Percentage Of Macropores Research Articles

Applicability of a Fractal Model for Sandstone Pore-Fracture Structure Heterogeneity by Using High-Pressure Mercury Intrusion Tests

Pore structure heterogeneity affects the porosity and permeability variation of tight sandstone, thereby restricting sandstone gas production. In total, 11 sandstone samples were taken as a target in the northwest margin of the Junggar Basin. Then, scanning electron microscope and high-pressure mercury injection tests are used to study the distribution of a pore and fracture system in the target sandstone. On this basis, single and multifractal models are used to quantitatively characterize the heterogeneity of pore structure, and the applicability of the classification model in characterizing the heterogeneity of the pore-fracture structure is explored. The results are as follows. (1) The target samples are divided into two types, with the mercury removal efficiency of type A samples ranging from 44.6 to 51.8%, pore size mainly distributed between 100 and 1000 nm, and pore volume percentage ranging from 43 to 69%. The mercury removal efficiency of type B samples ranges from 14 to 28%, and pore diameter distribution is relatively uniform. (2) Different fractal models represent different physical meanings. The calculation results of sponge and thermodynamic fractal models indicate that the heterogeneity of pore structure distribution in the type B sample is significantly stronger than that in type A, which is inconsistent with the conclusions of the Sierpinski model. This is because the aforementioned two models characterize the complexity of pore surface area, while the Sierpinski model characterizes the roughness of pore volume. The comparison shows that there is a significant correlation between the thermal dimensionality value DT and the volume percentage of macropores and mesopores. Therefore, the thermodynamic model can better quantitatively characterize the heterogeneity of macropore and mesoporous pore distribution. (3) The results indicate that higher pore volume range is mainly influenced by mesopores and macropores. From the relationship curve between mercury removal efficiency and single fractal dimension, it can be seen that mercury removal efficiency is greatly affected by distribution heterogeneity of the lower value area of pore volume, and it has no obvious relationship with distribution heterogeneity in the lower value area of the pore volume.

Study on Mechanical Properties and Microscopic Mechanism of PVA-Modified Recycled Brick Aggregate Concrete

This paper addresses a range of environmental issues stemming from the improper disposal of construction waste and its low recycling rate by examining the effects and mechanisms of polyvinyl alcohol (PVA) solution in modifying recycled aggregates. Basic physical properties, energy-dispersive spectroscopy (EDS), X-Ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to study these effects and mechanisms. Tests on basic mechanical properties were performed to assess the impact of aggregate modification and the brick-concrete ratio on recycled brick-aggregate concrete’s mechanical characteristics. Nuclear magnetic resonance and microhardness tests were performed to analyze the influence exerted by PVA modification on the interfacial transition zone (ITZ), microstructure, and pore structure, thus exploring the connection between modified recycled-brick-aggregate concrete’s microstructure and its icromechanical properties. The findings show that the water absorption and crushing index of recycled aggregates (RA) immersed in a 10% PVA solution for 24 h decrease significantly, while the apparent density increases most notably. This phenomenon can be ascribed to the development of a PVA coating on the exterior of the reused aggregates. The optimal mechanical properties for recycled brick aggregate concrete (RAC) occur when the replacement rate is 30% and the brick-concrete ratio is 1:1. The compressive strength is 44.2 MPa, the bending strength is 15.6 MPa, and the splitting tensile strength is 3.85 MPa. Additionally, the modification with PVA results in a higher percentage of transition pores, while simultaneously reducing the percentage of macropores. There is an uptick in the frequency of harmless and less harmful pores, and a declining proportion of harmful and more harmful pores. The ITZ’s structural morphology in the RAC is effectively improved by the coating structure formed through the bonding of the polymer with cement hydration products, and PVA modification reduces the thickness of this zone.

Changes in mineral fraction and pore morphology of coal with acidification treatment: contribution of clay minerals to methane adsorption.

