Carbonation Depth Research Articles

Optimal design of sustainable slag concrete considering sustained stress and carbonation resistance

Ground granulated blast furnace slag (GGBFS) is broadly utilized as a mineral admixture in concrete production. This study shows a procedure for the optimal design of a sustainable concrete mix with GGBFS considering carbonation coupled with stress. First, the objective of optimal design is positioned as the total cost of materials and CO2 emissions. The proposed procedure covers different constraints, such as strength, slump, and carbonation durability with sustained stress. Second, a genetic algorithm is used to find the optimal mixtures considering the objective function and various constraints. This analysis results show the following: (1) For low-strength concrete, carbonation is a critical factor and can dominate the mixture of sustainable concrete. Moreover, stress levels and types affect the carbonation and optimal mixture. A rich mixture is essential for structural elements with high-level stress. In contrast to compressive stress, the influence of tensile stress on mixtures is much more apparent. (2) For strong concrete, carbonation depth is less than cover depth and is not a dominant constraint in designing the mixture, and strength is the dominant factor in designing high-strength concrete. In summary, the suggested model is a general way to design mixtures considering strength, slump, carbonation durability with sustained stress.

Experimental study on carbonation behavior of seawater sea sand recycled aggregate concrete

The carbonation behavior of seawater sea sand recycled aggregate concrete (SSRAC) was investigated in this study. Considering different added water, fine aggregates, and coarse aggregates, the specimens were divided into 12 groups for the accelerated carbonation test by 7 days, 14 days, and 28 days. Among them, river sand, sea sand, and mixed sand (the proportion of sea sand and shell sand was 4:1) were used as fine aggregates. The results show that the carbonation depths of concretes with different mixtures all increase over time. When the replacement ratio of recycled coarse aggregate (RCA) is not less than 50%, sea sand is the most suitable fine aggregate to acquire best carbonation resistance, while river sand is the worst. On the contrary, when the replacement ratio of RCA is not more than 30%, river sand is the most suitable fine aggregate, while sea sand is the worst. It can also be speculated that the most appropriate replacement ratio of RCA is 50% when sea sand is applied as fine aggregates in SSRAC. At the same time, 30% replacement ratio of RCA is appropriate when mixed sand is applied as fine aggregates in SSRAC.

Deterioration of an industrial reinforced concrete structure exposed to high temperatures and dry-wet cycles

This paper presents the results of an in-situ test and experimental study on a reinforced concrete wet quenching tower that had been exposed to high temperature and dry-wet cycles for 34 years. Fourteen concrete cylinder samples were drilled along the height. The variations in the carbonation depth, compressive strength, pH, phase compositions, substance contents and morphologies of concrete along the height and depth of the tower were tested. The carbonation depth of concrete at the top of the tower was 2.3 times greater than the bottom, and the compressive strength of concrete at the top was only about 30% of the bottom. Variations of pH with the content of CaCO3 in different depths have been quantified. The pH at different depths of concrete in the severe dry-wet cycle zone fluctuated around 9.0, the content of CaCO3 was around 8%. Calcium carbonate coexisted with gypsum in the transition zone of carbonated concrete. A modified stochastic carbonation depth model is proposed for concrete exposed to high temperatures with dry-wet cycles and was in acceptable agreement with natural carbonation test results.

Enhancing CO2 balance in concrete through carbonation during a service life using organic liquid emitting diode (OLED) as a binder

Worldwide, reduction in emission of greenhouse gas such as carbon dioxide (CO2) is a crucial issue in construction and building industries from a sustainability perspective. The present study aims to achieve a higher CO2 balance in concrete as the role of capture and storage during service life by using an organic liquid emitting diode (OLED) waste glass as a cementitious binder. Concrete with 0%, 10%, 20%, and 30% of OLED waste glass was fabricated for the experimental works. The amount of potential CO2 uptake through carbonation under a natural exposure was evaluated based on carbonation depth and molecular concentration favorable to react with CO2, which is determined by quantitative X-ray diffraction (Q-XRD). Simultaneously, compressive strength was monitored until 96 weeks. Also, the CO2 emission of the blended concrete in the pre-construction stage was assessed by a life cycle assessment. As a result, the concrete modified by OLED waste glass exhibited an excellent strength at all ages and replacement levels due to more significant pozzolanic activity, confirmed by Q-XRD results. In addition, OLED addition enhanced the CO2 balance in the concrete over twice in value at the maximum because of the reduction of CO2 emitted in cement production and increased CO2 absorption in the carbonation process. The results are in good agreement that OLED waste glass can be successfully used as a binder for developing green concrete with CO2 neutralization. However, it must be further examined the mechanical properties and durability at various aspects.

