Aggregates Of Different Sizes Research Articles

Phosphatase activities and available nutrients in soil aggregates affected by straw returning to a calcareous soil under the maize–wheat cropping system

The objective of this study was to investigate the effects of different rates of straw returning on soil aggregate stability, phosphatase activities, and the available nitrogen (N) and phosphorus (P) within different soil aggregate sizes. The experiment included five treatments: 1) no straw returning and no chemical fertilizer, 2) chemical fertilizer only (150 kg N ha-1, 75 kg P ha-1, and 75 kg K ha-1), 3) 20% straw returning with chemical fertilizer, 4) 60% straw returning with chemical fertilizer, and 5) 100% straw returning with chemical fertilizer. Soil samples were collected 3.5 years after the start of the experiment and separated into four aggregate sizes (<0.25 mm, 0.25–1 mm, 1–2 mm, and 2–7 mm) using the dry sieving method. Soil acid phosphomonoesterase (AcP) and alkaline phosphomonoesterase (AlP); phosphodiesterase (PD); pyrophosphatase (PrA) activities; and soil NO3−−N, NH4+−N, and resin-P were determined within soil aggregates. The results showed that straw returning rates did not significantly impact soil aggregate distribution. However, straw returning increased soil AcP, AlP, and PD in <2 mm aggregates, and high rates of straw returning led to high enzyme activities. Soil phosphatase activities were also higher in 1–2 mm aggregates. All straw returning and chemical fertilization treatments increased soil NO3−−N and resin-P concentrations but had much less effect on soil NH4+−N concentrations. Additionally, the study revealed that soil pH, the concentrations of NH4+−N, NO3−−N, resin-P, and CaCO3 significantly influenced soil phosphatase activities, but their impact varied across different sizes of aggregates.

Astrocytic clearance and fragmentation of toxic proteins in Alzheimer’s disease on large-scale brain networks

The human brain is the most complicated biological structure on the planet. A major challenge of brain network modelling lies in its multi-scale spatio-temporal nature, covering scales from synapses to the whole brain. The coupled multiphysics and biochemical activities which spread through such a complex system shape brain capacity inside a structure-function relationship that requires a particular mathematical framework. Next-generation coupled-based mathematical modelling approaches to brain networks and the analysis of data-driven dynamical systems are needed to advance state-of-the-art therapeutic strategies for treating neurodegenerative diseases (NDDs) that affect millions of people worldwide, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). Importantly, AD is marked by the presence of amyloid-beta (Aβ) plaques and tau (τ) proteins. Some disease-specific misfolded proteins can interact with healthy proteins to form long chains and aggregates of different sizes that have different transport properties and toxicity. An improved large-scale brain network model is proposed here to understand the pathogenesis of AD, especially the role of astrocytes in the presence of misfolded proteins (Aβ and τ). The idea involves astrocytic clearance, which assists in eliminating toxic Aβ via fragmentation. We use the general Smoluchowski theory of nucleation, aggregation, and fragmentation to predict the development and propagation of aggregates of misfolded proteins in the brain. It has been shown that the developed model leads to different size distributions and propagation along the network. We predicted that astrocytic clearance varies with the aggregate size, which is key to slowing down AD progression. The clearance and fragmentation of toxic proteins span several spatial and temporal scales, and this research will potentially yield new insight into the associated processes and brain networks in health and disease. Detailed multi-scale brain modelling provides a promising approach for consolidating, organizing, and bridging the data sets of data-driven brain network models.

Mesoscopic Mechanical Properties of Aggregate Structure in Asphalt Mixtures and Gradation Optimization.

