Long-term Carbonation Research Articles

Effects of Curing Conditions, Age, and Particle Size on CO<sub>2</sub> Sequestration of Basic Oxygen Furnace Slag Used in Concrete

Mineral sequestration technology is one of the most effective carbon capture and storage techniques. Basic oxygen furnace slag (BOFS), one of the by-products generated during the steelmaking process, has a particularly high potential for mineral sequestration compared to other similar wastes such as blast furnace slag and ladle slag. In the case of BOFS, mineral sequestration not only contributes to carbon uptake but also stabilizes its internal structure. So far, most of the investigations on BOFS mineral sequestration rely on accelerated carbonation involving high pressures and supplying concentrated CO2 in a short period. Although these studies are useful for investigating the overall potential for carbon capture of BOFS, they are less useful for practical applications on a large scale. Moreover, it is hard to draw any conclusions regarding the carbonation reactions lasting for years in stockpiles of BOFS. This research identified the consequences of long-term carbonation on BOFS samples and determined the best conditions for natural mineral sequestration.

Influence of Corrosion on Lifespan of Reinforced Concrete Structures: A Comprehensive Review

Carbonation-induced corrosion is a major concern for reinforced cement concrete (RCC) structures, impacting their long-term durability and structural integrity. This review synthesizes the findings on the deterioration mechanisms in concrete structures, focusing on carbonation, chloride-induced corrosion, and time-dependent deterioration. The analysis includes discussions on predictive likelihood methods for estimating bridge reliability, the impact of environmental factors on carbonation, and standardized testing methods for assessing concrete durability. The review highlights the importance of understanding material characteristics and environmental conditions in designing durable concrete structures, emphasizing the processes of carbonation, its impact on rebar corrosion, and strategies for mitigation. Sheltered concrete carbonation resistance in metropolitan tropical climates is 10-20% lower than open exposure. SCM concretes exhibit equivalent or greater long-term carbonation resistance to OPC concretes, as evidenced by the increase in carbonation depth ( Δ xd) at ages greater than 5 years. The paper concludes with recommendations for integrating advanced modeling techniques and empirical studies to develop robust maintenance strategies and improve concrete mix designs for enhanced durability.

Study of the impact of sediments on the mechanical behavior of concrete and towards the penetration of carbon dioxide

Dam reservoirs are exposed to a loss of water storage capacity due to the phenomenon of siltation. This particularity can be expressed by the siltation of reservoirs and the entrainment of particles transported by watercourses. Siltation of reservoirs is a critical state which causes a reduction in the storage capacity of dams. Algeria is characterized by a semi-arid climate, which annually loses a considerable volume of water storage. The carbonation of concrete is influenced by a number of parameters which accelerate its kinetics. These parameters are the porosity of the concrete, the quantity of lime contained in the cement, the concentration of CO2 in the atmosphere and the humidity of the environment. It should be noted that, water being the vector for moving aggressive agents, carbon dioxide can only diffuse through the concrete if the latter is not completely saturated and not perfectly dry at the same time. Another factor increasing the permeability of concrete is the amount of limestone added to the cement during its manufacture at the factory. This permeability allows the diffusion of CO2 or other aggressive agents in the concrete. The addition of limestone to cement must therefore be used with caution. The objective is to propose economically competitive and easy-to-implement formulations which allow the valorization of these materials in the making of ordinary concrete by partial substitution of cement (10, 20 and 30%) and its influence on the progress of long-term carbonation after six years of curing in the open air. The sediment is treated by calcination at 750°C to make it active. Natural carbonation tests were carried out on the study concretes in order to evaluate their durability. The results obtained confirmed the possibility of producing concretes incorporating calcined sludge at dosages of up to 30% without compromising the quality of these concretes from the point of view of behavior in the face of attacks by the dissolution of carbon dioxide from the air in the interstitial solution of concrete, meeting economic, ecological and technological objectives.

