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This study investigates the gasification of cellulose, lignin, corn stover (rich in cellulose) and walnut shells (rich in lignin) using CaO as a catalyst. The objective was to understand the effect of the different biomass components on the gasification products and the performance of the CaO catalyst. Notable results indicate distinctive product distribution: cellulose yields higher liquid (58%) and CO (95.36%) products, while lignin produces increased H2 (47.88%), CH4 (34.34%), and CO2 (29.58%). Gasification of biomass feedstocks, corn stover (cellulose-rich) and walnut shell (lignin-rich), aligns with pure cellulose and lignin trends. Catalyst characterization highlights that cellulose exhibits a greater tendency for coke formation, leading to elevated tar compounds and coke deposition on the catalyst surface. The solid residue from cellulose gasification displays a smaller pore volume (5.70 m2/g) and specific surface area, indicating undesirable catalyst rearrangement. XRD analysis indicates a higher carbonation rate of CaO in lignin-rich gasification, leading to increased CaCO3 formation. Further results show a higher CO2 concentration (3.35 mol/kg) and lower CO production (0.54 mol/kg) in corn stover gasification, contrasting with walnut shell (CO2: 14.24 mol/kg, CO: 1.24 mol/kg). The study underscores the quantitative assessment of biomass composition for optimizing gasification processes, vital for catalyst selection and ensuring efficient CO2 capture in industrial applications. [ABSTRACT FROM AUTHOR]

In urban and industrial settings, one of the most prevalent durability challenges faced by reinforced concrete (RC) structures is the corrosion of steel reinforcement due to carbonation. While numerous studies have explored the characteristics of stone aggregate concrete concerning carbonation-induced corrosion of reinforcement, there is limited research on concrete made with brick aggregates. As a result, an investigation into the impact of carbonation on pre-existing reinforced concrete structures utilizing brick aggregates has been undertaken, and its findings have been compared with existing research. Within this study, a total of 84 concrete core samples, with diameters measuring 67 mm and 50 mm, were extracted from selected structural components of four pre-existing reinforced concrete structures utilizing brick aggregates, which ranged in age from 17 to 73 years. The collection of core samples and their testing procedures adhered to the relevant ASTM methods. Furthermore, carbonation depths were assessed in accordance with BS standards using phenolphthalein solution. Additionally, 24 concrete dust samples were gathered from the same locations to establish correlations with the core sample results. The experimental outcomes revealed a direct relationship between carbonation depth and concrete age, indicating that carbonation depth increases with concrete age. This study also demonstrated that the rate of carbonation is influenced by the concrete's grade, with an inverse relationship between them. Therefore, it is crucial to consider carbonation in scenarios involving low-strength concrete, particularly those with compressive strengths below 25 MPa, when the concrete is exposed to harsh environmental conditions and inadequate concrete cover. Consequently, when constructing new structures, employing relatively high-strength concrete is advisable to ensure extended service life by mitigating the effects of carbonation.

Most papers on kidney stones arising from infection concentrate on the mineral struvite. In this contribution, we would like to call attention to other mineral phases such as highly carbonated calcium phosphate apatite, ammonium urate, and whitlockite, by presenting clinical and chemical data. We start with epidemiological data which emphasize the increase in the prevalence of kidney stones related to infection. Then we present a statistical analysis of more than 85,000 stones which have been analysed at the Laboratoire des Lithiases of Assistance Publique-Hôpitaux de Paris which gives insights regarding the link between urinary tract infection and struvite, carbonated calcium phosphate apatite (carbapatite), and also surprisingly whitlockite. Some information regarding the pathogenesis of kidney stones linked to infection, the nature of the bacteria which have been identified, and the approach to precisely analyse infrared spectra to identify struvite, carbapatite, and whitlockite, conclude this first part. To complete this clinical description, we describe the crystallographic structure and the chemistry of three relevant compounds namely carbonated calcium phosphate, struvite, and whitlockite. To conclude this second part, the dependence of crystallite morphology of struvite on pH and on the presence, or absence, of bacteria, is described. Based on clinical and chemical data, it is becoming clear that struvite is not the only mineral intimately related to renal infectious processes, but that whitlockite and carbapatite with a high carbonation rate are strongly associated with urinary tract infection as well.