The accurate calculation of the contribution which provided by clay minerals in coal on methane adsorption not only bares a significant importance for evaluating the effectiveness of acid stimulation in improving permeability and estimating the coalbed methane reserves but also serves a guide for the governance and utilization of methane resources. In this study, hydrochloric acid (HCl) and hydrofluoric acid (HF) were used to remove specific minerals in Qingdong coal samples. We firstly analyzed the mineral compositions of coal samples with different acidification treatments based on the X-ray diffraction (XRD) experiments, together with analysis of the changes in pore morphology and adsorption capacity. The results showed that acidification did not significantly change the shape of the pores, which remained slit-/plate-like pore. However, the altered adsorption capacity of the coal samples was attributed to changes in pore structure and mineral distribution. Acid erosion of mesopores promoted the transition from mesopores to macropores, contributing to an increase of 8.4% and 24.36% in the percentage of macropores in coal samples treated with HCl and HF, respectively. Fractal dimension D1 grew from 2.2193 to 2.3888 and 2.2572, respectively, but D2 decreased from 2.6146 to 2.5814 and 2.5433, indicating an increment in pore surface roughness and a simplification of the pore structure. The mineral richness of the coal seams should be taken into consideration when applying acid stimulation to increase permeability due to that the acidification products may block the passage of gas migration when the mineral content is slight, which can hinder gas extraction. The aim of this study is to quantitatively determine the contribution rate of clay minerals in coal to methane adsorption with a calculation method is provided by combining pore parameters and limit adsorption capacity, resulting in a contribution rate of 15%.

Micromorphology of pores and water erosion in Inceptisol soil after application of pig slurry

The application of pig slurry (PS) to soil is known to change its chemical and physical properties. However, little is known about the alterations that PS causes in pore morphology and water erosion. This research evaluated the influence of PS on the morphology of the pores in the surface layer of the soil and on water erosion in an Inceptisol subjected to simulated rainfall. The soil was cultivated with black oats and the treatments (doses) 0, 50, 100 and 200 m3 ha-1 of PS were applied to the crop residue. The experimental design was completely randomized. Six simulated rainfall lasting 60 minutes and planned constant intensity of 65 mm h-1 were applied to the treatments. Undisturbed soil samples were collected in the 0-0.05 m layer, 24 h before and 24 h after the first, third and sixth rainfall events. Image analysis was performed, determining the percentage of macropores and mesopores, number, diameter and shape of the pores, using the micro morphometry technique. PS doses of 100 and 200 m3 ha-1, combined with simulated rainfall, favored surface sealing and pore rearrangement. There was an increase in the number of small and rounded pores, without interconnection between them, with a consequent increase in water erosion until the moment of stabilization of the superficial crust.
 Keywords: micro morphometry, organic fertilizer, porometry.

Aging deterioration of mechanical properties on coal-rock combinations considering hydro-chemical corrosion

Coal-rock masses located in water-rich environments, such as heavy water mines, and water-isolated coal-rock pillars installed underground, are consistently subjected to erosion from acidic groundwater. In this study, we employed various techniques including acoustic emission (AE), digital image correlation (DIC), scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), and X-ray diffraction (XRD) to investigate the evolution of mechanical properties and AE damage characteristics of coal-rock combinations under water-chemical corrosion. Moreover, we analyzed the microscopic deterioration mechanism. Our results reveal that as the acidity of the solution increases, the cumulative energy and AE count of the specimen decrease to varying degrees. The AE ringing counting process can be categorized into stable, active, and sharp development stages. Moreover, as the pH value of the solution decreases, the AE b-value follows a “V" type variation. The dynamic b-values demonstrate localized sudden drops, indicating the occurrence of large-scale cracks. The internal cracks within the coal-rock combination transform from shear cracks to tensile cracks, corresponding to a transition in failure mode from shear failure to cleavage failure. Furthermore, a detailed analysis of the deterioration mechanism of the coal-rock combination under water-rock interaction was conducted. Under on-site groundwater conditions (pH = 6.24), the overall degradation of uniaxial compressive strength (UCS) and elastic modulus reached 13.37% and 28.73%, respectively. The physical, chemical, and mechanical effects of the water-chemical solution induce microstructural changes within the coal-rock combination. Consequently, the total percentage of macropores (>1 μm) in the sandstone section increased by 8.85%, reaching 35.3%, thereby further deteriorating its mechanical properties. In contrast, the proportion of macropores in the coal section only increased by 0.95%. Therefore, water-rock action has a more severe damaging impact on the sandstone section compared to the coal section of the combination.