Enhancing the carbonation and chloride resistance of concrete by nano-modified eco-friendly water-based organic coatings

To effectively improve the carbonation and chloride resistance of concrete with eco-friendly waterborne organic coatings, two nanomaterials (i.e., nano-SiO2 and nano-TiO2) were utilized to modify the water-based polyurethane and epoxy resin paints at dosages of 1 wt%, 2 wt%, and 3 wt%, and the coated concrete specimens were fabricated. Then, accelerated aging experiments of ultraviolet irradiation were conducted on the coated concrete specimens, followed by accelerated carbonation or Coulomb electric flux experiments. In addition, partial coating film samples were analyzed by scanning electron microscopy and Fourier transform infrared spectroscopy. Results show that the application of water-based organic coatings can substantially improve the carbonation and chloride resistance of concrete. The two-component water-based epoxy resin coating exhibited a higher quality than the one-component water-based polyurethane coating, thus resulting in better improvement of the carbonation and chloride resistance of concrete. However, the anti-aging capability of water-based epoxy resin coating is lower than that of water-based polyurethane coating, resulting in the rapid decline of the carbonation or chloride resistance of coated concrete after ultraviolet aging. The addition of nano-SiO2 or nano-TiO2 to the water-based organic coating can reduce the defects in the coating, effectively improve the density of the coating, and further improve the carbonation and chloride resistance of the coated concrete, with average improvement ranges of 51–74 % and 24–27 %, respectively. Meanwhile, the addition of nano-SiO2 or nano-TiO2 can help reduce the damage of water-based coatings caused by ultraviolet irradiation, thereby improving the long-term carbonation and chloride resistance of coated concrete, among which the improvement effect of nano-TiO2 is higher than that of nano-SiO2.

Influences of titanium dioxide nanoparticles on regulation of crystalline growth and early carbonation of cementitious composites

As the major source of carbon emission in the construction industry, Cement has presented an urgent challenge that demands the resolution of its high carbon emission issue. Utilizing in-situ CO2 capture from plant sites for the carbonation curing of cementitious materials can be regarded as an effective carbon sequestration method. This study employs low-concentration CO2 curing to modify nano titanium dioxide (NT)-enhanced cementitious materials. By investigating the influence of highly homogeneous NT on the crystalline growth and microstructural evolution of hydration product Ca(OH)2, this research further explores the impact of low-concentration CO2 curing on the early-stage carbonation behavior of the surface layer of cementitious materials. The results of this study indicate incorporation of 2 wt% NT promotes the degree of cement hydration, particularly during the first three days, leading to a 31.11% increase in the generation of the hydration product Ca(OH)2 at 1 day and 20.82% increase at 3 days compared to the blank sample, and a significant reducing of the crystalline size and directional growth index of Ca(OH)2 to increase the specific surface area of Ca(OH)2, thereby promote early carbonation of the cementitious mortar surface. The carbon uptake of the specimens at 28 days reaches 0.94 kg/m2 after exposure to 3% CO2 concentrations, forming a dense protective layer of calcium carbonate on the surface. The gas permeability coefficient of the surface decreases by 79.57%, enhancing the resistance of long-term continuous carbonation. This study provides innovative ideas for the cement industry in terms of utilizing surface carbonation of the substrate to promote carbon sequestration technology.

Artificial neural network model to estimate the long-term carbonation depth of concrete exposed to natural environments

Artificial neural network model to estimate the long-term carbonation depth of concrete exposed to natural environments

The influence of reactive MgO on the hydration and carbonation performance of slag-rich cement system

