RESUMEN
In the last decades, nano-silica (NS), nano-alumina (NA), and nano-calcium oxide (NC) particles have been incorporated into cementitious materials, and it seems that each one of them contributes uniquely to the materials' properties. This research explores the influence of each nanomaterial on the fresh properties of cement pastes and their compressive strength evolution over one year. Low proportions (1.5% by weight) of nanomaterials were added to cement pastes, and their fresh properties, such as heat of hydration and X-ray diffraction patterns in the first hours, were analyzed. The compressive strength and open porosity were also measured long-term. The acceleration of hydration heat in NA-cement pastes is linked to enhanced hydration product formation at early ages. Among the tested nanomaterials, NA increased compressive strength by 10% at later ages. Although the fresh properties of NC-cement pastes remained unaffected, their open porosity decreased by 54% at 28 days. In contrast, the increase in heat of hydration in NS-cement pastes did not result in significant strength improvement. Based on these findings, NA was selected for ultra-high-performance cement (UHPC)-based material use. Its incorporation not only preserved the ultra-high-performance (UHP) properties but also provided additional benefits such as an increase in compressive strength under a CO2 atmosphere. Through detailed analysis, this research establishes that nano-alumina incorporation optimizes the microstructural development and compressive strength of ultra-high-performance cement-based systems, presenting a novel advancement in enhancing the mechanical properties and durability of these materials under various environmental conditions.
RESUMEN
The Microbiologically Induced Corrosion (MIC) of concrete sewer pipes is a commonly known problem that can lead to the destruction of the system, creating multiple public health issues and the need for costly repair investments. The present study focuses on the development of a magnesium hydroxide coating, with optimized properties to protect concrete against MIC. The anti-corrosion properties of the respective coating were evaluated by using short and long duration accelerated sulfuric acid spraying tests. The coating presented satisfying adhesion ability, based on pull-off and Scanning Electron Microscopy (SEM) analysis measurements. The surface pH of the coated concrete was maintained at the alkaline region (i.e., >8.0) throughout the duration of all acid spraying tests. The consumption of the coating, due to the reaction (neutralization) with sulfuric acid, was confirmed by the respective mass and thickness measurements. The protection ability of this coating was also evaluated by recording the formation of gypsum (i.e., the main corrosion product of concrete) during the performed tests, by X-ray Diffraction (XRD) analysis and by the Attenuated Total Reflectance (ATR) measurements. Finally, a long duration acid spraying test was additionally used to evaluate the behavior of the coating, simulating better the conditions existing in a real sewer pipe, and the obtained results showed that this coating is capable of offering prolonged protection to the concrete substrate.
RESUMEN
The present study proposes nano-calcium oxide (NC) and nano-silica (NS) particles as healing agents in cement pastes, taking into account the curing conditions. Two series of specimens were treated in water and under wetting-drying cycles. The addition of NC (1.5%wt of binder) triggered early healing since cracks were healed within 14 days in underwater immersion and before 28 days at wetting-drying cycles. Attenuated Total Reflectance (ATR) spectroscopy and SEM analysis revealed that the healing products were mainly aragonite and calcite in water conditions and more amorphous carbonates under wetting-drying cycles. The combination of NS and NC (3.0%wt in total) offered healing under both curing conditions before 28 days. The presence of NS assisted toward porosity refinement and NC increased the carbonates' content. The newly formed material was dense, and its elemental analysis by SEM revealed the C-S-H compounds that were also verified by ATR.
RESUMEN
In this study we demonstrate - for the first time - the suitability of methyl propiolate - an alkylester of propiolic acid - as a thiol derivatizing reagent for capillary electrophoresis. Glutathione (as analyte in yeast samples) and N-acetylcysteine (as internal standard) were selected as model compounds. Several parameters affecting the separation efficiency (buffer pH, concentration, and separation voltage) and the derivatization yield (pH, reaction time and reagent concentration) were thoroughly investigated. Validation was carried out towards the determination of glutathione in commercially available yeast samples. The LOD was 1.5µmolL(-1) and the linearity was obeyed in the range of 25-200µmolL(-1). The accuracy in terms of recoveries ranged between 95.9% and 113.6%. The approach proved to be free from matrix effects, while the results were confirmed by a corroborative method based on liquid chromatography coupled to post-column derivatization.