Shrinkage Curve Research Articles

Exploring Soil–Water Characteristic Curves in Transitional Oil Sands Tailings

Soil–water characteristics curves (SWCC) have proved useful in estimating parameters used in modeling unsaturated geotechnical properties of soils including permeability and strength. Either saturation, gravimetric, and instantaneous and initial volumetric water content designation can be used to develop SWCCs. Studies have shown that any of the designations will give good estimates for soils that do not undergo volume change with suction change whereas, for soils that undergo substantial volume change, only saturation and instantaneous volumetric water content designation obtained by incorporating shrinkage curves can give correct estimates. Transition oil sands tailings have fines content that cannot be categorized as sandy or fine materials, and research on volume change with suction change in these materials is limited. In this study, HyProps, Tempe cells, and a chilled-mirror water potential meter were used to measure suction and corresponding water contents for samples that were prepared by mixing coarse sand and Fluid Tailing by ratios that mimic transition zone tailings. Shrinkage tests were also performed to observe the extent of volume change with suction increase. Air Entry Values (AEV) estimated from SWCCs based on gravimetric water content were found to be lower than those estimated from saturation-based SWCCs due to substantial volume changes in these materials with suction increase. The use of saturation water content designation is recommended in estimating AEV for transitional oil sands tailings. This is useful information in predicting the long term unsaturated geotechnical behavior of these materials for environmental management and safety purposes.

Influence of the pressure of compacted glass powders on the final structure of sintered glass-ceramics

In reported investigation we studied sintered glass-ceramics from a model diopside glass with moderate crystallization ability by in-situ optical dilatometeric experiments. The initial glass was ground and sieved below 75 μm. Then thus prepared powders were pressed with different pressures between 50 and 250 MPa. In this way were obtained samples out of pressed powders with different initial porosities determined with gas pycnometry. Then the samples were heat treated in a contactless horizontal optical dilatometer and their porosities were measured one more time. Both pressed green samples and synthesized glass-ceramics were analyzed further with X-Ray micro tomography.We observed that the densification of all samples completes in the same moment which corresponds to the formation of a critical percentage crystal phase. Notwithstanding the continuation of the crystallization process, we obtain materials with different percentage of residual porosity. Then no volume variation of the system is observed. This approach is well demonstrated by the first derivative of the shrinkage curves with time.After the end of the shrinkage of the system, the crystallization leads to the formation of crystallization induced porosity (called by us CIPs) observed here.

Effect of Calcium Carbide Residue on Shrinkage Mechanism of Clayey Subgrade Soil

ABSTRACT Calcium carbide residue (CCR) has been identified as an effective replacement for traditional lime for the stabilization of expansive soils. The shrinkage of expansive clay severely threatens the foundation layers’ long-term stability. The efficacy of CCR stabilization in reducing compressibility and enhancing the strength and stiffness of clay has been widely reported; however, the calcium-based additive stabilized soil tends to lose its engineered integrity under field-exposed seasonal moisture variation, specifically, shrinkage induced by prolonged drying. In this study, the shrinkage characteristic of CCR-treated clay (6%, 9%, and 12%) slurry was investigated by digital image analysis and mercury displacement method to quantify volumetric shrinkage strain. The results were compared with those of 4% and 6% lime-treated clay, which revealed the higher efficacy of CCR in reducing shrinkage strain by 47–57%. A characteristic shrinkage curve that depicted the significant variation of shrinkage phases in CCR-treated clay samples is developed. The dominance of the proportional shrinkage phase is observed in both untreated and treated clay samples. The shrinkage caused by evaporation, hydration, and decalcification is postulated in treated clays. This study is expected to contribute to the understanding of shrinkage mechanisms of CCR-treated clay and assist in the future design of stabilized embankment sections or subgrade for unpaved roads.

