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Geopolymer is a new type of low-carbon and green cementitious material, and carbonation behavior is closely related to the calcium content within geopolymers. Therefore, investigating the influence of calcium content on the carbonation resistance of geopolymers is an urgent issue to address. To this end, this study utilized low-calcium fly ash and metakaolin as raw materials to prepare fly ash-metakaolin-based geopolymer pastes (FMGP). Additionally, high-calcium geopolymer slag and carbide slag were used to partially replace fly ash in FMGP. Standard curing and rapid carbonation tests were conducted, comparing them with ordinary Portland cement pastes. The study analyzed the effects of different slag and carbide slag contents on the microstructures, mechanical properties, phase composition, and carbonation resistance of FMGP before and after carbonation. The results revealed that the introduction of slag or carbide slag significantly enhanced the compressive strength of FMGP before carbonation, with a maximum increase of up to 39.29%. However, after carbonation, there was a noticeable decrease in compressive strength, with reductions exceeding 25%. In addition, FMGP incorporating slag or carbide slag maintained a carbonation rate of approximately 3.20 mm/d1/2 or less, and the pH of the pore solution after 28 days of carbonation remained between 11 and 11.5. Moreover, carbonation of FMGP containing slag or carbide slag resulted in pore refinement, though changes in gel properties had a more significant impact on mechanical properties than alterations in pore structure. FMGP incorporating slag or carbide slag developed a less stable Aragonite crystalline phase due to decalcification of the gel structure after carbonation. Additionally, the incorporation of slag or carbide slag promoted the hydration reactions of FMGP and the formation of C-(A)-S-H gel. [ABSTRACT FROM AUTHOR]

Given the pressing threat of global warming, it is imperative to promote CO2 emission reduction within the cement industry which is widely recognized as a major contributor to the overall carbon footprint. Limestone clay cement (LCC) emerges as a promising alternative to Portland cement. However, to facilitate the implementation of LCC technology, it is urgent to address the low early-age compressive strength issue. Inspired by the successful implementation of nano-engineered cementitious material, we hereby introduce a novel nanomaterial, graphene oxide (GO), into unconventional LCC paste (cement:clay:limestone = 65%:20%:15%, water/binder ratio: 0.45). Experimental results revealed that the 0.09% GO by weight of the LCC binder was the optimal dosage in this work, which improved the compressive strength of the LCC paste at 7, 14, and 28 days by 25.6, 21.6, and 20.3%, respectively. Advanced characterizations were then conducted, suggesting that the admixed GO not only enabled a higher polymerization degree of binder hydrates (which benefited the development of compressive strengths) but also improved the carbonation resistance of LCC paste. These findings not only offer valuable insights for researchers but also provide practical guidance for engineers in the field. Notably, the admixed GO converted the unstable orthorhombic crystal systemic aragonite to the stable trigonal crystal systemic calcite, which offers insights into the technology of carbon sequestration in concrete.

Expanded polystyrene concrete (EPSC) is increasingly utilized in buildings as a green building material. To investigate the effect of high-tenacity polypropylene (HTPP) fibers on the carbonation resistance (CR) of EPSC, five groups of EPSC specimens with HTPP fiber volume fractions of 0%, 0.6%, 0.9%, 1.2%, and 1.5% were prepared. Rapid carbonation tests were conducted to measure the carbonation depth (CD) and uniaxial compression strength (UCS) of the specimens at different carbonation ages (3, 7, 14, and 28 days). The CD and UCS of the specimens were calculated and analyzed. The results indicated that the HTPP fibers dramatically improved the CR of EPSC, with a decrease in the CD of up to 29.5% at 28 days. A model for predicting the CD of EPSC was developed. The model for the strength after carbonation also showed good agreement with the experimental results. Scanning electron microscopy (SEM) was used to examine the microstructure of the HTPP-reinforced EPSC, while the mechanism of HTPP fibers to enhance the CR of EPSC was elucidated. The findings of this study provide valuable insights for the application of EPSC as a structural material. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For the purpose of enhancing the utilization rate of limestone powder (LP) in concrete and maximizing its activity effect. In this paper, the replacement methods for replacing fly ash (FA) with fine particles and manufactured sand (MS) with coarse particles were proposed. The content of LP replacing FA increased from 10% to 50%, and the content of LP replacing MS increased from 5% to 20%. The effects of LP replacing FA alone, replacing MS alone and particle-screened LP replacing both FA and MS on the workability, mechanical properties, durability of concrete were compared. Analysis of variance (Anova) was used to determine the importance level of the test parameters on the performance characteristics of concrete. The results suggested that LP replacing MS improved the workability and strength of concrete, and ameliorated the carbonation and chloride ion permeability resistance. However, the amount of LP substitution was very low, only 10%. Compared with LP replacing FA alone, the screened substitution improved the cohesion and water retention of concrete. The improvement in strength at 7 and 28 days was better, which was 1.6 MPa and 1.3 MPa higher than replacing FA alone. And there was no significantly adverse effect on the durability of concrete. Moreover, it was conducive to enhancing the utilization rate of LP. According to the research results, the effect of the interaction between LP content and the mixing method on the performance of concrete cannot be ignored. In addition, the screened substitution method was more environmentally friendly and economical, because it was conducive to the recycling of solid waste and landfill waste treatment.