Particle media are widely used in engineering and greatly influence the performance of engineering materials. Asphalt mixtures are multi-phase composite materials, of which coarse aggregates account for more than 60%. These coarse aggregates form a stable structure to transfer and disperse traffic loads. Therefore, knowing how to adjust the structural composition of coarse aggregates to optimize their performance is the key to optimize the performance of asphalt mixtures. In this study, the effects of different roughness and different sizes on the interlocking force and contact force of coarse aggregates were investigated through means of simulation (DEM), and then the formation-evolution mechanism of the coarse aggregate structure and the role of different sizes of aggregates in the coarse aggregate structure were analyzed. Subsequently, the optimal ratio of coarse aggregates was explored through indoor tests, and finally, the gradation of asphalt mixture based on the optimization of fine structure was formed and verified through indoor tests. The results showed that the major model can effectively reveal the role of different types of aggregates in the fine structure and the relationship between the strength of contact forces between them and clarify that the strength of the fine structure increases with the increase in aggregate roughness. Hence, the coarse aggregate structure can be regarded as a contact force transmission system composed of some strong and sub-strong contact forces. Their formation-evolution mechanism can be regarded as a process of the formation of strong and sub-strong contact forces and the transformation from sub-strong contact force to strong contact force. Moreover, the dynamic stability of the optimized graded asphalt mixture was increased by 30%, and the fracture toughness was increased by 26%.

Spatiotemporal Assembly and Immigration of Heterotrophic and Anammox Bacteria Allow a Robust Synergy for High-Rate Nitrogen Removal.

The novel partial denitrification-driven anammox (PD/A) is an energy-efficient method for nitrogen removal from wastewater. However, its stability and efficiency are impeded by the competition between heterotrophic denitrifying bacteria and relatively slow-growing anammox bacteria. In this study, a PD/A granular sludge system was developed, which achieved a nitrogen removal efficiency of 94% with 98% anammox contribution, even as the temperature dropped to 9.6 °C. Analysis of bacterial activity in aggregates of different sizes revealed that the largest granules (>2.0 mm) exhibited the highest anammox activity, 2.8 times that of flocs (<0.2 mm), while the flocs showed significantly higher nitrite production rates of PD, more than six times that of the largest granules. Interestingly, fluorescent in situ hybridization (FISH) combined with confocal laser scanning microscopy (CLSM) revealed a nest-shaped structure of PD/A granules. The Thauera genus, a key contributor to PD, was highly enriched at the outer edge, providing substrate nitrite for anammox bacteria inside the granules. As temperature decreased, the flocs transformed into small granules to efficiently retain anammox bacteria. This study provides multidimensional insights into the spatiotemporal assembly and immigration of heterotrophic and autotrophic bacteria for stable and high-rate nitrogen removal.

The aggregation effect of organic matter on bauxite residue particles and its improvement mechanism

Introduction: Understanding organic amendment and the agglomeration of bauxite residue particles is vital to soil amelioration of bauxite residues. In this study, a pot culture experiment was conducted to illustrate the aggregation of organic amendment on bauxite residues particles and its improvement mechanism. The single organic amendment and its combination with soil inoculum were conducted to explore the aggregation effect of organic matter on bauxite residue particles, and its correlations with microbial rehabilitation.Methods: The dry- and wet-sieving method were used to obtain different sizes of aggregates. The concentrations of soil organic carbon and iron and aluminum (Fe/Al) oxides in the forms extractable by DCB (Fed/Ald) and oxalate (Fe0/Al0) were measured. Microbial rehabilitation after 180 days incubation was determined with the methods of Biolog Ecoplate™ and the high-throughput sequencing.Results and Discussion: The results showed that over 180 days incubation, the alkalinity of bauxite residues was significantly decreased with the organic amendment based on the value of pH, EC and ESP (down to 9.26, 0.61 m/cm and 55.5%, respectively, in HS3). Secondly, organic amendment significantly promoted microbial community establishment and ecological function recovery. Moreover, the MWD value of aggregates also increased to 0.73 mm from the initial 0.32 mm, companied with the increase of the Fe/Al oxidizes. The further Pearson relationship analysis and the characterization of EPMA and SEM indicated that the organic matter and Fe/Al oxides played important roles in cementing fine bauxite residues particles and increasing aggregates stability, while this aggregation process was accelerated by the establishment of microbial ecology in bauxite residues. Therefore, organic amendment was more implication in soil amelioration of bauxite residues other than the directive modifications on alkalinity.

