Porosity Reduction Research Articles

The Effect of High-Pressure Hydrostatic Extrusion on Mechanical Properties of Printed with Fused Deposition Modeling PLA and PLA-Diatomaceous Earth Composites

Three-dimensional printing enables rapid prototyping, customization, and on-demand production. Polylactide is a popular biopolymer filament used in 3D printing. However, due to its brittleness and low mechanical strength, it often needs to be reinforced with filler particles. Diatomaceous earth shows great potential as a filler material due to its abundant and natural occurrence, biocompatibility, and environmental friendliness, as well as its excellent mechanical properties. Cold hydrostatic extrusion was used to improve the compressive strength of 3D-printed parts. Both neat and reinforced with 10% diatomaceous earth filaments were used to 3D print cylindrical billets, followed by post-processing using hydrostatic extrusion. X-ray microtomography showed a significant reduction in total and open porosity and average pore size, from ~20 µm to less than 10 µm in the Polylactide (PLA) and Diatomaceous (DE) composite. Compression tests showed a significant improvement in the compressive strength of PLA from ~60 MPa to ~100 MPa, while PLA with DE achieved an impressive almost twofold increase to 80–120 MPa. This was attributed to a reduction in pore size, as well as pore closure, which mitigates crack initiation in semi-brittle PLA. In addition, it has been proposed that hydro extrusion-induced structural rearrangement is an important strengthening factor.

Mechanical Strength Optimization of HDPE Biocomposite with Water Hyacinth Fiber Reinforcement using a Dispersing Agent

This study investigates the impact of a polyamine amides dispersing agent (BYK W-980) on the mechanical performance of the High-Density Polyethylene/Water Hyacinth Fiber (HDPE)/(WHF) composites. The dispersing agent was employed to improve the fiber distribution, enhance the fiber-matrix interaction, and reduce the fiber agglomeration, which negatively affects the mechanical properties of the composite. The Scanning Electron Microscopy (SEM) analysis revealed that the dispersing agent, particularly DA2, effectively minimized fiber agglomeration and promoted a more uniform fiber distribution within the HDPE matrix. The density testing indicated a reduction in porosity and an increase in composite density following the dispersing agent treatment. The mechanical testing demonstrated significant improvements with DA2 yielding the optimal results: a 19.54% increase in tensile strength, a 24.33% increase in flexural modulus, and an 18.53% increase in impact strength. The X-ray Diffraction (XRD) analysis showed an increase in the crystallinity index of the WHF, suggesting enhanced structural regularity, which supported the observed improvements in mechanical performance. Overall, the utilization of the polyamine amides dispersing agent, particularly DA2, significantly enhanced the mechanical properties and fiber-matrix interaction of the HDPE/WHF composites.

Prediction of Strength Properties of Reinforced and Stabilized Sandy Soil as a Building Foundation Material

Sandy soils are a type of geomaterial that may require improvements due to lack of cohesion. In this study, first, the lack of cohesion of sand was resolved using clay, and the soil was stabilized with cement and lime (4% and 3% of the dry weight of materials, respectively) and finally reinforced with recycled tire fibers of 20 to 30 mm in length for improved strength and ductility. Next, 747 samples with different fiber contents at different curing temperatures and ages were prepared and a unconfined compressive strength (UCS) test was carried out. Next, a novel approach employing multivariate nonlinear regression techniques and obtained empirical data was applied to formulate a mathematical model for predicting the UCS and the modulus of elasticity (Es) of the reinforced and stabilized soil. This model can serve as a valuable tool for building engineers in designing building foundations. The comparison of the obtained UCS and Es results and those predicted using the proposed model showed a correlation of >95% (R2 ≥ 0.95). The fibers effectively increased the failure strain, thus resulting in the greater ductility of the samples. As an example, in 14-day samples cured at 60 °C with 0%, 0.4%, 1%, 1.7%, and 2.5% fibers, the failure strain showed an incremental trend of 1.47%, 1.87%, 2.08%, 2.20%, and 2.92%, respectively. Scanning electron microscopy (SEM) was used to study the microstructure of the samples and to explain the strength experimental outcomes. SEM images showed a desirable interaction between the fiber surfaces with the soil mass and the reduction in porosity and the occurrence of pozzolanic reactions through stabilization. The results also showed that the reinforcement effectively improved the ductility, as desired for building foundations; however, it resulted in reduced strength, although a greater strength compared to the untreated soil was achieved. Although soil stabilization has been widely studied, limited research focuses on stabilizing soil with clay, lime, cement, and recycled tire fibers. This study offers design engineers an estimation scheme of the strength properties of stabilized and reinforced foundations.

