Hygrothermal Properties of a Composite Based on Clay Soils and Diatomite

The purpose of this paper is to make a contribution to the use of diatomite as a mineral additive in the composition of compressed earth blocks. The aim is to study the influence of diatomite on the hygrothermal behaviour of composites based on clay soils. For this reason, two clay soils with different physicochemical and mineralogical compositions were incorporated with diatomite at percentages ranging from 5% to 50% with a step of 5 to produce compressed earth blocks. After assessing the hydric and thermal characteristics of the composites, it was found that the incorporation of diatomite into the clay matrix favours the absorption of water by capillary action for all the composites. The diatomite-amended blocks subjected to the rain erosion test were less eroded than the unamended blocks. In addition, BYD composites were found to be more resistant than BTD composites, due to the high percentage of clay in T soil. The thermal conductivity of the latter decreases respectively from 0.72 to 0.29 W/m∙K for BTD composites and from 0.52 to 0.21 W/m∙K for BYD composites. This reduction proves the thermal insulating properties of diatomite. Despite the high capillary absorption capacity of these composites, they have good thermal properties, enabling them to be used in the construction of buildings for improved indoor thermal comfort.

Clay Materials for Ceramics Application from N’Djamena in the Chad Republic: Mineralogical, Physicochemical and Microstructural Characterization

Herein, we report some characteristics of the clayey materials (CMs) collected from Kaliwa (C1), Kabé (C2) and Malo (C3) district in N’Djamena (Chad). Three samples were characterized applying XRF, XRD, FTIR, SEM. In addition, TGA/DSC were performed to control decomposition/mass loss and show phase transitions respectively of CMs. Geochemical analysis by XRF reveals the following minerals composition: SiO2 (~57% - 66%), Al2O3 (~13% - 15%), Fe2O3 (~6% - 10%), TiO2 (~1% - 2%) were the predominant oxides with a reduced proportion in C1, and (~7%) of fluxing agents (K2O, CaO, Na2O). Negligible and trace of MgO (~1%) and P2O5 was noted. The mineralogical composition by XRD shows that, C1, C2 and C3 display close mineralogy with: Quartz (~50%), feldspar (~20%) as non-clay minerals, whereas clays minerals were mostly kaolinite (~15%), illite (~5%) and smectite (~10%). FTIR analysis exhibits almost seemingly similar absorption bands characteristic of hydroxyls elongation, OH valence vibration of Kaolinite and stretching vibration of some Metal-Oxygen bond. SEM micrographs of the samples exhibit microstructureformed by inter-aggregates particles with porous cavities. TGA/DSCconfirm the existence of quartz (570˚C to 870˚C), carbonates (600˚C - 760˚C), kaolinite (569˚C - 988˚C), illite (566˚C - 966˚C), MgO (410˚C - 720˚C) and smectite (650˚C - 900˚C). The overall characterization indicates that, these clayey soils exhibit good properties for ceramic application.

Using Sorghum Stalk as a Partial Replacement of Lime in the Stabilization of Red Clay Soil for Road Sub-Grade Construction

This research aimed at testing the viability of using Sorghum Stalk Ash (SSA) as a partial replacement of lime in the stabilization of red clay soils for road subgrade construction. Red clay soils have been identified as highly expansive soils, which are affected by both climatic conditions and loading patterns. The consideration of both traffic loading patterns and climatic effects on these soils has been taken into account. A penetration test of 2.5 mm has been used on both pure red soils and stabilized soils at 10% and 15% partial replacement of lime with SSA and showed an improvement in the CBR of stabilized red clay soils up to 11.6%. Again, the PI of stabilized soils at 15% partial replacement of lime reduced up to 11.2%. The results obtained on both CBR and PI of these red clay soils are within the recommended values for the effective subgrade required for laying both permanent and flexible pavements. As a result, a recommendation of making use of SSA to lower the quantities of lime and its costs used in the stabilization of highly expansive soils have been tested through this research. However, further research on a more percentage partial replacement of lime to improve the PI of these soils to below 10% while keeping the CBR levels within the road construction regulations is welcomed.

