Effect Of Initial Water Content Research Articles

CO2 carbonation-induced improvement in strength and microstructure of reactive MgO-CaO-fly ash-solidified soils

An innovative approach combining CO2 accelerated carbonation with industrial by-products is systematically investigated to produce low-carbon and sustainable cementing materials, in which reactive MgO-CaO-FA (fly ash) blends are introduced to replace traditional Portland Cement (PC) with high energy consumption, mineral resources demand and CO2 emissions. The effect of initial water content, carbonation time, binder amount and mass ratio of MgO/CaO on the mechanical and microstructural properties of carbonated solidified soils is analyzed through unconfined compressive strength (UCS), scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The carbonation efficiency and carbon footprint of cementitious materials are evaluated under different schemes. The test results indicate that CO2 carbonation combined with reactive MgO-CaO-FA blends is proved highly effective and reliable to improve the strength performance of soil samples. The compressive strength of carbonated soils increases with binder content and mass ratio of MgO/CaO, which is related to the densification of pore system by carbonation products. An optimum UCS is reached at 6 h of carbonation, followed by a plateau or an important decrease with carbonation time. Water content controls the diffusion and permeability rate of CO2, affecting the chemical contact between Ca2+/Mg2+ released from MgO-CaO-FA blend and dissolved CO2 and further the strength of carbonated samples. XRD and SEM results demonstrate that the strength gain is mainly attributed to the formation of carbonation products (CaCO3, MgCO3), facilitating the densification and cementation of solidified materials. High-Ca FA promotes the carbonation efficiency by reducing porosity and providing nucleation sites for carbonate precipitation, while reactive MgO plays a more important role than CaO in developing binding capacity and building skeleton structure. The carbon footprint analysis reveals that compared with PC, the net CO2 emissions of MgO-CaO-FA blends are effectively reduced by 38.8–64.7%. The coupling technique of CO2 carbonation with industrial by-products is proved a feasible alternative to traditional PC in soil solidification.

Effects of Initial Water Content on Microstructure and Mechanical Properties of Lean Clay Soil Stabilized by Compound Calcium-Based Stabilizer

Initial water content significantly affects the efficiency of soil stabilization. In this study, the effects of initial water content on the compressibility, strength, microstructure, and composition of a lean clay soil stabilized by compound calcium-based stabilizer were investigated by static compaction test, unconfined compression test, optical microscope observations, environment scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. The results indicate that as the initial water content increases in the range studied, both the compaction energy and the maximum compaction force decrease linearly and there are less soil aggregates or agglomerations, and a smaller proportion of large pores in the compacted mixture structure. In addition, for specimens cured with or without external water supply and under different compaction degrees, the variation law of the unconfined compressive strength with initial water content is different and the highest strength value is obtained at various initial water contents. With the increase of initial water content, the percentage of the oxygen element tends to increase in the reaction products of the calcium-based stabilizer, whereas the primary mineral composition of the soil-stabilizer mixture did not change notably.

Theoretical bounds for the exponent in the empirical power-law advance-time curve for surface flow

A fundamental and widely applied concept used to study surface flow processes is the advance-time curve, which indicates the time at which water arrives at any given distance along a field length. The advance-time curve is typically characterized by an empirical power law with an exponent r and a numerical prefactor p (i.e., x=ptr). In the literature, different values of r have been reported for various situations and types of surface irrigation. Invoking concepts from percolation theory, a theoretical approach from statistical physics for quantifying transport properties in complex systems, we relate the exponent r to the backbone fractal dimension Db (r = 1/Db). The backbone, through which transport occurs predominantly in a system, is formed by multiply connected loops composed of several paths that bring fluid from an initial point to a final point. The backbone fractal dimension Db, characterizing the complex structure of the backbone, depends on two factors: dimensionality of the system (e.g., two or three dimensions) and percolation class (e.g., random or invasion percolation with/without trapping). We show that the theoretical bounds of Db are well in agreement with experimental ranges of r reported in the literature for two furrow and border irrigation systems. We further use the value of Db from the optimal path class of percolation theory to estimate the advance-time curves of four furrows and seven irrigation cycles (i.e., 28 experiments). The optimal path is the most energetically favorable path through a system. Excellent agreement was obtained between the estimated and observed curves. We also discuss the indirect effects of initial water content, inflow rate, surface slope, and infiltration rate (soil texture) on system dimensionality, percolation class and, consequently, the backbone fractal dimension value. More specifically, we postulate that for closely-spaced furrows with steep slopes, low infiltration rates, and relatively high inflow rates, the wetting front advance will be mostly quasi one-dimensional. Since the backbone fractal dimension in one dimension is 1, one should expect the exponent r to be near 1.