Study on the Influence of Specimen Size and Aggregate Size on the Compressive Strength of Rock-Filled Concrete

Rock-filled concrete (RFC) technology is a new type of mass concrete construction technology, which consists of two basic components: the force transfer frame formed by large-size rock accumulation and the matrix formed by self-compacting concrete (SCC) filling. Its unique construction method also distinguishes RFC from ordinary concrete in terms of its force characteristics. In this paper, RFC is considered as a composite material consisting of aggregate and SCC; based on the realistic failure process analysis (RFPA) method, the effects of specimen size and aggregate size on the compressive strength of RFC were studied. Firstly, RFC cube specimens were prepared and uniaxial compression tests were conducted. During the preparation process, in order to eliminate the influence of factors such as shape, spatial distribution state, and volume share of aggregates on the compressive strength, aggregates of different sizes were set as spheres and arranged in simple cubic stacking; then a numerical model of RFC with different specimen sizes and different aggregate sizes was established for uniaxial compression numerical simulation experiments to analyze the variation law and failure pattern of the RFC compressive strength. The results indicate that the compressive strength of RFC exhibits a significant size effect and follows a negative exponential function distribution law; with the same volume fraction of aggregate, the smaller the aggregate size, the higher the compressive strength of the RFC will be, and this increasing trend gradually levels off. Based on the findings of this study, it is recommended that the size effect and the reduction of aggregate size on dam strength be taken into account in the design of RFC dams.

Soil aggregates affect the legacy effect of copper pollution on the microbial communities

Soil aggregates provide spatially heterogeneous microhabitats for microorganisms and their activities. In metal contaminated soil, the microbial community is shaped by both metal stress and aggregate sizes. However, it remains unclear whether and how aggregate sizes affect the legacy effect of metal pollution on microbial communities. Here, we investigated the legacy effect of long-term copper (Cu) pollution on the distribution patterns of the bacterial and protistan communities in soil aggregates. Our results showed that soil aggregates of different sizes possessed distinct bacterial and protistan communities under Cu-polluted and unpolluted conditions (aggregate effects), as reflected by distinct α-diversity and community compositions. The bacterial and protistan communities in micro- and macro-aggregates were more responsive to Cu pollution than those in mega-aggregates, primarily because micro- and macro-aggregates contained a greater number of Cu susceptible bacterial and protistan species. Ciliophora and Chlorophyta displayed great sensitivity to Cu, especially in small aggregate-size fractions, and could serve as a bio-indicator of Cu pollution. Furthermore, the magnitude of aggregate effects on microbial communities was weakened in Cu-polluted soils compared to unpolluted soils. With decreasing aggregate sizes, the co-occurrence networks between bacteria and protists became more complex, connected and compact. Robustness analysis showed that phagotrophic protists played essential roles in sustaining the network stability, especially in mega-aggregates. Our findings highlight the asymmetrical changes in microorganisms in aggregates under long-term Cu pollution, providing a novel insight into the legacy effects of metal pollution on soil microbiomes at the micro-level.

Microbial functional genes within soil aggregates drive organic carbon mineralization under contrasting tillage practices

AbstractSoil organic carbon (SOC) transformation is susceptible to tillage practices. Conservation tillage is known to optimize soil structure, improve microbial community diversity and increase SOC storage. However, how soil aggregate distribution and microbial community structure and function within aggregates affect SOC transformation under long‐term conservation tillage remains unclear. In this study, SOC mineralization dynamics were studied in situ and under laboratory conditions to examine the mechanisms by which C functional genes within soil aggregates of different sizes (i.e., mega‐, macro‐, and micro‐aggregates) influence SOC mineralization under long‐term tillage (i.e., zero, chisel, and plow tillage) in a dryland. The results indicated that in the winter wheat and summer maize rotation cropping system, SOC‐derived CO2‐C emissions were 143.99 and 133.29 g CO2‐C m−2 h−1 lower under chisel and zero tillage than that under plow tillage, respectively. Moreover, after 180 days of laboratory incubation, SOC mineralization in micro‐ and macro‐aggregates was 1.98 and 1.63 mg CO2‐C g−1 d−1 higher than that in mega‐aggregates, respectively. The aggregate‐associated differential modules of bacterial co‐occurring networks may be directly governed by bacterial community diversity and composition, which might play critical roles in driving SOC mineralization in response to different tillage intensities. Moreover, aggregate‐associated functional genes involved in labile and recalcitrant C compositions, which were determined by shotgun metagenomic sequencing, were associated with SOC mineralization and were significantly affected by the legacy effect of tillage intensity and aggregate size. Particularly, partial least squares path modeling revealed that genes involved in simple sugar metabolism exerted significantly positive effects on SOC mineralization, except for the effects of tillage intensity and aggregate size. Overall, this study showed that decreased abundances of labile C decomposition‐related functional genes within aggregates and community composition changes, as elucidated by the differences in bacterial network modules, under conservation tillage inhibit SOC mineralization. These findings may help in the development of adaptive soil tillage strategies for reducing carbon emissions in agroecosystems.