To enrich the choice of minor addition for cement production, the paper investigated the influence of reactive MgO on the long-term hydration and carbonation behavior of slag-rich cement paste. Three different mixtures (cement-slag-MgO, C3S-slag-MgO, and cement-slag) were adopted in the study, and specimens were sealed cured for 90 days, followed by a six-month accelerated carbonation test. It was found that the addition of MgO did not modify the phase assemblage evolution and microstructure development of slag-rich cement paste fundamentally during hydration and carbonation. Brucite occurred as the main hydration product of MgO. As for its carbonation product, Mg-containing carbonate phases and magnesium silicate hydrates were found to agglomerate with each other in the matrix. Compared with cement-slag mixture, cement-slag-MgO blend exhibited a slightly higher carbonation depth and a lower CO2 binding capacity. Brucite did bind some CO2; however, it cannot compensate the reduction of C–S(A)−H gel phase and portlandite due to the substitution of cement clinker with MgO. Therefore, the addition of MgO reduced the carbonation resistance of the corresponding system from a long-term perspective.

Modelling of the evolving contributions of gas transport, cracks and chemical kinetics during atmospheric carbonation of hydrated C3S and C-S-H pastes

This modelling study investigated the physicochemical and kinetic controls of the mineralogical evolutions of cementitious materials subject to accelerated atmospheric carbonation. Simulations are based on published experimental results on two samples, a hydrated C3S and a C-S-H paste, carbonated for 1 year at 55 % RH at 3 % CO2. For the C3S paste, reactive transport simulations accurately reproduced the mineralogical observations at different time intervals. However, for the C-S-H paste, in which significant cracks appeared, basis simulations could not reproduce the long-term carbonation extent. 2D simulations suggested that potential preexisting cracks could not fully explain the seemingly increasing carbonation rates. A final simulation using a simplified description of the crack appearance during carbonation gave the most accurate representation of the experimental results (degradation depths, mineralogy evolution). This demonstrates that, to accurately estimate the durability of cementitious materials subject to carbonation under dry conditions, coupled geochemical-mechanical descriptions are required.

Chloride migration and long-term natural carbonation on concretes with calcined clays: A study of calcined clays in Argentina

The use of calcined clays as supplementary cementitious materials is one of the strategies to reduce the CO2 emissions from cement and concrete industry as they provide good mechanical and durable properties after proper calcination and grinding. In Argentina, calcined common brick clays have a significant relevance due to their proximity to the largest Portland cement plants. The aim of this study is to analyze the resistance to chloride ingress and natural carbonation up to 36 months of concretes using calcined common brick clay and calcined low-grade kaolinitic clay. The latter exhibits a much lower chloride migration coefficient than the Portland cement concrete from 28 days on, while the calcined common brick clay requires a 90 days curing to obtain lower chloride ingress. Although the blended concretes exhibit greater carbonation depths than the reference after 36 months, it is lower than the given threshold of 10 mm. Hence, durable concretes with calcined clay can be obtained if they are properly cured.

Orthogonal Test Design for the Optimization of Preparation of Steel Slag-Based Carbonated Building Materials with Ultramafic Tailings as Fine Aggregates

The high carbonation potential makes ultramafic tailings ideal aggregates for carbonated building materials. This paper investigates the preparation condition of ultramafic tailings and steel slag through orthogonal experiments. The results show that compressive strength has a positive exponential correlation with the CO2 uptake of the carbonated compacts. The optimized conditions include a slag-tailings ratio of 5:5, a carbonation time of 12 h, a grinding time of 0 min, and a water-solid ratio of 2.5:10, when the compressive strength of the carbonated compacts reaches 29 MPa and the CO2 uptake reaches 66.5 mg CO2/g. The effects on the compressive strength ordered from high to low impact are the slag/tailings ratio, carbonation time, grinding time of steel slag, and water–solid ratio. The effects on the CO2 uptake ordered from high to low impact are the slag–tailings ratio, water–solid ratio, carbonation time, and grinding time of steel slag. A high water–solid ratio hinders the early carbonation reactions, but promotes the long-term carbonation reaction. Steel slag is the main material being carbonated and contributes to the hardening of the compacts through carbonation curing at room temperature. Ultramafic tailings assist steel slag in hardening through minor carbonation and provide fibrous contents. The obtained results lay a solid foundation for the development of tailings-steel slag carbonated materials.

