on concrete" can be more accurately described as the "physical sulfate attack on carbonated concrete." [ABSTRACT FROM AUTHOR]

Highlights • MgSO 4 crystallization distress on concrete combining the carbonation is confirmed. • Concrete carbonation plays a detrimental role in the physical sulfate attack on Portland cement concrete. • The factors accelerating the concrete carbonation, such as the large W/C ratio and the cement replacement by mineral admixtures, can promote the occurrence of physical sulfate attack on concrete. Abstract Based on the definition of physical salt attack, the Guide to Durable Concrete (ACI 201.2R) suggests that MgSO 4 cannot lead to crystallization distress on concrete. In this paper, concretes consisting of 30% fly ash (FA), 20% limestone powder (LP), 50% slag (SG) and pure Portland cement (PC) were acceleratingly carbonated for 20d before being partially immersed in a 10% MgSO 4 solution. After 150d of partial exposure, MgSO 4 crystallization was attributed to the damage of the outer layer of carbonated FA, SG, LP concrete specimens in the evaporation zone. The outer layer of FA and LP concretes used as reference had also become carbonated and detached due to MgSO 4 crystallization. The test results supported the idea that MgSO 4 crystallization distress can occur in concrete through carbonation, and that concrete carbonation should be considered when analyzing physical salt attack on concrete. [ABSTRACT FROM AUTHOR]

Highlights • 'Inorganic gel casting' feasible for highly porous glass-ceramics from vitrified MSWI bottom ash. • Hardening achieved with a low molarity alkaline solution, by formation of carbonate phases. • Hardened foams transformed into glass-ceramics by low temperature sinter-crystallisation. • Leaching of heavy metals from final product remaining under the thresholds specifications. Abstract The transformation of vitrified waste, such as bottom ash from municipal waste incineration, into cellular glass-ceramics is convenient, if the additional processing is simple and inexpensive. The present paper aims at presenting a possible route to achieve this goal, based on the recently proposed mechanical foaming of alkali-activated suspensions of waste glass powders, followed by sinter-crystallization at moderate temperatures (from 800 to 900 °C). Compared to previously studied glasses, in this experiment bottom ash-derived glass suspensions underwent progressive hardening at low alkali molarity and in limited times. The firing did not alter the open-celled structure that had developed upon low temperature foaming, owing to a significant crystallization. With an overall porosity of 80%, the optimized foams exhibited a remarkable compressive strength (>6 MPa). Finally, the process had no negative impact on the leaching of toxic elements, which remained well below the thresholds for inert materials. [ABSTRACT FROM AUTHOR]

Highlights • Proposed a residual strain-based effective CO 2 diffusion coefficient. • Established a theoretical carbonation model for fatigue-damaged concrete. • Verified the theoretical carbonation model by multiple experiments. • Identified the effect of fatigue damage degree on concrete carbonation. • Identified the effect of fatigue damage gradient on concrete carbonation. Abstract This paper presents the theoretical modeling of carbonation in fatigue-damaged concrete. First, a residual strain-based effective carbon dioxide diffusion coefficient in fatigue-damaged concrete was proposed. Based on that, the general carbonation equations were established for concrete with uniform compressive, gradient compressive and gradient tensile damage patterns. Then a numerical program was written to solve the established partial differential carbonation equations. Subsequently, the numerical carbonation model was validated by comparing the predicted carbonation depths with experimental results. Finally, parametric studies were conducted on carbonation in commonly used concretes with various fatigue damage patterns, which separated the effects of residual strains and residual curvatures. The parametric studies showed that fatigue damage did not alter the widely accepted proportional relationships between carbonation depths and square roots of exposure durations. Moreover, the effects of exposure conditions on carbonation of concrete were far more influenced by residual strains than by residual curvatures. [ABSTRACT FROM AUTHOR]

