234 research outputs found
Influence of Selected Supplementary Cementitious Materials on Properties of 3D Printable Cementitious Mixture for Application in Additive Manufacturing
In comparison with other industries that have incorporated larger automation and digitalization towards their manufacturing process, the construction industry is significantly behind the curve even though it accounts for 13% of the industrial expenditure worldwide. Also, the construction industry significantly lags behind other industries in terms of annual growth in productivity at only 1%. The introduction of digital technologies like 3D printing of concrete into the construction sector can improve product performance and logistical issues in construction. 3D printing or additive manufacturing is a technique, wherein materials are assembled layer-by-layer to form a 3D object or element, without the need for any formwork. The main challenges faced by this technology are developing a well-characterized and tunable rheology of materials used, integrating reinforcement into the construction, developing appropriate standards for design and printing of concrete structures that are well-calibrated and accepted by the construction industry, etc. There is a growing interest in investigating additive manufacturing processes using cement-based materials in the construction industry.
Of fundamental interest in designing cementitious mixtures that are suitable for 3D printing is the ability to control not only the rheology of the mix but also other printability characteristics such as buildability, open time, shape stability and bond between the layers. These characteristics can be affected by using a combination of mineral and/or chemical admixtures.
The focus of the present study was to examine the influence of binary and ternary mixtures of cementitious materials containing silica fume (SF), meta-kaolin (MK) and ground granulated blast furnace slag (slag) with portland cement on rheological and 3D printability characteristics. These materials were used in combination with specific chemical admixtures such as superplasticizer (SP), viscosity modifying agent (VMA), set retarder and additive, polypropylene fibers. In this study, the replacement levels of SCMs such as SF, slag and their combinations have been studied for various properties like flow, open time, setting time, rheology and mechanical properties. Findings from this study indicate that achieving a flow between 126% and 133% based on standard flow test (ASTM C1437) was essential in obtaining a mixture that is extrudable. The time-gap effect, i.e. the gap in time between the casting of two adjacent layers, on the properties of the printed layers was studied by determining the flow behavior, rheological and hardened properties of the material which were measured at different time gaps of 0min, 5mins, 10mins, and 20mins. The effect of aggregate shape on the rheological and mechanical properties of these 3D printed assemblages was studied by using various replacement levels of natural sand (more rounded shape aggregate particles) with manufactured sand (more angular shaped particles) in the cementitious mixture. The bond between the layers of the cementitious materials, i.e. interlayer shear strength in the fresh state, has been evaluated for all binary and ternary blends containing Portland cement, MK and slag using a shear test developed in house, known as J-shear test.
The findings from this study indicate that achieving a finite flow value in the fresh state, along with adequate rheological properties (yield stress and plastic viscosity) are essential in developing a feasible 3D printable cementitious mixture. In general, as long as the bond between the layers is adequate, the mechanical properties of the 3D printed assemblages are not significantly different from the monolithic casting of the mixtures. For a given set of cementitious material combinations, the shape of aggregate particles has a definite influence on the rheological characteristics of the mix which can impact the 3D printability of the mixtures. It can be concluded that the presence of higher percentages of angular particles in the mix will lower the flow of the mix and increase the yield stress and plastic viscosity of the mix.
The impact of vibration on the flow behavior of all the mixtures was investigated in this study. It can be concluded that inducing vibration in fresh mixtures significantly enhanced the flow of the mixtures and improved the rheological properties of all mixtures, to allow for 3D printing. However, the duration of vibration needed to achieve adequate flow depended on individual mixtures. Mixtures with higher contents of fine SCMs such as MK and SF, and mixtures with more angular aggregate particles needed longer duration of vibration to achieve adequate flow values needed for suitable 3D printing.
In conclusion, the principal findings from this research study indicate that various parameters such as mixture proportions, types of SCMs and chemical admixtures, aggregate characteristics and physical manipulation factors such as induced vibration can impact the 3D printability of a cementitious mixture. By suitably tuning of all of the elements, a 3D printable cementitious mixture can be produced that has adequate printability, extrudability, buildability and shape retention. Additional research is needed to investigate and calibrate the findings from this study to validate the 3D printability of larger elements and full-scale structures
ASSOCIATION OF MATERNAL CHARACTERISTICS WITH COMPLICATIONS OF PREGNANCY: A CROSS-SECTIONAL STUDY AMONG MIDDLE SOCIOECONOMIC PREGNANT WOMEN
Objective: The objective of the study was to determine the association of maternal characteristics with complications of pregnancy among middle socioeconomic women.
Methods: The enrolled subjects were divided into two groups as complicated and uncomplicated group based on the occurrence of complications in current pregnancy and their sociodemographic details along with present and past medical and medication history was collected.
Results: The mean age of the study subjects was 25.33±4.22 years. Maternal characteristics such as age, parity, body mass index, maternal education, and employment status did not have a statistically significant association with the complications of pregnancy at p<0.05. However, the first antenatal visit at the gestational age <8 weeks had a statistically significant association with the complications of pregnancy at p=0.02.
