Carbonation Depth Research Articles

Influence of Unit Water Content Control on Concrete Performance in the Ready-Mixed Concrete Production Process.

This study examined the effects of increasing concrete unit water content and artificially controlling water content on concrete performance in the production process of ready-mixed concrete. Results showed that changes in the unit water content of 20 concrete mix proportions without air-entraining significantly reduced concrete compressive strength, increased porosity, and in-creased occurrence of bleeding. A unit water content increase of 25 kg/m3 or more may reduce the compressive strength of concrete below the design standard and significantly affect the occurrence of bleeding water. Moreover, an extra unit water content of at least 25 kg/m3 could significantly affect the diffusion of chloride ions in the concrete. The carbonation depth of concrete was extremely high with the increase in unit water content and water addition. In the production of concrete requiring at least normal strength or durability, the extra water change to total unit water content should be maintained at 15 kg/m3 or less. And a water-cement ratio of 48% or less and a unit water content of 155 kg/m3 or less are considered effective for management of concrete quality. Considering the aggregate type, absorption rate, and moisture state, the management of unit water content error in concrete production processes requires greater.

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.

Carbonation of Shale Ceramsite High-Strength Lightweight Concrete Incorporating Graphene Oxide

The growing demand of concrete for improving durability has stimulated extensive research on graphene oxide (GO). Carbonization, as an irreversible deterioration, should be paid more attention to high-strength lightweight concrete (HSLWC) with the characteristics of porous structure. In this study, the effect of different low content of GO on the carbonation depth of HSLWC made from shale ceramsite was experimentally investigated. Subsequently, the effect of GO on pore distribution of HSLWC was analyzed. Four groups of grade 60 HSLWC were designed for comparative experiments, in which 0.00%, 0.01%, 0.03% and 0.05% (by weight of cement) GO were added, respectively. The results indicated that GO could effectively reduce the carbonization depth of HSLWC. When GO content was 0.05%, the carbonization depth was reduced by approximately 23%. The main reason was that GO not only reduce the total porosity but also refine the pores, thus improving the carbonization resistance of HSLWC.

The Influence of Salt Erosion on the Mechanical Performances of Ultra-High-Performance Concrete with Secondary Aluminum Dross

Secondary aluminum dross containing a large amount of active substance can be used to prepare concrete. The mechanical strengths, the mass loss rate (MR) and the relative dynamic modulus of elasticity (RME) of ultra-high-performance concrete with secondary aluminum dross are researched. The NaCl freeze–thaw cycles (F-Cs) and dry–wet alternation (D-A) effects with NaCl and Na2SO4 are considered. The corresponding permeability of chloride ions and the carbonation depth (Dc) are obtained. The scanning electron microscope (SEM) photos are researched to reveal the variation of the mechanical mechanism. Results show that after specimens’ suffering from the action of 20 NaCl D-As, the MR of ultra-high-performance concrete is the highest. Specimens exposed to 200 NaCl F-Cs show the lowest MR and CMC. The RME of UHPC under salt actions increase in the order of 20 NaCl D-As < 20 Na2SO4 D-As < 200 NaCl F-Cs. After suffering 200 NaCl F-Cs, 20 Na2SO4 D-As and 20 NaCl D-As, the corresponding Dc values are 1.86 mm to 2.31 mm, 1.79 mm to 2.23 mm and 2.11 mm to 2.76 mm. The flexural strength decreases at the rates of 0.99%–25%, 3.92%–27.84% and 1.47%–21.59% respectively. The MR increases and the RME decreases as the cubic function changes with the amount of salt erosion. After the secondary aluminum dross is added, the CMC decreases at the rates of 0% to 11.53%, 0% to 33.17% and 0% to 8.41% during the process of the salt action. The SAD can reduce the Dc with the decreasing rates of 19.48%, 23.55% and 19.73%. The SAD can increase the compactness of ultra-high-performance concrete. Ultra-high-performance concrete suffering from 20 NaCl D-As shows the largest number and the highest width of cracks. However, when the specimens are exposed to 20 Na2SO4 D-As, the number of cracks is the lowest and the width is the narrowest.

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.

