Carbonate Concretions Research Articles

Passivation of Steel Reinforcement in Low Carbon Concrete

Both the high CO2 emissions associated with cement production and the increasing demand for concrete call for the use of binder types that can be produced in a more climate-friendly way than that of ordinary Portland cement. To ensure that these binders can also be used in reinforced concrete structures, their influence on the corrosion behavior of embedded steel reinforcement must be investigated. In the study presented here, the passivation behavior of steel in mortars made from various new types of binders is investigated. In addition to alkali-activated materials with high and low calcium contents, a calcium sulfoaluminate cement and a binder produced from calcium silicate hydrate (C-S-H) phases, synthesized in an autoclave, were investigated. While the steel clearly passivated in the alkali-activated slag and the C-S-H binder, the calcium sulfoaluminate cement showed the lowest open circuit potentials and polarization resistances, indicating a less effective level of passivation. The metakaolin geopolymer with a potassium-based activator showed an onset of passivation that was dependent on the environment of the specimens at an early age, whereas the alkali-activated fly ash with a sodium-based activator showed a delay in passivation that was not influenced by the environment of the specimens at an early age.

Extraction of Carbonation Rate from Depth Profile of Concrete Carbonation by using Pseudo-analytical Solution of Two-component Reaction-diffusion Equation

Extraction of Carbonation Rate from Depth Profile of Concrete Carbonation by using Pseudo-analytical Solution of Two-component Reaction-diffusion Equation

Effect of carbonation on development of reactive MgO-based pervious concrete

Pervious concrete, developed to solve urban flooding and overloaded drainage issues, has limited strength due to its large void ratio. Reactive MgO cement (RMC) is a sustainable cement gaining strength through carbonation, which can have a more pronounced carbonation-induced enhancement in mechanical properties compared with Portland cement. However, its carbonation degree was limited due to the dense microstructure. To address both issues, pervious concrete using RMC was developed, and its void ratios were leveraged to facilitate the carbonation of RMC. Experimental results revealed that compared with that of samples cured under ambient environment (i.e. 4.7–15.7 MPa), the compressive strength of RMC-based pervious concrete cured under accelerated carbonation (11.2–39.7 MPa) and water/CO2 cycles (10.3–29.6 MPa) was enhanced by 77–278%. As the design void ratio increased from 0.15 to 0.30, the permeability coefficient of pervious concrete increased from 0.1 to 2.3 mm/s, while the carbonation of RMC-based pervious concrete also benefited from high void ratio, with the highest 28-day carbon sequestration ratio reaching 12.7%, as indicated by XRD, TGA tests and SEM observations. Furthermore, a mathematical model was established to estimate the thickness of cement paste on aggregates in pervious concrete, which was less than 1 mm and decreased as the design void ratio increased.

Chemical durability evaluation of copper grit aggregate concrete against Alkali-Silica-Reaction, carbonation and chloride penetration

This study aims to explore the effects of varying proportions of copper grit (CG) as fine aggregate on the alkali-silica reaction (ASR), accelerated carbonation test (ACT), and rapid chloride penetration test (RCPT) of concrete. Other complementary experiments including the rate of water absorption and compressive strength of copper grit aggregate mortar (CGAM), as well as compressive strength, split tensile strength, and sorptivity test of copper grit aggregate concrete (CGAC), were conducted. The results indicate that a higher CG content, particularly at around 80% replacement in the concrete mix, enhances strength without inducing expansive ASR and mitigates carbonation and chlorination rates in concrete. Moreover, the compressive strength of CGAM increases up to a 60% replacement ratio. Water absorption decreases from 62.1 gm/cm2 for the control specimen to 47.9 gm/cm2 for mortar with 100% CG replacement. ASR test results show no significant expansion up to a 20% replacement ratio of CG, with further increases in replacement resulting in expansion below the threshold limit of 0.1%. A notable 27% increase in compressive strength is observed for 80% CG replacement at 28 days of CGAC. Additionally, carbonation depth decreases with an increase in CG quantity in CGAC mixes, with the lowest depth observed for 80% CG replacement. The carbonation coefficient remains below the threshold limit, indicating high-quality CGAC. Furthermore, the service life of CGAC was predicted and microstructural characteristics of both CGAM and CGAC were examined via Field Emissions Scanning Electron Microscopy (FESEM). The findings underscore the potential of utilizing CG as a substitute for conventional sand in mortar and concrete production, offering a promising ecological alternative for conserving natural resources and safeguarding the environment.