Towards a scientific-based assessment of long-term durability and performance of cementitious materials for radioactive waste conditioning and disposal

Because of its solid structure, low permeability, slow diffusion and good chemical retention for many radionuclides, cementitious materials are often used for conditioning radioactive waste and are omnipresent in many radioactive waste disposal facility concepts as engineered barriers. Cementitious materials are not in geochemical equilibrium with the surrounding disposal environment and will undergo slow but significant geochemical, physical and mechanical changes. The evolution and the consequences on their performance have to be assessed over extreme long time scales ranging from a few hundreds of years to several tens of thousands of years. For a deep understanding of the long-term geochemical and microstructural alteration processes, a synergy between (i) experimental studies, (ii) multi-scale modelling and (iii) coupled reactive transport models is necessary and a prerequisite to assess the long-term performance. This paper presents an overview of some recent developments in these three approaches. From an experimental point of view, well-designed accelerated degradation tests are required as a basis for mineralogical and microstructural characterization and for measurement of macroscale properties as diffusion coefficient, permeability and water sorptivity. From multiscale modelling perspective, deployment of thermodynamic model, continuum scale, mesoscale and pore scale models are key to advancing the understanding of material evolution. In particular, an overview of pore-scale models is presented that explicitly accounts for the heterogeneity of cement paste for calculating flow, transport and ageing processes and effects on microstructure and macroscopic properties. Some of these developments are discussed in the context of long-term carbonation and leaching of cementitious materials. Finally, the paper discusses opportunities in the context of immobilization of waste, including some recent modelling work.

Carbonation model for concretes with fly ash, slag, and limestone calcined clay - using accelerated and five - year natural exposure data

Supplementary cementitious materials (SCMs) can be used in concrete to enhance sustainability and reduce the concrete industry's carbon footprint. However, some negative perceptions about their long-term carbonation resistance are obstacles for large-scale implementation of such concretes. This study evaluated the carbonation resistance of 34 concretes (with Ordinary Portland Cement, fly ash, blast furnace slag, and limestone calcined clay) in natural tropical exposure conditions (Open and Sheltered) for 5 years and in accelerated exposure conditions (1 and 3% CO2) for 112 days. Using these data and the square root of time function, the carbonation coefficients (KCO2, natl and KCO2, accl) of these concretes were estimated and a good correlation between them could not be observed. Hence, a more generic model (named as “A-to-N model”) to estimate the KCO2, natl using the KCO2, accl, CO2 concentration, and mixture proportion of concrete was developed, for which the mean absolute percent error is about 12% (reasonable accuracy). Using the A-to-N model, the carbonation depth at 50 years was estimated for various concretes. SCM concretes with low water-binder ratio and optimal binder content showed high resistance against carbonation at later ages; such information along with the target cover depth must be used while selecting materials for concrete design. Based on the model developed, a relatively simple ‘service life design chart’ was developed. This chart can be used by engineers to set the target KCO2, natl or KCO2, accl, and select the cover depth and binder type to provide the target service life (i.e., corrosion initiation time). This paper clearly shows that SCMs can be used to design concretes with comparable long-term carbonation depth as OPC concretes.

Effect of variability of hemp shiv on the setting of lime hemp concrete

Lime hemp concrete (LHC) is one of the most environmentally friendly alternatives to traditional building materials, which is normally used as an insulation material. The lime hemp concrete is made up of hemp shiv and aerial (or hydraulic) lime and has the ability to offer better thermal and acoustic performances. However, it is reported that the shiv/matrix reaction does not always meet the expectations, thus the properties of hemp concrete may be affected by certain characteristics, such as origin, retting time, harvest time, etc. of the used hemp. During this work, the authors have studied the influence of variability of hemp shiv on the setting of LHC. The results depicted that the soluble components (e.g., organic acids, simple sugars, etc.) from hemp shiv had a significant impact on the setting and hardening of mortars. This study also proved that hemp containing more soluble components tends to involve a longer setting time and hinders long-term carbonation reaction of binders. Furthermore, the experimental results also showed that water treatment can effectively remove these soluble agents from hemp shiv and improve the compatibility between shiv and binder in the composite.