Nanomaterials possess great application prospects in improving the performance of cementitious materials. However, their high agglomeration hinders their efficient utilization in cementitious matrices. Consequently, surface modification has recently attracted attention as a method to enhance dispersibility. In this study, silica was employed to modify the surface of nanoscale titanium dioxide (NT), resulting in the synthesis of silica-coated nanoscale titanium dioxide (SCNT) composite material. In particular, the dispersibility of SCNT was investigated, and its influence on the compressive strength development of modified cement paste was analyzed. Additionally, the mechanisms affecting cement hydration behavior and microstructure evolution were comprehensively analyzed. Lastly, the impact of SCNT on the carbonation resistance of cementitious materials was further explored. Interestingly, the research results indicate that the surface SiO2 coating treatment improves the dispersibility of NT. More precisely, compared to 3 % NT, the addition of 3 % SCNT can increase the compressive strength of cement paste by 20.52 % at 3 days and 16.52 % at 28 days. Specifically, the incorporation of SCNT promotes cement hydration, refines the crystal size of Ca(OH)2, reduces the crystal orientation growth index of Ca(OH)2, and enhances the polymerization degree of calcium silicate hydrate (C-S-H), optimizing the pore structure. Furthermore, the 28-day permeability coefficient of 3 % SCNT mortar is reduced by 99.98 % compared to the blank group, effectively enhancing the carbonation resistance of cementitious materials. Overall, the findings of this study will contribute to the development of high-performance and multifunctional nanocomposite cementitious materials.

Copyright of Fly Ash Comprehensive Utilization is the property of Hebei Fly Ash Comprehensive Utilization Magazine Co., Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To understand the influence of slag chemistry on the carbonation resistance of slag-rich cement, this paper explored the carbonation characteristics of blended cement systems with different Al2O3 contents in slag through accelerated carbonation test. Irrespective of slag chemistry, three main CO2 binding phases were identified during accelerated carbonation test, i.e. carbonated Ca-Al AFm phases (amorphous or nano-crystalline), carbonated hydrotalcite-like phase, and calcium carbonate (amorphous calcium carbonate, vaterite, and calcite). Additionally, it was noted that the classification employed for slag reactivity (based on slag chemistry) cannot be extended to predict carbonation resistance of slag-rich cement directly. The main challenge occurred for slag with high alumina content. The experimental results showed that Al2O3-rich slag exhibited a high reactivity and can be considered as a reactive component in the blended mixture; however, it did not contribute to carbonation resistance of the mixture. Especially for CO2 binding capacity, it was similar for systems with varied alumina content in slag (from 3.69 to 18.19 wt.%) in the completely carbonated area. [ABSTRACT FROM AUTHOR]

Die Einflussfaktoren auf den Carbonatisierungswiderstand des 11Å‐Tobermorits in dampfgehärteten Baustoffen sind bislang nicht systematisch untersucht worden. In der Vergangenheit haben Forschungen gezeigt, dass ein geringer Carbonatisierungswiderstand mit einem auffällig hohen Trockenschwindwert einhergeht. Daher wurde durch das DIBt ein Grenzwert für das Schwinden von Porenbetonen von 0,4 mm/m eingeführt. Es ist jedoch nicht systematisch untersucht, ob ein geringer Carbonatisierungswiderstand per se mit niedrigen Schwindwerten beim Trocknungsschwinden einhergehen. In einem von der DFG geförderten Forschungsprojekt werden unterschiedliche potentielle Einflussfaktoren auf die Carbonatisierung von Porenbeton untersucht, wofür Modellporenbetone hergestellt wurden, die sich im Sulfatgehalt unterscheiden. Für eine möglichst hohe Vergleichbarkeit werden die äußeren Einflussfaktoren wie die Luft‐ und Materialfeuchtigkeit, Temperatur und Kohlendioxidkonzentration konstant gehalten. Im Rahmen dieser Untersuchungen wurden kleinformatige Prismen extrahiert, an denen die Festigkeitsentwicklung mit zunehmender Carbonatisierung unter ansonsten gleichen Bedingungen untersucht wurde. Die spezifische Oberfläche dieser Prüfkörper wurde mit dem BET‐Verfahren vor und nach der Carbonatisierung charakterisiert, um Rückschlüsse auf die Veränderung der Mikrostruktur zu ziehen. Zudem wurde an aus den Prismen extrahierten Pulverproben die Phasen nach der Carbonatisierung mineralogisch analysiert. [ABSTRACT FROM AUTHOR]

The production of cements with calcined clay is becoming increasingly important for the cement industry for ecological and economic reasons. Especially the combination of the cement constituents granulated blast furnace slag (S) and calcined clay (Q) next to Portland cement clinker (K) is very promising in terms of cement properties, durability and CO2 saving potential. Due to a lack of knowledge and experience, such KSQ cements have not yet been produced in Europe. With the help of design of experiments and statistical evaluation, both the influence of the cement composition and the reactivity of the clinker and calcined clays used on the cement and concrete properties were determined. For this purpose, a total of 64 different cement compositions consisting of at least 20 wt.% clinker (two different qualities), a maximum of 59 wt.% granulated blast furnace slag and a maximum of 49 wt.% calcined clay (two different qualities) were investigated. It could be shown that in a wide range of compositions, the production of KSQ cements of strength class 42,5 acc. EN 197‐1 is possible, whereby the water demand of the cements was mainly determined by the amount of calcined clay. Most of the corresponding concretes exhibited a high resistance to carbonation, chloride and freeze thaw attack. [ABSTRACT FROM AUTHOR]

