Carbonate Concretions Research Articles

Finite-Element-Based Time-Dependent Service Life Prediction for Carbonated Reinforced Concrete Aqueducts

This study proposes a time-dependent reliability analysis method for aqueduct structures based on concrete carbonation and finite element analysis. The primary goal of this study is to improve the reliability assessment of reinforced concrete aqueducts by incorporating environmental factors such as carbonation over time. First, a three-dimensional finite element model of a reinforced concrete aqueduct is established using the Midas 2022 Civil software, incorporating a time-varying function derived from a predictive model of concrete carbonation depth. Point estimation is then integrated with structural finite element analysis to calculate the first four moments of random variables as functions of concrete carbonation. Additionally, the original performance function is transformed into a normal distribution using dual power transformation and the Jarque–Bera test. The high-order unscented transformation (HUT) is subsequently employed to estimate the first four moments of the transformed performance function, facilitating the calculation of time-varying reliability indices for the carbonated concrete aqueduct. Based on the time-varying reliability index data, a reliability function corresponding to different time points is fitted and applied to service life prediction. The results demonstrate that the proposed method effectively reduces large errors associated with the fourth-moment method in calculating large reliability indices. Furthermore, the comparison with Monte Carlo simulation (MCS) results validates the high efficiency and accuracy of the proposed method, offering a valuable tool for addressing the reliability challenges of aqueducts exposed to carbonation and other environmental factors over time.

Performance optimisation of alkali-activated slag ultra-low carbon concrete (AAS-ULCC) for shield tunnel segments by steel fibres

Performance optimisation of alkali-activated slag ultra-low carbon concrete (AAS-ULCC) for shield tunnel segments by steel fibres

Experimental Study on the Effects of Crack Width and Crack Depth on the Carbonation of Concrete in Electric Power Utility Tunnels

An underground electric power utility tunnel is an important piece of infrastructure. Securing the durability of such structures is essential to ensuring their long lifecycles. However, the concrete of an electric power utility tunnel is likely to be carbonized, owing to long-term exposure to high carbon dioxide. Moreover, the carbonation of concrete may be intensified by damage, such as cracks. In this study, the characteristics of carbonation in electric power utility concrete were examined based on crack width and depth. The results of the experiment showed that the crack width was an important variable in the carbonation of concrete in an electric power utility tunnel. Carbonization proceeded at the tip of the crack, even if the crack was deep and the width was small.

Carbonation and Compressive Strength Properties of Electric Power Utility Tunnel Concrete Exposed to a Carbon Dioxide Environment

Recently, the service lives of electric power utility tunnels have been increasing rapidly; however, inspection and maintenance tasks are difficult, and the economic loss owing to the end of tunnels’ lifespans is substantial. Moreover, electric power utility tunnels are exposed to high carbon dioxide. Because their interiors are sealed environments, the tunnels are significantly affected by carbon dioxide. Carbon dioxide can cause concrete carbonation, which can lead to a decline in the performance of electric power utility tunnels. In this study, the carbonation characteristics of concrete were analyzed, and the effect of carbonation on the mechanical performance was evaluated.

Relationship Between the Carbonation Depth and Microstructure of Concrete Under Freeze-Thaw Conditions.

Concrete structures in cold regions are affected by freeze-thaw cycles (FTCs) and carbonation, which lead to the premature failure of concrete structures. The carbonation depth, relative dynamic elastic modulus (RDEM), compressive strength, porosity, and pore size distribution of concrete under FTC conditions were tested through an accelerated carbonation experiment to study the carbonation performance evolution. The freeze-thaw effect mechanism on concrete carbonation was further analyzed via the obtained relationship between carbonation depth and pore structure. The results showed that the FTC, as a powerful source of concrete damage, accelerates the carbonation reaction. Carbonization products fill some microcracks caused by the freeze-thaw process, improve the compressive strength and dynamic elastic modulus, and alleviate the damage to concrete caused by the FTC. After carbonization under freeze-thaw damage conditions, the content of macropores with d > 1000 nm decreases, while the content of transition pores with d ≤ 10 nm increases, which is the direct reason for the decrease in porosity and the improvement in strength. Therefore, the carbonation durability of concrete under freeze-thaw conditions can be improved by controlling the content of macropores with d > 1000 nm and increasing the content of transition pores with a pore size of 10 nm ≤ d < 100 nm. In addition, the relationship between carbonation depth and pore structure under freeze-thaw conditions was established, and the research results can provide a reference for the study of the carbonation performance of concrete under freeze-thaw conditions.