The influence of climate change on the suitable habitats of Allium species endemic to Iran

Identifying the consequences of global warming on the potential distribution of plant taxa with high species diversity or a high proportion of endemic species is one of the critical steps in conservation biology. Here, present and future spatial distribution patterns of 20 Allium endemic species were predicted in Iran. In this regard, the maximum entropy model (MaxEnt) and seven environmental factors were applied. In addition, optimistic (RCP2.6) and pessimistic (RCP8.5) scenarios of 2050 and 2080 were also considered to predict the future spatial distributions. The results showed that annual mean temperature (BIO1), temperature annual range (P5-P6) (BIO7), soil organic carbon content, annual precipitation (BIO12), and depth of soil were the most important environmental variables affecting the distributions of the studied taxa. In total, the model predictions under the future scenarios represented that the suitable habitats for all Allium species endemic to Zagros except for A. saralicum and A. esfahanicum are most probably increased. In contrast, the suitable habitats for all species in Azerbaijan Plateau, Kopet Dagh-Khorassan region, and Alborz except for A. derderianum are most likely decreased under the future climate conditions. The present study indicates that the habitats of Alborz, Azarbaijan, and Kopet Dagh-Khorassan will be probably very fragile and vulnerable to climate change and most species will respond strongly negatively under applied scenarios, while Zagros species occupy new habitats by expanding their distributions. Therefore, determining conservation strategies for the species in these regions seems to be very important and high priority for decision makers.

Carbonation Model and Prediction of Polyvinyl Alcohol Fiber Concrete with Fiber Length and Content Effects

Durability is an important aspect of reliability of concrete structures. In order to establish the carbonation model of polyvinyl alcohol (PVA) fiber concrete including the influences of PVA fiber length and volume content, a series of accelerated carbonation experiments were carried out on the normal concrete specimens and PVA fiber concrete specimens with fiber lengths of 3 mm, 6 mm, 12 mm and 18 mm and fiber volume contents of 0.1%, 0.3%, 0.5%, 0.75%, 1.0% and 1.5%, respectively. The experimental conditions remained at temperature of 20 ℃, humidity of 70%, and carbon dioxide concentration of 20%. It was found that the addition of PVA fibers could improve the carbonation resistance of concrete considerably. Within the investigated range of fiber length and content, the carbonation resistance of concrete is first strengthened and then weakened with increasing PVA fiber length or content. The quadratic carbonation depth prediction model could characterize the influences of PVA fiber length and content better than the linear model. The carbon dioxide diffusion equation was established by introducing a PVA fiber influence factor and its parameters were determined from the carbonation depth prediction model. The carbonation process of PVA fiber concrete under the accelerated carbonation experiment condition was simulated. Both the model and the numerical method were validated by comparison between the experimental and numerical results. Finally, the influences of added PVA fibers on the carbonation life and durability of reinforced concrete components were further studied numerically. The results showed that compared with the normal concrete component, the durability of PVA fiber concrete components is significantly improved.

The Use of Graphite to Improve the Stability of Saudi Class G Oil-Well Cement against the Carbonation Process.

Oil-well cement physical characteristics considerably change after being carbonated by a CO2-rich solution. In this study, the influence of graphite particles in the characteristics of oil-well cement reacted with a CO2-rich solution at 130 °C and 10 MPa for 10 days was studied. After 10 days of carbonation, incorporating 0.2% by weight of cement (BWOC) of graphite into the cement slurry decreased the carbonation depth by 29.8% as confirmed by the direct measurement and the micro-computerized tomography scan technique. The addition of 0.2% BWOC of graphite also reduced the cement matrix permeability by 31.4% and increased its compressive strength by 16.4% and tensile strength by 23.8% compared to the sample without graphite. The decrease in the cement matrix portlandite concentration and permeability of the samples prepared with graphite contributed to promote the cement matrix carbonation resistance. The microscopic images also proved that the incorporation of graphite delayed the leaching of calcium carbonate, and this is also attributed to decreasing the cement strength deterioration.

