Characterization and performance of eco and crack-free high-performance concrete for sustainable infrastructure

The main objective of this study is to develop, characterize, and validate the performance of a new class of environmentally friendly, economical, and crack-free high-performance concrete referred to as Eco and crack-free HPC that is proportioned with high content of recycle materials. Two classes of Eco-HPC are designed for: (I) pavement (Eco-Pave-Crete); and (II) bridge infrastructure (Eco-Bridge-Crete). Eco-HPC mixtures were designed to have relatively low binder content up to 350 kg/m3 and develop high resistance to shrinkage and superior durability. A stepwise mixture design methodology was proposed to: (i) optimize binder system and aggregate skeleton to optimize packing density and flow characteristics; (ii) evaluate synergy between shrinkage mitigating materials, fibers, and moist curing duration to reduce shrinkage and enhance cracking resistance; and (iii) validate performance of Eco HPCs. The composition-reaction-property correlations were developed to link the hydration kinetics of various binder systems to material performance in fresh state (rheological properties) and hardened state (strength gain and shrinkage cracking tendency). Results indicate that it is possible to design Eco-HPC with drying shrinkage lower than 300 µstrain after 250 days and no restrained shrinkage cracking even after 55 days. Reinforced concrete beams made with Eco-Bridge-Crete containing up to 60% replacement of cement with supplementary cementitious materials and recycled steel fibers developed significantly higher flexural toughness compared to the reference concrete used for bridge applications. In parallel, autogenous crack healing capability of concrete equivalent mortar mixtures was monitored using microwave reflectometry nondestructive testing technique. Research is in progress towards analyzing life cycle assessment of Eco-HPCs under field condition --Abstract, page iii

The study of potassium ferrate application efficiency for advanced treatment of sewage

زمینه و هدف: طیف وسیعی از منعقد کننده‌ها، اکسیدان‌ها و گندزداها در تصفیه آب و فاضلاب استفاده می‌شوند. یون فرات به عنوان یک اکسیدان قوی بالاترین پتانسیل اکسیداسیون-احیاء را بین همه اکسیدان‌ها و گندزداها در تصفیه آب و فاضلاب داراست. یون فرات (شش ظرفیتی) در آب به یون هیدروکسید فریک احیا می‌شود و می‌تواند در یک فرآیند چند منظوره به عنوان منعقد کننده، اکسیدان و گندزدا مورد استفاده قرار گیرد. هدف از این مطالعه بررسی فرآیند تصفیه پیشرفته پساب فاضلاب شهری با استفاده از فرات پتاسیم بود. روش بررسی: در این مطالعه نیمه تجربی تصفیه پیشرفته فاضلاب شهری توسط فرات‌پتاسیم در مقیاس آزمایشگاهی روی پساب فاضلاب گندزدایی نشده با تعیین اثر متغیرهای pH و غلظت بر میزان حذف کدورت، ترکیبات ارگانی آب (COD) و فسفر مورد بررسی قرار گرفت. به منظور تعیین کارایی گندزدایی فرات پتاسیم نیز اثر سه متغیر زمان تماس، غلظت فرات و pH روی فرآیند گندزدایی با استفاده از شاخص (MPN (Most Probable Number مشخص شد. یافته‌ها: بهترین راندمان حذف ترکیبات ارگانی آب و کدورت با استفاده از فرات‌پتاسیم در شرایط بهینه (5=pH و غلظت mg/L10) به ترتیب 65 و 90 بود. pH و غلظت بهینه فرات ‌پتاسیم در حذف فسفر نیز 5=pH و غلظت mg/L 12 بود که موجب حذف 72 درصدی فسفر شد. بهترین شرایط کاربرد فرات پتاسیم به عنوان گندزدا در غلظت mg/L 4 و زمان تماس های 25 دقیقه و 6=pH بود. نتیجه گیری: فرات ‌پتاسیم به عنوان یک ماده شیمیایی مؤثر اکسید کننده، گندزدا و منعقد کننده می ‌تواند در تصفیه انواع پساب های شهری و صنعتی مورد استفاده قرار گیرد و با این کار دسترسی به چند هدف در یک فرآیند را میسر گرداند

