Fine-grained Concrete Mix Design using Statistical Methods for Ultra-thin Whitetopping Overlay Application

Whitetopping is a thin layer structure covering on an existing asphalt pavement to improve resistance to rutting and increase the durability road surface. This thin layer usually made of concrete without coarse aggregate, is used mainly to repair the old damaged asphalt road surface without altering its texture. Due to the high longevity, using this type of concrete for reinforcing and repairing roads in unfavorable climatic conditions as in Vietnam brings technical, economic, environmental effective, and suitable with the trend of sustainable development. This article shows results on mix design of high performance fine - grained concrete used for thin whitetopping overlays from materials available in Vietnam by using statistical methods. The Design Expert 11.0 software was used to evaluate the influence and relationship between the influencing variables such as the ratio Water/Binder and the Sand/Binder ratio and concrete strength through the regression equation determination by experimental planning method. After checking the compatibility, the maximum value of the compressive strength and optimum mix design were found through solving this mathematical model. The concrete with optiumum proportion has good workability, high abrasion resistance; its compressive strength develops rapidly at early age and achieves more than 100MPa at 28 days. Using this Fine-grained concrete will help increasing durability and reduce the maintenance cost in the future

Eco-friendly Super Sulphated Cement Concrete Using Vietnam Phosphogypsum and Sodium Carbonate Na2CO3

Sustainable development is one of the critical topics in the construction industry today, especially in reducing CO2 emissions and production energy costs. There have been many studies worldwide on using ground granulated blast furnace slag combined with phosphogypsum (PG) to replace binder (B) in making concrete. However, this topic in Vietnam has not received much attention despite the large backlog of phosphogypsum waste. One of the main disadvantages limiting the feasibility of super-sulphated binders in concrete is the relatively slow hydration and hardening processes, which affect the rate of strength development of mortar and concrete, especially at an early age. In this study, the use of Na2CO3 salt as a quick, solid additive can overcome the disadvantages of this type of binder. Research results show that using 15 to 25% phosphorus gypsum waste (PG) and a combination of 60 to 80% finely granulated blast furnace slag (GGBFS) with a small amount of cement and an activator like Na2CO3can replace cement in making concrete. The concrete mix has good workability, and the maximum compressive strength after 28 days can reach over 50 MPa. Using industrial wastes as the main ingredients to make binders will improve sustainable development, reducing environmental pollution and the cost of mortar and concrete products in construction. Doi: 10.28991/CEJ-2022-08-11-06 Full Text: PD

Étude de la microstructure des liants ettringitiques influence sur les propriétés macroscopiques : Résistance et variation dimensionnelle

The ettringite binder whose composition is mainly formed by the calcium aluminate cement and calcium sulfate, are widely used in mortars for technical applications such as patching mortars, the self -leveling screeds, repair mortars etc… thanks to their fast hardening ability and high early strength. However, depending on the amount and types of raw materials used in the composition, the properties of these types of binder have different behaviors at early age and at long-term. And in particular in this work, the influence of the nature and dosage of calcium sulfate on the consequences of ettringite mortars hydration as the beginning of setting time, the change from the liquid state to the solid state, dimensional change, the resistance, porosity, the progress of hydration and ageing until 330 days at different conservation conditions were determined. These characteristics were assessed by different experimental techniques such as rheology, chemical shrinkage, autogenous shrinkage, isothermal calorimetry, infrared spectroscopy, mercury intrusion porosimetry, X-ray diffraction, Thermogravimetric analysis.Les liants ettringitiques dont la composition est formée principalement par du ciment d’aluminate de calcium et par du sulfate de calcium, sont très utilisés dans le cadre des mortiers techniques pour des applications telles que les mortiers de ragréage, les chapes autonivelante, les mortiers de réparation…. en raison de leurs propriétés de durcissement rapide et de résistance initiale élevée. Néanmoins, en fonction de la quantité des matières premières utilisées dans la composition et de leur nature, ces liants peuvent présenter à jeune âge ainsi qu’à long terme, des comportements différents. En particulier et dans le cadre de ce travail, l’influence de la nature et du dosage en sulfate de calcium sur l’hydratation des mortiers ettringitiques comme le début de prise, le changement de l’état liquide à l’état solide, les variations dimensionnelles, la résistance et le vieillissement à long terme (jusqu’à 330 jours) pour différentes conditions de conservations ont été déterminées. Ces caractéristiques ont été évaluées selon différentes techniques expérimentales de rhéologie, de mesure des variations volumiques, de calorimétrie isotherme, de spectroscopie infrarouge, de porosimétrie par intrusion de mercure, de diffraction des rayons X et thermogravimétrie

A Review of Occupational Stress among Certain Jobs in Vietnam

Background: Stress in the modern workplace is globally considered a risk factor for workers’ health and safety. However, a review of the prevalence and associated factors of occupational stress in developing countries like Vietnam was largely lacking. This review aimed to describe the situation of occupational stress among certain jobs from studies carried out in Vietnam. Methods: The review was implemented by using key words to search on online and offline, international and national database. After going through 2 stages of selections, total 25 eligible articles were chosen and used for this review. Results: The results showed the prevalence of occupational stress was varied and ranged from 6.4% to 90.4%. The study population focused on health workers, factory workers, students, academic staff and officers. The prevalence of each occupation ranged from 6.4% to 90.4% in health workers; 20.7% to 89.6% in factory workers; and 22.8% to 68.3% in students. Conclusions: In conclusion, the prevalence of occupational stress was very varied between and within each occupation. Therefore, a new way to develop in enhancing the occupational stress data, particularly in developing countries, is urgently needed

