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Amine-based absorption is the primary contender for postcombustion CO2 capture from fossil fuel-fired power plants. However, significant concerns have arisen regarding the formation and emission of toxic nitrosamine and nitramine byproducts from amine-based systems. This paper reviews the current knowledge regarding these byproducts in CO2 capture systems. In the absorber, flue gas NOx drives nitrosamine and nitramine formation after its dissolution into the amine solvent. The reaction mechanisms are reviewed based on CO2 capture literature as well as biological and atmospheric chemistry studies. In the desorber, nitrosamines are formed under high temperatures by amines reacting with nitrite (a hydrolysis product of NOx), but they can also thermally decompose following pseudo-first order kinetics. The effects of amine structure, primarily amine order, on nitrosamine formation and the corresponding mechanisms are discussed. Washwater units, although intended to control emissions from the absorber, can contribute to additional nitrosamine formation when accumulated amines react with residual NOx. Nitramines are much less studied than nitrosamines in CO2 capture systems. Mitigation strategies based on the reaction mechanisms in each unit of the CO2 capture systems are reviewed. Lastly, we highlight research needs in clarifying reaction mechanisms, developing analytical methods for both liquid and gas phases, and integrating different units to quantitatively predict the accumulation and emission of nitrosamines and nitramines. [ABSTRACT FROM AUTHOR]

This paper presents a study of cellulose pulp fiber-cement composites subjected to supercritical carbonation at a very early age. The raw materials used for the creation of cementitious composite mixes include: Portland cement, limestone filler, and cellulose pulp. Composites were produced by a slurry vacuum dewatering process and subjected to curing conditions which studied the effect of supercritical carbonation concentration (0% and close to 100% of CO 2 ), the effect of cellulosic pulp (unbleached or bleached), and durability. All samples were subjected to mechanical, physical, and microstructural tests. The initial period of thermal curing (varying from 24 h to 48 h) and exposure time to carbonation (from 1 h to 2 h), did not have a statistically significant effect on the mechanical performance of the composites. However, the flexural test results of carbonated composites reinforced with bleached pulp showed a statistically significant improvement when compared to unbleached pulp reinforcement (24% increased average modulus of rupture). Thus, for cementitious composites cured with supercritical carbonation, the use of bleached cellulosic pulp, 24 h of thermal hydration and 1 h in an environmental chamber provided the optimal curing conditions and the most desirable properties in this study. [ABSTRACT FROM AUTHOR]

Sorptivity is broadly used for characterising the pore connectivity of cementitious materials, with applications in design for durability. A water sorptivity coefficient (WSC) is typically obtained from the ratio between the amount of absorbed water and t 0.5 . This relationship is however not linear for cementitious materials, and conventions are needed for the computation. Variable criteria in the literature complicate the comparison of WSCs. This paper proposes a new approach for describing the entire absorption process. We substantiate the hygroscopicity of calcium silicate hydrates and the effect of swelling during the process as the main causes for the anomalous capillary absorption by cementitious materials. We present a theoretical model with a single descriptive coefficient of capillary absorption progressing linearly with t 0.25 . The model fits remarkably well to experimental data, and it solves the problem of lack of linearity with t 0.5 . A full description of the transport process is then offered. [ABSTRACT FROM AUTHOR]

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

This paper presents a study on process parameters and building strategy for the deposition of Colmonoy 227-F powder by CO 2 laser with a focal spot diameter of 0.3 mm. Colmonoy 227-F is a nickel alloy especially designed for mold manufacturing. The substrate material is a 10 mm thick plate of AISI 304 steel. A commercial CO 2 laser welding machine was equipped with a low-cost powder feeding system. In this work, following another one in which laser power, scanning speed and powder flow rate had been studied, the effects of two important process parameters, i.e. hatch spacing and step height, on the properties of the built parts were analysed. The explored ranges of hatch spacing and step height were respectively 150–300 μm and 100–200 μm, whose dimensions were comparable with that of the laser spot. The roughness, adhesion, microstructure, microhardness and density of the manufactured specimens were studied for multi-layer samples, which were made of 30 layers. The statistical significance of the studied process parameters was assessed by the analysis of the variance. The process parameters used allowed to obtain both first layer-to-substrate and layer-to-layer good adhesions. The microstructure was fine and almost defect-free. The microhardness of the deposited material was about 100 HV higher than that of the starting powder. The density as high as 98% of that of the same bulk alloy was more than satisfactory. Finally, simultaneous optimization of density and roughness was performed using the contour plots. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on carbonation in fatigue-damaged concrete. Uniaxial and eccentric fatigue loads were exerted on prism specimens to obtain concrete with uniform compressive, gradient compressive, and gradient tensile damage patterns. Carbonation tests were subsequently conducted on these fatigue-damaged concrete specimens. Fatigue tests showed that while elastic modulus decreased and residual strain increased with loading cycles, stresses redistributed in eccentrically fatigued specimens, but strains maintained linear distribution at all times. Carbonation tests showed that the widely accepted proportional relationships between carbonation depths and square roots of exposure durations also applied to carbonation in fatigue-damaged concrete. Also, carbonation rates evolved linearly with residual strains in concrete with low damage gradients, and a 75% increase could be observed at a residual strain of 0.002. In addition, fatigue damage with low gradients did not significantly sway the ways that relative humidity, temperature, and carbon dioxide concentration affected carbonation of concrete. [ABSTRACT FROM AUTHOR]

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

Although the literature presents intensive studies based on monitoring cement hydration in adiabatic and semi-adiabatic environments, such as non-conventional differential thermal analysis (NCDTA) systems, studies of cement hydration in controlled climatic chambers are very rare. Using three W/C ratios (0.5, 0.6 and 0.7) and three relative humidity conditions (60, 80 and 100%) at 25 °C, the authors analyzed in real time the evolution of cement hydration reaction during the first 24 h in an environmental-controlled chamber. The main objective of this paper is to present two new developed systems of NCDTA (NNCDTA) and non-conventional TG and to show, using high-strength sulfate-resistant Portland cement pastes in a controlled chamber as application examples, how the developed systems measure on real time the thermal effects and the mass changes that occur during hydration and carbonation reactions. The captured CO mass can be quantified as it occurs by carbonation curves. The results are in agreement with the mechanical and structural properties of the used pastes and with their TG/DTG data, after being processed by different operational conditions. Carbonation for 24 h alters significantly the cement hydrated paste composition, resulting in final poor mechanical resistance properties. However, carbonation for 1 h, in specific conditions, enhances them when compared to a non-carbonated reference paste, due to a final higher content of silica and alumina hydrated phases and to a lower mass ratio between that of their combined water and their total mass as well. [ABSTRACT FROM AUTHOR]