Experimental Study on Carbonation Durability of Kaolin Strengthened with Slag Portland Cement.

Slag Portland cement is an environmentally friendly and energy-saving product, which is widely used in cement-reinforced soil. This study used slag Portland cement-reinforced soil as the research object and P.O 42.5 + kaolin (POK) as the reference group. The carbonation depth and strength of P.S.A 42.5 + kaolin (PSK) at different curing times were analyzed using carbonation depth, uniaxial ground pressure strength, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The test results show the following: (1) The active substances in PSK samples can react with calcium hydroxide produced during cement hydration and can reduce the content of OH−. The PSK samples react with OH− and CO2 in the carbonation environment. Both processes considerably reduce the content of OH−. (2) Due to the decrease in OH− content, the carbonation durability of slag Portland cement-reinforced soil is significantly less than that of ordinary Portland cement. (3) The carbonation of slag Portland cement-reinforced soil improves its strength. (4) The results of SEM + EDS and XRD confirm the carbonation depth and strength of the POK and PSK samples. The results show that PSK has important applications in subgrade or building grouting materials and in cement-soil mixing piles (walls).

Research into Carbon Dioxide Curing’s Effects on the Properties of Reactive Powder Concrete with Assembly Unit of Sulphoaluminate Cement and Ordinary Portland Cement

Excessive emissions of carbon dioxide can lead to greenhouse effect thus destroying the ecological balance. Therefore, effective measures need to be taken to reduce the emission of carbon dioxide. In this study, the influence of carbon dioxide curing on the mechanical strength and NaCl freeze-thaw deterioration of reactive powder concrete (RPC) with the assembly unit of sulphoaluminate cement and ordinary Portland cement was investigated. The ratio of sulphoaluminate cement ranged from 0% to 100% by the total mass of cement with the curing age ranging from 1 d to 28 d. The mechanical strength of RPC with 50% ordinary Portland cement and 50% sulphoaluminate cement containing the polypropylene fibers ranging from 1% to 4% by volume of RPC were investigated. Moreover, the following mass and mechanical strength loss rates, the carbonation depth, the chloride ion migration coefficient and the relative dynamic elastic modulus (RDEM) during NaCl freeze-thaw cycles were determined. Finally, the scanning electron microscope (SEM) and X-ray diffraction were applied in investigating the carbonation process of RPC. Results showed that the addition of sulphoaluminate cement could improve the mechanical strength of RPC at low curing age (lower than 7 d). However, when the cuing age reached 7 d, the sulphoaluminate cement demonstrated negative effect on the mechanical strength. Moreover, the carbon dioxide curing led to increases in the mechanical strength and when ordinary Portland cement was added the enhancing effect was more obvious. Furthermore, the carbon dioxide curing could effectively improve the resistance of NaCl freeze-thaw cycles and increase the carbonation depth. Finally, the increasing dosages of polypropylene fibers were advantageous to the mechanical strength and the resistance of NaCl freeze-thaw cycles. From the researching results of the microscopic performance, the carbon dioxide curing could improve the compactness of hydration products and reduce the content of calcium hydroxide especially at the curing age of 3 days.

Engineering statistical models for carbonation depth

Based on generalized linear models and gamma degradation processes, two models predicting the natural carbonation of reinforced concrete (R.C) structures are proposed. They include the main factors influencing the carbonation process (material, environmental and curing factors) and their effects are evaluated from a large sample of natural carbonation depths measured experimentally worldwide. Then, predicted carbonation values are obtained using both the proposed models and the fib model for sheltered R.C structures exposed in the field. It is revealed that the proposed models have a rather high level of accuracy compared to the fib model and may be proposed as valuable alternatives.

