Shrinkage Curve Research Articles

Shrinkage of Micro-Synthetic Fiber-Reinforced Mortar

Repair materials have been developed in this research by adding micro-synthetic fibers in cement-based mortar. In addition, accelerator is incorporated in the mortar to obtain high early strength of the repair materials. Their shrinkage behavior is of interest. This study aims to determine the shrinkage of the micro-synthetic fiber-reinforced mortar and propose models to reflect their shrinkage behavior. The results show that rapid developments of shrinkage are observed at an early age where the 3-day shrinkage already attains about 40–50% of the 84-day shrinkage value. Moreover, after 14 days of age the shrinkage curves tend to approach the asymptotic value. The ACI 209.2R-08 and CEB-MC 90-99 models do not reflect the shape of the shrinkage curves of the micro-synthetic fiber-reinforced mortar. Therefore, this research proposes a modified ACI 209.2R-08 and CEB-MC 90-99 that can describe the shrinkage behavior of the micro-synthetic fiber-reinforced mortar. The accuracy of the modified models has been confirmed quantitatively using the method of best fit line, residual analysis, and coefficient of error.

In-situ assessment of soil shrinkage and swelling behavior and hydro-thermal regimes with a thermo-time domain reflectometry technique

The shrinkage and swelling behaviors of clayey soils could lead to cracks and erosions inducing severe damages to agricultural lands and engineering projects. Thus, improving the understanding of shrink-swell characteristics is crucial to nonrigid soils. However, it remains difficult for in-situ monitoring of soil shrink-swell processes continuously and nondestructively. The objective of this study was to present a thermo-time domain reflectometry (thermo-TDR) technique for determination of soil shrinkage and swelling dynamics and hydro-thermal regimes in-situ during wet-dry cycles. A field experiment on two clayey soils (a paddy soil and an alluvial soil) was conducted to evaluate the performance of the thermo-TDR method for in-situ determination of soil volume changes and associated hydraulic and thermal properties during wet-dry cycles. The results showed that both soils experienced considerable shrinking and swelling processes with maximum vertical deformations of 2.4 and 1.8 cm for the paddy soil and alluvial soil, respectively, and with maximum horizontal deformations of 370 and 280 cm2 for the paddy soil and alluvial soil, respectively, during a 36-day period. The thermo-TDR method provided volume change values (shown as the bulk density) agreed well with independent core-sampling measurements with an average RMSE of 0.15 Mg m−3 and a R2 of 0.46. A better agreement was observed between thermo-TDR measured bulk densities and values from the ruler-image processing method with an average RMSE of 0.07 Mg m−3 and a R2 of 0.77. Besides, the thermo-TDR method gave consistent in-situ soil shrinkage curve and water retention surface measurements by combining with soil matric potential sensors. Unlike rigid soils, the paddy and alluvial soils showed complicated hydro-thermal regimes in response to the shrink-swell processes. We conclude that the thermo-TDR technique is a reliable tool for continuous in-situ determination of soil shrink-swell processes. Future studies should focus on development of comprehensive soil heat and water transport models accounting for both moisture content and volume changes.

Pyrolysis and CO2 gasification of biomass in high-temperature stage microscope: Morphological evolution and thermal behaviors

The morphological evolution of biomass particles during pyrolysis and char gasification was investigated by a high-temperature stage microscope (HTSM), and realistic particle shrinkage characteristics were obtained in combination with weight loss properties. Also, product properties were obtained on a fixed-bed and the influence of the physicochemical properties of the char on the gasification activity was considered. Several typical biomass samples were selected, including poplar sawdust, rice husk, and steamed rice. As a starchy biomass, steamed rice particles underwent intense swelling at 300–330 °C, followed by shrinkage, and finally formed an internal loose and porous char, which was significantly different from lignocellulosic biomass. For lignocellulosic biomass, poplar sawdust and rice husk particles showed similar shrinkage processes during pyrolysis. By comparing the curves of particle shrinkage and weight loss, the development of internal pore volume of particles was reflected in a general way, which can better guide the construction of biomass shrinkage mechanism model. The gasification activity of the three biomass pyrolysis chars differed considerably and consistent conclusions were obtained in terms of particle shrinkage, weight loss, and gas products. The poplar sawdust char showed acute shrinkage of particles and loss of weight, exhibiting the strongest gasification activity, 6 times that of rice husk char and steamed rice char. The gasification activity of the char depended mainly on the degree of graphitization and was almost independent of the mesoporous structure. In the temperature range of 800–900 °C, higher gasification temperatures corresponded to more rapid particle shrinkage and weight loss, higher gas product yield, and greater gasification activity.

