Sealed Conditions Research Articles

Mitigation of efflorescence for multi-componential geopolymer: Influence of steel slag, flue gas desulfurization gypsum and pre-curing periods

Efflorescence is always a major problem that prohibits the wide application of geopolymer. It reduces mechanical strength, increases surface degradation and lowers the durability of geopolymer. This study investigates the efflorescence and mitigation techniques of the geopolymer synthesized with fly ash (FA), granulated blast furnace slag (GBFS), steel slag (SS) and flue gas desulfurization gypsum (FGD). It was found that pre-curing in sealed condition for 3 and 7 days could improve both the compressive strength and the efflorescence resistance of the geopolymers in both ambient and accelerated conditions. Adding SS improved the compressive strength of multi-componential geopolymers by forming more C-(A)-S-H and N(C)-A-S-H gels, while was not effective in reducing efflorescence. The efflorescing problem became more serious with the addition of FGD due to the formation of new efflorescence product of Na2SO4. It was also found that the w(OH−), w(CO32−) and w(Na+) of the leachate obtained by soaking geopolymer in deionized water can describe the efflorescence more quantitively than visual characterization. The correlation between the porosity, w(Na+), efflorescence and compressive strength was also established, which shed light on better understanding and mitigating the efflorescence of multi-componential geopolymers.

Leakage Threshold of a Saddle Point

The threshold condition for leakage inception is of great interest to many engineering applications, and it is essential for seal design. In the current study, the leakage threshold is studied by means of a numerical method for a mechanical contact problem between an elastic bi-sinusoidal surface and a rigid flat surface. The coalesce process of the contact patches is first investigated, and a generalized form of solution for the relation between the contact area ratio and the average applied pressure is acquired. The current study shows that the critical value of the average applied pressure and the corresponding contact area required to close the percolation path can be represented as a power law of a shape parameter, if the effect of the hydrostatic load from the pressurized fluid is ignored. With contact patches merged under a constant applied load, the contact breakup process is investigated with elevated sealed fluid pressure condition, and it is shown that the leakage threshold is a function of the excess pressure, which is defined as a ratio between the average applied pressure and the critical pressure under dry contact conditions.Graphical abstract

Influence of some factors on the mechanical properties of cement-treated clay for shallow mixing in Vietnam: A comparative study

The compressive strength of cement-treated soil is known as the most crucial factor, which governs the quality of cement-treated soils. Indeed, many factors affect the compressive strength of cement-treated soils, including cement types and contents, water/cement ratio, soil types, as well as curing conditions, etc. In which, curing conditions, cement types, and soil types are the most important factors that govern the compressive and durability of cement-treated clay. Three cement types and two types of clay were used to prepare the specimens of cement-treated clay with three cement dosages (100, 150, and 200 kg/m3 of soil). The specimens of cement-treated clay were cured under two conditions (sealed and drying). The results showed that drying conditions significantly increased the unconfined compressive strength of cement-treated soils regardless of cement types, cement contents, soil types, and ages as compared to those under sealed conditions. The unconfined compressive strength of specimens under drying conditions was approximately 1.3–2.5 times higher than that under sealed conditions. Cement type significantly affected the performance (compressive strength and elastic modulus) of cement-treated clay regardless of cement content. The cement-treated clay specimens under sealed conditions showed a ductile failure mode while those under drying conditions exhibited a brittle failure mode. Finally, soil type significantly influenced the compressive strength and elastic modulus of cement-treated clay regardless of cement content and curing condition.