This study seeks to analyze how the degree of carbonation and the application of waterproofing and anticorrosive materials affect carbonation in water reservoirs among the water treatment facilities managed by the Seoul Metropolitan Government. To guarantee similarity of the experimental group, 42 highly similar water reservoirs were selected from among the water supply reservoirs currently in operation in Seoul. On-site carbonation assessments were performed in order to derive the carbonation rate coefficients. In the water reservoirs with applied waterproofing and anticorrosive materials immediately after public service, the upper and lower limits were D = 1.13 t and D = 0.29 t , respectively, whereas those of the water reservoir applied with waterproofing and anticorrosive materials after 15 years of service life were D = 1.89 t and D = 0.94 t , respectively. The comparative analysis showed that the rate of reduction in the carbonation rate was about 10.4% to 16.8% in the water reservoirs applied with waterproofing and anticorrosive methods after 15 years of service life. However, reduction in the carbonation rate was about 46.4% to 74.3% in the water reservoirs applied with waterproofing and anticorrosive methods at the initial stage of service life. It was confirmed that the early application of waterproofing and anticorrosive materials is effective in suppressing carbonation of concrete water reservoir structures. [ABSTRACT FROM AUTHOR]

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This study seeks to analyze how the degree of carbonation and the application of waterproofing and anticorrosive materials affect carbonation in water reservoirs among the water treatment facilities managed by the Seoul Metropolitan Government. To guarantee similarity of the experimental group, 42 highly similar water reservoirs were selected from among the water supply reservoirs currently in operation in Seoul. On-site carbonation assessments were performed in order to derive the carbonation rate coefficients. In the water reservoirs with applied waterproofing and anticorrosive materials immediately after public service, the upper and lower limits were D = 1.13t and D = 0.29t, respectively, whereas those of the water reservoir applied with waterproofing and anticorrosive materials after 15 years of service life were D = 1.89t and D = 0.94t, respectively. The comparative analysis showed that the rate of reduction in the carbonation rate was about 10.4% to 16.8% in the water reservoirs applied with waterproofing and anticorrosive methods after 15 years of service life. However, reduction in the carbonation rate was about 46.4% to 74.3% in the water reservoirs applied with waterproofing and anticorrosive methods at the initial stage of service life. It was confirmed that the early application of waterproofing and anticorrosive materials is effective in suppressing carbonation of concrete water reservoir structures.

Carbonation of cementitious binders implies gradual capture of CO2 and significant compensation for the abundant cement-related CO2 emissions. Therefore, one should always look at the CO2-sequestration-to-emission ratio (CO2SP/EM). Here, this was done for High-Volume Fly Ash (HVFA) mortar (versus two commercial cement mortars). Regarding their CO2 sequestration potential, effects of accelerated testing (at 1–10% CO2) on as such estimated natural carbonation degrees and rates were studied. Production related CO2 emissions were evaluated using life cycle assessment with no/economic allocation for fly ash. Natural carbonation rates estimated from accelerated tests significantly underestimate actual natural carbonation rates (with 29–59% for HVFA mortar) while corresponding carbonation degrees are significantly overestimated (67–74% as opposed to the actual 58% for HVFA mortar). It is advised to stick with the more time-consuming natural tests. Even then, CO2SP/EM values can vary considerably depending on whether economic allocation coefficients (Ce) were considered. This approach imposes significant portions of the CO2 emissions of coal-fired electricity production onto fly ash originating from Germany, China, UK, US and Canada. Ce values of ≥0.50% lower the potential CO2SP/EM values up to a point that it seems no longer environmentally worthwhile to aim at high-volume replacement of Portland cement/clinker by fly ash. [ABSTRACT FROM AUTHOR]