Carbon dioxide concentration and light conditions may greatly vary between mountainous and lowland areas determining the photosynthetic performance of plants species. This paper aimed to evaluate the photosynthetic responses of Lotus corniculatus, growing in a mountain and a lowland grassland, under low and high radiation and CO concentration. Net photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO concentration were measured while the water-use efficiency and the ratio of variable to maximal fluorescence were calculated. Photosynthetic response curves to different levels of radiation and intercellular CO partial pressure were estimated. Our results showed that high radiation and CO concentration enhanced water-use efficiency of plants at both sites, enabling them to use more efficiently the available water reserves under drought conditions. The increase of radiation and CO concentration would enhance the photosynthetic performance of the mountainous population of L. corniculatus, which overall seems to express higher phenotypic plasticity. [ABSTRACT FROM AUTHOR]

Ductility is an important factor used in the design of para seismic structures. In this paper, the effect of the carbonation and the type of cement (limestone cement (CEM II) and ordinary Portland cement (CEM I)) on ductility and compressive strength of concrete is investigated. From two concrete formulations, cubic samples of size 10 cm,10 cm and 10 cm) and beam samples of size (10 cm,10 cm and 40 cm) were made and subjected to the accelerated carbonation test over several periods for this purpose. The cubic samples were used for measurements of carbonation depths and compressive strength, beam samples were made for measurements of carbonation depths and displacement ductility. Based on these experiments, the results show that displacement ductility is reduced by carbonation. On the other hand, the compressive strength increases with the duration of exposure to carbonation. Moreover, for concrete formulated with Portland cement (CEM I), it is noted that the rate of reduction of the displacement ductility coefficient is 30% for the 7th day of exposure to accelerated carbonation for the carbonated samples compared to the control samples. However, the concrete samples formulated with calcareous additions cement (CEM II), the reduction rate of the displacement ductility coefficient is only 14% for the carbonated samples compared to the control samples. The results obtained show that the compressive strength, increases with the duration of exposure to carbonation for the two concretes and it is more important for the concrete with ordinary Portland cement, the rate of increase is about 12%. Hence, the carbonation decreases the service life of reinforced concrete structures mainly their ductility capacity and consequently their resistance against seismic actions. [ABSTRACT FROM AUTHOR]

As the low content of calcium-bearing components in demolished recycled fine aggregates (RFA) significantly limits the carbon dioxide (CO2) curing efficiency, the effects of pre-soaking demolished RFA with calcium source solutions before the curing process are presented in this paper. Effects of varied types of calcium source solutions, including calcium hydroxide (CH), calcium chloride (CL) and calcium nitrate (CN) on the curing process are investigated. In addition, the influence of the other two parameters pertaining to curing conditions, namely, the carbon dioxide pressure and curing temperature, on the curing process are also studied. The experimental results show that, after the pre-soaking and curing process, the values of powder content, water absorption and crush value are all decreased for RFA. Furthermore, the compressive strength of mortars at 28 d are increased by as much as 56%. In addition, CN pre-soaking allows the RFA to achieve the lowest water absorption, and CL pre-soaking enables the mortars to obtain the highest compressive strength at 28 d; increasing gas pressure brings about a minor improvement in the properties of RFA and mortars, and curing temperature has complex effects on the carbonation reactions. [ABSTRACT FROM AUTHOR]

This paper investigated the performance and environmental impacts of reactive magnesia cement (RMC)-based formulations containing pulverized fuel ash (PFA) and ground granulated blast furnace slag (GGBS). Concrete samples, whose binder component was composed of RMC with 0–50% PFA and GGBS replacement were subjected to carbonation curing for up to 28 days. The performance of each sample was analyzed and compared to corresponding Portland cement (PC)-based samples via porosity, water sorptivity, compressive strength and thermal conductivity measurements. The performance results were supported with the assessment of the environmental impact of each sample throughout their production and utilization phases. Samples in which 50% of the binder component was replaced by PFA indicated the highest strength development, reaching strengths as high as 60 MPa at 28 days, which were 33% higher than those of the corresponding RMC control sample. The advantageous strength gain demonstrated by RMC-PFA samples was associated with a reduction in sample porosity due to the filler effect of PFA as well as the formation of strength providing phases through the hydration and carbonation reactions. The use of both PFA and GGBS decreased the environmental impacts of RMC formulations, which was reflected as lower CO 2 emissions, as well as reduced damage on human health and eco-system quality when compared to RMC and PC samples. The environmental efficiency calculations involving a combination of the net CO 2 emissions and mechanical performance of each sample revealed the benefits of supplementary cementitious materials within RMC formulations. [ABSTRACT FROM AUTHOR]

In this paper, the supercritical carbonation process of cement-based materials is modelled by introducing a random porosity field to simulate the heterogeneous geometry of the carbonation profile. The suitability of two different random fields of porosity, based on the probability density function (PDF) and the ellipsoidal autocorrelation function (EAF) methods, are investigated, respectively, in simulating the distribution of porosity in cement mortar. After incorporating the above random fields into an established supercritical carbonation model, it is found that with some modifications, the EAF method with consideration of spatial correlation produces better simulation of the irregularities of the carbonation zones that have been observed from experimental results. It is also found that for given average porosity and coefficient of variation, the predicted average and maximum carbonation depths have much smaller coefficients of variation. The validated EAF supercritical carbonation model is then used in parametric studies that are conducted to assess the effect of various factors on the carbonation depth of the chemical process. [ABSTRACT FROM AUTHOR]

This paper presents a study on rapid hardening behaviors of β-CS by accelerated carbonation curing. β-CS cubes compacted at various molding pressures were subjected to different CO concentration for accelerated carbonation curing. The CO uptake and microstructure changes were analyzed by thermogravimetric analysis (TG), QXRD, FT-IR and MAS-NMR. The results indicated that CO uptake was affected by molding pressure and CO concentration seriously. TG analysis indicated that the carbonation reaction was rapid in the first hour. The carbonation degree reached 21.6% and giving a compressive strength of 85.7 MPa after 6 h carbonation in 99.9% CO concentration. And it showed a much less carbonation degree in 20.0% CO. Calcite, vaterite and amorphous silica-rich phase formed in the carbonation progress. The FT-IR and NMR analysis indicated β-CS was decalcified to C-S-H gel and further decalcified to formation of an amorphous silica gel composed of Q and Q silicate tetrahedral. The chain length of C-S-H gel increased from to 2.67 to 6.36 with prolonged carbonation time, showing a lower C/S ratio and higher polymerization and also resulting in a lower C-S-H content. [ABSTRACT FROM AUTHOR]

