Proportion Of Aggregates Research Articles

Assessing the Effects of Libyan Iron Slag on Self-Compacting Concrete Characteristics

The current study addresses the growing environmental issue of waste from blast high furnaces, particularly iron and steel plants in Libya. It investigates the fresh and mechanical properties of Self-Compacting Concrete (SCC) by substituting conventional aggregate with slag aggregate. The fresh properties of SCC were assessed using slump flow diameter, T50 flow time, J-ring, and L-box tests. Its mechanical properties were also evaluated, including compressive strength, flexural strength, splitting tensile strength, and Ultrasonic Pulse Velocity (UPV). Various replacement ratios were tested, 30%, 60%, and 100% for coarse aggregate, 10%, 20%, and 30% for fine aggregate, and combinations of coarse and fine aggregate at specified ratios. The results indicated that higher slag powder content slightly increased the setting times. The coarse slag aggregate proportions negatively impacted the filling ability, while fine aggregate proportions enhanced it. The passing ability decreased when 60% of coarse slag was used as a replacement, but it improved with a 100% coarse slag replacement. Interestingly, replacing 60% of coarse aggregate with slag enhanced compressive strength. Meanwhile, the best flexural and splitting tensile strengths were observed with 20%-30% replacements of both coarse and fine aggregates with slag. All slag aggregate mixtures were classified as of excellent quality based on UPV assessments, highlighting their potential as sustainable construction materials.

A Study on Effect of Addition of Recycled Bituminous Material to Stone Matrix Asphalt Using Polymer Modified Bitumen (PMB-40)

Stone Matrix Asphalt (SMA) is a gap-graded mix with a high proportion of coarse aggregate, binder, and fiber additives for stability. A high concentration of coarse aggregate enhances stone-on-stone contact and interlocking, resulting in strength and durability. Stabilizing additives prevent bitumen draindown material. This study assesses the influence of incorporating Recycled Asphalt Pavement (RAP) into Stone Matrix Asphalt (SMA) along with Polymer Modified Bitumen (PMB-40) in road construction to increase performance and sustainability. The study aims to determine the optimal binder content and evaluate the mechanical properties of SMA mixtures using varied RAP percentages (0%, 15%, 20%, and 25%) and cellulose fibers. The study also looks at important performance indicators such as Marshall Stability, Draindown characteristics, Indirect Tensile Strength (ITS), and Tensile Strength Ratio (TSR). The results indicate that the optimum binder content for RAP-modified SMA falls between 6.2% and 6.4%. The addition of RAP improved the mechanical performance, with RAP-modified mixes demonstrating a 5–7% increase in Marshall Stability and a 15–20% improvement in ITS as compared to control samples. Superior resistance to moisture-induced damage and cracking can be seen by TSR values that continuously exceed the mandatory minimum of 0.90. The combination of 15-25% RAP and 0.3% cellulose fibers significantly reduced draindown, ensuring proper binder retention during mixing and placement. These results show that by adding RAP to SMA mixes not only helps to preserve natural-environmental resources but also improves durability and resistance to environmental pressures. The study supports continued efforts to create environmentally friendly infrastructure by confirming that recycled bituminous materials can be used without sacrificing structural integrity

Simulation and experimental study of single axis load of resin-based concrete at macro-micro scale

ABSTRACT This study focuses on resin-based concrete, a novel composite material in which resin replaces the traditional cementitious binder, forming a three-phase composite consisting of aggregate, resin matrix, and interfacial transition zones. Four random aggregate models were generated using the Monte Carlo method and their stability was verified. Subsequently, a two-dimensional micro-model was established, and the simulation results were compared with experimental data, yielding a maximum error of 8%, which validated the feasibility of the model. The findings indicate that circular aggregates exhibit lower load-bearing capacity, while irregular aggregates demonstrate higher capacity. Although the peak compressive strength is similar among different aggregate shapes, the crack propagation paths vary significantly. The load-bearing capacity of resin-based concrete increases with aggregate content up to an optimal value of approximately 80%, beyond which it decreases. At this optimal content, crack paths transition from branched to near-linear. In terms of aggregate grading, higher coarse aggregate proportions enhance load-bearing capacity and promote linear crack propagation, whereas higher fine aggregate proportions reduce capacity and result in multiple irregular crack paths. Finally, the numerical simulation results were used to guide macroscopic experiments, and orthogonal experiments were conducted to determine the optimal mixture proportions of different resin binders.