An investigation into the long-term carbonation of vegetal concretes containing a viscosity modifying agent

In modern times issues such as sustainability and carbon footprint have become subjects of significant interest on a global scale. A leading industry in greenhouse emissions is the construction industry, and the industry’s carbon footprint needs to be reduced in order to meet emissions targets. Hemp concrete and rapeseed concrete are two alternative sustainable building materials that can help the construction sector improve and meet those targets. Because of their relatively recent introduction, limited studies are available on the durability of these materials. This paper investigates the effect of long-term accelerated carbonation on hemp and rapeseed concretes manufactured with a natural cement and, in some cases, a polyacrylic acid viscosity modifying agent (VMA). Natural carbonation in an outdoor environment was also studied. It was found that the mixes carbonated quickly under accelerated conditions, however no impact on mass or specimen dimensions were observed. In the case of the VMA mixes, it was found that the compressive strength of the samples was improved compared to the equivalently aged control samples. However, it was found that compressive strength was actually inhibited in the untreated mixes when compared with the control samples.

Enhancing carbonation and chloride resistance of autoclaved concrete by incorporating nano-CaCO3

Abstract Three nano-CaCO3 (NC) replacement levels of 1, 2, and 3% (by weight of cement) were utilized in autoclaved concrete. The accelerated carbonation depth and Coulomb electric fluxes of the hardened concrete were tested periodically at the ages of 28, 90, 180, and 300 days. In addition, X-ray diffraction, thermogravimetry, and mercury intrusion porosimetry were also performed to study changes in the hydration products of cement and microscopic pore structure of concrete under autoclave curing. Results indicated that a suitable level of NC replacement exerts filling and accelerating effects, promotes the generation of cement hydration products, reduces porosity, and refines the micropores of autoclaved concrete. These effects substantially enhanced the carbonation and chloride resistance of the autoclaved concrete and endowed the material with resistances approaching or exceeding that of standard cured concrete. Among the three NC replacement ratios, the 3% NC replacement was the optimal dosage for improving the long-term carbonation and chloride resistance of concrete.

Carbonation resistance of concrete treated with nano-SiO2- modified polymer coatings

This work investigated the effects of nano-SiO2 incorporation on the carbonation resistance of polymer-coated concrete. Three types of organic film-forming coatings, namely, polyurethane, chlo- rinated rubber, and epoxy resin coatings, were modified with 0.4, 1.2, or 2.0 wt.% nano-SiO2 particles. Concrete specimens were then treated with the modified coatings and subjected to accelerated carbona- tion experiments after periodic ultraviolet irradiation. The macro- and microappearances of the coatings after ultraviolet aging were also observed. Results indicated that the carbonation resistance of polymer- coated concrete samples gradually decreased as the polymer coating aged. The incorporation of nano- SiO2 improved the short-term carbonation resistance of coated concrete by increasing coating density and reducing microdefects in the coating film. The presence of nano-SiO2 strengthened the long-term carbonation resistance of coated concrete by shielding and absorbing ultraviolet light and attenuated coating aging. Excessive nano-SiO2 content, however, weakened the carbonation resistance of coated concrete. Thus, a nano-SiO2 dosage of approximately 0.4 wt.% should be applied to develop concrete coatings with the optimal carbonation resistance.