Mechanical properties of a clay soil reinforced with rice husk under drained and undrained conditions

Fiber-reinforced soils have been increasingly used in geotechnical engineering.Over the years,research has sought to understand and investigate the influences of fibers as reinforcement in soilefiber mixtures.This study assessed the behavior of clayey soil in the city of Curitiba(Paraná,Brazil),adding rice husk fiber(RHF),an industrial waste from Cooperativa Agroindustrial in Alegrete(Rio Grande do Sul,Brazil).To evaluate the effect of the presence of natural RHF on the mechanical behavior of compacted soil,aspects such as the influence of fiber content and the drained and undrained behaviors of the soil were evaluated through unconfined triaxial compression tests.The following tests were realized:soil granulometry,specific mass of solids and Atterberg limits.Specimens were produced in quadruplicate for the soil and mixtures using the RHF contents of 0.5%,0.75%,1%and 1.5%to determine the unconfined compressive strength(UCS).Triaxial tests were realized on a pure soil specimen and the specimens with 1%RHF under confining pressures of 50 kPa,100 kPa,200 kPa and 400 kPa.The interactions at the interface between husk surface and soil were analyzed using scanning electron microscopy(SEM).In UCS tests,specimens with RHF percentages of 1%and 1.5%presented the highest results,with an increment of 36%compared to the soil without RHF.The results of the consolidated drained triaxial compression tests show that in terms of effective stress,there was a small difference in the strength of the compacted pure soil and soil with the addition of RHF.For the undrained tests,the strength increased with the inclusion of husk,with a reduction of 50%in cohesion and an increment of 22%in friction angle for specimens containing RHF compared to the soil without RHF additions.

Experimental Study of the Behaviour of Lime-Stabilized Clay Soil Blocks by Simple Compression for Wall Construction

This study addresses an experimental approach to stabilizing clay soils with lime.In the preliminary stage and in order to require characteristic properties,untreated clay and sand samples are collected on site and subjected to laboratory identification tests.Then,the so-called“trial and error”process based on production test series is used to mix with water by varying the proportions of the constituents.Using a manual press with a capacity of 5 to 10 tonnes,equipped with a 10×15×28 cm^(3) mould,the free-standing and heavy blocks are produced from the firm mixtures retained.After cures of 7,14 and 28 days,the results of the tests show that the resistance to compression(RC)of the blocks in the dry state increases depending on the lime dosage and the duration of cure.At 6%lime and around 25%sand,the value of the RC of 4,966 MPa after 28 days is higher than the recommended values for load-bearing walls by the Construction Materials Center(CMC)of N’Djamena(2.4 MPa)and CRATerre(4.0 MPa).On the other hand,a 24-h stay of the dry blocks in the water causes the RC to fall from 69%to 72%depending on the lime dosage.However,the absorption coefficient of 2.23 g/cm^(2)·s^(1/2) of blocks with 6%lime is much less than 20 g/cm^(2)·s^(1/2),limit value below which the NFP554 standard qualifies the low capillarity blocks.In short,this stabilization approach makes it possible to obtain blocks resistant to aesthetic appearance,low capillarity and cost to build walls.

Short-term Effects of Tillage Practices on Organic Carbon in Clay Loam Soil of Northeast China

A tillage experiment, consisting of moldboard plow （MP）, ridge tillage （RT）, and no-tillage （NT）, was performed in a randomized complete block design with four replicates to study the effect of 3-year tillage management on SOC content and its distribution in surface layer （30 cm） of a clay loam soil in northeast China. NT did not lead to significant increase of SOC in topsoil （0-5 cm） compared with MP and RT; however, the SOC content in NT soil was remarkably reduced at a depth of 5-20 cm. Accordingly, short-term （3-year） NT management tended to stratify SOC concentration, but not necessarily increase its storage in the plow layer for the soil.