Structural, volumetric and water retention behaviors of a compacted clay upon saline intrusion and freeze-thaw cycles

This study investigates the evolution of the structural, volumetric and water retention behaviors of a compacted clay during soaking and desiccation considering the influences of freeze-thaw (FT) cycles and saline intrusion. Compacted specimens were subjected to different FT cycles and then submerged in NaCl solution with different concentrations to facilitate the saline intrusion and measure the swelling behaviors. Shrinkage curve and filter paper tests were thereafter performed to reveal the clay's volumetric and water-retention characteristics during desiccation. Mercury intrusion porosimetry and field emission scanning electron microscopy tests were conducted to observe the evolution of the clay's microstructure. Experimental results show that the clay's micropores decrease and macropores increase after FT cycles, which is associated with the migration of water, growth of ice crystals, and development of FT-induced cracks during FT cycles. Similar observations were obtained from specimens after the saline intrusion, which is attributed to the osmotic and osmotically-induced consolidation. FT-induced cracks significantly reduce the clay's swelling and shrinkage potentials. FT cycles result in the shrinkage of micropores which leads to a reduction in the water retention capacity in the low suction range (capillary regime). The salinization suppresses the swelling of the clay and prolongs its primary and secondary swelling stages. The shrinkage potential initially increases and then decreases with increasing saline concentration. Salinization has significant influences on the osmotic suction and thus alters the clay's water-retention curves in terms of total suction. It demonstrates little impact on the clay's water-retention curves in terms of matric suction. • Studied joint effects of FT action and saline intrusion on a compacted clay. • Micropores decrease and macropores increase upon FT cycles and salinization. • Swelling and shrinkage potentials reduce after FT cycles and saline intrusion. • Salinity and FT mainly affect adsorptive and capillary effects, respectively.

Effect of grain boundary state and grain size on the microstructure and mechanical properties of alumina obtained by SPS: A case of the amorphous layer on particle surface

The work was aimed at the investigation of kinetics of Spark Plasma Sintering (SPS) of the α-Al2O3 particles with amorphous surface layers and investigation of the effect of the amorphous layers on the grain growth and on the mechanical properties of alumina. The objects of investigations comprised:(i) submicron α-Al2O3 powder, (ii) submicron α-Al2O3 powder with the amorphous layers on the particles' surfaces, and (iii) the fine-grained α-Al2O3 powder. The submicron powders (i) and (ii) were used to analyze the effect of the amorphous layers on the sintering kinetics. Powders (i) and (iii) were used to analyze the effect of the initial particle sizes on the shrinkage kinetics. The effect of the temperature regime and of the rate (Vh) on the shrinkage kinetics of the submicron and fine alumina powders has been studied. The shrinkage curves were analyzed using the Young–Cutler and Coble models. The sintering kinetics was shown to be determined by the intensity of grain boundary diffusion for the submicron powders and by simultaneous lattice diffusion and grain boundary one for the fine powders. The amorphous layers on the surfaces of the submicron α-Al2O3 particles were found to affect the grain boundary migration rate and the Coble equation parameters at the final stages of SPS. The abnormal characteristics of the alumina ceramics sintered from the submicron powder with the amorphous layers on the particles’ surfaces were suggested to originate from the increased concentration of the defects and of the excess free volume at the grain boundaries formed during crystallization of the amorphous layers.