Single-parameter concrete carbonation model for varying environmental exposure conditions

Carbonation-induced reinforced steel concrete corrosion is a prominent concern related to engineering design and maintenance. The Durability Index (DI) approach was developed in South Africa to address this concern and enhance the durability performance of reinforced concrete structures. This approach relies on durability index tests, which are associated with transport mechanisms linked to specific deterioration processes. The carbonation of concrete is primarily influenced by the microstructure and transport characteristics of the concrete. Environmental exposure conditions also influence the rate of carbonation. The focus of the research reported here was to develop a carbonation model that could predict the rate of carbonation of concrete exposed to, or sheltered from, rain, with the permeability coefficient (k) from the Oxygen Permeability Index (OPI) test (DI test) as the key unifying variable. The model development was based on natural carbonation data and the drying profiles (experimentally measured) of 48 different concretes. Concrete microstructure was varied by varying the water-to-cement ratio, curing conditions, and by using SCMs. The resulting carbonation model was able to predict the rate of carbonation of concrete, allowing for different exposure conditions. A unique feature of this model is its use of a single material property, the 'k' value, to effectively address both CO2 diffusion and the drying process within concrete. The model displayed sensitivity towards the influence of variation in CO2 concentration, concrete microstructure, and the environmental exposure conditions, making this a simplified, effective and practical concrete carbonation prediction model.

Iron-carbonate concretions with inverse magnetic fabrics; a record of environmental changes in the middle Eocene marine marls of the Southern Pyrenees?

AbstractThis paper deals with the detailed analyses of magnetic fabrics, accompanied by stable isotopic composition and microscopic observations, in centimetric and metric scale authigenic carbonate concretions embedded in the Eocene flysch deposits of the Southwestern Pyrenees. Sampling was focused in the carbonate concretions, (in both metric and centimetric scale), in the marls lateral and nearby to the concretions and in the marls located several meters away from the concretions. The inverse magnetic fabrics (kmax axes cluster perpendicular to bedding plane) detected in these concretions constitute a fast methodology to uncover the presence of iron-carbonate minerals and the paleoenvironmental significance of their authigenic origin. The subfabric analyses indicate that magnetite is present in all four types of samples with normal magnetic fabric (kmin axes perpendicular to bedding). Paramagnetic fabric (low temperature anisotropy of magnetic susceptibility when magnetic susceptibility increases ~ 3.8 times the one at room temperature) overlaps the room temperature magnetic fabric. The microscope observations reveal that iron-enriched dolomite is the main carrier of the inverse fabric in the carbonate concretions at room temperature. The stable isotopic composition indicates minor differences between the Eocene marls and the carbonate concretions and, when compared with previous data, they suggest a marine pore water origin due to bacterial activity during burial. We relate the early diagenetic growth of the concretions to an enhancement in bacterial activity driven by the increased terrigenous and terrestrial organic matter supply during the Middle Eocene Climate Optimum (MECO), a period of global warming.

The Universal Classification system for assessing the embodied carbon of concrete in Canada

Concrete is known to be the most prevalent human-made material globally owing to its durability, versatility and affordability which; however, contributes significantly to global CO2 emissions. Consequently, efforts have intensified to reduce concrete's embodied carbon, with emerging or conventional alternative technologies aiming to mitigate emissions and produce "sustainable" and "low carbon" concrete; a set of terms which have been used inconsistently leading to potential greenwashing and confusion in the industry. Simultaneously, there is a pressing need for tools and policies to guide the design of low-carbon concrete structures and infrastructure. This paper introduces an embodied carbon classification system as a practical solution to address industry confusion and facilitate sustainable practices in the concrete construction sector. It consists of a universally applicable tool that can be used by designers, manufacturers, asset owners and policy makers to enable a robust evaluation of the embodied carbon concrete, develop pathways to concrete decarbonisation.