Evaluating the Impact Performance of Environmentally Friendly Asphalt Concrete Slabs Containing Different Proportions of Recycled Concrete Aggregate and Corrugated Steel Fibers

The current research focuses on recycling construction waste by producing asphalt concrete mixtures containing varying proportions of recycled concrete aggregate (RCA), ranging from 0 to 50%. To ensure the improvement of the asphalt mixtures' properties in terms of Marshall stability, flow, bulk density, air void ratio, and splitting tensile strength, steel fibers were added at a volume fraction of 1.0%. The experimental program consisted of 12 asphalt cylinders with a diameter of 102 mm and a height of 64 mm, cast with different asphalt mixtures to study the effects of varying RCA proportions as well as the addition of steel fibers on the mechanical properties of the asphalt concrete mixtures. The stability of the asphalt mixtures decreased by 17.6%, 23.2%, and 28.8% when RCA was used at ratios of 30%, 40%, and 50%, respectively, compared to the reference mixture. The Marshall stability of asphalt mixtures containing steel fibers was higher than that of their counterparts without fibers. Moreover, 12 asphalt slabs were cast with different ratios of RCA in preparation for testing under the impact load resulting from the free fall of a 10-kg steel mass from a height of 2 m. The results revealed that the ratio between the back and front crater diameters for slabs containing 10%, 20%, 30%, 40%, and 50% RCA after incorporating steel fibers was 1.15, 1.17, 1.15, 1.28, and 1.36, respectively. These ratios were smaller than those of the counterpart slabs without steel fibers by 18%, 19%, 19%, 7%, and 18%, respectively. Moreover, due to the low accuracy of existing mathematical models for predicting the penetration depth of asphalt slabs made with RCA, this research presents a developed mathematical model capable of accurately predicting the penetration depth of such slabs. This model considers both the ratio of RCA and the steel fibers within the asphalt mixtures.

Soil Aggregation, Aggregate Stability, and Associated Soil Organic Carbon in Huron Mountains Forests, Michigan, USA

Soil organic carbon (SOC) plays a critical role in regulating the global carbon (C) cycle, with forest soils serving as significant C sinks. Soil aggregate stability and the distribution of SOC in different aggregate fractions would be affected by different forest types. In this study, we investigate the distribution and dynamics of SOC within different soil aggregate fractions across three main forest types in the Huron Mountains, Michigan, USA: white birch–eastern hemlock mixed forest, eastern-hemlock-dominated forest, and sugar maple forest. We hypothesize that variations in species composition and soil depth influence SOC storage and aggregate stability through mechanisms such as root interactions, microbial activity, and soil structure development. Soil samples were collected from three depth intervals (0–20 cm, 20–40 cm, and 40–60 cm) and analyzed for aggregate size distribution and SOC content. The results showed that aggregate size distribution and SOC stocks differ significantly across forest types, with the white birch–eastern hemlock mixed forest exhibiting the highest proportion of large aggregates (>1.0 mm), which contribute to more stable soil structures. This forest type also had the highest total aggregate mass and mean weight diameter, indicating enhanced soil stability. In contrast, sugar maple forest displayed a greater proportion of smaller aggregates and a lower macroaggregate-to-microaggregate ratio, suggesting fewer stable soils. SOC stocks were closely linked to aggregate size, with macroaggregates containing the highest proportion of SOC. These differences in SOC distribution and soil aggregate stability can be attributed to several underlying mechanisms, including variations in plant root interactions, microbial activity, and the physical properties of the soil. Forests with diverse species compositions, such as the white birch–eastern hemlock mixed forest, tend to support more complex root systems and microbial communities, leading to improved soil aggregation and greater SOC storage. Additionally, forest management practices such as selective thinning and mixed-species planting contribute to these processes by enhancing soil structure, increasing root biomass, and promoting soil microbial health. These interactions play a crucial role in enhancing C sequestration and improving soil health. Our findings emphasized the importance of forest composition in influencing SOC dynamics and soil stability, offering insights into the role of forest management in C sequestration and soil health. This study provided a reference to a deeper understanding of SOC storage potential in forest ecosystems and supports the development of sustainable forest management strategies to mitigate climate change.