One of the paths to CO2 emissions reduction in the concrete industry is to use low-clinker cements, providing at the same time the performance of concrete that is adequate for application in concrete structures. This paper explores the impact of the clinker replacement with high amounts of limestone powder (21–70% in the powder phase) on concrete carbonation resistance. To quantify this impact, the empirical relationship between the carbonation resistance and the compressive strength of the high-volume limestone powder concrete (HVLPC) was established. For that purpose, the regression analysis was applied on the experimental results collected from the published research. The service life analysis based on the full probabilistic approach was performed using the fib Model Code 2010 prediction model and proposed empirical relationship. The first-order reliability method (FORM) was applied to solve the limit state function of reinforcement depassivation with a reliability index equal to 1.3. The obtained minimum concrete cover depths were 40–110% higher compared to those prescribed in the current European standard EN 1992-1-1:2004 for indicative strength classes. Based on the full probabilistic analysis, recommended cover depths are given for all carbonation exposure classes, commonly applied concrete strength classes, and service lives of 50 and 100 years. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Expanded polystyrene concrete (EPSC) is increasingly utilized in buildings as a green building material. To investigate the effect of high-tenacity polypropylene (HTPP) fibers on the carbonation resistance (CR) of EPSC, five groups of EPSC specimens with HTPP fiber volume fractions of 0%, 0.6%, 0.9%, 1.2%, and 1.5% were prepared. Rapid carbonation tests were conducted to measure the carbonation depth (CD) and uniaxial compression strength (UCS) of the specimens at different carbonation ages (3, 7, 14, and 28 days). The CD and UCS of the specimens were calculated and analyzed. The results indicated that the HTPP fibers dramatically improved the CR of EPSC, with a decrease in the CD of up to 29.5% at 28 days. A model for predicting the CD of EPSC was developed. The model for the strength after carbonation also showed good agreement with the experimental results. Scanning electron microscopy (SEM) was used to examine the microstructure of the HTPP-reinforced EPSC, while the mechanism of HTPP fibers to enhance the CR of EPSC was elucidated. The findings of this study provide valuable insights for the application of EPSC as a structural material.

Driven by the scarcity of river sand and accompanying environmental concerns, sea sand is emerging as an alternative material. However, the durability of construction products can be jeopardized by chloride ions in raw sea sand. Alkali-activated cementitious materials possess high chloride binding capacity, alleviating some of these risks. But its carbonation resistance is weaker. In alkali-activated sea sand slag (AASS) mortars, the interaction effects and mechanisms of carbonation and chloride ions are still unclear. To address this, our study investigates the effects of alkali equivalent and sea sand substitution rates on carbonation resistance and chloride ion distribution in AASS mortar. Mortar specimens were prepared with varying alkali equivalents (4–6%) and sea sand substitution rates (0–100%), followed by mechanical strength, carbonation depth, chloride ion distribution, and microstructure. Our results reveal that higher alkali equivalents improve mechanical performance and carbonation resistance. Although the presence of shells in sea sand slightly reduces strength, an optimal substitution rate of 30% refines pore structure and thereby enhances durability. Conversely, higher sea sand substitution negatively affects resistance due to poor gradation. Increased alkali equivalent slightly escalated peak chloride concentration, whereas higher sea sand amplified the concentration gradient, expediting chloride transport. Through TG and MIP analyses, optimal resistance was verified at 5% alkali equivalent and 30% sea sand substitution. In conclusion, appropriate sea sand incorporation can improve AASS mortar durability, making sea sand a feasible alternative material.

Properties of recycled aggregate concrete (RAC) are influenced by the composition and particle size distribution of recycled coarse aggregate (RCA). The study herein designed seven distinct groups of RACs with varying aggregate fractal dimensions (D) and one group of natural concrete (NAC). The impact of D on the workability, compressive strength, resistance to chloride ion penetration, and carbonation resistance of RAC was measured. It was found that an increase in the D value led to a decrease in the slump and slump flow, with the compressive strength and chloride ion penetration increasing and then decreasing, and carbonation gradually declined. The optimal fractal dimension was thereby determined to be 2.547 by a strength model accommodating two parameters of D and the curing age. Additionally, the mass percentage of each particle size for the corresponding gradation was presented. The compressive strength and chloride permeation resistance of RAC (D = 1.0) relative to RAC (D = 2.5) was increased by 16.7% and 13.3%, respectively. Furthermore, the carbonation depth of RAC (D = 2.5) was comparable to that of NAC. Additionally, the carbonation resistance of RAC was influenced by both the size distribution and the degree of natural carbonation of RCA, resulting in four distinct features relative to NAC. It is thereby feasible to enhance RAC performance through the manipulation of RCA's fractal dimensions. [ABSTRACT FROM AUTHOR]

Recently, research into finding long-term solutions to CO2 mitigation in the cement and concrete sectors was initiated since commonly used supplementary cementitious materials are not globally available in sufficient amounts. One of the possible solutions to that problem is to develop concrete with a higher percentage of limestone in the powder phase. This work presents a critical overview of the state-of-the-art in the field of the carbonation resistance of limestone powder concrete. Experimental research performed so far has shown that if the simple replacement of cement with limestone powder is applied in the standard mix design, a maximum of 10-15% of cement (clinker) could be replaced to maintain similar carbonation resistance. It has also been proven that the dilution effect of weakly inert limestone powder can be compensated for with several measures in the mix design of concrete. By adjusting the cement, limestone, and water content and their particle size distribution, it is feasible to design concrete formulations with up to 50% limestone in the powder phase that are comparable to referent Portland cement concrete in terms of rheological and mechanical performance and carbonation resistance. This is an environmentally significant reduction in the clinker content, but it comes at the cost of a larger superplasticizer content. Prediction models for the carbonation resistance of the limestone powder concrete are poorly developed. Amongst them, the fib MC 2010 prediction model is considered relatively simple and robust; however, it has not yet been proven that the model is applicable to concrete with a higher content of limestone powder (>15-20% of the powder phase). The future research should be oriented towards further optimization of the concrete mix design and implementing this model on the middle-and high-content limestone concrete carbonation.