Influence of Desaturation and Shrinkage on Evaporative Flux from Soils

An assessment of evaporation losses from soils is critical for sustainable agriculture in semi-arid regions. The purpose of this research was to determine the effect of desaturation and shrinkage on evaporative flux from representative soils. Results indicated that the surface area did not change for silty sand (6% volume reduction) and substantially increased for lean clay (17% volume reduction). The evaporative flux for silty sand decreased from 31 to 25 mg/m2∙s in Stage II, remained constant during Stage III, and decreased to 11 mg/m2∙s in Stage IV. In contrast, the lean clay showed a longer Stage II (34 to 14 mg/m2∙s), a near constant Stage III, albeit a similar Stage IV (13 to 3 mg/m2∙s). The air entry and residual suction values were 1 kPa and 100 kPa for silty sand and 5 kPa and 1400 kPa for lean clay. In both soils, the total suction merged with the matric suction at Stage II–Stage III boundary. Furthermore, the shrinkage curve was J-shaped for silty sand with the only void ratio decrease in Stage II, whereas that for the lean clay showed a significant void ratio decrease in Stage II, marginal decrease in Stage III, and no decrease in Stage IV. Under high demand, the silty sand exhibited Stage III and Stage IV evaporation, whereas the lean clay also showed significant flux during Stage II. For the investigated range of water content, the total water loss under high demand was found to be 7 times that under low demand.

A critical saturated state-based constitutive model for volumetric behavior of compacted bentonite

In recent years, more and more unique volumetric behaviors, including the nonlinear compression and unloading curves in the e-lnp plane, and different types of swelling and shrinkage curves obtained from suction-controlled swelling and shrinkage tests, etc., which are significantly different from those of nonexpansive clays, have been reported on compacted bentonite. More importantly, limitations were encountered when describing the unique behavior with existing constitutive models for unsaturated expansive soils. In this study, a new concept of critical saturation state (CSS) was proposed for compacted bentonite, in which, as the saturated state was reached, the matric suction still remained nonzero in the soil. Incorporated with this concept, a constitutive model was proposed. In this model, the CSS curve was defined in the suction-isotropic stress plane, delimiting the unsaturated zone. To validate the model, the volume change tests conducted on compacted GMZ bentonite under different stress paths were simulated. Good agreement confirmed that the proposed model could well describe the volume change behavior, including the swelling on hydration, shrinkage during drying, nonlinear compression, and unloading behavior.

Parametric dependency of a constitutive model describing solid state sintering of cemented carbides

This study focuses on an inverse modelling approach, using FEM to simulate the sintering of WC-Co powder using a continuum model. From a previously developed constitutive model of cemented carbide, the dependency of the material parameters is investigated in a sensitivity study. A value of sensitivity is assigned to all the material parameters and calculated at different steps in the sintering process, which represent its importance for capturing the shrinkage during sintering. The approach is that only the more sensitive parameters should be fitted when changing experimental setup or material composition, leaving the less important parameters constant, resulting in fewer tests and iterations. This approach is tested in an optimization of WC-Co powder sintering cycle, where the shrinkage curve is experimentally determined. It is concluded that some of the material parameters play a minor role in the modelling and could be set as constants in an optimization. The constitutive material model alone is unable to capture all features that appeared in the shrinkage curve during the experiment. Improvements of the model are discussed. An additional investigation, performed without heating rate dependency, shows that the remaining material parameters could compensate for the omitted heating rate for a known sintering cycle without losing accuracy.

Impact of calcareous concretions on soil shrinkage of a Vertisol and their relation model development

Shajiang black soil (Vertisol) has a high shrinkage capacity and contains many calcareous concretions (CC). We assume the volume of CC to be rigid during wetting and drying cycles. Thus, the soil containing CC may have different shrinkage behavior from that of fine soils (without CC). We aimed to quantify the effects of CC content and size on soil shrinkage behavior, as well as to develop a model to characterize the relationship among the void ratio (e), moisture ratio (υ), and solid volume of CC (Csv) in Shajiang black soil. Four different sizes (2–5, 5–10, 10–20 and, 20–30 mm) of the CC at a rate of 10% on mass, and four different contents (0, 5%, 10%, and 20% on mass) of 5–10 mm CCs were mixed into the fine soils to prepare the CC-soil mixtures. Our results showed that the increasing CC content significantly reduced the saturated void ratio (es), coefficient of linear extensibility (COLE), and shrinkage index of all pores except the medium pores (P < 0.05), but the CC size did not. The shrinkage curves of the CC–soil mixtures were proportional to that of the fine soil, which was modified by the portion of CC volume in the CC–soil mixtures. We proposed a new numerical equation based on Peng and Horn shrinkage model (2005) to illustrate the relationship among e– υ –Csv. The shrinkage curve of the CC–soil mixture was predicted well (R2 = 0.95–0.98) by the new model based on that of fine soil and the CC volume modification. However, the proposed model underestimated the volume change for the dry side of the shrinkage curve, in which the swelling and shrinkage of fine soil matrix among CCs were partially concealed. Our work demonstrates that the CC in the Shajiang black soil does not change soil shrinkage behavior except the modification of void ratio, and thus its shrinkage curve can be estimated from that of the non-CC soil. It can be concluded that this study provides a useful model for estimating the shrinkage behavior of soils containing rigid coarse inclusions.

