•Influence of no volume change assumption on the SWRC for low plastic soils is evaluated.•Low plastics soils undergo significant amount of volume change (about 60% of total volume) during drying.•A ...new methodology is proposed to determine unambiguous SWRC irrespective of the initial water content.•Consideration of VSC becomes mandatory after soil plasticity and clay content above 15 and 11%, respectively.
The study of unsaturated behavior of soils pivots around the relationship between soil suction and the amount of water content present in the soil mass, which is termed as soil–water retention curve (SWRC). The drying SWRC is generally determined by neglecting the volume change behavior of the soil for low plastic soils. Such a procedure is bound by an inherent assumption that the soil exhibit zero or negligible volume change and can lead to approximations in important SWRC parameters, including saturated volumetric water content, residual water content, and fitting parameters, which are essential for the estimation of unsaturated hydraulic characteristics of the soil. This study deals with the determination of SWRC parameters for a range of soils starting from non-plastic to high plastic soils, with and without considering volume change characteristics. For this purpose, the SWRC of six different natural soils were experimentally measured using a miniature tensiometer (T5) and a dew point potentiometer (WP4C), while the VSC of the used soils were measured using the balloon method. Efforts were made to critically understand the influence of no volume change assumption on the SWRC parameters, unsaturated hydraulic conductivity function, and flow of water through 1D soil column. The experimental results indicated that the no volume change assumption underpredicted the water retention curves of low plastic soils, and this error in SWRC increases with the soil plasticity. The measured VSC of the used soils further revealed that there could be a range of saturated volumetric water content (VWC) depending on the initial state of the soil sample, which also influences the sensitivity of the SWRC parameters. Therefore, the present study proposed a new methodology to determine unambiguous SWRC (in terms of VWC-suction) for a particular soil type combining both the measured VSC data and SWRC data. Based on the obtained results, it was recommended that the details of VSC must be incorporated along with the measured SWRC data for soils having plasticity and clay content higher than 15 and 11%, respectively.
Capillary pressure is frequently measured to evaluate the shrinkage performance of concrete but has been limited to pressures <100 kPa preventing a better understanding of the early age factors ...affecting concrete durability. In this study, high capacity tensiometers (HCTs) were employed for the first time to investigate the behavior of early age concrete. The evolution of capillary pressure in Self-Consolidating Concrete (SCC) with and without shrinkage reducing admixture was evaluated. The results demonstrate that HCTs are capable of measuring capillary pressure beyond 1500 kPa. This transformative new record of capillary pressure behavior has enabled the development of a model for the capillary pressure in early age concrete correlated to water evaporation, self-desiccation, setting time, temperature, and hydration processes. This ability to quantify real-time capillary pressure change in concrete generates important implications for optimizing the commercial durability of SCC and for understanding the link between early age concrete processes and resultant mechanical performance.
•A new four stage model of the capillary pressure in early age concrete is presented.•Bleeding, setting time, evaporation, and hydration govern the length of stages.•A novel technique consisting of the use of HCT is used to measure the capillary pressure of SCC up to 2 MPa.•Evaporation and self-desiccation govern the rate and value of capillary pressure.•The effect of curing time on the capillary pressure of SCC with/out SRA is different.
Interfacial viscoelastic moduli in a weak gel Jaber, Ahmad; Roques-Carmes, Thibault; Marchal, Philippe ...
Journal of colloid and interface science,
09/2022, Letnik:
622
Journal Article
Recenzirano
Display omitted
The measurement of interfacial viscoelastic moduli provides information on the ability of surface-active agents to texture the interface. However, the contribution of the bulk ...rheology cannot be ignored in particular when the continuous phase exhibits a gel-like behavior, even with low modulus.
Between 2 and 6 g/L, κ-carrageenan aqueous solutions have no significant activities at interfaces. At low concentrations or high temperatures, they behave like Newtonian liquids. Upon heating or cooling, a reversible liquid/gel transition appears with a hysteresis where the rheological behavior can be easily modulated by adjusting κ-carrageenan concentration. The frequency dependence of bulk and interfacial viscoelastic moduli are determined using a conventional shear rheometer and a drop tensiometer with a polyisobutene oil, respectively.