Statistical models for porous asphalt mixtures containing pulverized surface dressed pavement material/low-density polyethylene waste

Porous asphalt (PA) mixtures typically contain a high proportion of coarse aggregates with minimal fine aggregates, along with a binder that creates ample space for water drainage. Since road construction consumes large quantities of aggregates, recycling and reusing materials have become common practices. This study focuses on developing PA by partially replacing traditional aggregates with pulverized surface-dressed pavement material (PSM) and modifying bitumen with low-density polyethylene (LDPE). The mixtures were produced using 60/70 penetration grade bitumen modified with 2%, 4%, and 6% LDPE waste and 20%, 40%, 60%, and 80% PSM. Adding LDPE waste to the bitumen altered key properties, such as the softening point, penetration, flashpoint, and ductility, resulting in a stiffer binder. Replacing aggregates with PSM reduced both stability and flow, leading to a lower Marshall quotient. Flow values for all trial mixes did not meet AAPA (2004) standards, while stability values slightly decreased as LDPE content increased from 2% to 6%. Despite this, all samples met the AAPA (2004) stability standard. The sample containing 2% LDPE and no PSM exhibited the highest Marshall quotient. Linear regression models were developed from experimental data to highlight the relationships between the measured responses and the variables. These polynomial equations demonstrated a strong correlation, indicated by high coefficients of determination. The study introduces an innovative approach by incorporating PSM and LDPE, largely unexplored in PA production, especially in Nigeria. The major societal benefits include reducing environmental pollution through plastic waste reuse, conserving natural aggregates, and promoting cost-effective construction practices. By advancing the use of recycled materials, this research supports sustainable infrastructure development while maintaining compliance with industry standards.

Experimental Analysis on Quality of Coarse and Fine Aggregate Produce from Crusher Plants of Syangja District of Nepal

Does quality address grade? No, quality standards do not demand the best quality. However, they establish the minimum requirements for engineering uses or conformance with the code provisions or standards, free from faults and defects. Quality control by detection, quality assurance by prevention, and total quality by improving the quality of materials using quality policy and quality planning are necessary for any crusher plant or entrepreneur to achieve customer and society satisfaction. Aggregate must meet specific standards or code provisions for optimum engineering use to get better quality and higher strength concrete. The aggregates' types and quality significantly influence the concrete's properties; hence, the aggregates used to produce concrete that meets the required specifications are a prime concern. The aggregates' quality is significantly related to the concrete's strength, workability, and durability. The physical and mechanical properties of coarse and fine aggregate were analyzed in this research. The test results found that the P1, P3, and P4 crusher plants comply with all physical and mechanical parameters of the IS 383:2016 code provision. In contrast, the crusher plant of P2 does not comply with IS 383:2016 standard on optimizing the coarse and fine aggregate proportion in all-inaggregate analysis. The Gradation of fine aggregates of all the crusher plants does not lie in the grading zone as classified by IS code 383:2016. The inert material satisfying code provisions and standards helps to gain strength, durability, and other concrete parameters during mixed design for concrete production.

Design of Self-Compacting Concrete with Reduced Cement Content by Aggregate Packing Method.

