Increase In Compressive Strength Research Articles

Long-term durability of iron-rich geopolymer concrete in sulphate, acidic and peat environments

This study assesses the behaviour of iron-rich type F fly ash geopolymer concretes (GC) exposed to simulated sulphate, acidic, and peat environments, typical of those encountered in tropical peatlands. GC and Portland cement (PC) concrete of comparable strengths were exposed to a range of simulated solutions for 18 months, including 5 % magnesium sulphate (MgSO4), 5 % sodium sulphate (Na2SO4), 1 % and 3 % sulfuric acid (H2SO4) and peat. The GC generally outperformed PC in all conditions. The GC showed a significant increase in strength in the first year, along with enhanced durability properties. Microstructural analysis indicated a decrease in total porosity and pore size. This was attributed to continuing geopolymerization leading to the foration of additional N-A-S-H gel, which filled the pores and solidified the concrete matrix. However, compressive strength decreased at 18 months due to crack propagation caused by drying shrinkage. In Na2SO4, GC attained an 8.9 % and 6.3 % increase in compressive strength at 12 and 18 months, respectively, again attributed to ongoing geopolymerization. GC exposed to MgSO4 exhibited a significant decrease in compressive strength of approximately 11 % at 12 months and 19.8 % at 18 months, attributed to the formation of lower-strength M-A-S-H from reaction between MgSO4 and N-A-S-H gel. After 12 months GC exposed to 1 % and 3 % H2SO4 demonstrated a decrease in compressive strength of approximately 1.2 % and 4.5 %, respectively, together with 2 % and 3 % mass loss. Chemical and microstructural data confirmed this strength reduction due to the vulnerability of N-A-S-H to when exposed to H2SO4. GC exposed to peat solution exhibited a 1.25 % increase in compressive strength at 12-month, but a decrease of 11.3 % at 18-month. Microstructural analysis observed a reduction in Na+ within GC matrix, and the presence of gypsum. The reduction in pore sizes and total porosity suggested generation of zeolite crystalline material was contributing to the pore filling.

Influence of waste glass powder on printability and mechanical properties of 3D printing geopolymer concrete

Geopolymers represent a promising solution for reducing carbon emissions in 3D printing concrete (3DPC). This study explores the utilization of waste glass powder (WGP) as a novel precursor material to evaluate its influence on the printability and hardened mechanical properties of 3D printing geopolymer concrete based on slag and fly ash. Experimental results indicate that WGP content below 10% accelerates hydration and enhances buildability, whereas content exceeding 10% slows hydration but improves extrudability. Mechanical tests on cured specimens demonstrate a notable increase in compressive and flexural strength with increasing WGP content from 0% to 20%. Microstructural and chemical analyses of the 20% WGP variant reveal a denser morphology and an optimized Si/Al ratio.

Phase evolution and microstructure changes induced by accelerated carbonation in natural hydraulic lime paste with GGBFS addition

Carbonation is a primary factor driving the continuous improvement of the long-term performance of natural hydraulic lime (NHL). This research systematically examines the impact of accelerated carbonation (3 % CO2) on the carbonation depth, phase composition, microstructure, and compressive strength of hardened natural hydraulic lime (NHL) pastes mixed with different amounts of ground granulated blast furnace slag (GGBFS), termed as S-NHL. The findings show that the hydration reaction products of GGBFS and Ca(OH)2 (CH), such as C3AH10, C4AĈH11, and C-S-H, densify the microstructure of S-NHL, resulting in a decrease in carbonation depth with increasing GGBFS content. Accelerated carbonation (AC) promotes the rapid transformation of a significant quantity of CH into calcite in S-NHL, with the carbonation of CH occurring more readily than the carbonation of hydration reaction products. Throughout the AC process, NHL contains only calcite-type calcium carbonate. In contrast, after 28 days of AC, the carbonation of hydration reaction products such as C3AH10 and C-S-H in S-NHL produces a minor amount of aragonite and vaterite. AC continuously reduces the total pore volume and porosity of S-NHL, but the average pore diameter and most probable pore diameter initially decrease and then slightly increase. AC significantly reduces the large pores in S-NHL, ultimately resulting in pores predominantly composed of capillary pores (50–1000 nm). AC facilitates the development of compressive strength in S-NHL paste, with the increase in compressive strength being positively correlated with its CH content.