Terminal Fan Deposition and Diagenetic Control in the Lower Paleogene of the Shahejie Formation, Bonan Sag, Bohai Basin, China: Insights into Reservoir Quality

In the Bonan area, the lower fourth member of the Shahejie Formation (Es4x) is buried beneath a sedimentary pile ranging from 2500 to 5000 m. Understanding the impact of diagenetic alterations on these deeply buried reservoirs is crucial for effective hydrocarbon exploration and production. This study employs a terminal fan sedimentation model, encompassing depositional environments such as feeder channels, distributary channels, floodplains, and basinal zones, to provide insights into the spatial distribution of reservoir properties and their influence on the localization of optimal reservoirs within the sag. The analysis integrates diagenetic facies with well log responses, subsurface porosity trends, and permeability variations across the formation. The petrographic analysis indicates that the sandstone is composed primarily of litharenite, feldspathic litharenite, lithic arkose, and minor amounts of arkose. The dominant clay cement is illite, accompanied by mixed-layer smectite/illite, chlorite, and kaolinite. Thin section observations reveal secondary porosity formed through the dissolution of quartz grains, volcanic rock fragments, and feldspar, along with their associated cements. These sandstones exhibit relatively good sorting, with average porosity and air permeability values of 14.01% and 12.73 mD, respectively. Diagenetic alterations are categorized into three processes: porosity destruction, preservation, and generation. Key diagenetic mechanisms include compaction, cementation, replacement, and dissolution, with compaction exerting the most significant control on reservoir porosity reduction. Statistical analysis indicates that the average porosity loss due to compaction is approximately 13.3%, accounting for about 38% of the original porosity. The detrital rock cement predominantly comprises quartz (42%), feldspar (32%), clay minerals (14%), and carbonate (12%). Under the prevailing depositional conditions, porosity is enhanced by dissolution and fracturing, while late-stage diagenetic cementation by clay and carbonate minerals—excluding chlorite—adversely affects reservoir quality. Consequently, the distributary zone is identified as the primary target for exploration.

3D basin modeling of the Lower Saxony Basin, Germany: the role of overpressure in Mesozoic claystones with implications for nuclear waste storage

Abstract Jurassic and Cretaceous organic-lean claystone formations in the Lower Saxony Basin (LSB), Germany, are considered for nuclear waste storage due to their favorable physical properties. Understanding the burial and thermal history of these formations, including overpressure generation and its impact, is crucial for site selection. Past undetected overpressures may result in erroneous estimation of present-day petrophysical properties. Therefore, this study investigates the evolution and spatial distribution of overpressure in claystones in northern Germany on a rather large scale, focusing on Jurassic and Lower Cretaceous units. Utilizing 3D numerical basin modeling, this study: (i) reconstructs the geodynamic evolution of the LSB, (ii) identifies key mechanisms driving overpressure during burial, (iii) detects areas of high pore-to-lithostatic pressure ratios susceptible to fracturing, and (iv) assesses overpressure’s influence on the evolution of petrophysical properties. Results reveal that during the fastest burial phase, overpressure generation began, primarily driven by disequilibrium compaction coupled with gas generation, peaking around 99 Ma at the basin’s depocenter. During the Late Cretaceous uplift, thousands of meters of sediment were eroded within the basin’s depocenter, and overpressure dissipated. According to the model, absolute overpressures were higher for Jurassic than Cretaceous claystones, but dissipation was slower for Cretaceous claystones leading to relatively higher pore-to-lithostatic pressure ratios during uplift. During overpressure buildup, the porosity reduction slowed due to undercompaction effects, underscoring overpressure’s influence on petrophysical properties. While Pleistocene glaciations caused localized overpressure, they did not impact the petrophysical properties of the assessed units. Glacial-induced erosion, however, is projected to reduce remaining overpressure substantially. Graphical abstract

