Mechanical Strength of Saline Sandy Soils Stabilized with Alkali-Activated Cements

This is the final version. Available on open access from MDPI via the DOI in this recordData Availability Statement: Data that support the findings of this study are available from the corresponding author upon reasonable request.Saline soils usually cannot satisfy the requirements of engineering projects because of their inappropriate geotechnical properties. For this reason, they have always been known as one of the problematic soils worldwide. Moreover, the lack of access to normal water has intensified the use of saline water resources such as seawater in many construction and mining projects. Although cement stabilization is frequently used to improve the engineering properties of saline soils, Portland cement’s usage as a binder is constrained by its negative consequences, particularly on the environment. In this line, the effects of NaCl on the microstructural and mechanical properties of alkali-activated volcanic ash/slag-stabilized sandy soil were investigated in this study. Moreover, the effects of binder type, slag replacement, curing time, curing condition, and NaCl content on the mechanical strength of stabilized soils were examined. In addition, microstructural analyses, including XRD, FTIR, and SEM–EDS mapping tests, were performed to understand the physical and chemical interaction of chloride ions and alkali-activated cements. The results show that alkali-activated slag can be a sustainable alternative to Portland cement for soil stabilization projects in saline environments. The increase in sodium chloride (NaCl) content up to 1 wt.% caused the strength development up to 244% in specimens with 50 and 100 wt.% slag, and adding more NaCl had no significant effect on the strength in all curing conditions. Microstructural investigations showed that the replacement of volcanic ash with slag resulted in the formation of C-S-H and C-A-S-H gels that reduced the porosity of the samples and increased mechanical strength. Furthermore, surface adsorption and chemical encapsulation mechanisms co-occurred in stabilized soil samples containing slag and volcanic ash.National Elites Foundation, IranEuropean Union Horizon 2020MatSoi

A NEMO-HWSN solution to support 6LoWPAN network mobility in hospital wireless sensor network

IPv6 Low-power Personal Area Networks (6LoWPANs) have recently found renewed interest because of the emergence of Internet of Things (IoT). Mobility support in 6LoWPANs for large-scale IP-based sensor technology in future IoT is still in its infancy. The hospital wireless network is one important 6LoWPAN application of the IoT, it keeps continuous monitoring of vital signs of moveing patients. Proper mobility management is needed to maintain connectivity between patient nodes and the hospital network. In this paper, first we survey IPv6 mobility protocols and propose a solution for a hospital architecture based on 6LoWPAN technology. Moreover, we discuss an important metric like signaling overload to optimize the power consumption and how it can be optimized through the mobility management. This metric is more effective on the mobile router as a coordinator in network mobility since a mobile router normally constitutes a bottleneck in such a system. Finally, we present our initial results on a reduction of the mobility signaling cost and the tunneling traffic on the mobile PAN

Mechanical strength of saline sandy soils stabilized with alkali-activated cements

Saline soils usually cannot satisfy the requirements of engineering projects because of their inappropriate geotechnical properties. For this reason, they have always been known as one of the problematic soils worldwide. Moreover, the lack of access to normal water has intensified the use of saline water resources such as seawater in many construction and mining projects. Although cement stabilization is frequently used to improve the engineering properties of saline soils, Portland cement’s usage as a binder is constrained by its negative consequences, particularly on the environment. In this line, the effects of NaCl on the microstructural and mechanical properties of alkali-activated volcanic ash/slag-stabilized sandy soil were investigated in this study. Moreover, the effects of binder type, slag replacement, curing time, curing condition, and NaCl content on the mechanical strength of stabilized soils were examined. In addition, microstructural analyses, including XRD, FTIR, and SEM–EDS mapping tests, were performed to understand the physical and chemical interaction of chloride ions and alkali-activated cements. The results show that alkali-activated slag can be a sustainable alternative to Portland cement for soil stabilization projects in saline environments. The increase in sodium chloride (NaCl) content up to 1 wt.% caused the strength development up to 244% in specimens with 50 and 100 wt.% slag, and adding more NaCl had no significant effect on the strength in all curing conditions. Microstructural investigations showed that the replacement of volcanic ash with slag resulted in the formation of C-S-H and C-A-S-H gels that reduced the porosity of the samples and increased mechanical strength. Furthermore, surface adsorption and chemical encapsulation mechanisms co-occurred in stabilized soil samples containing slag and volcanic ash

A comprehensive comparative investigation on solar heating and cooling technologies from a thermo-economic viewpoint—A dynamic simulation