A New Boosting Algorithm for Shrinkage Curve Learning

To a large extent, classical boosting denoising algorithms can improve denoising performance. However, these algorithms can only work well when the denoisers are linear. In this paper, we propose a boosting algorithm that can be used for a nonlinear denoiser. We further implement the proposed algorithm into a shrinkage curve learning denoising algorithm, which is a nonlinear denoiser. Concurrently, the convergence of the proposed algorithm is proved. Experimental results indicate that the proposed algorithm is effective and the dependence of the shrinkage curve learning denoising algorithm on training samples has improved. In addition, the proposed algorithm can achieve better performance in terms of visual quality and peak signal-to-noise ratio (PSNR).

The role of heating rate on the sintering of glass powders

AbstractIt is proposed that heating rate affects the apparent sintering temperatures of glass powders. The accumulation of thermal energy over time, or heat work (K s), is calculated over the range from the glass transition temperature to sintering temperature with the logarithm of time for heating rates from 1 to 60 K/min. The required heat work is independent of heating rate for two silicate glass powders but shows a decreasing heat work requirement for increasing heating rates for a borosilicate glass powder. Small cylindrical powder compact samples were used to minimize heat‐transfer problems and were observed thermoanalytically using a hot‐stage microscope. The densification temperature, defined as the peak in the shrinkage versus temperature curve, increases with increasing heating rate and is sensitive to the initial compact density. The use of mechanically pressed compacts with similar compact densities minimizes the contribution of initial density, allowing the comparison of sintering behavior as a function of heating rate.

Improving internal curing efficiency through adjusting ab- and desorption curve of superabsorbent polymer in cement pastes using sodium carbonate

Superabsorbent polymer (SAP) has a prominent effect on relieving autogenous shrinkage of low w/c cement-based materials. It is quite important to improve internal curing efficiency of SAP considering the concrete performance and economic cost. In this paper, proper Na2CO3 dosage by cement mass was added into cement pastes to improve internal curing efficiency of SAP. Through X-ray radiography, the ab- and desorption curves of SAP in cement pastes with different Na2CO3 dosage were characterized. Through corrugated tube method, the autogenous shrinkage curves in SAP-containing cement pastes with and without optimal Na2CO3 dosage were obtained. From the view of effective internal curing water content of SAP, internal curing efficiency of SAP with 0.2 wt% SAP dosage and optimal 0.4 wt% Na2CO3 dosage can be improved by 52.3%, compared to that without Na2CO3. From the view of autogenous shrinkage curves, to achieve same internal curing effect, 0.4 wt% SAP dosage can be approximately reduced to 0.3 wt% SAP dosage, with 25% reduction rate of SAP dosage through adding 0.4 wt% optimal Na2CO3 dosage. Further, the mechanism of improving internal curing efficiency of SAP with proper Na2CO3 dosage is revealed.

Experimental Investigation on the Impact of Drying–Wetting Cycles on the Shrink–Swell Behavior of Clay Loam in Farmland