CONCEPTS AND AWARENESS ABOUT SELF-HARM AND SUICIDAL THOUGHTS AMONG HIGH SCHOOL STUDENTS CURRENTLY

The article focuses on understanding concepts and awareness of suicidal thoughts and self – harm behaviors based on quantitative and qualitative data. The quantitative database will be taken from a survey of high school students living and studying in Ho Chi Minh City. The qualitative database is taken from in-depth interviews focusing on teachers, parents, and students. The article presents the main results of the research. First, focus on the research basis including subjects, objects, and research methodology. Second, include views on suicidal thoughts and self-harm from many different perspectives, manifestations and causes of these behaviors, the prevalence of self-harm/suicidal thoughts, and consequences. Third, conclude and propose some recommendations to minimize the problem

Childhood Acute Poisoning at Haiphong Children\u27s Hospital: A 10-Year Retrospective Study

INTRODUCTION: Children are most often harmed by acute poisoning, which may cause disability or even death. This demonstrates the critical necessity for epidemiologic studies specific to each nation and area since they aid in developing plans for the prevention of acute poisoning. There are no data or outdated data on acute poisoning in children in Vietnam. This research would partly fill this existing gap and compare the trend with other places across the globe. METHODS: A retrospective study was conducted in the 10-year period from 2012 to 2021 in Haiphong Children\u27s Hospital, Vietnam. RESULTS: There were 771 children hospitalized due to acute poisoning. Children in the 1-5-year-old group accounted for the highest rate, at 506 (65.6%). The mean age was 4.5 ± 4.1 years old. The male-to-female ratio was 1.2/1. Nonpharmaceutical chemicals were the most common agent in 331 cases (42.9%), including cleaning products 63 (19.0%), rat poison 60 (18.1%), and petrol 42 (12.7%). Medications were the second most common agent in 290 cases (37.6%), mostly paracetamol 60 (20.7%) and sedatives 40 (13.8%). There were 633 (82.1%) children exposed to poisons unintentionally. CONCLUSION: Children between the ages of 1 and 5 are more likely to be exposed to harmful substances. The most common agents were nonpharmaceutical chemicals followed by pharmaceuticals. Most incidents were inadvertent. Finally, our research may provide insights that public health authorities might use to plan practical actions

HYDROGEN DEFECTS ON THE SURFACE OF LEAD-FREE FERROELECTRIC Na0.5_{0.5}Bi0.5_{0.5}TiO3_3 MATERIALS

Hydrogen atomic chemisorption and adsorption at all possible vacancy sites on the surface of perovskite Na0.5Bi0.5TiO3 (110) were explored using calculations from density functional theory. Our calculations reveal that a pristine Na0.5Bi0.5TiO3 (110) surface can exhibit direct and indirect transitions characterized by optical bandgaps of 2.68 eV and 2.75 eV, respectively. The density of states of the Na0.5Bi0.5TiO3 (110) surface indicates predominant electron transitions from O-2p valence bands to Ti-3d and Bi-6p conduction bands in the low-energy range. Hydrogen substitution at vacancies can induce magnetism, whereas hydrogen adsorption enhances both the magnetism and conductivity of the surface system. In particular, the charge density reveals electron transfer between cations and hydrogen atoms, providing insight into the variations in hydrogen bonding properties in these surface systems. These observations expand our understanding of hydrogen chemisorption and adsorption on defect sites, providing a novel avenue for investigating and potentially developing environmentally friendly multiferroic materials for advanced electronic devices

New record for Asia-Pacific of Protoperidinium anomaloplaxum (Peridiniales, Dinophyceae) from Vietnamese waters

Minusculum (Lebour) Balech is one of four subgenera of the genus Protoperidinium Bergh 1881. Only five species of this subgenus have been discovered worldwide, most of which are distributed in cold waters. In this study, Protoperidinium anomaloplaxum (Balech) Balech is reported from Vietnam and thus for the first time from Asia-Pacific waters. This species is illustrated with line drawing, light and scanning electron microscopic photographs and described details of the ornamentation of the thecal plates as well as its geographic distribution.

SURVEY ON VOCABULARY LEARNING STRATEGIES OF HIGH–QUALITY ENGLISH STUDIES PROGRAM STUDENTS, SCHOOL OF FOREIGN LANGUAGES, CAN THO UNIVERSITY, VIETNAM

This research study aimed to investigate the usage of vocabulary learning strategies among English Studies students at Can Tho University (CTU), specifically those under the high-quality program at the School of Foreign Languages (SFL). The primary objective of the study was to identify the most commonly used strategies for learning English vocabulary and to compare the similarities and differences in how these strategies were applied among students by academic year. A total of 200 survey responses from SFL, CTU got involved in the study, and 12 of whom joined a semi-structured interview. The data gathered were analyzed using both descriptive and inferential statistical techniques. The results of this study provided insights into effective vocabulary learning strategies and would facilitate the improvement of English language teaching and learning practices at the university level.  Article visualizations