Rapid 24 GHz microwave sintering of alumina – yttria-stabilized zirconia ceramic composites

Samples of alumina – 3 % yttria-stabilized zirconia (YSZ) composites were sintered in rapid processing regimes using 24 GHz microwave heating at rates of up to 200 °C/min and zero hold time. The final relative density was 96–99 % for the samples containing 1.5 and 7.5 wt % YSZ and 98–99 % for the samples containing 13 wt % YSZ. The microwave sintering kinetics were compared for the processes carried out by direct and susceptor-assisted microwave heating. Under direct microwave heating, the effect of an intense microwave electromagnetic field with an estimated absorbed power density of up to 130 W/cm3 resulted in a shift of the shrinkage curves by about 100 °C towards lower temperatures compared to the case of susceptor-assisted heating. The grain size of the samples sintered by direct microwave heating decreased with an increasing heating rate. The mechanical properties were slightly higher for the materials sintered under susceptor-assisted microwave heating. The samples containing 13 wt % YSZ exhibited a microhardness of about 20 GPa and a fracture toughness of about 7 MPa m1/2.

Coupled hydro‐mechanical pore‐scale modeling of biopore‐coated clods for upscaling soil shrinkage and hydraulic properties

AbstractEarthworms and plant roots are vital for macropore formation and stabilization. The organo‐mineral coating of biopore surfaces also regulates macropore‐matrix mass exchange during preferential flow. The influence of finer‐textured burrow coatings on macroscopic soil properties during shrinkage could potentially be assessed by upscaling pore‐scale hydraulic and mechanical simulations. The aim was to investigate the influence of micro parameters (particle size, stiffness, and bond strength) on macro parameters (i.e., shrinkage curve and soil hydraulic properties). Drainage experiments and simulations were carried out using biopore‐coated clod‐size samples compared to those without coating. Simulations were performed using a two‐phase pore‐scale finite volume coupled with discrete element model (DEM‐2PFV). The structural dynamics was characterized by analyzing the pore volume and soil shrinkage curve obtained from numerically determined data. The soil hydraulic parameters were described using uni‐ and bimodal van Genuchten (vG) functions. The drainage simulations revealed hydro‐mechanical dynamics characterized by Braudeau‐shrinkage curve subdomains: The matrix‐only samples, with lower particle bond strength, exhibited relatively higher shrinkage. The coated samples, with higher particle stiffness and bond strength, displayed greater hydro‐mechanical stability. The numerically determined initial value of the saturated hydraulic conductivity (Ks) was about 70 times larger for matrix‐only samples than for coated samples. As expected, for the nonrigid soil structures, constant Ks, α, and n values for bimodal vG model resulted in prediction errors. Upscaling DEM‐2PFV pore‐scale model outcomes quantifies micro‐coating effects on macro hydro‐mechanics. This yields void ratio‐based soil water retention and hydraulic conductivity functions, advancing macroscopic soil hydraulic models and enhancing structured soil flow and transport descriptions.

Evaluating the role of soil properties on volumetric shrinkage characteristics of marine and inland clays

ABSTRACT Clayey soils that exhibit swelling and shrinkage behaviour have paved the way for various engineering problems such as foundation failure, slope stability issues, failure of earthen dams, cracking of clay liners, etc. The shrinkage behaviour of soil is often quantified by employing various direct and indirect experimental techniques to establish the Soil Shrinkage Curve (SSC), a relationship between soil volume change and moisture content. However, SSC can reveal only the overall volume change and does not exclusively comprehend the variation of volumetric shrinkage in linear and radial directions. Hence, a series of desiccation tests were performed on marine and inland clayey soils of different consistencies to evaluate the contribution of volumetric shrinkage in these orientations. From this study, it has been observed that the linear component of volumetric shrinkage was higher for soil samples with a consistency state between 1.0 and 1.5 times the liquid limit. However, the radial component of volumetric shrinkage was found to be higher at the end of the desiccation test for soils with an initial moisture content at or below the liquid limit. Furthermore, the results obtained from the present study have been utilised to establish the influence of soil properties on radial, linear, and total volumetric shrinkage.