Supplementary cementitious materials (SCMs) like fly ash (FA) and blast furnace slag (BFS) are normally used to replace parts of Ordinary Portland cement (OPC) to reduce the cost and CO 2 emission. During the carbonation, a relatively high amount of C-S-H with low Ca/Si ratio will be carbonated in cement paste blended with SCMs. Therefore, it’s very important to figure out the influences of the carbonation of C-S-H on the pore structure of SCMs blended cement paste. In this paper, Mercury Intrusion Porosimetry (MIP) are used to determine the pore volume and size distribution of capillary pores. Results reveal that carbonation of most of the species of C-S-H results in increased porosity of cement paste. Total and effective capillary porosity of pastes blended with high amount of BFS increase after carbonation. This will bring adverse effects on the durability of blended cement concrete exposed to the carbonation. [ABSTRACT FROM AUTHOR]

In many cases, service life of reinforced concrete structures is severely limited by chloride penetration until the steel reinforcement or by carbonation of the covercrete. Water repellent treatment on the surfaces of cement-based materials has often been considered to protect concrete from these deteriorations. In this paper, three types of water repellent agents have been applied on the surface of concrete specimens. Penetration profiles of silicon resin in treated concrete have been determined by FT-IR spectroscopy. Water capillary suction, chloride penetration, carbonation, and reinforcement corrosion in both surface impregnated and untreated specimens have been measured. Results indicate that surface impregnation reduced the coefficient of capillary suction of concrete substantially. An efficient chloride barrier can be established by deep impregnation. Water repellent surface impregnation by silanes also can make the process of carbonation action slow. In addition, it also has been concluded that surface impregnation can provide effective corrosion protection to reinforcing steel in concrete with migrating chloride. The improvement of durability and extension of service life for reinforced concrete structures, therefore, can be expected through the applications of appropriate water repellent surface impregnation. [ABSTRACT FROM AUTHOR]

This study investigated the factors affecting the carbonation of alkali-activated slag concrete (AASC). Concrete durability plays an important role in the longevity of concrete structures, but aggressive chemical agents can leave major undesirable impacts on the durability of concrete. One of such chemical agents is CO 2 gas, whose penetration into concrete leads to a carbonation process which facilitates the electrochemical corrosion of steel reinforcements. One of the weaknesses of alkali-activated slag concrete in comparison with Portland cement concrete is its lower resistance against carbonation. Thus, in this paper, we studied the effect of such parameters as alkaline solution to slag ratio, partial replacement of slag with microsilica, compressive strength, and curing method on the carbonation of alkali-activated slag concrete. The samples were subjected to accelerated carbonation by being placed in a CO 2 gas chamber for two cycles of 14 and 28 days, and then the resulting depth of carbonation was measured and analyzed. A sample of ordinary Portland cement concrete was used as the control sample. The SEM images taken from the samples were studied to determine the changes in the structure of the cement paste. The results showed that the replacement of 15% of slag with microsilica has a significant positive effect on the carbonation depth of alkali-activated slag concrete. Compared with the exponential relationships offered for ordinary concrete in the literature, the relationship between compressive strength and carbonation depth of AAS concrete was linear. The results showed that carbonation depth decreases with increase in compressive strength and decrease in AAS concrete permeability. [ABSTRACT FROM AUTHOR]

This paper proposes a novel CO 2 capture technology from the integration of partial oxy-combustion and the Calcium-Looping capture process based on the multicycle carbonation/calcination of limestone derived CaO. The concentration of CO 2 in the carbonator reactor is increased by means of partial oxy-combustion, which enhances the multicycle CaO conversion according to thermogravimetric analysis results carried out in our work, thus improving the CO 2 capture efficiency. On the other hand, energy consumption for partial oxy-combustion is substantially reduced as compared to total oxy-combustion. All in all, process simulations indicate that the integration of both processes has potential advantages mainly regarding power plant flexibility whereas the overall energy penalty is not increased. Thus, the resulting energy consumption per kilogram of CO 2 avoided is kept smaller than 4 MJ/kg CO 2 , which remains below the typical values reported for total oxy-combustion and amine based CO 2 capture systems whereas CO 2 capture efficiency is enhanced in comparison with the Calcium-Looping process. [ABSTRACT FROM AUTHOR]

In this paper, a novel composite La 0.9 Ca 0.1 Fe 0.9 Nb 0.1 O 3-δ /Sc 0.2 Zr 0.8 O 2−δ (LCFNb/ScSZ) is developed and investigated as a fuel electrode candidate for direct electrolyzing carbon dioxide (CO 2 ) in solid oxide electrolysis cells (SOECs). XRD patterns of LCFNb powder sintered in CO 2 at 850 °C for 10 h indicate that no secondary phases are found during the heat treatment and linear thermal expansion results prove that the LCFNb is compatible with ScSZ electrolyte used in this work. The electrolyser with porous LCFNb membrane cathode fabricated by infiltration method shows impressive electrochemical performance. The current density of 1.97 A/cm 2 at 2.0 V at 800 °C is obtained. The polarization resistance Rp of the SOEC decreases with the increase of the applied voltage between the electrodes. The obtained lowest Rp is as low as 0.113 Ω cm 2 at 2.0 V and this value is much lower than its many other perovskite and nickle-based counterparts. Besides, the LCFNb/ScSZ cathode shows excellent stability in pure CO 2 at different applied voltage, especially at 2.0 V. Furthermore, the LCFNb/ScSZ electrode exhibits the current efficiencies close to theoretical ones for CO 2 electrolysis, indicating that the LCFNb/ScSZ composite ceramic is an excellent cathode for zirconia-based high temperature electrolyser. [ABSTRACT FROM AUTHOR]