Highlights: • A green ECC is developed based on MgO and fly ash through accelerated carbonation. • Compression, tension, and multiple cracking characters are evaluated. • CO 2 uptake and materials sustainability of the newly developed ECC are assessed. • ECC with 1-d carbonation achieves both environmental and technical benefits. Abstract The use of reactive magnesium oxide (MgO) is widely recognized in carbonated concrete formulations associated with permanent sequestration of CO 2. Engineered Cementitious Composite (ECC) is an advanced fiber reinforced cement-based composite with high tensile ductility and intrinsically tight crack width. In this paper, we investigate an alternative binary binding system for ECC: reactive MgO and fly ash cured with an accelerated carbonation process. Compressive strength, density, carbonation depth, tensile performance and crack pattern of the carbonated reactive MgO-based ECC were investigated at various curing ages. In addition, the CO 2 uptake and materials sustainability, in terms of energy consumption, net CO 2 emission and cost of the newly developed ECC were assessed. The objective of this research is to further advance the application of reactive MgO and utilization of CO 2 in the construction industry through novel ECC material. It was observed that carbonation curing densifies the binding system, thus leading to an increase in both compressive and first cracking tensile strengths of ECC. The tensile strain capacity of the carbonated reactive MgO-based ECC achieved up to 6% with an average crack width below 60 μm after 1-day carbonation. Compared to conventional ECC (M45) and concrete, the 1-day carbonated reactive MgO-based ECC could reduce the net CO 2 emission by 65% and 45%, respectively. It is concluded that environmental and technical benefits could be simultaneously achieved for the 1-day carbonated reactive MgO-based ECC incorporated with 50% fly ash. The findings of this research shed light on further applications of reactive MgO cement in the precast industry. [ABSTRACT FROM AUTHOR]

This paper addresses the effect of concrete carbonation on the propagation and dispersion of electromagnetic (EM) waves and the capability of two EM, non-destructive techniques to detect this pathology. A capacitive technique operating at low frequency (around 33 MHz) and a ground penetrating radar (GPR) with a 1.5 GHz antenna were tested for the monitoring of reinforced concrete structures. To better understand the phenomena involved in concrete carbonation, the results of two complementary experimental campaigns were analyzed for saturated concretes. First, the dispersion curves of complex permittivity were measured for both carbonated and non-carbonated samples by a cylindrical coaxial EM cell. Due to carbonation, the permittivity decreased and the level of dispersion reduced slightly. Second, using GPR (coupled at approximately 900 MHz) and capacitive measurements conducted on controlled slabs, it was confirmed that the real part of the relative permittivity decreased within a range of 2 at 33 MHz and a range of 1 to 900 MHz, while the radar signal amplitude increased. [ABSTRACT FROM AUTHOR]

Abstract The long-term durability and their mechanisms of alkali-activated cement based materials have remained largely elusive. In this paper, carbonation of alkali-activated slag (AAS) mortars activated by NaOH and waterglass with different alkali dosages and silicate moduli has been investigated after exposure to 3 ± 0.2% (v/v) CO 2 at 20 ± 2 °C/65 ± 5% RH for 56 days. The results show that carbonation resistance of the AAS mortars increases with increase of not only alkali dosage but also silicate modulus. In addition to the higher pore solution alkalinity and slag reaction extent, the relatively higher carbonation resistance of the AAS mortars is attributed to the lower porosity and average pore size. The loss of compressive strength for the waterglass activated slag mortars after carbonation is due to decalcification of C-A-S-H phase, whereas the carbonation of katoite contributes to the increase of compressive strength of the NaOH activated slag mortars. [ABSTRACT FROM AUTHOR]

Highlights: • Olivine and serpentine behave differently with respect to mechanical activation. • Mechanical pre-treatment is effective to activate olivine containing materials. • Combining chemical and mechanical activation is favorable to activate serpentine. • An integrated mineral carbonation process may put mechanical activation into practice. Abstract Mechanical activation is one of the most efficient pretreatment methods used to accelerate the reaction rate in the mineral carbonation technology. This paper reviews the current research related to this technique with a specific focus on three types of magnesium silicates - olivine and serpentine, and partially serpentinized olivine. First, the effects of mechanical activation on magnesium silicates are listed and compared with regard to a variety of milling conditions, including diverse energy inputs, grinding aids and mill types. Then, the existing literature determines the extents of mechanical activation, reviewed with respect to downstream carbonation processes, including direct gas/solid carbonation, direct aqueous carbonation, indirect aqueous carbonation, and indirect solid/solid mechanochemical carbonation. Finally, suggestions are made for further study on applying mechanical activation in an integrated mineral carbonation process, in order to lower the energy consumption of commercial systems. [ABSTRACT FROM AUTHOR]