Multiscale analysis of pore structure in clay due to freeze-thaw

The variation of pore structure due to freeze-thaw (F-T) plays a vital role in revealing the thaw settlement mechanism of soils. In this study, remolded saturated clay specimens experienced unidirectional freezing and natural thawing in an open or closed system (i.e., with or without water supply). X-ray computed tomography (CT) and mercury intrusion porosimetry (MIP) were conducted to analyze pore structural characteristics, including macropores, mesopores, and micropores, along the temperature gradient direction before and after F-T. The longitudinal pore binary images, obtained by processing CT images, were used to assess the changes in porosity, pore shape, and orientation of macropores and mesopores due to F-T. The results indicate that the total longitudinal-sectional porosity and macropore percentage increased, whereas the mesopore percentage decreased. F-T considerably influenced the shape and orientation of macropores but had minimal effects on mesopores. The most significant changes occurred in the unfrozen zone due to F-T in an open system but near the final freezing front in a closed system. Additionally, Micropore porosity, diameter, and thermal fractal dimension were analyzed based on MIP data. The results showed that micropore porosity and diameter decreased, with significant changes occurring in the unfrozen zone of the open and closed systems. The micropore porosity and diameter decreased more in the unfrozen zone and near the final freezing front after F-T in a closed system, whereas a smaller decrease occurred in the frozen zone. The thermal fractal dimension value increases after F-T, indicating that the micropore structure became complex. In general, the multiscale pore analysis demonstrated that pore structure, including macropores, mesopores, and micropores, is significantly affected by F-T in the open system compared to the closed system.

Effect of Ultra-Fine Cement on the Strength and Microstructure of Humic Acid Containing Cemented Soil

The peat soil in the Dianchi Lake area of Yunnan, China, is widely distributed, bringing many problems to engineering. The peat soil foundation is usually treated by the cement mixing method, and the reinforcement effect of cemented soil is mainly affected by humic acid (HA). Ultra-fine cement (UFC) can improve cement performance and reduce cement consumption, decreasing CO2 emissions and the impact of human activities on the environment. Simulated peat soils in different environments are prepared with HA reagent and cohesive soil, reinforced by composite cement curing agent mixed with ultrafine cement (UFC). The relationship among the UFC proportion, HA reagent content, soaking time, and sample strength was studied. The unconfined compressive strength test (UCS), scanning electron microscope (SEM), and PCAS microscopic quantitative test techniques were used to explore the mechanism of the effect of UFC on the strength of HA-containing cemented soil. The increasing UFC proportion in the composite cement curing agent gradually increased HA-containing cemented soil’s strength. UFC significantly reduced the percentage of macropores in HA-containing cemented soil and made the microstructure denser. The HA-containing cemented soil’s qu increased the most when the UFC proportion increased from 0% to 10%. The solidification effect of the composite cement curing agent mixed with UFC was always stronger than that of OPC. The composite cement curing agent with a UFC proportion of 10% is practical. Cement is still an important building material in the current construction industry, and UFC provides a new method for reducing environmental impact in engineering construction.

Effect of carbon fiber on the properties of polymer cement based building sealant

AbstractThe working property, bond property, and mechanical property of five kinds of polymer cement based building sealant (PCBS) with different carbon fiber content were tested. The effect of carbon fiber on the properties of PCBS was discussed by analyzing the variation of the leveling performance, consistency, low temperature flexibility, surface dry time, elastic recovery rate, tensile mechanical property, and shear mechanical property of PCBS with carbon fiber content. And the modification mechanism of carbon fiber on PCBS was interpreted using scanning electron microscopy and mercury intrusion porosimetry techniques. The results shows that PCBS still has good working property and bonding property with carbon fiber addition. As the carbon fiber content increases, the leveling performance and low temperature flexibility of PCBS are unaltered., the consistency increases, while the surface drying time and elastic recovery rate decrease. The tensile and shear mechanical properties of PCBS can be improved by adding carbon fiber. With the increase of carbon fiber content, the strength performance indexes of PCBS increase, while the energy consumption performance indexes first increased followed by a decrease. When the carbon fiber content is 0.1%, the properties of PCBS is the best. The pore structure of PCBS gradually deteriorates, and the total porosity and the percentage of macropores increase with carbon fiber addition. Carbon fiber primarily exerts cracking resistance and internal deterioration effects in PCBS.