This article presents the procedure for designing self-compacting cement concrete characterized by minimal free space and a maximally compacted mineral skeleton. Such a designed mix allows for lower cement consumption and an increased amount of mineral additives. The paper presents a broad analysis of the influence of different aggregate proportions (36 recipes) and verification of the properties of the concrete mix using CEM I 42.5 R cements and fly ash. As a result of the appropriately compacted mineral skeleton, only 17% free space was obtained, which will allow the amount of cement to be reduced from 500 kg/m3 to 350 kg/m3 while fully maintaining the properties of the mix and hardened concrete. After 90 days of curing, SCC concrete was characterized by a compressive strength above 68 MPa and a small 2.1% decrease in compressive strength after 100 freeze-thaw cycles.

A 2-year pure biochar addition enhances soil carbon sequestration and reduces aggregate stability in understory conditions

The enhancement of soil aggregate size and stability is crucial for mitigating climate change and improving carbon sequestration in forest ecosystems. Biochar, derived from rice husks, has been suggested as an effective mean to increase soil carbon storage. However, isolating biochar’s specific effects on soil aggregate formation and carbon sink capacity can be complex due to the overlapping influences of fertilization and understory vegetation cultivation. Our study circumvented these variables by incorporating different amounts of biochar into plantation soil without any additional cultivation or fertilization, conducting a detailed two–year field experiment. The findings revealed that biochar significantly increased the organic carbon content and density in the uncultivated under–forest Ferralsols, thus enhancing its carbon sink function. Intriguingly, while biochar raised the proportion of small soil aggregates (< 0.25 mm) and their organic carbon levels, it decreased the fraction of larger aggregates (> 0.25 mm), adversely affecting soil aggregate stability. These results suggest that biochar may compromise soil aggregate structure and stability in the absence of plant growth. The positive impact of biochar on soil carbon storage was found to depend more on its inherent inert carbon content than on soil type. Moreover, biochar alone was insufficient to increase the quantity of soil macroaggregates without the binding action of plant root exudates. Biochar’s key function appears to be in enhancing the soil aggregate–forming processes facilitated by plant roots and microorganisms. Therefore, for optimal carbon sequestration in forest soils, integrating biochar application with appropriate agricultural practices is advisable.

Laboratory mix preparation and investigation of mechanical behaviour of polyurethane-bound porous rubber pavement

With the rise in stormwater runoffs, permeable pavement like polyurethane-bound porous rubber pavement (PRP) offers a viable solution for urban stormwater management. Composed of stone and recycled crumb rubber aggregates bound by polyurethane, PRP features high air voids. This study explores PRP’s mechanical behaviour and freeze–thaw durability in cold climates, essential for sustainable urban infrastructure. We developed methods for sample preparation and air void assessment in PRP and conducted tests on compressive and indirect tensile strength, plus moisture-induced damage. Two scenarios were investigated: one examined four new mixes of varied compositions, and the other focused on mixes with different binders (aliphatic and aromatic). Our investigation reveals insights into PRP’s mechanical behaviour under colder climate conditions. The study shows that higher proportions of stone aggregates and binders enhance mechanical strength, while increased rubber content improves freeze–thaw durability. Furthermore, we found that different binders affect strength variations. The study concludes PRP is effective for low-traffic pavements in colder, freeze–thaw regions.