Abstract Quantification of the CO 2 binding capacity of reinforced concrete is of high importance for predicting the carbonation potential and service life of concrete structures. Such information is still not available for alkali activated materials that have received extensive attention as a sustainable substitute for ordinary Portland cement (OPC)-based concrete. To address this gap, this paper evaluates the CO 2 binding capacity of ground powders of alkali activated fly ash (FA) and ground granulated blast furnace slag (GBFS) pastes under accelerated carbonation conditions (1% v/v CO 2 , 60% RH, 20 °C) for up to 180 days. The CO 2 binding capacity, the gel phase changes, and the carbonate phases are investigated with complementary TG-DTG-MS, FT-IR and QXRD techniques. Five mixtures with different FA/GBFS ratio are considered. CEM I and CEM III/B pastes are also studied to provide a baseline for comparisons. The results showed that the alkali-activated pastes have a lower CO 2 binding capacity in comparison to cement-based pastes. Furthermore, alkali-activated pastes have similar CO 2 binding capacity regardless of the FA/GBFS ratio. It was observed that the silicate functional groups corresponding to the reaction products in the pastes were progressively changing during the first 7 days, after which only carbonate groups changed. It was also found that the CO 2 bound in the alkali-activated pastes occurs to a substantial extent in amorphous form. Graphcal abstract fx1 [ABSTRACT FROM AUTHOR]

Abstract This paper presents a study on the carbonation activated binders prepared from pure calcium silicate phases, which included tricalcium silicate (3CaO.SiO 2 , [C 3 S]), β-dicalcium silicate (β-2CaO.SiO 2 , [β-C 2 S]), γ-dicalcium silicate (γ-2CaO.SiO 2 , [γ-C 2 S]), tricalcium disilicate (rankinite, 3CaO.2SiO 2 , [C 3 S 2 ]), and monocalcium silicate (wollastonite, CaO.SiO 2 , [CS]). The overall study consisted of three experimental parts, with individual focus on the following issues: (i) reaction kinetics, (ii) mechanical performance at the microscale, and (iii) mechanical performance at the macroscale. Carbonation of calcium silicate phases was found to occur in two distinct stages, namely: phase boundary controlled stage and product layer diffusion controlled stage. Theoretical solid-state reaction approach, including contracting volume model and Jander's equations were used to determine the carbonation rate constants for the calcium silicate phases. Phase boundary controlled stage was found to be dominantly dependent on the type of the starting calcium silicate phases. On the other hand, during the diffusion controlled stage the reaction rate constants were found to depend on the type of carbonation products (in this case Ca-modified silica gel and calcium carbonate). The mechanical properties of the individual microscopic phases were evaluated using nanoindentation test whereas the overall strength of the carbonated paste was evaluated using macroscale three-point bending test. Correlations between the mechanical performances and microstructural characteristics revealed the performance controlling factors of the carbonation activated binders. The higher bound water contents of the carbonated matrix tend to increase the short-term (up to 3 h) creep deformation of the matrix when subjected to constant stress. The presence of a higher proportion of poorly-crystalline forms of calcium carbonates (i.e., vaterite and amorphous calcium carbonate) were observed to increase the flexural strength but decrease the elastic modulus of the carbonated matrix. [ABSTRACT FROM AUTHOR]