Due to the large amount of CO2 generated during steelmaking, to resume production as soon as possible, a fast repair material with good carbonation resistance is needed to repair the factory building. First, the performance of an ordinary Portland cement (OPC)-calcium sulfoaluminate cement (CSA) system under an accelerated carbonization environment was studied. Next, the OPC-CSA system with a CSA content of 15 wt% was selected to be modified by adding calcium hydroxide (CH). The findings showed that the addition of 15 wt% CSA to the OPC-CSA system resulted in the highest mechanical properties. Specifically, the flexural strength and compressive strength after 84 d of carbonization were 18% and 15% higher, respectively, compared to those of OPC alone. The degradation of the mechanical properties of the OPC-CSA system due to carbonation was improved by adding CH. The flexural strength (3.0 wt% CH) and the compressive strength (4.5 wt% CH) of the OPC-CSA-CH system after 84 d of carbonization were 13% and 5% higher, respectively, than those of the OPC-CSA system. The addition of CH increased the alkalinity of the OPC-CSA system and enhanced the stability of Aft, resulting in better carbonation resistance in the OPC-CSA-CH system. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To advance the use of industrial solid waste and recycled concrete, this study explores the impact of fly ash and slag powder on the mechanical properties, freeze–thaw resistance, and carbonation resistance of manufactured sand recycled aggregate concrete (MRAC). Different FSMRAC (Fly Ash and Slag Powder MRAC) mixtures were prepared by varying the amounts of fly ash and slag powder. The results show that fly ash and slag powder enhance the splitting tensile strength of MRAC more than its compressive strength. when the contents of fly ash and slag powder are 0% and 30%, respectively, the FSMRAC attains maximum compressive strength of 48.6 MPa and splitting tensile strength of 3.8 MPa, representing increases of 2.96% and 5.6% in compressive and splitting tensile strengths, respectively, compared to MRAC. A total addition of 30% fly ash and slag powder effectively reduces the loss of mechanical properties under freeze–thaw conditions. When the fly ash-to-slag powder ratio (F:S) exceeds 1.5, it improves carbonation resistance and compressive strength; when the ratio is below 1.5, it enhances splitting tensile strength resistance to freeze–thaw cycles. Slag powder promotes hydration and improves mechanical properties, while fly ash densifies the concrete matrix and lowers the carbonation rate. Response Surface Methodology (RSM) analysis indicates that both materials improve MRAC’s properties. Higher fly ash content benefits compressive strength and carbonation resistance, while higher slag powder content improves splitting tensile strength.

One of the paths to CO2 emissions reduction in the concrete industry is to use low-clinker cements, providing at the same time the performance of concrete that is adequate for application in concrete structures. This paper explores the impact of the clinker replacement with high amounts of limestone powder (21–70% in the powder phase) on concrete carbonation resistance. To quantify this impact, the empirical relationship between the carbonation resistance and the compressive strength of the high-volume limestone powder concrete (HVLPC) was established. For that purpose, the regression analysis was applied on the experimental results collected from the published research. The service life analysis based on the full probabilistic approach was performed using the fib Model Code 2010 prediction model and proposed empirical relationship. The first-order reliability method (FORM) was applied to solve the limit state function of reinforcement depassivation with a reliability index equal to 1.3. The obtained minimum concrete cover depths were 40–110% higher compared to those prescribed in the current European standard EN 1992-1-1:2004 for indicative strength classes. Based on the full probabilistic analysis, recommended cover depths are given for all carbonation exposure classes, commonly applied concrete strength classes, and service lives of 50 and 100 years.

Steel slag stone can be used as a substitute for coarse aggregate in concrete. In this study, the performance of steel slag concrete (SSC) in the wall brick structure was analyzed. The specimens with a steel slag replacement rate of 0%, 20%, 25%, 30%, 35%, 40%, 45%, and 50% were designed, and the slump, stability, and carbonation resistance were tested. The results showed that the slump decreased with the increase of the replacement rate of steel slag stone. At the 60th min, the slump of SSC50 was 74 mm, which was 25.25% smaller than SSC00. When the replacement rate was more than 30%, cracks or fractures appeared, and the stability was destroyed. Twenty-eight days after the carbonation experiment, with the increase of the replacement rate, the carbonation resistance of the specimen decreased, and the performance was best when the replacement rate was 25%. The experimental results show that the performance of SSC is the best when the replacement rate of steel slag stone is 25%, which can be further promoted and applied in practice.

Predicting carbonation resistance via early site tests is crucial for controlling the longevity and durability of concrete structures. Therefore, this study aimed to provide a nondestructive approach for predicting carbonation resistance utilizing in situ air-permeability and surface moisture measurements. The Torrent air-permeability method, coupled with surface moisture measurements by the electrical impedance method, was applied to 25 specimens produced using different cement types, water-to-binder ratios, and curing periods to obtain test data at various ages from 1 to 18 months; the carbonation depths were measured at 6, 12 and 18 months. To overcome the challenge of the moisture effect on measured values during the drying process, the kT5 indicator, permeability coefficient at the reference moisture of 5.0% was utilized. Strong correlations between kT5 and the carbonation rates were obtained that allowed the latter's prediction from tests of air-permeability and surface moisture performed at relatively early ages (e.g., 1 or 3 months). Guidance on the procedure is outlined. [ABSTRACT FROM AUTHOR]