CHARACTERISATION OF THE UNDRAINED SHEAR STRENGTH OF EXPANSIVE CLAYS AT HIGH INITIAL WATER CONTENT USING INTRINSIC CONCEPT

Twenty-four direct shear tests were conducted on remolded/reconstituted specimens to studythe effect of initial water content on the undrained shear strength of expansive clays. The laboratory testsillustrate that the shear behavior of the studied clayey soil is dependent on both the confining pressure and theinitial water content at which the specimen was prepared. In fact, the undrained shear strength decreases withincreasing initial water content. Similarly to the compression behavior, the intrinsic concept can also be usedto predict the undrained shear strength of the studied soil. Additionally, the relationship between the void index,which is a normalized invariant of void ratio, and the undrained shear strength can be defined uniquely by astraight line. The experimental results also show that the normalized undrained shear strength, which is definedas the ratio of the peak undrained shear strength to the normal stress, varies with the initial water content from0.25 to 0.50. Moreover, a decreasing trend is found for the range of pre-consolidation stress between 50 and400 kPa.

Effect of initial water content and pore water chemistry on intrinsic compression behavior

ABSTRACTThe effect of initial water content (w0) and pore water chemistry on the intrinsic compression curve of clays was investigated experimentally. The test results indicate that w0 had a considerable effect on the intrinsic compression curve of a clay, and the degree of the effect is a function of pore water chemistry. The fundamental mechanism of the effect of w0 and pore water chemistry on the intrinsic compression curve is through its influence on the microstructure of clays. For relatively stable flocculated microstructures, the effect of w0 will disappear under a small value of effective vertical consolidation stress, σ′v, for example, σ′v < 20 kPa; under one-dimensional deformation condition, but for a dispersive microstructure, the effect of w0 can remain up to σ′v > 1,000 kPa. Furthermore, it has been shown that when σ′v is larger than the remolded yield stress, almost all the test data follow the intrinsic compression line (ICL) proposed by Burland. Finally, based on the test data, a new equation for estimating void ratio () under σ′v = 100 kPa on ICL from the void ratio (el) corresponding to the liquid limit water content has been proposed.

Tensile behaviour analysis of compacted clayey soil reinforced with natural and synthetic fibers: effect of initial compaction conditions

In this paper, the technique of soil reinforcement using short and randomly distributed fibres was proposed in order to evaluate its effect on tensile behaviour of compacted clayey soil. For that purpose, a new test method was developed using a specially designed direct tensile test apparatus. The device allows an inside compaction without any soil disturbance, suited particularly for sensitive samples with high-water contents. The efficiency of natural and synthetic fibres on improving tensile-strain characteristics of compacted-reinforced clay were first evaluated by varying fibre length and content. Pull-out tests were carried out on the different types of fibres, then SEM and EDS analysis were used to identify the interaction nature of the fibre and the soil matrix. The effect of initial water content and dry density was then investigated. The results indicated that, for some range of initial water content and dry density, short fibres can significantly improve tensile-strain characteristics of the reinforced soil by delaying crack initiation and reducing its propagation velocity. Moreover, longer natural fibres were found more effective than synthetic ones in restraining tensile cracks. Various fibre avoidance mode of crack growth were analysed and associated mechanisms were discussed.