Soil shrink–swell behavior is a common phenomenon in farmland, which usually alters the process of water and solute migration in soil. In this paper, we report on a phenomenological investigation aimed at exploring the impact of drying–wetting cycles on the shrink–swell behavior of soil in farmland. Samples were prepared using clay loam collected from farmland and subjected to four drying–wetting cycles. The vertical deformation of soil was measured by a vernier caliper, and the horizontal deformation was captured by a digital camera and then calculated via an image processing technique. The results showed that the height, equivalent diameter, volume and shrinkage-swelling potential of the soil decreased with the repeated cycles. Irreversible deformation (shrinkage accumulation) was observed during cycles, suggesting that soil cracks might form owing to previous drying rather than current drying. The vertical shrinkage process consisted of two stages: a declining stage and a residual stage, while the horizontal shrinkage process had one more stage, a constant stage at the initial time of drying. The VG-Peng model fit the soil shrinkage curves very well, and all shrinkage curves had four complete shrinkage zones. Drying–wetting cycles had a substantial impact on the soil shrinkage curves, causing significant changes in the distribution of void ratio and moisture ratio in the four zones. However, the impact weakened as the number of cycles increased because the soil structure became more stable. Vertical shrinkage dominated soil deformation at the early stage of drying owing to the effect of gravity, while nearly isotropic shrinkage occurred after entering residual shrinkage. Our study revealed the irreversible deformation and deformation anisotropy of clay loam collected from farmland during drying–wetting cycles and analyzed the shrink–swell behavior during cycles from both macroscopic and microscopic points of view. The results are expected to improve the understanding of the shrink–swell behavior of clay loam and the development of soil desiccation cracks, which will be benefit research on water and solute migration in farmland.

Unified Elastic Modulus Characteristic Curve Equation for Variably Saturated Soils

A soil’s elastic modulus is a fundamental property defining the soil’s reversible stress-strain relation under mechanical and environmental loadings. It has been observed that a soil’s elastic modulus can increase up to several orders of magnitude from fully saturated to dry conditions due to two distinct soil water retention mechanisms: adsorption and capillarity. Adsorption affects interparticle stress through van der Waals and electrostatic attraction and interparticle friction coefficient through water film retained by soil sorptive potential. Capillarity governs interparticle stress through capillary pressure and surface tension. The onset and scaling laws of the two mechanisms depend on the soil properties of specific surface area, pore-size distribution, cation exchange capacity, and soil mineralogy. These mechanisms are unified by a proposed elastic modulus characteristic curve (EMCC) equation. It is demonstrated that the proposed EMCC equation can well describe the moisture-dependent elastic modulus of a wide array of soils. Further, an interrelation among the EMCC equation, suction stress and soil shrinkage curves is established, which can greatly facilitate predicting suction stress from soil shrinkage curves and vice versa, further validating the EMCC equation in capturing soil’s hydromechanical behavior. The practical importance of the EMCC equation is demonstrated through prediction of ground heave of various soils due to a hypothetical flooding event.

Sintering behavior of BaCe0.7Zr0.1Y0.2O3-δ electrolyte at 1150 °C with the utilization of CuO and Bi2O3 as sintering aids and its electrical performance

BaCe0.7Zr0.1Y0.2O3-δ (BCZY) is one of the promising electrolytic candidate for solid oxide fuel cell (SOFC) due to its good proton conductivity and better stability. Herein, the effect of dual sintering aids such as CuO-Bi2O3 upon the sinterability at low temperature, improved electrochemical properties, and thermo-chemical changes about proton-conducting BaCe0.7Zr0.1Y0.2O3-δ electrolyte were investigated in detail. FESEM micrographs and shrinkage curves revealed significant improvement in sinterability and densifications of BCZY electrolyte. The dense pellets were sintered with CuO-Bi2O3 (2–3 mol %) as sintering aids at a temperature of 1150 °C for 5 h. The perfectly uniform distribution of sintering aids increased the linear shrinkage of BCZY from 5% till 19–21%. The crystallite size and grain growth within the structure was enhanced due to the formation of the melting phase of Bi2O3 and Cu2+ incorporation in the perovskite structure. The elevated and improved electrochemical measurement for BCZY with 2 mol% of CuO-Bi2O3 as sintering aid categorized it well suited for solid oxide fuel cells.

Study of the volumetric behavior of a residual tropical clay

This paper focuses on the volumetric behavior of residual tropical soils. Two residual tropical soils belonging to the same geological formation and located in the coastal sedimentary basin of Gabon are studied. These soils are known as pelitic soils. As the hydromechanical behavior of residual tropical soils is still relatively unknown, it is interesting to study the influence of suction on the volumetric behavior of these soils through shrinkage curves. The purpose of this study is twofold. First, to study the volume variations in the two studied residual tropical soils with suction changes. Secondly, to propose a modelling of soil-water retention curves (SWRCs) of these soils. For this purpose, shrinkage tests are carried out to study the volume variations of the studied soils. These tests are supported by determining a bilinear approximation model to enable the variation in suction during drying to be estimated. Tests to determine SWRCs at different initial dry densities are used to calibrate the bilinear approximation model between void ratio and suction. The modified Kovács model (MK model) has been adapted to model SWRCs of the studied soils.