This study investigates and compares the carbonation depth, carbonation rate and degree of carbonation of mortar specimens made with different binder systems. The interplay and influence of limestone filler (LF) particle size, LF content and ground-granulated blast-furnace slag (GGBFS) on the compressive strength, carbonation depth, carbonation rate and degree of carbonation are evaluated. Specimens were exposed to an accelerated carbonation environment of 3 ± 0.5% CO 2 concentration, 50 ± 5% relative humidity and a temperature of 23 ± 2 ֯C for up to 12 weeks. It was found that: (i) ∼9.8% LF in Portland limestone cement does not significantly impact the carbonation depth and compressive strength; (ii) the use of 25% GGBFS as a cement replacement in addition to LF increases the carbonated area of specimens; (iii) the use of coarse size LF as cement replacement increases the k-factor of the carbonation rate, which is neglected in BS-EN-16757; and (iv) the use of LF and/or GGBFS in this study increases the clinker degree of carbonation from 60.7% up to 78.8% in the carbonated area. • Use of course limestone filler (CLF) leads to a greater carbonation. • k-factors suggested by BS-EN-16757 do not reflect the impact of CLF • 1-week of accelerated carbonation can be converted to 0.6 years of natural carbonation • "Rate of reabsorbed CO 2 per unit mass of binder" is calculated [ABSTRACT FROM AUTHOR]

Highlights • The compressive strength of SAAC decreased with the increase of carbonation depth. • Phase component and microstructure significantly changed with the increase of carbonation depth. • An appropriate value of the carbonated substance reaction coefficient based on experimental results was proposed for SAAC. • A practicable mathematical model displays a high potential for the estimations of carbonation rate in SAAC. Abstract Carbonation could not be ignored because of the significant deterioration of mechanical property and durability of sand autoclaved aerated concrete (SAAC). A better understanding and quantification are necessary for maintaining and repairing the existing structures of SAAC. A practicable mathematical model based on the Fick's first law was established, which was evaluated by the data of accelerated carbonation experiment. Carbonation behavior was studied by means of phenolphthalein test, SEM and XRD. Because the tobermorite generated by hydration gradually transformed into calcite, the compressive strength of samples showed an obvious decline with carbonation depth increased. Furthermore, the experimental date of B05 bulk density class SAAC samples and the calculated values of model have shown good agreements. [ABSTRACT FROM AUTHOR]

Abstract: The effects of steam addition during calcination on the carbonation behavior of calcium‐based sorbents in cyclic calcination/carbonation experiments were investigated. Variations in the CaO conversion rate during carbonation were measured to evaluate the influence of operating conditions and particle size on the carbonation reaction in kinetic‐ and diffusion‐controlled reaction regimes. Surface sintering and particle aggregation during cyclic calcination/carbonation affected the sorbent surface area, pore volume, and possibly the pore size, resulting in less sorbent recyclability and a trigger time retard in the fast kinetic‐controlled carbonation. Steam addition during calcination positively affected the recyclability of the sorbents and altered the carbonation behavior. [ABSTRACT FROM AUTHOR]

In the absence of a carbonation model for soil cement, this research aims to assess the compatibility and applicability of an analytical model initially developed for concrete. Carbonation can be observed in any pavement layer which includes cement or lime. For instance, carbonation damages the cement-modified crushed rocks as a typical material for base course layer due to poor curing of material or cracking of asphalt. Experimental laboratory tests are utilised here in accelerated carbonation conditions to evaluate the analytical model. Cylindrical specimens are subjected to one-dimensional carbonation condition. Weight and ratio of constituents of mixes, as well as environmental factors, such as CO 2 concentration and relative humidity are recorded for analytical estimation of failure progresses. Nanosilica is also introduced in mixes to explore its effects during carbonation reactions. Results show linear correlations between experimental records and analytical model calculations. Thus, it can be concluded that carbonation rate can be predicted in soil cement also. In addition, the inclusion of nanosilica has a positive influences by slowing of the carbonation progress. [ABSTRACT FROM AUTHOR]

In this study, the influence of three mixture variables named Sand/Aggregate ratio, Liquid/Binder ratio, and Paste/Aggregate ratio on the cementitious properties were studied. The durability of cementitious including absorption, absorption rate, resistivity, rapid chloride permeability index, and carbonation rate were examined. Results showed that the alkali-activated slag cementitious has superior durability. The trends of influences on the composites properties for these three mixture variables are similar to those for the ordinary Portland cement concrete. It means that the experiences for making the ordinary Portland cement concrete should be able to be used for the alkali-activated slag cementitious. This paper also provides a lot of data for the alkali-activated slag cementitious for future development of the mix design.