Discrete element modelling of the uniaxial compression behavior of pervious concrete

Pervious concrete (PC) has been widely used in recent years. With increasing attention on PC, it promotes further understanding of its mechanism responsible for the resulted performance. The objective of this study is to propose a 3D discrete element method (DEM) model to simulate the uniaxial compression process and analyze the meso mechanical properties of PC. The user-defined ellipsoid composed of pebble discrete elements was used to simulate aggregate. In the DEM, the mechanical behaviors of materials were simulated with contact constitutive models of discrete elements. The linear contact model and parallel-bond model were employed to simulate the strength properties between two adjacent aggregates, and between cement paste and aggregate. The parallel-bond parameters were calibrated based on the stress-strain curve obtained from the laboratory test. The reliability of the method was verified by comparing the virtual results with the laboratory tests of PC with 6 groups of different aggregate sizes. It was proved that the DEM model established can be used to simulate the rising section of the stress-strain curve of PC accurately. The maximum absolute error of uniaxial compressive strength is 0.67 MPa, and the relative error is within 5%. By analyzing the number of contact points, the contribution rate of different sizes of aggregates to the contact force and the distribution of the force chain, it can be concluded that the coarse aggregate plays a major role in resisting compression load in PC, while fine aggregate mainly increases the number of contact points to achieve force transmission.

Long-term combined organic manure and chemical fertilizer application enhances aggregate-associated C and N storage in an agricultural Udalfs soil.

Little information is known on whether carbon (C) and nitrogen (N) immobilization is synchronized in different sizes of aggregates under different agricultural management practices. Carbon and N concentrations and the C/N ratios in different sizes of aggregates down to 40 cm depth were determined after long-term application of chemical fertilizers combined with manure or without manure in a wheat-rice cropping system. Manure application usually produced significantly (P < 0.05) higher C and N concentrations and lower C/N ratios in bulk soil and in different sizes of aggregates down to 20 cm depth than the other treatments, and the 1.5 MNPK treatment at 0-10 cm depth had the highest SOC concentration of 26.3 g/kg. The C and N concentrations in bulk soil and all aggregate fractions decreased markedly with increasing soil depth. Among water stable aggregates in all soil depths, the highest C (48.2-66.4%) and N (47.8-68.3%) concentrations as a percentage of SOC were found in the small macroaggregates (2000-250 μm, SM). Manure application significantly (P < 0.05) increased the mass and C and N concentrations of SM and SM fractions down to 20 depth. The mean C/N ratios of silt-clay within large and small macroaggregates (inter-SC) were 1.57 and 1.46 units lower than those of silt-clay particles, respectively, indicating that inter-SC had relative high N availability. Moreover, the C and N content of SM down to 40 cm depth tended to saturation with increasing C input rate. Overall, manure application effectively improved soil structure, SM were the dominant particles involved in soil C and N storage, and inter-SC were the main particles responsible for N availability.

Alterations of ecosystem nitrogen status following agricultural land abandonment in the Karst Critical Zone Observatory (KCZO), Southwest China.

