Carbonation Resistance Research Articles

Carbonization test and orthogonal polynomial regression analysis of steel fiber reclaimed concrete

To enhance the carbonation resistance of reclaimed concrete, several key factors affecting its performance were investigated. An orthogonal array L16(4³×2⁶) was employed to design the carbonation tests for steel fiber (SF) reinforced concrete. The study included varying SF volume ratios, along with considerations of different concrete ages (T) and water-cement ratios (W/R). The effect of SF volume ratio, regenerated crude aggregate (RCA) replacement rate, W/R, and T on the carbonation resistance of recycled concrete was analyzed. The test results indicated a trend of increasing carbonation depth over time. However, a lower W/R ratio resulted in a reduced carbonation depth. Notably, a 50% RCA replacement rate led to a shallower carbonation depth compared to other replacement rates. After 28 d, recycled concrete containing 1% SF exhibited a carbonation depth that was 6.9%, 1.5%, 1.5%, and 9.3% lower than concrete with 0%, 0.5%, 1.5%, and 2% SF, respectively. Therefore, the incorporation of 1% SF was found to be the most effective in improving carbonation resistance. Orthogonal polynomial regression analysis was employed to develop a regression equation relating carbonation depth to SF volume ratio, RCA replacement rate, W/R, and T. The regression coefficients were calculated and tested, leading to the identification of the optimal regression equation and its corresponding confidence interval.

Enhancing Carbonation Resistance of Low-Activity Coal Gangue-Based LC3 Cementitious Materials with Ca(OH)₂ and Gypsum Additives

Enhancing Carbonation Resistance of Low-Activity Coal Gangue-Based LC3 Cementitious Materials with Ca(OH)₂ and Gypsum Additives

Effects of CaO-based expansive agent on carbonation resistance of marine concrete

Effects of CaO-based expansive agent on carbonation resistance of marine concrete

Hydrogen enriched natural gas-fueled solid oxide fuel cells supported by Ni-Cu co-doping CeO2-δ catalyst-modified finger-like pore anode

Hydrogen blending in natural gas pipelines is one of the key technologies to realize the long-distance hydrogen transmission, which facilitates the large-scale hydrogen utilization. Solid oxide fuel cells can directly use hydrogen enriched natural gas (HENG, with 20 % H2) to generate electricity without separating and purifying the hydrogen, which enables the efficient conversion of hydrogen energy. In this work, finger-like pore anodes and Ni0.05Cu0.05Ce0.9O2-δ (NCCO) catalyst are prepared to address the need for anode performance and stability with hydrogen-doped natural gas fuels. The results show that NiCu@CeO2 precipitates NiCu nano-alloys on the surface after reduction treatment, which is beneficial for the anode activity. With NCCO catalyst, the maximum power densities of the single cells are 970 mW cm−2 and 700 mW cm−2 at 750 °C under wet H2 and HENG fuel atmospheres, respectively. At 750 °C, the methane conversion is as high as 46 %. More importantly, the single cell can run smoothly for 150 h, with the constant voltage (0.8 V) discharge and HENG as fuel gas. Our results confirm that the synthesized NCCO catalysts have excellent ability to catalyze CH4 and carbon resistance.

Effect of Different Tempering Media on Fracture Toughness and Mechanical Properties of Carbon Steel