The effect of concentration and temperature is analyzed and the frequency dependence of interfacial moduli is correlated with those of the bulk. In presence of a gelled κ-carrageenan solutions, an elastic behavior of the interface appears and strengthens as the elastic modulus of the suspended phase is high. It turns out that the oscillating pendant drop method could be a sensitive indicator of the presence of very weak gels, even hardly detected by a shear classical rheometry.
Soil-water characteristic curve (SWCC) correlates the water content of a soil to its soil suction, which is a very important property of unsaturated soils. Osmotic tensiometers (OTs) have shown their ...capability in high soil suction measurement. This study tried to use OT combined with a pressure plate and WP4C dewpoint potentiometer to determine the SWCC of a residual soil. Three OTs with different measuring ranges (900 kPa, 1200 kPa, 2300 kPa) were prepared for soil suction measurement. The temperature effect on the pressure variations of OTs was illustrated based on Flory-Huggins polymer theories and an appropriate calibration equation was proposed to eliminate the temperature effect on the accuracy of soil suction measurement using OT. The OT showed a fast response in soil suction measurement and the equilibrium can be established in 10–15 min during SWCC measurement. Comparison of the SWCC data obtained from the pressure plate, OT, and WP4C dewpoint potentiometer proves that the OT had good performance in the determination of SWCC, especially for the transition zone (i.e., 10–1500 kPa suction range), by providing more data points to define the SWCC in a shorter period. The results show that the usage of OT will shorten the time required for the determination of SWCC and could be considered as a new and reliable technique in SWCC measurement.
•OT combined with a pressure plate and WP4C dewpoint potentiometer to determine the SWCC of a residual soil.•Insiginificant pressure decay effect for short-time suction measurement using OT.•Temperature calibration based on Flory-Huggins polymer theories to improve the accuracy of OT suction measurement.•OT provided more data points to define the SWCC especially in the transition zone in a shorter period.
Soil-water characteristic curve (SWCC) and coefficient of permeability (k) are amongst the most crucial soil properties in unsaturated soil mechanics for soil moisture conservation. The direct ...measurement and prediction of such properties are important to engineering applications, but they are complicated. This study developed a new experimental setup (the OT permeameter) using osmotic tensiometers (OTs) and the continuous evaporation method. The proposed OT permeameter could directly measure SWCC and k up to 1000 kPa suction within one to two weeks. Moreover, the proposed setup is fully automated and data processing was minimal. In addition, a new general equation has been developed to predict and best fit the unsaturated k measurement. The proposed equation uses a minimal number of parameters that carry physical meaning and provides an intuitive and easy way to predict and best-fit k measurement. The accuracy and robustness of both the proposed OT permeameter and prediction equation were evaluated using published data and experimental data from this study.
Peat-based casings have been used for button mushroom (Agaricus bisporus) cultivation for decades but there is environmental pressure to find sustainable alternatives. This work aimed to characterise ...the physicochemical properties of peat and peat-substituted casings and to determine their influence on mushroom cropping to enable alternatives to be identified. British milled peat and German wet-dug peat casings produced smaller mushrooms than Irish wet-dug peat casing although yield was unaffected. Substitution of milled or wet-dug peat casings with 25% v/v bark, green waste compost or spent mushroom casing, except Irish wet-dug peat casing with spent peat mushroom casing, caused reductions in mushroom yield and/or size. These poorer results of casings compared with Irish wet-dug peat casing corresponded with lower water retention volumes at matric potential (Ψm) −15 kPa but not after drainage from saturation or at −1 kPa. Air-filled porosity (17–22% v/v), compacted bulk density after drainage (670–800 g L−1) and electrical conductivity (0.30–0.54 mS cm−1) of casings were unrelated to their mushroom cropping performance. In-situ casing measurements with electronic tensiometers confirmed laboratory casing physical analysis: at the same casing Ψm, Irish wet-dug peat casing had a higher water content than German wet-dug peat casing and produced larger mushrooms for the same yield. Solid-state foam-based tensiometers were more robust than water-filled tensiometers but they did not detect the full decrease in casing Ψm during a flush of mushrooms. The results indicate that if sustainable materials are to replace wet-dug peat casing with the same mushroom yield and size quality performance, they should have equivalent water retention volumes at Ψm −15 kPa. Measurement of casing Ψm with electronic tensiometers to control mushroom crop irrigation should assist in this transition.