Thermal Performance Evaluation of PCM-Impregnated Aggregates in Hot Mix Asphalt: Mitigating Urban Heat Island Effects

The Urban Heat Island (UHI) phenomenon, in which the temperature in urban regions is higher relative to that in surrounding rural areas, is primarily attributed to human activities and urban development. This temperature escalation poses various challenges, impacting energy consumption, human well-being, and the overall urban environment. This study explores the potential of phase change materials (PCMs) as an addition to asphaltic mixes in alleviating the UHI effect. PCMs can store and release thermal energy through phase transition and exhibit valuable thermal properties for temperature management. In the context of UHI, PCMs play a pivotal role in alleviating the surplus heat amassed in urban areas. This study evaluates the effectiveness of shape-stabilized PCM-impregnated aggregates to reduce pavement temperature. The mechanical and thermal performance of the four different bituminous mixes has been evaluated in this study. A decrease in marshall stability while an increase in marshall flow has been observed with the increase in the proportion of PCM-impregnated aggregates in the mix. Based on the thermal analysis of PCM-modified mixes, a temperature drop of 5.03 °C and 2.9 °C in core temperature was observed in the case of 70% and 35% replacement with PCM-impregnated aggregates. The introduction of PCM-impregnated aggregates into the mix lowers the rate of increase and decrease in temperature of the asphaltic mix in direct sunlight. Electrical resistivity increased by around 4% and 8.6% for 35% and 70% replacement as compared to control sample.

Effects of tree species composition in plantation forest on soil aggregate stability and organic carbon pools in northeastern China

Forest tree species composition influences soil aggregate stability (SAS) and labile organic carbon (LOC) components, which may affect soil organic carbon (SOC) sequestration. Despite the general belief that mixed forests enhance SOC storage, evidence suggests that certain monocultures may outperform mixed forests. Therefore, information on the specific impact of tree species mixing on SOC through SAS and LOC remains limited. This study aimed to investigate the effects of tree species composition on SAS and LOC in 49-year-old monoculture (Larix gmelinii (Lg), Pinus koraiensis (Pk)) and mixed conifer-broadleaf (Larix gmelinii - Fraxinus mandshurica (LF), and Pinus koraiensis - Populus ussuriensis (PP)) stands, and its impact on SOC sequestration. We measured SAS indices (including mean weight diameter (MWD), geometric mean diameter (GMD), and > 0.25 mm water stable aggregate proportion (WSA)), SOC storage, and LOC components (easily oxidized organic carbon (EOC), microbial biomass carbon (MBC), and dissolved organic carbon (DOC)) in 0–40 cm soil horizons during the growing season (June, August, and October). Our results showed that tree species composition significantly influenced SAS and SOC components, with the highest SAS found in the 0–20 cm soil horizon in Pk and PP forests (p < 0.05) (Jun.: MWD Pk: 0.98, GMD Pk: 1.88, WSA Pk: 1.79, MWD PP: 0.98, GMD PP: 1.90, WSA PP: 1.81; Aug.: MWD Pk: 0.99, GMD Pk: 1.85, WSA Pk: 1.77, MWD PP: 0.99, GMD PP: 1.89, WSA PP: 1.81; Oct.: MWD Pk: 0.98, GMD Pk: 1.86, WSA Pk: 1.76, MWD PP: 0.97, GMD PP: 1.83, WSA PP: 1.73) and the highest SOC components in the LF stand (p < 0.05) (soil horizon 0–20 cm: Jun.: SOC: 110.23 g/kg, EOC: 92.81 g/kg, MBC: 1418.39 mg/kg, DOC: 1090.01 mg/kg; Aug.: SOC: 108.46 g/kg, EOC: 79.57 g/kg, MBC: 1369.91 mg/kg, DOC: 1316.11 mg/kg; Oct.: SOC: 109.78 g/kg, EOC: 44.37 g/kg, MBC: 1782.6 mg/kg, DOC: 671.05 mg/kg). Correlation analysis revealed significant relationships between SOC and LOC components (p < 0.05, r EOC = 0.43, r MBC = 0.46, r DOC = 0.17) but not associated with SAS (p > 0.05, r MWD = −0.07, r GMD = −0.07). Tree species composition in plantation stands significantly affects SAS and SOC pools. In conclusion, the positive effect of mixed coniferous and broad-leaved forests on SAS and SOC pools is also contingent upon the tree species identity. The results suggest that targeted selection of tree species could better enhance SAS and SOC pools in plantation than a mere increase in species richness.