In this study, the effect of different thermal carbons on the impact resistance of heavy carbon, which contains 0.4% of. The focus was on how the resulting biochemistry affects the microstructure of the steel, and thus its mechanical properties. Steps: Impact test before heat treatment: Charpy impact test was performed on pre- impact specimens before any specimen was made. This test helps to determine the original impact of the steel without any modification in its microstructure. Tempering procedure: After that, it was further investigated by exposing it to high temperatures and then cooling it rapidly. This method is for market formation, which is a must. It was retested after tempering. The results showed a significant increase in the shock cases after tempering due to the formation of the texture which increased the strength of the specimen. Flame tempering (surface heat treatment): In this type of treatment, only the surface is heated with a flame and cooled rapidly, which results in the formation of a strong martensite texture on the surface, while the core of the specimen remains softer. When tested, it did get shock, but the amount of increase that occurred with full shock was not reduced. The reason for this is that the hardening in God is only on the surface while the core of the eye remains flexible, which leads to a reduction in contrast. Carburizing (surface heat treatment): Carburizing treatment is performed on some samples, which is a method that involves adding carbon to the outer surface of the fulminate and cooling it rapidly, resulting in a solid, hard material. When performing the shock test, it did get a shock that improved, but a case like flame hardening, you did not have very many shocks in full hardening.

Productive Poplar Genotypes Exhibited Temporally Stable Low Stem Embolism Resistance and Hydraulic Resistance Segmentation at the Stem-Leaf Transition.

Breeding tree genotypes that are both productive and drought-resistant is a primary goal in forestry. However, the relationships between plant hydraulics and yield at the genotype level, and their temporal stabilities, remain unclear. We selected six poplar genotypes from I-101 (Populus alba) × 84 K (P. alba × Popolus tremula var. glandulosa) for experiments in the first and fourth years after planting in a common garden. Measurements included stem embolism resistance, shoot hydraulic resistance and its partitioning between stems and leaves, vessel- and pit-level anatomy, leaf carbon acquisition capacity, carbon allocation to leaves, and aboveground biomass (yield proxy). Significant genetic variations in hydraulic properties and yield were found among genotypes in both years. Productive genotypes had wide vessels, large thin pit membranes, small pit apertures, and shallow pit chambers. Hydraulic resistance was negatively correlated with yield, enabling high stomatal conductance and assimilation rates. Productive genotypes allocated less aboveground carbon and hydraulic resistance to leaves. Temporally stable trade-offs between stem embolism resistance and yield, and between hydraulic segmentation and yield, were identified. These findings highlight the tight link between hydraulic function and yield and suggest that stable trade-offs may challenge breeding poplar genotypes that are both productive and drought-resistant.

The Influence and Mechanism of Polyvinyl Alcohol Fiber on the Mechanical Properties and Durability of High-Performance Shotcrete

This study investigates the impact of polyvinyl alcohol (PVA) fibers on the mechanical properties and durability of high-performance shotcrete (HPS). Results demonstrate that PVA fibers have a dual impact on the performance of HPS. Positively, PVA fibers enhance the tensile strength and toughness of shotcrete due to their intrinsic high tensile strength and fiber-bridging effect, which significantly improves the material’s splitting tensile strength, deformation resistance, and toughness, and the splitting tensile strength and peak strain have been found to be increased by up to 30.77% and 31.51%, respectively. On the other hand, the random distribution and potential agglomeration of PVA fibers within the HPS matrix can lead to increased air-void formations. This phenomenon raises the volume content of large bubbles and increases the average bubble area and diameter, thereby elevating the pore volume fraction within the 500–1200 μm and >1200 μm ranges. Therefore, these microstructural changes reduce the compactness of the HPS matrix, resulting in a decrease in compressive strength and elastic modulus. The compressive strength exhibited a reduction ranging from 10.44% to 15.11%, while the elastic modulus showed a decrease of between 8.09% and 12.67%. Overall, the PVA-HPS mixtures with different mix proportions demonstrated excellent frost resistance, chloride ion penetration resistance, and carbonation resistance. The electrical charge passed ranged from 133 to 370 C, and the carbonation depth varied between 2.04 and 6.12 mm. Although the incorporation of PVA fibers reduced the permeability and carbonation resistance of shotcrete, it significantly mitigated the loss of tensile strength during freeze–thaw cycles. The findings offer insights into optimizing the use of PVA fibers in HPS applications, balancing enhancements in tensile properties with potential impacts on compressive performance.