Unravelling Temperature Ramping Rates in Fabricating NaCl‐Induced Porous Co/N‐C Electrocatalysts for Oxygen Reduction Reaction

AbstractPyrolysis is a necessary procedure for synthesizing carbon‐based nonprecious metal electrocatalysts via stimulating interaction and carbonization of precursors. In this work, ramping rates that correlated with thermal gradient has been investigated to reveal the configuration evolution of the precursors. Spectra characterizations demonstrated that ramping rates affected decomposition and aromatization of precursors. Increasing ramping rates improved the percentage of doped nitrogen and defects, promoting dispersion of Co atoms in the carbonaceous matrix and increasing density of active sties. In addition, the size variation of NaCl template under different ramping rates modifies the porous structure of Co/N−C electrocatalysts, greatly increasing the percentage of macropores and micropores at rapid ramping rates. As a result, electrocatalysts obtained at 5 °C min−1 exhibit comparable catalytic activity to that of Pt/C due to highly dispersed active sites and rational percentage of porosity, facilitating the sufficient reaction of oxygen along the catalysts. These results shed lights on regulating physical properties of carbonaceous electrocatalysts.

Creep mechanical and microstructural insights into the failure mechanism of loess landslides induced by dry-wet cycles in the Heifangtai platform, China

Affected by groundwater fluctuations, the loess around the hydro-fluctuation zone near the groundwater table is frequently subjected to periodic dry-wet cycles. The investigation on the creep characteristics and microstructural evolution associated with the mechanical response of loess after the application of dry-wet cyclings is of great significance to better understand the loess landslide mechanism. Triaxial creep tests and scanning electron microscopy (SEM) were conducted on intact loess specimens obtained from Heifangtai platform, Gansu, China. The micrographs were processed using IPP software and the microstructural information of soil pores were obtained. Results of triaxial creep test revealed that the application of dry-wet cyclings causes the creep deformation of loess soils to increase significantly, and they showed that the long-term strength and dry-wet cycle follow an exponentially decreasing function, indicating that the reduction in the long-term strength of loess soils is greater in the first five dry-wet cycling compared with that in the subsequently dry-wet cyclings. The microstructural analysis showed that aggregates were found to cluster upon the application of drying-wetting cycling, followed by the rearrangement of soil skeletons, transforming the initial relatively dense structure into a loosen one with a greater percentage of macro-pores which are more sensitive to creep deformation of loess soils. Additionally, it is observed that the microstructural evolution is dependent on the number of dry-wet cyclings. As the dry-wet cycles increase, the flatter and irregular macro-pores increased gradually at the expense of meso-pores. In addition, the mechanism of irrigation-induced loess landslides is revealed from the perspective of variation in creep characteristics of loess after the dry-wet cycles, which can be summarized into three stages, namely, the dry-wet cycle stage of the loess around the hydro-fluctuation zone; the long-term creep-liquefaction stage of the deep loess, and the slip surface transfixion stage.