Probabilistic assessment of the depassivation limit state of reinforced concrete structures based on inspection results

The aging of our concrete structures has led to a growing need to assess their actual condition, not only for maintenance purposes, but also to plan the extension of their service life. Today, only few methods that use inspection data can be found in the literature for performing that assessment, and are usually based on the Bayesian probability theory, which requires prior information on the structures condition and often demands specific statistical knowledge and software that are not familiar to most practitioners. In this article, a probabilistic methodology based on a frequentist approach is presented for assessing the limit state of depassivation of concrete structures, using inspection results on cover depth, carbonation depth and depth of critical chloride content. It introduces the concept of passivation curve, which depicts the confidence of the estimated percentage of passivated steel bars, providing a valuable tool for supporting the decision-making for the life-cycle management of concrete structures. Its application is demonstrated using the inspection data from five real structures up to 41 years old. This article also discusses the experimental and code requirements for the condition assessment of concrete structures and the physical interpretation of the probability of passivation in the context of inspection. The relevance of experimental conditions for the determination of the critical chloride content of concrete is highlighted, as well as the urgent need to get data on its in situ distribution.

Effect of mixed fibers on fly ash-based geopolymer resistance against carbonation

In this study, the resistance of mixed fiber reinforced fly ash-based geopolymer incorporated with different polyvinyl alcohol (PVA) fibers and modified multi-walled carbon nanotubes (MWCNTs) against carbonation was analyzed using the accelerated carbonation test. The resistance enhancing effects of modified geopolymer were investigated using the carbonation depth and compressive strength tests. Meanwhile, X-ray diffraction(XRD), Fourier transforms infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP), and field emission scanning electron microscopy(FE-SEM) were used to evaluate the mineralogical phases, geopolymerization process, micropore structures, and microscopic morphologies, respectively. The experimental results showed that the resistance of geopolymer against carbonation decreased compared to that of cement mortar. However, the incorporation of an appropriate amount of modified MWCNTs and PVA fibers can enhance the resistance of the geopolymer against carbonation. Moreover, accelerated carbonation decreases the compressive strength of geopolymers while increasing the corresponding compressive strength of cement mortars. The addition of an appropriate amount of modified MWCNTs and PVA fibers can enhance the compressive strength of geopolymers. The resistance of the modified geopolymer against carbonation is best when incorporated with 0.10% modified MWCNTs and 2.00% PVA fibers. After carbonation, the microstructure of the modified geopolymer becomes loose. Moreover, accelerated carbonation decreased the porosity of the modified geopolymer and increased the proportion of harmful pores.

Observed slump of sea land breeze in Brisbane under the effect of aerosols from remote transport during 2019 Australian mega fire events

Abstract. The 2019 Australian mega fires were unprecedented considering their intensity and consistency. There has been much research on the environmental and ecological effects of these mega fires, most of which focused on the effect of huge aerosol loadings and the ecological devastation. Sea land breeze (SLB) is a regional thermodynamic circulation closely related to coastal pollution dispersion, yet few have looked into how it is influenced by different types of aerosols transported from either nearby or remote areas. Mega fires provide an optimal scenario of large aerosol emissions. Near the coastal site of Brisbane Archerfield during January 2020, when mega fires were the strongest, reanalysis data from Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) showed that mega fires did release huge amounts of aerosols, making aerosol optical depth (AOD) of total aerosols, black carbon (BC) and organic carbon (OC) approximately 240 %, 425 % and 630 % of the averages in other non-fire years. Using 20 years' wind observations of hourly time resolution from a global observation network managed by the National Oceanic and Atmospheric Administration (NOAA), we found that the SLB day number during that month was only 4, accounting for 33.3 % of the multi-years' average. The land wind (LW) speed and sea wind (SW) speed also decreased by 22.3 % and 14.8 % compared with their averages respectively. Surprisingly, fire spot and fire radiative power (FRP) analysis showed that heating effects and aerosol emission of the nearby fire spots were not the main causes of the local SLB anomaly, while the remote transport of aerosols from the fire centre was mainly responsible for the decrease of SW, which was partially offset by the heating effect of nearby fire spots and the warming effect of long-range transported BC and CO2. The large-scale cooling effect of aerosols on sea surface temperature (SST) and the burst of BC contributed to the slump of LW. The remote transport of total aerosols was mainly caused by free diffusion, while the large-scale wind field played a secondary role at 500 m. The large-scale wind field played a more important role in aerosol transport at 3 km than at 500 m, especially for the gathered smoke, but free diffusion remained the major contributor. The decrease of SLB speed boosted the local accumulation of aerosols, thus making SLB speed decrease further, forming a positive feedback mechanism.