Ultrafast Stiffening of Concentrated Thermoresponsive Mineral Suspensions

Extrusion-based 3D printing with rapidly hardening polymeric materials is capable of building almost any conceivable structure. However, concrete, one of the most widely used materials for large-scale structural components, is generally based on inorganic binder materials like Portland cement. Unlike polymeric materials, a lack of precise control of the extent and rate of solidification of cement-based suspensions is a major issue that affects the ability to 3D-print geometrically complex structures. Here, we demonstrate a novel method for controllable-rapid solidification of concentrated mineral suspensions that contain a polymer binder system based on epoxy and thiol precursors as well as one or more mineral fillers like quartz and calcite. The thermally triggered epoxy-thiol condensation polymerization induces rapid stiffening of the hybrid suspensions (0.30 ≤ ϕ ≤ 0.60), at trigger temperatures ranging between 50 °C and 90 °C achieving average stiffening rates up to 400 Pa/s. The use of nucleophilic initiators such as 1-methylimidazole provides control over the activation temperature and curing rate, thereby helping to achieve an adjustable induction period and excellent thermal latency. By using multiple techniques, we provide guidelines to create designer compositions of mineral suspensions that utilize thermal triggers to achieve thermal latency and ultrafast stiffening – prerequisite attributes for 3D-manufacturing of topologically-optimized structural components

Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK.

BACKGROUND: A safe and efficacious vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), if deployed with high coverage, could contribute to the control of the COVID-19 pandemic. We evaluated the safety and efficacy of the ChAdOx1 nCoV-19 vaccine in a pooled interim analysis of four trials. METHODS: This analysis includes data from four ongoing blinded, randomised, controlled trials done across the UK, Brazil, and South Africa. Participants aged 18 years and older were randomly assigned (1:1) to ChAdOx1 nCoV-19 vaccine or control (meningococcal group A, C, W, and Y conjugate vaccine or saline). Participants in the ChAdOx1 nCoV-19 group received two doses containing 5 × 1010 viral particles (standard dose; SD/SD cohort); a subset in the UK trial received a half dose as their first dose (low dose) and a standard dose as their second dose (LD/SD cohort). The primary efficacy analysis included symptomatic COVID-19 in seronegative participants with a nucleic acid amplification test-positive swab more than 14 days after a second dose of vaccine. Participants were analysed according to treatment received, with data cutoff on Nov 4, 2020. Vaccine efficacy was calculated as 1 - relative risk derived from a robust Poisson regression model adjusted for age. Studies are registered at ISRCTN89951424 and ClinicalTrials.gov, NCT04324606, NCT04400838, and NCT04444674. FINDINGS: Between April 23 and Nov 4, 2020, 23 848 participants were enrolled and 11 636 participants (7548 in the UK, 4088 in Brazil) were included in the interim primary efficacy analysis. In participants who received two standard doses, vaccine efficacy was 62·1% (95% CI 41·0-75·7; 27 [0·6%] of 4440 in the ChAdOx1 nCoV-19 group vs71 [1·6%] of 4455 in the control group) and in participants who received a low dose followed by a standard dose, efficacy was 90·0% (67·4-97·0; three [0·2%] of 1367 vs 30 [2·2%] of 1374; pinteraction=0·010). Overall vaccine efficacy across both groups was 70·4% (95·8% CI 54·8-80·6; 30 [0·5%] of 5807 vs 101 [1·7%] of 5829). From 21 days after the first dose, there were ten cases hospitalised for COVID-19, all in the control arm; two were classified as severe COVID-19, including one death. There were 74 341 person-months of safety follow-up (median 3·4 months, IQR 1·3-4·8): 175 severe adverse events occurred in 168 participants, 84 events in the ChAdOx1 nCoV-19 group and 91 in the control group. Three events were classified as possibly related to a vaccine: one in the ChAdOx1 nCoV-19 group, one in the control group, and one in a participant who remains masked to group allocation. INTERPRETATION: ChAdOx1 nCoV-19 has an acceptable safety profile and has been found to be efficacious against symptomatic COVID-19 in this interim analysis of ongoing clinical trials. FUNDING: UK Research and Innovation, National Institutes for Health Research (NIHR), Coalition for Epidemic Preparedness Innovations, Bill & Melinda Gates Foundation, Lemann Foundation, Rede D'Or, Brava and Telles Foundation, NIHR Oxford Biomedical Research Centre, Thames Valley and South Midland's NIHR Clinical Research Network, and AstraZeneca

Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK

Background A safe and efficacious vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), if deployed with high coverage, could contribute to the control of the COVID-19 pandemic. We evaluated the safety and efficacy of the ChAdOx1 nCoV-19 vaccine in a pooled interim analysis of four trials. Methods This analysis includes data from four ongoing blinded, randomised, controlled trials done across the UK, Brazil, and South Africa. Participants aged 18 years and older were randomly assigned (1:1) to ChAdOx1 nCoV-19 vaccine or control (meningococcal group A, C, W, and Y conjugate vaccine or saline). Participants in the ChAdOx1 nCoV-19 group received two doses containing 5 × 1010 viral particles (standard dose; SD/SD cohort); a subset in the UK trial received a half dose as their first dose (low dose) and a standard dose as their second dose (LD/SD cohort). The primary efficacy analysis included symptomatic COVID-19 in seronegative participants with a nucleic acid amplification test-positive swab more than 14 days after a second dose of vaccine. Participants were analysed according to treatment received, with data cutoff on Nov 4, 2020. Vaccine efficacy was calculated as 1 - relative risk derived from a robust Poisson regression model adjusted for age. Studies are registered at ISRCTN89951424 and ClinicalTrials.gov, NCT04324606, NCT04400838, and NCT04444674. Findings Between April 23 and Nov 4, 2020, 23 848 participants were enrolled and 11 636 participants (7548 in the UK, 4088 in Brazil) were included in the interim primary efficacy analysis. In participants who received two standard doses, vaccine efficacy was 62·1% (95% CI 41·0–75·7; 27 [0·6%] of 4440 in the ChAdOx1 nCoV-19 group vs71 [1·6%] of 4455 in the control group) and in participants who received a low dose followed by a standard dose, efficacy was 90·0% (67·4–97·0; three [0·2%] of 1367 vs 30 [2·2%] of 1374; pinteraction=0·010). Overall vaccine efficacy across both groups was 70·4% (95·8% CI 54·8–80·6; 30 [0·5%] of 5807 vs 101 [1·7%] of 5829). From 21 days after the first dose, there were ten cases hospitalised for COVID-19, all in the control arm; two were classified as severe COVID-19, including one death. There were 74 341 person-months of safety follow-up (median 3·4 months, IQR 1·3–4·8): 175 severe adverse events occurred in 168 participants, 84 events in the ChAdOx1 nCoV-19 group and 91 in the control group. Three events were classified as possibly related to a vaccine: one in the ChAdOx1 nCoV-19 group, one in the control group, and one in a participant who remains masked to group allocation. Interpretation ChAdOx1 nCoV-19 has an acceptable safety profile and has been found to be efficacious against symptomatic COVID-19 in this interim analysis of ongoing clinical trials