Summary of Durability Analysis of Concrete Structures

The service life of concrete is closely related to the durability of concrete structure, with the development of infrastructure construction in our country, more and more attention has been paid to the study on the durability of concrete structure. This paper mainly analyzes the relevant factors affecting the durability of concrete structures, such as sulfate corrosion, chlorine salt corrosion, steel corrosion and concrete carbonization. At the same time, this paper studies from the perspective of life prediction of concrete structure to provide some reference for durability design of concrete structure.

How Does Diversification of Producer Services Agglomeration Help Reduce Carbon Emissions Intensity? Evidence from 252 Chinese Cities, 2005–2018

Mitigating carbon emissions intensity (CEI) and promoting carbon neutrality at the city level are essential for addressing the challenges of global climate change and advancing sustainable development. This study examines the influence of producer services agglomeration diversification (PSAD) on CEI using an unbalanced panel dataset including 252 Chinese prefectural-level cities from 2005 to 2018 for empirical analyses. We find that improving PSAD in a city can significantly mitigate CEI. Stronger PSAD accelerates a city’s industrial structure transformation from secondary- to tertiary-dominated in addition to boosting green development capabilities, both of which are confirmed to have concrete carbon emissions reduction effects. Furthermore, PSAD only significantly alleviates CEI in non-eastern cities in China, and the benefits of carbon emissions reduction are stronger after 2010. Our policy insights highlight land utilization in shaping the intracity layouts of producer services agglomerations (PSAs) and stress regional-level measures. Recognizing regional differences and integrating PSAs allocation with broader institutional measures can amplify PSAD’s benefits.

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.

Investigating the use of calcined clay of Sindh, Pakistan, on mechanical properties and embodied carbon of concrete

Investigating the use of calcined clay of Sindh, Pakistan, on mechanical properties and embodied carbon of concrete

Determination of the ability of migrating steel corrosion inhibitors to passivate corroding reinforcement in reinforced concrete structures

Introduction. The corrosion condition of steel reinforcement in reinforced concrete structures and products is the main factor determining their bearing capacity and durability. The alkalinity of the pore liquid of concrete (at pH > 11.8) in reinforced concrete structures and products under normal conditions ensures the passive state of steel reinforcement. In the presence or when chloride, sulfate and other analogous ions enter the concrete, the steel reinforcement of reinforced concrete structures and products depassives, despite the pH value > 11.8, and begins to corrode. In addition, depassivation and subsequent corrosion of steel reinforcement occur during carbonation (neutralization) of the protective layer of concrete due to a decrease in pH < 11.8. One of the promising options for slowing down or stopping the corrosion processes of steel reinforcement is currently the use of migrating corrosion inhibitors.
 
 The aim of the work was to obtain experimental data on the ability of migrating steel corrosion inhibitors to inhibit or completely stop the corrosion of reinforcement in reinforced concrete structures and products initiated by the presence of chloride ions (Cl-) in concrete or neutralization of the protective layer of concrete in relation to steel reinforcement.
 
 Materials and methods. The following types of migrating steel corrosion inhibitors were used for testing:
 
 – Cortec MCI-2020 (manufacturer – KORTEK RUS (KORTEK) LLC, suppliers – Ettrilat LLC, MONUMENT LLC);
 
 – IFKHAN-80 (manufacturer and supplier – IFKHAN LLC);
 
 – Basf Master-Protect 8000 CI (former name Protectosil ® CIT. Suppliers – MBS Construction Systems LLC, MPKM LLC, LKM-FLEET LLC).
 
 The determination of the ability of migrating steel corrosion inhibitors to inhibit or completely stop the corrosion of reinforcement was carried out by accelerated electrochemical research methods in accordance with State Standard 31383-2008 "Protection of concrete and reinforced concrete structures from corrosion. Test methods".
 
 Results. All three types of migrating steel corrosion inhibitors inhibit corrosion of steel reinforcement initiated by the presence of chloride ions in concrete by the age of 90 days. All three types of migrating steel corrosion inhibitors by the age of 30 days do not inhibit the corrosion of steel reinforcement initiated by concrete carbonation.
 
 Conclusions. According to the results of the work, it was revealed that the migrating steel corrosion inhibitors inhibit the corrosion of steel reinforcement initiated by the presence of chloride ions in concrete, while the corrosion initiated by the carbonation of concrete is not slowed down or stopped by migrating steel corrosion inhibitors.