Effect of drying\u2013wetting cycles on aggregate breakdown for yellow\u2013brown earths in karst areas

BackgroundDrying and rewetting process, frequently occurred during climatic changes, is an important process in soil aggregate slacking and dissolution. The severer interference of human activities on global climate makes the extreme climate scenarios like drought and rainstorm occur frequently. Therefore, there is necessity to further our understanding on the impact of the drying–wetting cycles and initial water content on the breakdown of soil aggregates. The typical yellow–brown earth composed of water–stable and water–unstable aggregates is selected. Variations of water-stable aggregate size distributions after drying-wetting cycles are measured by wet sieving, under variable initial water content and cycles respectively.ResultsDrying-wetting cycles cause a significant aggregate slaking, especially within the first two cycles. After that, most aggregates show more slacking resistant. The variation curves of the proportion of water-stable aggregates with the size 1–5 mm shows a coexistence of slaking process and supplement. The critical initial water content (about 24%) and turning point (with the aggregate size of 0.3 mm) are proposed to describe the effects of initial water content on size distribution of water-stable aggregates. Overall, the increase of initial water content strengths the water stability. In addition, the mathematical model for the relative leakage ratio based on the drying–wetting cycle, initial water content and size distribution are established.ConclusionsThe findings reported in this paper may be capable of supporting the intensive study for the breakdown mechanism and assessing the leakage potential under the influence of climate change. However, there exists a certain mismatch between the drying-wetting cycles in the tests and in practice, mainly in the frequency and intensity, which should be paid more attention.

Stress–Strain–Electrical Evolution Properties and Damage-Evolution Equation of Lateritic Soil Under Uniaxial Compression

Abstract Finding an internal variable that characterizes the effects of change in the mesoscopic structure of soil and can be nondestructively measured simultaneously with stress and strain during the entire compressive process is an intriguing problem for geotechnical engineers and researchers. In this study, the geoelectrical resistivity technique, combined with a mechanical test, was applied to explore the stress–strain–electrical evolution properties of lateritic soil during the entire process of uniaxial compression. Complete testing data were obtained for the stress–strain and resistivity–strain curves. Results show that both curves for each specimen were identified by six distinct stages. The effects of initial water content and dry density were analyzed and indicated that soil failure patterns and initial electrical resistivity are significantly influenced by the initial water content. The initial electrical resistivity of lateritic soil decreases when the dry density increases. Electrical resistivity was regarded as an internal variable to characterize information on damage change. Damage-evolution equations were proposed; these equations include three variables, namely, stress, strain, and electrical resistance, as well as data-fitting parameters (c, d and β).

Effect of Initial Water Content on Foaming Quality and Mechanical Properties of Plant Fiber Porous Cushioning Materials

A porous, wood-fiber-based cushioning material for packaging was prepared in this study using poplar fiber and wood powder raw materials as an environmentally friendly resource. Water, the foaming agent azodicarbonamide and sodium bicarbonate, starch, and nucleating agent French chalk were used as additives, and the ingredients were subjected to hot-press molding. The effects of the initial water content on the foaming quality and mechanical properties of the plant fiber porous cushioning materials were explored. The results showed that the initial water content had a substantial influence on the foaming quality and mechanical properties of plant fiber porous buffer materials. When the initial water content was 69.3%, the initial embryo viscosity was the most suitable for bubble growth, and the porosity, pore size, and distribution of the samples were optimal. Furthermore, the mechanical properties of the samples were the strongest. The foaming mechanism of the plant fiber porous cushioning material was similar to the foaming mechanism of a polymer foaming material. Thus, the embryo viscosity had the greatest influence on the bubble growth process.