Analysis and Prediction Model Reinforced UHPC Shrinkage Property

This paper explores the shrinkage of reinforced UHPC under high-temperature steam curing and natural curing conditions. The results are compared with the existing shrinkage prediction models. The results show that the maximum shrinkage strain of reinforced UHPC after steam curing is 164 με and gradually becomes zero. As for natural curing, the maximum shrinkage strain is 173 με and the value stabilizes on the 10th day after pouring. This indicated that steam curing can significantly reduce shrinkage time. Compared with the plain UHPC tested in the previous literature, the structural reinforcement can significantly inhibit the UHPC shrinkage and greatly reduce the risk of cracking due to shrinkage. By comparing the results in this paper with the existing models for predicting the shrinkage strain development, it is found that the formula recommended in the French UHPC structural and technical specification is suitable for the shrinkage curve in the present paper.

Experimental Study on Field Shrinkage of Deck Panel of Composite Girder Cable-stayed Bridge

In order to study the shrinkage performance of the deck panel of the composite girder cable-stayed bridge, the shrinkage test of the deck panel members of the real bridge was carried out in the field with the background of the Malukou Great Bridge, comparing the difference between the shrinkage values measured in the test and the theoretically calculated values of shrinkage in the various specifications, and finally the shrinkage equations and curves of the deck panel in 180d were fitted based on the test data. The results show that: on 180d, the shrinkage strain calculated by JTG D62-2018, the current design specification used for highway bridges in China, is only 66.30% of the test shrinkage, and the small prediction of bridge deck shrinkage may cause problems in terms of structural cracking; based on the large differences between various specifications for the shrinkage strain of bridge decks, It is recommended to use the actual shrinkage strain measured by the bridge deck shrinkage test as the real shrinkage curve as the data source to accurately assess the deformation and stress state of the bridge deck.

Microwave dielectric characterization and densification mechanism analysis of CaO‐B2O3‐SiO2 glass–ceramic/Al2O3 composites for LTCC applications

AbstractIn this study, nine component points were designed based on a CaO‐B2O3‐SiO2 (CBS) glass system with a high boron content, and CBS glass/Al2O3 composites were developed for low‐temperature co‐fired ceramic (LTCC) applications. Furthermore, the densification process, phase compositions, microstructures, and properties were investigated. The results indicated that the softening of glass and interfacial reaction between the glass and Al2O3 were the two most important factors affecting LTCC's densification process. The real‐time shrinkage rate of LTCC during sintering was simulated using the thermal shrinkage curve and combined with DTA and X‐ray diffraction. It was proven that the formation of the CaAl2(BO3)O phase contributed to the reduction in glass viscosity and promoted the formation of a dense structure. The LTCC composite with 30 vol% glass sintered at 850°C exhibited a coefficient of thermal expansion of 4.55–6.35 ppm/◦C, εr of 3.5–5.0, and a minimum tan δ of 0.0018 at 15 GHz. Therefore, these properties make the CBS–LTCC more suitable for high‐frequency applications.

Glass Microspheres Thermo-Deformation Sintering Processes in the Technologies of Obtaining Materials for Underwater Technical Equipment

Abstract In this work, the important scientific and technical problem of creating multifunctional composite materials for shipbuilding and ocean engineering was solved. The work aimed to study the thermal deformation processes of sintering glass microspheres to obtain lightweight glass composites with a cellular structure that provides positive buoyancy and sound insulation properties. For this purpose, glass microspheres of Na2O‒SiO2 and Na2O‒B2O3‒SiO2 composition with a dispersion of 10 to 60 μm were used as raw materials. They were sintered to form a closed, porous structure. The theoretical substantiation of technological parameters is based on the concepts of solid state and glassy state chemistry and physicochemical concepts of glass softening processes. The process of hot-pressing glass microspheres without plasticisers and additives was investigated. The author’s own laboratory equipment was used for the experiments. The sintering intensity was determined from the results of shrinkage processes; the kinetic shrinkage curves were constructed in semilogarithmic coordinates. The glass composite samples were examined by optical and electron microscopy. As a criterion, the storage of spherical microspheres under the influence of simultaneous heating to 700 °C with the application of pressure in the range of 0,5 to 1,5 MPa was chosen. It was established that the formation of a predominantly closed-porous structure of glass composites with a density of 350...600 kg/m3 occurs by the mechanisms of viscous glass phase flow through liquefaction processes in the walls of microspheres. At the same time, shrinkage processes in the linear direction reach up to 50%. The acoustic properties were investigated by measuring the differences in sound pressure levels in octave frequency bands using a Kundt pipe. The water absorption of the glass composite samples was determined at hydrostatic pressures up to 20 MPa. The research results were compared with the characteristics of analogue composites, such as syntactic foams and foam glass. The developed materials can be used in the design and manufacture of technical equipment for research and maintenance of underwater infrastructure. The prospects for further research are related to the feasibility study and marketing research on implementing the developed glass composites.