Improvement of Hydrophobic Surface and Mechanical Properties of Beta‐Hemihydrate Desulfurization Gypsum by Graphene Modification

AbstractBeta‐hemihydrate desulfurization gypsum (β‐HDG) is considered one of the green and low‐carbon building materials, which is widely used in the fields of construction materials and decoration. Nevertheless, its inherent deficiency in water resistance and other drawbacks significantly limit its application scope. In this study, the gypsum‐based materials with surfaces that exhibit hydrophobic properties were prepared. The surface contact angle was analyzed to examine the surface hydrophobic characteristics. The compressive strength, flexural strength, ratio of compressive strength to flexural strength, water absorption rate, and softening coefficient of hardened specimens were measured to assess the mechanical properties. Furthermore, the pore structure and microstructure of hardened specimens were characterized to evaluate the impact of hydrophobically modified reduced graphene oxide (H@rGO). Furthermore, when the content of H@rGO was 0.15 wt%, the thermal conductivity of specimen was 0.55 W/m•K with optimal mechanical properties; the surface hydrophobicity of the hardened sample was significantly improved, with the surface contact angle, water drop penetration time, and softening coefficient reaching 113.898°, 567s, and 0.77, respectively. This enhancement was accompanied by a reduction in pore size and total porosity in the hardened samples, thereby contributing to the improved softening coefficient and mechanical properties of gypsum‐based composites. Because of lower energy consumption in H@rGO process and extensive utilization of industrial solid waste, the preparation process of incorporating H@rGO into β‐HDG exhibits superior cost‐effectiveness.

Evaluating the Impact of Wastewater Irrigation on Soil Health and Maize Productivity

The increasing scarcity of freshwater resources necessitates the exploration of alternative water sources for agricultural irrigation. This study evaluates the impact of different water sources canal water, tubewell water, sewerage water, and industrial wastewater on soil health and maize productivity. Conducted over two growing seasons, the experiment was laid out in a randomized complete block design with four replications at research area of Ayub Agriculturte Research Institute, Faisalabad. Key soil physical properties, including bulk density, porosity, and infiltration rate, were assessed pre- and post-irrigation. Concurrently, maize growth parameters such as germination rate, plant height, biomass, and grain yield were meticulously recorded. The results indicated that soil irrigated with sewerage and industrial wastewater exhibited significant increases in bulk density and reductions in porosity and infiltration rates compared to canal and tubewell water. Despite these alterations in soil physical properties, maize irrigated with sewerage water showed a comparable growth pattern to that irrigated with canal and tubewell water, with no significant differences in germination rate or plant height. However, grain yield and biomass were significantly higher in plots irrigated with canal water, followed closely by tubewell water, sewerage water, and lastly, industrial wastewater. Industrial wastewater irrigation notably decreased soil health and maize productivity due to the presence of heavy metals and other pollutants. In contrast, sewerage water, while still inferior to canal and tubewell water, provided a viable alternative, maintaining acceptable soil health and maize yield levels. This study underscores the potential of using treated wastewater for irrigation in regions facing water scarcity, highlighting the need for stringent quality monitoring and treatment protocols to mitigate adverse effects on soil health and crop productivity.

Study on the mechanical properties and water stability of steel slag-fly ash geopolymer for base Stabilisation

ABSTRACT Modification of fly ash geopolymer with steel slag: Preparation of steel slag-fly ash geopolymer paste using steel slag andvarying dosages of NaOH-Na2SiO3 as variables. The study aims to investigate the workability, strength, and strengthening mechanismof this paste material, as well as to assess its mechanical properties and water stability in stabilized gravel. The results showed thatincorporating steel slag could decrease the fluidity and setting time of fly ash geopolymer while increasing its strength. When the steelslag and activator was 30% and 18%, respectively, the compressive strength at 7 and 28 days was the highest, reaching 19.3 and 24.9MPa, respectively. The strength of geopolymer-stabilized gravel was equivalent to that of cement-stabilized gravel. When thegeopolymer content is modified to 6%, the unconfined compressive strength at 7 and 28 days is 5.2 and 6.1 MPa, respectively. After28 days of curing, the water stability has significantly improved, with a water stability coefficient exceeding 0.9. The addition of steelslag can enhance the reactivity of the reaction system, facilitate the formation of C-(A)-S-H gel, increase the bonding strength, and fillthe internal pores, resulting in a 23.3% reduction in porosity, a denser structure, and improved strength.