© 2020 The Authors. Energy Science & Engineering published by the Society of Chemical Industry and John Wiley & Sons Ltd. The yearly thermo-economic performance is dynamically investigated for three solar heating and cooling systems: solar heating and absorption cooling (SHAC), solar heating and ejector cooling (SHEC), and heating and solar vapor compression cooling (HSVC). First, the effects of important design parameters on the thermo-economic performance of the systems to supply the heating and cooling loads of the building are evaluated. The systems are parametrically analyzed with the weather conditions of Tehran, Iran. The results show that the life cycle costs (LCC) of the SHAC and HSVC systems are alike and much lower than those of the SHEC system. The HSVC system exhibits the best performance from exergetic and solar fraction viewpoints. The comparative analysis shows that the energy efficiencies of the SHAC and SHEC systems are higher in colder climatic conditions. However, the collector efficiency of the HSVC system declines in colder climates, mainly due to the lower solar intensities relative to in hotter climates. Further, the solar fraction of the SHAC system is higher than the SHEC technology under all climatic conditions. Moreover, higher values of solar fractions are obtained under colder weather conditions for the SHEC and HSVC systems. The best economic performance is observed for the SHAC and HSVC technologies, having significantly lower LCCs than the SHEC system. These lower LCCs under colder climatic conditions are due to the lower cost of supplying the heating load compared to the cooling load. Furthermore, all systems exhibit enhanced exergetic performance in colder weather conditions. The yearly thermo-economic performance is dynamically investigated for three solar heating and cooling systems: SHAC, SHEC, and HSVC. In addition, the effects of important design parameters on the thermo-economic performance of the systems to supply the heating and cooling loads of the building are evaluated

Effect of CO2 exposure on the mechanical strength of geopolymer-stabilized sandy soils

In recent years, there has been growing interest in developing methods for mitigating greenhouse effect, as greenhouse gas emissions continue to contribute to global temperature rise. On the other hand, investigating geopolymers as environmentally friendly binders to mitigate the greenhouse effect using soil stabilization has been widely conducted. However, the effect of CO2 exposure on the mechanical properties of geopolymer-stabilized soils is rarely reported. In this context, the effect of CO2 exposure on the mechanical and microstructural features of sandy soil stabilized with volcanic ash-based geopolymer was investigated. Several factors were concerned, for example the binder content, relative density, CO2 pressure, curing condition, curing time, and carbonate content. The results showed that the compressive strength of the stabilized sandy soil specimens with 20% volcanic ash increased from 3 MPa to 11 MPa. It was also observed that 100 kPa CO2 pressure was the optimal pressure for strength development among the other pressures. The mechanical strength showed a direct relationship with binder content and carbonate content. Additionally, in the ambient curing (AC) condition, the mechanical strength and carbonate content increased with the curing time. However, the required water for carbonation evaporated after 7 d of oven curing (OC) condition and as a result, the 14-d cured samples showed lower mechanical strength and carbonate content in comparison with 7-d cured samples. Moreover, the rate of strength development was higher in OC cured samples than AC cured samples until 7 d due to higher geopolymerization and carbonation rate

Investigating accelerated carbonation for alkali activated slag stabilized sandy soil

Portland cement as a commonly used material in soil stabilization projects, releases considerable amounts of CO2 into the atmosphere, highlighting the need to use green binders such as ground granulated blast furnace slag as a substitute for cement. On the other side, extensive research is being conducted on accelerated carbonation treatment to decrease the industry’s carbon footprint. Carbonation transforms CO2 into carbonate minerals. This study investigates the influence of accelerated carbonation on the unconfined compressive strength (UCS) of soil stabilized with alkali-activated slag under ambient and oven curing conditions. Effects of curing time, binder content, relative density, and carbonation pressure (100, 200, and 300 kPa) were also studied. Furthermore, a calcimeter test was conducted to determine the amount of carbonate generated, which reflects CO2 sequestration in soil. The results showed that the carbonated samples achieved higher strength than the non-carbonated samples. However, a slight decrease in UCS was observed with the increase in CO2 pressure. The generated carbonate content directly correlated with the UCS of the samples, which explained the higher strength of carbonated samples. Also, the ambient curing condition was more favorable for the samples stabilized with GGBS, which can be attributed to the supply of required moisture. Results from XRD, SEM, and FTIR indicated that the strength development was due mainly to the formation of carbonation products (CaCO3), which facilitated the densification of solidified materials

Self-Decision Route Selection for Energy Balancing in wireless sensor betworks.

