Experimental Investigation on Chloride Diffusion Coefficient of Self-compacting Concrete in the Oman Sea

Chloride ion penetration is an important parameter influencing the service life of a concrete structure, especially in aggressive environments. Severe chloride-induced corrosion of reinforced concretes has been reported in the southern part of Iran in the region of Oman Sea. In this paper, the effect of different environmental conditions of the Oman Sea on chloride penetration and mechanical properties of self-compacting concrete (SCC) and normal concrete (NC) is investigated. For this purpose, a number of prismatic specimens were exposed to various environmental conditions such as tide, submersion and atmospheric conditions. Surface chloride concentration and diffusion coefficient of SCC in these zones were calculated based on Fick’s second law, at 28, 90 and 150 days and compared with NC. Based on the values obtained in this study, relationships are proposed for concrete permeability and surface chloride of self-compacting concrete (SCC) at different ages in different aggressive environments. By determining the corrosion time based on these relations, it is observed that for a given water-to-cement ratio, the self-compacting concrete (SCC) has higher durability compared to normal concrete (NC)

Influence of Nano-silica and Crack Width on Corrosion Parameters of Pre-cracked Reinforced Concrete Beams

This paper presents an experimental study on the durability of both sound and cracked reinforced concrete (RC) beam specimens. Using nano-silica (NS) can improve the durability properties of reinforced concrete. So, RC beams with three nano-silica percentages of 0 %, 1.5 %, and 3 % were prepared. In addition, to consider the effect of cracking on corrosion, crack widths between 0.1 mm and 0.5 mm, and cover depths of 30 mm and 45 mm were considered. All beam specimens were subjected to 5 % NaCl solution and monitored weekly for half-cell potentials (HCP). The presented results include the HCP evaluation and diffusion factor values in sound and cracked concrete beams exposed to chloride attack. The experimental results indicated that the chloride diffusion coefficient increases with extending crack width. Nano-silica improved the permeability characteristics of concrete, HCP and also diffusion factor values. Regressive models of the chloride diffusion factor and HCP values were proposed for influencing parameters, i.e., nano-silica and crack width with two different cover depths

Modelling of repair techniques for masonry arch bridges

Small scale centrifuge models were used to study the behaviour of arches repaired using different techniques. The models under test were 1/12th scale replicas of a 6 metre single span three ring arch. Two types of arch geometry, with span/rise of 4 and 2, were studied as a shallow and deep arch geometry. The models were tested in a centrifuge under a steady equivalent gravity of 12g. Two types of 2-D and 3-D arch models were studied which had the same geometry but different in the addition of spandrel walls. The 3-D models were built with spandrel walls but without any wing walls or parapet. Both 2-D and 3-D arch models were tested under rolling and failure loads. The models were usually tested with fourteen passes of a rolling load and then up to the observation of first signs of failure to enable them to be suitable for applying a repair method. The repaired models were tested using the same procedure but up to the full failure load. To understand the behaviour of the arch models under unsymmetrical loads different roller weights were applied at different positions. The arch deflection and the soil/masonry interaction in arch extrados were measured in all the tests and compared with each other. Plastic mesh reinforcement, stitching, and concrete slab on top of the soil backfill were applied as repair methods to the 2-D arch models. A review of the results has shown an increase in arch stiffness, decrease in deflections and a significant improvement in the ultimate load carrying capacity. A significant effect on the pressure distribution on the arch barrel was observed due to the application of the concrete slab on top of the backfill. Stitching of arch barrel and the barrel to the spandrels, applying partial saddle concrete and strengthening of spandrel wall using reinforced concrete were tested in the 3-D arch models. The results showed improvements in the stiffness and ultimate arch load carrying capacity due to these repair techniques. The results provide a valuable data base for validation of numerical models and an initial attempt to use them with a commercial finite element program is included.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Modelling of repair techniques for masonry arch bridges