The granite processing industry, due to its sawing and polishing activities, is responsible for producing an enormous quantity of granite powder waste, herein referred to as granite industry by-product (GIB). GIB is a hazardous pollutant that poses a threat to ecosystems, thus emphasizing the urgent need to find a sustainable and technologically viable way of utilizing GIB and thereby minimizing its risks. The paper aims to assess the feasibility of GIB as a possible sand replacement in the manufacturing of concrete. At a 0.50 water-to-cement ratio (w/c), feasibility studies were performed and analyses were done for 10, 25, 40, 55, and 70% sand replacement by GIB in the manufacturing of concrete. Strength and durability of concrete with different percentages of GIB particles were ascertained by comparing the results of compressive strength, flexural strength, abrasion, shrinkage, permeability, carbonation, acid attack, chloride penetration, and corrosion tests with the results from a control concrete. Test results were ably explained by using auxiliary analyses such as scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The encouraging results proved the suitability of GIB concrete as a sustainable construction material. Optimal replacement level of river sand by GIB was found to be 25%. [ABSTRACT FROM AUTHOR]

This paper reports for the first time the stabilization of soil using olivine and the application of novel techniques utilizing alkaline activation and carbonation. A rigorous study addressed the effect of carbon dioxide pressure and alkali concentration (10-M sodium hydroxide soil additions from 5 to 20%) between 7 and 90 days. Microstructural and compositional changes were evaluated using microscopic, spectroscopic, and diffraction techniques. Results demonstrate the advantages of using olivine in the presence of NaOH and the associated increases in soil shear strength of up to 40% over 90 days. Samples subjected to carbonation for a further 7 days led to additional increases in soil strength of up to 60%. Microstructural investigations before and after carbonation attributed the strength development to the formation of Mg(OH)2, hydrated magnesium carbonates, and M─S─H, A─S─H gel phases. The impact of this work is far reaching and provides a new soil stabilization approach. Key advantages include significant improvements in soil strength with a lower carbon footprint compared with lime or cement stabilization. [ABSTRACT FROM AUTHOR]

In majority of exposure environments for concrete structures, there is a high probability of the cyclic occurence of both chloride ingress and carbonation. This paper reports a detailed investigation on the influence of carbonation on both the ingress and distribution of chlorides in three different types of concretes, by comparing results from exposure to chlorides, chlorides before carbonation and chlorides after carbonation. Concretes studied were of 0.55 water-binder ratio with 100% Portland Cement (PC), 70% PC + 30% pulverized fuel ash (PFA) and 85% PC + 10% PFA + 5% microsilica (MS) as binders. Chloride profiles were compared to assess the effects of all variables studied in this research. The effect of carbonation was quantified by measuring the consumption of hydroxyl ions (OH − ), air permeability and chloride migration coefficient. The results indicated that carbonation of concrete increases chloride transport, but the precise nature of this is dependent on the combined regime as well as the type of binder. In general, it was found that carbonation of chloride contaminated concretes results in a decrease of their chloride binding capacity, that is it releases the bound Cl − in concretes and pushes chlorides inwards, as has been established previously by other researchers. However, it is established in this research that the combined regimes detrimentally affect the service life of concrete structures, particularly when chloride induced corrosion is a concern. [ABSTRACT FROM AUTHOR]

The replacement of sulfate minerals by calcium carbonate polymorphs (carbonation) has important implications in various geological processes occurring in Earth surface environments. In this paper we report the results of an experimental study of the interaction between anhydrite (100), (010), and (001) surfaces and Na2CO3 aqueous solutions under ambient conditions. Carbonation progress was monitored by glancing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). We show that the reaction progresses through the dissolution of anhydrite and the simultaneous growth of calcite. The growth of calcite occurs oriented on the three anhydrite cleavage surfaces and its formation is accompanied by minor vaterite. The progress of the carbonation always occurs from the outer-ward to the inner-ward surfaces and its rate depends on the anhydrite surface considered, with the (001) surface being much more reactive than the (010) and (100) surfaces. The thickness of the formed carbonate layer grows linearly with time. The original external shape of the anhydrite crystals and their surface details (e.g., cleavage steps) are preserved during the carbonation reaction. Textural characteristics of the transformed regions, such as the gradation in the size of calcite crystals, from ∼2 µm in the outer region to ∼17 µm at the calcite-anhydrite interface, the local preservation of calcite crystalographic orientation with respect to anhydrite and the distribution of the microporosity mainly within the carbonate layer without development of any significant gap at the calcite-anhydrite interface. Finally, we compare these results on anhydrite carbonation with those on gypsum carbonation and can explain the differences on the basis of four parameters: (1) the molar volume change involved in the replacement process in each case, (2) the lack/existence of epitactic growth between parent and product phases, (3) the kinetics of dissolution of the different surfaces, and (4) the chemical composition (amount of structural water) of the parent phases. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation of the strength, permeability, abrasion, carbonation, and shrinkage characteristics of concrete containing various percentages of copper tailing as partial replacement of natural fine aggregates. M 25 Grade concrete was designed as per specific national specifications. Copper tailing was used to replace natural sand in the range of 0-80%. It was observed that the copper-tailing concrete with up to 80% substitution exhibited a comparable compressive and flexural strength when compared to the control specimens. From the abrasion test, it was noted that the specimens could be implemented in general-purpose and heavy-duty floor tiles. The shrinkage strains, water permeability, and carbonation of copper-tailing concrete were observed to be increasing with increasing replacement amounts of copper tailing. The concrete containing copper tailing replacing up to 70% of natural fine aggregates could be recommended for all applications, and substitution levels beyond 70% could be recommended for nonstructural applications, pavements, etc. [ABSTRACT FROM AUTHOR]

Mineral carbonation is one of the ways to reduce carbon dioxide gas in the atmosphere, which has attracted industrial and academic interest for its permanent storage of CO 2 with no leakage of threat. This paper focuses on development of new energy-saving and economic alkali sources for seawater decalcification by mineral carbonation process, with which not only carbon dioxide could be sequestrated, but also the calcium ions in the seawater could be removed. Magnesium hydroxide was firstly tested as the alkali source in a simple Ca 2 + ,Mg 2 + //Cl − -H 2 O system, showing the ability of assisting in the decalcification according to the monitor of calcium ions concentration in solution and the analytical results of the sediments using XRD and SEM. This innovative approach permits the use of moderate temperature and pressure conditions in the process of seawater decalcification with mineral carbonation and the production of pure CaCO 3 with a potential sale value. Then it is inspired that the brine pretreatment waste of soda ash plant, mainly containing Mg(OH) 2 and CaCO 3 , may act as the alkali source. Therefore, the seawater decalcification processes using the brine pretreatment waste of soda ash plant as alkali source by CO 2 were carried out. [ABSTRACT FROM AUTHOR]

