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Abstract:For optimum production of ultra-high performance concrete (UHPC), the material and microstructural properties of UHPC cured under various heat treatment (HT) conditions are studied. The effects of HT temperature and duration on the hydration reaction, microstructure, and mechanical properties of UHPC are investigated. Increasing HT temperature accelerates both cement hydration and pozzolanic reaction, but the latter is more significantly affected. This accelerated pozzolanic reaction in UHPC clearly enhances compressive strength. However, strength after the HT becomes stable as most of the hydration finishes during the HT period. Particularly, it was concluded that the mechanical benefit of the increased temperature and duration on the 28 day-strength is not noticeable when the HT temperature is above 60 • C (with a 48 h duration) or the HT duration is longer than 12 h (with 90 • C temperature). On the other hand, even with a minimal HT condition such as 1 day at 60 • C or 12 h at 90 • C, outstanding compressive strength of 179 MPa and flexural tensile strength of 49 MPa are achieved at 28 days. Microstructural investigation conducted herein suggests that portlandite content can be a good indicator for the mechanical performance of UHPC regardless of its HT curing conditions. These findings can contribute to reducing manufacturing energy consumption, cost, and environmental impact in the production of UHPC and be helpful for practitioners to better understand the effect of HT on UHPC and optimize its production.

Background:The McGrath videolaryngoscope (VL) provides excellent laryngoscopic views, but directing an endotracheal tube can be difficult, and thus the routine use of a stylet is recommended. The goal of this study is to determine the appropriate angle (60° vs 90°) of the stylet when using the McGrath VL by comparing the time to intubation (TTI).Methods:One hundred and forty patients aged 19 to 70 years (American Society of Anesthesiologists classification I or II) who required tracheal intubation for elective surgery were randomly allocated to 1 of 2 groups, at the 60° angle (n = 70) or the 90° angle (n = 70). Anesthesia was induced with propofol, fentanyl, and rocuronium. The primary outcome was TTI assessed by a blind observer. Glottic grade, use of optimal external laryngeal manipulation, failed intubation at first attempt, ease of intubation, and severity of oropharyngeal bleeding were also recorded.Results:The mean TTI was significantly shorter in the 60° group than in the 90° group (29.3 ± 6.4 vs 32.5 ± 9.4 s, P = 0.022). The glottic grade and degree of intubation difficulty were not significantly different between the 2 groups.Conclusions:When intubating the patients with the McGrath videolaryngoscope, the 60° angled stylet allowed for faster orotracheal intubation than did the 90° angled stylet.

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Sandwich panels comprising prefabricated ultra-high performance concrete (UHPC) composites can be used as ecofriendly and multi-functional structural elements. To improve the structural and thermal performance of composite sandwich panels, combinations of UHPC and expanded polystyrene (EPS) beads were investigated. High-performance expanded polystyrene concrete (HPEPC) was tested with various EPS bulk ratios to determine the suitability of the mechanical properties for use as a high-strength lightweight aggregate concrete. As a core material in composite sandwich panels, the mechanical properties of HPEPC were compared with those of EPS mortar. The compressive strength of HPEPC is approximately eight times greater than that of EPS mortar, and the thermal conductivity of approximately a quarter that of EPS mortar. The structural behavior of composite sandwich panels was empirically analyzed using different combinations of cores, face sheets, and adhesive materials. In the flatwise and edgewise compression tests, sandwich panels with HPEPC cores had high peak strengths, irrespective of the type of face sheets, as opposed to the specimens with EPS mortar cores. In the four-point bending tests, the sandwich panels with HPEPC cores, or reinforced UHPC face sheets combined with adhesive mortar, exhibited higher peak strengths than the other specimens, and failed in a stable manner, without delamination.

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