Improved properties of wire arc directed energy deposited thin-walled Al-6Mg-0.3Sc component via laser shock peening

ABSTRACT Heat treatment free aluminum alloys have been developed for wire arc directed energy deposition (DED) large thin-walled components, but their further performance enhancement methods remain unexplored. In this study, laser shock peening (LSP) treatment was performed on wire arc DED Al-6Mg-0.3Sc components. The results show that LSP creates a gradient microstructure with submicro-grains near the surface. The effects of LSP on defects were quantified by quasi-in-situ CT, demonstrating a reduction in porosity by over 68% together with decreased size. Simultaneously, tensile strength increases by 39.5% to 295.8 ± 6.4 MPa with only a marginal loss of elongation, as compared to the as-deposited (AD) state. This was due to the accumulation of dislocations and continuous dynamic recrystallization lead to grain refinement, as well as the appearance of a triple heterogeneous microstructure. Therefore, this study offers a novel solution for manufacturing of high-performance heat treatment free large thin-walled components.

Porosity control and properties improvement of Al-Cu alloys via solidification condition optimisation in wire and arc additive manufacturing

ABSTRACT This study presents an innovative liquid-nitrogen cooling (LNC) strategy to address hydrogen porosity in Wire and Arc Additive Manufactured (WAAM) Al-Cu alloys, which negatively affects part properties. A coupled thermo-mechanical finite element model, calibrated with in-situ measurements, is used to analyse the thermal, mechanical and metallurgical evolutions of two single-walls fabricated with conventional gas cooling (CGC) and LNC, respectively. A hydrogen solute coupling model evaluates hydrogen supersaturation during solidification. The LNC strategy significantly reduces porosity by optimising the solidification process: (i) Grain size is reduced, lowering hydrogen concentration at the solid/liquid interface; (ii) The length and duration of the hydrogen supersaturation region are shortened due to higher temperature gradients; (iii) Enhanced Marangoni convection and reduced molten pool depth facilitate hydrogen bubble escape. Compared to the CGC part, the LNC part shows a 63.8% reduction in pore density and a 59.4% reduction in overall porosity, achieving a final porosity of 0.39%. This improves mechanical properties, with the LNC component displaying a yield strength of 100.3 MPa, ultimate tensile strength of 250.1 MPa and elongation to failure of 19.4%. Despite a slight increase in residual stresses, the LNC strategy prevents cracking in Al-Cu alloys with high cracking susceptibility.

Influence of in situ heating and laser remelting on martensitic precipitation-hardening stainless steel fabricated by laser powder bed fusion

AbstractThe introduction of in situ heat-assisted fabrication and laser remelting as novel techniques within laser-based additive manufacturing aims to mitigate porosity and reduce surface roughness. However, a comprehensive understanding of the impact of in situ heating and laser remelting on mechanical properties and microstructure is still lacking, particularly for precipitate-hardenable metals like 15-5PH and 17-4 PH stainless steel, which can yield mechanical properties comparable to conventionally fabricated materials. This study presents experimental findings that demonstrate the efficacy of in situ heating during laser powder bed fusion (LPBF) in significantly reducing porosity and enhancing the material’s ductility. The performed XRD analyses indicate that the retained austenite phase increased in samples fabricated with heat-assisted LPBF. There is a reduction in the experimentally measured ultimate tensile strength, yield strength, and hardness in the precipitate-hardenable stainless steel samples that were fabricated by the introduced method using a heated plate. The experimental results reveal a 25% increase in ductility for heat-assisted LPBF fabrication compared to without heated substrate. In addition, SEM fractography analysis indicates a significant reduction in crack size and porosity in samples produced by heat-assisted LPBF.