Low-Temperature Sintering and Infiltration of High-W Contacts

AgW materials exhibit excellent properties and are widely used as contact materials in low- and medium-voltage switches. In this study, a pre-sintering and infiltration method was employed to pre-sinter W powder with Cu, Ni, and (Cu+Ni) additions in the low temperature range of 950–1050 °C. The low-temperature sintering behaviours of W skeletons with different additives were investigated. Subsequently, AgW (70 wt%), AgW (75 wt%), AgW (80 wt%), and AgW (85 wt%) materials were prepared through infiltration at 1050 °C. The microstructure morphology and physical properties of high-W contact materials were investigated using a metallographic microscope and scanning electron microscope. The mechanism of low-temperature sintering–infiltration of high-W contact materials was elucidated. The results indicate that pure W and 1% Cu-added W skeletons experience minimal linear shrinkage within the temperature range of 950–1050 °C. The linear shrinkage curves of W skeletons with different additives coincided under the conditions of 950–1000 °C/90 min. At 1050 °C, after sintering for 150 min, the particle boundaries in the W skeleton were fully spheroidised, with a dihedral angle of 120°. At 1050 °C and after 150 min of infiltration, cross-sectional micrographs of the AgW material revealed the presence of irregular Ni layers, where Ni spatially enveloped/encapsulated Ag. With an increase in the W content, the electrical conductivity and relative density of AgW (70–85) materials decreased, whereas the hardness of the materials increased.

Mechanical and thermal properties of mud dauber nests under atmospheric drying

Mud dauber wasps construct soil nests to protect their offspring from predators, extreme temperatures, and rainwater. The mechanical and thermal properties of these nests are important for the reproductive success of mud daubers. The previous study showed that the high densities and strengths of mud dauber nests were due to the repetitive tapping and atmospheric drying used by mud daubers during nest construction. This study investigated the effect of atmospheric drying on the mechanical and thermal properties of mud dauber nests. The soil shrinkage curve, elastic modulus, suction stress characteristic curve, soil water retention curve, shear strength, and thermal conductivity function of mud dauber nest soils were measured by performing drying cake tests, direct shear tests, unconfined compression tests, and thermal conductivity measurements. This study showed atmospheric drying could increase Young’s moduli (from hundreds to thousands of kPa), the magnitudes of suction stress (up to 64 kPa), and shear strengths (e.g., unconfined compressive strength increased up to 2100 kPa) of mud dauber nests. The thermal conductivity was reduced by 47% due to atmospheric drying. Investigation of mud dauber nests under atmospheric drying could provide insights and inspiration to improve human manufacturing and manipulation of soils for earthen building construction.

DEVELOPMENT OF SHRINKAGE AND CREEP PREDICTION MODELS FOR HIGH PERFORMANCE CONCRETE BY FAST-ACCESS CLOUD-BASED DATABASE

This study presents the first analysis system and fast-access cloud database for shrinkage and creep of high-performance concrete in the world, named “shrinkage and creep database in Taiwan”, SCDT. SCDT not only has the most comprehensive experimental data, including NU, JSCE, Europe and TW database, but provides design tool for researchers and engineers. It can further facilitate the development of prediction models for localized concrete. Users can obtain the shrinkage and creep curves based on their selected prediction models in SCDT. Comparisons of predicted results of selected models and test results in chosen database can be generated in seconds. Examples of development of shrinkage and creep prediction models in Taiwan based on model B4 by using SCDT to reflect high performance concrete characteristics in Taiwan is also presented in this study. Users anywhere in the world can easily access SCDT to browse and upload data, receive predictive results, or develop predictive models.