Abstract This paper first introduced a numerical carbonation model (NCM) for fatigue-damaged concrete. Then, based on the NCM, a simplified carbonation model (SCM) for fatigue-damaged concrete was established, comprised of a non-damaged concrete contribution term and a fatigue damage contribution term, through Monte Carlo simulations. Both the NCM and SCM were verified by experimental results reported in the literature. Subsequently, an incremental method was proposed to consider the time-variant fatigue damage and exposure conditions. Finally, a case study was conducted, which determined that cumulating fatigue damage could have a big influence on carbonation depth evolution. Meanwhile, differences in the cumulating fatigue damage could lead to noticeable differences in carbonation depth evolution among different points in the same concrete bridge. Moreover, drastic increases of CO 2 concentration and temperature could induce relationships of carbonation depths with square roots of service times to remarkably deviate from the proportional laws widely accepted under a time-invariant environment. [ABSTRACT FROM AUTHOR]

The production of precipitated calcium carbonate (PCC) from steel slag has been proposed as a potential method of simultaneously reducing the CO 2 emissions from the steelmaking process and turning its waste stream into a valuable product. On average the production of one ton of steel results in two tons of CO 2 emissions and 600 kg of slag. Globally, more than 400 Mt of steel slag are produced annually. If all the slag were used for the production of PCC, 64 Mt CO 2 could be utilized and 145 Mt of calcium carbonate would be produced. In 2014 the research group Energy Engineering and Environmental Protection at Aalto University in Finland has designed, constructed and tested the world’s first mineral carbonation pilot plant test facility that converts steel slag and CO 2 into PCC. In batch mode the pilot plant can handle up to 20 kg of solid steel slag and 190 L of liquid solvent, and it can produce about 10 kg of calcium carbonate. The solvent can be regenerated and reused in the calcium extraction stage, which makes the process economically more feasible. Almost 80% of the calcium in the slag was extracted, while more than 70% of the CO 2 was utilized and converted into PCC. In high temperature carbonation tests, ammonia gas was detected from the flue gases. At 60 °C more than 2 vol.% of NH 3 was detected in the flue gas, and at 50 °C it was 0.65 vol.%, while at 45 °C the NH 3 concentration in the flue gas was only 0.11 vol.%. To avoid ammonia evaporation, aragonite PCC can be produced at 45 °C by optimizing the CO 2 flow rate. The paper presents the process design as well as the early results achieved from the pilot plant. The paper also presents technical challenges that occurred during the scale-up work and experiments. [ABSTRACT FROM AUTHOR]

This paper presents a study on the carbonation behaviors of hydraulic and non-hydraulic calcium silicate phases, including tricalcium silicate (3CaO·SiO or CS), γ-dicalcium silicate (γ-2CaO·SiO or γ-CS), β-dicalcium silicate (β-2CaO·SiO or β-CS), rankinite (3CaO·2SiO or CS), and wollastonite (CaO·SiO or CS). These calcium silicate phases were subjected to carbonation reaction at different CO concentration and temperatures. Thermogravimetric analysis (TGA) tests were performed to quantify the amounts of carbonates formed during the carbonation reactions, which were eventually used to monitor the degree of reactions of the calcium silicate phases. Both hydraulic and non-hydraulic calcium silicates demonstrated higher reaction rate in case of carbonation reaction than that of the hydration reaction. Under specific carbonation scenario, non-hydraulic low-lime calcium silicates such as γ-CS, CS and CS were found to achieve a reaction rate close to that of CS. Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscope (SEM) tests were performed to characterize the carbonation reaction products of the calcium silicate phases. The FTIR spectra during the early stage of carbonation reaction showed formation of calcium silicate hydrate (C-S-H) from CS, γ-CS, β-CS, and CS phases with a similar degree of polymerization as that of the C-S-H that forms during the hydration reaction of CS. However, upon further exposure to CO, these C-S-H phases decompose and eventually converted to calcium-modified (Ca-modified) silica gel phase with higher degree of silicate polymerization. Contradictorily, CS phase started forming Ca-modified silica gel phase even at the early stage of carbonation reaction. This paper also revealed the stoichiometry of the Ca-modified silica gel that formed during the carbonation reaction of the calcium silicate phases using the SEM/energy dispersive spectroscopy (EDS) and TGA results. [ABSTRACT FROM AUTHOR]

