Carbonate Concretions Research Articles

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

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.

Origin and preservation mechanisms of organic matter in carbonate concretions from Lower Cambrian black shales in South China

Carbonate concretions are widely used in paleoclimate, paleoenvironmental, and paleontological studies, and even in the study of potential life on Mars. These petrological, elemental, isotopic, and lipid biomarker signals in Meso-Cenozoic carbonate concretions (relatively low thermal maturity) can effectively preserve details of seawater conditions and benthic ecosystems during the deposition of their host sediments/rocks. However, such research on Precambrian-Cambrian carbonate concretions under highly mature conditions remains scarce, and the ability of these ancient carbonate concretions to retain their original biogenic information remains uncertain. To achieve that, this study examines two Cambrian carbonate concretions, using samples from the center, transition, and rim of each, and their adjacent host black shales from the Lower Cambrian Qiongzhusi Formation in the Yangtze Block, South China. Organic and inorganic geochemical analyses were combined to elucidate the origin and preservation process of organic matter (OM) in these ancient Cambrian carbonate concretions. The results show that the thermal maturity of OM within these concretions (1.8 % EqVRo) is relatively low compared to their adjacent host shales (2.9 % EqVRo). Hopanes and steranes are detectable in both free and calcite-occluded hydrocarbons within these concretions, with concentrations of individual compounds ranging from 0.001 to 0.800 μg/g TOC, whereas kerogen-bound hydrocarbons lack detectable biomarkers. The results indicate that the two Cambrian carbonate concretions were formed mainly within the iron reduction and bacterial sulfate reduction zones, extending to depths of 10 to 38 m below the sediment-water interface. The OM within these concretions mainly inherited the initial unaltered signature of OM from the Qiongzhusi host shale. The carbonate concretions protected the internal OM from further thermal and secondary (e.g., biodegradation) alteration processes and might also prevent the formation of the conventional macromolecular skeletal kerogen manifested by the absence of bound biomarkers. The biomarkers, in both free and occluded forms, in the Cambrian carbonate concretions still retained their original source information, providing valuable insights into ancient biogeochemical processes during sediment burial and ancient seawater chemistry during the early Cambrian.

Concrete carbonation in tropical urban and urban/marine environments after 20 years of natural exposure

This work is part of the DURACON project, which seeks to characterize the durability of concrete exposed to environmental conditions prevailing in Ibero-America and is based on the exposure of unreinforced and reinforced concrete specimens in marine and urban environments in each participating Ibero-American country. This research presents the results obtained from exposing unreinforced and steel-reinforced concrete specimens to prevailing environmental conditions in twelve natural exposure sites in Mexico during an exposure period of approximately 20 years to determine an empirical model that allows predicting the value of the carbonation rate, k′CO2, as a function of the nth-root of time (NRT) for the concretes evaluated. The concrete specimens, plain and reinforced, exposed to the elements in these cities were manufactured with two types of concrete, one with a w/c ratio = 0.65 and the other with a w/c ratio = 0.45. The tests mainly focused on measuring the concrete carbonation front depth during the ∼ 20 years of exposure and the measurement of environmental parameters at the exposure sites, such as temperature, relative humidity, rainfall, and atmospheric CO2 concentration. The electrochemical parameters of the reinforcing steel (half-cell potential, Ecorr, and current density, icorr) in the reinforced specimens were also obtained after ∼ 20 years of exposure to corroborate which sites showed lower or higher corrosion activity. This model to obtain k′CO2 as a function of the environmental parameters of the Mexican exposure sites and the physical properties of the concretes was compared with the value of kCO2 obtained from the square root of time (SRT) model. It was found that the k′CO2 values were 30 % higher on average than the kCO2 obtained with the empirical SRT equation. However, it should be noted that k′CO2 must be linked to the corresponding nth-root of time, whereas the value of n to obtain kCO2 is constant and equal to ½. An agreement was also obtained between the probability of activation of the reinforcing steel, using the corrosion parameters (Ecorr and icorr), and the probability of eCO2 ≤ 15 mm (lowest concrete cover used in this study).