Strength characteristics and carbonation depth evolution of modified magnesium slag based solid waste storage backfill materials

CO2 storage is one of the effective ways to achieve China's 30·60 dual carbon goal. The study of the interaction between CO2 and storage backfill material lays a foundation for the long-term stability and gas tightness of CO2 storage. Based on the modified magnesium slag-based solid waste backfill material constructed by the storage, in order to explore the strength characteristics and carbonation depth evolution of the CO2 storage backfill material, the interaction between CO2 and the storage backfill material was analyzed from the perspectives of uniaxial compressive strength, carbonation depth test, pore structure distribution, microstructure and phase composition. The results show that carbonation can significantly improve the compressive strength of the storage backfill material, and the carbonation depth increases with the increase of carbonation time, and increases slowly after complete carbonation. The later the initial carbonation age, the faster the growth rate of compressive strength and carbonation depth, and the greater the growth rate. After high concentration CO2 curing, the diffusion rate and carbonation degree of the storage backfill material gradually decreased from the outside to the inside, and the calcium carbonate content also gradually decreased. The carbonation can significantly reduce the porosity of the sample, gradually transform from large pores to small pores, and the pore size distribution and pore structure are significantly improved. Therefore, the later the initial carbonation age is, the more beneficial the carbonation effect is for the long-term stability and air tightness development of the backfill material of the CO2 storage, which provides important theoretical guidance for the construction and storage method of the CO2 storage.

Synergic effect of metal-organic frameworks and process parameters on the properties of concrete subjected to accelerated carbonation

This study aims to develop a novel concrete that integrates a metal-organic frameworks (MOF) and accelerated carbonation curing to offset the emissions attributed to cement production. A MOF, NH2-MIL-125(Ti), was synthesized to sequester CO2 in concrete through accelerated carbonation curing. Its impact on the concrete properties was assessed while examining various process parameters, including MOF content, initial curing duration, carbonation curing duration, and carbonation curing pressure. The parameters were evaluated through CO2 uptake, phenolphthalein indicator solution, compressive strength, water absorption, and volume of permeable voids. The microstructure of carbonated MOF-incorporating concrete was characterized using powder X-ray diffraction analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. Experimental results showed that the addition of MOF promoted a higher degree of carbonation of cement, especially with a longer initial curing duration and higher pressure. Incorporating up to 6% MOF, by cement mass, in concrete cured for 20 h in open air, followed by 20 h of carbonation curing at a pressure of 1 bar, led to a CO2 uptake of 19%, carbonation depth of 11 mm, and 28-day strength of 46 MPa, water absorption of 4%, and permeable pore voids volume of 11%. Exceeding 6% MOF addition did not improve the uptake or performance. Microstructure characterization highlighted the formation of calcite, aragonite, and calcium silicate hydrate and the consumption of calcium hydroxide. The MOF-incorporating concrete can be used in construction applications to mitigate CO2 emissions while maintaining concrete performance.

Valorisation of the Effect of Waste Aluminum Sawdust on Concrete: Durability Characteristics and Environmental Impacts

The aim of this study is to examine the effect of replacing waste aluminum sawdust (AS) with fine aggregate on the strength and durability properties of concrete. For this, concrete mixtures with a cement dosage of 400 kg/m3, water/cement (W/C) ratio of 0.40-0.50-0.60 were prepared. Aluminum sawdust obtained from Elazığ industrial site was added to the concrete mixtures by replacing 0%, 0.5% and 1% fine aggregate by volume. After curing in the curing pool for 28 days, the produced concrete samples were placed in the carbonation tank and exposed to the accelerated carbonation test in three different time periods as the 1st, 3rd and 7th days. Tests of compressive strength, splitting tensile strength, ultrasound transmission velocity, porosity and carbonation depth were performed on concrete samples before and after carbonation. The samples that were exposed to carbonation were compared with the samples that did not undergo carbonation. In addition, the microstructure of AS concrete was investigated using scanning electron microscopic images (SEM). In the microscopic images, larger cracks, openings and interfacial voids were observed in the concrete matrix with the addition of AS. However, due to the formation of ettringite in these gaps and cracks after carbonation, the cavities became smaller. As a result of the experiments, it was observed that the optimum W/C ratio was 40% and the AS amount was 0.5% in the use of AS in concrete. In addition, it was found that the carbonation effect improves the compressive and splitting tensile strength and increases the ultrasound transmission rate. Finally, life cycle assessment (LCA) was conducted to evaluate the environmental impacts of the prepared concrete samples. Considering the large amount of natural aggregate consumption, it is thought that the use of waste materials in concrete will provide environmental and economic benefits.