Embodied Carbon in Concrete: Insights from Indonesia and Comparative Analysis with UK and USA

Concrete is the most widely used construction material globally. However, its production, particularly that of cement, is a significant source of carbon dioxide (CO2) emissions, contributing to approximately 8% - 10% of the global anthropogenic CO2 emissions. This study aims to analyze and compare the embodied carbon (eCO2) of various concrete strength grades commonly utilized in Indonesia to offer insights for enhancing sustainability in the construction industry. The methodology involved designing concrete mixes according to Indonesian standards and calculating carbon emissions for each component. The findings revealed that the eCO2 in the Indonesian concrete mixes was significantly higher than that reported in the UK and US databases. This higher carbon footprint emerges primarily due to the greater cement content found in the Indonesian mixes. Nevertheless, the current study demonstrated that using fly ash as a supplementary cementitious material can substantially reduce the eCO2, with the mix containing fly ash showing a 42% reduction in emissions compared to the mix without fly ash. This research emphasizes the necessity for the Indonesian construction industry to adopt sustainable practices, including optimized mix designs and the use of low-carbon materials such as fly ash. In doing so, significant reductions in the carbon footprint of concrete can be achieved, contributing to the global efforts to mitigate climate change and to promote sustainability in construction practices.

Quantitative Analysis of Carbonation Degree of Mortar Based on Multiple Interactive Influences.

This study conducts quantitative analysis of the degree of mortar carbonation under the influence of a multi-dimensional interaction. The HABT method is used to determine the degree of mortar carbonation and is compared with the TGA method. The result shows that the determination result of the HABT method is only 3.86% higher than that of the TGA method. This method is suitable for determining the degree of carbonation. The study analyzes the influence of factors such as water-reducing agents on the degree of carbonation, demonstrates the relationship between pore structure and mortar carbonation, and explores the degree of carbonation of corner areas and general edges. It is found that as time prolongs, the degree of carbonation and carbonation depth will no longer show a linear relationship. Carbonation time also affects the direction of the carbonation front line and the effect of water-reducing agents on concrete carbonation. The degree of carbonation is linearly related to carbonation time and the number of exposed surfaces. The water~cement ratio and the number of exposed surfaces affect the porosity of concrete. There is interaction in the multi-dimensional area of mortar. The degree of carbonation at two-dimensional corners is 1.20~1.25 times that at general edges, and the degree of carbonation at three-dimensional corner areas is 2.03~2.11 times that at general edges. Accounting based on general edges will underestimate the carbon sink capacity of mortar structures.

Desmoinesian (middle Pennsylvanian) radiolarians from the Excello Shale of Kansas, USA

Desmoinesian (Middle Pennsylvanian) radiolarians are described from carbonate concretions found in the black phosphatic facies in strata of the Excello Shale Member of the Fort Scott Limestone (Marmaton Group) in southeastern Kansas (K69 section), USA. Ten new species of radiolarians are described: Albaillella kansaensis, Holdsworthella trifurca, Pseudoalbaillella deformata, Entactinia jayhawkensis, E. heckeli, E. boardmani, Apophysiacus martiali, Moskovistella insolita, Palacantholithus umbrelliformis, and Ormistonella perrara. The Kansas radiolarian assemblage is different from the assemblage described from the Excello Shale of Iowa in the preservation and taxonomic composition. The radiolarians are preserved as pyritized internal molds or regular tests replaced by pyrite, and unidentifiable organic material. The domination of entactinarians and albaillellarians in the Kansas assemblage and their poor to excellent preservation indicate the formation of early diagenetic calcareous concretions in anoxic conditions. The appearance of the spicular radiolarian genus Palacantholithus indicates an influx of relatively cold water connected with upwelling. The Kansas location was much farther offshore (450 km basinward) compared to the Iowa localities suggesting a difference in thermocline depth, affecting water temperature, oxygenation, and nutrients.