Evaluating the mechanical and durability properties of sustainable lightweight concrete incorporating the various proportions of waste pumice aggregate

Traditional waste management faces significant environmental, social, and economic challenges, while concrete's high resource consumption highlights the need for improved, low-density alternatives. Consequently, lightweight concrete (LWC) has emerged as a favored solution. Recent interest in using pumice aggregate in concrete arises from its advantageous properties, such as low unit weight, which enables the construction of lighter buildings and reduces the load on structural elements. This study aimed to create lightweight, sustainable concrete using underutilized waste pumice aggregate (WPA). Concrete specimens with waste pumice aggregate ratios of 20 %, 40 %, 60 %, 80 %, and 100 % were analyzed at 7 and 28 days, with results contrasted against the virgin sample. The testing protocol encompassed detailed laboratory evaluations of concrete properties, including workability, density, strength, impact energy, ultrasonic velocity, water absorption, and cost analysis. Experimental results indicated that the inclusion of Waste pumice aggregate as a lightweight aggregate in concrete, in contrast to conventional aggregates, results in reduced workability, density, and strength metrics, as well as heightened water absorption, diminished impact energy, and lower ultrasonic pulse velocity. Sustainable or green concrete from M-20 to M-60 along strength ≥17 MPa is for load-bearing applications, while M-80 and M-100 whose strength is <17 MPa are for non-load-bearing uses.

Contributions of mineral and organic cement agents to soil aggregation under potato production in Eastern Canada

Soil aggregation, a critical determinant of soil health and quality, results from the bonding of soil particles by various cementing agents, such as soil organic carbon, biota, ionic bridging, clay, and carbonates. This process varies across soil profiles due to agricultural practices and weathering disturbances. In this study, we analyzed the contribution of different cementing agents to soil aggregation within three soil horizons (Ap1, Ap2, and B) in potato production in Eastern Canada. We collected soil samples from 29 sites in Quebec Province for aggregate-size distribution analysis and cementing agent determination. Our findings reveal variations in aggregate proportions among the horizons, with horizon B exhibiting a smaller proportion of 2–4.75 mm aggregates (10.42%) compared to horizons Ap1 and Ap2 (20.28% and 18.71%, respectively). The hierarchy of cementing agents' impact on soil aggregation ranks polyvalent metals as the most influential, followed by organic matter (C&N) and silts and clays. However, accurately estimating aggregate stability through regression analysis based on these selected cementing agents remains challenging.

Changes in plant carbon inputs alter soil phosphorus dynamics in a coniferous forest ecosystem in subtropical mountain area

Plant carbon input aboveground and underground influences soil biological and physicochemical processes in forest ecosystems. However, compared with the well-known interactions between plant carbon and soil carbon or nitrogen, the impact on soil phosphorus (P) dynamics remains unclear. Here we investigated soil P dynamics in aggregates and bulk soil after one-year of plant carbon removal treatments (RL, removing litter; TG, tree girdling; RLTG, combination of removing litter and tree girdling; CK, control) under subtropical Pinus yunnanensis forest in a soil P-enriched degraded mountain area. Compared to CK, tree girdling significantly decreased the macroaggregate proportion and increased the microaggregate proportion by changing soil total carbon (TC) and Fe concentration. With the decrease of soil TC, the increase of HCl-Pi (inorganic P extracted by HCl) in microaggregate and silt and clay was significantly higher than that in macroaggregate. In addition, easily-available P and non-available P at bulk soils significantly declined and increase under RL and TG treatments, respectively. Redundancy analysis revealed that Fe, TC, and acid phosphatase activity were the main factors affecting P fractions in bulk soils. Higher δ18OP (oxygen isotope composition of phosphate) values of HCl-Pi pool and its significantly negative relationship with soil TC across the all carbon removal treatments, suggesting the weakened ability for plant to unlock soil bioavailable inorganic P combined with minerals induced by different plant carbon removal treatments. Overall, our results highlight that the importance of litter and root carbon in regulating soil P fractions and dynamics by altering the proportion of soil aggregates and the physicochemical properties of bulk soil.