Secondary succession after agricultural land abandonment generally affects nitrogen (N) cycle processes and ecosystem N status. However, changes in soil N availability and NO3 - loss potential following secondary succession are not well understood in karst ecosystems. In the Karst Critical Zone Observatory (KCZO) of Southwest China, croplands, shrub-grass lands, and secondary forest lands were selected to represent the three stages of secondary succession after agricultural land abandonment by using a space-for-time substitution approach. The contents and 15N natural abundance (δ 15N) of leaves, soils, and different-sized aggregates at the three stages of secondary succession were analyzed. The δ 15N compositions of soil organic nitrogen (SON) in aggregates and soil to plant 15N enrichment factor (EF = δ 15Nleaf -δ 15Nsoil), combined with soil inorganic N contents and δ 15N compositions were used to indicate the alterations of soil N availability and NO3 -loss potential following secondary succession. Leaf N content and SON content significantly increased following secondary succession, indicating N accumulation in the soil and plant. The δ 15N values of SON also significantly decreased, mainly affected by plant δ 15N composition and N mineralization. SON content in macro-aggregates and soil NH4 + content significantly increased while δ 15N values of NH4 + decreased, implying increases in SON stabilization and improved soil N availability following secondary succession. Leaf δ 15N values, the EF values, and the (NO3 --N)/(NH4 +-N) ratio gradually decreased, indicating reduced NO3 - loss following secondary succession. Soil N availability improves and NO3 - leaching loss reduces following secondary succession after agricultural land abandonment in the KCZO.

Divergent responses of phoD- and pqqC-harbouring bacterial communities across soil aggregates to long fertilization practices

Microbial community composition differs between soil aggregate sizes, which markedly affects phosphorus cycling in agroecosystems. The genes phoD and pqqC regulate phosphorus mobilization and act as molecular markers of phosphate-mobilizing bacteria, but differences in phoD- and pqqC-harbouring bacterial communities between different-sized aggregates remain unclear. The abundance and community composition of phoD- and pqqC-harbouring bacteria were determined in three aggregate size classes (> 250, 63–250, and < 63 µm) in calcareous soil from northwest China in a 38-year experiment. The > 250 and < 63 µm aggregates showed the lowest and highest cumulative relative abundance, respectively, of operational taxonomic units in phoD- and pqqC-harbouring bacterial communities. Simpler co-occurrence networks (fewer nodes, links, and shorter network diameter) were found in > 250 and < 63 µm aggregates, compared to 63–250 µm aggregates. For phoD and pqqC gene networks, > 250 and < 63 µm aggregates (phoD: α-Proteobacteria and Actinomycetia; pqqC: Actinomycetia) contained keystone taxa distinct from 63 to 250 µm aggregates (phoD: Rubrobacteria and γ-Proteobacteria; pqqC: β-Proteobacteria). Total nitrogen (TN) and Olsen-P significantly affected the abundance and community richness of phoD- and pqqC-harbouring bacteria. phoD and pqqC gene abundance was determined by TN in > 250 µm aggregates, whereas they were indirectly determined by Olsen-P in < 63 µm aggregates. Our results emphasized the distinct distribution characteristics of phosphate-mobilizing bacterial communities in different-sized aggregates and identified the main factors regulating phoD and pqqC gene abundance.

Diversity and assembly of active bacteria and their potential function along soil aggregates in a paddy field

Numerous studies have found that soil microbiomes differ at the aggregate level indicating they provide spatially heterogeneous habitats for microbial communities to develop. However, an understanding of the assembly processes and the functional profile of microbes at the aggregate level remain largely rudimentary, particularly for those active members in soil aggregates. In this study, we investigated the diversity, co-occurrence network, assembly process and predictive functional profile of active bacteria in aggregates of different sizes using H218O-based DNA stable isotope probing (SIP) and 16S rRNA gene sequencing. Most of the bacterial reads were active with 91 % of total reads incorporating labelled water during the incubation. The active microbial community belonged mostly of Proteobacteria and Actinobacteria, with a relative abundance of 55.32 % and 28.12 %, respectively. Assembly processes of the active bacteria were more stochastic than total bacteria, while the assembly processes of total bacteria were more influenced by deterministic processes. Furthermore, many functional profiles such as environmental information processing increased in active bacteria (19.39 %) compared to total bacteria (11.22 %). After incubation, the diversity and relative abundance of active bacteria of certain phyla increased, such as Proteobacteria (50.70 % to 59.95 %), Gemmatimonadetes (2.63 % to 4.11 %), and Bacteroidetes (1.50 % to 2.84 %). In small macroaggregates (SMA: 0.25-2 mm), the active bacterial community and its assembly processes differed from that of other soil aggregates (MA: microaggregates, <0.25 mm; LMA: large macroaggregates, 2-4 mm). For functional profiles, the relative abundance of important functions, such as amino acid metabolism, signal transduction and cell motility, increased with incubation days and/or in SMA compared to other aggregates. This study provides robust evidence that the community of active bacteria and its assembly processes in soil aggregates differed from total bacteria, and suggests the importance of dominant active bacteria (such as Proteobacteria) for the predicted functional profiles in the soil ecosystem.