Enhancing anti-carbonation properties of oil well cement slurry through nanoparticle and cellulose fiber synergy

The anti-carbonation property of oil well cement (OWC) is critical for sealing efficiency of wellbores under geological CO2 sequestration. However, gas migration through OWC around wellbores may lead to a deterioration and failure of the entire storage system. Developing carbon-resistant cement has been the emerging trend in the research community. Previous studies mainly focused on nanoparticles alone to enhance performance of OWC, and the purpose of the research is to explore the synergy of nanoparticles and cellulose fiber (CF) in enhancing engineering properties (e.g., carbonation resistance) of oil well cement slurry. The focus was on investigating compressive strength, permeability, pore structure, and carbonation depth associated with the micro-level texture in a CO2 corrosion environment using X-ray diffraction, Scanning Electron Microscopy, and thermogravimetric analysis methods. Four nanoparticles, namely, nano-SiO2 (NS), nano-TiO2 (NT), nano-Al2O3 (NA), and nano-CaCO3 (NC), were selected for the mixture design. Results indicated that the incorporation of 1∼2 % NPs into the OWC paste resulted in a notable decrease in portlandite and an increase in calcium silicate hydrates, thereby enhancing compressive strength and hydration process. In addition, the single admixture of CF could minimize the formation of cracks in the cement matrix and reduce the average carbonation depth by 54 %. More importantly, the synergy of CF and NP significantly improved the resistance of OWC to carbonation, and the OWC mixed with CF and NS displayed the highest carbonation resistance.

Evaluation on Preparation and Performance of a Low-Carbon Alkali-Activated Recycled Concrete under Different Cementitious Material Systems.

A green, low-carbon concrete is a top way to recycle waste in construction. This study uses industrial solid waste slag powder (S95) and fly ash (FA) as binders to completely replace cement. This study used recycled coarse aggregate (RCA) instead of natural coarse aggregate (NCA). This is to prepare alkali-activated recycled concrete (AARC) with different cementitious material systems. Alkali-activated concrete (AAC) mixtures are modified for strength and performance based on the mechanical qualities and durability of AARC. Also, the time-varying effects of the environment on AARC properties are explored. The results show that with the performance enhancement of RCA, the mechanical performance of AARC is significantly improved. As RCA's quality improves, so does AARC's compressive strength. At a cementitious material content of 550 kg/m3, AARC's 28d compressive strengths using I-, II-, and III-class RCA were reduced by 2.2%, 12.7%, and 21.8%, respectively. I-class AARC has characteristics similar to natural aggregate concrete (NAC) in terms of shrinkage, resistance to chloride penetration, carbonization, and frost resistance. AARC is a new type of green building material that uses industrial solid waste to prepare alkali-activated cementitious materials. It can effectively reduce the amount of cement and alleviate energy consumption. This is conducive to the reuse of resources, environmental protection, and sustainable development.

Impacts of nano C-S-H-PCE on durability-related properties of Portland cement composites with high-volume GGBFS

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.

Utilizing incineration bottom ash-infused steel fiber-reinforced concrete: An analysis of compressive strength and carbonation durability

This study has developed concrete with moderate strength, and excellent carbonation resistance, by blending incineration bottom ash with steel fibers into the concrete mixture. Through single-factor experiments, investigate the effects of bottom ash content and steel fiber volume fraction on the mechanical properties and carbonation resistance of concrete. The results indicate that the addition of steel fibers effectively reduces the adverse effects of incineration bottom ash content on the compressive strength and carbonation level of concrete. When the bottom ash content is 20 % and the steel fiber content is 2 %, the compressive strength of concrete reaches 56.1 MPa, and the carbonation depth drops to 4.19 mm after 28 days. In addition, a carbonation depth prediction model was established based on the compressive performance of concrete, accurately predicting the carbonation depth at different carbonation stages.