Passivation performance of Nb microalloyed rebar in concrete carbonation environments with different pH

In this study, XPS sputtering depth, SEM and electrochemical tests (CV, EIS, M-S, i-t, DPP) were used to study the structural composition and formation mechanism of surface passive film of Nb microalloyed rebar in SCPS with different pH. The results showed that after passivation for 10 d in SCPS with different pH, compared with CS rebar, the stability and compactness of surface passive film of 34Nb rebar gradually increased with the decreases of pH. Firstly, with the decreases of pH, the outer layer of surface passive film of 34Nb rebar was composed of Fe oxides and Fe hydroxides, and the inner layer was composed of Fe oxides and Nb oxides, thus increasing the mass ratio of Fe3+/Fe2+ and Nb2O5/(NbO2 + NbO). Secondly, with the decreases of pH, the addition of Nb promoted the formation of Fe oxides in 34Nb rebar, obtaining the excellent Rct, Ecorr and Ep. Finally, with the decreases of pH, the addition of Nb promoted the enrichment of Nb oxides in 34Nb rebar, inhibiting the degradation of Fe oxides, and the passive film exhibited the P-N type semiconductor, thus significantly decreasing the carrier density and enhancing the passivation rate of 34Nb rebar.

Comprehensive study of sequester-based carbon concrete in an acidic environment using artificial neural networks

Comprehensive study of sequester-based carbon concrete in an acidic environment using artificial neural networks

High resolution paleo-hydrological record from carbonate deposits in the Roman aqueduct of Traconnade (Aix-en-Provence, SE France)

Carbonate deposits in aqueducts are potential valuable archives of the paleo-hydrological record for the Roman period. Here we present a new high-resolution record from carbonate deposits in the aqueduct of Traconnade built for Aix-en-Provence, the Roman city of Aquae Sextiae. As its name indicates, Aquae Sextiae was built around an abundant source of water but its development, like other ancient cities, required good management of this resource. Through a combination of micromilling and in situ analysis (LA–MC–ICPMS) on thin sections, we measured geochemical variations (stable isotopes and trace elements) and performed sampling for absolute UTh dating. Geochronological results based on classical correction and isochron along with archaeological observations confirm that the carbonate concretion was deposited in Roman times on the walls of the Traconnade aqueduct, built no later than 140 CE. Carbonate δ18O records document the presence of clear geochemical cycles that were mainly controlled by seasonal variations in temperature and δ18O from water circulating in the aqueduct. Minima and maxima in δ18O values were attributed to summer and winter conditions, respectively in agreement with the modern spring’s stable isotope values. The other tracers (Mg/Ca, Sr/Ca and δ13C) also show marked cyclicities with maximum values occurring in summer. The enrichment in trace elements and δ13C were linked to processes occurring during dry periods (1) prior precipitation of calcite in the epikarst, and/or (2) a greater degree of CO2 degassing. The geochemical variations in Ba/Ca, U/Ca and Rb/Ca behave differently and their co-variations may reflect the water-rock interactions in the karst system. We highlight that these tracers can be used as a proxy for intense precipitation events, occurring frequently during autumn. The Traconnade aqueduct carbonate provides sufficient temporal resolution to explore environmental variations on a seasonal scale. These results suggest the occurrence of a double rainy season (spring and autumn) in the Aix-en-Provence region, similar to present-day climatic conditions. Our study confirms the high potential of aqueduct concretions for paleohydrological studies.

Resistance to acid, alkali, chloride, and carbonation in ternary blended high-volume mineral admixed concrete

The World Bank study predicts that 4 °C warming will bring high temperatures, sea-level rise, and saltwater intrusion to coastal areas, damaging coastal concrete structures. Increased CO2 from industrialization exacerbates this, necessitating durable, low-carbon concrete. Combined use of fly ash (FA) and ground granulated blast furnace slag (GGBFS) as high-volume OPC replacements boosts performance while reducing concrete’s carbon footprint. In this perspective current study examines the durability of concrete against aggressive agents (H2SO4, MgSO4, NaCl, and CO2) causing premature deterioration of concrete structures. Initially, three cost-effective sustainable concrete mix designs were developed, incorporating 50% replacement of OPC with locally available supplementary cementitious materials, specifically FA and GGBFS. These mixes were then evaluated for their mechanical and durability performances. The impact of aggressive ions (SO4 2−, Cl−, and CO3 2−) was studied by examining the changes in mechanical performance and phase assemblages. Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) techniques were used to estimate the phase compositions. Ternary blended concrete having 50% OPC+ 30% GGBFS + 20% FA exhibited optimal synergistic performance, enhancing pozzolanic and hydraulic reactions for better resistance to harmful ions. The sorptivity test confirmed that as the GGBFS content increased, the sorption rate decreased, indicating the higher reactive nature of GGBFS to that of FA. Deleterious compounds formed due to the action of SO4 2-, Cl-, and CO3 2- were identified to be ettringite (Ca6Al2(SO4)3(OH)12.32H2O, AFt) and gypsum (CaSO4.2H2O, Gy), Friedel’s salt (Ca4Al2(OH)12Cl2.4H2O, Fs) and polymorphs of calcium carbonate (CaCO3), respectively through TG mass loss curve. These results were corroborated by FTIR analysis, which showed predominant characteristic bands at 662 cm−1 for SO4 2−, 459 cm−1 for Mg–O stretching, 790 cm−1 for Al–OH bending, and 1431-1443 cm−1 for C–O, confirming the presence of the deleterious compounds.