The combined effect of carbonation and chloride ingress in concrete is studied in this paper. Based on the change of the pore structure and the chemical equilibrium, a comprehensive model is proposed for this problem. A coupled simulation of the transports of carbon dioxide, chloride ions, heat and moisture is carried out. Several sets of experimental data were compared with the prediction by the numerical model developed in this paper, for its verification. Parametric study shows that the differences between the combined mechanism and the independent mechanisms are significant in many aspects. [ABSTRACT FROM AUTHOR]

Information on the effects of incorporating fine recycled ceramic aggregates on concrete's durability is very scarce. This paper presents an experimental study using aggregates sourced from crushed red clay ceramic bricks (CBAs) and sanitary ware (SWA). Different concrete mixes were produced where the fine natural aggregate fraction was partially or fully replaced (20%, 50% and 100%, by volume) by each of these materials. Shrinkage, water absorption by immersion, water absorption by capillary action, carbonation and chloride ion penetration tests were carried out. Results show that using fine CBA provides better performance in terms of water absorption by capillarity and chloride ion penetration, contrarily to shrinkage, water absorption by immersion and carbonation penetration. Using fine SWA leads to a similar performance in terms of shrinkage, but all other properties are significantly and detrimentally affected. Notwithstanding the increased water requirement due to the high absorption capacity of CBA and the formation of agglomerated particles with SWA, this paper shows that a judicious use of these materials may allow the production of adequate structural concrete; in mixes with SWA the use of superplasticizers is a very effective approach in preventing the formation of clusters, even providing a better performance than the control concrete. [ABSTRACT FROM AUTHOR]

Information on the effects of incorporating fine recycled ceramic aggregates on concrete's durability is very scarce. This paper presents an experimental study using aggregates sourced from crushed red clay ceramic bricks (CBAs) and sanitary ware (SWA). Different concrete mixes were produced where the fine natural aggregate fraction was partially or fully replaced (20%, 50% and 100%, by volume) by each of these materials. Shrinkage, water absorption by immersion, water absorption by capillary action, carbonation and chloride ion penetration tests were carried out. Results show that using fine CBA provides better performance in terms of water absorption by capillarity and chloride ion penetration, contrarily to shrinkage, water absorption by immersion and carbonation penetration. Using fine SWA leads to a similar performance in terms of shrinkage, but all other properties are significantly and detrimentally affected. Notwithstanding the increased water requirement due to the high absorption capacity of CBA and the formation of agglomerated particles with SWA, this paper shows that a judicious use of these materials may allow the production of adequate structural concrete; in mixes with SWA the use of superplasticizers is a very effective approach in preventing the formation of clusters, even providing a better performance than the control concrete. [ABSTRACT FROM AUTHOR]

• Revealing the coupling effects on chloride ion transport caused by carbonation, FT cycles, loading states and levels, temperature, and saturation. • Modelling essentially the chloride ion transport under the coupling effects of carbonation, FT cycles, loading states and levels, temperature, relative humidity, saturation and concrete deterioration. • Revealing the degradation laws of flexural capacity of the multi-factor corroded beams. Reinforced concrete (RC) structures are often exposed to coinstantaneous deterioration effects such as carbonation, chloride corrosion, freeze–thaw cycles and external loads which causing deterioration of concrete and reinforcement. This paper discussed the effects of carbonation, freeze–thaw cycles and sustained loads on chloride ion transport and proposed a chloride ion transport model taking porosity as the main coupling variate. The attenuation law of the corroded beams under coupling corrosion factors was studied. Through chloride immersion tests, it was found that applying freezing and thawing cycles and sustained tensile stress can enhance chloride transport capacity by coarsening the pores; Carbonation and low compressive stress can repress the chloride ion transport by densifying concrete, but the compressive stress beyond about 0.7 times the compressive strength and tensile stress would enhance the penetrating capacity due to the damage of the internal microstructure of concrete. Then, a comprehensive and unified theoretical model of chloride ion transport considering the coupling of carbonation, freeze–thaw cycle, sustained loading and other factors was proposed and verified by taking porosity as the main coupling variable quantity. This model could essentially explain the effects of various factors on chloride ion transport and has good consistency with the test results. Finally, the flexural bearing capacity of the corroded beams was tested, and the failure characteristics, crack characteristics, ultimate bearing capacity, load–displacement relationship and strain distribution of the corroded beams under different corrosion conditions were researched. The results show that the flexural capacity of the corroded beams suffered the coupling effects of multiple corrosion factors degrades, and the bearing capacity decreases with the increase of the corrosion degree of carbonation-freezing thawing cycles; The continuous tensile stress applied to the test beams in the corrosion process intensifying the degradation of bending bearing capacity and ductility, the continuous compressive stress increases the flexural capacity and improves the ductility slightly, but excessive compressive stress significantly degrades the flexural capacity; When chloride ions are used as the third kind of corrosive substance for coupling corrosion, the tensioned or without-load corroded beams have obvious degradation in bending bearing capacity, while the corrosion beams bearing continuous compressive stress have no obvious degradation in bending bearing capacity. [ABSTRACT FROM AUTHOR]