Achieving sustainable performance: synergistic effects of nano-silica and recycled expanded polystyrene in lightweight structural concrete

Lightweight concrete, particularly polystyrene concrete, has been extensively utilized in civil engineering for decades. The incorporation of waste expanded polystyrene (EPS) as a filler material in the production of lightweight concrete presents significant advantages from a circular economy perspective. Prior research indicates that increasing the proportion of lightweight aggregates, such as EPS, typically results in reductions in strength and bulk density. The utilization of substantial amounts of EPS waste in the formulation of structural polystyrene concrete is crucial for advancing sustainable construction practices. This study investigates the effects of varying nano-silica content on the bulk density, compressive strength, flexural strength, splitting tensile strength, and water penetration depth of structural polystyrene concrete. Concrete specimens were prepared by substituting 25%, 50%, 75%, and 100% of sand with EPS waste, while evaluating nano-silica contents of 0.75%, 1%, and 1.25%. The findings reveal that increasing the volume fraction of EPS corresponds to a decrease in the concrete’s bulk density. This research provides critical insights into optimizing structural lightweight concrete, thereby promoting advancements in sustainable construction applications.

Developing alkali-activated controlled low-strength material (CLSM) using urban waste glass and red mud for sustainable construction

Using industrial waste in controlled low-strength material (CLSM) offers many benefits and addresses waste management issues. However, identifying optimal CLSM design while balancing environmental impacts and engineering properties poses a notable challenge. Herein, new alkali-activated CLSM formulations based on urban waste glass and red mud (RM) are proposed for the first time with systematic investigations into the material properties and sustainability. The formulations involve the ternary blends of slag, glass powder (GP) and RM as the binders and crushed glass as aggregate. Our observations show RM has a clay-like texture with complex crystalline phases rich in Al and Fe. Increasing the proportion of RM to GP notably decreases the flowability, extends the setting time and impairs the mechanical properties. Nevertheless, red mud demonstrates a crucial role of reducing bleeding level especially for the mixtures with high proportions of glass aggregate. The standard leachate tests as per toxicity characteristic leaching procedure (TCLP) show the heavy metals leached from the CLSM are below the concentration limits and exhibit low mobility. The microstructural and thermodynamic analyses reveal the precipitation of calcium-(sodium-)aluminosilicate hydrate (C-(N-)A-S-H) as the major binding material. The reactive Fe and Al in red mud most probably contribute to the formation of hydrogarnet phases. Moreover, the suggested CLSM formations typically exhibit reduced carbon emissions and lower costs compared to the traditional CLSM produced with cement and fly ash, underlining their environmental sustainability and cost-effectiveness. This study provides a potential guideline for the flowable fill construction in the regions with bauxite producers.

Early age time-dependent mechanical properties of 3D-printed concrete with coarse aggregates

Incorporating coarse aggregate into 3D-printed concrete is essential for promoting its practical application, yet the impact on the early age time-dependent mechanical properties, crucial for the multilayer structure stability and quality, is underexplored. In this study, 3D-printed concrete with coarse aggregate (3DPCA) with varying mortar-to-coarse aggregate ratios (M/A) and coarse aggregate gradations were prepared, of which uniaxial unconfined compression and direct shear performance were experimentally investigated. The fundamental formulations between the early age mechanical parameters and the resting time of 3DPCA were characterized and then utilized in a digital model simulating actual printing. Results indicated that the 3DPCA early age mechanical properties, including compressive strength, Young's modulus, cohesion, and friction angle, increased with longer resting time and decreasing M/A, and higher proportions of aggregates above 9.5 mm. High coarse aggregate content caused three distinct compressive strength-displacement curve stages and complicated strength eigenvalue extraction. Coarse aggregate gradation affected shear properties more than content, with larger aggregates improving cohesion and friction angles. The failure mode prediction model based on ABAQUS could accurately predict the maximum collapse layer of 3DPCA that occurred in overall unstable collapse and over-expansion failure but was incapable of localized deformation.