Influence of Dimensions of UHMW-PE Protuberances on Sliding Resistance and Normal Adhesion of Bangkok Clay Soil to Biomimetic Plates

A number of investigations into application of polymers for macro-morphological modification of tool surface have been carried out. These researches, with extensive stress on convex or domed protuberations as one of the widely used construction units, have tried to harness benefits from using polymers in agriculture. Ultra high molecular weight polyethylene （UHMW-PE） has proved an emerging polymer in its application to reduce soil adhesion. This research was conducted to study the effect of shape （flat, semi-spherical, semi-oblate, semi short-prolate and semi long-prolate） and dimensions （base diameter and dome height） on sliding resistance and normal adhesion of biomimetic plates. To incorporate both shape and size, a dimensionless ratio of height to diameter （HDR） was introduced to characterize the effect of construction unit＇s physique. Experiments were conducted in Bangkok clay soil with dry （ 19.8% d.b.）, sticky （36.9% d.b.） and flooded （60.1% d.b.） soil conditions respectively. Soil at sticky limit exhibited the highest sliding resistance （77.8 N） and normal adhesion （3 kPa to 7 kPa）, whereas these values were 61.7 N and 〈0.2 kPa in dry, and 53.7 N and 0.5 kPa to 1.5 kPa in flooded soil conditions. Protuberances with HDR ≤ 0.5 lowered sliding resistance by 10% - 30% and the same reduced normal adhesion by 10% - 60%. The amount of reduction in both sliding resistance and normal adhesion was higher in flooded soil. Lighter normal loads obviously produced lesser resistance and adhesion.

Effects of a new nitrification inhibitor 3,4-dimethylpyrazole phosphate(DMPP) on nitrate and potassium leaching in two soils

In this study, soil column was used to study the new nitrification inhibitor 3,4-dimethylpyrazole phosphate （DMPP） on nitrate （NO3^-- N） and potassium （K） leaching in the sandy loam soil and clay loam soil. The results showed that DMPP with ammonium sulphate nitrate （ASN） （（NH4）2SO4 and NHaNO3） or urea could reduce NO3^--N leaching significantly, whereas ammonium （NH4^＋-N） leaching increased slightly. In case of total N （NO3^--N＋NH4^＋-N）, losses by leaching during the experimental period （40 d） were 37.93 mg （urea）, 31.61 mg （urea＋DMPP）, 108.10 mg （ASN）, 60.70 mg （ASN＋DMPP） in the sandy loam soil, and 30.54 mg （urea）, 21.05 mg （urea＋DMPP）, 37.86 mg （ASN）, 31.09 mg （ASN＋DMPP） in the clay loam soil, respectively. DMPP-amended soil led to the maintenance of relatively high levels of NH4^＋ -N and low levels of NO3^--N in soil, and nitrification was slower. DMPP supplementation also resulted in less potassium leached, but the difference was not significant except the treatment of ASN and ASN＋DMPP in the sandy loam soil. Above results indicate that DMPP is a good nitrification inhibitor, the efficiency of DMPP seems better in the sandy loam soil than in the clay loam soil and lasts longer.

A nonlinear interface structural damage model between ice crystal and frozen clay soil

The shear properties of ice-frozen soil interface are important when studying the constitutive model of frozen soil and slope stability in cold regions. In this research, a series of cryogenic direct shear tests for ice-frozen clay soil interface were conducted. Based on experimental results, a nonlinear interface structural damage model is proposed to describe the shear properties of ice-frozen clay soil interface. Firstly, the cementation and friction structural properties of frozen soil materials were analyzed, and a structural parameter of the ice-frozen clay soil interface is proposed based on the cryogenic direct shear test results. Secondly, a structural coefficient ratio is proposed to describe the structural development degree of ice-frozen clay soil interface under load, which is able to normalize the shear stress of ice-frozen clay soil interface,and the normalized data can be described by the Duncan-Chang model. Finally, the tangent stiffness of ice-frozen clay soil interface is calculated, which can be applied to the mechanics analysis of frozen soil. Also, the shear stress of ice-frozen clay soil interface calculated by the proposed model is compared with test results.

Stress and Displacement Distribution of Soft Clay Slope with 2D and 3D Elastoplastic Finite Element Method

Based on elastoplastic model, 2D and 3D finite element method （FEM） are used to calculate the stress and displacement distribution in the soft clay slope under gravity and uniform load at the slope top. Stability analyses indicate that 3D boundary effect varies with the stress level of the slope. When the slope is stable, end effect of 3D space is not remarkable. When the stability decreases, end effect occurs; when the slope is at limit state, end effect reaches maximum. The energy causing slope failure spreads preferentially along y-z section, and when the failure resistance capability reaches the limit state, the energy can extend along x-axis direction. The 3D effect of the slope under uniform load on the top is related to the ratio of load influence width to slope height, and the effect is remarkable with the decrease of the ratio.