Combined effects of initial water content and heating parameters on solar pyrolysis of beech wood

The combined effects of feedstock water content and heating parameters (final temperature and heating rate) on solar pyrolysis product distribution, and on the composition and LHV (lower heating value) of the gas products, were investigated. Beech wood sawdust with 0%, 6%, 11% and 41% initial water content were pyrolyzed in a solar reactor at 900, 1200 and 1600 °C with heating rate ranging from 10 to 150 °C/s. Due to the advantage of solar pyrolysis (high temperatures and heating rates), high water content beech wood can be upgraded into CO- and H2- rich gas products. Under the used operating conditions, the beech wood drying and pyrolysis proceed simultaneously, which gives rise to a process combining pyrolysis, gasification and reforming. As a result, the combined effects of water content and temperature or heating rate are reinforced, which favors tar steam reforming into more gas product.

Experimental study on settling velocity of soil particles in dredged slurry

ABSTRACTStudying sedimentation and consolidation of dredged slurry has significant implications to the design of storage yard and subsequent ground improvement. In this study, settling velocity of soil particles in dredged slurry during sedimentation and consolidation processes was investigated using an improved multilayer extraction sampling (MES) method. A series of sedimentation column tests were performed on dredged slurry with three different initial water contents. Distributions of volume of soil particles and density of dredged slurry were first obtained by the MES method, settling velocity of soil particles was then calculated by volume flux function approach. It was found that the density and velocity inflection points can be used to distinguish the settling zone and the consolidation zone. The experimental results reveal that the velocity of soil particles was quite low and monotonically decreased with sedimentation height at low initial water content throughout the whole test period, whereas it was increased at 0–1 hours and almost remained constant at 1–7 hours in the settling zone at high initial water content. The effects of initial water content on sedimentation and consolidation mode of dredged slurry and the settling velocity of soil particles were discussed. The relationship between settling velocity of soil particles and particle diameter was also studied. It is indicated that the measured velocity of soil particles was much lower than that calculated by the Stokes equation, and it was related to 0.4881–0.5906 order of particle diameter at 0–1 hours and 0.1117–0.1825 order of particle diameter at 1–7 hours for the test slurries.

Effect of rainfall infiltration on the hydraulic response and failure mechanisms of sandy slope models

This paper presents experimental results obtained from silty sand slope models subjected to an artificial rainfall. Four models were constructed to evaluate the effect of initial water content and rainfall intensity on the hydraulic behavior and failure mechanisms of the slopes. The models were instrumented with volumetric water content sensors to monitor the advance of the water front, and inclinometers to measure lateral movements of the slope. The models were subjected to rainfall intensities ranging from 25 to 50 mm/h, and durations from 19 to 152 minutes. The influence of low intensity rainfall events before a high intensity rainfall is discussed herein. The results showed that the time the slope models required to reach failure was influenced by the soil initial water content, being shorter at high initial water contents. These results are useful to understand the behavior of unsaturated natural slopes and embankments exposed to rainfall infiltration, and to complement the existing laboratory database existing in this subject.

E–log σv′ relationship for marine clays considering initial water content to evaluate soil structure

ABSTRACTUsing the data of conventional consolidation tests, the linear ln v–ln relation (v = 1 + e is a specific volume) was determined in the region of large effective stresses, and was named as high water content compression line (HWCL). A unique relation between normalized ln v−ln was obtained for twenty-one clays with narrow band. Based on the normalized HWCL, e–log relation of normally consolidated clay with a specified initial water content was proposed. In this model, the beginning part shows a linear e–log relation in the range of <σ′HWCL and, in the latter part of the range of ≥σ′HWCL, e–log relation is on the HWCL, where σ′HWCL is the converging pressure to HWCL. It was shown that the empirical Cc–wL relations could be explained using the HWCL based model with the consideration of initial water contents. By using the proposed model, the change of compression properties of marine clay due to soil structure formed in the deposition process was shown schematically, and the effects of soil structure of in situ marine deposits were evaluated, considering the effect of initial water content.

