Performance of geopolymer mortars prepared by different alkaline solutions under elevated temperature

Fire has severe effects on concrete as it causes a significant deterioration in its properties. Geopolymers (GP) are considered as an emerging alternative binder to Portland-cement OPC). This paper presents an investigation of the performance of fly ash (FA) based GP-mortars made with different alkaline solutions after exposure to elevated temperatures (200, 400, 600, and 800 ℃).  The main investigated parameters were the type of hydroxide (NaOH and KOH), type of silicate (Na2SiO3 and K2SiO3), molarity levels of NaOH, Na2SiO3/NaOH ratios, alkaline-solution to FA ratio and sand to FA ratio. Compressive, flexural, and indirect tensile strengths were measured before and after exposure to elevated temperatures. Moreover, SEM analysis was conducted on GP and OPC mortars. The results showed that performance of GP mortars containing Na2SiO3 with KOH was better than GP mixes that contained Na2SiO3 with NaOH or K2SiO3 with KOH after exposure to elevated temperatures. A higher loss rate in mechanical properties after exposure to 800℃ was observed as the NaOH molarity increased. Increasing Na2SiO3/NaOH ratio up to 2.5 caused an increase in the mechanical properties, while increasing that ratio from 2.5 to 3 caused higher loss in the mechanical properties of GP mortars. After exposure to 800 ℃, sand to FA ratio of 2 and alkaline solution to FA ratio of 0.5 gave higher residual strengths than the other ratios. Behavior of GP mortar was found to be better than OPC mortar after exposure to elevated temperatures. SEM images showed that the structure of the GP mortar, after exposure to elevated temperatures, was denser than that of the OPC mortar. Empirical equations capable of predicting the residual mechanical properties of GP-mortars made using different alkaline solutions with good correlation have been proposed

Performance of geopolymer mortars prepared by different alkaline solutions under elevated temperature

Fire has severe effects on concrete as it causes a significant deterioration in its properties. Geopolymers (GP) are considered as an emerging alternative binder to Portland-cement OPC). This paper presents an investigation of the performance of fly ash (FA) based GP-mortars made with different alkaline solutions after exposure to elevated temperatures (200, 400, 600, and 800 ℃).  The main investigated parameters were the type of hydroxide (NaOH and KOH), type of silicate (Na2SiO3 and K2SiO3), molarity levels of NaOH, Na2SiO3/NaOH ratios, alkaline-solution to FA ratio and sand to FA ratio. Compressive, flexural, and indirect tensile strengths were measured before and after exposure to elevated temperatures. Moreover, SEM analysis was conducted on GP and OPC mortars. The results showed that performance of GP mortars containing Na2SiO3 with KOH was better than GP mixes that contained Na2SiO3 with NaOH or K2SiO3 with KOH after exposure to elevated temperatures. A higher loss rate in mechanical properties after exposure to 800℃ was observed as the NaOH molarity increased. Increasing Na2SiO3/NaOH ratio up to 2.5 caused an increase in the mechanical properties, while increasing that ratio from 2.5 to 3 caused higher loss in the mechanical properties of GP mortars. After exposure to 800 ℃, sand to FA ratio of 2 and alkaline solution to FA ratio of 0.5 gave higher residual strengths than the other ratios. Behavior of GP mortar was found to be better than OPC mortar after exposure to elevated temperatures. SEM images showed that the structure of the GP mortar, after exposure to elevated temperatures, was denser than that of the OPC mortar. Empirical equations capable of predicting the residual mechanical properties of GP-mortars made using different alkaline solutions with good correlation have been proposed

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely

Predicting the ingredients of self compacting concrete using artificial neural network

