The aim of this study is to investigate systematically the chloride diffusivity and chloride threshold of a wide range of calcium-rich and fly ash-dominated alkali-activated samples in light of their ...compositional differences. To this end, the effects of various fly ash (FA)-to-slag ratios, of alkali concentrations and of silicate content in the activator were investigated. The electrochemical aspects of the passive samples were also assessed. Results show the prominent role of calcium in the matrix to reduce the chloride diffusivity. While higher alkali concentration increased the porosity and chloride diffusivities in general, lower modulus ratios provided considerably better performance in the FA-dominated samples. Chloride threshold values range between 0.19 (wt% binder mass) for calcium-rich mortars fabricated at low levels of alkalinities and 0.69 for FA-dominated mortars fabricated with highly alkaline activators. Half-cell potential and polarization resistance of alkali-activated samples were in general lower than their Portland cement counterparts.
Geopolymer concrete (GPC) has significant potential as a more sustainable alternative for ordinary Portland cement concrete (PCC). However; as a rather new engineering material, there are some ...concerns over the durability aspects of geopolymer-based binders. In this study, the performance of chloride-contaminated reinforced GPC specimens manufactured using a blended low-calcium fly ash and slag cement is investigated by long-term monitoring of corrosion parameters such as open circuit corrosion potential, polarization resistance and Tafel slopes. The electrochemical results are validated by contrasting the electrochemical mass losses with the mass losses obtained from the gravimetric measurements. The investigated low-calcium fly ash-based GPC exhibit a comparable electrochemical performance to a similar strength PCC during the propagation phase of corrosion. Additionally, some of the conventional classifications which are commonly used to assess the severity of corrosion in Portland cement-based corroding systems might need some recalibration to be used for low-calcium fly ash-based corroding systems.
Moisture transport plays a key role in determining the different durability-related features of cementitious materials. In this paper, moisture sorption in a range of low-calcium (geopolymer-type) ...and calcium-rich alkali-activated binders are studied and compared with that of Portland cement-based binders. Through the analysis of water vapor sorption isotherms (WVSI) and mercury intrusion porosimetry (MIP) test results, two vastly different pore structures were observed. Fly ash-based geopolymer-type binders showed a very porous structure where a large volume of mesopores coexisted with a significant volume of macropores. Alkali-activated slag binders, however, had a very fine pore structure, with a relative lack of large macropores. The different pore structure of fly ash-based and slag-based binders led to amplification of pore blocking and cavitation in blended systems by the addition of slag. Analysis of the sorption kinetics showed the prominent effect of the presence of calcium in the matrix to reduce the permeability.
Recently published studies have found an impaired immune response after SARS‐CoV‐2 vaccination in solid organ recipients. However, most of these studies have not assessed immune cellular responses in ...liver and heart transplant recipients. We prospectively studied heart and liver transplant recipients eligible for SARS‐CoV‐2 vaccination. Patients with past history of SARS‐CoV‐2 infection or SARS‐CoV‐2 detectable antibodies (IgM or IgG) were excluded. We assessed IgM/IgG antibodies and ELISpot against the S protein 4 weeks after receiving the second dose of the mRNA‐1273 (Moderna) vaccine. Side effects, troponin I, liver tests and anti‐HLA donor‐specific antibodies (DSA) were also assessed. A total of 58 liver and 46 heart recipients received two doses of mRNA‐1273 vaccine. Median time from transplantation to vaccination was 5.4 years (IQR 0.3–27). Sixty‐four percent of the patients developed SARS‐CoV‐2 IgM/IgG antibodies and 79% S‐ELISpot positivity. Ninety percent of recipients developed either humoral or cellular response (87% in heart recipients and 93% in liver recipients). Factors associated with vaccine unresponsiveness were hypogammaglobulinemia and vaccination during the first year after transplantation. Local and systemic side effects were mild or moderate, and none presented DSA or graft dysfunction after vaccination. Ninety percent of our patients did develop humoral or cellular responses to mRNA‐1273 vaccine. Factors associated with vaccine unresponsiveness were hypogammaglobulinemia and vaccination during the first year after transplantation, highlighting the need to further protect these patients.
The vast majority of heart and liver transplant patients develop humoral or cellular responses to mRNA‐1273 vaccine. See editorial by Danziger‐Isakov and Sester on page 3827.
The long-term corrosion process of reinforced concrete beams is studied in this paper. The reinforced concrete elements were stored in a chloride environment for 17years under service loading in ...order to be representative of real structural conditions. At different stages, cracking maps were drawn, total chloride contents were measured and mechanical tests were performed. Results show that the bending cracks and their width do not influence significantly the service life of the structure. The chloride threshold at the reinforcement depth, used by standards as a single parameter to predict the end of the initiation period, is a necessary but not a sufficient parameter to define service life. The steel–concrete interface condition is also a determinant parameter. The bleeding of concrete is an important cause of interface de-bonding which leads to an early corrosion propagation of the reinforcements. The structural performance under service load (i.e.: stiffness in flexure) is mostly affected by the corrosion of the tension reinforcement (steel cross-section and the steel–concrete bond reduction). Limit-state service life design based on structural performance reduction in terms of serviceability shows that the propagation period of the corrosion process is an important part of the reinforced concrete service life.
Our aim in this paper is to introduce a set of relationships linking the distribution of reinforcement corrosion and the width of cover crack that results from such corrosion. This work is based on ...experimental results obtained on the longitudinal reinforcements of two beams naturally corroded over periods of 14 and 17 years. We first compared these experimental results with existing models linking crack width and attack penetration. Noting that such models only partially predict actual experimental data, we put forward a new model using the parameter of reinforcement cross-section loss.
The main purpose of this research is to study the time dependent behaviour of a geopolymer concrete. The geopolymer binder is composed of 85.2 % of low calcium fly ash and only 14.8 % of ground ...granulated blast furnace slag. Both drying shrinkage and creep are studied. In addition, different curing conditions at elevated temperature were used. All experimental results were compared to predictions made using the Eurocode 2. The curing regime plays an important role in the magnitude and development of both creep and drying shrinkage of class F fly ash based geopolymer concrete. A minimum of 3 days at 40 °C or 1 day at 80 °C is required to obtain final drying shrinkage strains similar to or less than those adopted by Eurocode 2 for ordinary Portland cement (OPC) concrete. Creep strains were similar or less than those predicted by Eurocode 2 for OPC concrete when the geopolymer concrete was cured for 3 days at 40 °C. After 7 days at 80 °C, creep strains became negligible.
Brain images are believed to have a particularly persuasive influence on the public perception of research on cognition. Three experiments are reported showing that presenting brain images with ...articles summarizing cognitive neuroscience research resulted in higher ratings of scientific reasoning for arguments made in those articles, as compared to articles accompanied by bar graphs, a topographical map of brain activation, or no image. These data lend support to the notion that part of the fascination, and the credibility, of brain imaging research lies in the persuasive power of the actual brain images themselves. We argue that brain images are influential because they provide a physical basis for abstract cognitive processes, appealing to people’s affinity for reductionistic explanations of cognitive phenomena.
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