CALCULATION AND EXPERIMENTAL DEPENDENCIES OF INITIAL CARBONATION OF CONCRETE COMPRESSIVE STRENGTH CLASSES C12/15...C50/60

The article substantiates the need to study the preliminary carbonization of concrete. Based on laboratory studies of concrete samples of compressive strength classes С12/15…С50/60, mixture compositions of workability grades P1 (OK = 4 cm), a system of calculated and experimental dependencies of initial carbonization КС0 = f(Ц) was obtained. The dependencies were checked using mathematical statistics methods, which showed the adequacy of the obtained dependencies. Obtained depending on the preliminary carbonization КС0 = f(fG c,cube) on the guaranteed compressive strength of concrete for mixtures of workability grade P1. By mathematical processing of the dependence coefficients derived from the dependence of the initial carbonization КС0 = f(Цр) and КС0 = f(fG c,cube) for classes of concrete in terms of compressive strength С12/15…С50/60, mixture compositions of workability grades G1 (8 s) and G2 (15 s).

Influence of stockpile design on carbonation of waste concrete: Implications for carbon management in China.

Enhancing the sequestration capacity of waste concrete is crucial for achieving carbon neutrality within the construction industry. Although existing studies primarily focus on theoretical analysis of concrete carbon sequestration, limited attention has been paid to explore the potential of waste concrete sequestration during stockpiling phase under varying environmental conditions. To fill this knowledge gap, we developed a CO2 uptake calculation model tailored for the stockpiling phase of waste concrete. This model investigates the impact of crush size, stacking method and environmental conditions on the total carbon sequestration capacity and efficiency, identifying the most advantageous approach. Our findings reveal the following: (1) Increasing the crush size of waste concrete enhances its carbon sequestration capacity, albeit extends the sequestration duration. A crush size of 5-20 mm is deemed optimal for achieving the desired sequestration efficiency. (2) The optimal stacking method involves smaller piles with reduced radii and angles. (3) High temperatures and humidity levels accelerate the sequestration rate. Practical measures such as watering and covering can be employed to enhance carbon sequestration. (4) In 2021, China's waste concrete exhibited a declining sequestration potential from the southeast to the northwest and northeast regions. The maximum sequestration potential has the capacity to neutralize up to 4% of the carbon emissions generated by the construction industry in that year. This research provides a foundation for accurate assessment and the development of effective carbon sequestration strategies for waste concrete.

Monitoring CO 2 , CO and CH 4 , affected or not by ventilation and anthropogenic activities, in the galleries of the Underground Research Laboratory (URL) of Meuse/Haute-Marne

The alternation between periods of ventilation and non-ventilation of the galleries in the Meuse/Haute-Marne Underground Research Laboratory (URL) within the Callovian–Oxfordian argillaceous rock affects the contents of CO 2 , CO and CH 4 in atmospheric air. Monitoring the evolution of the gas composition in the galleries was conducted over a period of about 4 months. Two models of IR laser spectroscope (Picarro) were used, one to measure CO 2 , CO and CH 4 concentrations and the other to measure CH 4 isotopic compositions. The results show a night and day periodicity with the highest concentrations at night-time and the lowest during the daytime in the URL. Long-term monitoring of these gases at the surface shows the same evolution, but with different amplitudes. Moreover, in the URL, a weekday and weekend or holiday periodicity were superimposed. The concentrations of CO 2 in the galleries are influenced by human activities and ventilation. During working days, the galleries are ventilated, and human activities increase the CO 2 concentrations. Conversely, during weekends and holidays, CO 2 concentrations decrease owing to the cessation of ventilation and human activities, and consumption of CO 2 by concrete carbonation. The data analysis confirms a CH 4 source from the rock and reveals compelling evidence of CO sources that probably originate from rock and/or gallery engineered structure materials. Despite the difficulties in quantifying local sources and sinks of these gases, this study demonstrates the feasibility of obtaining valuable insights into their variability. This study provides information on potential sources and sinks of CO 2 , CO and CH 4 in this context.

