Mechanical Strength and Chloride Ions' Penetration of Alkali-Activated Concretes (AAC) with Blended Precursor.

The purpose of this study was to investigate the properties of hardened alkali-activated concrete, which is considered an eco-friendly alternative to Portland cement concrete. In this paper, the precursors for alkali-activated concrete preparations are blends of fly ash and ground-granulated blast-furnace slag in three slag proportions: 5%, 20%, and 35%, expressed as a percentage of fly ash mass. Thus, three concretes were designed and cast, denominated as AAC5, AAC20, and AAC35. Their physical and mechanical characteristics were investigated at 28 and 180 days, as well as their properties of chloride ion transport. The modified NT BUILD 492 migration test was applied to determine the chloride ions' penetration of the alkali-activated concretes. Improvement of mechanical strength and resistance to chloride aggression was observed with ground-granulated blast-furnace slag content increase in the compositions of the tested concretes. Mercury intrusion porosimetry tests provided insight into the open pore structures of concretes. A significant decrease in the total pore volume of the concrete and a change in the nature of the pore diameter distribution due to the addition of ground granulated blast furnace slag were demonstrated.

Applicability of Selected 3D Printing Materials in Electrochemistry.

This manuscript investigates the chemical and structural stability of 3D printing materials (3DPMs) frequently used in electrochemistry. Four 3D printing materials were studied: Clear photopolymer, Elastic photopolymer, PET filament, and PLA filament. Their stability, solubility, structural changes, flexibility, hardness, and color changes were investigated after exposure to selected organic solvents and supporting electrolytes. Furthermore, the available potential windows and behavior of redox probes in selected supporting electrolytes were investigated before and after the exposure of the 3D-printed objects to the electrolytes at various working electrodes. Possible electrochemically active interferences with an origin from the 3DPMs were also monitored to provide a comprehensive outline for the use of 3DPMs in electrochemical platform manufacturing.

Fracture Behavior of Long Fiber Reinforced Geopolymer Composites at Different Operating Temperatures.

The aim of this article was to analyze the fracture behavior of geopolymer composites based on fly ash or metakaolin with fine aggregate and river sand, with three types of reinforcement: glass, carbon, and aramid fiber, at three different temperatures, approximately: 3 °C, 20 °C, and 50 °C. The temperatures were selected as a future work temperature for composites designed for additive manufacturing technology. The main research method used was bending strength tests in accordance with European standard EN 12390-5. The results showed that the addition of fibers significantly improved the bending strength of all composites. The best results at room temperature were achieved for the metakaolin-based composites and sand reinforced with 2% wt. aramid fiber-17 MPa. The results at 50 °C showed a significant decrease in the bending strength for almost all compositions, which are unexpected results, taking into account the fact that geopolymers are described as materials dedicated to working at high temperatures. The test at low temperature (ca. 3 °C) showed an increase in the bending strength for almost all compositions. The grounds of this type of behavior have not been clearly stated; however, the likely causes of this are discussed.

Electroanalysis of Fentanyl and Its New Analogs: A Review.

The review describes fentanyl and its analogs as new synthetic opioids and the possibilities of their identification and determination using electrochemical methods (e.g., voltammetry, potentiometry, electrochemiluminescence) and electrochemical methods combined with various separation methods. The review also covers the analysis of new synthetic opioids, their parent compounds, and corresponding metabolites in body fluids, such as urine, blood, serum, and plasma, necessary for a fast and accurate diagnosis of intoxication. Identifying and quantifying these addictive and illicit substances and their metabolites is necessary for clinical, toxicological, and forensic purposes. As a reaction to the growing number of new synthetic opioid intoxications and increasing fatalities observed over the past ten years, we provide thorough background for developing new biosensors, screen-printed electrodes, or other point-of-care devices.

Creep and Shrinkage Behaviour of Disintegrated and Non-Disintegrated Cement Mortar.

One way to prevent cement from ending up in landfills after its shelf life is to regain its activity and reuse it as a binder. As has been discovered, milling by planetary ball mill is not effective. Grinding by collision is considered a more efficient way to refine brittle material and, in the case of cement, to regain its activity. There has been considerable research regarding the partial replacement of cement using disintegrated cement in mortar or concrete in the past few decades. This article determines and compares the creep and shrinkage properties of cement mortar specimens made from old disintegrated, old non-disintegrated, and new non-disintegrated Portland cement. The tests show that the creep strains for old disintegrated and old non-disintegrated cement mortars are close, within a 2% margin of each other. However, the creep strains for new non-disintegrated cement mortar are 30% lower. Shrinkage for old disintegrated and non-disintegrated cement mortar is 20% lower than for new non-disintegrated cement mortar. The research shows that disintegration is a viable procedure to make old cement suitable for structural application from a long-term property standpoint. Additionally, it increases cement mortar compressive strength by 49% if the cement is disintegrated together with sand.