Microwave dielectric characterization and thermal analysis of B2O3-La2O3-ZnO glass-ceramic/Al2O3 composites for LTCC applications

High frequency performance and the content of glass are the direct factors affecting the performance of LTCC. In order to reduce the content of glass and improve the performance, we conducted a systematic study on the composition regulation of B2O3-La2O3-ZnO (BLZ) glass. Glass with low softening point is helpful for LTCC to achieve compact structure. DSC shows that the softening point of BLZ glass can be reduced from 580 ℃ to 537 ℃ by adjusting the composition. XRD analysis indicate that the glass and Al2O3 formed ZnAl2O4 interfacial phases. Combined with the thermal shrinkage curve, it can be proved that the softening of glass and the formation of interfacial phases are the reasons for the shrinkage and densification of LTCC. The lowest coefficient of thermal expansion of 2.878 ppm/℃ was obtained, and the minimum loss of LTCC is 0.00277 at 15 Ghz. These properties are making LTCC more suitable for high-frequency applications.

Evaluating innovative direct and indirect soil suction and volumetric measurement techniques for the determination of soil water retention curves following drying and wetting paths

Soil Water Retention Curves (SWRC) are a main characterising component in constitutive models developed for describing unsaturated soils behaviour. Their determination requires establishing a combination of accurate soil matric suction measurements and volumetric measurements. While direct suction methods are always preferred, current methods, such as high capacity tensiometers, are limited to a measuring range of only 1.5 MPa. In this work, the novel Northumbria High Capacity Tensiometer, with an extended measuring range of up to 3.5 MPa, is used in a simplified continuous-drying setup, with proposed modifications to enhance the equalisation times and volumetric measurements. The results are then compared and validated with direct and indirect methods in both drying and wetting paths. At the same time, different volumetric measurement techniques were assessed in order to establish an understanding of Soil Shrinkage Curves (SSCs) that describe the moisture-voids relationship during drying and wetting and has the potential to be used for indirect determination of volumetric dimensions of soil specimens. Hysteresis was observed in the water retention behaviour but not in the volumetric behaviour. An established SSC model is proposed in this work and is fitted to experimental data in order to indirectly estimate volumetric measurements from the water content of small-scale specimens. The proposed novel approach standardises volumetric measurements determination, leading to uniform and complete-range SWRCs.

Sintering and microstructural behaviors of mechanically blended Nd/Sm-doped MOX

ABSTRACT Additive MOX pellets are fabricated by mechanically blending the additive material powder and MOX powder. Nd2O3 and Sm2O3 are chosen as the additive materials to simulate the corresponding soluble fission products dispersed in MOX. Shrinkage curves of the MOX pellets are obtained by dilatometry, which reveal that the sintering temperature is shifted toward a value higher than that of the respective regular MOX. The additives, however, promote grain growth and densification, which can be explained by the effect of oxidized uranium cations to a pentavalent state. Ceramography reveals large agglomerates after sintering, and Electron Probe Micro-Analysis confirms that inhomogeneous elemental distribution, whereas XRD reveals a single face-centered cubic phase except for Sm-doped specimens indicating a small peak of Sm2O3. Finally, by grinding and re-sintering the Nd2O3-doped MOX, the cation distribution homogeneity is significantly improved, which can simulate spent nuclear fuels with soluble fission products.