An Investigation on Bacterial Air-Entrained Concrete Permeability using Statistical Modeling

Abstract In recent decades, bacterial self-healing concrete has gradually reached its deserved popularity because of its ecofriendly ability to heal cracks spontaneously. This study investigates the simultaneous effects of several factors such as air voids, bacterially impregnated mix water, curing environment, and surface treatment on the permeability of concrete. For this study, experiments were conducted using water absorption, water permeability, and carbonation depth as the response variables. The experiments were performed within the framework of a fractional factorial split-plot design, which led to a decrease in the number of experiments without loss of precision. For this purpose, 126 cubic specimens of different dimensions were cast. The statistical random effect model was run to study the significant relationships between the factors and the response variables. Results revealed that the use of bacteria in the mixed water led to significantly reduced water absorption (about 19 %) and carbonation depth under acidic conditions (about 32 %). Furthermore, water absorption decreased with increasing air voids in the bacteria-laden air-entrained concrete specimens up to 31 % and 50 % for the specimens with 5 and 8 % air voids, respectively, suggesting that air voids probably protected the bacteria from exposure to the deadly alkaline and dry conditions inside the concrete.

Development of hybrid machine learning-based carbonation models with weighting function

Carbonation of concrete has significant influence on the service life of constructions and great effort has been made to establish an accurate and efficient model of carbonation that incorporates both internal and external factors. We present a hybrid machine learning (ML) approach that combined two single ML models: artificial neural network (ANN) and support vector machine (SVM). A literature survey generated a database containing 532 records of accelerated carbonation depth measurements for concrete mixtures inclusive of fly-ash blends. Six inputs comprising cement content, fly-ash replacement level, water–binder ratio (w/b), CO2 concentration, relative humidity and exposure time were selected for modeling, justified by grey relational analysis. The four ML models had excellent accuracy in predicting the carbonation depth of concrete, with the correlation coefficient ranging from 0.9788 to 0.9946, but the two hybrid ML models achieved superior performance to the single ANN and SVM models with characteristic higher correlation coefficients, lower mean value for the absolute error and lower standard deviation for its distribution. In addition, compared with other commonly known empirical carbonation models, the hybrid ML models showed more accurate carbonation depth prediction with smaller root mean square error. Furthermore, the weightings of the contributions of six selected factors to carbonation depth disclosed that CO2 concentration, w/b and binder content had higher relative importance to carbonation depth and should be given greater weighting in future carbonation model development.

Experimental Investigation on Deterioration Mechanisms of Concrete under Tensile Stress-Chloride Ion-Carbon Dioxide Multiple Corrosion Environment

The adverse effects of a hostile marine environment on concrete structures inevitably result in great economic loss and may contribute to catastrophic failure. There is limited information on the durability of concrete in a tensile stress-chloride ion-carbon dioxide (TCC) multiple-corrosion environment. The objective of this study is to explore the impact of a TCC multiple-corrosion environment on concrete considering three coupled factors of compressive strength, Cl− penetration, and carbonation. Dry–wet cycle tests were conducted to determine the strength degradation and Cl− penetration concentration of concrete in a hostile multiple-corrosion marine environment. The results show that the effects of water-soluble chloride ions (Cl−), carbon dioxide (CO2), and tensile stress on concrete are not a simple superposition, but involve obvious interaction. The compressive strength of a concrete specimen first increases and then decreases in chlorine salt-carbon tests. The Cl− concentration and tensile stress affect the carbonation depth of concrete, which increases with an increase in Cl− concentration, and with the application of tensile stress. The Cl− concentration has an obvious effect on the carbonation depth. In addition to experimental observations, a stepwise regression equation was established based on the multiple linear regression theory. A correlation analysis considering different factors was conducted to reflect the corrosion results more directly.

Study on carbonation resistance and micromechanism of shotcrete in high geothermal tunnels

The internal structure of shotcrete is often damaged under variable high-temperature curing conditions. To study the carbonation resistance and microscopic mechanism of shotcrete in high geothermal tunnels, accelerated carbonation tests were performed under different initial curing conditions (40 °C, 60 °C, 80 °C, relative humidity 55%). The results show that with increasing curing temperature, the carbonation rate is faster due to the increase in microcracks and pores in shotcrete caused by variable high-temperature curing. It is speculated that 60 °C is a critical point. When the curing temperature exceeds 60 °C, the carbonation resistance of shotcrete more significantly decreases. A carbonation depth prediction model including curing temperature was established. With increasing carbonation age, the mechanical strength of shotcrete increases, but the splitting tensile strength decreases at a later stage. The carbonation reaction will produce CaCO3-based carbonation products and fill microvoids to make the shotcrete structure denser.