Utilization of Waste Brick Powder as a Partial Replacement of Portland Cement in Mortars

Partially substituting Portland cement (PC) with waste brick powder (WBP) is an effective method to reduce environmental pollution. In this paper, the effects of a WBP with low pozzolanic activity on the fresh and hardened properties of blended cement with 0–40% WBP or 50% of WBP+GGBFS (by mass) were studied. Sodium sulphate (SS) (1.5 and 2.5%, related to powder mass) was used to activate the blended cement with 40% WBP or 50% WBP+GGBFS at 20 °C. Results show that the performance of blended cement is decreased with the increase in WBP content since the WBP with low pozzolanic activity mainly contributes to the dilution effect. Binary cement with 10% WBP shows a similar carbonation depth and chloride migration coefficient to PC. Ternary cement with 10% WBP and 40% GGBFS exhibits a slightly lower strength at 90 days and a lower chloride migration coefficient than PC. The SS solution increases the compressive strength at 2 days and decreases the compressive strength at 28 and 90 days. Moreover, the SS solution results in a lower carbonation depth and chloride migration coefficient, except for ternary cement with 10% WBP and 40% GGBFS, which shows a higher carbonation depth at 42 and 68 days. This paper provides a reference for the application of WBP to produce green mortars.

Assessment of CO2 Capture in FA/GGBS-Blended Cement Systems: From Cement Paste to Commercial Products

The cement industry’s intricate production process, including kiln heating and fossil fuel use, contributes 5–8% of global CO2 emissions, marking it as a significant carbon emitter in construction. This study focuses on quantifying CO2 capture potential in blended cement systems through the utilisation of phenolphthalein and thermalgravimetric methodologies. Its primary objective is to assess the CO2 absorption capacity of these blended systems’ pastes. Initial evaluation involves calculating the carbon capture capacity within the paste, subsequently extended to estimate CO2 content in the resultant concrete products. The findings indicate that incorporating ground granulated blast-furnace slag (GGBS) or an ettringite-based expansive agent did not notably elevate carbonation depth, irrespective of their fineness. Conversely, the introduction of fly ash (FA) notably augmented the carbonation depth, leading to a substantial 36.4% rise in captured CO2 content. The observed distinctions in carbonation behaviour primarily stem from variances in pore structure, attributable to distinct hydration characteristics between GGBS and FA. Thermal analysis confirms the increased stabilisation of CO2 in FA blends, highlighting the crucial influence of material composition on carbonation and emission reduction. Incorporating both GGBS and FA notably diminishes binder emissions, constituting almost half of PC-concrete emissions. Initially, 60% GGBS shows lower emissions than 50% FA, but when considering CO2 capture, this emission dynamic significantly changes, emphasising the intricate influence of additives on emission patterns. This underscores the complexity of evaluating carbonation-induced emissions in cementitious systems.

Study on the physical encapsulation mechanism of heavy metals in fly ash carbonation solidification based on synthetic pellets

The physical encapsulation mechanism prevents the leaching of heavy metals by forming calcium carbonate-encapsulated fly ash through the reaction of carbon dioxide and calcium oxide. However, current research in this area primarily involves qualitative analysis, focusing on various methods to enhance the fixation effect of heavy metals. There is a lack of quantitative description regarding how physical encapsulation solidifies heavy metals, and the solidification mechanism of heavy metals is challenging to verify through macroscopic experiments. In this paper, a method for synthesizing small fly ash particles into pellets is proposed to quantitatively study the mechanism of physically encapsulating heavy metals. The data from the carbonation reaction and leaching reaction are fitted using the shrinking core model. The depth of carbonation increases with the lengthening of carbonation time, and the physical encapsulation strengthens the immobilization of heavy metals. The leaching of heavy metals after carbonation can be categorized into three stages based on the shrinking core model: external diffusion, internal diffusion, and chemical reaction control. Synthetic pellets enhance all three stages, especially the external diffusion, which is not detectable with fly ash powder. The fitting results of the experimental data for the carbonation reaction of the enlarged synthetic pellets and the shrinking core model are both above 0.9. This indicates that the primary barrier to leaching of heavy metals is the physical encapsulation formed by the carbonation reaction following the shrinking core model. The physical encapsulation serves as the primary mechanism for the solidification of heavy metals during the carbonation process.