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

Accelerated carbonation curing (ACC) is a new technique for curing of concrete that entails sequestering carbon dioxide (CO 2 ) gas into freshly cast concrete, resulting in the improvement of physico-mechanical properties and durability characteristics of concrete. This paper presents the results of an experimental study conducted to evaluate the effects of carbonation pressure and duration on the CO 2 uptake and evolution of strength of a concrete mixture. Concrete specimens were cured under six ACC pressures varying from 10 to 60 psi, applied for a duration of 1–10 h in a closed chamber. The effectiveness of varying ACC pressure and duration on the properties of concrete was assessed by measuring compressive strength gain, CO 2 uptake, morphology and mineralogy of concrete. It was noted that ACC at 60 psi (414 kPa) for 10 h resulted in the maximum strength gain and CO 2 uptake, leading to a post-ACC compressive strength of more than 200% of the pre-ACC strength, and a CO 2 uptake of about 11% by mass of cement. Finally, the analysis of variance of the experimental data indicated that the duration of ACC controls the concrete properties more than the pressure used for ACC. [ABSTRACT FROM AUTHOR]

In this paper, we show the effects of subducted carbonates on geochemical processes during subduction-zone metamorphism (SZM) through the study of an eclogite-facies marble coexisting with metabasite from the ultrahigh pressure metamorphic belt of the Chinese Western Tianshan orogen. Between the marble and metabasite is a titanite-rich contact resulting from fluid-facilitated metamorphic reactions between the two lithologies, and recording elemental changes of geodynamic significance. Because this titanite-rich contact is dominated by titanite (an important host for high field strength elements, HFSEs) without white micas (an important host for large ion lithophile elements, LILEs), HFSEs are largely conserved in titanite whereas LILEs are moved away. This observation emphasizes the potential significance of subducting carbonate in retaining HFSEs in the slab through the formation and stabilization of titanite, contributing to the characteristic “arc signature” unique to subduction-zone magmatism (i.e., high LILEs, low HFSEs). The implicit assumption in this interpretation is that the observed lithological assemblage represents residues of subducting oceanic crust that has undergone major episodes of dehydration. Subducted carbonates also have significant implications for the origin of mantle isotopic heterogeneity as revealed from oceanic basalts. [ABSTRACT FROM AUTHOR]

This paper presents a study carried out on concrete made with seven Tunisian cements with varying limestone filler content (binders) and manufactured on an industrial scale. The purpose of the study is to promote portland-limestone cement in countries where these cements are not usually used. The mechanical aspects of the concrete's behavior were examined over a period of 3 days to 1 year. Permeability and accelerated and natural carbonation as a function of initial curing time were also studied over periods that were occasionally even longer. The results show that limestone filler does have a beneficial action on some properties, such as strength at early age, but is less beneficial for other properties, such as carbonation. However, the addition of limestone filler leads to concretes of entirely acceptable properties for current uses, certainly if filler content does not exceed 25%, and if optimized grinding of binders is conducted. [ABSTRACT FROM AUTHOR]

The mineral sequestration using waste products is a method of reducing CO2 emissions that is particularly interesting for major emitters and producers of mineral wastes, such as iron and steel industries. The CO2 emissions from iron and steel production amounted to 6,181.07 kt in 2014 (PNIR 2016). The aforementioned industry participates in the EU emission trading system (EU ETS). However, blast furnace processes produce mineral waste - slag with a high content of CaO which can be used to reduce CO2 emissions. Metallurgical slag can be used to carry out direct (a one-step process) or indirect (two-stage process) process of mineral sequestration of carbon dioxide. The paper presents the degree of carbonation of the examined samples of granulated blast furnace slags defined by the six-digit code (10 02 01) for the waste and the respective two-digit (10 02) chapter heading, according to the Regulation of the Minister of the Environment of 9 December 2014 on the waste catalogue. The carbonation process used the direct gas-solid method. The slags were wetted on the surface and treated with CO2 for 28 days; the obtained results were compared with the analysis of fresh waste products. The analyzed slags are characterized by a high content of calcium (nearly 24%), while their theoretical binding capacity of CO2 is up to 34.1%. The X-ray diffraction (XRD) analysis of the phase composition of slags has revealed the presence of amorphous glass phase, which was confirmed with the thermogravimetric (DTA/TG) analysis. The process of mineral sequestration of CO2 has resulted in a significant amount (9.32%) of calcium carbonate - calcite, while the calculated degree of carbonation of the examined blast furnace slag is up to 39%. The high content of calcium, and a significant content of CaCO3-calcite, has confirmed the suitability of the discussed waste products to reduce carbon dioxide emissions. [ABSTRACT FROM AUTHOR]

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

In a series of our previously published papers, we reported a broad range of experiments and theoretical studies devoted to the interaction of carbon dioxide with the anatase titania surface. In the current study, we demonstrate oxygen mobility between gaseous carbon dioxide and solid natural clay minerals. This surprising feature implies that such behaviour is typical not only for titania but also for oxides with different chemical composition and structure. The oxygen mobility was demonstrated by the interaction of isotopically labelled carbon dioxide – C 18 O 2 – with the mineral surfaces. In most cases, we observed rapid oxygen exchange between the gas and the mineral. It was therefore discovered that carbon dioxide is more active than was previously thought because it exchanges its oxygen atoms with inorganic surfaces. Moreover, this feature seems to be very significant in natural clays of various compositions. This finding points not only towards high activity of CO 2 but also towards high surface reactivity of clays, which are quite common surface minerals on Earth and other planets. [ABSTRACT FROM AUTHOR]

Dolomite is an alternative material for producing precipitated calcium carbonate (PCC) particles, which have widespread industrial applications depending on their morphology and particle sizes. These properties are readily controlled by the production conditions such as reaction time, temperature, stirring speed, and CO 2 flow rate. In this paper, we investigate the influences of these experimental conditions on the production of synthetic aragonite crystals from dolomite using a leaching carbonation process. The proposed process is believed so be more eco-friendly than other methods suggested in the literature because the CO 2 released from the dolomite during the leaching stage is stored for use in the carbonation stage. The experimental results indicate that the morphology of the produced PCC is influenced not only by the reaction time and temperature, but also the stirring speed and CO 2 flow rate. The required reaction time decreases with an increase in the CO 2 flow rates. However, calcite forms along with the aragonite crystals at higher CO 2 flow rates. We successfully synthesized pure aragonite crystals in the reaction temperature range of 40–70 °C at a fixed CO 2 flow rate of 3.00 l/min, and at a stirring speed of 750 rpm. The d 90 values of the aragonite crystals at various temperatures ranged from 18.47 to 25.99 μm. We fit the experimental results by a single-term exponential model. Additionally, we obtained a Mg-rich solution and CO 2 gas as by-products, which are in high demand. [ABSTRACT FROM AUTHOR]