Experimental and numerical investigation of moisture variations in unbound pavements with sprayed seals during drying and wetting

Unbound pavements with sprayed seals are one of the major types of flexible pavements used worldwide. Sprayed sealing can be considered as an economical surfacing method in particularly Australia and New Zealand due to the low initial cost. However, moisture can enter the underlying pavement layers through sprayed seals as they are variably permeable, resulting in significant performance losses in underlying pavement structural layers. Hence, an in-depth understanding of how moisture varies in the base layer under different sprayed seals is essential for designing and maintaining pavement to meet the required long-term performance.This paper investigates moisture variations in unbound base layers under typical sprayed seals using experimental and numerical techniques. Pavement layers were replicated in the laboratory in columns with three different sealing conditions such as unsealed, 10 mm single-single sealed and 14 mm single-single sealed. The moisture variations in the base layers were monitored under drying and wetting conditions using moisture sensors over several months with targeted experiments. Moreover, this study characterises two typical types of sprayed seal samples collected from operating road surfaces using X-ray tomography and laboratory experiments. The experimental results show that typical single-single sprayed seals exhibit porosity in the range of 5% to 8%, leading to saturated permeability from 10−6 to 10−7 m/s. The numerical simulations show that significant drying and wetting of the base layer occurs when the pavement operates under actual climatic conditions. In addition, this study reveals that for a given seal condition, it is easier for moisture to enter the unbound base than drying out of the base layer once the moisture has entered. However, the drying rate depends on the saturation condition of the base layer before drying begins.

Experimental and numerical study on an innovative protective measure for high strength concrete using the bilayer method

Fire-induced spalling is an ongoing primary concern in the application of high-strength concrete in building structures. A reliable and practical protective method is thus highly desirable and critical for the prevention of fire-induced spalling. Therefore, an innovative bilayer method, in which high strength concrete is surrounded by a layer of normal strength concrete of sufficient thickness, is proposed. A total of 20 columns are cast to investigate the feasibility of the bilayer design, of which 15 are put to fire testing and the other five to ambient compression testing. The effects of protective layer thickness, duration of exposure to fire, sealed condition and reinforcement confinement are investigated. Experimental results indicate that the performance of bilayer columns is similar to that of high strength concrete columns with regard to strength and deformation. Fire-induced spalling occurs within the first 30 min of heating at an interface temperature of around 150 °C. Lastly, a minimum effective thickness of 100 mm is recommended to prevent spalling.

Bactericidal Effect and Associated Properties of Non-Electrolytic Hypochlorite Water on Foodborne Pathogenic Bacteria.

This study investigated the broad-spectrum bactericidal activity of non-electrolytic hypochlorite water (NEHW) and detected its hydroxyl radical content compared with that of slightly acidic electrolytic water (SAEW). Based on the results of UV scanning and storage stability, higher hypochlorite content and stronger oxidation were found to be responsible for the stronger bactericidal effect of NEHW. NEHW can achieve 99% bacterial disinfection effect by treating with 10 mg/L available chlorine concentration for more than 5 minutes. At the same time, the storage stability of NEHW was higher than that of SAEW. After 20 days of storage under sealed and dark conditions, the pH value only increased by 7.9%, and the effective chlorine concentration remained nearly 80%. The results showed that NEHW had higher germicidal efficacy and storage stability than SAEW.

Effect of environmental conditions on the volume deformation of cement mortars with sewage sludge ash

Sewage sludge ash (SSA) is obtained from wastewater sludge incineration, and it can be recycled in cement-based materials. The environmental conditions show significant influence on the volume deformation of cement-based materials with SSA. So in this study, the effect of environmental conditions on the volume deformation of mortars with SSA was investigated, and the underlying mechanism was preliminarily studied with isothermal calorimetry, X-ray diffraction (XRD) and thermogravimetry (TG). The results indicated that, under seal condition, SSA caused obvious expansion after the rapid shrinkage at very early age, and reduced the 28d autogenous shrinkage of mortars. Under drying condition, the addition of SSA enlarged the drying shrinkage of mortars. Under water immersed condition, the mortars expanded before the age of 7d, and more SSA led to more obvious expansion. The addition of SSA resulted in more ettringite formed in mortars under sealed and water immersed conditions, leading to the expansion of mortars. The findings of this study could help to control the volume deformation of mortars with SSA.