The hardening kinetics of a lime based mortar is based on the uptake of carbon dioxide from the ambient air. The presence of watervapour is required in order to enable the reaction between the CO2 and the lime (calcium hydroxide). Via this reaction the hardening of air lime is net uptaker of CO2. An extensive literature study was made on the fundamentals of the carbonation process in mortars with different compositions. The results of the study indicate that carbonation ranges from 80 % up to 90 %. It is clear that the mechanism and the kinetics of the carbonation depend strongly on the mineralogy, texture of mortars, type of additive used, the lime use for the mortar, the width of the walls, thickness of the mortar (less carbonation when mortar depth increases) as well as the timeframe allowing for the carbonation process to take place. Under natural conditions, actual building practice and depending on the thickness of the mortar/plaster, carbonation takes between a few weeks and several years. The results of this study were used for the environmental footprint study in order to calculate the capture of CO2 that occurs progressively during the hardening of a building materials containing lime. [ABSTRACT FROM AUTHOR]

• The influence mechanism of CO 2 , RH and temperature on cement-based materials was analyzed in detail. • The theoretical relationship between environmental factors and carbonation was analyzed. • The numerical analysis process of coupling effect of environmental factors on carbonation is introduced. • Based on the review of carbonation under different environmental factors, the future research directions are prospected. For in situ reinforced concrete structures, carbonation has been considered as a risk that needs to be inhibited for the past decades; while a pronounced carbonation in early age concretes is now regarded as a good method to reduce carbon footprint for civil engineering industry, and needs to be promoted. Therefore, a thorough understanding on controlling the extent of carbonation in various types of concretes and at different stages needs to be delivered, so as to meet the opposite demands in various cases. By controlling environmental conditions, including temperature, humidity and CO 2 concentration, different degrees of carbonation can be achieved. However, even though significant amount of carbonation works have been carried out, there is still a lack of a unified conclusion and summary discussion on the impacts from external factors. In this review, impacts of temperature, humidity, CO 2 concentration and their coupling effects on carbonation of concretes are summarised, aiming to facilitate promotion and inhibition of the process in practice. Meanwhile, future perspectives to gap the current research status and precise carbonation control are raised. [ABSTRACT FROM AUTHOR]

Since closure of the Woodsreef Asbestos Mine, located in the Great Serpentinite Belt (GSB), New South Wales, Australia, extensive carbonate-rich crusts have formed by recessive weathering of fine-grained material on the surface of the tailings pile. A relationship exists between the mode of carbonate occurrence, the mineralogy and the isotopic fingerprint of carbonates from the tailings pile. Vertical carbonate crusts, covering most of the tailings, predominantly consist of the hydrated Mg-carbonate hydromagnesite (Mg5(CO3)4(OH)2·4H2O), which has precipitated from evaporating meteoric waters incorporating atmospheric CO2, as reflected in high δ 18O, δ 13C and F14C signatures, respectively. Low and variable concentrations of magnesite, dolomite and calcite represent bedrock carbonate, which has formed during alteration of the serpentinite bedrock before mining and is characterised by moderately high δ 18O, low δ 13C and F14C, a signature typical for ‘weathering-derived’ magnesite deposits in the GSB. The carbonate fraction of deep cement samples, collected from 70 to 120cm below the surface, representing the bulk tailings material at depth, predominantly consists of pyroaurite (Mg6Fe2(CO3)(OH)16·4H2O) and, despite stable isotope signatures similar to bedrock, contains significant radiocarbon. This indicates that pyroaurite, forming under different conditions as hydromagnesite, may represent an additional trap for atmospheric CO2 in the Woodsreef mine tailings. The distribution of carbonates and quartz, together with the absence of isotopic mixing trends between bedrock carbonate and atmospheric-derived carbonate, strongly indicates that dissolution and re-precipitation of bedrock carbonate is not a dominant process in the Woodsreef tailings. The cations for carbonate formation are instead derived from the dissolution of serpentine minerals (lizardite and chrysotile) and brucite. The internal standard method and the reference intensity method have been used with X-ray diffraction data to estimate the abundance of the two major carbonate minerals hydromagnesite and pyroaurite, respectively. Considering the formation of hydromagnesite on the outer surface of the tailings pile alone or together with formation of pyroaurite within the tailings pile we conclude that, between 1400 and 70,000t of atmospheric CO2 have been sequestered in the mine tailings since closure of the mine 29a ago. Carbonation rates of 27gCm−2 y−1 and 1330gCm−2 y−1 are significantly higher than background rates of CO2 uptake by chemical weathering and demonstrate the potential of passive carbonation of mine tailings as a cost and energy effective alternative for storage of CO2 in carbonate minerals. [ABSTRACT FROM AUTHOR]