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

Disposal of stone wastes has become one of the major environmental problems in the world. The use of marbles, granites and sandstones as a building material has increased and the disposal of unused stones possess a severe threat to the society. Every year tonnes of stone wastes have been generated, and it was estimated that almost 25% of stone goes as wastes while processing and cutting them. Over the years, the quarrying area has expanded, and the use of modern machinery had led to the cutting of hardest of stones and exposing the soft underbelly of sandstones. One of the possible solutions for the utilisation of these sandstone wastes is to incorporate them into cement concrete as the replacement for natural coarse aggregates. This paper presents the results of experimental research to examine the suitability of quartz sandstone as a substitute for natural coarse aggregates in cement concrete. The quartz sandstone wastes were used in definite percentages and replaced for coarse aggregates from 0% to 100% at every 20% interval. The article presents with tests such as pull off strength, carbonation, sulphate attack, porosity and extended results of compressive strength, flexural strength. It was observed that the compressive strength, flexural strength and the sulphate attack resistance were lower than that of control concrete; but upto a certain level of replacement, they showed better resistance to pull off and carbonation. Also, the decrease in strength was found to be comparable to that of control specimens. It was concluded that there is a propitious future for the use of quartz sandstone wastes as a partial substitute for natural coarse aggregates in concrete, which can lead to a greater environmental and sustainable benefits. [ABSTRACT FROM AUTHOR]

In this paper, cyclic voltammetry technique, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and Mott-Schottky measurement combined with surface morphology observation were applied to investigate the electrochemical behavior of carbon steel (CS) and three Cr modified low alloy steels in the carbonated cement extract solution. Results show that pH plays an important role in the formation of passive films on steel rebars. In non carbonated cement extract solution, corrosion behaviors of CS and Cr modified steel vary slightly, and Cr addition brings down the amount of defects in passive film. In carbonated cement extract solution, pitting potential shifts negatively as pH value decreases. Polarization resistance declines and the density of the current carrier in the passive film increases. With Cr content increasing, corrosion current density declines; pitting potential, polarization resistance and passivation range are magnified. Besides, the effect of Cr is more significant in lower pH. The good-to-poor sequence of corrosion resistance is: 5Cr > 3Cr > 1.5Cr > CS, and 5Cr steel possesses the best corrosion resistance. [ABSTRACT FROM AUTHOR]

NaNO3 modified MgO sorbents have a large theoretical CO2 capture capacity, but their practical capture performance at medium temperatures (350-400 °C) is poor for the high thermodynamic equilibrium partial pressure of CO2 at these temperatures. The thermodynamic limitations for NaNO3 modified MgO sorbents can be relaxed by adding alkali or alkaline earth carbonates, and the effective carbonation temperature can be shifted to the higher temperatures (350-400 °C) to satisfy the requirement of fast kinetic reactions. In this paper, the CO2 absorption characteristics of NaNO3 modified MgO with or without CaCO3 are compared experimentally to verify the promoting effects of CaCO3. Based on the CaCO3 promoting theory, the methods of stage heating during carbonation and partial decomposition during regeneration were adopted to improve the CO2 absorption ability of NaNO3 modified MgO sorbents at 350 °C. Combined with the composition of fuel gas, effects of increasing CO2 partial pressure and H2O were tested, and they both accelerated the carbonation rates of the sorbents, which forecasted the application potential of NaNO3 modified MgO sorbents. [ABSTRACT FROM AUTHOR]

[Display omitted] • A mineral-carbonation-based process is used for the synthesis of nanosized amorphous CaCO 3. • The synthesis of alkanolamine-based DESs with improved CO 2 delivery properties is reported. • DES-H 2 O systems act as inhibitors in the crystallization pathway. • Size- and morphology-controlled synthesis of CaCO 3 nanoparticles is achieved via DES-H 2 O systems. This paper proposes a novel synthesis method for nanosized amorphous CaCO 3 based on advanced mineral carbonation using the macromolecular properties of deep eutectic solvents (DESs). DESs are generally synthesized by mixing hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs), and their properties vary depending on the HBDs and HBAs used for the synthesis. To synthesize DESs with CO 2 -philic properties, monoethanolamine (MEA) was selected as the HBD because it possesses a CO 2 -active site. However, alkanolamine-based DESs are difficult to use in practical applications because of their high viscosity following CO 2 absorption. To mitigate the onset of high viscosity, H 2 O was added to the synthesized DESs, with the molar ratio HBA:HBD:H 2 O as 1:5:10 and 1:5:15. In the proposed process, CO 2 was captured by the DESs-H 2 O system and converted into particle-size- and morphology-controlled CaCO 3. Nanosized amorphous CaCO 3 (ACC) with average particle sizes of 38.1 and 48.0 nm was formed by DESs based on the molar ratio of 1:5:10. The results demonstrated the need for an adequate ratio of H 2 O to DES to form nanosized ACC, implying that the strength of hydrogen bonding in DES-H 2 O systems is the primary factor affecting the performance of the solvent. The DES-H 2 O systems with inter- and intramolecular hydrogen bonding inhibited the crystallization of CaCO 3. The findings of this study are applicable to CO 2 utilization processes designed for the production of nanosized ACC. [ABSTRACT FROM AUTHOR]

• Modifications of the microstructure due to carbonation seems to be limited to intra-granular porosity. • The segmented 3D image allows determining the macroscopic diffusivity tensor. • CO 2 diffusion coefficient depends mainly on the inter-granular porosity network. Recycled aggregates compacted in road layers are made of a majority of concrete aggregates which can mineralize atmospheric CO 2. Previous studies showed that carbonation modifies the microstructure of recycled concrete aggregates, but little information is available in the case of compacted recycled aggregates. Furthermore, carbonation kinetics depends on CO 2 diffusion through the compacted material, which is linked its microstructure. This paper presents an investigation of the evolution of both microstructure and CO 2 diffusion coefficient of compacted recycled aggregates during carbonation in two different environments by X-ray tomography. Segmented 3D images were analyzed to fully extract resolved pore structures. In addition, the CO 2 diffusion coefficient variations were investigated by calculating the macroscopic diffusivity tensor in the segmented 3D images. We show that the numerical results are very similar to previous experimental results from gas diffusion tests and that the diffusivity coefficients can be estimated by using only the larger pore network (pore size > 5.5 µm). These findings suggest that nondestructive imaging approaches, such as micro-Computed Tomography (µCT), are a relevant alternative to experimental characterization methods. [ABSTRACT FROM AUTHOR]