A novel ultrasonic-velocity-based concrete carbonation monitoring method based on step-wise stretching technique

Carbonation is a common and slow process that occurs in cement-based material, resulting in durability degradation of reinforced concrete structures. In this research, the relative velocity change (d v/ v) of both ultrasonic direct waves and coda waves are extracted based on the step-wise stretching method for concrete carbonation monitoring. To this end, two-dimensional mesoscale models are established to investigate the ultrasonic propagation behaviors and assess the effectiveness of direct waves and coda waves on concrete carbonation monitoring. The numerical results indicate that direct waves could evaluate the initial carbonation, but exhibit limited sensitivity for severe carbonation. Conversely, the d v/ v values of coda waves show a linear correlation with carbonation depth in all conditions. Accelerated concrete carbonation experiments are conducted to validate the numerical findings. The experimental results and numerical findings mutually corroborate, validating the effectiveness of velocity changes of coda waves on all-stage concrete carbonation monitoring. This research contributes a novel method for monitoring concrete carbonation and enhances the understanding of ultrasonic wave propagation in concrete.

An Improved Fick Model for Predicting Carbonation Depth of Concrete

Concrete carbonation can weaken its strength, cause the corrosion of steel reinforcement, and shorten its service life. Predicting the concrete carbonation depth is a critical aspect of assessing concrete durability. Currently, mathematical models for the concrete carbonation depth, exemplified by the Fick model, suffer from a low fitting accuracy and limited applicability due to the complexity and variability of concrete materials and service environments. In light of this, this work proposes an improved Fick model that incorporates a correction term to effectively enhance the curve fitting accuracy. The correction term in the improved model provides a reasonable adjustment for deviations in the development pattern of the concrete carbonation depth from the Fick model under different conditions, thereby broadening the applicability of the new model compared to the Fick model. Several sets of experimental data on the concrete carbonation depth are used to validate the universality and superiority of the new model. The results of the case studies indicate that the average prediction error and standard deviation of the new model are significantly smaller than those of the Fick model. For the first two examples, in most situations, the average prediction error and standard deviation of the new model are less than 50% of those of the Fick model, with the lowest average prediction error being only 4% and the lowest standard deviation being only 2% of the Fick model’s respective values. For the third example, the new model demonstrates superior predictive capability for the later-stage concrete carbonation depth compared to the Fick model and the ANN model. Specifically, for the carbonation depth of the concrete on the 56th day, the relative error between the predicted value of the new model and the measured value is only 2%, which is much smaller than the 27% of the Fick model and the 12% of the ANN model. These results demonstrate the unique advantage of the proposed model in predicting the carbonation depth, especially when only a limited amount of experimental data are available.

Pleistocene to early Holocene paleoenvironmental evolution of the Abrolhos depression (Brazil) based on benthic foraminifera.

The paleoenvironmental evolution of the Abrolhos Depression (AD) on the southern Abrolhos Shelf during the global post-Last Glacial Maximum (LGM) transgression is investigated through benthic foraminifera analysis. Downcore sediment samples (core DA03A-5B) collected at a depth of 63m provide insights into the formation and paleoenvironmental variations of AD over the past 18 kyr BP. The core is divided into four biofacies based on foraminifera assemblages. At the base, the presence of carbonate concretions indicates a karstic surface, marking the initiation of the paleolagoon formation at approximately 13 kyr BP with low density of foraminifera, where species such as Elphidium sp. and Hanzawaia boueana (EH Biofacies) were more abundant. During the Younger Dryas (YD) (12.8-12.5 kyr BP), the AD exhibits two distinct phases: an initially confined lagoon environment with reduced circulation characterized by the dominance of the species Ammonia tepida (At Biofacies), followed by increased circulation characterized by higher density, richness, and diversity of benthic foraminifera. The end of the YD is identified by a significant biofacies change, indicative of a shallow marine environment, where the dominant species were A. tepida and Elphidium excavatum (AE Biofacies), supported by sedimentological and geochemical proxies. This paleoenvironmental shift is associated with Meltwater Pulse (MWP) -1B, suggesting a connection to a shallow marine environment. As sea levels continue to rise, the AD transitions into an open marine setting. However, around 8 kyr BP, a change occurs with the absence of A. tepida and the occurrence of planktonic and other benthic foraminifera typical of the outer shelf, indicating depths greater than 50m (HQ Biofacies). The findings highlight the complex interplay between climate fluctuations, sea-level changes, and the formation of coastal environments during the LGM transgression. This study contributes to our understanding of paleoenvironmental dynamics, adding valuable insights to the evolutionary history of AD. The results emphasize the importance of integrating benthic foraminifera analysis, radiocarbon dating, and geochemical proxies to reconstruct paleoenvironments accurately. Overall, this research enhances our knowledge of global continental shelf evolution during the post-LGM transgression and provides valuable information for future paleoenvironmental studies.