Effect of key design parameters on the physical / mechanical properties of coarse aggregated UHPC and its structural response subjected to bending

This study experimentally investigates the effect of key design parameters on the physical, mechanical and structural performance of coarse aggregated ultra-high performance concrete (CA-UHPC), with an aim to provide design guidance for on-site engineering applications. The variables of maximum aggregate size, aggregate content, fiber dosage and curing condition are selected for investigation. The results showed that increasing aggregate size does not significantly affect the compressive strength, but somewhat increases the elastic modulus and fracture energy; the increase of aggregate content results in a reasonable increase of compressive strength and elastic modulus. In particular, the 480 kg/m3 coarse aggregated UHPC shows a compressive strength of ∼150 MPa, elastic modulus of ∼50 GPa, autogenous shrinkage of <200 µε, and outstanding durability. The structural specimens fabricated with coarse aggregated UHPC exhibit excellent load-carrying capacity and ductility when subjected to four-point bending. More importantly, it was found that the effect of curing condition on the structural performance is insignificant. The results of this study can provide insights into the development of advanced UHPC materials and structures and promote their applications in practice.

Numerical study on Slurry-induced Fracturing Pressure of Cohesive Soil

The stability of the tunnel face during the slurry shield tunnelling is controlled by the slurry pressure in the slurry chamber, and excessive slurry pressure will cause fracturing on excavation face. In order to prevent the occurrence of slurry fracturing, it is necessary to conduct a detailed study on the slurry support pressure when the slurry fracturing occurs. In this study, the hydraulic fracturing experiment of cohesive soil samples was carried out by the self-developed hydraulic fracturing device, and the improved XFEM was used to simulate the experiment process. The influence of various factors on the fracturing pressure was analyzed, and the accuracy of the numerical simulation method was also verified. In addition, the calculation method of fracturing pressure of soft cohesive soil is obtained by fitting the influence of each factor. The results show that the improved XFEM can accurately simulate the shear failure of soft cohesive soil. The fracturing pressure increases linearly with the increase in the circumferential pressure, indicating that a higher overburden of the tunnel can help resist the initial fracturing induced by shield tunneling. The fracturing pressure increases with an increase in the unconfined compressive strength as well as the slurry viscosity. Based on the regression analysis of the numerical results, an empirical approach was proposed for estimating the slurry-induced fracturing of soil.

New insights into the evolution mechanism of mechanical and shrinkage properties of UHPC under sustained sub-elevated temperatures

In this paper, the mechanical properties, damage pattern, mass loss, and drying shrinkage of ultra-high performance concrete (UHPC) under sustained sub-elevated temperatures (60 ℃-200 ℃) are studied. The effect of UHPC mixture, temperature levels and durations are analyzed. The performance evolution mechanism is revealed based on the analysis of hydration products and microstructures. Results show that at 150 ℃, the water loss of C-S-H gel is continuous (>90d). After sustained action at 100 ℃-200 ℃ for 3d or 7d, UHPC shows obvious expansion, which is attributed to the interlayer water evaporation of gel phase causing spacing between the gel sheets. At 60 ℃ and 100 ℃, the strength incresear and the mean chain length (MCL) decrease are associated with the increase in the SiO4 tetrahedron production in the C-S-H gel phase. At 150 °C and 200 °C, the increase of C-S-H gel’s MCL, gel phase stiffening, and pore structure refinement are important reasons for the increase in compressive strength of UHPC.

The Influence of the Comonomer Ratio and Reaction Temperature on the Mechanical, Thermal, and Morphological Properties of Lignin Oil-Sulfur Composites.

