Microstructural and Mechanical Characteristics of Alkali-Activated Binders Composed of Milled Fly Ash and Granulated Blast Furnace Slag with µ-Limestone Addition.

Concrete is the most used construction material, needing large quantities of Portland cement. Unfortunately, Ordinary Portland Cement production is one of the main generators of CO2, which pollutes the atmosphere. Today, geopolymers are an emerging building material generated by the chemical activity of inorganic molecules without the Portland Cement addition. The most common alternative cementitious agents used in the cement industry are blast-furnace slag and fly ash. In the present work, the effect of 5 wt.% µ-limestone in mixtures of granulated blast-furnace slag and fly ash activated with sodium hydroxide (NaOH) at different concentrations was studied to evaluate the physical properties in the fresh and hardened states. The effect of µ-limestone was explored through XRD, SEM-EDS, atomic absorption, etc. The addition of µ-limestone increased the compressive strength reported values from 20 to 45 MPa at 28 days. It was found by atomic absorption that the CaCO3 of the µ-limestone dissolved in NaOH, precipitating Ca(OH)2 as the reaction product. SEM-EDS analysis showed a chemical interaction between C-A-S-H- and N-A-S-H-type gels with Ca(OH)2, forming (N, C)A-S-H- and C-(N)-A-S-H-type gels, improving mechanical performance and microstructural properties. The addition of µ-limestone appeared like a promising and cheap alternative for enhancing the properties of low-molarity alkaline cement since it helped exceed the 20 MPa strength recommended by current regulations for conventional cement.

Green Synthesis of Magnetic Nanoparticles of Iron Oxide Using Aqueous Extracts of Lemon Peel Waste and Its Application in Anti-Corrosive Coatings.

Lately, the development of green chemistry methods with high efficiency for metal nanoparticle synthesis has become a primary focus among researchers. The main goal is to find an eco-friendly technique for the production of nanoparticles. Ferro- and ferrimagnetic materials such as magnetite (Fe3O4) exhibit superparamagnetic behavior at a nanometric scale. Magnetic nanoparticles have been gaining increasing interest in nanoscience and nanotechnology. This interest is attributed to their physicochemical properties, particle size, and low toxicity. The present work aims to synthesize magnetite nanoparticles in a single step using extracts of green lemon Citrus Aurantifolia residues. The results produced nanoparticles of smaller size using a method that is friendlier to health and the environment, is more profitable, and can be applied in anticorrosive coatings. The green synthesis was carried out by a co-precipitation method under variable temperature conditions. The X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) characterization showed that magnetite nanoparticles were successfully obtained with a very narrow particle size distribution between 3 and 10 nm. A composite was produced with the nanoparticles and graphene to be used as a surface coating on steel. In addition, the coating's anticorrosive behavior was evaluated through electrochemical techniques. The surface coating obtained showed good anticorrosive properties and resistance to abrasion.

Relación del acoso escolar y conductas de riesgo a trastornos de la alimentación en escolares mexicanos / Relationship of school bullying and risk behaviors to eating disorders in Mexican schoolchildren

Fundamentos: El objetivo de la presente investigación fue determinar la prevalencia entre el acoso escolar obullying y las conductas de riesgo a trastornos de la conducta alimentaria (TCA), en escolares mexicanos dequinto y sexto grado escolar. Cuyos resultados aporten al programa en línea que se va diseñar para suprevención.Métodos: Se obtuvo una muestra de 3641 escolares mexicanos entre 9-14 años a los cuales, se les aplicó laencuesta Health Behaviour in School-aged Children (HBSC) y el CBCAR, cuestionario diseñado y validado enadolescentes mexicanos, para evaluar las conductas de riego a TCA. Se aplicó la encuesta en línea, con elformato del programa “NutriNet” del Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán(INCMYNSZ), protocolo con el visto bueno de los comités del Instituto y del Hospital General de México.Resultados: Se observó una mayor incidencia de presentar conductas alimentarias de riesgo en escolares queson acosados tanto en los escolares abusadores y en los escolares que participan en pleitos o peleas,observándose diferencia estadística significativa (p ≥ 0,05).Conclusiones: El bullying constituye un factor de riesgo a padecer un trastorno de la conducta alimentaria. (AU)

Background: The aim of this research was to determine the prevalence of bullying and risk behaviors foreating disorders in Mexican schoolchildren in 5th and 6th grade. Whose results contribute to the onlineprogram that will be designed for its prevention.Methods: A sample of 3,641 Mexican schoolchildren between 9-14 years old was obtained. To whom, theHealth Behavior in School-aged Children (HBSC) survey and the CBCAR, a questionnaire designed andvalidated in Mexican adolescents were applied to evaluate risk behaviors to eating disorders. The onlinesurvey was applied, with the format of the "NutriNet" program of the National Institute of Medical Sciencesand Nutrition Salvador Zubiran (INCMYNSZ), protocol with the approval of the committees of the Instituteand the General Hospital of Mexico.Results: A higher incidence of presenting risky eating behaviors was observed in schoolchildren who arebullied both in abusive schoolchildren and in schoolchildren who participate in fights, observing a statisticallysignificant difference (p ≥ 0.05).Conclusions: Bullying is a risk factor for developing an eating disorder. (AU)

Effect of Mineral Aggregates and Chemical Admixtures as Internal Curing Agents on the Mechanical Properties and Durability of High-Performance Concrete.

In the present work, the effect of mineral aggregates (pumice stone and expanded clay aggregates) and chemical admixtures (superplasticizers and shrinkage reducing additives) as an alternative internal curing technique was investigated, to improve the properties of high-performance concrete. In the fresh and hardened state, concretes with partial replacements of Portland cement (CPC30R and OPC40C) by pulverized fly ash in combination with the addition of mineral aggregates and chemical admixtures were studied. The physical, mechanical, and durability properties in terms of slump, density, porosity, compressive strength, and permeability to chloride ions were respectively determined. The microstructural analysis was carried out by scanning electronic microscopy. The results highlight the effect of the addition of expanded clay aggregate on the internal curing of the concrete, which allowed developing the maximum compressive strength at 28 days (61 MPa). Meanwhile, the replacement of fine aggregate by 20% of pumice stone allowed developing the maximum compressive strength (52 MPa) in an OPC-based concrete at 180 days. The effectiveness of internal curing to develop higher strength is attributed to control in the porosity and a high water release at a later age. Finally, the lowest permeability value at 90 days (945 C) was found by the substitutions of fine aggregate by 20% of pumice stone saturated with shrinkage reducing admixture into pores and OPC40C by 15% of pulverized fly ash. It might be due to impeded diffusion of chloride ions into cement paste in the vicinity of pulverized fly ash, where the pozzolanic reaction has occurred. The proposed internal curing technology can be considered a real alternative to achieve the expected performance of a high-performance concrete since a concrete with a compressive strength range from 45 to 67 MPa, density range from 2130 to 2310 kg/m3, and exceptional durability (< 2000 C) was effectively developed.