Compressive Behavior of Stainless Steel–Concrete–Carbon Steel Double-Skin Tubular (SCCDST) Members Subjected to External Hydraulic Pressure

The new-type stainless steel–concrete–carbon steel double-skin tubular (SCCDST) members, characterized by their exceptional corrosion resistance and mechanical bearing capacity, have promising applications in ocean engineering, particularly in deep-water engineering. The external hydraulic pressure and interfacial action of various materials intensify the complexity of composite performance of SCCDST members. This paper describes an analytical investigation on the concentric compressive performance of SCCDST members under external hydraulic pressure. The full-range mechanism, including load–displacement response, bearing capacity contribution, and contact pressures, was investigated through the finite element (FE) model that was validated by the failure mode, bearing capacity, and response of axial load versus strain. Subsequently, influences of key geometric–physical parameters were analyzed, e.g., diameter-to-thickness ratios (Do/to, Di/ti), material strengths (fyo, fyi, and fc), hollow ratios (χ), and water depths (H). Typical results indicate that: the initial active confinement action derived from the hydraulic pressure can enhance the interfacial contact pressure and axial compression capacity of SCCDST members due to the tri-axial compression state; the enhancement of confinement effect is mainly from the interfacial interaction between outer stainless steel tube and concrete infill; influence of water depth on bearing capacity cannot be ignored, e.g., the bearing capacity of an SCCDST member with larger hollow ratio (χ = 0.849) is not enhanced under a higher hydraulic pressure (H = 900 m) because of the cross-sectional buckling failure risk. Finally, a modified method considering the effect of water depth was proposed and verified for SCCDST members under hydraulic pressure.

Bond-slip behaviour of textile-reinforcement in 3D printed concrete

Integration of reinforcement in extrusion-based 3D concrete printing (3DCP) is one of the significant challenges that limit its structural application. Providing textile reinforcement having high tensile strength, easy formability and non-corrosive nature as a potential reinforcement for 3DCP members enhances their structural performance. However, the bond between the printed concrete and the textile reinforcement is an essential factor that affects the composite action. This study investigates the bond-slip behaviour of three types of textile reinforcements (i.e., AR-glass, basalt and carbon) in high-performance 3D printable concrete. The bond characteristics were evaluated using pull-out load test specimens. The effect of rheological properties like viscosity and yield strength on the bond behaviour was evaluated by varying the cement content with two different replacement dosages of fly ash and slag. The modification of the nozzle to incorporate textile reinforcement as an in-process reinforcement method for 3DCP is also discussed. Test results showed that the addition of fly ash reduced the viscosity and yield strength, thereby enhancing the bond strength and pull-out load. However, reduced viscosity and yield strength resulted in poor buildability. When compared to the control mix, the mix with 15% slag replacement showed 40% increased bond strength with good buildability and easy pumping. The modified nozzle incorporates the textile reinforcement during printing, and scanning electron microscopy images show that the printable concrete was observed to bond well with the multifilament yarns of the textile. Furthermore, analytical modelling was conducted to predict the pull-out load versus slip behaviour, and a comparison of the predicted and experimental behaviour is presented.

Effect of silica fume on fracture analysis, durability performance and embodied carbon of fiber-reinforced self-healed concrete

Nowadays concrete industry is trying to develop sustainable and energy efficient materials. One of the techniques is to develop crack free concrete. Therefore, this study focusses on the use of different supplementary materials like silica fume as substitute of cement to characterize the self-healing capacity of fiber-reinforced concrete in order to produce crack free concrete. The employed concrete consists of cement Type-I, synthetic fibers of polyvinyl alcohol (PVA) type with 0.5 % by the total volume of the mix, and two different types of self-healing materials. Cement was replaced by silica fume (SF) up to 15 % with an increment of 2.5 %, sand passing from sieve # 16 and CA of size 12 mm was used to produce high-strength concrete. Three-point bending test and microscopic examination were used to investigate the role of fibers on the self-healing efficiency of fiber-reinforced concrete specimens. Specimens were pre-cracked in the range of 50–100 μm at 14 days of curing and then, placed in water for 14, 56-days water condition to assess the effect of self-healing. Digital high-range microscope was used to measure crack width after pre-cracking and at the end of every exposure duration. After the specified exposure duration, specimens were microscopically observed again to check the crack healing and re-loaded up to final failure. Outcomes were taken in terms of peak load increase value after healing stage (FCPL), controlling crack propagation due to healing effect termed as (IFTR), effect of cracking on fracture energy in terms of (IFER) and Embodied Carbon and Embodied Energy. It was found from test results that the healing efficiency in terms of FCPL, IFTR, and IFER was improved, due to the use of silica fume as it has lower surface area then OPC, which triggers healing rate faster by accumulation of healed produces near crack surface in early age. Furthermore, durability performance in terms of embodied carbon and embodied energy is also reduced because of full-crack healing, which shows profound healing effect.