Controls on Mineral Carbonation Reactions in Basalt Fracture Networks

Basalts could provide secure long-term CO2 sequestration through mineral carbonation. Here, a series of flow-through experiments was conducted to investigate the effects of temperature, brine chemistry, and transport limitations on carbonation reactions in basalt microfractures. Post-reaction sample characterization revealed that carbonates preferentially formed in diffusion-limited vesicles and dead-end fractures, while injection paths were altered to clay minerals. The extent of secondary precipitation increased with increasing influent [NaHCO3] (from 6.3 to 640 mM) and temperature (from 100 to 150°C). Elevated [NaHCO3] also enhanced Mg- and Fe-uptake into carbonate minerals while carbonation at low [NaHCO3] was limited to Ca-carbonates that were strongly localized on Ca-rich pyroxene grains, consistent with predictions from complimentary 2D reactive transport models. The results highlight how complex coupling between fluid chemistry and transport conditions govern the extent and location of mineral carbonation reactions in natural basalts, which can inform selection of favorable storage sites and CO2 injection schemes with respect to long-term carbonation efficiency.

Long-term effectiveness of carbonation resistance of concrete treated with nano-SiO2 modified polymer coatings

For studying the influences of nano-SiO2 on the long-term carbonation resistance of concrete treated with polymer coatings, three types of organic film-forming paints, such as polyurethane, epoxy resin, and chlorinated rubber, were selected, and nano-modified paints with the addition of 0.5, 1.5, and 3.0 wt% of nano-SiO2 particles were prepared and applied on concrete specimens. Ultraviolet radiation, natural exposure, and accelerated carbonation experiments were performed on coated concrete specimens. In addition, scanning electron microscopy and Fourier transform infrared spectroscopy experiments were conducted. The results indicate that the carbonation resistance of concrete with polymer coatings deteriorates gradually with aging. Nano-SiO2 particles can reduce the micro-defects in coating, and enhance the compactness of coating, thus increasing the carbonation resistance of coated concrete. Furthermore, the addition of nano-SiO2 can alleviate the damages of ultraviolet irradiation on polymer molecules, and then enhance the long-term effectiveness of carbonation resistance of coated concrete. However, a suitable nano-SiO2 dosage of about 1.5 wt% exists, and excessive dosage decreases or even loses the useful functions. Based on carbonation resistance of coated concrete and an S-shaped curve, a new service life prediction model for polymer coatings is established. Owing to the contribution of nano-SiO2, the average service life of chlorinated rubber, epoxy resin, and polyurethane coatings can be lengthened by 78%.

Durability studies of nano-engineered fly ash concrete

Mechanical and durability properties of nano-engineered fly ash concrete have been carried out using various concrete mixes containing 30–50% fly ash (FA), 3% silica nanoparticles (SNPs) and 6% silica fume (SF) at constant water/cement (w/c) ratio of 0.29. Durability parameters i.e. carbonation (2% CO2, 20 °C, 65% RH) and sulphate attack (5% magnesium sulphate) were investigated using these specimens after exposing them up to 180 days. Long-term carbonation results revealed that SNPs incorporated mixes show a reduction of carbonation depth up to 73% with respect to control specimens containing 30% FA. Similarly, SNPs incorporated specimens show significant resistance towards the sulphate attack of about 39% as compared to control specimens. For the comparison purpose, SF containing specimens were also evaluated, however, higher resistance were observed for SNPs incorporated concrete specimens. Diffusion coefficient and service life of SNPs incorporated specimens were studied using Meta and Demis model, revealed exponential enhancement in the service life of SNPs incorporated concrete mixes.

The role of graphene oxide in limited long-term carbonation of cement-based matrix

Carbonation leads to a drop in the alkalinity of cementitious materials because carbon dioxide mainly attacks calcium phases and converts them into carbonated phases. The carbonation rate depends on the ease with which carbon dioxide can proceed from outer to internal surfaces. In this study, graphene oxide (GO) is used to enhance the resistance of cement matrix against carbon dioxide attack. Graphene oxide was added to cement mix sufficient amount of water to produce cementitious matrix. Visual colour change, porosity and compressive strength tests were performed to investigate effect of the carbonation on cementitious materials. The results show very low carbonation depth in the graphene oxide cement mix. After 18 months, the plain cement mixture was nearly fully carbonated compared to only about 4 mm for the GO mix. This significant result can be attributed to the influence of interlocking of GO to different anionic and cationic ions.