Although lignin is a plentiful biomass resource, it continually exists as an underutilized component of biomass material. Elemental sulfur is another abundant yet underutilized commodity produced as a by-product resulting from the refining of fossil fuels. The current study presents a strategy for preparing five durable composites via a simple one-pot synthesis involving the reaction of lignin oil and elemental sulfur. These lignin oil-sulfur composites LOSx@T (where x = wt. % sulfur, ranging from 80 to 90, and T represents the reaction temperature in °C) were prepared via the reaction of elemental sulfur and lignin oil (LO) with elemental sulfur. The resulting composites could be remelted and reshaped several times without the loss of mechanical strength. Mechanical, thermal, and morphological studies showed that LOSx@T possesses properties competitive with some mechanical properties of commercial building materials, exhibiting favorable compressive strengths (22.1-35.9 MPa) and flexural strengths (5.7-6.5 MPa) exceeding the values required for many construction applications of ordinary Portland cement (OPC) and brick formulations. While varying the amount of organic material did not result in a notable difference in mechanical strength, increasing the reaction temperature from 230 to 300 °C resulted in a significant increase in compressive strength. The results reported herein reveal potential applications of both lignin and waste sulfur during the ongoing effort toward developing recyclable and sustainable building materials.

Sustainable enhancement of fly ash-based geopolymers: Impact of Alkali thermal activation and particle size on green production

Addressing the challenges posed by the slow reactivity of fly ash (FA) with alkali at ambient temperatures, this study delves into the enhancement of FA-based geopolymers through alkali thermal activation (ATA). The ATA process, conducted at 550°C for 1 h, significantly increases the availability of reactive silica and alumina, which are essential for geopolymerization. A critical focus of the research is the influence of FA particle size on ATA’s efficacy and the resultant mechanical properties of the geopolymers. Findings reveal that the ATA process facilitates the rapid dissolution of the vitreous phase in FA. This leads to a sequential release of silica and alumina, which is pivotal for the geopolymer’s matrix development. Notably, geopolymers synthesized from finely milled FA, post-ATA, demonstrate a marked increase in compressive strength, escalating from 30.51 MPa to an impressive 38.46 MPa. The study meticulously delineates geopolymerization into four distinct stages—initial dissolution, depolymerization, geopolycondensation and gelation, and final diffusion, with the initial dissolution and final diffusion stages being paramount in defining the reaction kinetics and the ultimate strength of the geopolymer. This enhanced understanding paves the way for optimizing FA utilization in geopolymers, promising a more sustainable and efficient pathway for producing construction materials with superior mechanical properties.

Dynamic properties of CO2-cured foam concrete at different loading rates: Effect of the foam admixtures and addition of polypropylene fiber

This paper investigated the dynamic mechanical properties of CO2-cured foam concrete under varying conditions, focusing on the effects of foam admixture and fiber reinforcement. The study tends to enrich the knowledge regarding the performance of CO2-cured foam concrete under different loading rates, especially in relation to density and matrix strength. The foam admixture of the specimens ranges from 26% to 55%, achieving density from 600 kg/m3 to 1,000 kg/m3. The specimens were loaded at strain rates from 80 s-1 to 398 s-1. Experimental results revealed the dynamic elastic modulus, dynamic compressive strength, and Dynamic Increase Factor (DIF) showed a strong correlation with the foam admixture and density. In addition, the incorporation of polypropylene (PP) fibers effectively improved the mechanical behavior of the foam concrete, achieving up to a 17% increase in dynamic compressive strength. This comprehensive analysis highlights the critical role of foam admixture and fiber reinforcement in determining the dynamic properties of CO2-cured foam concrete and provides valuable insights for optimizing the dynamic performance of foam concrete in various construction applications.