Process modeling guides operational variables that affect CO2 utilization during the accelerated carbonation of concrete

AbstractAccelerated concrete carbonation is an expanding option for decarbonizing construction. Factors such as concrete mixture design and carbonation environment can influence the maximum CO2 utilization that can be achieved during such a process. A carbonation process designed to utilize a water‐saturated dilute CO2 source wherein 2 < CO2 concentration (v/v%) < 16, was modeled in AspenPlus©. A regression model was developed to correlate CO2 uptake, relative humidity (11%–100%), CO2 concentration ([CO2] = 2—16 v/v%), and temperature (T = 11–74°C) conditions within a carbonation reactor. It was determined that [CO2] was the most significant variable as higher concentrations enhanced CO2 transport through the concrete. The energy use intensity per mass of CO2 utilized (kWh/kgCO2) was determined across a range of processing conditions. As a function of the operational conditions, accelerated carbonation provides a net CO2 reduction of up to 28 kgCO2/tonne of concrete; a reduction of up to ~45% compared to typical formulations.

Synergistic effect of recycling waste coconut shell ash, metakaolin, and calcined clay as supplementary cementitious material on hardened properties and embodied carbon of high strength concrete

Researchers are investigating eco-friendly binders like coconut shell ash (CSA), metakaolin (MK), and calcined clay (CC) as supplementary cementitious materials (SCM) in high-strength concrete (HSC). Abundantly available as industrial or agricultural waste, these materials, when combined with Portland cement (PC), offer synergistic benefits. This not only improves concrete performance but also addresses waste disposal issues, presenting a sustainable and environmentally friendly solution for long-term use in HSC production. However, this study performed on fresh and mechanical characteristics of HSC blended with CSA, MK, and CCA alone and together as SCM after 28 days of curing. A total of 504 samples of standard concrete were cast and the cubical samples were tested to achieve the targeted compressive strength about 80 MPa after 28 days. The experimental results indicated that the rise in tensile, flexural and compressive strengths of 9.62%, 8.27%, and 10.71% at 9% of CSA, MK, and CC as SCM after 28 days of curing. As SCM content increases, the density, porosity and water absorption of concrete decrease. Moreover, the workability of fresh concrete is getting reduced when the concentration of SCMs increases in HSC. In addition, the concrete's sustainability assessment revealed that employing 18% MK, CC, and CSA as SCM reduced carbon emissions by approximately 11.78%. It is suggested that using 9% CC, MK and CSA together in HSC yields the best results for practical applications in civil engineering.

Prediction model for calculation of the limestone powder concrete carbonation depth

The efficient way to mitigate the impact of the concrete industry on climate change is to reduce the clinker content in the concrete mix. Beside incorporating supplementary cementitious materials (SCMs), it is possible to use high filler content combined with concrete mix optimization. Limestone powder emerges as a promising filler mineral due to its availability and ready-to-use technology. In this work, the carbonation resistance of concrete with a high limestone powder content (45–65% of the powder phase) was experimentally tested. Test results showed that, with an optimized mix design featuring low water content and increased paste and plasticizer volume, concrete mixes satisfied high workability and strength demands for commonly applied strength classes. However, carbonation resistance remains a challenge. After two years in indoor natural conditions, carbonation depths were 8%, 28%, and 67% greater than referent Portland cement concrete for mixes with 47%, 58%, and 65% limestone powder content, respectively. Further analyses showed the inapplicability of the existing fib Model Code 2010 service life prediction model to limestone powder concrete. Based on a comprehensive database of experimental results, the modification of the fib prediction was proposed. A full probabilistic service life analysis revealed that for concrete with more than 20% limestone powder content and for both 50 and 100-years’ design service life, the currently prescribed concrete cover depths in European standards should be increased, depending on the carbonation exposure class.

Identification of carbonation‐induced corrosion of steel in concrete by electrochemical testing

AbstractCarbonation‐induced corrosion of steel in concrete can allow for premature degradation of structures. Corrosion probes in health monitoring systems can assess concrete carbonation and steel corrosion rates. The electrochemical noise (EN) technique has advantages for corrosion sensing. Instrumented concrete columns were fitted with a carbonation chamber for accelerated testing. EN was assessed through statistical evaluation of noise time signatures, noise resistance, and spectral analysis. The mean noise potential for the electrodes showed electronegative potential and correspondingly high rms noise current, indicative of corrosion activation in carbonated concrete. The estimated corrosion rates obtained from the noise impedance were comparable to those resolved from the polarization resistance and noise resistance. The shot noise analysis indicated isolated spontaneous noise events associated with the activation of local steel anodes. The outcomes of the testing indicate that the placement of low‐cost sensors and passive EN measurements can be used to monitor the onset of carbonation‐induced corrosion of steel in concrete and provide estimates on corrosion rates.