Carbonation resistance of fly ash/slag based engineering geopolymer composites

Engineering geopolymer composites (EGC) are promising environmentally friendly building materials with excellent mechanical properties. However, the durability of EGC is compromised by gradual carbonation from atmospheric exposure. For the first time, this study provided an insight of the carbonation of EGC by comprehensively investigating the effect of mix design, such as fly ash/ground granulated blast furnace slag ratio (FA/GGBS ratio), alkali content, water/binder ratio (W/B ratio) and polyethylene (PE) fibre content, on its carbonation resistance. Our results showed the components in EGC affected the carbonation through the alternation of microstructures. An increase of FA content and W/B ratio significantly increased the carbonation depth by 206.6 % and 116.3 % respectively due to the increased porosity and transition pore fraction, resulting in more than 30 % reduction in tensile strength and 15 % reduction in compressive strength. However, increased alkali and fibre content prevent carbonation with around 60 % and 26 % decrease of the carbonation depth, leading to a less loss of the mechanical properties. Furthermore, we tested the pH values of the EGC along the carbonation depth, proposing a novel approach to assess the carbonation degree by dividing the area into completely carbonated area (pH around 9.21–10.44) and non-carbonated area (pH around 12.58–13.37). These findings provide insights for mitigating carbonation effects in EGC and facilitate the widespread use of this sustainable material in construction applications, ensuring long-term durability and reliability.

Combined effects of carbonation and salt solution on chloride desorption, pH, and composition of fly ash blended pastes

The most consumed human-made material, concrete, is permeable and chloride-bearing deicers penetrate the concrete, causing deterioration. Chloride ions exist in concrete in two forms: free and bound chlorides. Free chlorides are the primary cause of chloride-induced corrosion because they can move in concrete pores, reaching the rebar surface to initiate corrosion. Bound chlorides are those chloride ions that are adsorbed by the concrete matrix and cannot actively participate in reinforcement corrosion. Although chloride binding is a beneficial process, chloride binding is reversible. In addition, most concrete infrastructures are subject to environmental attacks such as carbonation, causing pH reduction in the concrete pore solution and subsequently resulting in the release of bound chlorides (chloride desorption). The combined effects of carbonation and chloride attack on fly ash containing pastes are not well-studied, particularly concerning their impact on chloride desorption, pH changes, and compositional changes. This investigation aims to address this gap by exposing fly ash-blended cement paste to NaCl salt solution and carbonation. This study quantifies chloride desorption, monitors pH change, and analyze the compositional changes in pastes, including the measurement of Friedel's salt, portlandite, and calcite contents. Samples were first exposed to NaCl solution for 35 days and then 4 weeks of accelerated carbonation, during which their pH and composition at different depths were monitored. XRD and TGA tests were utilized to identify and quantify the main phases. The results show that carbonation reduced the pH from 13 to nearly 11 in OPC pastes and 10 in fly ash pastes. The inclusion of 15 % fly ash led to weakened carbonation resistance compared to OPC. After combined exposure to the salt solution and carbonation, the calcite content, representing carbonation, in fly ash pastes significantly increased by 190.9 % after one week carbonation and 282.1 % after two weeks of accelerated carbonation. Friedel's salt content, indicating bound chloride, dropped by roughly 78 % in OPC paste and 87 % in fly ash paste after one week of carbonation and completely dissolved after two weeks of carbonation. The results emphasize the importance of considering chloride desorption, similar to chloride binding, which has been incorporated into service life models. This negligence can lead to an overestimation of the service life of concrete infrastructures.