Accelerated carbonation experiments about the development of carbonation rates of ordinary Portland cement concrete under different artificial climates were carried out. Six water cement ratios and six climate condition combinations of temperature and relative humidity were used. Results indicate that changes of concrete carbonation rate with environmental temperature agree the Arrhenius law well, which suggests concrete carbonation rate has obvious dependence on temperature. The higher the temperature is, the more quickly the concrete carbonates, and at the same time it is also affected by environmental relative humidity. Thereafter, the apparent activation energy E of concrete carbonation reaction was obtained, ranging from 16.8 to 20.6 kJ/mol corresponding 0.35-0.74 water cement ratio, and lower water cement ratio will cause the apparent activation energy increase. Concrete carbonation rates will increase 1.1-1.69 times as temperature increase every 10 °C at the temperature range of 10 to 60 °C. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the technical feasibility of the mineral carbonation of flue gas desulfurization (FGD) gypsum to sequester CO2 was assessed by considering various reaction parameters. Unlike other natural and industrial materials, FGD gypsum showed very high carbonation reactivity at room temperature and atmospheric pressure. Under optimum conditions, calcium carbonate with a purity exceeding 90% could be obtained within 10 min at a carbonation rate of approximately 95%. Thus, mineral carbonation of FGD gypsum was found to be technically feasible. The use of excess ammonia (110–120%) was found to be desirable for enhancing the stability of the reaction and for obtaining high-purity CaCO3. An increase in the CO2 flow rate accelerated the carbonation reaction significantly but decreased the CO2 sequestration efficiency. Therefore, the flow rate should be optimized by considering the reaction rate and CO2 sequestration efficiency. While an increase in the solid-to-solution ratio increased the extent of temperature rise in the slurry, it did not affect the carbonation rate, which remained high at 95% for s/s ratios up to 50%. The use of a CO2/N2 gas mixture only slowed the carbonation reaction, and did not affect the CaCO3 purity and carbonation rate. [Copyright &y& Elsevier]

The single influence of capillary porosity and coupling effects of absolute basicity and capillary porosity on concrete carbonation were investigated. The experimental results showed that carbonation rate of concrete at a given absolute basicity (AB) increased moderately with the increase of the porosity ranging from 6.2% to 9.25%, and increased rapidly with porosity from 9.25% to 12.8%.The coupling effect mainly embodied in disappeared mutation point of capillary porosity, and the distributing regions of carbonation depth were clearly partitioned in the coupling influence of absolute basicity and capillary porosity. A design method on carbonation related durability of concrete based on the coupling effects was proposed. [ABSTRACT FROM AUTHOR]

In the original paper, the simple power function used correlates carbonation rate with air permeability in carbonated concrete rather than in non-carbonated concrete. However, the reported air permeability tests were conducted for non-carbonated concrete, which was not consistent with their theoretically-established function. This discussion modifies the original theoretical function through incorporation of a porosity-related term which connects air permeability in non-carbonated concrete with that in carbonated concrete. Consequently, a new analytical model to estimate carbonation resistance through air permeability in non-carbonated concrete is proposed and calibrated using experimental results reported in the original paper. [ABSTRACT FROM AUTHOR]