Preparation and study of ceramics based on kaolin DD3 with the addition of tri-calcium phosphate

In this work, samples based on local kaolin DD3 were prepared with and without the addition of tricalcium phosphate (TCP) in varying weight percentages (5%, 10%, and 15%). These samples were sintered at different temperatures, ranging from 900°C to 1300°C, for two hours to assess their behavior and properties. The results of the analysis demonstrated that the incorporation of TCP significantly enhanced the sintering process. Specifically, TCP reacted with cristobalite and alumina, forming anorthite, while simultaneously promoting the formation of mullite from the kaolin component. Additionally, TCP contributed to a reduction in porosity, leading to denser samples. This improvement in the sintering process positively influenced the mechanical properties of the samples, particularly microhardness, which showed noticeable enhancement. In samples with a lower percentage of TCP, the thermal expansion was almost linear between room temperature and 1000°C, further indicating the beneficial effects of TCP on the material's performance. These findings highlight the potential of TCP as an additive to optimize the sintering behavior and properties of kaolin-based materials.

The Influence of Air Gap Length on the Characteristics and Performance of Hybrid Polyethersulfone/Cellulose Nanocrystal/Multiwalled Carbon Nanotubes Hollow Fiber Membrane for Humic Acid Removal

ABSTRACTReady‐made or commercial hollow fiber (HF) membranes have limited performance for removing humic acid (HA) from water streams unless they undergo surface modification. Alternatively, a membrane can be tailor‐made specifically for HA removal by developing a new formulation and adjusting its fabrication parameters. In this study, to enhance the performance and antifouling properties of HF membranes, a hybrid membrane was developed by blending polyethersulfone (PES) with cellulose nanocrystals (CNC) and multiwalled carbon nanotubes (MWCNT). The effect of air gap length during the dry–wet spinning process was investigated, ranging from 3 cm to 12 cm, to regulate the properties of the hybrid membrane. The membranes were evaluated in terms of morphology (FESEM and AFM), porosity, and hydrophilicity (contact angle). Water flux, HA rejection, and flux recovery ratio (FRR) were also measured. The air gap length significantly influenced the fiber structure, with the finger‐like structure expanding from the outer surface to the center of the fiber as the air gap extended up to 9 cm. This increase in air gap length resulted in a significant reduction in porosity, decreasing from 75.59% to 43.45%, while simultaneously enhancing the contact angle from 78° to 89.60°. The membrane produced at a 9 cm air gap length exhibited the best performance, with a pure water flux of 15.83 LMH, HA rejection over 95%, and a high FRR of 98.78%. The synergistic effect of combining CNC with MWCNT and simply adjusting the air gap distance proves to be an effective approach for preparing custom‐made HF membranes for HA removal.

The Mechanism of Inhomogeneous Mass Transfer Process of Separators in Lithium-Ion Batteries.

The liquid-phase mass transport is the key factor affecting battery stability. The influencing mechanism of liquid-phase mass transport in the separators is still not clear, the internal environment being a complex multi-field during the service life of lithium-ion batteries. The liquid-phase mass transport in the separators is related to the microstructure of the separator and the physicochemical properties of electrolytes. Here, in-situ local electrochemical impedance spectra were developed to investigate local inhomogeneities in the mass transfer process of lithium-ion batteries. The geometric microstructure of the separator significantly impacts the mass transfer process, with a reduction in porosity leading to increased overpotentials. A competitive relationship among porosity, tortuosity, and membrane thickness in the geometric parameters of the separator were established, resulting in a peak of polarization. The resistance of the liquid-phase mass transfer process is positively correlated with the viscosity of the electrolyte, hindering ion migration due to high viscosity. Polarization is closely related to the electrochemical performance, so a phase diagram of battery performance and inhomogeneous mass transfer was developed to guide the design of the battery. This study provides a foundation for the development of high stability lithium-ion batteries.