Formulation and characterization of one-part Ca-based alkali-activated slag-steel slag materials

This study aims to develop one-part Ca-based alkali-activated materials (OCAM) using steel slag (SS) and slag powder (SP) with a Ca-based activator. The effects of SS replacement rate on the flowability, setting time, and mechanical properties of paste were systematically investigated. Furthermore, methods such as Mercury intrusion porosimetry (MIP), heat of hydration, X-ray diffraction (XRD), and scanning electron microscope (SEM) were used to compare the effects of calcium oxide (CO) and calcium hydroxide (CH) on the microstructure of the OCAM. The results indicate that the addition of SS enhances mortar flowability and setting time, with optimal mechanical properties when the SS replacement rate is 20 %. However, strength gradually decreases as the replacement rate increases beyond this point. In addition, the incorporation of CO further enhances the mechanical properties of mortar. MIP test results show that the use of CO reduces the internal porosity and refines the micropore structure, although it also increases drying shrinkage. The hydration heat test results reveal that the use of CO increased the total heat release of the sample in the initial 72 h and accelerated the early hydration reaction. Moreover, XRD and SEM results indicate that CO improves carbonation resistance.

Effect of nitrogen-doped type on fracture toughness improvement and crack growth resistance of carbon nanotube/epoxy nanocomposites: Combined multiscale analysis approach

Recently, nitrogen-doped carbon nanotubes (N-doped CNTs) have received great attention in nanocomposite design. It has become highly necessary to develop predictive models to elucidate their toughning behavior. In this study, the effects of CNTs with three different types of N-doped functional groups (quaternary, pyrrolic, and pyridinic) on the fracture toughness (FT) and crack growth of polymer nanocomposites are predicted using a multiscale analysis approach. To scale up from the nanoscale to the macroscale, a multiscale analysis approach integrating molecular dynamics, micromechanics theory, linear fracture mechanics theory, and a phase-field fracture model (PFFM) is adopted. The toughness enhancement trends of the three different types of N-doped functional groups were quantified by considering four toughening mechanisms (CNT debonding, plastic nanovoid growth, CNT pull-out, and CNT rupture), and compared with experimental result. The results show that the excellent interphase and interfacial properties of quaternary and pyridinic functional groups significantly improve the FT and crack growth resistance of N-doped CNT/epoxy nanocomposites. Our study provides high-performance solutions for experimental studies pertaining to the FT and crack growth of N-doped CNT/epoxy nanocomposites.

Comparison between the structural characteristics and process activity of bulk and mesoporous Ni-Co-Ce/Al2O3 catalysts in the dry reforming of methane

Dry reforming of methane (DRM) is a potential way to exploit greenhouse gases and generate hydrogen. Catalyst deactivation is the biggest DRM commercialization obstacle. Lately, Ni-Co bimetallic catalysts have demonstrated improved carbon resistance over Ni-based catalysts. The aim of this research is not just to investigate the impact of Ni-Co catalysts on the DRM activity, but also to evaluate the Ni-Co alloy creation effect on the catalyst characteristics and activity. Mesoporous alumina (MA) was used as a catalyst support for Ni-Co particles in this process and its structure and activity were compared to those of bulk alumina (BA) supported catalysts. In addition, cerium was included into all of the catalysts developed as a suitable promoter for reducing the amount of deposited coke. The results obtained from the XRD and nitrogen adsorption/desorption analysis indicated the formation of a mesoporous structure and nanocrystalline morphology in the Ni-Co/MA samples, as compared to the Ni-Co/BA ones. The results showed that the bimetallic 2Ni-1Co-1Ce/MA sample had the best catalytic activity, with a CH4 conversion of 98.30 %, CO2 conversion of 96.35 %, and H2 yield of 96.30 % at 700 °C.