A study on the carbonation of binary and ternary blended cement mortar and concrete

ABSTRACT Carbonation of concrete has always been a durability concern leading to the corrosion of steel in reinforced concrete. The present paper deals with carbonation resistance of cement mortar and concrete when supplementary cementitious materials like fly ash and blast furnace slag partially replaces cement. The work had been carried out in two phases, first being the measure of carbonation depth and compressive strength of the samples with water binder ratios of 0.35, 0.5 and 0.65 to train the artificial neural network. Based on the results from carbonation depth, the consistency of Fick’s law of diffusion that governs the carbon dioxide (CO2) ingress into concrete has been ascertained with the help of linear-programming problem. In the second phase of the study, cement mortar samples of water binder ratios 0.4, 0.5 and 0.6 had been tested to verify the reliability of phenolphthalein indicator in identifying the depth of carbonation with the help of microscopic analysis such as Thermo gravimetric analysis (TGA). The same specimens have been used to identify the phases of crystalline materials of post-carbonation samples using X-Ray diffraction (XRD). An attempt has been made to quantify the carbonated products of calcium hydroxides and C-S-H.

Effect of different cement content and water cement ratio on carbonation depth and probability of carbonation induced corrosion for concrete

Nowadays transportation infrastructure is subjected to a high percentage of carbon dioxide emissions. CO 2 greatly affects the carbonation depth of concrete, which can affect the deck for reinforced concrete bridges causing corrosion to steel reinforcement. Cement content and water to cement ratio greatly influence the carbonation depth of concrete. This study aims to investigate the effect of climate change on carbonation depth by considering different Representative Concentration Pathways [RCPs]. In addition, the effect of different compressive strengths on the carbonation depth was investigated in this research. Additionally, the effect of different cement contents on the probability of carbonation-induced corrosion has been investigated. Two parameters are considered, namely, the cement content 400 kg/m3, 350 kg/m3, and 250 kg/m3 and, the water to cement ratio [0.45 and 0.55]. This study RCPs for CO2 concentrations. The RCP [2.6, 4.5, 6, and 8.5] trajectory was used by the Intergovernmental Panel on Climate Change [IPCC], which represents low emission pathways, intermediate emission pathways, and high emission pathways, respectively. Carbonation depth has been estimated using Yoon’s and Stewart’s equations. Furthermore, the probability of carbonation-induced corrosion has been investigated using Monte Carlo simulation and the first-order reliability method at different cement contents for RCP 8.5. The percentage increase in the carbonation depth using Yoon’s compared to Stewart’s equations for concrete mixes which consist of different water to cement ratios and cement content for the years 2025 and 2100 for both RCP 2.6 and RCP 8.5 were calculated. Finally, the probability of carbonation-induced corrosion conducted by FORM for cement content of 250 kg/m3 has been increased by 18% compared to the probability of carbonation including cement content equal to 400 kg/m 3 for the year 2100.

Evaluation of Concrete Durability Based on Cloud Model and D-S Evidence Theory

The environment in alpine region is complex and harsh, and the durability of concrete is seriously affected by freeze-thaw and salt invasion. In this paper, the relative dynamic modulus of elasticity, chloride permeability coefficient, mass loss rate and carbonation depth are selected as the evaluation indexes of concrete durability in Northeast China. Based on prior knowledge and expert group decision-making, the durability grade is divided and the evaluation standard is established; The evaluation model of concrete durability based on cloud model and D-S evidence theory is established. According to the engineering experimental data, the membership degree of concrete durability evaluation index in different grades is obtained through the correlation measurement of cloud model. The normalized evidence is formed and fused by D-S evidence theory. The results show that the durability grade of concrete is grade I, which is consistent with the actual project. It shows that using cloud model and evidence theory evaluation model to evaluate the durability of concrete is a new and effective method.