Ultra-High-Performance Concrete (UHPC) is characterized by having an ultra-compact matrix resulting in ultra-high mechanical properties, low permeability to water and gases, and improved ductility provided by the addition of fibers. The production of structures with this type of concrete is advantageous in some situations, especially in aggressive environments since it significantly increases durability. However, high dosages of Portland cement and silica fume are commonly adopted, increasing not only the cost but also the environmental impact, jeopardizing its use, mainly in the present context where the sustainability of the construction sector is a global priority. In this sense, improving the eco-efficiency of this type of concrete is mandatory. The objective of this work is to develop eco-ultra-high-durability concrete (eco-UHDC). The UHDC matrix was optimized, focusing mainly on durability and looking for the lowest environmental impact, where several parameters were varied: cement replacement ratio, additions in binder matrix and its relative proportions, water/binder ratio, type of fibers, and its proportion. The developed eco-UHDC was characterized both in fresh and hardened states, in terms of mechanical properties, time-dependent properties, and durability. This last topic includes the characterization of durability parameters under laboratory conditions and in a real environment, namely, in the tidal zone of the coast of Cape Verde. The results of resistance to carbonation and chloride penetration were used to predict the service life of structures produced with these eco-UHDC. The optimization of the UHDC matrix allowed the development of mixtures with only 60% of cement in relation to the total amount of powder of the matrix, maintaining good workability and the desired mechanical characteristics (compressive strength higher than 100 MPa and flexural strength higher than 12 MPa). The results also showed that considering only the requirements related to durability, the cover of structures produced with these optimized mixtures can be lower than the values recommended by Eurocode 2, with differences that can reach 55%, mainly when pozzolan of Cape Verde is used as partial replacement of Portland cement. [ABSTRACT FROM AUTHOR]

Cement production is the primary source of global CO2 emissions in the construction industry. Blast furnace slag (BFS) has been examined as a potential substitute for cement to reduce CO2 emissions. In addition, this substitution increases the long-term strength and improves the chemical resistance of mortar. However, a glassy film is formed on the surface of BFS while it is generated as a byproduct, lowering the initial strength of mortar. Notably, this film is destroyed in an alkaline environment. Thus, several studies have used solutions with various alkali activators. However, alkali activators are unsafe, as they are strong alkaline materials, and have low economic efficiency. This study experimentally improved the initial hydration reactivity of a mortar containing BFS as a substitute for cement, thereby improving its initial strength. We observed an increase in carbonation resistance. In addition, this study focused on evaluating the compressive strength and carbonation resistance of mortar prepared using BFS and alkaline water obtained from the electrolysis of a K2CO3 electrolyte. Results show that alkali-activated mortar using an electrolyzed alkaline aqueous solution has higher strength and contains more hydration products than that using conventional mixing water. [ABSTRACT FROM AUTHOR]

This study focused on the carbonation resistance of concretes incorporating dolomite powder with water–binder ratio (w/b) of 0.55 and 0.36. The micro-morphology, micro-pore structure and carbonation depth of cement-based materials incorporating dolomite powder were investigated by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and carbonization test box. The 28-day carbonation depth of concretes with a w/b of 0.55 in the case of dolomite powder at 50 wt% replacement level decreased by 39.62% compared with that of pure concretes. The carbonation resistance of concretes was improved with increasing dolomite powder dosage due to the fact that dolomite powder had the pore refinement efficiency on the carbonated cement pastes. The service life of concretes with a w/b of 0.55 incorporating dolomite powder under natural carbonation condition was obtained based on Alekseyev's carbonation correction model. The durability life of concrete structure with a w/b of 0.55 was prolonged with the addition of dolomite powder. After carbonation for 28 days, concretes with a w/b of 0.36 were hardly affected by carbonation corrosion. The pore structure of concretes with a w/b of 0.36 became dense, inhibiting the penetration of CO2 into the concretes due to a lower water–binder ratio. [ABSTRACT FROM AUTHOR]

Replacing Portland cement (PC) with high-volume ground granulated blast furnace slag (GGBFS) reduces carbon emissions but decreases the early strength of PC materials. Although using nano-calcium silicate hydrate (n-C-S-H) has been demonstrated to enhance the early strength of high-volume GGBFS-blended cement (HVGBC), its effects on durability still needs further research. This study investigates the impacts of n-C-S-H-polycarboxylate (PCE) composites on the properties of HVGBC-based materials, including compressive strength, anti-chloride permeability, and carbonation resistance, as well as the pore structure characterized using Mercury Intrusion Porosimetry (MIP) and X-ray Computed Tomography (CT). The results indicated that using n-C-S-H-PCE remarkably elevated the compressive strength of PC with 50 wt% GGBFS within 7 d of curing. Adding 1 wt% n-C-S-H-PCE increased the hydration degree of PC and GGBFS and significantly improved the resistance of the mortar to chloride penetration and carbonation compared with those of the pure PC mortar. MIP and 3D visualization by CT revealed that using an appropriate amount of n-C-S-H-PCE formed a dense microstructure, thus improving the early strength and durability. This work gives some insights into using the effective addition of n-C-S-H-PCE to dramatically elevate the early mechanical properties of HVGBC composites while maintaining their excellent durability. [Display omitted] • Using nano C-S-H-PCE (CSH) boosts the early strength of high volume GGBFS-blended cement mortars. • The combination of CSH and GGBFS gains synergetic reinforcing effect on the durability. • Adding CSH causes a remarkable improvement in the hydration degree of cement and GGBFS. • Visualization models of 3D pore distribution gives an evidence for the pore refinement of CSH. [ABSTRACT FROM AUTHOR]

Although accelerated carbonation resistance has been extensively tested, there are no recommendations for the application of test results in codes of practice. The main objective of this study was to determine the limit values of accelerated carbonation resistance to satisfy the required service life of reinforced concrete structures with concrete covers as prescribed in EN 1992-1-1. The service life of 50 years was considered, as well as all carbonation exposure classes (from XC1 to XC4). A full probabilistic analysis was conducted using the fib-Bulletin 34 carbonation prediction model. Using the limit state function and a defined reliability index, the upper limits of the inverse effective carbonation resistance (R-1 ACC) for all exposure classes and in a function of concrete cover depth were determined. The determined values of R-1 ACC presented in this study represent the upper limit of the average value, as well as the maximum deviation of one sample in relation to this average value. Thus, a simple assessment of concrete quality is allowed in terms of carbonation resistance based on the accelerated carbonation depth measurements.