Site‐specific effects of winter cover crops on soil water storage

AbstractAddition of an overwintering cereal rye (Secale cereale L.) cover crop (CC) to midwestern maize (Zea mays L.)‐based systems offers several environmental benefits, but the long‐term effects of this practice on soil hydrological properties are not well understood. We utilized four long‐term (10+ yr) trials (two commercial fields, two research plots) in Iowa that included a replicated winter rye CC and no‐cover treatment in no‐till maize/soybean [Glycine max (L.) Merr.] systems. We took intact 7.62‐cm diam. soil samples from a 10‐to‐18‐cm depth shortly after cash crop planting in the spring. We measured the soil water retention curve using matric potentials ranging from saturation to –500 cmH2O. In addition, we measured organic matter, textural composition, and bulk densities of the soil samples. At the depth sampled, CCs did not meaningfully affect bulk density, water contents at saturation, or air‐entry potentials at any trial, nor increase the percentage of macropores. At two trials, soil water content at field capacity (–100 cmH2O) in the CC treatments was 2.5 vol% (SE: 1.2%; commercial field) and 2.4 vol% (SE: 1.3%; research plot) higher compared with the no‐cover treatments. This increase could meaningfully reduce the amount of water drained from a field after a saturating rain and should be considered when assessing CC impacts on landscape hydrology. The presence or absence of a CC effect on field capacity was not related to CC aboveground biomass production, previous cash crop, or soil texture at the trial sites. Based on our results, a causal model, and previous literature we hypothesize CC root characteristics are key to understanding variable effects of CCs on soil water storage. Our results indicate it is possible for CCs to meaningfully affect soil water storage, but more research is needed on the mechanisms by which these changes occur.

A microstructural investigation on hydraulic conductivity of soft clay

The hydraulic conductivity is a key parameter in geotechnical engineering. It is closely associated to soil microstructure. In practice, consolidation stress, dry density, and natural structure of soil can affect pore diameter and distribution of soil. Thus, to investigate soil hydraulic conductivity, their effects on microstructure and the corresponding hydraulic conductivity were analyzed. The undisturbed soil and the remolded soil with different dry densities were studied by the oedometer tests, hydraulic conductivity tests, and field emission scanning electron microscope (FESEM) tests. The results indicate that the natural structure inside the undisturbed soil is the intrinsic reason that affects hydraulic conductivity. The increase of consolidation stress mainly reduces the number and size of interaggregate pores in terms of provoking aggregation of soil particles. The increase in dry density will fill the interaggregate pores and weaken their connectivity. The area percentage of macropores can be used to reflect the change of soil microstructure. The consolidation stress is the main factor dominating the area percentage of macropores under a high-stress level. A stable intrinsic structure will be developed to inhibit the soil deformation when dry density is 1.4 g/cm3 or above, which helps to restrain the reduction of area percentage and slow down the decrease of hydraulic conductivity. Finally, a brief statistical regression analysis indicates that the area percentage of pores whose diameter larger than 0.4 μm is significantly related to the hydraulic conductivity, which are responsible for seepage in soft clay.

Effects of different conductive ions on pore-structure evolution of medium- and high-rank coal bodies induced by electric pulses

Electric pulse fracturing technology is a new type of coal seam fracturing and permeability increasing technology based on high-pressure shock wave technology. Compared with conventional technology, electric pulse fracturing has the advantages of a higher energy efficiency, less environmental pollution, and a shorter fracturing time, but having the disadvantages of rapid energy loss and a small fracture radius. To reduce the energy loss of electric pulses and increase the fracture radius, the experimental system of high-voltage electric pulse was employed in this study. The effects of NaCl, CaCl2, and AlCl3 conductive ions on the evolution of the pore structure induced by electric pulses were examined for medium- and high-rank coal bodies. The experimental results indicated the adsorption capacity of coal for ions was positively correlated with the valence of the cations and the soaking time, and the amount of ions adsorbed was larger when the solution was more alkaline. Amounts of ions adsorbed onto the coal surface decreased in the following order Al3+ > Ca2+ > Na+. After the treatment, the conductivity of the coal was significantly improved, making the plasma channel in the coal body more fully developed in the process of high-voltage electric pulse impaction, thus reducing significantly the breakdown voltage of the coal samples. Additionally, tthe total pore volume, total specific surface area, porosity, and average pore diameter of the treated coal increased and that the percentages of macropores and mesopores increased, indicating that the pore structure of coal samples is significantly improved.