Fibre and textile-reinforced mortars are increasingly being used for a variety of building applications, including the strengthening of masonry structures. Lime mortars reinforced with sustainable fibres (such as vegetable or cellulosic fibres) may provide an interesting solution. In this paper, a mixture of commercial lime with 20% metakaolin addition was used to produce composites reinforced with non-woven flax fabrics that were cured at different moisture contents (from 0 to 100%) for 7 or 14 days in a CO 2 incubator. The composites were characterised to determine their flexural behaviour, carbonation level and microstructure. According to the results, no differences exist in the flexural strength of the composites made in the moisture range of 33%–66%. At 7 days of curing, they attained Modulus of Rupture (MOR) values that exceeded 5.5. MPa. Moreover, it was observed that under high moisture conditions, the permeability of the fibres allows for CO 2 access, despite the saturation of the pores of the matrix – allowing a reaction in the vicinity of the fibres –, while under dry conditions, the fibre's moisture retention does not permit the carbonation of the matrix in their vicinity, even though complete carbonation takes place after 14 days. [ABSTRACT FROM AUTHOR]

[Display omitted] • The BSE-IA and EDS analysis were employed for characterize the ITZs of RAC. • Aggregate enhancements could take obviously strengthening effect on ITZs. • Soaking RCA in CEM-SF slurries had a better improvement effect on ITZs. • The Ca/Si atomic ratio of ITZs was reduced after enhancement of RCA. Recycled concrete aggregate (RCA) enhancement is an important method to improve the performance of recycled aggregate concrete (RAC). However, the quantitative studies on the change of microstructure of interfacial transition zones (ITZs) were few and far, especially after enhancement of RCA with different methods. This paper investigated the influence of carbonation enhancement (carbonation time, soaking in CH saturated solution and then carbonation) and chemical enhancement (respectively soaking in Na 2 SiO 3 saturated solution and cement-silica fume (CEM-SF) slurries) of RCA on the change of microstructure of ITZs (including the ITZ between old aggregate-new paste (ITZ 1) and ITZ between old paste-new paste (ITZ 2)) in RAC. The porosity, the un-hydrated cement particles (UH) content, the volume fraction of hydration products (VFHP) in ITZs and the width of ITZs were obtained by backscattered electron imaging analysis (BSE-IA) and energy dispersive spectrometer (EDS) analysis. Results showed that the carbonation enhancement of RCA could not effectively strengthen ITZ 1. However, soaking RCA in Na 2 SiO 3 saturated solution and CEM-SF slurries could decrease the porosity and the UH content, develop the VFHP, and reduce the width of ITZ 1 , then strengthening ITZ 1. Both carbonation and chemical enhancement could take obviously improvement on ITZ 2. Additional calcium sources could be added to RCA by soaking in CH saturated solution, improving the effect of carbonation enhancement of RCA. Soaking in CEM-SF slurries had a better improvement effect on ITZs. After RCA was soaked in CEM-SF slurries, the porosity in ITZ 1 and ITZ 2 decreased by 36.8% and 44.0%, the UH content of ITZ 1 and ITZ 2 decreased by 22.6% and 53.6%, the VFHP of ITZ 1 and ITZ 2 increased by 22.6% and 20.9%, and the width of ITZ 1 and ITZ 2 decreased by 42.9% and 50%. EDS analysis showed that the Ca/Si atomic ratio of ITZs was reduced after RCA enhancement, which generated more hydration products and then decreased the porosity and the width of ITZs. [ABSTRACT FROM AUTHOR]

• Magnesia refractories are able for granulates manufacturing. • Mg based binders showed hydration, hydroxylation and carbonation processes. • CO 2 curing modified the granules bulk density. • CO 2 curing did not modify the granules water absorption. • CO 2 curing increased the granules mechanical properties. This paper analyzes the ability of two Spent Refractory Wastes (SRW) for the manufacturing of recycled granulates for construction applications. A binary magnesium oxide and ground granulated blast furnace slag hydraulic binder was considered as an agglomerating agent for the granulates manufacturing. Influence of curing atmosphere was carried out: in air, 20 % CO 2 and 100 % CO 2 atmosphere up to 28 days. Granulometry, thermal analysis, particle density, bulk density, water absorption and mechanical strength tests were performed to characterize the granulates. SRW showed their ability for the granulates manufacturing. Results demonstrated the existence of a residual reactivity of the wastes considered. A direct relationship between the CO 2 content of the curing atmosphere and the granulates hydration degree was observed. Carbonation process increased from 7 days to 28 days and direct relationships were observed between the CO 2 content and the carbonation degree as well as between the binder dosage and the carbonation degree. CO 2 curing reduced the water absorption and increased the compressive strength of the granulates. [ABSTRACT FROM AUTHOR]

This paper investigates the long-term performance of structural concretes in China southeast coastal area, the city of Shenzhen, exposed to atmosphere and chlorides. The structural concretes, incorporating large quantity of supplementary cementitious materials (SCM), were among the first massive application of such mixtures in construction in China. In both cases, in-field sampling and tests have been conducted during more than 20 years for the resistance of concretes to carbonation and chloride ingress respectively. The synthetic analysis of these results shows that (1) the concretes have substantial strength growth in atmospheric environment with exposure age, but the carbonation rate does not all obey the square root law of exposure time; (2) the protection of silane impregnation of high-performance concrete against chloride ingress maintains its hydrophobic effect after nearly 20 years; (3) Notable "skin" effect of surface concrete was observed for both atmospheric and marine exposures. [ABSTRACT FROM AUTHOR]