• Addition of GGBFS improves the carbonation resistance of calcined clay-GGBFS geopolymer. • The increase in activator modulus reduces the initial and final setting time. • GGBFS enhances the formation of amorphous phases (C-(A)-S-H/C-(N)-A-S-H) leading to better densification. • pH of hardened geopolymer pastes increases with increasing GGBFS content. • Increasing GGBFS content in binder results in lower porosity and higher compressive strength. Alkali-activated materials are obtained from the alkaline activation of a precursor rich in SiO 2 and Al 2 O 3 , which can be derived from by-products or industrial residues. Calcined clay is a potential candidate as a precursor for this type of material. Large amounts of suitable clays for alkali-activated materials are available around the world. This paper evaluated the performance of different alkaline-activated mortars using calcined clays (low grade) and ground-granulated blast-furnace slag (GGBFS), including physical and mechanical performance, reaction products phases, microstructure, and resistance to accelerated carbonation. The results indicate that the increase in GGBFS content up to 60% has a significant effect on the properties of the mortars, due to the effect of Ca-rich phases such as C-(A)-S-H/C-(N)-A-S-H, promoting the densification of the microstructure, and an increase in pH from 11.91 to 12.78 for specimens with 100% calcined clay and 60% GGBFS respectively, leading to a better carbonation resistance. On the other hand, adding GGBFS leads to a reduction in concrete initial and final setting time and lowers thermal stability compared to the reference calcined clay material. The increase in the modulus ratio of the activator from 1 to 1.5 also improves the mechanical properties and resistance to carbonation of geopolymer mortars with various binder compositions. [ABSTRACT FROM AUTHOR]

This paper evaluates the lifecycle economic and environmental benefits of implementing CO 2 utilization and storage within advanced engineered cementitious composite (ECC) railway ties. Using CO 2 -treated ECC ties can yield lifecycle benefits primarily due to enhanced material properties – increased lifespan in this case – instead of due to the stored CO 2 that would otherwise enter the atmosphere. Sequestration-based policies such as 45Q in the United States would therefore not incentivize deployment of ECC railway ties, despite their considerable CO 2 avoidance opportunities. To reach these conclusions, cradle-to-grave lifecycle models were developed for ECC ties and conventional concrete ties and evaluated under 1000 possible use-phase scenarios. The models incorporated premature tie failures – consistent with real-world observations – that were used to study a wide range of non-linear impacts arising from the random nature of tie failures and replacements. The results show that past studies that neglected premature failure of ties may have underestimated lifecycle greenhouse gas (GHG) emissions of concrete rail ties by nearly three times. Overall, servicing a track with ECC ties instead of concrete ties can reduce the lifecycle costs and GHG emissions by 12% and 21% respectively, based on median values of 1000 model run results. The expected benefits would be larger for entities like Amtrak that plan to expand concrete tie infrastructure despite significant challenges with premature concrete tie failures. The results of this study suggest that the lifespan of ECC ties needs to be at least 25% longer than concrete ties to achieve net lifecycle benefits. The possibility of this should be tested and confirmed under real-world conditions. [ABSTRACT FROM AUTHOR]