Abstract: Successive calcination–carbonation cycles, using CaO as sorbent, have been performed either in a classical fixed bed reactor or using a thermogravimetric analyser. Significant differences in carbonation efficiencies were obtained, possibly due to different conditions prevailing for CaO sintering during the calcination stage. The effect of the presence of on sintering was confirmed. A simple model of the decay of the carbonation capacity along cycles based on the specific surface area of non-sintered micrograins of CaO is able to predict the decrease of the extent of conversion obtained after 40 carbonations along calcination–carbonation cycles. The asymptotic extent of conversion is obtained when all the micrograins present within a grain are sintered. A detailed model of the carbonation shows that the voids present between the micrograins are filled up by carbonate when a critical thickness of the carbonate layer around each micrograin reaches 43nm. Then, carbonation becomes controlled by diffusion at the scale of the whole grain, with the diffusion coefficient decreasing (at ) from to as carbonation proceeds from 50% conversion to 76% (first cycle). This scale change for diffusion is responsible for the drastic decrease of the carbonation rate after the voids between micrograins are filled up. [Copyright &y& Elsevier]

Abstract: Rates of carbonation for reinforced concrete bridges were investigated for three localities in South Africa: Cape Peninsula, Durban and Johannesburg. Carbonation data from approximately 90 in-service bridges aged between 11 and 76 years were interpreted in terms of influence of materials and environment on carbonation rates. The data were grouped with respect to concrete strength grade and exposure condition prior to statistical analysis. Bridges in Johannesburg had the highest rates of carbonation owing to the relatively dry environment. Durban bridges had lower carbonation rates than Johannesburg bridges, but higher than bridges in the Cape Peninsula, ascribed to differences in ambient temperature and the nature of precipitation. Overall, average carbonation rates for Grade 30 concretes over a 30-year period varied from approximately 0.3mm/annum in Cape Peninsula structures to approximately 0.7mm/annum for Johannesburg structures. Exposure condition, characterised by degree of shelter, had little influence on carbonation rate in Durban and Johannesburg bridges, ascribed to the average relative humidity and duration of precipitation at these localities. Carbonation rates for older bridges were lower than for newer structures, attributed possibly to changes in cement characteristics with time related to the need for fast track construction in modern structures. [Copyright &y& Elsevier]

• The thermal conductivity of bio-composites is optimized using natural additives. • The mechanical strength is sufficient to support the self-weight of bio-composites. • Effect of additives on microstructural changes and carbonation-hydration mechanisms. • Changes in morphology of the binder's microstructure influence mechanical behaviour. The aim of this study was to optimize the thermal performances of a bio-composite based on cereal straw and mineral binders. The purpose is to reduce its thermal conductivity by decreasing the amount of mineral binder while maintaining sufficient mechanical properties to ensure self-bearing. Three additives, namely hemoglobin, casein and gelatin, from a renewable and biodegradable biomass source were used. Thermal and mechanical characterization of the composites was carried out. The influence of the additives on the carbonation-hydration mechanisms, microstructure changes and macroscopic properties was investigated. The microstructure and the mineralogy of the binders without and with additives was investiagted through microstructural analysis (SEM, DRX and TGA). The optimized composites have an interesting thermal conductivity with acceptable mechanical properties for use in building insulation. [ABSTRACT FROM AUTHOR]

• As the quality of concrete increases, carbonation rate decreases. • Carbonation rate is more sensitive to concrete quality than duration of curing. • Indoor-exposed concretes had higher carbonation rates than outdoor-exposed ones. • Blended cement concretes had higher carbonation rates than plain PC concretes. • Gas permeability and water sorptivity are incorporated in the carbonation model. This paper reports an investigation on the influence of inland exposure conditions, concrete quality and cover depth on carbonation-induced corrosion initiation of steel in concretes exposed to urban, inland environment. 100 mm concrete cube specimens of were prepared using five types of binder namely plain Portland cement (CEM I 52.5 N, PC), 70/30 PC/FA (fly ash), 50/50 PC/BS (blast furnace slag), 90/10 PC/SF (silica fume) and 60/30/10 PC/BS/SF at three w/b ratios of 0.40, 0.60 and 0.95. For all the concretes, two companion sets of specimens were cast and cured for 7 and 28 days before being exposed to natural indoor, outdoor-sheltered and outdoor-unsheltered environments. Concrete quality was characterized using water sorptivity and oxygen permeability. Carbonation depths were measured at 6-month intervals up to 2 years. The results show that as the quality of the concrete increases the rate of carbonation rate decreases. The results also show that carbonation rate is more sensitive to concrete quality (binder type and w/b ratio) than duration of curing. The indoor-exposed specimens exhibited higher carbonation rates than the corresponding outdoor-exposed concretes. Blended cement concretes showed higher carbonation rate than to the plain PC concretes. An empirical carbonation rate prediction model incorporating both gas permeability and water sorptivity as input parameters is proposed. [ABSTRACT FROM AUTHOR]

