Cohesive Crack Growth in Macro-Synthetic Fiber Reinforced Concrete

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Stress-Crack Separation Relationship for Macrosynthetic, Steel and Hybrid Fiber Reinforced Concrete

An experimental evaluation of the crack propaga tion and post-cracking response of macro fiber reinforced concrete in flexure is c onducted. Two types of structur al fibers, hooked end steel fibers and continuousl y embossed macro-synthetic fibers are used in this study. A fiber blend of the two fibers is evaluated for spec ific improvements in the post peak residual load carrying response. At 0.5% volume fraction, both steel and macrosynthetic fiber reinforced concrete exhibits load recovery at large crack opening. The blend of 0.2% macrosynthetic fibers and 0.3% steel fibers shows a significa nt improvement in the immediate post peak load response with a significantly smaller load drop and a constant residual load carrying capacity equal to 80% of the peak load. An analytical formulation to predict fle xure load-displacement behaviour considering a multi-linear stress- crack separation (σ -w) relationship is developed. An inverse analysis is developed for obtaining the multi- linear σ -w relation, from the experimental response. The � -w curves of the steel and macrosynthetic fiber reinforced concrete exhibit a stress recovery after a significant drop with increa sing crack opening. Significant residual load carrying capacity is attained only at large crack separation. The fiber blend exhibits a constant residual stress with increasing crack sepa ration following an initial decrease. The constant residual stress is attained at a small crack separation

Correlation between endothelial dysfunction, inflammatory status, oxidative stress and total (nitrite/ nitrate) in subjects with diabetes mellitus type 2

Background: Diabetes Mellitus is a systemic metabolic disorder associated with Endothelial dysfunction and increased systemic inflammatory state with oxidative stress leading to increased Cardiovascular risk. This study planned to correlate the level of Endothelial dysfunction with oxidative stress and inflammatory status.Methods: Study was conducted in 60 Diabetes Mellitus subjects of both genders with duration of more than two years. Endothelial dysfunction assessed as Augmentation Pressure and Augmentation Index generated from Radial artery waveforms by tonometer using Spygmocor PWA system. Plasma Total Nitrite/ Nitrate, High sensitive C - Reactive Protein, Malondialdehyde and Glutathione were measured.Results: Out of total 60 Diabetes Mellitus subjects 16 subjects were with Coronary Artery Disease. There was no significant difference in High sensitive C - Reactive Protein, Glutathione, Malondialdehyde and Total Nitrite/ Nitrate between Diabetes Mellitus with Coronary Artery Disease and without Coronary Artery Disease, however significant difference (p=0.02) was observed Augmentation Pressure between Diabetic alone (12.8±5.19 mm of Mercury) and diabetics with Coronary Artery Disease (16.13±33.47 mm of Mercury) and Augmentation Index (p=0.04) between Diabetic alone (29.8±5.68 mm of Mercury) and diabetics with Coronary Artery Disease (40.01±5.74). As endothelial function is age dependent the subjects were divided into three age groups (20-40 years, 40-60 years and more than 60 years). High sensitive C - Reactive Protein, Glutathione, Malondialdehyde, Total Nitrite/ Nitrate and Augmentation Index did not differ in the three age groups while Augmentation Pressure (p=0.0096) showed significant difference between age group 20-40 years (10.59±3.24) and age group more than 60 years (15.83±3.92).Conclusions: There is significant endothelial dysfunction observed in Diabetes Mellitus subjects and Diabetes Mellitus with coronary artery disease showed greater endothelial dyfunction. Thereby concluding that Diabetes Mellitus subjects were at higher risk for development of coronary artery disease and as endothelial dysfunction is an early event, it may have some prognostic value

Investigation on the roles of solution-based alkali and silica in activated low-calcium fly ash and slag blends

An evaluation of strength-gain in binders with equal mass proportions of low-calcium fly ash and slag activated with alkaline solutions containing dissolved silica is conducted. The roles of Si and Na in the activating solution on compressive strength, reaction kinetics, and content and phase composition of reaction products are evaluated. The early reactions within the activated binder are due to the dissolution and hydration of slag. In the presence of silica, there is early precipitation of calcium silicate hydrate (CSH) before the hydration of slag. Silica in the activating solution delays the primary hydration of slag. The reactivity of silica depends on the SiO2/Na2O ratio in the activating solution. A less polymerized form of silica with higher reactivity is produced at a higher Na content in the activating solution. More reactive silica form produces a more rapid early precipitation of CSH following the initial dissolution of slag. Fly ash in the binder provides additional Si and Al to the calcium aluminosilicate hydrate (CASH) formed from the slag reaction. The Na identified in the reaction products is in a water-soluble form and not chemically bound to the CASH. The Na does not contribute directly to the compressive strength. In the long-term, the content and the silica incorporation in the CASH scales with the silica content in the activating solution and it does not depend on the form of silica. Increasing the activating solution silica content results in its larger incorporation in CASH and produces compressive strength enhancement. The form of silica has a negligible effect on the dissolution of fly ash in the binder and ultimate strength achieved. © 202

Extractive Spectrophotometric determination of Dimethoate in Environmental Samples with Azure-B

A new simple and selective spectrophotometric method is developed for the determination of dimethoate by using Azure-B is described. The method was based on the alkaline hydrolysis of dimethoate in presence of sodium ethoxide to form sodium dimethyl dithiophosphate (Na-DMDTP). The Na-DMDTP was formed as an ion-pair complex with cationic dye, azure-B. The ion-pair complex was extracted into chloroform. The color of the organic layer was measured at 535 nm. The method was applied to the determination of dimethoate residues in water, grain and soil samples

X-ray Diffraction-Based Quantification of Amorphous Phase in Alkali-Activated Blast Furnace Slag

The X-ray diffraction (XRD) signature of the glassy phase in blast furnace slag undergoing alkaline dissolution is evaluated. The intensity signature of the glassy phase present in slag can consistently be decomposed into three underlying pseudo-Voigt (PV) peaks. It is shown that the fundamental underlying characteristics of the XRD signature of the undissolved glassy phase of slag in terms of the underlying PV peaks do not change after dissolution in an alkaline solution. The stability of the calcium ions depends on the [OH−] concentration in the solution. An intensity-based procedure is developed for quantifying the unreacted glassy phase content in alkali-activated slag. The XRD profile information of the glassy phase in raw slag is suitable for fitting the intensity profile of the dissolved glassy phase. The mass percentage of the unreacted glassy phase of slag within alkali-activated slag is validated with selective acid dissolution. A procedure for determining the degree of reaction in alkali-activated slag is established. The procedure developed here could be used to determine the activity of slag in an alkaline environment. Copyright © 2021 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959