Deformation mechanisms of cement paste with ultra-low water-to-cement ratios under different curing conditions at early ages

Cement-based materials with ultra-low water-to-cement ratios (w/c) swell with external water supply, which may cause cracking and strength reduction. Studies on the volumetric stability of cement-based materials ignore the possible expansion occurring in the material before the starting point, standard curing (20 ± 2 ℃ and relative humidity (RH) > 95 %) for 28 d. Thereby, the deformation and mechanical properties of cement paste cured under standard and sealed conditions at early ages were compared. Deformation mechanisms were investigated by thermogravimetric analysis, 1H nuclear magnetic resonance relaxometry, and pore structure measurement. The saturation degree and hydration degree were both estimated. The results show that swelling occurs in cement-based materials with ultra-low w/c under standard curing, with increasing flexural and compressive strength. Gel water and capillary water contribute to large proportions of the total absorbed water. Cement paste with low w/c produces higher swelling when absorbs the same amount of water. Deformation mechanisms are attributed to the mitigation of self-desiccation shrinkage, calcium-silicate-hydrate gel swelling due to water absorbed, and solid volume increase of solids after hydration.

Development of early age autogenous and thermal strains of alkali-activated slag-fly ash pastes

Replacing ordinary Portland cement-based materials with alkali-activated industrial wastes is often limited because of significant volume changes occurring in these materials at early age. This experimental study aims to quantify the extent of the volume changes and explore the underlying mechanisms of pastes composed of slag and fly ash (ratio 50:50) which are activated by sodium hydroxide and sodium silicate. Eight compositions were tested, with silica modulus (Ms) varying between 1.04 and 1.58 and with solution-to-binder ratios (S/B) varying between 0.47 and 0.70. Specimen length changes in sealed conditions are monitored by applying repeated thermal variations in an adapted AutoShrink device and are accompanied by isothermal calorimetry, uniaxial compressive strength, and internal relative humidity (IRH) tests. This way, the temporal evolutions of autogenous strains, the coefficient of thermal expansion (CTE), the heat release, the apparent activation energy (Ea), the IRH and the strength are determined and compared to each other. Both the measured autogenous shrinkage and CTEs are rather large; they amount to 4,000–5,000 μm/m and roughly 40 μm/m/°C, respectively, at material ages of 2 weeks. An increase in S/B leads to a decrease in autogenous shrinkage and an increase in CTE. An increase in the Ms causes a decrease in both the autogenous shrinkage and the CTE. Most strikingly, autogenous shrinkage evolves linearly with the cumulative heat released by the binders. The IRH remains continuously above 94% during the first 2 weeks. The apparent activation energy amounts to roughly 74 kJ/mol and is virtually unaffected by S/B and Ms.

A predictive model for seal condition in an automated patch clamp system

A predictive model for seal condition in an automated patch clamp system

A new model simulating the development of gas condensate reservoirs

A new simulation model for the development of gas condensate reservoirs is introduced based on the influence that phase change, non-Darcy flow, and capillary pressure have on the production of gas condensates. The model predicts well performance, including bottom-hole pressure, oil/gas production rate, oil/gas recovery, gas–oil ratio, and the change in produced fluid composition. It also calculates dynamic characters, such as the change of pressure field and oil/gas saturation field during the development of gas condensate reservoirs. The model is applicable to different boundary conditions (both constant-pressure and sealed boundary) and different production modes (both constant-pressure and constant-volume production modes). Model validation attempted using numerical simulation results for sealed boundary conditions with constant-pressure production mode has shown a relatively good match, proving its validity. For constant-pressure boundary conditions with constant-volume production mode, four stages are defined according to the dynamic behavior of production performance in the development of gas condensate reservoirs.