Porosity Reduction and Strength Increase of SS316&Cu Produced through Cold Spray Additive Manufacturing

Porosity Reduction and Strength Increase of SS316&Cu Produced through Cold Spray Additive Manufacturing

Maximizing Nano-Silica Efficiency in Laboratory-Simulated Recycled Concrete Aggregate via Prior Accelerated Carbonation: An Effective Strategy to Up-Cycle Construction Wastes.

Herein, the study explores a composite modification approach to enhance the use of recycled concrete aggregate (RCA) in sustainable construction by combining accelerated carbonation (AC) and nano-silica immersion (NS). RCA, a major source of construction waste, faces challenges in achieving comparable properties to virgin aggregates. Nano-silica, a potent pozzolan, is added to fill micro-cracks and voids in RCA, improving its bonding and strength. AC pretreatment accelerates RCA's natural carbonation, forming calcium carbonate that strengthens the aggregate and reduces porosity. Due to the complexity of the original RCA, a laboratory-simulated RCA (LS-RCA) is used in this study for the mechanism analysis. Experimental trials employing the composite methodology have exhibited noteworthy enhancements, with the crushing index diminishing by approximately 23% and water absorption rates decreasing by up to 30%. Notably, the modification efficacy is more pronounced when applied to RCA derived from common-strength concrete (w/c of 0.5) as compared to high-strength concrete (w/c of 0.35). This disparity stems from the inherently looser structural framework and greater abundance of detrimental crystal structures in the former, which impede strength. Through a synergistic interaction, the calcium carbonate content undergoes a substantial increase, nearly doubling, while the proportion of calcium hydrate undergoes a concurrent reduction of approximately 30%. Furthermore, the combined modification effect leads to a 15% reduction in total porosity and a constriction of the average pore diameter by roughly 20%, ultimately resulting in pore refinement that equates the performance of samples with a water-to-cement ratio of 0.5 to those with a ratio of 0.35. This remarkable transformation underscores the profound modification potential of the combination approach. This study underscores the efficacy of harnessing accelerated carbonation in conjunction with nano-silica as a strategic approach to optimizing the utilization of RCA in concrete mixes, thereby bolstering their performance metrics and enhancing sustainability.

The Influence of Resin Volume Fraction on Selected Properties of Polymer Concrete.

Polymer concrete is a promising material with applications in construction and architecture; however, guidelines for its design and optimization are not well-established in the literature. This study aimed to evaluate how resin volume fraction and aggregate size distribution affect key properties of polyester polymer concrete, including flexural strength, compressive strength, water absorption, and material cost. Three types of quartz aggregates with different particle size distributions were used, as follows: small (below 0.5 mm, quartz dust), medium (0.2-2.0 mm, quartz sand), and large (2.0-10.0 mm, quartz gravel). The resin volume content varied from 5% to 30%. Differences in apparent density, open porosity, water absorption, flexural strength, compressive strength, and material cost were analyzed as functions of resin volume content and aggregate size. The results showed that apparent density and mechanical properties are positively correlated with resin content for small and medium aggregates; however, in the case of large aggregates, flexural strength decreased when the resin volume content exceeded 20%. A significant reduction in material porosity and water absorption (to ~0.4% and ~0.2%, respectively) was observed at high resin volume fractions.

Structural Evolution of an Optimized Highly Interconnected Hierarchical Porous Mg Scaffold under Dynamic Flow Challenges.