Comparative study of LuxY1-xAG (x=0..1) laser ceramics doped with 5% Yb3+

Materials with high thermo mechanical properties are required as laser media for high-powered lasers. One of such materials is lutetium-aluminum garnet (LuAG) doped with ytterbium. In the present work, we discuss for the first time a full comparative study of 5% Yb-doped LuYAG ceramics with variation Lu/Y ratio. Samples were prepared with addition of B2O3, MgO and SiO2 which were used as sintering aids. Grain sizes, shrinkage curves, lattice constants and transmission spectra were measured for all samples. Thermal conductivity was measured in a wide temperature range for all studied samples. Output power of 12 W and 60% slope efficiency were obtained on the 5% Yb:LuAG disk laser.

The investigation and regulation of fusion characteristics of coal ash with high sulfur and basic oxides level for the slagging gasifier

The slagging gasifier is one of the best options for coal utilization to achieve carbon neutral due to high carbon conversion and low contaminative gas emission. The slagging gasifier requires proper ash fusibility to ensure smooth slag tapping, but the knowledge concerning fusion behaviors of coal ash with high sulfur and basic oxides level is unclear, which results in the limited utilization of coal which contains high level of sulfur and alkali in ash. Here, the fusion behaviors of coal ash with high sulfur and basic oxide level with/without additives are characterized by ash fusion temperature (AFT) analyzer and thermal mechanical analysis (TMA), and the underlying mechanism is revealed by combination of thermogravimetry (TG), X-ray diffractometer (XRD), and thermodynamic calculation. The results demonstrate that standard ashing procedure impacts the transformation of minerals of coal ash with high sulfur and basic oxide level. The influence of volatiles discharging during standard ash preparation on the shrinkage curve depends on the liquid phase sintering behavior. Besides, the performance of additives connects the ability of additives to volatiles retention. Specifically, accumulation of sulfates by additives leads to the AFTs of Neimeng coal ash increase with increasing additives in the range of 0 to 20%, while the retention of Na-containing minerals by kaolinite gives rise to the dropping AFTs of Wucaiwan coal ash. The study can support the utilization of coal which contains high level of sulfur and alkali in coal ash in the slagging gasifier.

Densification, microstructure and optical properties of YAG transparent ceramics prepared by dry-pressing and gelcasting

The effects of dry-pressing and gelcasting on the densification, microstructure and optical properties of YAG transparent ceramics were researched. The gelcasting samples had smoother and more uniform surface without agglomeration, but its average pore size was larger than that of the dry-pressing samples. The dynamic densification curves showed three continuous transition stages. The initial temperature of densification for the gelcasting samples was higher than that for the dry-pressing samples, but the initial temperature of obvious grain growth for the gelcasting samples were relatively lower. After being sintered at 1750 °C for 10 h, the transmittances at 1064 nm of samples (thickness of 1 mm) prepared by dry-pressing and gelcasting were about 77.79% and 81.26%, respectively. These two forming methods had difference influences on the microstructure, the dynamic shrinkage curves and the microstructure evolution of green bodies or ceramics, which could further impact the properties of YAG transparent ceramics. In a word, the gelcasting had certain advantages over the dry-pressing in preparing YAG transparent ceramics.

Measuring shrinkage of undisturbed soil peds

AbstractMethods to measure shrinkage curves typically either disturb natural aggregate structure or include difficult or slow volume measurement techniques. Additionally, most shrinkage curves are obtained by serial measurement of a few samples. We obtained shrinkage curves by collecting rapid, one‐off measurements of volume and moisture content for each of 200 undisturbed peds extracted from a field soil, taking measurements as peds slowly dried in the laboratory. The large sample size increased robustness of the shrinkage curve parameter estimates to noise generated by this rapid measurement technique, but a much smaller sample would have resulted in similar parameter estimates.