Study of the mechanical properties, durability, and microstructure of an ultra-high-performance fiber-reinforced concrete containing recycled fillers

Abstract In this article, a specific mix design of the ultrahigh-performance fiber-reinforced concrete (UHPFRC) was proposed and applied for Algerian materials that are currently in use. In the absence of a general mix design that limits their use and reuses waste materials, the present mix design can help reduce the high manufacturing cost of this type of concrete and make it more environmentally friendly. Here, we have looked for a reference mix design based on local ordinary aggregates, and then, we introduced the recycled fillers from ceramic waste and granulated blast furnace slag into our mix design, and we studied their effects on the properties of the fresh state (density, workability, and air content) and in the hardened state, namely compressive and flexural tensile strength, modulus of elasticity, ultrasonic and sclerometer resistance, as well as durability tests (capillary and immersion absorption, porosity, and chemical resistance). The microstructure analysis was carried out using scanning electron microscopy, complemented by energy-dispersive X-ray spectroscopy. Comparison of the results of UHPFRC using ceramic waste and slag fillers with the control UHPFRC after 28 days shows an increase in compressive strengths of approximately 8 and 7%, respectively, as well as an increase in flexural tensile strengths of 17 and 2%, respectively. In addition, there was a decrease in porosity of 17 and 42%, respectively. The results reveal that it is possible to produce UHPFRC based on local materials and improve its performance, durability, and microstructure with recycled fillers.

A DOPO-eugenol linear siloxane as a highly effective liquid flame retardant also imparting improved mechanical properties to an epoxy amine network

A liquid bio-derived eugenol-containing phosphorus silicone hybrid molecule (EGDS-DOPO) that endows excellent flame-retardancy and enhanced mechanical performance to an epoxy amine network at low levels of addition was successfully synthesized and characterised. The EGDS-DOPO significantly improved the flame retardancy requiring only 5 wt% of EGDS-DOPO to achieve a limiting oxygen index (LOI) of 34.9 % and a UL 94 V-0 rating. Cone calorimetry measurements reveal a reduction of the peak heat release rate, the total heat release, and total smoke production by 62.2 %, 34.0 % and 47.5 %, respectively when EGDS-DOPO concentration was 20 wt%, compared to the unmodified epoxy network. Viscosity remained low throughout cure, and despite some retardation of reactivity, the epoxy amine resin remains fast curing and suitable for liquid moulding composite fabrication technologies. Moreover, the modified EGDS-DOPO epoxy networks display a glass transition temperature (Tg) between 218.5 °C and 174.1 °C, a hydrophobic surface with water contact angle of 97.5°–106.6°, a low moisture ingress of 2.35 %–2.91 %, and improved overall mechanical properties in flexure (maximum 39.8 % increase in flexural strength and 27.0 % in flexural modulus), compression (maximum 24.5 % and 35.0 % increase in compressive strength and modulus, respectively), and fracture toughness (maximum 28.0 %).

Unleashing high-volume waste plastic recycling in sustainable cement mortar with synergistic matrix enabled by in-situ polymerization

The substantial energy consumption and CO2 emissions associated with the production and transportation of concrete and its components have necessitated the search for suitable replacements, particularly waste materials such as plastic, to mitigate their environmental impact. The emergent challenge of employing recycled waste plastics (RWP) in concrete centers around their poor interactions with the cement matrix. Here, a synergistic approach with in-situ polymerization by using sodium acrylate (SA) at various doses (0 %, 0.5 %, 1 %, 2 %) was employed to produce environmentally-friendly mortars. Recycled polypropylene (PP) particles were adopted as the aggregate to replace natural sand in cement mortar. Results indicate decreased water contact angel by 46 % and increased pull-off strength by 25 % for SA-polymerized PP. Moreover, mortars with 2 % SA exhibited a 31 % increase in compressive strength, a 64 % increase in flexural strength, a 76 % reduction in water sorptivity, and a 13.6 % decrease in total porosity. The formation of interconnected polymeric networks in the cement matrix and interfacial transition zone (ITZ) contributes to structural densification, highlighting the superior engineering properties. These findings present a promising pathway towards sustainable and resource-efficient building materials, fostering a circular economy for plastics.