The development of Mg and its alloys as bone screws has garnered significant attention due to their exceptional biocompatibility and unique biodegradability. Notably, the controlled release of Mg2+ ions during degradation can positively influence bone fracture healing. The advantages of Mg raise appeal for application in bone tissue engineering. However, porous Mg scaffolds, while offering high surface areas, face challenges in maintaining slow degradation rates and preserving interconnectivity, which are crucial features for tissue ingrowth. To address these issues, this study introduces a highly interconnected hierarchical porous Mg scaffold and investigates its degradation behavior within a bioreactor, simulating body fluid flow rates to mimic the in vivo degradation performance at different implantation sites. The focus lies on elucidating the evolution of the porous structure, particularly the impact of degradation behavior on scaffold interconnectivity. Our findings reveal that the initial high interconnectivity of the scaffold is significantly influenced by the flow rate. The dynamic fluid flow modulates the transport of degradation byproducts and the deposition patterns. At lower flow rates, Mg2+ ions accumulate within pores, leading to the formation of substantial deposits that directly reduce porosity. Specifically, after 42 days, porosities decreased to 68.80 ± 2.31, 58.52 ± 2.53, and 41.25 ± 2.82% at flow rates of 2.0, 1.0, and 0.5 mL/min, respectively. This porosity reduction and pore space occlusion by deposits sequentially hinder the interconnectivity. The magnitude of decreased porosity could be used to evaluate the ability of the microarchitecture to maintain scaffold interconnectivity. Meanwhile, the long-term degradation deposition behavior of the highly interconnected hierarchical porous Mg scaffold potentially revealed the structural integrity loss from the original design to its in vivo degraded structure at different body fluid flow rates. The present work might bring valuable insight into the design of pore strut and interconnectivity characterization methods for the progress of a high-performance tissue engineering scaffold.

Recycled ceramic brick powder utilization in fiber reinforced 3D printing concrete: an eco-friendly substitute to conventional fine aggregates

The incorporation of recycled ceramic brick powder (RCBP) into conventional cast concrete has proofed its efficacy in substituting aggregates, improving strength, and contributing to environmental sustainability. Concurrently, 3D printing technology is emerging as a pivotal trend in intelligent construction. This study investigates the collaborative interaction mechanisms of 3D-printed RCBP concrete. Compressive and four-point bending tests along the x, y, and z-axis are conducted to evaluate its strength and anisotropy. Subsequently, the hydration products and pore structural characteristics were analyzed employing Scanning Electron Microscope (SEM) and X-CT experiments. Additionally, an environmental life cycle analysis is performed utilizing OpenLCA software. The results determined an optimal RCBP content of 25-wt% yields satisfactory performance in macro-mechanical properties (with maximal 65.57MPa for compressive strength and 12.66 MPa for flexural strength) and micro-structural characterization. Specifically, the drainage consolidation effect achieved through 3D printing technology mitigates the typical decline observed in conventional RCBP concrete. However, exceeding the 25-wt% threshold leads to a noticeable decline in mechanical strength due to inhomogeneous particle gradation and excessive aggregation of RCBP particles, despite a significant reduction in porosity. Furthermore, as RCBP incorporation increases from 0-wt% to 100-wt%, four environment impact indicators including Global warming potential (GWP), Acidification Potential (AP), Ozone Depletion Potential (ODP), and Abiotic depletion potential (ADP) respectively decline by 24.86%, 6.59%, 0.49%, and 0.62%, demonstrating exceptional environmental benefits. Notably, the tremendous influence on GWP is attributed to the remarkable carbon sequestration of RCBP, aligning with national carbon neutrality goals and advancing sustainable construction practices.

Study on the Influence of Carbonation on the Microstructure of Cement-based Materials Based on BSE Technique

Background: The influence of carbonation on the interfacial transition zone (ITZ) microstructure of cement-based materials was significant. However, the width of ITZ is about tens of microns, and studying its micro-characteristics (such as porosity, hydration products, content of unhydrated cement, etc.) by macro test was difficult. Methods: Backscattered electron (BSE) imaging technology and gray scale analysis method were used to analyze the cement-based materials with water-binder (W/B) ratios of 0.53 and 0.35, respectively. Results: BSE and gray scale analysis showed that in the ITZ, the porosity of 0.53P (Portland cement paste), 0.35P (Portland cement paste), 0.53F (fly ash), and 0.35F (fly ash) decreased by 24.1%, 28.9%, 49.5%, and 64.2% respectively, whereas the content of hydration products increases after carbonation, and the matrix also shows the same rule. At the same time, the smaller W/B ratio, the greater the porosity reduction, and the filling effect of carbonation on the specimens with supplementary cementitious material (SCM) was more significant than that of pure cement specimens. Conclusion: The porosity of the ITZ decreased after carbonation, however it remained higher than that of the matrix. Consequently, the ITZ remained a vulnerable zone with a greater diffusion rate of CO2 compared to the matrix even after carbonation.