Carbonation processes cannot be ignored as regards durability and service-life of new concrete structures, and their correct understanding and quantification are essential for maintenance and repair works on existing structures. This paper initially presents a new meta-model developed to calculate carbonation front depth based on the analytic solution of Fick’s first law. The only input data required by this non numerical model are: (i) material variables (concrete mix design, maximum nominal aggregate size, cement type, and chemical composition of cement type CEM I and cement density); (ii) technological parameters (initial curing period ( t c )); (iii) environmental parameters (ambient temperature ( T ), relative external humidity ( RH ) and CO 2 concentration in the air ([ CO 2 ] ext )). Consequently, this model is fully suitable for the prediction of carbonation depth in the case of new reinforced concrete structures, for which these required parameters are well-known. The meta-model is validated using data from the literature on short and long-term natural carbonation exposure conditions. Most of the experimental data concern CEM I, CEM II, CEM III cement types, and CEM I additives (fly ash (FA)) with various water to cement ( W / C ) ratios and t c . The meta-model is also compared with two already available models: Papadakis’ model and Yang’s model. The three model predictions are compared with the corresponding values found in the literature. The results confirm that the prediction of the new meta-model proposed here for estimation of carbonation depth is the most accurate in every case. [ABSTRACT FROM AUTHOR]

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

Low methane content landfill gas may be enriched by removing carbon dioxide. An innovative process, based on carbon dioxide capture and storage by means of accelerated carbonation of bottom ash is proposed and studied for the above purpose. Within this research framework we devoted a preliminary research activity to investigate the possibility of improving the way the contact between bottom ash and landfill gas takes place: this is the scope of the work reported in this paper. Two different types of reactors – fixed bed and rotating drum – were designed and constructed for this purpose. The process was investigated at laboratory scale. As the aim of this phase was the comparison of the performances of the two different reactors, we used a pure stream of CO 2 to preliminarily evaluate the reactor behaviors in the most favorable condition for the process (i.e. maximum CO 2 partial pressure at ambient condition). With respect to the simple fixed bed reactor concept, some modifications were proposed, consisting of separating the ash bed in three layers. With the three layer configuration we would like to reduce the possibility for the gas to follow preferential paths through the ash bed. However, the results showed that the process performances are not significantly influenced by the multiple layer arrangement. As an alternative to the fixed bed reactor, the rotating drum concept was selected in order to provide continuous mixing of the solids. Two operating parameters were considered and varied during the tests: the filling ratio and the rotating speed. Better performances were observed for lower filling ratio while the rotating speed showed minor importance. Finally the performances of the two reactors were compared. The rotating drum reactor is able to provide improved carbon dioxide removal with respect to the fixed bed one, especially when the rotating reactor is operated at low filling ratio values and slow rotating speed values. Comparing the carbon dioxide specific removal obtained by using the rotating reactor (35–37 g/kg BA ), in the best operating conditions, with that measured for the fixed bed reactor (21–23 g/kg BA ), an increase of about 61–66% is observed. [ABSTRACT FROM AUTHOR]

At present, prescriptive regulations with regard to concrete cover and composition are applied to provide sufficient durability of reinforced concrete members under exposure conditions with different degrees of severity. In view of current knowledge on deterioration mechanisms and their modelling, it is planned to change from these deemed-to-satisfy specifications to a performance-based design approach in future standards. In such specifications, concrete durability design is based on the statistically characterized performance of concrete, determined in standardized tests with respect to defined classes of concretes with similar performance. This paper presents the results of a study in which concrete mixes were tested and analysed with respect to their carbonation resistance. Compositions with similar performance are grouped into carbonation resistance classes. These classes are described statistically and requirements for performance testing are given. In addition, composition requirements are introduced in order to determine concrete performance depending on mix composition prescriptively. Finally, an example is given for the assessment of concrete performance with regard to carbonation. This work was carried out at the request of JWG under CEN TC 250/SC2 and CEN TC 104/SC1 as an input and starting point for the ongoing committee work to implement the methodology from the fib Model Code for Concrete Structures 2010 in the next generation (2021) of European concrete standards. [ABSTRACT FROM AUTHOR]

The only option for carbon capture and storage (CCS) in Finland is mineral carbonation, which has been extensively researched at Åbo Akademi University (ÅA). Finding suitable minerals for mineral carbonation in different regions of Finland will keep transportation of either CO 2 or the actual mineral at a lowest possible level. Four different rocks from different regions in Finland have been compared with respect to composition and possibility to extract magnesium. This paper presents experiments applying thermal solid/solid extraction. It was found that a mixture of ammonium sulphate (AS) and ammonium bisulphate (ABS) could extract a significant part of magnesium compared to tests using only AS or ABS. Serpentinite rock is also the best option for magnesium extraction while diopside and magnesiohornblende are much less reactive. Continuous mixing during the experiment in a rotary tube and adding some water to the solid/solid mixture gives better extraction results. The binding capacities of CO 2 in the serpetinites with respect to the magnesium extractions achieved in this study are 240 kg CO 2 /ton rock (Serp-A) and 207 kg CO 2 /ton rock (Serp-B). [ABSTRACT FROM AUTHOR]

In the literature, the effects of curing, sheltering and CO 2 concentration under natural carbonation are not fully understood. There is either controversy or limited research available regarding these factors, while most investigations are based on accelerated carbonation. The currently available research on natural carbonation is particularly constrained and limited. From a practical viewpoint, natural carbonation is more important as it represents the behavior of real structures. This paper reviews the influences of different curing methods and their durations; sheltered and unsheltered exposure conditions, and different atmospheric CO 2 concentration levels, on carbonation of concrete under the natural outdoor exposure environment. The various curing methods examined are moist-curing, steam-, air- and oven-curing. It is found that curing effects are coupled with the type of cement. For cements containing no more than 30% fly ash or 50% slag, three-day curing is sufficient to stabilize long-term strength and carbonation behavior of concrete under site conditions. Different types of normal curing do not significantly alter natural carbonation behavior. An equation is suggested which accounts for the effect of unsheltered outdoor exposure on carbonation. Also, correction factors are proposed to account for different atmospheric CO 2 levels under natural carbonation. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation regarding the coupled effect of carbonation and chloride aerosol ingress on the durability performance of fly ash concrete. Test results demonstrate that carbonation significantly affects the chloride ingress profile, reduces the chloride binding capacity, and accelerates the rate of chloride ion diffusion. On the other hand, the carbonation rate of fly ash concrete is reduced by the presence of chlorides aerosol. The interaction nature between concrete carbonation and chloride aerosol ingress is also demonstrated by the microscopic analysis results obtained from scanning electron microscope and mercury intrusion porosimetry. [ABSTRACT FROM AUTHOR]