The severity of platelet activity in young cattle of the Kholmogory breed at the end of early ontogenesis

Of great scientific interest is the assessment of the functionality of platelets in dairy calves at the end of early ontogenesis. 44 healthy calves of the Kholmogory breed were observed, obtained from completely healthy cows after their 2nd-3rd pregnancy. During the observation period, the young animals developed an acceleration of the process of platelet aggregation in vitro. This was accompanied in calves by an increase in the number of activated platelets in the blood and the number of their aggregates of different sizes. An increase in the functionality of platelets occurred in calves during the phase of plant nutrition due to an increase in the amount of all adenosine phosphates, an increase in the synthesis of thromboxane in them, an increase in the content of actin and myosin in them, and an intensification of their self-assembly in the case of the participation of platelets in hemostasis. The increase in hemostatic capabilities noted in calves of the Kholmogory breed is of great importance for the success of their growth and development processes during the phase of plant nutrition.

Investigation on dynamic response and compaction degree characterization of multi-layer asphalt pavement under vibration rolling

&lt;abstract&gt; &lt;p&gt;Asphalt mixture is composed of asphalt binder with aggregates of different sizes and compacted under static or dynamic forces. In practical engineering, compaction is a critical step in asphalt pavement construction to determine the quality and service life of pavement. Since the dynamic response characteristics of asphalt pavement can reflect the compaction state of asphalt mixture in the process of compaction, the establishment of the relationship between dynamic response characteristics and compaction degree is definitely significant. In this paper, a series of vibration sensors were adopted to capture the dynamic response signal of the vibration drum and asphalt mixture in the process of vibrating compaction for different surface courses of pavement. Then, the change regulations of vibration acceleration of vibrating drum and asphalt mixture were analyzed, and the quantitative linear relationship was established between accelerations of vibrating drum and asphalt pavement compactness. Further, the concept of evaluation unit (i.e., within 2 meters along the driving direction of the roller) and prediction method of compaction degree were proposed as well. The results showed that under the same vibration compaction condition, the compaction degree values of the top, middle and bottom layers have obvious differences, which should be taken seriously into consideration in the compaction process. Meanwhile, there is little difference which respectively are 2.8, 1.3 and 0.82% for the top, middle and bottom layers between the compaction degrees obtained by the proposed method and measured test. Therefore, the average value of the acceleration peak value of vibration drum within the evaluation unit can be adopted as the characterization index of the compaction degree of asphalt pavement. The investigation of this study can provide the technical reference for compaction control of asphalt pavement to a large extent.&lt;/p&gt; &lt;/abstract&gt;

A Review Analysis on Effect of Different Sizes of Aggregates on Self Compacting Concrete as an Innovative Development in Concrete Construction

A Review Analysis on Effect of Different Sizes of Aggregates on Self Compacting Concrete as an Innovative Development in Concrete Construction

Effect of Ionic Strength on Heat-Induced Gelation Behavior of Soy Protein Isolates with Ultrasound Treatment.

This study investigated the effect of ultrasound on gel properties of soy protein isolates (SPIs) at different salt concentrations. The results showed that ultrasound could significantly improve the gel hardness and the water holding capacity (WHC) of the salt-containing gel (p < 0.05). The gel presents a uniform and compact three-dimensional network structure. The combination of 200 mM NaCl with 20 min of ultrasound could significantly increase the gel hardness (four times) and the WHC (p < 0.05) compared with the SPI gel without treatment. With the increase in NaCl concentration, the ζ potential and surface hydrophobicity increased, and the solubility decreased. Ultrasound could improve the protein solubility, compensate for the loss of solubility caused by the addition of NaCl, and further increase the surface hydrophobicity. Ultrasound combined with NaCl allowed proteins to form aggregates of different sizes. In addition, the combined treatment increased the hydrophobic interactions and disulfide bond interactions in the gel. Overall, ultrasound could improve the thermal gel properties of SPI gels with salt addition.

Insights into the Effect of Aggregate Sizes on the Soil Radiation Interaction Properties Based on X-ray Fluorescence.