Self compacting concrete (SCC) is a highly flowable type of concrete that spreads into form without the need of mechanical vibration. This paper presents a comparative study between two methodologies which have been applied on two different data sets of SCC mixtures, which were gathered from the literature, using artificial neural network (ANN). The two methodologies aim to get the best prediction accuracy for the SCC ingredients using the 28-day compressive strength and slump flow diameters as inputs of the ANN. In the first methodology, the ANN model is constructed as a multi input â multi output neural network with the six ingredients as outputs. In the second methodology, the ANN model is constructed as a multi input â single output neural network where the six ingredient outputs are predicted separately from six different neural networks of multi input â single output type. Also, the influence of the mixes homogeneity on the prediction accuracy is investigated through the second data set. The results demonstrate the superiority of the second methodology in terms of accuracy of the predicted outputs. Moreover, the uniformity of the training data assures the accuracy of the predicted ingredients. Keywords: Self compacting concrete (SCC), Artificial neural network (ANN), Concrete mix design, Concrete compressive strength, Slump flo

Heart rate variability as an indicator of COVID-19 induced myocardial injury: a retrospective cohort study

Abstract Background Heart rate variability (HRV) is a valuable indicator of autonomic nervous system integrity and can be a prognostic tool of COVID-19 induced myocardial affection. This study aimed to compare HRV indices between patients who developed myocardial injury and those without myocardial injury in COVID-19 patients who were admitted to intensive care unit (ICU). Methods In this retrospective study, the data from 238 COVID-19 adult patients who were admitted to ICU from April 2020 to June 2021 were collected. The patients were assigned to myocardial injury and non-myocardial injury groups. The main collected data were R-R intervals, standard deviation of NN intervals (SDANN) and the root mean square of successive differences between normal heartbeats (RMSSD) that were measured daily during the first five days of ICU admission. Results The R-R intervals, the SDANN and the RMSSD were significantly shorter in the myocardial injury group than the non-myocardial group at the first, t second, third, fourth and the fifth days of ICU admission. There were no significant differences between the myocardial injury and the non-myocardial injury groups with regard the number of patients who needed mechanical ventilation, ICU length of stay and the number of ICU deaths. Conclusions From the results of this retrospective study, we concluded that the indices of HRV were greatly affected in COVID-19 patients who developed myocardial injury

Serpentinite-hosted talc-magnesite deposits of Wadi Barramiya area, Eastern Desert, Egypt: Characteristics, petrogenesis and evolution

Enormous quantities of practically untapped talc–magnesite rocks are distributed in the Wadi Barramiya area in intimate spatial and genetic association with the ophiolitic serpentinites. These deposits are an important potential source of magnesia, which is used in a broad spectrum of strategic industries. Barramiya ophiolitic serpentinites represent obducted oceanic slices onto island-arc successions. They occur as elongated mountainous ranges in the form of anticlinal–synclinal sheets demarcating the general ENE-WSW brittle–ductile shear zones of the area. The serpentinite-hosted talc–magnesite deposits of Barramiya area are located: (a) along major faults that cut the serpentinite slices, or (b) at thrust contacts between obducted serpentinites and other mélange components (more siliceous country rocks of island-arc affinity). The latter were regionally metamorphosed at greenschist up to middle amphibolite facies conditions. The talc–magnesite rocks represent in situ fissure-fed metasomatic products of serpentinite precursors via extensive rock–fluid interactions. The main fluids involved in the transformation processes of serpentinites to talc–magnesite were SiO2aqueous solutions and CO2. The deposits located along the fault systems cutting the serpentinite-host are magnesite-rich, whereas those located at the contacts between serpentinites and the more siliceous country rocks are typically talc-rich. Based on the proportional distribution of talc and magnesite in conjunction with other accessories, the rocks have been distinguished into assemblages. Their characteristics, petrogenesis and evolution from serpentinite precursors are elaborated in the light of their petrography, XRD, EDAX, and XRF data. Constraints on the conditions of their formation include temperature of about 490 °C and a maximum XCO2 of about 0.13. New mapping was undertaken for the area using remote sensing and GIS techniques. Accordingly, the Barramiya talc–carbonate rocks were more precisely mapped as separate layers and their reserve estimation was accomplished