Hybrid nanoSiO2 (HNS) modified cement pastes were explored as a kind of surface protection material (SPM). The carbonation resistance and mechanical properties of SPMs coated samples were tested. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP) were further employed to evaluate the chemical composition and microstructure characteristics of SPM. Besides, thermodynamic modeling was adopted to simulate the changes in the phase assemblages of SPM under the carbonation process. The results showed that SPM with 1 wt% HNS could effectively enhance the carbonation resistance. The incorporation of HNS could densify the microstructure and refine the pore structure. Moreover, the thaumasite can be stable at ambient temperature with the addition of HNS, which is beneficial to maintain alkalinity under the carbonation process. [ABSTRACT FROM AUTHOR]

Properties of recycled aggregate concrete (RAC) are influenced by the composition and particle size distribution of recycled coarse aggregate (RCA). The study herein designed seven distinct groups of RACs with varying aggregate fractal dimensions (D) and one group of natural concrete (NAC). The impact of D on the workability, compressive strength, resistance to chloride ion penetration, and carbonation resistance of RAC was measured. It was found that an increase in the D value led to a decrease in the slump and slump flow, with the compressive strength and chloride ion penetration increasing and then decreasing, and carbonation gradually declined. The optimal fractal dimension was thereby determined to be 2.547 by a strength model accommodating two parameters of D and the curing age. Additionally, the mass percentage of each particle size for the corresponding gradation was presented. The compressive strength and chloride permeation resistance of RAC (D = 1.0) relative to RAC (D = 2.5) was increased by 16.7% and 13.3%, respectively. Furthermore, the carbonation depth of RAC (D = 2.5) was comparable to that of NAC. Additionally, the carbonation resistance of RAC was influenced by both the size distribution and the degree of natural carbonation of RCA, resulting in four distinct features relative to NAC. It is thereby feasible to enhance RAC performance through the manipulation of RCA’s fractal dimensions.

Alkali-activated slag (AAS) cement is one type of alkali-activated binders free from Portland cement. The main problems of this type of cement are its high drying shrinkage and low carbonation resistance that hinder its wide use. In the current paper, the authors tried to suppress this high drying shrinkage and enhance the carbonation resistance of this type of binder by incorporating quartz powder (QP). For that reason, slag was partially replaced with QP at ratios of 10–30 wt%. The flowability of each mixture was measured using a hand-driven flow table. The initial reading of drying shrinkage was monitored after 24 h from casting and continued up to 90 days. After initial curing, some specimens were exposed to atmospheric natural carbonation for one year, whilst the remaining specimens were sealed and used as references. Different techniques such as thermogravimetric analysis and its derivative (TGA/DTG), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) were used to analyze the results. The results showed that the incorporation of QP in the matrix increased the flowability and compressive strength, decreased the drying shrinkage, increased the carbonation resistance, and refined the microstructure. [ABSTRACT FROM AUTHOR]

The utilization of marine waste and resources to produce eco-friendly building materials is essential for the sustainable development of the construction industry on islands and coastal areas. The sea sand and coral sand sourced from coral waste are the most promising. Therefore, the objective of this work is to investigate the feasibility of coral/sea sand as fine aggregate to prepare an environment-friendly marine mortar. The effects of various volume fractions of coral sand intended to replace sea sand on the flowability, physical performances, carbonation resistance, and microstructure of the prepared marine mortars were evaluated. The experimental results showed that as the sea sand replacement by coral sand was increased, the flowability and dry bulk density decreased, while the water absorption increased. Encouragingly, usage of a combination of coral and sea sands enhanced the flexural strength of marine mortars. A mixture containing 80 vol% of coral sand showed the best effect. The carbonation depth of marine mortar was found to noticeably increase with increasing replacement ratios of sea sand by coral sand, closely relating to the increase in the volume of capillary and large pores. In particular, the combined utilization of coral sand and sea sand resulted in a compacted interfacial transition zone (ITZ) between fine aggregates and the matrix.

Due to the large amount of CO2 generated during steelmaking, to resume production as soon as possible, a fast repair material with good carbonation resistance is needed to repair the factory building. First, the performance of an ordinary Portland cement (OPC)-calcium sulfoaluminate cement (CSA) system under an accelerated carbonization environment was studied. Next, the OPC-CSA system with a CSA content of 15 wt% was selected to be modified by adding calcium hydroxide (CH). The findings showed that the addition of 15 wt% CSA to the OPC-CSA system resulted in the highest mechanical properties. Specifically, the flexural strength and compressive strength after 84 d of carbonization were 18% and 15% higher, respectively, compared to those of OPC alone. The degradation of the mechanical properties of the OPC-CSA system due to carbonation was improved by adding CH. The flexural strength (3.0 wt% CH) and the compressive strength (4.5 wt% CH) of the OPC-CSA-CH system after 84 d of carbonization were 13% and 5% higher, respectively, than those of the OPC-CSA system. The addition of CH increased the alkalinity of the OPC-CSA system and enhanced the stability of Aft, resulting in better carbonation resistance in the OPC-CSA-CH system.