The effects of roots and earthworms on aggregate size distribution and their associated carbon under contrasting soil types and soil moisture conditions

Soil’s potential as a carbon sink is uncertain due to biotic and abiotic interactions. Soil aggregates are important carriers of organic carbon (OC), and clarifying the response of aggregates and their associated OC to plant roots and earthworms can better understand the carbon cycle in terrestrial ecosystems. Herein, we determined the regulatory role of plant roots (Lolium perenne) and earthworms (Metaphire tschiliensis) in isolation and in combination on aggregate size distribution and their associated OC and readily oxidizable OC (ROOC) under contrasting soil types (Phaeozems and Anthrosols) and soil moisture conditions (constant wetting, CW; wetting–drying cycle repeated four times, 4WD) by a laboratory microcosm experiment. Results showed that earthworm presence significantly increased plant biomass by 30 % and 221 % in Phaeozems and Anthrosols, respectively (p < 0.05). For Phaeozems, plant alone (P) and plant and earthworm in combination (PE) had lower proportion of large aggregate (5–8 and 2–5 mm) than bare soil (CK) under 4WD condition (p < 0.05). For Anthrosols, the PE treatment decreased the proportion of 5–8 and 2–5 mm aggregate by 45 % and 25 %, respectively, under CW condition, and decreased the proportion of 5–8 mm aggregate by 37 % under 4WD condition (p < 0.05). Moreover, the proportion of 5–8 and 2–5 mm aggregate in P treatment was lower under CW condition (6.92 % and 22.13 %) but was higher under 4WD condition (11.49 % and 32.55 %) than those in CK (14.69 % and 29.91 %; 8.85 % and 20.56 %) (p < 0.05). Our results further indicated that the PE treatment had relatively higher OC and ROOC contents, especially for small aggregates in Anthrosols. The study indicates that plant roots and earthworms significantly influence aggregate turnover and the carbon cycle, with soil type and moisture playing a crucial role.

Influence of long-term ecological reclamation on carbon and nitrogen cycling in soil aggregates: The role of bacterial community structure and function

Understanding the influence of microbial taxa and functions on soil carbon (C) and nitrogen (N) cycling, particularly concerning soil aggregate sizes, is crucial for ecosystem management. This study examines the taxonomic and functional dynamics of soil bacterial communities within different aggregate sizes over time. Soil samples from a reclamation forest on the Loess Plateau in North China were collected across reclamation ages of 0, 3, 18, and 28 years. Soil aggregates were categorized into large macro-aggregates (>2000 μm), small macro-aggregates (250–2000 μm), and micro-aggregates (<250 μm) using a modified dry-sieving method. Soil aggregate stability, C and N concentrations, newly derived plant C, enzyme activities, bacterial communities, and functional genes in each aggregate fraction were systematically analyzed. There was a notable increase in soil aggregate stability and a higher proportion of large aggregates was found with increasing forest age. There were significant differences in bacterial community structures, particularly between micro-aggregates and large macro-aggregates and across different forest ages. Reclamation led to an increased abundance of copiotrophic bacterial taxa. Decreases in N-acquiring enzyme activity in micro-aggregates were contrasted by an increase in C, N, and phosphorus (P) acquisition activities in larger aggregates over time. Larger aggregates showed a faster recovery of C and N cycling genes accompanied by a significant enhancement in acetyl-CoA and ammonia oxidation processes, underscoring their importance in soil nutrient cycling. These results highlight the critical role of aggregate size in shaping microbial community structures and functions that influence soil C and N cycling during reclamation and provide new perspectives highlighting the significance of incorporating aggregate size considerations into soil management and reclamation strategies.