Determination of Diffusion Coefficient and Analysis of Diffusion Factors of Cr(Ⅵ) Ion in Clay Soil

Some laboratory diffusion tests were conducted with diffusion device to determine the diffusion coefficient of Cr(Ⅵ) ion passing through Dalian red clay samples. The concentrations of Cr(Ⅵ) at different places of the samples were then measured spectrophotometrically after a standing time of 1 000 d. A one-dimensional solute transport equation was used to simulate the transport of Cr(Ⅵ) through clay samples. Back-calculation of diffusion coefficient of Cr(Ⅵ) was made with finite difference method. Parametric analysis was conducted to simulate variations in soil dry density, temperature, pH and standing time. The results show that the method used in this paper is simple and effective. The diffusion coefficient of Cr(Ⅵ) in Dalian red clay varies from 1.50×10-7 cm2/s to 2.08×10-7 cm2/s. After 1 000 d diffusion, the concentration of the source solution drops down to 1.27 mg/L from 62.5 mg/L, and the diffusion distance is only 3.5 cm. Under the assumption that diffusion coefficient is constant, the diffusion effect becomes more obvious with lower density, lower temperature, higher pH value, and much more time.

Soil-Water Charateristics of Tropical Clay Soil under High and Low Suction Conditions

Tropical clay soil was compacted at different moisture conditions (dry, wet and optimum) and compactive efforts (Reduced proctor, Standard proctor, West African standard and Modified proctor). Experimental Soil-Water Characteristics (SWC) of the soil was derived using the pressure plate extractor equipment and SWC Curves (SWCC) plotted as gravimetric water content versus logarithm of matric suction. The Air Entry Values (A.E.V) obtained from experimental work ranged from 21 kPa to 59 kPa and compared favourably well with those estimated from predictive models with values of 23 kPa to 52 kPa. Specimens compacted with greater compactive effort (Modified proctor) and at optimum moisture content produced the largest air entry value of 59 kPa and reduced air voids. Changes observed in the shape of the SWCC were consistent with changes in pore size which occurred by varying compaction conditions. The shape of the soil-water characteristics curve was found to depend on the soil structure, compactive water content and compactive effort and not solely on the percentage of fine particles.

Analysis on effective stress formula and consolidation of gassy muddy clay

In order to found an applicable equation of consolidation for gassy muddy clay, an effective stress formula of gas-charged nearly-saturated soils was introduced. And then, a consolidation equation was derived. Subsequently, supposing soils were under tangential loading, the expressions of pore water pressure were presented. The analytic solution of pore water pressure was attempted to be validated by the measured values in a real embankment. The parameters in the expressions of pore water pressure were gotten by the method of trial. The result shows that the consolidation model is rational and the analytic solution of pore water pressure is correct. The following conclusions can be made: 1) the influence of bubbles on the compressibility of pore fluid should be considered; 2) the effective stress would be influenced by bubbles, and the consolidation would depend on the compressibility of soil skeleton: the softer the soils are, the more distinct the influence of bubbles is; for normal clay, the influence of bubbles on the effective stress may be commonly neglected.

Recycling of Spent Mushroom Substrate （SMS） in Avocado Orchards

Spent mushroom substrates （SMS） are usually treated as wastes. One of the main beneficial uses of SMS is as soil amendment, after further composting, for horticulture. Avocado orchards in Northern Israel, are grown mainly on heavy clay soils, suffering from poor drainage and limited aeration. This situation can cause yield decrease and lead to tree＇s degeneration. In the present study, two soil cover （mulch） treatments were compared, in an avocado orchard, as means to solve this problem： SMS and cattle manure compost （CMC）. The yields of two avocado varieties were higher on SMS than CMC mulch. Thick growth of avocado roots was found in and under both mulch types. Soil＇s electrical conductivity （EC） values were high under both mulch types, although they later decreased, due to annual rainfall. There are treatments （leaching etc.） that can be used, for minimizing the increase of soil＇s salinity after SMS application. Enhancement of avocado root growth into and under the mulch can lead to improvement of avocado trees growth, especially on heavy un-drained soils. Therefore, SMS recycling is advantageous for both avocado and mushroom growers. The commercial utilization of SMS in avocado orchards should be done carefully, with monitoring its impact on soil＇s EC （salinity） and taking the needed measures to avoid unnecessary damages.