SOIL WATER CHARACTERISTIC CURVES OF COMPACTED KAOLIN FOR VARIOUS INITIAL MOISTURE CONTENT

The soil water characteristic curve (SWCC), also known as soil water retention curve (SWRC), describes the relationship between water content and soil suction in unsaturated soils. The importance of SWCC can be seen, as the relationship affects geotechnical properties such as shear strength, volume change, permeability and deformability of unsaturated soils. This paper presented a preliminary study on the effect of initial water content and the density on SWCC on unsaturated compacted kaolin. Filter paper technique was used for suction measurement on the unsaturated compacted kaolin soil. Filter paper was used to determine total suction and matric suction through contact and noncontact technique. The calibration curve was used to relate with the gravimetric water content obtained in filter paper with corresponding suction. A comparison on SWCC established through filter paper was also compared with that of the axis translation technique (pressure plate extractor). The study found that the initial water content and the density respectively, have great influence on the SWCC of compacted kaolin. However, the combined effect could be seen significantly at lower suction

Compression Behavior of Secondary Clay Minerals at High Initial Water Contents

This study shows the influence of initial water content on the compression behavior of secondary clay minerals: kaolin, illite, and montmorillonite. Oedometer tests were carried out on these minerals with different initial water contents which are ranging from one to two times their corresponding liquid limits. The findings show that the initial water contents can result in different compression behaviors of secondary clay minerals. The compression indices of secondary clay minerals, and , increase nonlinearly with increasing initial water contents, and compression behaviors among samples become insignificant gradually. Meanwhile, it is also noticed that the effect of initial water content on of montmorillonite is smaller than that of kaolin and illite. However, the effect of initial water contents on of secondary clay minerals is close. Due to the remolded yield stresses existing in remold soils, all the e∼logσ′ compression curves of the three secondary clay minerals present an inverse ‘S’ shape. The initial water contents have different effects on remolded yield stress of secondary clay minerals. It has most significant effect on illite, and less effect on kaolin and montmorillonite.

Effect of initial water content and calcination temperature on photocatalytic properties of TiO2 nanopowders synthesized by the sol–gel process

The effects of initial water content and calcination temperature on sol–gel synthesized TiO2 powders were studied. Mother solutions had water/Ti-precursor mole ratios (R ratio) of 1, 5, 10, and 50. Dried aerogels were calcined for 3h at temperatures of 300, 400, and 500°C to obtain crystallized TiO2 nanopowders in the range of 15–30nm. FE-scanning electron microscopy and X-ray diffraction techniques were employed to investigate the morphological and structural properties of the nanopowders synthesized. Profound effect of gel viscosity was observed on the formation mechanism and extent of crystallinity in the powders. Methylene blue degradation test results suggest, photocatalytic performance is enhanced as initial water content and calcination temperature increased. Band-gap energy of the powders ranged from 3.09 to 3.27eV. Overall, this study shows that initial water content and calcination regime have a profound effect on the phase assembly, crystallite size, band-gap energy, and photocatalytic performance of sol–gel synthesized TiO2 nanopowders.

Effect of Initial Water Content on the Properties of Compacted Expansive Unsaturated Soil

Unsaturated soil can raise many geotechnical problems upon wetting and drying resulting in swelling upon wetting and collapsing (shrinkage) in drying and changing in the soil shear strength. The classical principles of saturated soil are often not suitable in explaining these phenomena. In this study, expansive soil (bentonite and sand) were tested in different water contents and dry unit weight chosen from the compaction curve to examine the effect of water content change on soil properties (swelling pressure, expansion index, shear strength (soil cohesion) and soil suction by the filter paper method). The physical properties of these soils were studied by conducting series of tests in laboratory. Fitting methods were applied to obtain the whole curve of the SWRC measured by the filter paper method with the aid of the (Soil Vision) program. The study reveals that the initial soil conditions (water content and dry unit weight) affect the soil cohesion, soil suction and soil swelling, where all these parameters marginally decrease with the increase in soil water content especially on the wet side of optimum.&#x0D; &#x0D;