In many wireless sensor network (WSN) applications, data from the monitored environmental phenomenon only need to be sampled intermittently and transmitted to the base station. Hence, an intelligent protocol that balances the traffic load among the nodes and minimizes their energy usage, especially during routing and idle listening, which is necessary to extend the network lifetime. In this paper, a load balancing model that balances the rate of energy dissipation of the sensor nodes across the network is proposed. The proposed energy balancing scheme distributes the traffic load regularly and slowly over the sensor nodes during routing, such that the overall network life time is optimized, and the sensors die almost all at the same time. The proposed energy balancing protocol reduces the high energy consumption during the transmission and reception states, this is done by introducing multi-hop instead of single-hop communication of each node with the sink. Simulation results show that the proposed energy balancing protocol reduces the transmission energy usage by up to 64%, while the reception energy usage is reduced up to 67%. Moreover, the system throughput as well as the network lifetime increased up to 79% and 66%, respectively

Experimental investigation of sandy soil stabilization using chitosan biopolymer

The performance of an environmentally friendly biopolymer synthesised from secondary resources to overcome the wind erosion of sandy soil was investigated in this study. The study employed a multi-scale approach to investigate the mechanical, erosional, and hydraulic properties of sandy soil. At the macroscale, experimental techniques such as unconfined and triaxial compression tests, permeability measurements, contact angle assessments, and wind tunnel experiments were utilized to characterize the bulk behavior of the soil. Concurrently, molecular dynamics (MD) simulations were conducted at the nanoscale to predict surface mechanical characteristics and elucidate chemical interactions at the molecular level. Results show that when the outer surface of the sandy particles is coated with a sparse concentration of biopolymer, the sandy aerosol inhibitory performance is significant even under extreme storm conditions reaching speeds of 140 km/h of storms. The study on the impact of biopolymer content, curing time, and curing conditions revealed that the addition of chitosan biopolymer has the ability to enhance the bonding between particles and significantly enhance the mechanical properties of sandy soil. The atomic insight from molecular dynamics reveals huge entanglement between sandy particles and biopolymer by Van der Waals interaction. The results of the Unconfined Compressive Strength test indicate that chitosan enhances the compressive strength of sand by up to 320 kPa. Additionally, the triaxial test demonstrated that the application of chitosan led to a 34.2 kPa improvement in the cohesion of sand. Furthermore, analysis of the permeability test results revealed a decrease in the hydraulic conductivity coefficient from 1.6 × 10^-6 m/s to 5.7 × 10^-7 m/s, representing a reduction of approximately 35 %

An improved routing mechanism using bio-inspired for energy balancing in wireless sensor networks

Planning of energy-efficient protocols is critical for wireless sensor networks (WSNs) because of the constraints on sensor node's energy. Therefore, the routing protocol should be able to achieve uniform power dissipation during transmission to the sink node. In this paper, we present a self-optimization scheme for WSN which is able to utilize and optimize the sensor nodes' resources, especially the batteries, to achieve balanced energy consumption across all sensors. This method is based on Ant Colony Optimization (ACO) meta heuristic which is adopted to enhance the paths with the best quality function. The assessment of this function depends on multi-criteria metrics such as the minimum residual battery power, hop numbers and average energy of both route and network. This method also distribute the traffic load of sensor nodes throughout the WSN leading to reduced energy usage, extended network life time and reduced packet loss. Simulation results show that our scheme performs much better than Energy Efficient Ant-Based Routing (EEABR) in terms of energy consumption and efficiency

Inertial manipulation of bubbles in rectangular microfluidic channels

Inertial microfluidics is an active field of research that deals with crossflow positioning of the suspended entities in microflows. Until now, the majority of the studies have focused on the behavior of rigid particles in order to provide guidelines for microfluidic applications such as sorting and filtering. Deformable entities such as bubbles and droplets are considered in fewer studies despite their importance in multiphase microflows. In this paper, we show that the trajectory of bubbles flowing in rectangular and square microchannels can be controlled by tuning the balance of forces acting on them. A T-junction geometry is employed to introduce bubbles into a microchannel and analyze their lateral equilibrium position in a range of Reynolds (1 < Re < 40) and capillary numbers (0.1 < Ca < 1). We find that the Reynolds number (Re), the capillary number (Ca), the diameter of the bubble ([D with combining macron]), and the aspect ratio of the channel are the influential parameters in this phenomenon. For instance, at high Re, the flow pushes the bubble towards the wall while large Ca or [D with combining macron] moves the bubble towards the center. Moreover, in the shallow channels, having aspect ratios higher than one, the bubble moves towards the narrower sidewalls. One important outcome of this study is that the equilibrium position of bubbles in rectangular channels is different from that of solid particles. The experimental observations are in good agreement with the performed numerical simulations and provide insights into the dynamics of bubbles in laminar flows which can be utilized in the design of flow based multiphase flow reactors