Very low frequency waves as selective probe for Cysticercus tenuicollis, Hydatid cyst and Coenurus cerebralis bio-analysis using single cell-signal recording

Comparative electric behavior of Cysticercus tenuicollis, Hydatid cyst and Coenurus cerebralis at the Very Low Frequency (VLF) region has been studied in detail. This investigation could be significant, because of the economic and public health importance of these parasitic infections in domestic animals. In this report, a single cell signal recording technique has been adopted for comparison using a stainless steel (type: 316, diameter: ~ 300 µm, height: 2.00 cm) two identical electrode system, implanted on the surface of the tested cysts with inter electrode distance of 0.50 cm at a ~ 6.0 giga ohm (GΩ) sealed condition (based on the situation of the implanted electrode system). This process was achieved based on applying electrical interaction between the cysts and the VLF electrical signal. Relative to the measured time domain signal (Current–time diagram), the frequency domain (Current-frequency diagram) was estimated via applying a “Discrete Fast Fourier Transform” (DFFT) algorithm at a fixed time interval (5.0 min). Factors, having important influence on the sensitivity of the detection system including the type (waveform) of different alternating-current (AC) triggering stimulus signals (such as direct current, square wave, triangular, sin (t), etc.), the amplitude, as well as the frequency were optimized automatically through a written “Visual Basic 6” program by one-factor-at-a-time method. Direct applying this AC triggering VLF voltage to the cysts resulted in tracing an AC electrical current vs. time that considered as the time domain wave. However, this electrical current was decayed rapidly versus time during maximum 30.0 s time scale. Applying the DFFT algorithm to the measured time domain, resulted in accessing to the frequency domain at the selected frequency range between 2 and 5 kHz that was considered as the selected frequency for the selective differentiation of C. tenuicollis, Hydatid cyst and C. cerebralis. The related probable mechanism of this process may be attributed to the correlation between the triggering potential and the cyst’s electrical surface charge (Zeta potential) as the current source under similar conditions. The results of this study may help to introduce a new detection system for in vivo recognition of the cysts in future.

One-pot synthesis of a new class of alkynyl anionic synthons: the 4-(2',2-trimethylsilylethynylphenoxymethyl)-2H-chromen-2-ones

An efficient approach for the synthesis of a new class of anionic synthons: the 4-(2',2-trimethylsilylethynylphenoxymethyl)-2H-chromen-2-ones employing a one-pot three-component reaction is reported. Reaction of trimethylsilylacetylene, o-iodophenol and nine different bromomethylcoumarins in THF solvent at 80 °C under sealed tube conditions gave nine novel 4-(2',2-trimethylsilylethynylphenoxymethyl)-2H-chromen-2-ones in greater than 90% isolated yields. All compounds were spectroscopically characterized by elemental analysis, FT-IR, MS, 1H-, and 13C-NMR techniques.

A study both to measure and to visualize the scattering of fine particles generated during dental treatment

There is an urgent need to examine the risk of infection from aerosols generated during dental treatment and to review infection control. However, existing research on aerosol particles associated with dental treatment is by no means sufficient, and little research has been done on the details of aerosol particle generation in the clinical environment, the mechanisms, and patterns of distribution in open and closed spaces, the time they are suspended in the air, the amount and size of particles present. Therefore, to minimize the influence of background particles, laser beams, a high-sensitivity camera, and a particle counter were used in a large super-clean laboratory (SCL) to investigate the dynamics of aerosols generated during dental micromotor operation. The large number of aerosol particles generated by the use of the micro-engine rose rapidly within 30 seconds and were suspended in the room atmosphere. Within a 100 cm radius of the user, the scattering peaked at about 90 seconds. The particles were further diffused into the room with the passage of time, reaching a maximum at 210 seconds and gradually decreasing thereafter, confirming that the 4 x 4 m room had returned to equilibrium. The experiment was conducted under sealed conditions in the SCL without the use of any suction device inside or outside the oral cavity. Although the conditions did not faithfully reproduce the actual conditions in a dental clinic, we were able to obtain groundbreaking results that demonstrated for the first time the scattering of fine particles, eliminating various possible complications in the background. At present, our knowledge of the infectivity of COVID-19 from patients' oral cavity and saliva is still insufficient, and further studies and information are needed.