The impact of κ-carrageenan on the pea protein gelation by high pressure processing and the gelling mechanisms study

The transition toward sustainable and health-conscious diets has intensified plant-based proteins, particularly pea protein. This research explored the gelation mechanisms of pea protein with κ-carrageenan by high-pressure processing (HPP) as an alternative to traditional thermal methods. Suspensions containing 15% pea protein with 0.1–1% κ-carrageenan were subjected to HPP at 100–600 MPa for 5–30 min. Increasing κ-carrageenan concentration reduced the pressure required to obtain good gels, rendering HPP more energy efficient. Pea protein gels with 1% κ-carrageenan at 600 MPa demonstrated a 27-fold increase in compressive strength compared to 15% pea protein alone by HPP and over 5 times the strength of heat-induced counterparts. Gel textures could be tailored by modulating HPP conditions and κ-carrageenan concentrations. Fourier transform infrared spectroscopy, confocal laser scanning microscopy, and scanning electron microscopy characterized protein unfolding, phase separation, and network formation to study the gelation mechanisms. Results revealed that HPP induced protein tertiary structure unfolding, facilitating phase separation and uniform submicron κ-carrageenan particle distribution in the protein matrix. This, along with a more compact protein network induced by HPP, enhanced gel strength, compensating for limited cysteine in pea protein for disulfide bonds. Higher pressures intensified protein unfolding and aggregation, with κ-carrageenan particles evenly distributing into smaller particles, further strengthening gel structures. Conversely, heating-induced gelation caused more random protein aggregation, leading to coarser and weaker gel networks. This research highlights HPP's effectiveness over traditional heating methods in preparing strong pea protein gels with minimal κ-carrageenan and provides preliminary insights into tailoring HPP and κ-carrageenan for desirable gel textures.

Experimental analysis of mechanical properties of dredged sludge solidified by carbonized under the synergistic action of magnesium oxychloride cement and lime

The environmentally friendly magnesium oxychloride cement (denoted as MOC thereinafter) shows promising application prospects. Meanwhile, more emphasis is being paid to the environmental issues created by CO2 emissions. In this paper, carbonation-composite solidification technology is adopted to introduce MOC-lime cementitious material into sludge solidification. The effects of initial water content (H2O/MgCl2 molar ratio), lime content, MgO/MgCl2 molar ratio, and carbonation time on the mechanical properties and micro-mechanisms of sludge solidification were investigated using unconfined compressive strength (UCS), pH value, carbonation depth, mass loss rate, scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests. The results show that the UCS of sludge solidification decreases with an increase in H2O/MgCl2 molar ratio, and increases first and then decreases with an increase in lime content, reaching a maximum value at H2O/MgCl2 molar ratio of 24.3 and lime content of 4 %. Notably, carbonation significantly improves the UCS of the samples, and with an increase in carbonation time, the mass loss rate and carbonation depth increase, while the pH value decreases. Additionally, uncarbonated samples show an increase in compressive strength with an increase in MgO/MgCl2 molar ratio, as the hydration products gradually transform from amorphous gel to crystalline phases 3, phases 5, and brucite (Mg(OH)2). Finally, XRD and SEM results indicate that the underlying mechanism for the significant improvement in strength and microstructure of the samples after carbonation is the formation of a block-like crystalline network with good binding ability, consisting of chlorartinite, nesquehonite, calcium carbonate, and C-S-H gel. This study promotes the use of MOC-based gel materials as a green stabilizer for sludge solidification, and the carbonation technique employed can improve the mechanical properties of solidified soil and significantly reduce the curing time.

Examination of the use of binderless zeolite blend as backfill materials to enhance CO2 adsorption in coal mine working face