Soils subjected to disaggregation can break into aggregates of different sizes composed of sand, clay, and silt particles. Each aggregate contains different oxides, which can vary according to the aggregate size and influence its properties, such as the radiation interaction parameters. These parameters are relevant in the evaluation of radiation shielding and soil physical properties. Thirteen tropical/subtropical soils of contrasting textures (clayey and loamy/sandy) with two aggregate sizes (2-1 mm and <45 μm) were studied. The radiation parameters analyzed were the atomic (σA), electronic (σE), and molecular (σM) cross-sections; the effective atomic number (Zeff); and the electron density (Nel). We verified that the aggregate sizes affected the major oxides (SiO2, Al2O3, Fe2O3). In general, the attenuation coefficient and Zeff were sensitive to the clayey soils' aggregate sizes (low photon energies). However, the loamy/sandy soils did not exhibit differences among the parameters. As the photon energy increased, only Zeff presented differences for most soils. We also verified that σM, Zeff, and Nel were the most sensitive parameters to the soil composition. Although the soil chemical composition was influenced by the studied aggregate sizes, the radiation parameters exhibited differences for only some of these parameters. This means that the aggregate size is practically irrelevant when radiation parameters are determined based on X-ray fluorescence.

Particulate and mineral-associated organic carbon fractions reveal the roles of soil aggregates under different land-use types in a karst faulted basin of China

Soil aggregation has been recognized as the main mechanism of organic carbon (C; OC) stabilization, and OC dynamics within aggregates are closely linked to soil OC (SOC) sequestration. To unravel the roles of different-sized aggregates and the associated OC fractions in SOC accumulation, SOC stocks (SOCS), aggregate distributions, and OC fractions within aggregates were measured under five typical land-use types (cropland, grassland, shrubland, plantation forest, and natural forest) in a karst faulted basin, China. Land-use type had distinct effects on SOCS in the topsoil (0–10 cm) and along the soil profile (0–60 cm), and the primary factors influencing SOCS varied with the soil horizons. Plantation forest had the highest SOCS (51.2 Mg C ha−1) in the topsoil, whereas the SOCS in shrubland (182.7 Mg C ha−1) was distinctively higher than those of other land-use types across the soil profile. Soil microbial biomass C and mean weight diameter were the major factors driving SOCS variation in the topsoil layer and the entire soil profile, respectively. OC content within macroaggregates (>0.25 mm) was significantly positively correlated with the SOC content of bulk soil, whereas only the mass proportion of large macroaggregates (>2 mm) showed a positive relationship with SOC. Additionally, mineral-associated OC (MAOC) was the dominant fraction of SOC and was abundant in macroaggregates. However, particulate OC (POC) within aggregates was relatively enriched in the topsoil and microaggregates. Considering the decomposition and distribution characteristics of OC fractions in different-sized aggregates, we suggest that the POC/MAOC ratios of macro- and microaggregates could respectively reflect aggregate capacity to sequestrate MAOC and POC across different land-use types. Overall, shrubland is the optimal land-use type for rocky desertification control in the karst fault basin, due to the protection of POC and MAOC within different-sized aggregates.

Analytical evaluation of compressive strength for concrete with rubber fine aggregates and the predictive model

Recycling scrap tires as alternatives to materials to produce rubberized concrete will facilitate environmental protection and considerable conservation of natural resources. The accurate prediction of compressive strength for rubberized concrete will promote their development and application. In order to predict the compressive strength of rubberized concrete further accuracy, the rubberized concrete with rubber fine aggregates of different sizes, contents and pretreatment methods in compressive strength of 16.5–34.3 MPa were designed in this paper, and their cubic compressive strength was studied. Then, effects of the rubber aggregates on concrete mesostructure and the influence mechanism on compressive strength were analyzed through the technology of computed tomography and scanning electron microscope, as well as analyses of void structure of hardened concrete. The regularity of the varying cubic compressive strength of rubberized concrete with changing rubber size, content and the pretreatment method was clarified. The influence mechanism of the rubber on concrete compressive strength was revealed. Finally, a forecast model of cubic compressive strength for rubberized concrete with a good predictive ability was proposed, which can provide good references for design and engineering application of rubberized concrete.