Influence of chemical composition, porosity and fractal dimension on the electrical conductivity of carbon blacks

Carbonaceous materials analyzed in this investigation were six nanometric particle size carbon blacks. Carbons were texturally characterized by gas adsorption (N2, 77 K), helium and mercury density and mercury porosimetry measurements. Electrical conductivity was determinated by impedance spectroscopy, at room temperature. Several works related to the electrical conductivity and to textural parameters of carbon blacks, such as: porosity, specific surface area, etc., have been carried out. However, there are a type of parameters, such as the fractal dimension, the percentage of macropores, the particle size, or the packing density, that are also related to the electrical conductivity, but they have not been previously investigated. In this work, it has been researched how the increase in interparticle/intraparticle porosity decreases the electrical conductivity of the samples studied. Therefore, it is possible to conclude that in this study a complete research work on electrical conductivity has been carried out.

Instrumentation of Infiltrometers with Arduino to Determine Soil Water Infiltration Rate

The intense mobilization of the soil inappropriately causes a reduction in the percentage of macropores and in the rate of soil water infiltration with reduction of crop yield. Due to the difficulty of using the Muntz concentric ring method, researchers have used mathematical models to estimate infiltration based on soil physical parameters such as, soil texture that does not reflect physical reality in relation to infiltration rate, leading to errors. To automate the use of the infiltrometer ring method, there are no hydrometers that record small flows in non-pressurized hydraulic systems, making it difficult to automate the method for field determination. For this purpose, six Muntz double rings were instrumented with an electromechanical system coupled to the “Tipin Buked” (weighbridge) with the ability to record flows from 8 cm3∙minute−1 on a memory card. The results indicate that the models of the regression equations describe 93% to 99% of the real values, showing the accuracy of the equipment. This work aimed to modify the Muntz method to reduce field work and automate the determination of water infiltration rate in the soil.

Sulfation, pore, and fractal properties of hydrated spent calcium magnesium acetate from calcium‐based looping

AbstractHydration of the spent calcium‐based sorbent from calcium‐looping can improve its inadequate pore characteristics. The hydrated sorbent can be used for desulfurization before calcium‐based looping, which decreases the SO2 concentration in the flue gas entering the calcium‐based looping and also decreases the cost of CO2 capture. The effects of hydration time, hydration temperature, and liquid‐solid ratio on the reactivation performance of a hydrated spent calcium‐based sorbent were studied using spent calcium magnesium acetate (CMA) in this study. Fractal analysis based on the pore structure data of the hydrated sorbents was also conducted, and the relationship between the fractal dimension and the desulfurization performance of the hydrated spent sorbents was also investigated. The results showed that the sulfation conversion rate of the hydrated spent CMA decreased slowly at first, and then increased with hydration time. The conversion rate also increased with the hydration temperature but it decreased with the liquid‐solid ratio. The maximum sulfation conversion of the hydrated spent CMA under the optimized conditions was 68.0%, which approached that of fresh CMA. Compared to that of spent CMA, the sulfation conversion increased by 53.3%. The spent CMA consisted mainly of mesopores and macropores. After hydration, the volumes of both types of pores increased. However, the mesopore percentage decreased, while the macropore percentage increased. The hydrated spent CMA had obvious fractal characteristics. There was an optimum range for the fractal dimension of the samples, 2.31 < D < 2.35, at which the sulfation conversion was maximized. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Investigating the contribution of different sizes of pore spaces to the permeability of heterogeneous carbonate rocks using Markov Chain Monte Carlo and lattice-Boltzmann simulation

ABSTRACT Different sizes of pore spaces play different roles in fluid flow properties of rocks. The advantages of image analysis were employed to study the effect of different sizes of pore spaces, including micropores (10–50 µm), mesopores (50–100 µm) and macropores (>100 µm), on their contribution in the permeability of carbonates. First, all of the original binarized photomicrographs were subdivided into three images each contains one class of pores. Then, the three-dimensional digital models of the images were reconstructed using Markov Chain Monte Carlo method. Then, the models were integrated using a superposition operation. Finally, the lattice Boltzmann method was used to estimate the permeability of each model. The results show: (1) higher percentage of macropores provides higher permeability, while growth of micropores percentage has insignificant effect on flow properties due to lack of pores connectivity; (2) In spite of negligible permeability of micropores lonely, they can improve the carbonate rock permeability in cooperation with the meso- and macropores; (3) the estimated permeability from the superposed digital models were closer to the reality compared with the not-processed models, which were reconstructed without pore differentiation.