White mud (WM) is a solid waste produced in the process of papermaking and it remains to be effectively utilized. It contains a large amount of CaCO 3 and residual alkali metal ions. This paper aims to explore the effect of WM on carbonation resistance of alkali activated slag. The changes in mechanical properties and microstructure of alkali activated white mud/slag (AAWS) after natural carbonation and accelerated carbonation were analyzed. The results indicate that the mechanisms of natural carbonation and accelerated carbonation are different. The carbonation depth achieved in 90 days of natural carbonation can be reached in just 14 days of accelerated carbonation. Samples with 15 wt% WM blended possesses the smallest carbonation depth and the highest compressive strength. WM can effectively mitigate the natural carbonation of AAWS by dissolving Mg2+ and Ca2+. Mg2+ can migrate to increase the solubility of calcite, promote the generation of hydrotalcite to absorb carbon dioxide, and reduce the carbonation degree. Ca2+ will migrate after the carbonation and decalcification of the gel product and reduce the decalcification sensitivity. This study offers a sustainable approach for improving the carbonation resistance of AAWS. • WM inclusion promotes the generation of hydrotalcite for CO 2 absorption. • The migration of Mg2+ from WM increases the solubility of calcite and promotes the formation of aragonite and vaterite. • Ca2+ dissolved from WM reduces the decalcification sensitivity of AAWS. [ABSTRACT FROM AUTHOR]

To promote both strength development and durability of cement, a new nanoscale cement additive (CCP) was designed and synthesized via a one-pot coprecipitation approach. CCP mainly comprised cellulose nanocrystals (CNCs), calcium silicate hydrate (C-S-H), and polycarboxylate ether (PCE). The crosslinking network of CNCs and surface attachment with PCE considerably increased the stability of the nano-C-S-H suspension, in which no precipitation was observed even after 180 days of storage. The addition of C-S-H nanoparticles in CCP considerably promoted cement hydration in the early stage of hydration, reducing the time required to reach the peak of hydration heat flow by 3.7 h. Therefore, CCP considerably increased the early flexural strength and compressive strength of cement pastes by 48.4 % and 82.7 %, respectively (vs. blank control, 16 h), and, due to the short circuit diffusion of CNCs, it still maintained a 12.3 % enhancement effect in flexural strength after 28 days. Notably, the addition of CCP improved the pore structure of cement pastes and decreased the carbonation depth by 43.9 %. Results indicate that CNCs and C-S-H nanoparticles synergistically enhance both the strength and carbonation resistance of cement pastes. This study contributes to the field of construction by using renewable biomass as a resource, accelerating the construction process, enhancing cement performance, and avoiding frequent maintenance. [Display omitted] • CCP were first synthesized using CNCs and PCE as colloid stabilizers. • CCP had better long-term stability compared to C-S-H-PCE nanocomposites. • CCP enhanced the early strength and carbonation resistance of cement paste. • The synergy of CNC and C-S-H on cement hydration is revealed. [ABSTRACT FROM AUTHOR]

A series of nano CaCOs concrete composites are prepared by adding different contents of nano CaC()3 (0, 2 wt%, 4 wt% and 6 wt%) into ordinary Portland cement. The lattice structure, micro morphology, pore distribution, mechanical properties and carbonation resistance of concrete composites are analyzed and characterized, and the mechanism of nano CaCOs toughened concrete composites is discussed. The results show that an appropriate amount of nano CaCOs doping makes the hydration products of concrete composites have better crystal form, higher crystallinity, denser and more uniform surface, effectively reducing the proportion of harmful holes and multi harmful holes, and improving the proportion of harmless holes and less harmful holes. When the doping content of nano CaCOg is 4 wt%, the surface improvement effect of concrete composites is the best, the lowest carbonation depth is 5.91 mm, and the compressive strength and splitting strength reach the maximum, which are 37.92 and 2.37 MPa respectively. Tt can be seen that the optimum doping ratio of nano Ca-C()s is 4 wt%. [ABSTRACT FROM AUTHOR]

This research describes a genetic algorithm-based process for the optimization design of sustainable concrete with limestone powder. The objective of the optimization design was set as the embodied energy. The restraints of the optimization design consist of strength, workability, and carbonation resistance along with stress. The result of the research is shown as follows: (1) for low-strength concrete, carbonation dominates the mixture design of limestone hybrid concrete. Furthermore, the levels of stress and stress types modify the carbonation and optimization mixtures. The influence of tensile stress on optimization mixtures was much more apparent than compressive stress. (2) For concrete with high strength, strength dominates the mixture design of limestone hybrid concrete. (3) The optimization mixtures with low carbon footprints overlapped with those with low embodied energy. In addition, the new knowledge of the research is shown as follows: (1) find the decisive factor of concrete mixture design, (2) show a material design method considering structural stress, and (3) validate for various aims of optimal material design. In summary, the proposed model can be regarded as a common approach for the design of concrete mixture in consideration of strength, workability, carbonation resistance, and structural stress. [ABSTRACT FROM AUTHOR]

Geopolymers are green materials with three-dimensional silicon and aluminum tetrahedral structures that can be serving as environmentally friendly construction materials and therefore have the potential to contribute to sustainable development. In this paper, the mechanism and research progress regarding the carbonation resistance, structural fire resistance, corrosion resistance, permeation properties and frost resistance of geopolymer concretes are reviewed, and the main problems with the durability of geopolymer concretes are discussed. Geopolymers possess the superb mechanic property and their compression strengths could be higher than 100 MPa. Generally, the higher the GPC strength, the better the carbonation-resistant. GPC has excellent fire resistance, due to geopolymers are acquired an inorganic skeleton which is affected by the alkali content, alkali cation, and Si/Ai ratio. There are a large number of Al-O and Si-O structures in geopolymers. Geopolymers do not react with acids at room temperature and can be used to make acid-resistant materials. Besides, GPC owning low porosity volume shows good resistance to permeability. The freezing-thawing failure mechanism of geopolymer concretes is mainly based on hydrostatic and osmotic pressure theory. GPC has poor frost resistance, and the freezing-thawing limit is less than 75 times.

