Evolution of microstructure and transport properties of cement pastes due to carbonation under a CO2 pressure gradient: a modeling approach

Most carbonation models only account for diffusion as the main transport mechanism rather than advection. Nevertheless, in the case of concrete used for underground waste disposal facilities, concrete may be subjected to a high hydrostatic pressure and the surrounding environment may contain a high dissolved CO2 concentration. Therefore, a combination of diffusion and advection should be taken into account. This is also the case in accelerated carbonation where a high CO2 pressure gradient is applied in which advection in the gas phase has a significant contribution to the carbonation process. This study aims at developing a model to predict the evolution of the microstructure and transport properties of cement pastes due to carbonation under accelerated conditions in which a pressure gradient of pure CO2 is applied. The proposed model is based on a macroscopic mass balance for carbon dioxide in gaseous and aqueous phases. Besides the prediction of the changes in transport properties (diffusivity, permeability), the model also enables to predict the changes in microstructure. Data from accelerated tests were used to validate the model. Preliminary verification with experimental results shows a good agreement

THE EFFECTS OF TEACHER INTERACTIVE FEEDBACK ON EFL STUDENTS’ PARAGRAPH WRITING PERFORMANCE

This study aims to investigate the effectiveness of using teacher interactive feedback (TIF) on students' paragraph writing performance. Furthermore, it examines students' attitudes towards this strategy. The study took place in a lower secondary school and used both qualitative and quantitative data. Participants were 86 students who were randomly assigned to the experimental group (EG) and the control group (CG). While students in the EG learned to write the paragraph utilizing the TIF, students in the CG learned to write the paragraph using the traditional technique. Before the intervention, students in both groups took a pre-test to gauge their level of writing proficiency. The results were then compared to relevant data. The experiment spanned eight weeks during which a post-test was then administered to students in both groups to evaluate their development, particularly that of the EG. To obtain insights into TIF, questionnaires and semi-structured interviews were conducted. The findings from the study demonstrated a considerable improvement in paragraph writing skills through interactive feedback (IF) and paragraph writing instruction. Additionally, the majority of students showed their enthusiasm towards learning to write using TIF and expected to continue practicing this strategy in the future.  Article visualizations

THE EFFECTS OF USING VIDEOS IN ENGLISH SPEAKING LESSONS ON HIGH SCHOOL STUDENTS' SPEAKING PERFORMANCE, KIEN GIANG PROVINCE, VIETNAM

Students' speaking abilities are widely thought to play an important role in speaking classes and high school English teachers endeavor to improve their students' speaking performance. The purpose of the current study was to examine whether incorporating videos before and after speaking sessions had a substantial impact on students’ speaking development. The participants were 78 high school students in Kien Giang province. The study used a quasi-experimental mixed-methods design. The participants were organized into two groups: the control group and the experimental group. Both groups underwent a pre-test to check group homogeneity and for later comparison. The students in the experimental group participated in the speaking class where video integration was introduced at the beginning and end of each lesson whereas the students in the control group attended regular speaking classes. The intervention lasted for twelve weeks. A posttest was then given to students of the two groups to check progress in speaking performance. Furthermore, the attitudes of the students in the experimental group were measured using Likert-style questionnaires and semi-structured interviews. Data collected from the pre-test, post-test, and questionnaire were subjected to analysis via SPSS. The findings of the study indicate that the application of videos in speaking classes significantly influenced students' speaking performance. Additionally, students show positive attitudes towards using videos in their speaking classes.  Article visualizations

Management of solar energy in microgrids using IoT-based dependable control

© 2017 IEEE. Solar energy generation requires efficient monitoring and management in moving towards technologies for net-zero energy buildings. This paper presents a dependable control system based on the Internet of Things (IoT) to control and manage the energy flow of renewable energy collected by solar panels within a microgrid. Data for optimal control include not only measurements from local sensors but also meteorological information retrieved in real-time from online sources. For system fault tolerance across the whole distributed control system featuring multiple controllers, dependable controllers are developed to control and optimise the tracking performance of photovoltaic arrays to maximally capture solar radiation and maintain system resilience and reliability in real time despite failures of one or more redundant controllers due to a problem with communication, hardware or cybersecurity. Experimental results have been obtained to evaluate the validity of the proposed approach

Higgs-gauge boson interactions in the economical 3-3-1 model

Interactions among the standard model gauge bosons and scalar fields in the framework of SU(3)_C X SU(3)_L X U(1)_X gauge model with minimal (economical) Higgs content are presented. From these couplings, all scalar fields including the neutral scalar $h$ and the Goldstone bosons can be identified and their couplings with the usual gauge bosons such as the photon, the charged $W^\pm$ and the neutral $Z$, without any additional condition, are recovered. In the effective approximation, full content of scalar sector can be recognized. The CP-odd part of Goldstone associated with the neutral non-Hermitian bilepton gauge boson $G_{X^0}$ is decouple, while its CP-even counterpart has the mixing by the same way in the gauge boson sector. Masses of the new neutral Higgs boson $H^0_1$ and the neutral non-Hermitian bilepton $X^0$ are dependent on a coefficient of Higgs self-coupling ($\lambda_1$). Similarly, masses of the singly-charged Higgs boson $H_2^\pm$ and of the charged bilepton $Y^\pm$ are proportional through a coefficient of Higgs self-interaction ($\lambda_4$). The hadronic cross section for production of this Higgs boson at the LHC in the effective vector boson approximation is calculated. Numerical evaluation shows that the cross section can exceed 260 $fb$.Comment: 22 pages, 1 figure, submitted to Phys. Rev.