Small scale centrifuge models were used to study the behaviour of arches repaired using different techniques. The models under test were 1/12th scale replicas of a 6 metre single span three ring arch. Two types of arch geometry, with span/rise of 4 and 2, were studied as a shallow and deep arch geometry. The models were tested in a centrifuge under a steady equivalent gravity of 12g. Two types of 2-D and 3-D arch models were studied which had the same geometry but different in the addition of spandrel walls. The 3-D models were built with spandrel walls but without any wing walls or parapet. Both 2-D and 3-D arch models were tested under rolling and failure loads. The models were usually tested with fourteen passes of a rolling load and then up to the observation of first signs of failure to enable them to be suitable for applying a repair method. The repaired models were tested using the same procedure but up to the full failure load. To understand the behaviour of the arch models under unsymmetrical loads different roller weights were applied at different positions. The arch deflection and the soil/masonry interaction in arch extrados were measured in all the tests and compared with each other. Plastic mesh reinforcement, stitching, and concrete slab on top of the soil backfill were applied as repair methods to the 2-D arch models. A review of the results has shown an increase in arch stiffness, decrease in deflections and a significant improvement in the ultimate load carrying capacity. A significant effect on the pressure distribution on the arch barrel was observed due to the application of the concrete slab on top of the backfill. Stitching of arch barrel and the barrel to the spandrels, applying partial saddle concrete and strengthening of spandrel wall using reinforced concrete were tested in the 3-D arch models. The results showed improvements in the stiffness and ultimate arch load carrying capacity due to these repair techniques. The results provide a valuable data base for validation of numerical models and an initial attempt to use them with a commercial finite element program is included

An Efficient Entropy-Based Method for Reliability Assessment by Combining Kriging Meta-Models

Meta-models or surrogate models are convenient tools for reliability assessment of problems with time-consuming numerical models. Recently, an adaptive method called AK-MCS has been widely used for reliability analysis by combining Mont-Carlo simulation method and Kriging surrogate model. The AK-MCS method usually uses constant regression as a Kriging trend. However, other regression trends may have better performance for some problems. So, a method is proposed by combining multiple Kriging meta-models with various trends. The proposed method is based on the maximum entropy of predictions to select training samples. Using multiple Kriging models can reduce the sensitivity to the regression trend. So, the propped method can have better performance for different problems. The proposed method is applied to some examples to show its efficiency

Single course of high dose dexamethasone is more effective than conventional prednisolone therapy in the treatment of primary newly diagnosed immune thrombocytopenia

INTRODUCTION: Immune thrombocytopenia (ITP) is an immune disorder commonly presents as isolated thrombocytopenia. Generally corticosteroids are the main treatment of ITP. This study was designed to evaluate effectiveness of high dose dexamethasone comparing conventional corticosteroid therapy in the treatment of ITP. MATERIALS AND METHODS: In a randomized prospective study, sixty adult patients with newly diagnosed primary symptomatic ITP (Platelet count < 20,000) were evaluated. Patients divided into two groups. In group A, thirty patients (mean age of 24.9 years) received Dexamethasone 40 mg/IV/daily for four days (10 mg/q6h); and then Prednisolone 1 (mg)/(kg)/day/PO with rapid tapering of prednisolone (10 mg/week). From the other hand, in group B, thirty patients (mean age of 27.2 years) were treated with Prednisolone 1 (mg)/(kg)/day/PO for four weeks, then the drug tapered weekly. RESULTS: All the patients in group A showed favorable response within the first seven days, 27 cases presented complete response (CR) and three cases revealed response (R). In group B, 11 cases had CR, 13 cases showed R and six cases had No response (NR). After three months, rates of CR were 80% and 23.3% in group A and B; respectively. Responses were 16.7% and 33.3%, NRs were 6.6% and 43.3% in group A and B; respectively (P < 0.0001). After 6 months, CR was 73.3% vs.16.7%, and R was 16.7% vs.36.7% and NR was 10% vs. 46.7% in group A and B; respectively (P < 0.0001). After 12 months, there was no change in response rate in group A, but in group B 53% were non responsive, 40% showed R (chronic ITP) and complete response was observed only in 6.7% (P < 0.0001). Three cases in group A and 12 cases in group B had needed splenectomy (P < 0.00002). CONCLUSION: We showed that high dose dexamethasone is more effective than conventional steroid therapy in newly diagnosed ITP as initial treatment with less relapses and toxicities

The diagnostic value of the field assessment stroke triage for emergency destination tool in identifying the obstruction of large cerebral vessels; a systematic review and meta-analysis