The release and accumulation of CO2 in the working face of the coal mine is a major safety concern and requires an effective means to avoid the incidence of the mine. This present study therefore sought to develop a self-CO2 adsorbing backfill (SCAB) material to remove CO2 from the working environment, and simultaneously mitigate the movements of the surrounding rock layers. SCAB was formulated using coal mine solid waste activated with an alkali activator, and binderless 4 A zeolite was embedded in the backfill body. The total CO2 adsorption capacity was investigated using a CO2 flow-through method under ambient pressure and temperature conditions. The adsorption plateau was found in stages II and III respecting the predetermined curing time and zeolite contents. The maximum adsorption capacity was 143.8 mg-CO2/g-SCAB, resulting in an increase of up to 82 % in UCS compared to reference samples. The underlying mechanism was discovered in morphological analyses.1) The well distribution of zeolite in the SCAB body provided as diffusive pathways and adsorption sites for CO2 after standard curing. 2) The adsorbed CO2 underwent a desorption stage when the CO2 concentration decreased and reacted to the cementitious matrix of the SCAB body. 3) More CaCO3 crystals were generated and filled in the micro spaces of the SCAB body, which contributed to an increase in compressive strength. This study developed an effective approach to remove CO2 gas from the working face of the coal mine during backfilling. Adsorbed CO2 improved the strength of the material, provided as a novel multi-function backfill mining for sustainable green coal mining technology.

Carbon nanofibers encapsulated by polyethylene glycol increase the mechanical properties and durability of OPC mortars

Carbon nanofibers (CNF) are promising additives for the reinforcement of cementitious materials. However, due to their high specific surface and hydrophobic nature, CNF are difficult to disperse in ordinary Portland cement (OPC) mortars when using conventional plasticizers. In this work, we evaluate the production of mortars with CNF encapsulated by a thin layer of polyethylene glycol (PEG) covalently grafted at their surface (CNF@PEG). CNF@PEGs were chemically prepared using two methods with PEG of various molecular weights. In all cases, the dispersion of the CNF@PEG in water as well as in a simulated cement pore solution was improved. Remarkably, mortars fabricated with CNF@PEG4k (PEG of molecular weight 4000 g/mol) exhibited a 20 % increase in compressive strength, 10 % increase in flexural strength and 25 % increase of the Young's modulus measured after 7 days, in comparison to a reference mortar. Finally, electrochemical impedance spectroscopy (EIS) was used to assess the ionic resistivity of the mortar. Mortars containing CNF@PEG4K had an ionic resistivity 43 % higher than the reference sample at 28 days leading to better durability. These results demonstrate that encapsulation of CNF by PEG is a successful strategy to improve the mechanical performance and durability of CNF-containing OPC mortars.

Behavior of controlled low-strength material incorporating industrial by-products fly ash, quarry waste and concrete waste

The widespread generation of concrete waste from demolished structures presents a significant challenge in construction waste management. However, its integration into Controlled Low Strength Material (CLSM) presents a promising avenue for sustainable construction for utility fill or backfilling applications when suitable granular fills are not available. A low strength flowable fill mix necessitates a mix design that achieves a compressive strength below 0.7 MPa after 28 days for easy excavatability using hand tools. This study delves into the feasibility of replacing fly ash by incorporating concrete waste and quarry waste into CLSM formulations with minimal amounts of cement through laboratory investigations to engineer CLSM blends optimized for easy excavation, particularly for utility fills. Results indicate that the inclusion of concrete waste reduces the water demand and mitigates bleeding in CLSM, thereby enhancing the overall stability of the mix. Moreover, CLSM compositions exhibit densities akin to the density of sand. The addition of 10 % and 20 % of concrete waste led to substantial increases in unconfined compressive strength (UCS). The impact was more pronounced at lower cement contents, with significant early strength development observed when concrete waste was included.The split tensile strength was found to have a linear correlation with the UCS and the dry density of the mix. The formation of pozzolanic hydration products, particularly in mixes with higher fly ash content, was identified as a key factor contributing to strength development, while increased friction between particles of quarry waste further increased the strength and the same has been confirmed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The findings also revealed that a CLSM blend composed of, 30 % fly ash, 50 % quarry waste and 20 % concrete waste supplemented with an extra 3 % cement at 250 mm flowability could be used for backfilling applications where sufficient strength and excavatablity with hand tools is required.