• A probabilistic analysis of the natural carbonation of RCA concretes was conducted. • RCA anticipated the failure probability by up to 100 months compared to NCA. • RCA requires an equivalent cover depth of up to 1.4 compared to NCA. Carbonation is a phenomenon that involves several uncertainties associated with concrete properties and environmental factors. However, most existing studies have adopted a deterministic approach to deal with this phenomenon, which can lead to misinterpretations. This study aimed to carry out a probabilistic analysis of natural carbonation with data collected for over 30 months of recycled coarse aggregate (RCA) concretes and natural coarse aggregate concretes (NCA), used as reference. The probabilistic analysis showed that the cover depth collected in field presented a normal distribution behavior, in this way, random variables were generated to sample cover depth values to be used in time-dependent Monte Carlo simulations. A computational algorithm was developed in MATLAB to evaluate the probability of the carbonation depth (x c) overcoming cover depths (c d) of 15-, 20-, 25-, 30-, 35-, and 40-mm, usual values in structural design. The simulations showed that the RCA anticipated the probability of failure (x c ≥ c d) by up to 100 months compared to natural coarse aggregate (NCA) concrete. The results indicated that the total replacement of NCA by RCA requires increases of up to 1.4 in cover depth to perform equivalently to the reference concrete (with NCA). Moreover, regardless of the type of aggregate and w/c ratio, with the cover depth established in the Brazilian standard for urban environments, the evaluated concrete did not reach the minimum service life of 50 years established for structural elements of reinforced concrete. The methodology applied in this paper can be used to predict the service-life considering failure due to carbonation using the statistics response of experimental data. [ABSTRACT FROM AUTHOR]

This paper develops a kind of molded disc samples to investigate the carbonation and related behaviors of hardened cement pastes under different previous hydration degrees. Weight and length changes of cement pastes over time are monitored during a multistep process including carbonation, drying, rewetting, and redrying. The combination of X-ray diffraction (XRD) and thermogravimetric analysis (TGA) is used to identify and quantify the mineral compositions of carbonated cement pastes. An exponential function between CO 2 uptake capacity and hydration time of cement pastes is established, which shows that the CO 2 uptake capacity of cement pastes decreases dramatically at the very beginning days of hydration and then remaining relatively stable as hydration time is prolonged. Two reasons for this finding are revealed: i) the equilibrium between the carbonation and the post-carbonation reaction of carbonation product, i.e., silica-alumina gel; ii) refining of pore structures by hydration products which hinders carbonation. A clearer zonation of carbonation areas is proposed, and the spatial distribution equations of CO 2 absorption are initially established. By monitoring carbonation and drying behavior of cement pastes with different hydration ages, it is revealed that carbonation reduces drying shrinkage of cement pastes especially for early-age samples, whereas drying increases carbonation shrinkage. By investigating the water changes during the multistep process, it is found that water is little released during the carbonation of C–S–H gels. New insight into mechanism of carbonation shrinkage is provided by a newly proposed model. • Molded disc and multistep aided by self-made device are used for all-round study. • Exponential function between CO 2 uptake capacity and hydration time is established. • A clearer zonation of carbonation areas is proposed. • Carbonation reduces drying shrinkage for early-age cement pastes. [ABSTRACT FROM AUTHOR]

This paper reviews the effect of incorporating recycled aggregates, sourced from construction and demolition waste, on the carbonation behaviour of concrete. It identifies various influencing aspects related to the use of recycled aggregates, such as replacement level, size and origin, as well as the influence of curing conditions, use of chemical admixtures and additions, on carbonation over a long period of time. A statistical analysis on the effect of introducing increasing amounts of recycled aggregates on the carbonation depth and coefficient of accelerated carbonation is presented. This paper also presents the use of existing methodologies to estimate the required accelerated carbonation resistance of a reinforced recycled aggregate concrete exposed to natural carbonation conditions with the use of accelerated carbonation tests. Results show clear increasing carbonation depths with increasing replacement levels when recycled aggregate concrete mixes are made with a similar mix design to that of the control natural aggregate concrete. The relationship between the compressive strength and coefficients of accelerated carbonation is similar between the control concrete and the recycled aggregate concrete mixes. [ABSTRACT FROM AUTHOR]