• 240-day carbonation results of unloaded and loaded PC, FA and GGBS specimens. • Evaluating the carbonation coefficients in test specimens. • Estimating the carbonation depths in RC structures after 50 and 100 years exposure. • Eurocode durability requirements may be inadequate for 'green' concrete elements. Carbonation of concrete can lead to corrosion of reinforcing bars. By this reason its prediction is very important, in particular for durability design, e.g. determining the minimum thickness of the concrete cover. Although carbonation of concrete in reinforced concrete (RC) structures is influenced by applied loading, limited research has been carried out in this area, especially for 'green/low carbon' concretes, i.e. mixes containing supplementary cementitious materials such as fly ash (FA) and ground granulated blast-furnace slag (GGBS). This paper reports the influence of structural loading on carbonation of three types of concrete: Portland cement (PC), PC with 30% of FA and PC with 50% of GGBS, with two water/binder (w/b) ratios (0.40 and 0.55). Test specimens made with these concretes, i.e. 100-mm cubes (unloaded) and RC beams (loaded), were subject to accelerated carbonation (CO 2 content of 4%) for a duration of up to 240 days. Results of the tests are presented in this paper along with their analysis, in particular, the evaluation of the carbonation coefficients. The results clearly show a significant influence of loading on carbonation rate. Based on the test results, the estimated effects of loading on carbonation after 50 and 100 years exposure have been calculated. These estimates indicate that the current durability requirements in the Eurocodes may not be adequate for preventing the initiation of carbonation-induced corrosion in tensile zones of RC elements during their design working life. [ABSTRACT FROM AUTHOR]

Under marine and industrial-polluted environments, reinforced concrete structures (RC structures) are attacked by carbonation and chloride penetration; both can cause deterioration of steel and concrete. Thus their coupled effect will definitely intensify the serious corrosion of RC structures. This work evaluates the chloride binding and the subsequent species diffusion process incorporating with carbonation rate, under the condition of chloride-contaminated first and then carbonated, so as to explore the mechanism of carbonation influence on chloride binding. Hence, the unique and specific concept of carbonation rate, to elaborate the synergetic effect of different crucial environmental factors on carbonation, is adopted innovatively. The impact of the reorganization of physical microstructures is elucidated. Additionally, both the influence of dissolution threshold of bound chloride and concentration of carbon dioxide on binding, together with their incidence analysis are investigated. It is proved that this specialized carbonation rate, as a fundamental criterion, could be utilized to quantify bound chloride and corresponding debound process in concrete exposed to both chloride and carbonation environments. • Carbonation and chloride penetration are coupled together as durability problems for concrete. • Carbonation rate is adopted to elaborate the effect of carbonation on chloride binding. • Impacts of the reorganization of physical microstructures on binding effect is analyzed. • Impacts of the threshold of bound chlorides dissolution and carbon dioxide on binding are analyzed. • The influence degree between the above two analysis parameters are elucidated. [ABSTRACT FROM AUTHOR]

In this study, the influence of three mixture variables named Sand/Aggregate ratio, Liquid/Binder ratio, and Paste/Aggregate ratio on the cementitious properties were studied. The durability of cementitious including absorption, absorption rate, resistivity, rapid chloride permeability index, and carbonation rate were examined. Results showed that the alkali-activated slag cementitious has superior durability. The trends of influences on the composites properties for these three mixture variables are similar to those for the ordinary Portland cement concrete. It means that the experiences for making the ordinary Portland cement concrete should be able to be used for the alkali-activated slag cementitious. This paper also provides a lot of data for the alkali-activated slag cementitious for future development of the mix design. [ABSTRACT FROM AUTHOR]