Clay Addition to Sandy Soil Influence of Clay Type and Size on Nutrient Availability in Sandy Soils Amended with Residues Differing in C/N ratio

Addition of clay-rich subsoil to sandy soil results in heterogeneous soil with clay peds （2-mm） or finely ground （〈 2 mm） clay soil （FG）, which may affect the nutrient availability. The aim of this study was to assess the effect of clay soil particle size （FG or peds） and properties on nutrient availability and organic C binding in sandy soil after addition of residues with low （young kikuyu grass, KG） or high （faba bean, FB） C/N ratio. Two clay soils with high and low smectite percentage, clay and exchangeable Fe and A1 were added to a sandy soil at a rate of 20% （weight/weight） either as FG or peds. Over 45 d, available N and P as well as microbial biomass N and P concentrations and cumulative respiration were greater in soils with residues of KG than FB. For soils with KG residues, clay addition increased available N and initial microbial biomass C and N concentrations, but decreased cumulative respiration and P availability compared to sandy soil without clay. Differences in measured parameters between clay type and size were inconsistent and varied with time except the increase in total organic C in the 〈 53 μm fraction during the experiment, which was greater for soils with FG than with peds. We concluded that the high exchangeable Fe and A1 concentrations in the low-smectite clay soil can compensate a lower clay concentration and proportion of smectite with respect to binding of organic matter and nutrients.

Behavior and characteristics of compacted expansive unsaturated bentonite-sand mixture

Limited studies dealt with the expansive unsaturated soils in the case of large-scale model close to the field conditions and therefore, there is much more room for improvement. In this study, expansive （bentonite–sand （B–S） mixture） and non-expansive （kaolin） soils were tested in different water contents and dry unit weights chosen from the compaction curve to examine the effect of water content change on soil properties （swelling pressure, expansion indices, shear strength （soil cohesion） and soil suction） for the small soil samples. Large-scale model was also used to show the effect of water content change on different relations （swelling and suction with elapsed time）. The study reveals that the initial soil conditions （water content and dry unit weight） affect the soil cohesion, suction and swelling, where all these parameters slightly decrease with the increase in soil water content especially on the wet side of optimum water content. The settlement of each soil at failure increases with the increase in soil degrees of saturation since the matric suction reduces the soil ability to deform. The settlement observed in B–S mixture is higher than that in kaolin due to the effect of higher swelling observed in B–S mixture and the huge amount of water absorbed which transformed the soil to highly compressible soil. The matric suction seems to decrease with elapsed time from top to bottom of tensiometers due to the effect of water flowing from top of the specimen. The tensiometer reading at first of the saturation process is lower than that at later period of saturation （for soil sample B–S3, the tensiometer #1 took 3 d to drop from 93 kPa to 80 kPa at early stage, while the same tensiometer took 2 d to drop from 60 kPa to 20 kPa）.

Enhancing performance of soil using lime and precluding landslide in Benin(West Africa)

The past decade has been characterized by the development of infrastructure in the main cities in West Africa.This requires more comprehensive studies of geotechnical properties of the soil in the region with an aim of creating sustainable development.This paper examined the performance of the soil in Benin(West Africa).In this research,three objectives have been adopted in-depth on the performance characteristics of West Africans soil and aim to(i)accessing characteristics of soil types in the region;(ii)assessing the performance of these soils with 2%,3%and 5%of lime and(iii)characterizing landslide to evaluate the damage and potential instability.The methods used to examine these objectives are experimental tests according to standard French test.The particle size test,Proctor test,and Atterberg limits test which are physical tests and the mechanical tests such as dynamic penetration test,direct shear test,and oedometer test,were used to assess the first objective.The Proctor test and California bearing ratio test were examined for the second objective and geological,environmental,social and safety study of the river bank slide were evaluated for the third objective.This paper firstly reveals the unstable and stable areas in southern Benin(West Africa)with the presence of clays soil and gives an equation for predicting the unstable and stable area,and secondly shows that the proportion of percentage lime leading to the best performances varying between 2%and 3%.Finally,this paper shows that the sliding of a bank could be the consequence of the sudden receding water recorded in a valley.