Predicting Chemical Shrinkage in Hydrating Cements

This paper presents a prediction of chemical shrinkage volume created during the hydration of two cements over time using a thermodynamic model. Chemical shrinkage in hydrating cements is a result of internal volume change over time within sealed conditions due to exothermic reactions during hydration and the resulting precipitation of solid hydrates. Each precipitated phase will contribute to chemical shrinkage due to their individual reactions and stoichiometric properties. As these factors (including early age, drying and autogenous nature) contribute to the overall shrinkage of concrete which may cause long-term performance problems, they are important properties to understand. The current paper presents a thermodynamic model that quantifies the chemical shrinkage volume created during the first 1000 days of hydration using the cemdata18 database and a series of discrete solid phases (DSPs) to represent C-S-H, which has not been quantified in the literature to date. DSPs account for the amorphous and poorly crystalline nature of C-S-H in cement, and its incongruent dissolution behavior of C-S-H as calcium is released in solution more so than silicon. A description of chemical shrinkage in hydrating cements is provided, along with a review of past methods used to quantify its development over time. The paper also shows the linear relationship between chemical shrinkage and the overall degree of hydration.

Facile Preparation of a Bispherical Silver-Carbon Photocatalyst and Its Enhanced Degradation Efficiency of Methylene Blue, Rhodamine B, and Methyl Orange under UV Light.

The combination of organic and inorganic materials is attracting attention as a photocatalyst that promotes the decomposition of organic dyes. A facile thermal procedure has been proposed to produce spherical silver nanoparticles (AgNPs), carbon nanospheres (CNSs), and a bispherical AgNP-CNS nanocomposite. The AgNPs and CNSs were each synthesized from silver acetate and glucose via single- and two-step annealing processes under sealed conditions, respectively. The AgNP-CNS nanocomposite was synthesized by the thermolysis of a mixture of silver acetate and a mesophase, where the mesophase was formed by annealing glucose in a sealed vessel at 190 °C. The physicochemical features of the as-prepared nanoparticles and composite were evaluated using several analytical techniques, revealing (i) increased light absorption, (ii) a reduced bandgap, (iii) the presence of chemical interfacial heterojunctions, (iv) an increased specific surface area, and (v) favorable band-edge positions of the AgNP-CNS nanocomposite compared with those of the individual AgNP and CNS components. These characteristics led to the excellent photocatalytic efficacy of the AgNP-CNS nanocomposite for the decomposition of three pollutant dyes under ultraviolet (UV) radiation. In the AgNP-CNS nanocomposite, the light absorption and UV utilization capacity increased at more active sites. In addition, effective electron-hole separation at the heterojunction between the AgNPs and CNSs was possible under favorable band-edge conditions, resulting in the creation of reactive oxygen species. The decomposition rates of methylene blue were 95.2, 80.2, and 73.2% after 60 min in the presence of the AgNP-CNS nanocomposite, AgNPs, and CNSs, respectively. We also evaluated the photocatalytic degradation efficiency at various pH values and loadings (catalysts and dyes) with the AgNP-CNS nanocomposite. The AgNP-CNS nanocomposite was structurally rigid, resulting in 93.2% degradation of MB after five cycles of photocatalytic degradation.

Measurement and simulation of electrical resistivity of cement-based materials by using embedded four-probe method

The electrical resistivity of cement-based materials is an important index that can be used for designing durable, multifunctional, and smart concrete structures. However, the measurement and prediction of electrical resistivity are far from being well addressed for cement-based materials. In this study, a modified four-probe test using embedded fine copper rods as electrodes was developed to measure the electrical resistivity of cement-based materials. A coupled thermal-electrical analysis was conducted to verify the feasibility of the modified four-probe method. The simulated results show that a linear relation between the electrical resistivity and the apparent electrical resistance. The contact resistance of the interface between the specimen and the electrodes has little effect on the electrical resistivity. The applied voltage ranging from 4 V to 28 V has a minor influence on the measured electrical resistivity. The electrical resistivity of the specimens cured under standard condition is greater than that under sealed condition. The electrical resistivity of cement-based materials cured under both sealed and standard conditions increases with increasing curing age. A higher volume fraction of sand contributes significantly to a higher electrical resistivity of cement-based materials. Moreover, the homogenization results indicate that the differential scheme predictions coincide quite well with the measured electrical resistivity of cement-based materials with a wide range of sand volume fractions (0%∼60%). The Voigt scheme, the self-consistent scheme, and the Mori-Tanaka scheme can predict well the electrical resistivity of cement-based materials with a low volume fraction of sand (<20%), but fail to give a good prediction at a higher sand content.