Concrete Shrinkage Analysis with Quicklime, Microfibers, and SRA Admixtures

This research explores the effect of various humidity conditions and the efficiency of shrinkage-reducing admixtures on the free shrinkage strain of ordinary Portland cement (OPC) concrete and its mechanical properties. An OPC concrete C30/37 mixture was replenished with 5% of quicklime and 2% of organic-compound-based liquid shrinkage-reducing agent (SRA). The investigation revealed that a combination of quicklime and SRA led to the highest reduction in concrete shrinkage strain. Polypropylene microfiber addition was not so effective in reducing the concrete shrinkage as the previous two additives did. The prediction of concrete shrinkage without quicklime additive was performed according to EC2 and B4 model methods, and the obtained results were compared with the experimental ones. The B4 model evaluates the parameters more than the EC2 model does and, therefore, was modified to calculate the concrete shrinkage for the case of variable humidity and to evaluate the effect of quicklime additive. The experimental shrinkage curve that best coincides with the theoretical one was that obtained by the modified B4 model.

Influence of compaction on the soil shrinkage and swelling curves

The behaviour of soils undergoing deformation due to changes in water content can be described using Soil Shrinkage Curves (SSCs). The SSCs are normally influenced by several factors as the soil’s fabric, different compaction levels, residual void ratio, and the shrinkage limit. In this study, shrinkage curves at different compaction levels were obtained using both wax coating and image analysis as volumetric quantification methods. Both techniques returned consistent results. To fit the obtained experimental data, a single equation is proposed with fitting parameters pertaining to the physical characteristics of the soil samples used. The use of Mercury Intrusion Porosimetry (MIP) is also incorporated to further analyse the structure of the soils being studied. The effect of the drying path on the structure was more apparent in the size range of 100-2000 nm. The effects of compaction on soil structure and shrinkage behaviour were also discussed in the study. The presented work provides valuable insights on the effect of different compaction levels on the soil shrinkage behaviour.

Исследование влияния температурно-скоростных режимов электроимпульсного плазменного спекания на микроструктуру и механические свойства оксида алюминия: анализ механизмов спекания

The effect of temperature and heating rate on the shrinkage kinetics of submicron and fine-dispersed aluminum oxide powders was investigated. The objects of the study were (1) submicron powder α-Al2O3, (2) submicron powder α-Al2O3 with an amorphous layer on the particle surface, (3) fine powder α-Al2O3. Ceramic samples were obtained by spark plasma sintering (SPS). Based on a comparison of powders (1) and (2) of the same dispersity the influence of the amorphous layer on the sintering kinetics was analyzed. Based on the comparison of powders (1) and (3) the effect of the initial particle size on the shrinkage kinetics was analyzed. Shrinkage curves were analyzed using the Young-Cutler model and the Coble model. It is shown that the sintering kinetics of submicron powders is determined by the intensity of the grain boundary diffusion process, and of fine powders by simultaneously proceeding processes of volume and grain boundary diffusion. It was found that the presence of an amorphous layer on the surface of submicron α-Al2O3 powder influences the grain boundary rate and the parameters of the Coble equation at the final stage of SPS. It was suggested that the abnormal characteristics of ceramics SPSed from submicron powder with an surface amorphous layer are related to the presence of an increased density of defects and excess free volume on the grain boundaries formed in the process of crystallization of the amorphous layer.

Drying and wetting soil-water retention behaviour of a highly expansive clay under varying initial density

Expansive (or swelling) clays are the most prolific problem soil across Southern Africa and many parts of the world. Large volume changes due to seasonal wetting and drying cause millions of dollars’ worth of damage to engineering infrastructure yearly. Soil-water retention behaviour is dependent ondensity, and determining the correct retention curve may be key for reliable design of infrastructure. Soilwater retention curves and shrinkage curves were measured for recompacted samples of a highly expansive bentonite clay from South Africa. Four samples were prepared at varying initial dry densities between approximately 1200 and 1500 kg/m3 and subjected to total suction testing in a dewpoint hygrometer. The water content of each sample was varied through wetting and drying. The sample volume was measured after each suction reading, allowing relationships between suction and void ratio, degree of saturation and water content to be determined. The relationship between gravimetric water content and suction was not significantly influenced by initial density. Degree of saturation at a given suction varied significantly according to initial density. Volume reductions of 25% to 36% from saturated to residual conditions were recorded, and samples tended to a residual void ratio of 0.35 to 0.4. The swelling clay showed propensity for maintaining high suctions (over 300 MPa at residual conditions) and hysteretic response between primary drying and wetting.