Carbon–sulfur–calcium isotopic variability of lower Cambrian shale-hosted carbonate concretions: Insights into growth mechanisms and calcium cycling

Marine calcium cycling is closely linked with carbon cycling in the ocean, in which authigenic carbonates precipitated in sediments play a non-negligible role. However, calcium cycling during authigenic carbonate precipitation in organic-rich, shaly sediments in geological history remains underexplored. This study focuses on carbonate concretions (aggregates of authigenic carbonates) in the lower Cambrian Niutitang Formation, South China, to provide insights into calcium cycling during their growth. Sedimentological and mineralogical observations suggest that these concretions were formed through concentric growth by authigenic calcite and pyrite precipitation during the early diagenetic stage. Geochemical analyses reveal internal variations in “M-shaped” δ13Ccarb trends (from −11.9 ‰ to −4.4 ‰) and diverse δ34Spyr trends (from 4.7 ‰ to 14.0 ‰) along core-to-rim transects. These findings suggest formation through microbial sulfate reduction by organic matter in a shallow depth beneath the sediment–water interface. In contrast to the dynamic δ13Ccarb and δ34Spyr variations and multi-stage concentric growth, these carbonate concretions display nearly uniform δ44/40Cacarb values (from 0.80 ‰ to 1.03 ‰, average 0.96 ± 0.06 ‰, 1SD) and consistent internal trends, which are further attributed to strongly seawater-buffered porewater calcium geochemistry and small calcium isotope fractionation due to calcite precipitation at slow rates. This study confirms that early diagenetic carbonate concretions in the lower Cambrian Niutitang Formation are characterized by much heavier δ44/40Ca values compared to coeval shallow platform carbonates. In light of abundant authigenic carbonates observed in the lower Cambrian successions, their roles in calcium isotope mass balance in the early Cambrian ocean warrant further investigation in the future. Therefore, early diagenetic carbonate concretions in black shales could provide valuable insights into porewater and seawater calcium isotope signals, as well as early diagenetic and marine calcium cycling in geological history.

Monitoring CO 2 , CO and CH 4 , impacted 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 Callovo-Oxfordian argillaceous rock affects the content 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 infrared 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/day periodicity with the highest concentrations at nighttime 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, weekend/holiday periodicity 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 due to the cessation of ventilation and human activities, and consumption of CO 2 by concrete carbonation. The data analysis confirms CH 4 source coming from the rock and reveals compelling evidence of CO sources that are likely originating 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.

Report of RILEM TC 281-CCC: A critical review of the standardised testing methods to determine carbonation resistance of concrete

The chemical reaction between CO2 and a blended Portland cement concrete, referred to as carbonation, can lead to reduced performance, particularly when concrete is exposed to elevated levels of CO2 (i.e., accelerated carbonation conditions). When slight changes in concrete mix designs or testing conditions are adopted, conflicting carbonation results are often reported. The RILEM TC 281-CCC ‘Carbonation of Concrete with Supplementary Cementitious Materials’ has conducted a critical analysis of the standardised testing methodologies that are currently applied to determine carbonation resistance of concrete in different regions. There are at least 17 different standards or recommendations being actively used for this purpose, with significant differences in sample curing, pre-conditioning, carbonation exposure conditions, and methods used for determination of carbonation depth after exposure. These differences strongly influence the carbonation depths recorded and the carbonation coefficient values calculated. Considering the importance of accurately determining carbonation potential of concrete, not just for predicting their durability performance, but also for determining the amount of CO2 that concrete can re-absorb during or after its service life, it is imperative to recognise the applicability and limitations of the results obtained from different tests. This will enable researchers and practitioners to adopt the most appropriate testing methodologies to evaluate carbonation resistance, depending on the purpose of the conclusions derived from such testing (e. g. materials selection, service life prediction, CO2 capture potential).