Layered double hydroxides nanosheets for capturing chloride ions in magnesium oxychloride cement

As an alternative inorganic cementitious material, the application of magnesium oxychloride cement (MOC) is often limited due to its poor water resistance, which caused by the migration of Cl- to the surface. In this research, magnesium aluminum layered double hydroxides (Mg2Al-LDH) nanosheets were used to capture the free Cl- in MOC paste taking advantage of the enormous specific surface area of the Mg2Al-LDH nanosheets with ultrathin structure. The Cl- adsorption capacity of Mg2Al-LDH nanosheets in KCl solution was one order of magnitude higher than that of LDH particles prepared traditionally. The scumming of the MOC cube under high humidity was efficiently avoided at the optimum dosage of 2.0% Mg2Al-LDH nanosheets. The compressive strength of the MOC cured under sealed conditions increased by 13–118% over the control sample at various dosages in the range of 0.5–2.0%, and the maximum value of compressive strength was obtained at optimum Mg2Al-LDH dosage of 2.0%. The morphology of MOC under high humidity curing showed that more rod-like hydration products were formed by adding LDH nanosheets into MOC paste. The results demonstrated a suitable dosage of LDH nanosheets not only increased the efficiency of capturing Cl-, but also stimulated the formation of rod-like crystals and enhanced the compressive strength of the MOC cube.

SMART SEAL BASE ON WIFI USING WEB SERVICE PHP

Technological developments, especially in the IoT (Internet of Things), play a significant role in various fields. In addition to achieving a modern and efficient work environment, IoT can also play a role in the security sector, which has now become a significant need. One of the roles of IoT in the security sector is that it can be applied to calibrated TMWE (Measuring, Dosing, Weighing, and Equipment). So that it can guarantee the correctness of the measurement results from the TMWE, continuous monitoring can be carried out so that fraud does not occur. One of the innovations in this regard is the smart seal. The use of smart seals is prioritized for fixed TMWE, which is vulnerable to theft and breaches. This system is designed based on IoT, which is integrated with cloud services and GPS systems that allow the use of web-based applications for online monitoring of seal conditions by users. Data from the seal will be sent to the server via wifi network and stored in a database, to be displayed in web service with a user, admin, and signer access. In addition to providing information to users about the seal’s location, the use of the GPS also aims to make it easier for admins to detect the seal’s location in the event of a violation.

Fishhook characteristics of biodiesel lubricity during autoxidation

The effects of light, ventilation and antioxidant on biodiesel performance and the corresponding influence mechanisms are investigated during long-term storage. The biodiesel exhibits slow autoxidation and its physical/chemical properties change during storage. Light and ventilation conditions can accelerate the oxidation of biodiesel, thereby aggravating its degradation. During the autoxidation process of biodiesel, the grinding spot diameter firstly decreases from 165.01 μm to 131.45 μm and then increases to 362.5 μm, similar to the shape of a fishhook. During the initial storage stage, the fatty acid methyl ester in biodiesel is decomposed into carboxylic acid and small molecular substances such as aldehydes and ketones, thereby improving the lubricity of biodiesel and reducing the grinding spot diameter. After long-term storage, insoluble resins and sediments are generated, causing an increase in the grinding spot diameter. Specifically, the kinematic viscosity of biodiesel is increased to 4.407 mm2/s even under dark and sealed storage conditions.