Analytical Approach to Nonlinear Behavior Study of an Electric Vehicle

© 2019 IEEE. Permanent Magnet Direct Current (PMDC) motors have great application potentials in Electric Vehicles (EVs) industry, due to their advantages, such as no need for the field excitation arrangement, no input power consumption for the excitation, and having lower costs for low power rating applications. To analyze the nonlinear behavior of the EV equipped with the PMDC motor, the electromechanical equations related to a typical model of the PMDC motor are derived, and the electrical equivalent circuit related to the mechanical equations is presented in this paper. Homotopy Perturbation Method (HPM) and Variational Iteration Method (VIM) as the two analytical techniques are applied to solve the evolution equations. The performance of the PMDC motor that is concerned with the nonlinear parameters (viscous friction, torque, and inertia) is evaluated. In addition, the accuracy of the two analytical techniques is compared with the numerical solution. The results confirm the applicability of the two analytical techniques to analyze the nonlinear behavior of the system

Understanding the Role of Particle Packing Characteristics in Rheo-Physical Properties of Cementitious Suspensions: A Literature Review

Interest for enhancing particle packing of the solid skeleton in concrete stems efforts to reduce the content of cementitious materials and water/admixture demand, thus decreasing cost and environmental impact as well as improving material performance. Solid particles in cementitious suspensions can be classified as non-colloidal particles, such as aggregates, where only mechanical interactions exist; and colloidal particles, such as cementitious materials, where particle surface forces predominate over gravitational-shear forces, thus particles tend to agglomerate. This paper intends to review advances in knowledge on the effect of packing characteristics of colloidal and non-colloidal particles on rheo-physical properties of cementitious suspensions. Focus is placed on solid particle sizes ranging from 10 2 μm (representing cementitious materials) to 104 μm (representing coarse aggregate). The effect of the volume fraction and particle packing of solids (both colloidal and non-colloidal particles) on rheology and stability characteristics of cementitious suspensions is discussed. The rheological properties of cementitious suspension are primarily dominated by the relative solid packing fraction (Φ/Φm). There exists a critical transition volume fraction (Φc) of granular skeleton so-called percolation volume fraction beyond which direct frictional contacts among particles begin to dominate the rheological properties. Therefore, in order to design fluid concretes, the aggregate volume fraction should be kept below the critical transition value as well as the rheological properties of suspending fluid medium should be properly adjusted to secure adequate stability of aggregates. The optimization of particle packing of granular skeleton can improve the particle lattice effect, and consequently enhance the stability characteristics of concrete

Effect of Particle-Size Distribution and Specific Surface Area of Different Binder Systems on Packing Density and Flow Characteristics of Cement Paste

The particle-size distribution (PSD) and specific surface area (SSA) of binders significantly affect the fresh and hardened characteristics of cement-based materials. An experimental investigation was undertaken to evaluate the influence of PSD and calculated SSA of various binary and ternary binder systems on flow characteristics, packing density, and compressive strength development of cement paste. The influence of dispersion state of the binder on packing density was evaluated using the wet packing density approach to determine the optimum water demand (OWD) needed to achieve maximum wet density. The modified Andreasen and Andersen (A&A), Rosin–Rammler (RR), and power law grading models were employed to optimize the PSD of binder system to achieve maximum packing density, while maintaining relatively low water demand. The incorporation of high-range water reducing admixture (HRWRA) is shown to decrease the OWD and increase the packing density resulting from greater degree of dispersion of the binder. The combined effect of lower OWD, greater packing density, and higher SCM reactivity results in higher compressive strength. The increase in SSA from 425 to 1600 m2/kg results in an enhancement in packing density from 0.58 to 0.72, while further increase in SSA from 1600 to 2200 m2/kg reduces the packing density from 0.72 to 0.62. Binder systems using a distribution modulus between 0.21 and 0.235 determined from the A&A model exhibited 18%–40% lower minimum water demand (MWD) to initiate flow, 8%–35% higher OWD to reach maximum wet density, and 15%–25% higher packing density compared to the binder with 100% cement. Binder systems with lower A&A distribution modulus resulted in higher relative water demand (RWD) required to increase fluidity, thus reflecting greater level of robustness. Good correlations were established between the A&A distribution modulus, SSA, RR spread factor, and power law distribution exponent