Magnesium sulphate resistance of fly ash one-part geopolymers: Influence of solid alkali activators on physical, mechanical and chemical performance

The commitment to promoting circular economy and durable construction materials has led to the advocacy for one-part geopolymer (OPG), as an eco-friendly substitute for traditional ordinary Portland cement (OPC). Solid alkali activator is the fundamental component of OPG and significantly influences the sulphate resistance. To identify the types of solid alkali activators best suited for the development of sulphate-resistant OPGs, OPGs activated with Na2SiO3 (M-OPG), Na2SiO3+Na2CO3 (MC-OPG), Na2SiO3+NaOH (MH-OPG) and Na2SiO3+NaAlO2 (MA-OPG) were exposed to 5 % and 10 % of MgSO4 solutions for 28 days. The fine pore structures of MH-OPG and MC-OPG mitigated deterioration from the more concentrated MgSO4 solution, resulting in higher residual compressive strengths after exposure to the 10 % MgSO4 compared to the 5 %. Exposure to the 5 % MgSO4 solution resulted in strength deterioration for M-OPG, MH-OPG and MC-OPG due to the discontinuity of the aluminosilicate structure, as evidenced by the diminished Q4(3Al) sites. Conversely, the MA-OPG exhibited a 24.1 % increase in compressive strength, accompanied by the emergence of sodium magnesium aluminium silicate hydrate ((N,M)-A-S-H) gel. Hence, Na2SiO3+NaAlO2 should be acknowledged as the primary candidate for solid alkali activators in the development of sulphate-resistant OPGs.

Tailoring the mechanical strength and corrosion resistance of aluminum matrix composites through biochar reinforcement at varied weight percentages

This study introduces an innovative approach to fabricate aluminum matrix composites strengthened with biochar, derived from renewable biomass sources. A systematic investigation of varying biochar weight percentages (0, 2.5, 5, 7.5, and 10 wt%) reveals substantial improvements in mechanical properties and corrosion resistance. Mechanical assessments, including compressive strength and hardness, demonstrate a significant enhancement in mechanical strength with biochar incorporation. In this study, it was discovered that the composite with 7.5 wt% biochar exhibits an optimal balance, displaying an 8.83% increase in compressive strength and a 15.15% rise in hardness compared to the base aluminum matrix. The study further evaluates corrosion behavior through electrochemical analyses and immersion tests in 3.5% NaCl corrosive environments, highlighting the superior corrosion resistance of biochar-reinforced composites. Corrosion rates decrease by 73% in the composite with 10 wt% biochar for the 24 h immersion time, affirming its protective barrier against corrosive agents. This research provides quantitative insights into tailoring mechanical and corrosion properties in aluminum matrix composites through biochar reinforcement, offering a promising avenue for sustainable material development. The resulting materials exhibit not only an 8.83% increase in mechanical strength but also a 73% reduction in corrosion rates, offering valuable uses in industries that need strong, eco-friendly solutions.

On the Study of Thickness Gradients in Novel Star Honeycombs: Classical and Combinatorial Designs

Herein, a series of gradient designs are carried out to enhance further the energy absorption capacity of a novel star honeycomb. These include unidirectional and bidirectional gradient designs along the impact direction, while the gradient changes in the non‐impact direction are considered. Via the coupling of bidirectional and unidirectional directions, a combined gradient evolution method is further proposed. The in‐plane compression characteristics of these gradient honeycombs are systematically revealed based on the validated finite element method at low‐, medium‐, and high‐velocity impacts, respectively. The results show that honeycombs with gradient variations in the impact direction are realized as localized modes under both low‐ and medium‐velocity impacts, while honeycombs with gradient design only in the non‐impact direction exhibited global modes and “local + global” modes, respectively; under high‐speed impacts, honeycombs with gradient configurations in the non‐impact direction showed stepped layer‐by‐layer collapses, whereas honeycombs with gradient evolutions only in the impact direction collapsed in I‐shaped layers. Besides, the increase in compressive strength and specific energy absorption of honeycomb with combined gradient configuration can be up to 38.1% and 67.9%. This article provides a new idea of honeycomb gradient evolution, which can provide a reference for improving the energy‐absorption capacity of honeycombs.