Carbonation resistance of alkali-activated GGBFS/calcined clay concrete under natural and accelerated conditions

The carbonation resistance of alkali-activated materials (AAMs) is a crucial parameter for their applicability in concrete construction, yet the parameters influencing it are insufficiently understood to date. In the present study, the carbonation resistance of alkali-activated concretes with varying fractions of ground granulated blast furnace slag (GGBFS) and calcined clay (i.e., high, intermediate, and low Ca contents) were assessed under natural and accelerated conditions. Corresponding hardened AAM pastes were studied using X-ray diffraction, thermogravimetry, Raman microscopy, and mercury intrusion porosimetry. The carbonation resistance of the concretes at natural CO2 concentration depended principally on their water/(CaO + MgOeq + Na2Oeq + K2Oeq) ratio. The remaining variability for similar ratios was caused by differences between the pore structures of the AAMs. For concrete with favorable water/(CaO + MgOeq + Na2Oeq + K2Oeq) ratio and pore structure, the carbonation resistance was comparable to that of Portland cement concrete. The relationship between carbonation coefficients obtained under accelerated and natural conditions differed for concretes with high and low fractions of calcined clay, indicating that accelerated carbonation testing is less suitable to study the carbonation of low-Ca AAMs.

Enhancing the fracture toughness of aerospace-grade carbon fibre/epoxy composites by interlaying surface-activated low-melt polyaryletherketone (LMPAEK) meshes

This study proposed an innovative method for enhancing the interlaminar fracture resistance of carbon fibre/epoxy composites by incorporating structured low-melt polyaryletherketone meshes (LMPAEK) meshes. LMPAEK films were machined into structured hollow meshes and then surface-treated using high-power UV-irradiation. These treatments significantly increased the contact area and interface adhesion between the LMPAEK inserts and the composite matrix, leading to substantial improvement in the interlaminar fracture performance of the composite. Fracture test results demonstrated that the mode-I and mode-II fracture propagation energies of the LMPAEK-inserted composite at 22 °C were 1.04 times and 13.92 times higher, respectively, than those of the reference composite. Similarly, at 130 °C, their mode-I and mode-II fracture propagation energies were 1.36 times and 8.56 times higher, respectively. The remarkable fracture performance of the LMPAEK-inserted composites were attributed to the substantial plastic deformation and damage of the LMPAEK resins, which possessed exceptional mechanical properties and thermal resistance.

Mesoscopic simulation of concrete drying shrinkage with hydration kinetics

Shrinkage-induced cracking significantly impacts the durability of mass concrete structures. Quantitatively evaluating drying shrinkage of concrete proves challenging due to the time-consuming experiments and overlooked microstructure changes during the hydration process. To address this concern, this study initially characterized the long-term hydration products and microstructure of low-heat Portland cement (LHPC) through microstructural experiments. Subsequently, a novel high-resolution mesoscale framework is developed to investigate the drying shrinkage with hydration kinetics. High-resolution models consist of realistic-shaped aggregates are validated by the aggregate morphology and gradation parameters of core sample from mass concrete. Concurrently, the quantitative effects of internal and external factors on LHPC drying shrinkage are explored. Results indicated that LHPC possesses a denser microstructure, lower porosity, higher carbonation resistance, and 20% lower drying shrinkage compared to moderate-heat Portland cement, suggesting promising applications. Furthermore, experimental and computational findings suggested that increasing aggregate volume, controlling aggregate morphology, and adjusting curing time and humidity could be employed to reduce and manage drying shrinkage, ensuring concrete structure durability.

Enhancing carbonated mortar durability by electro-osmotic treatment of silane

Electro-osmotic treatment (EOT) of silane for enhancing the durability of carbonated mortar was investigated. During the EOT, silane was injected into carbonated mortar pores by applying an electric field, leading to deeper penetration depths. The durability enhancements of the carbonated mortar after EOT of silane were evaluated by examining water absorption, carbonation depth, sulfate resistance and chloride diffusion. The microscopic mechanism of the electro-injected silane treatment was determined by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The results indicated that the resistance to water absorption, sulfate diffusion and chloride diffusion were improved by the EOT of silane. The silane treatment had a limited impact on carbonation resistance. An impervious film with a dense structure was formed in the carbonated mortar through the EOT of silane, and this treatment did not introduce new crystal phases to the hydration products within the carbonated mortar.