Machine learning for predicting concrete carbonation depth: A comparative analysis and a novel feature selection

The accurate prediction of concrete carbonation depth is essential to prevent concrete from cracking and corrosion. However, identifying the critical parameters affecting carbonation depth is challenging due to the process’s complexity and the involvement of many variables. In this investigation, a range of computational techniques was employed to predict the carbonation depth of concrete, including artificial neural networks, random forests, decision trees, and support vector machines, on a dataset of 37 variables. Detecting the optimal variables to maximize the prediction accuracy is a complicated task. To address this, a novel technique called MOEA/D-ANN (Multi-objective Evolutionary Algorithm based on Decomposition and Artificial Neural Networks) was introduced in this study. This technique effectively determines the optimal significant variables, resulting in superior predictive performance. The effectiveness of the introduced technique was assessed by employing a conventional feature selection method called Regression Relief Feature Selection (RReliefF) as well. The results indicate artificial neural network was the most accurate model based on prediction accuracy when using the optimal feature set found by MOEA/D-ANN. Additionally, the MOEA/D-ANN approach demonstrated the ability to decrease the training time required for the modeling process. The findings demonstrate the usefulness of the MOEA/D-ANN method in developing accurate and efficient models for predicting concrete carbonation depth. Furthermore, this approach can be extended to other important properties of concrete, thereby improving the construction and maintenance of concrete structures.

Formation of ammonite concretions through organic decomposition in the iron-reduction zone

ABSTRACT The ammonites in spherical carbonate concretions often preserve their original three-dimensional (3-D) shell shapes and detailed fragile structures. However, the formation process of spherical ammonite concretions is not fully understood. Herein, the ammonite concretions identified in the Cretaceous (Campanian) Osoushinai Formation, Yezo Group, Japan, are examined to understand their formation process during soft-tissue decomposition after burial in marine sediments. In the Osoushinai Formation, almost all observed ammonites in concretions preserve their 3-D form without phragmocone deformation. The calcite filling in the remaining body chamber of ammonites (BC1) shows that shells were buried with soft tissues. These occurrences, negative δ13C values, and the near-zero δ18O values of BC1 as well as the concretions indicate that both BC1 and concretions rapidly formed from dissolved inorganic carbon derived from organic matter, including the soft tissue of dead organisms, in the shallow part of the sediments. The increasing Fe concentration in BC1 shows that BC1 formed in the iron-reduction (FeR) zone, where organic matter was decomposed owing to the activity of iron-reducing microorganisms. The similarity of the elemental and isotopic compositions of BC1 and concretions show that they concurrently formed in the FeR zone. In the Osoushinai Formation, an abundant influx of Fe(III) and intense bioturbation during the deposition of the formation promoted organic decomposition in the FeR zone, causing rapid formation of BC1 and concretions. Such rapidly formed calcite fillings and concretions protected fossils from deformation and dissolution during diagenesis to preserve their 3-D form. Overall, the findings of this study provide new insight into the relation between sedimentary environments and the fossil preservation process via rapid concretion formation.

Structural performance and durability assessment of ultrafine powdered concrete in modern buildings

Abstract This paper investigates the impact of various ultrafine powders on the flow characteristics and mechanical properties of concrete, with the aim of enhancing its overall performance. Examine the compressive and flexural strengths of cement, establish distinct matching ratios, and clarify the actual mixing quantity of silica fume and ultrafine powder. Analyze the durability of concrete structures and propose causes for carbonation and formation of concrete. Obtain the durability evaluation indexes, propose the variable weight fuzzy comprehensive judgment method, and establish the durability evaluation system for ultrafine powder concrete buildings. When the on-site test results for reinforcement corrosion, concrete strength, carbonation depth, cracks, and damage degree are added together, the values of each assessment vector of the fuzzy comprehensive evaluation are found. This lets us figure out the bridge’s durability grade. The highest compressive degree was achieved by both ultrafine silica-aluminum material and ultrafine mineral fishery powder at a 20% dosage. The submicron silica material achieved the highest compressive strength with a 40% dosage. In the test and analysis of the ultrafine powder concrete bridge building structure, the fuzzy comprehensive judgment grade is III. That is, there is a certain degree of damage state, and measures must be taken, which is consistent with the field test results.

Investigation of Carbonation of Concrete Based on Crushed Sand and Admixtures

Investigation of Carbonation of Concrete Based on Crushed Sand and Admixtures