Chloride Ions' Penetration of Fly Ash and Ground Granulated Blast Furnace Slags-Based Alkali-Activated Mortars.

Due to the need to reduce the CO2 emissions of mineral binders, researchers are considering the use of alkali-activated materials (AAMs) as an alternative to cementitious binders. The properties of AAMs can be more advantageous than those presented by cementitious binders, and thus they can replace Portland cement binders in some applications. Mechanical tests of AAMs are being conducted on an ongoing basis; however, durability issues related to reinforcing steel in conditions in which steel members interact with chloride ions remain unsolved. In this paper, the precursors for AAM preparations are blends of fly ash (FA) and ground granulated blast-furnace slag (GGBFS) in four slag proportions: 0%, 10%, 30% and 50% expressed as a percent of FA mass. Four alkali-activated mortars were prepared, denominated as AAM 0, AAM 10, AAM 30 and AAM 50, respectively. Their basic physical and mechanical characteristics were investigated, as were their gas transport properties. The nitrogen Cembureau method was applied to determine the permeability of the mortar. The transport properties of the chloride ions were determined using the modified NT BUILD 492 migration test. The comparison of results obtained demonstrated a positive effect of GGBFS addition in terms of an increase in bulk density, permeability, porosity and, at the same time, a reduction in chloride ion penetration. The water absorption tests also provided insight into the open pore structures of mortars. The measurements revealed a strong dependence between fluid transport through the mortars and the water absorption and initial water content of materials.

Voltammetric determination of heavy metals in honey bee venom using hanging mercury drop electrode and PLA/carbon conductive filament for 3D printer.

A new method for determination of selected heavy metals (Cd, Pb, Cu, Zn, and Ni) in honey bee venom was developed. Heavy metals are metabolized and incorporated into bee products, including honey and honey bee venom (apitoxin). Their composition reflects contamination of "bee environment", providing information about heavy metal contamination in the neighborhood of human dwellings. Moreover, assessment of bee products contamination is relevant for medicine, as they are a tool for promising therapeutic and chemoprophylactic strategies against COVID-19 (SARS-CoV-2). Owing to the complicated matrix, the developed method consists of wet mineralization with sulfuric acid, nitric acid, under increased temperature, and pressure and subsequent repeated boiling with concentrated nitric acid. Determination of the selected metals was carried out by anodic or cathodic stripping voltammetry on two types of electrodes: pen-type hanging mercury drop electrode (HMDE) and PLA filament with carbon conductive admixture (PLA-C) for 3D printer. Contents of lead and cadmium in all analyzed bee venom samples were on the level of mg kg-1, of nickel and copper about ten times higher, and of zinc on the level of g kg-1. The results achieved using HMDE were recorded with average relative standard deviation (RSD) 5.4% (from 3.2% to 8.6%) and using PLA-C 11.8% (from 6.5% to 18.0%). The results achieved using both electrodes proved to be equivalent with statistical probability higher than 95%.

Effect of Cement Type on the Mechanical Behavior and Permeability of Concrete Subjected to High Temperatures.

The paper presents experimental investigations concerning the influence of the cement type (CEMI 42.5 R Portland cement and CEMIII/A 42.5 N slag cement-with 53% granulated blast furnace slag) on the mechanical and transport properties of heated concretes. The evolution of properties due to high temperature exposure occurring during a fire was investigated. High temperature exposure produces changes in the transport and mechanical properties of concrete, but the effect of cement type has not been widely studied in the literature. In this paper, concretes were made with two cement types: CEMI and CEMIII, using basalt (B) and riverbed aggregates (RB). The compressive and tensile strength, as well as the static modulus of elasticity and Cembureau permeability, were tested after high temperature exposure to 200, 400, 600, 800, and 1000 °C. The evaluation of damage to the concrete and crack development due to high temperature effects was performed on the basis of the change in the static modulus of elasticity. The test results clearly demonstrated that permeability increases with damage, and it follows an exponential type formula for both types of cement.