Novel accelerated carbonation methods based on deep breathing analogous and prediction model for pressurized carbonation of concrete

This research proposes a novel deep breathing analogy (DBA) accelerated carbonation process. Inspired by the breathing mechanism of human lungs, the DBA method involves injecting pure CO2 into a reaction chamber at a specific pressure (inspiration) and subsequently evacuating the gas from the chamber to a negative pressure (exhalation). This process is repeated to remove excess water from the chamber and restore optimal carbonation conditions, which further enhances the efficiency of carbonation for the sample. The effectiveness of this method is evaluated based on weight gain, proportion of captured CO2 and carbonation depth. Results show that the DBA method significantly reduces the inhibition of carbonation. Based on the test results, a correlation between the proportion of captured CO2 and carbonation depth is established. Additionally, a more accurate prediction model for pressurized carbonation is proposed and the economic potential of concrete carbonation is studied.

Concrete carbonation depth prediction model based on a gradient-boosting decision tree and different metaheuristic algorithms

Carbonation is a significant factor contributing to the instability of concrete structures. This study proposes two prediction models based on the gradient boosting decision tree (GBDT) to address the challenge of predicting concrete carbonation depth. This study integrates GBDT with two metaheuristic algorithms, particle swarm optimization algorithm (PSO) and sparrow search optimization algorithm (SSA), forming two hybrid models, PSO-GBDT and SSA-GBDT, aimed at enhancing prediction accuracy. Six influencing parameters (FA, t, w/b, B, RH, and CO2) were selected as input features to train and evaluate the hybrid models, with the concrete carbonation depth was used as the output. A database containing 883 groups of cases was established. Finally, three classic models, GBDT, ANN and SVR, were compared against the two hybrid models. To enhance model generalization, all models were subjected to five-fold cross validation. Four evaluation indicators (RMSE, R2, MAE, and VAF) and Taylor diagrams were employed to comprehensively assess these models. The results indicated that the two hybrid models exhibited superior prediction performance in the dataset (training set: R2, VAF>0.98, testing set: R2, VAF>0.96). The SSA-GBDT model achieved the highest prediction performance (RMSE= 2.7008, R2= 0.9639, MAE= 1.7691, VAF= 0.9627). Additionally, the SSA-GBDT model identified exposure time (t) as the feature with the greatest impact. This study demonstrates the applicability of the SSA-GBDT models in predicting concrete carbonation depth, offering a novel approach for improving accuracy in such predictions.

Development of New Method for Concrete Carbon Emission evaluation: The Anti-freezing durability-oriented Carbon Emission Indicator (CEI) System and its application in design of low carbon HPC with high durability

This research focuses on the development of the Anti-freezing Durability-Oriented Carbon Emission Indicator (CEI) system for assessing concrete's carbon footprint with an emphasis on durability, particularly in freeze-thaw conditions. This novel approach reduces the environmental impact of concrete by integrating durability metrics into carbon emission evaluations. The paper presents experimental findings on mix designs for high-strength, low-carbon concrete, which demonstrate improved freeze-thaw durability. And found out that concrete mixes using sulfate-resistant cement with GGBS outperform those with FA and OPC in terms of low-carbon performance, in the newly developed 19 mixes, concrete mix incorporating air-entraining agents with sulfate-resistant cement and 40% GGBS as a supplementary cementitious material, namely the HPC1-P•HSRF-S group, demonstrates a distinct low-carbon advantage across various indicators.Overall, the inclusion of fibers is shown to improve freeze-thaw durability, though with limited impact on compressive strength. The research underlines the importance of optimizing concrete mix designs for both environmental and durability considerations, presenting a significant step towards more sustainable construction practices.