A Policy Impact Evaluation Model For Scotland: Decoupling Single Farm Payments

The purpose of this paper is to assess the impacts of decoupling single farm payments in Scotland. It focuses on aggregate impacts on the agricultural products in domestic and external markets and the spill-over effect of this on the non-agricultural sector as well as an aggregate impact on the Scottish GDP. In order to capture system-wide impacts of the policy reform, a CGE model was formulated and implemented using a social accounting matrix constructed for Scotland. The simulation results suggest that the Scottish agricultural sector may encounter declines in output and factor us as a result of the policy reform. However, this critically depends on two factors: (a) the price effect of the policy reform on Scottish agricultural products relative to the EU average as well as the conditions of changes in world agricultural market prices; and (b) the extent to which customers would be sensitive to price effects of the policy reform. As far as the spill-over effect to the non-agricultural sector is concerned, decoupling of direct payments seems to have a positive spill-over effect. Similarly, the aggregate GDP effect is positive under all simulation scenarios. Critically, the simulation experiments indicate that policy shock may have a symmetrical outcome across the two sectors, with contractions in agriculture being accompanied by expansions in the non-agricultural sector, mainly because of factor market interactions between the two sectors.

Effects of W/P ratio and limestone filler on permeability of cement pastes

Because of environmental and economic benefits, a fraction of cement is increasingly replaced by limestone fillers raising a question on to what extent limestone fillers affect the durability of cementitious materials. This work aims at understanding the effects of water/powder (w/p) ratio and limestone filler replacement on water permeability of cement pastes. A newly proposed technique using a controlled constant flow concept was applied to measure permeability of hardened cement paste samples following a factorial experimental design. It was observed that both limestone filler and w/p ratio significantly influence the water permeability. At a given w/p ratio, adding limestone filler made the microstructure coarser, especially for high w/p ratio. Nevertheless, if the comparison is based on a given water/cement (w/c) ratio instead of w/p ratio, the limestone filler replacement refined the microstructure in terms of capillary porosity and pore size distribution, resulting in permeability decreases of cement pastes. Furthermore, a modified Carmen-Kozeny relation was established which enables prediction of the permeability from capillary porosity and the critical pore diameter

Microstructural and permeability changes due to accelerated Ca leaching in ammonium nitrate solution

Although Ca leaching in cement-based materials is an extremely slow process, this process is relevant for long-term assessments of the evolution of concrete used in radioactive waste disposal systems. In the present work, an ammonium nitrate solution of 6 mol/l was used to accelerate the leaching kinetics of cement paste. The change of sample mass over time was monitored by weighing, whereas the amount of calci-um ion leached out during the test was followed by ion chromatography. A variety of post-analysis tech-niques like XRD, MIP and BET were used to characterize the microstructural changes and portlandite content, while the degraded front was determined by phenolphthalein spraying. The effect of accelerated leaching on transport properties was studied by measuring changes in water permeability. Results showed that (i) the porosity of the leached samples increased significantly, (ii) the critical pore size was shifted to larger radius and (iii) the BET specific surface area of the leached sample was also significantly increased. These changes resulted in a one to two order increase in water permeability depending on the immersed time

Decalcification of cement paste in NH4NO3 solution: microstructural alterations and its influence on the transport properties

Leaching of cement-based materials changes its properties such as a reduction in pH, an increase in porosity and transport properties and a detrimental effect on properties related to long-term durability. Therefore, a better understanding of leaching process is important including the relevant long-term effects for concretes used in waste disposal systems. However, the decalcification process is not easy to capture because it is extremely slow. In this study, an ammonium nitrate (NH4NO3) solution of 6 mol/l was used to accelerate the leaching kinetics. The experiments were performed on cement paste samples with different water/powder and limestone filler replacement ratios. The change of sample mass over time was monitored, and the amount of calcium ion leached out during the test was determined. Different post-analysis techniques like SEM, MIP and N2-adsorption were used to characterize the microstructural changes, while the degraded front was determined by phenolphthalein spraying. The effect of accelerated leaching on transport properties was studied by measuring the change in water permeability. Results show that (i) NH4NO3 solution is an aggressive but suitable agent to be used to accelerate the Ca leaching in cementitious materials while still keeping the “nature” of leaching; (ii) the square-root-time law of degradation is applicable under accelerated conditions; (iii) the porosity of the leached samples increases significantly and the critical pore size is shifted to larger radius; and (iv) the BET specific surface area of the leached sample is also significantly increased. These changes result in a significant increase in water permeability