Effect of composition and macropore percentage on mechanical and in vitro cell proliferation and differentiation properties of 3D printed HA/β-TCP scaffolds

HA/β-TCP scaffolds were fabricated by 3D printing and exhibited desirable biocompatibilityin vitro.

Porosity-permeability relationship in dual-porosity carbonate analogs

We have investigated the effect of micrite content and macroporosity on the porosity-permeability relationship of dual-porosity carbonates using analog samples created in the laboratory. Specifically, we control the micrite-to-coarse-grains ratio to produce samples in which the micrite content is the only parameter changing. We also introduce into the microstructures controlled volumes of an acetone-soluble solid material (camphor) at the expense of the micrite aggregates, which functions as macropores after being dissolved. With regard to the effect of micrite on the porosity-permeability relationship, our results indicated that adding micrite to samples exhibiting a grain-supported microstructure reduces porosity and permeability drastically. By increasing the micrite content up to approximately 30%, the sample becomes micrite supported, at which point adding more micrite increases the porosity but no longer affects the permeability significantly. Samples characterized by a high micrite content were found to have lower permeability at any given porosity. When macropores are introduced at the expense of micrite aggregates, permeability increases drastically with porosity. The rate of increase in permeability decreases, however, as the micrite content of the original microstructure increases. Additionally, at any given micrite content, the permeability increases as the percentage of macropores increases because such pores do contribute more significantly to fluid flow as compared with the micropores characterizing micrite aggregates. We used the varying micrite-to-coarse-grains ratio and its effect on the porosity-permeability relationship to inform the Kozeny-Carman relation for a pack of spheres. Our analysis determined that micrite affects the porosity-permeability relationship of carbonates by reducing the effective particle size and increasing the percolation porosity. Additionally, incorporating the content of micrite and macropores into the analysis of the porosity-permeability relationship increased the coefficient of determination ([Formula: see text]) from 0.24 to 0.78. We concluded that knowledge of micrite content and macroporosity is of paramount importance to interpret and model porosity-permeability relationships in carbonates.

Transport of Atrazine and Dicamba through Silt and Loam Soils

The objectives of this research were to determine the role of preferential flow paths in the transport of atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine) and dicamba (3-6-dichloro-2-methoxybenzoic acid) through silt and loam soils overlying the High Plains aquifer in Nebraska. In a previous study, 3 of 6 study areas demonstrated high percentages of macropores; those three areas were used in this study for analysis of chemical transport. As a subsequent part of the study, 12 intact soil cores (30-cm diameter by 40-cm height), were excavated sequentially, two from each of the following depths: 0-40cm and 40-80cm. These cores were used to study preferential flow characteristics using dye staining and to determine hydraulic properties. Two undisturbed experimental field plots, each with a 3-m2 surface area, were installed in three study areas in Nebraska. Each was instrumented with suction lysimeters and tensiometers at depths of 10cm to 80cm in 10-cm increments. Additionally, each plot was planted with corn (Zea mays). A neutron probe access tube was installed in each plot to determine soil water content at 15-cm intervals. All plots were enclosed with a raised frame (of 8-cm height) to prevent surface runoff. All suction lysimeters were purged monthly for three months and were sampled immediately prior to pre-plant herbicide application to obtain background chemical concentrations. Atrazine and dicamba moved rapidly through the soil, but only after a heavy rainfall event, probably owing to the presence of preferential flow paths and lack of microbial degradation in these soil areas. Staining of laboratory cores showed a positive correlation between the percent area stained by depth and the subsequent breakthrough of Br- in the laboratory and leaching of field-applied herbicides owing to large rainfall events. Suction lysimeter samples in the field showed increases in concentrations of herbicides at depths where laboratory data indicated greater percentages of what appeared to be preferential flow paths. Concentrations of atrazine and dicamba exceeding 0.30 and 0.05µg m1-1 were observed at depths of 10-30cm and 50-70cm after two months following heavy rainfall events. It appears from the laboratory experiment that preferential flow paths were a significant factor in transport of atrazine and dicamba. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government or GNS.