The desire of improving various processes like enhanced oil recovery (EOR), water treatment technologies, biomass extraction, organic synthesis, carbon capture etc. in which conventional surfactants ...have been traditionally utilized; prompted various researchers to explore the self-assembly and aggregation behavior of different kinds of surface-active molecules. Ionic liquids (ILs) with long alkyl chain present in their structure constitute the advantageous properties of surfactant and ILs, hence termed as surface-active ionic liquids (SAILs). The addition of ILs and SAILs significantly influence the surface-activity and aggregation behavior of industrially useful conventional surfactants. After a brief review of ILs, SAILs and surfactants, the prime focus is made on analyzing the self-assembly of SAILs and the mixed micellization behavior of conventional surfactants with different ILs.
The high-capacity tensiometer and thermocouple psychrometer measure xylem water potential with high accuracy and adequate response time, as demonstrated by simultaneous measurements on sapling stems.
...Abstract
The pressure chamber, the most popular method used to measure xylem water potential, is a discontinuous and destructive technique and is therefore not suitable for automated monitoring. Continuous non-destructive monitoring could until very recently be achieved only by use of the thermocouple psychrometer (TP). Here we present the high-capacity tensiometer (HCT) as an alternative method for continuous non-destructive monitoring. This provided us with a unique chance to cross-validate the two instruments by installing them simultaneously on the same sapling stem. The HCT and the TP showed excellent agreement for xylem water potential less than –0.5 MPa. Response to day/night cycles and watering was remarkably in phase, indicating excellent response time of both instruments despite substantially different working principles. For xylem water potential greater than –0.5 MPa, the discrepancies sometimes observed between the HCT and TP were mainly attributed to the kaolin paste used to establish contact between the xylem and the HCT, which becomes hydraulically poorly conductive in this range of water potential once dried beyond its air-entry value and subsequently re-wetted. Notwithstanding this limitation, which can be overcome by selecting a clay paste with higher air-entry value, the HCT has been shown to represent a valid alternative to the TP.
Cable control systems are widely used in GA aircrafts and gliders. The paper deals with the accuracy of measurement the tension of cables on the production stage and maintenance of aeronautical ...products. Producers of measuring instruments used to measure tension don’t explicitly define how to calibrate them and stipulate to use special methods and stands. The paper discusses the possible method of tension measurement, measuring tools, methods of calibration and possible errors the adopted measurement and calibration methods as well. The possible error analysis to take into consideration, the stands construction and details: measuring instruments system, temperature influence length of reference cable etc.
Significant advances in unsaturated soils testing have been gained through the development of high suction tensiometers allowing direct measurement of suction beyond 100kPa. This has allowed the ...implementation of techniques that measure and control suction directly, where the soil is tested in the same conditions as in nature. Previously, much reliance had been placed on indirect measurements of suction and on control of suction using the axis translation technique. It is argued that this technique should be avoided as the use of an elevated air pressure does not replicate natural conditions. This paper presents advances resulting from the use of high suction tensiometers for laboratory testing and field measurements. It also describes an automated suction control system using the air circulation method that can impose controlled cycles of drying and wetting.
► Development of high suction tensiometers. ► Identification of saturation and calibration procedures. ► An alternative to the axis translation technique for testing unsaturated soils. ► Determination of soil water retention curves with high suction tensiometers. ► An automated suction control system using air circulation.
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