Objective: In this study, we investigate the diagnostic value of the Field Assessment Stroke Triage for Emergency Destination (FAST-ED) tool in the diagnosis of large vessels occlusion (LVO) in a systematic review and meta-analysis.&nbsp;Methods: We conducted a search in Medline (PubMed), Embase, Scopus and Web of Science databases until the 21st of September 2022, as well as a manual search in Google and Google scholar to find related articles. Studies of diagnostic value in adult population were included. Screening, data collection and quality control of articles were done by two independent researchers. The data were entered and analyzed in STATA 17.0 statistical program.&nbsp;Results: The data from 30 articles were entered. The best cut-off points for FAST-ED were 3 or 4. The sensitivity and specificity of FAST-ED at cut-off points 3 were 0.77 (95% CI: 0.73-0.80) and 0.76 (95% CI: 0.72-0.80), respectively. These values ​​for cut-off point 4 were 0.72 (95% CI: 0.65-0.78) and 0.79 (95% CI: 0.75-0.82), respectively. Meta-regression showed that the sensitivity and specificity of FAST-ED performed by a neurologist was more accurate compared to emergency physician (p for sensitivity=0.01; p for specificity&lt;0.001) and emergency medical technicians (p for sensitivity=0.03; p for specificity&lt;0.001). Finally, it was found that the sensitivity of FAST-ED performed by the emergency physician and the emergency medical technician has no statistically significant difference (p=0.76). However, the specificity of FAST-ED reported by the emergency physician is significantly higher (p&lt;0.001). The false negative rate of this tool at cut-off points 3 and 4 is 22.5% and 28.8%, respectively.&nbsp;Conclusion: Although FAST-ED has an acceptable sensitivity in identifying LVO, its false negative rate varies between 22.5% and 28.8%. A percentage this high is unacceptable for a screening tool to aide in the diagnosis of strokes considering it has a high rate or morbidity and mortality. Therefore, it is recommended to use another diagnostic tool for the stroke screening

Herdeteknologi – modellering av betongens temperatur- og fasthetsutvikling

For many years, Heidelberg Materials Cement Norway has offered the Norwegian concrete market the curing technology software HETT97. This software is a planning tool for simulating temperature and strength development in constructions. In addition, the program considers the concrete composition, heat and strength development and conditions such as construction type, formwork types and weather conditions etc. This is crucial for proper planning of casting work, such as preventing freezing of fresh concrete in accordance with NS-EN 13670 +NA, which specifies that concrete must not freeze at temperatures below 0 °C until the achieved compressive strength in the concrete surface reaches 5 MPa. Additionally, high temperatures should be avoided in accordance with NS-EN 13670 +NA, which sets a maximum concrete temperature of 70 °C. A new version of the program, called HETT22, was released on October 25, 2022. It features a completely new user interface, enhanced functions, and an updated database for various types of concrete. To fully utilize the program's benefits, it is important to obtain the necessary documentation for determining the property functions of a concrete composition, measuring temperature development in an insulated box, and analyzing strength development at different temperatures. The concrete database in HETT22 aims to expand with concretes that meet the various low-carbon classes defined in the Norwegian Concrete Association publication no. 37, as these concrete types are increasingly in demand for projects. The objective of this master's thesis is to investigate how different binders affect concrete's temperature sensitivity, strength, and heat development. Extensive laboratory work has been conducted, consisting of 19 recipes with different cement types, resistance classes, and varying fly ash and silicafume content. These results were implemented into HETT22 software to expand the database. Furthermore, HETT22, with its new concrete compositions, will be used to simulate a chosen construction type. For each recipe, a 15-liter curing box was cast following NS 3657. To verify the results from the 15-liter curing boxes, two 1m3 curing boxes were also cast according to the Norwegian Road Administration's “Bruprosjektering” N400. The findings of this master's project revealed that several factors must be considered when examining concrete's temperature sensitivity, strength, and heat development. Key factors include the amount of silicafume and fly ash content, durability classes, low-carbon classes, and cement types. Among the different categories, it was observed that an increasing dosage of fly ash leads to a reduction in concrete's temperature sensitivity, temperature and heat development, as well as a decrease in strength development up to 28 days at 5 and 20 °C. However, at 35 °C, the results show the opposite pattern