Estudo preliminar do efeito da cura por carbonatação em geopolímeros

Abstract Carbonation curing differs from weathering carbonation since it is performed intentionally at the early ages of cement hydration. This cure involves applying different levels of CO2 (5% to 99%) to concrete for a short period of time, usually followed by conventional hydration. The objective of this article was to evaluate the carbonation curing in metakaolin-based geopolymer concretes, activated with NaOH and Na2SiO3, and compare them with Portland cement (PC) concrete. The following tests were applied: determination of pH, carbonation depth, water absorption by immersion, void index, and compressive strength. The results showed that after the carbonation curing, the geopolymer concrete had compressive strength and carbonation depth equivalent to the concrete with PC, but with a lower absorbed CO2 content. Although this type of cement absorbs less CO2 but is more sensitive to carbonation. The effect on the void ratio was not remarkable. Furthermore, the alkalinity of concretes can be partially recovered after subsequent curing by water immersion.

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.

New Hydrophobic Treatment for the Protection of Gypsum Artifacts

Gypsum has been widely used in traditional and monumental architecture in many countries of the Mediterranean area; however, due to its low water resistance and low mechanical strength, it can be subject to physical, chemical and biological degradation. To improve the preservation of gypsum-based plaster artifacts, a new hybrid inorganic-organic hydrophobic treatment is proposed in this work. This treatment is based on nanometric magnesium hydroxide (Mg(OH)₂) and organically modified silica (OrMoSil), a class of materials with intermediate performances between ceramic materials and polymers. The behaviour of the product was verified both as a protective on gypsum surface, as well as a consolidant added to the mixture of gypsum-based plasters. The treatment does not alter the aesthetic appearance of the surface, as verified through colorimetric analysis. As demonstrated by capillary water absorption and static contact angle measurements, the new hydrophobic protective coating proved to be very effective. Moreover, the new treatment is effective as a consolidant, leading to an improvement of the mechanical properties and to a reduction of the depth of carbonation. The new hydrophobic nanocomposite product is therefore a promising material for the protection and consolidation of gypsum monuments and artifacts of cultural interest.

The durability of spray steel fiber-reinforced recycled coarse aggregate concrete

To boost the application scope of coarse recycled aggregates (RA) with particle size in the range of 5–10 mm, a spray steel fiber reinforced coarse aggregate concrete (SSFRCAC) is developed, and the impact of cube compressive strength, RA replacement ratio, and steel fiber (SF) volume fraction on the durability of SSFRCAC is comprehensively examined through carbonization, sulfate attack, penetration, and freeze-thaw cycle tests. The anti-carbonation test results reveal that as the RA replacement ratio increases, the carbonation resistance of SSFRCAC decreases. The best anti-carbonation performance is achieved when the SF volume fraction is 1%. Additionally, a formula for calculating the carbonation depth is established. Based on the experimental data, the dynamic elastic modulus is recommended as the measurement standard for the freeze-thaw resistance cycle test. The sulfate resistance test results indicate that as the RA replacement ratio increases, the Sulfate Resistance coefficient also increases. SF block the thermal cracks of specimens and corrosion products as well as the formation of expansion cracks, so the corrosion resistance coefficient gradually tends to a certain stable level. According to the anti-permeability test results, the increase in the RA replacement ratio can suppress the anti-permeability performance. When the SF volume fraction is 1%, the concrete has the highest density and the best anti-permeability performance. Overall, the durability of SSFRCAC is found to be much better than that of general recycled SF Recycle aggregates concrete, which makes it more suitable for practical engineering applications.

Experimental study on carbonation depths of OPC and PPC concrete by conventional and advanced methods

Experimental study on carbonation depths of OPC and PPC concrete by conventional and advanced methods

Evaluation of Concrete Carbonation Based on a Fiber Bragg Grating Sensor.

The carbonation of concrete greatly affects its service life. In this paper, fiber Bragg grating (FBG) sensors were used to investigate the relationship between concrete carbonation and its mechanical properties. A T130 High Sensitivity Strain Cable Sensor with a good linearity was used to monitor the internal strain in concrete, to investigate the variation in the elastic modulus of concrete with carbonation time. A mathematical model of elastic modulus and carbonation time of concrete based on FBG was established. At the same time, the authors explored the relationship between the carbonation depth and compressive strength of concrete and the carbonation time using a phenolphthalein solution test and a compressive strength test, respectively. The experimental results indicate that the carbonation depth, compressive strength, and elastic modulus of concrete increase with carbonation time. In the early stage of carbonation, these three parameters increase rapidly, while they grow slowly in the later stage of carbonation. The varying trend of the elastic modulus of concrete is consistent with the compressive strength, which shows a binomial relationship. Therefore, the elastic modulus, measured using FBG sensors, is used as an indicator of the characterization of the carbonation resistance of concrete. This work provides a new approach for concrete carbonation detection and assessment.