Comparing the Thixotropic and Lightly Solidified Hardening Behavior of a Dredged Marine Clay

When a soil is disturbed upon remolding, it may lose part or all of its strength. As time passes, the structural arrangement of the soil particles would be restored to a stable form and the soil would regain hardness under constant volume and water content. The process is known as “thixotropic hardening”. On another note, dredged marine soils of the fine-grained type can be reused as a backfill material instead of being disposed to the open sea. The rest period required for the relocated soil to regain strength and stiffness, i.e. thixotropic hardening, needs to be estimated precisely. For this purpose, a study on the phenomena of strength and stiffness gain by a dredged marine clay was carried out. The strength and stiffness improvement with time was measured using the vane shear and fall cone tests respectively. The clay was remolded at different water contents in multiples of the soil’s liquid limit (LL), namely 0.75LL, 1.00LL and 1.25LL, in order to evaluate the effect of initial water content on thixotropic hardening. A separate series of samples were prepared with light solidification using cement, to examine the possibilities of enhancing the soil’s improvement in a shorter rest period. The results showed the dredged marine clay can potentially be used as a backfill material for reclamation works, with lower initial water content and light solidification contributing to accelerated better performance

Quantifying the effect of soil physical properties on the compressive characteristics of two arable soils using uniaxial compression tests

The compaction of cultivated soils by agricultural machines considerably affects both the structure and physical properties of soil, and thus can have major impacts on crop production and the environment. In this study, we have used experimentally determined soil compression curves to constrain two important soil compression properties for black and brown soil from northeast China: the compression index and pre-compression stress condition. We have investigated the impact of variable initial water contents (0.14, 0.16, 0.18, 0.20 and 0.22g/g) and initial bulk densities (1.20, 1.30, 1.45 and 1.60Mg/m3) on these compressive properties by performing uniaxial compression tests on both types of remolded soils. It was determined that the pre-compression stress values were higher for black soil than for brown soil, whereas the opposite was true for the compression indexes, suggesting that black soil is less vulnerable to soil compaction than brown soil. The effect of initial water content, bulk density and the mutual interaction between them significantly influenced the compression properties of both soils (P<0.01). The pre-compression stress condition of both arable soils showed a positive correlation with bulk density and a negative correlation with water content. By contrast, the compression index for both soils showed a prominent negative correlation with bulk density. The compression index of brown soil showed an insignificant dependence on water content, but showed a positive correlation for black soil. Consequently, cultivation operations should be avoided under low bulk densities and high water contents on the premise that the crops could grow well in order to reduce the risk of soil compaction.

A study on the behavior of the compacted bentonite in the presence of salt solutions

Wastes that are generally disposed off in an engineered landfill disposal site produce leachates. These leachates, which are very toxic in nature, once come in contact with percolating rain water, move downwards and pollute the ground water source. In order to prevent the ground water being polluted from the leachate, a liner is provided below the landfill disposal site. Generally, a compacted layer of bentonite is used as a barrier material at the waste disposal site. Because of its high swelling capacity and lower hydraulic conductivity, bentonite is used as a liner material. However, when bentonite comes in contact with salts present in leachates, its swelling property and hence also its hydraulic conductivity change. In this study, the effects of two different salt solutions, i.e. NaCl and CaCl2 by varying concentrations on bentonite were experimentally investigated. Tests were carried out to study the swelling potential, swelling pressure, and hydraulic conductivity of compacted bentonite. In order to study the effect of initial water content, study was carried out on two compacted samples varying in initial water content. Results indicate that liquid limit, plasticity, swell potential, and swell pressure decrease and hydraulic conductivity increases with increase in salt concentration. Result also shows that initial water content has a marginal effect on swelling pressure. However, the samples compacted on the dry side of optimum moisture content (OMC) exhibited a higher swelling pressure in comparison to the samples compacted at OMC.