Redox reaction models for carbonation of hardened cement under elevated temperature up to 1000°C

Concrete structures are exposed to various temperature environments and often come into contact with CO2 under these conditions. With the recent surge in interest in carbonation, there is a growing demand for a numerical model that can more comprehensively and flexibly account for the reactions of hydration, carbonation, decomposition, and recovery of cement hydrates. A comprehensive framework for concrete carbonation is proposed from a wide perspective of temperature with thermo-chemical modeling including de-carbonation and re-carbonation. By overlaying rates of bidirectional redox reactions, the dominant reaction at any temperature can be determined. The model framework, encompassing cement hydration, carbonation, de-hydration, de-carbonation, re-hydration, and re-carbonation, was experimentally validated by previous measurements of changes in weight and porosity under different CO2 concentrations and repeated exposure to high temperatures followed by post-fire-curing. These validations demonstrate a strong connection between the micro- and macroscopic properties of concrete in the proposed model. With this scheme, fire resistance of concrete composite under unexpected cases was explored computationally. Significant weight loss and strength reduction of cement paste are predicted after the first heating cycle, followed by gradual decline in subsequent repetitions of temperature. In the cases with water post-fire-curing, it is observed that the strength tends to restore even with repeated heating. In the cases with RH-60 % vapor post-fire-curing, the strength recovery is significantly increased by re-carbonation, but is still smaller than that of the cases with water post-fire-cuing.

Fundamentally understanding carbonation-induced corrosion of steel in environmentally friendly concretes

Reducing greenhouse gas emissions in concrete production is crucial to achieve sustainability goals. One of the primary solutions is employing environmentally friendly cements with lower clinker content, such as those containing supplementary cementitious materials. However, concretes produced with some of these cements are vulnerable to fast carbonation, which raises durability concerns regarding corrosion of the steel reinforcement. While traditional approaches focus on preventing concrete carbonation and corrosion initiation, evidence shows that corrosion rates of steel in carbonated concrete do not necessarily compromise durability. In this context, the fundamental understanding of the kinetics of carbonation-induced corrosion must be improved, considering the role of the concrete pore solution, pore structure, and moisture content, as discussed in this paper. Open questions and promising approaches to clarify them are also discussed. Based on this knowledge, corrosion propagation can be properly included in the service life design of reinforced concrete structures, reconciling the goals for both sustainable and durable structures.

Deterioration modelling of GFRP-reinforced cement-based concrete infrastructure in service under the natural inland atmospheric environment

The aim of this paper is to develop an interdisciplinary methodology for modelling the deterioration of GFRP-reinforced concrete (G-RC) structures in service under natural atmosphere. The evolution of concrete carbonation was analyzed using a multiscale physico-chemo-mechanical coupling platform, which has been validated through numerous successful applications in practical concrete structures. The coupled heat transfer and mass transport in cement-based concrete, including temperature, relative humidity (RH) and pH distributions, were analyzed and simulated using the multiscale platform based on detailed information about the cement type, concrete mixture, and weather records. The resulting data were used to assess the degradation of GFRP reinforcements embedded in concrete through the gas-liquid state shift equation and the chemical etching model (CEM). The concrete carbonation and the degradation levels of GFRP reinforcements were validated by the field data after 15 years of service, demonstrating the effectiveness of the established deterioration model.

Snapshot on 3D printing with alternative binders and materials: Earth, geopolymers, gypsum and low carbon concrete

The rapid development of 3D concrete printing now offers mechanical efficiency and freedom to push the limits of construction design. The digital manufacturing process holds potential for reducing carbon footprints through design optimization. Printable concrete, which is a mix of cement (based on ordinary Portland cement), aggregates, and admixtures, is attractive due to widespread and cost-effective constituents. However, many common formulations omit gravel, requiring higher cement paste volumes and inducing significant embodied carbon. Assessing the potential of low-carbon cements like Limestone Calcined Clay Cement (LC3), calcium aluminate cement (CAC), or magnesium-based cement for 3D printing is a current challenge that can address this issue. Tailoring these construction materials to printing applications and environmental needs now drives scientific exploration. This paper comprehensively reviews alternative materials and binders such as earthen materials, geopolymers, low carbon binders or gypsum-based materials, addressing fresh and hardened properties, developed digital processes, targeted applications, and discussing advantages and drawbacks of each alternative.