Carbonation resistance of sustainable self-compacting concrete with recycled concrete aggregate and fly ash, slag, and silica fume

This study focused on the problem of recycling construction and demolition wastes as well as industrial waste by-products into sustainable concrete materials. By combining addition of three different industrial waste by-products, an environmentally friendly recycled aggregate self-compacting concrete (RA-SCC) mix was put forward. Carbonation resistance and microstructure of SCC incorporating high volumes of industry by-products and recycled aggregates were studied in this paper. A total of 9 RA-SCC with 50%, 75% supplementary cementitious materials (SCMs) and different SCM combinations were prepared, which consist of binary mix with fly ash (FA), ternary mix with FA and ground granulated blast-furnace slag (GGBS), and quaternary mix with FA, GGBS, and silica fume (SF). An exposure period of 3, 7, 14, and 28 days was adopted for accelerated carbonation tests. The test results indicate that, as RCAs content increased, RA-SCC carbonation depth increased. The carbonation depth of SCC with 100% RCAs increased by 49.35% compared to that of normal SCC. In addition, carbonation resistance of RA-SCC mixes with a given compressive strength decreased with increasing SCM content. However, the loss in carbonation resistance was greatly mitigated by the combined addition of different SCMs, on account of the substitution of cement with industrial by-products and natural aggregates with RCAs. The combined addition of different SCMs enhanced the carbonation resistance of RA-SCC mixes. The test results were validated through microstructural analysis using scanning electron microscopy (SEM), and X-ray diffraction (XRD). A comparison between predictions calculated using existing models and measured carbonation depth was implemented. By taking into account the effect of RCAs and SCMs, a modified carbonation model in conjunction with fib carbonation model was put forward.

Electrochemical realkalisation of carbonated cementitious matrix: characterization research to influence of time and current density

The depassivation of reinforcement caused by the reduction of concrete alkalinity due to the concrete carbonation process can induce the appearance of steel corrosion. The restoration of alkalinity can be done by chemical realkalinization (CRA) or electrochemical realkalinization (ERA) methods. In this context, the present work aims to evaluate the influence of the application time and the current density used in the electrochemical realkalinization process. For the development of the research, mortar samples were molded with a reinforced bar for electrical connection and remained for 24 months in a carbonation chamber. After this period, the carbonation depth that occurred was verified and then the specimens were submitted to the electrochemical realkalinization process using 3 different current values, 0.5, 1.0 and 1.5A/m2 and remained at different periods (7 , 14 and 21 days) in the recovery process. Additional tests of absorption, compressive strength, carbonation depth measurements, mercury intrusion porosimetry (MIP) and thermogravimetric analysis (TGA) were also carried out on reference, carbonated and realkalinized specimens. Based on the results of the tests, it was observed that the recovery process starts after 7 days with the lowest current density used. A better current density x application time ratio was also observed considering the results of the mercury intrusion porosimetry and thermogravimetric analysis tests in conjunction with the realkalinization process.

Long term performance of concrete using accelerated carbonation curing: an effective CCUS technique

The induction of accelerated carbonation curing (ACC) as carbon capture, utilization, and sequestration (CCUS) technique helps in achieving the net zero target. ACC is one of the potential techniques to sequester the CO2 in concrete. However, the usage of ACC in reinforced concrete is still debatable. This paper investigates the effect of ACC on mechanical, permeation, mineralogy, hydration and microstructural characteristics of concrete with the long-term performance of reinforced concrete using linear polarization resistance (LPR) and carbonation depth. In order to study the effect of ACC duration on the properties of concrete, the specimen was subjected to 6, 12, and 24 hours (h) of carbonation curing. The results were compared with conventional water-curing specimens. ACC at 12 h provided the best results for tested properties. The results were varied by statistical analysis using ANOVA and stoichiometry. Based on the best 12-h duration, 2.13 kg of CO2 can be sequestered in 1 m3 (0.89 kg/t) of concrete.