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Using P.O42.5 Portland cement as raw material and nano-TiO2 as filler, different nano-TiO2 contents (0, 1%, 3% and 5%) were prepared. (mass fraction) of modified cement concrete, the mechanical properties, microscopic morphology and durability of concrete were analyzed and tested. The results show that with nanometer With the increase of TiO2 content, the compressive strengths of modified concretes 7 and 28d gradually increased, while the flexural strength of 28d showed a trend of increasing first and then decreasing. When the content of nano-TiO2 was 5% (mass fraction), the compressive strength of 7 and 28d reached the maximum, which were 38.11 and 49.35 MPa, respectively; When the content of TiO2 is 3% (mass fraction), the flexural strength of 28d reaches the maximum value of 6.72 MPa. SEM analysis found that the incorporation of an appropriate amount of nanometers After adding TiO2, the pore content of the modified concrete decreases, and the compactness of the matrix increases. However, after the addition of excessive nano-TiO2, agglomeration will appear, which affects the nano-structure. Particle buff. The wear performance test found that with the increase of nano-TiO2 content, the wear amount of the modified concrete first decreased and then increased. When the content of nano-TiO2 is 3% (mass fraction), the wear amount is at least 1.05kg/m2. The anti-carbonation performance analysis found that with the nanometer With the increase of TiO2 content, the carbonation depth of the modified concrete first decreased and then slightly increased. When the nano-TiO2 content was 3% (mass fraction) The carbonization depths of 7 and 28d are the smallest, which are 1.35 and 4.03 mm, respectively. Comprehensive analysis shows that when the content of nano-TiO2 is 3% (mass fraction) number), the comprehensive performance of modified cement concrete is the best. [ABSTRACT FROM AUTHOR]

Cement production is the primary source of global CO2 emissions in the construction industry. Blast furnace slag (BFS) has been examined as a potential substitute for cement to reduce CO2 emissions. In addition, this substitution increases the long-term strength and improves the chemical resistance of mortar. However, a glassy film is formed on the surface of BFS while it is generated as a byproduct, lowering the initial strength of mortar. Notably, this film is destroyed in an alkaline environment. Thus, several studies have used solutions with various alkali activators. However, alkali activators are unsafe, as they are strong alkaline materials, and have low economic efficiency. This study experimentally improved the initial hydration reactivity of a mortar containing BFS as a substitute for cement, thereby improving its initial strength. We observed an increase in carbonation resistance. In addition, this study focused on evaluating the compressive strength and carbonation resistance of mortar prepared using BFS and alkaline water obtained from the electrolysis of a K2CO3 electrolyte. Results show that alkali-activated mortar using an electrolyzed alkaline aqueous solution has higher strength and contains more hydration products than that using conventional mixing water.

Microbial induced carbonate precipitation (MICP) is a novel and environmentally-friendly method to improve the properties of recycled aggregate. This study focused on the optimization of MICP treatment process, mainly including the modification duration, the addition method of calcium source and the number of modification cycles, to improve the quality of recycled fine aggregate (RFA). Weight increase and water absorption decrease of RFA after MICP modification were used to evaluate the effects on the improvement in properties of RFA. The properties of the mortar with modified RFA were examined to investigate the effectiveness of the proposed MICP treatment process. The results show that the optimal MICP treatment process consisted of disposable addition of calcium source and repeating 3 modification cycles with single modification duration of 1 d, verified by the SEM observation and XRD analysis; the mortar with RFA modified by the proposed MICP process showed higher flexural strength and carbonation resistance, which can be explained by the better pore structure at a microscopic level.

In this study, modified municipal sludge was used in place of fine aggregate to manufacture concrete, and it's revealed how different quicklime and sludge contents affect concrete. The best modified sludge concrete group was used for the performance improvement test, after which the constitutive model, the carbonation depth prediction model, and the freeze-thaw damage model were fitted. The results showed that the compressive strength of the L10S10 was best in experiment of modified municipal sludge concrete. Under alkali activation, fly ash absorbed the remaining alkali in modified municipal sludge, promoted concrete hydration, and improved the mechanical characteristics of concrete. The F10N4 group had the best activation effect, with a compressive strength of 50.61 MPa. Test results could be accurately reflected by the constitutive model and carbonation depth prediction model that were devised. The freeze-thaw damage model based on relative dynamic elastic modulus has a correlation coefficient greater than 0.98. • The effect of modified municipal sludge on the mechanical properties of concrete is revealed. • The microscopic mechanism of alkali-activated modified municipal sludge concrete is studied. • The carbonation depth prediction model, freeze-thaw damage model of modified municipal sludge concrete is fitted. [ABSTRACT FROM AUTHOR]

Five recycled coarse aggregate (RCA) treatment techniques including flow-through carbonation, pressurized carbonation, wet carbonation, nano silica (NS) pre-spraying and combined pressurized carbonation with NS pre-spraying, were utilized to improve the performance of recycled aggregate concrete (RAC). The characteristics of the stress–strain curves of RACs including peak stress, peak strain, elastic modulus, ultimate strain and toughness were evaluated after using the above RCA treatment techniques. A theoretical model for natural aggregate concrete was used to analyse the stress–strain curve of RAC. Additionally, the carbonation resistance of RAC after using different RCA treatment techniques were investigated. The results showed that the calculated stress–strain curve of RAC based on the theoretical model matched well with the experimental results. Among the three types of carbonation techniques, pressurized carbonation caused the highest improvement in peak stress and elastic modulus of RAC, followed by flow-through carbonation, the last was wet carbonation. The NS pre-spraying method contributed to even higher improvement in peak stress and elastic modulus of RAC than the pressurized carbonation method. The combined pressurized carbonation with NS pre-spraying exhibited the highest enhancement of RAC because both the RCA and the new interface transition zone (ITZ) were improved. The carbonation resistance of RAC was improved after using all the studied RCA treatment techniques. [ABSTRACT FROM AUTHOR]