Linkage of microbial living communities and residues to soil organic carbon accumulation along a forest restoration gradient in southern China

Background:Forest restoration has been considered an effective method to increase soil organic carbon(SOC),whereas it remains unclear whether long-term forest restoration will continuously increase SOC.Such large uncertainties may be mainly due to the limited knowledge on how soil microorganisms will contribute to SOC accumulation over time.Methods:We simultaneously documented SOC,total phospholipid fatty acids(PLFAs),and amino sugars(AS)content across a forest restoration gradient with average stand ages of 14,49,70,and>90 years in southern China.Results:The SOC and AS continuously increased with stand age.The ratio of fungal PLFAs to bacterial PLFAs showed no change with stand age,while the ratio of fungal AS to bacterial AS significantly increased.The total microbial residue-carbon(AS-C)accounted for 0.95-1.66% in SOC across all forest restoration stages,with significantly higher in fungal residue-C(0.68-1.19%)than bacterial residue-C(0.05-0.11%).Furthermore,the contribution of total AS-C to SOC was positively correlated with clay content at 0-10 cm soil layer but negatively related to clay content at 10-20 cm soil layer.Conclusions:These findings highlight the significant contribution of AS-C to SOC accumulation along forest restoration stages,with divergent contributions from fungal residues and bacterial residues.Soil clay content with stand age significantly affects the divergent contributions of AS-C to SOC at two different soil layers.

Use of flue gas desulfurization gypsum to reduce dissolved phosphorus in runoff and leachate from two agricultural soils

Controlling dissolved phosphorus(DP)loss from high P soil to avoid water eutrophication is a worldwide high priority.A greenhouse study was conducted in which flue gas desulfurization gypsum(FGDG)was applied by using different application methods and rates to two agricultural soils.Phosphorus fertilizer was incorporated into the soils at 2.95 g kg^(-1)to simulate soil with high P levels.The FGDG was then applied at amounts of 0,1.5,and 15 g kg^(-1)soil on either the soil surface or mixed throughout the soil samples to simulate no-tillage and tillage,respectively.Ryegrass was planted after treatment application.The study showed that FGDG reduced runoff DP loss by 33%and leachate DP loss 38%in silt loam soil,and runoff DP loss 46%and leachate DP loss 14%in clay loam soil,at the treatment of 15 g kg^(-1)FGDG.Mixing applied method(tillage)provided strong interaction with higher FGDG.To overall effect,the mixing-applied method performed better in controlling DP loss from silt loam soil,while surface-applied(no tillage)showed its advantage in controlling DP loss from clay loam soil.In practice it is necessary to optimize FGDG concentrations,application methods,and DP sources(runoff or leachate)to get maximized benefits of FGDG application.The FGDG application had no negative effects on the soil and ryegrass.

Mapping of Total Carbon and Clay Contents in Glacial Till Soil Using On-the-Go Near-Infrared Reflectance Spectroscopy and Partial Least Squares Regression

Characterizing spatial variability of soil attributes, using traditional soil sampling and laboratory analysis, is cost prohibitive. The potential benefit of managing soils on a site-specific basis is well established. High variations in glacial till soil render detailed soil mapping difficult with limited number of soil samples. To overcome this problem, this paper demonstrates the feasibility of soil carbon and clay mapping using the newly developed on-the-go near-infrared reflectance spectroscopy (NIRS). Compared with the geostatistics method, the partial least squares regression (PLSR), with NIRS measurements, could yield a more detailed map for both soil carbon and clay. Further, by using independent validation dataset, the accuracy of predicting could be improved significantly for soil clay content and only slightly for soil carbon content. Owing to the complexity of field conditions, more work on data processing and calibration modeling might be necessary for using on-the-go NIRS measurements.