Conclusion: Early initiation of antenatal care along with adequate antenatal visits may reduce the risk of complications of pregnancy
The study of thyroid dysfunction in patients with abnormal uterine bleeding
Background: Abnormal uterine bleeding (AUB) is the most common gynecological condition observed during many women's reproductive period. AUB affects the quality of life, causing distress. Most of the cases are undiagnosed or not properly diagnosed. Multiple reasons are causing AUB, one of them is thyroid dysfunction. Nowadays, thyroid testing is readily available, which helps in diagnosis and better management of AUB.
Methods: A prospective observational study was conducted with 124 AUB cases using simple random sampling after approval from the ethics committee.
Results: Total thyroid dysfunction was noted in 32.26% of cases, and 70.16% were multiparous. About 34.1% of cases of menorrhagia and 54.2% of cases of oligomenorrhea had thyroid abnormalities.
Conclusions: For appropriate management of AUB, testing of thyroid levels is necessary
Developing a rational method to participation cementitious mortars containing Meta-Kaolin for application in additive manufacturing
There is a growing interest in adopting additive manufacturing processes using cement-based materials in the construction industry. However, the approach to developing a viable cementitious mixture for 3D printing has been empirical in nature and relies heavily on repeated trials, until suitable mixture proportions are determined for a given set of materials. Although the ultimate aim of the on-going study is to develop a rational approach for mixture proportioning cementitious mixtures for 3D printing, the focus of the present study is to examine the behavior of cementitious mixtures prepared with portland cement in combination with meta-kaolin and other admixtures such as super plasticizer (SP), viscosity modifying agent (VMA) and additives such as polypropylene (PP) fibers. In this parametric study, the influence of meta-kaolin addition at various dosage levels on the rheological and mechanical behavior of mortars was investigated Rheological properties of mortars (i.e. yield stress and plastic viscosity) were determined using ICAR PLUS rheometer to correlate the fundamental rheological properties with the performance measures such as extrudability, buildability, thixotropic open time and shape retention. Setting time of various mortar mixes were also determined using ASTM C403 method. The compressive strength and flexural strength of the material was evaluated. The bond behavior between the layers will be evaluated using pull-off testing (ASTM C 1583) in the future. The results from this investigation showed the relevance between the fundamental rheological properties and the performance measures for achieving a viable 3D printable mixture
Effect of Reynolds Number on Aerodynamics of Airfoil with Gurney Flap
Steady state, two-dimensional computational investigations performed on NACA 0012 airfoil to analyze the effect of variation in Reynolds number on the aerodynamics of the airfoil without and with a Gurney flap of height of 3% chord are presented in this paper. RANS based one-equation Spalart-Allmaras model is used for the computations. Both lift and drag coefficients increase with Gurney flap compared to those without Gurney flap at all Reynolds numbers at all angles of attack. The zero lift angle of attack seems to become more negative as Reynolds number increases due to effective increase of the airfoil camber. However the stall angle of attack decreased by 2° for the airfoil with Gurney flap. Lift coefficient decreases rapidly and drag coefficient increases rapidly when Reynolds number is decreased below critical range. This occurs due to change in flow pattern near Gurney flap at low Reynolds numbers
The Role of Parent-Child Interaction Therapy in Modifying Children’s Neural Profiles: A Resting EEG Study of Children’s Response to Experience
The neural networks responsible for coordinating top-down self-regulatory processes, or executive functions, undergo intense fine-tuning and reorganization in early childhood. For children faced with prolonged stress (e.g., chaotic household environment, uncertainty) or adversity (e.g., poverty, maltreatment), these executive function processes are sculpted to aid in retaining information about threats to well-being, which may be protective short-term, but can become particularly maladaptive over time. Interventions that modify the caregiving environment have been shown to buffer the effects of adversity on children’s neural development. Parent-Child Interaction Therapy (PCIT) is one such intervention that has been shown to improve both parenting behavior and child outcomes in meta-analyses and is one of the only interventions evidenced to reduce child maltreatment recidivism. The present study sought to evaluate the effects of PCIT on 3-8-year-old children’s theta/beta ratio, a neural marker of attention regulation as measured by electroencephalogram (EEG). Next, this study sought to examine whether individual differences in parenting changes across the PCIT intervention were related to children’s theta/beta ratio, for the PCIT group only.
Data for this dissertation were drawn from a randomized control trial investigating the biobehavioral mechanisms of change in parent and child self-regulation skills as a result of PCIT for child-welfare involved families (NIDA R01 036533; PIs: Skowron & Fisher). 204 parent-child dyads with a history of child welfare involvement were referred into the study by the local Lane County Department of Human Services and randomized to PCIT or services-as-usual control conditions. The hypothesis that adversity-exposed children in PCIT would show lower theta/beta ratios, indicative of better attention regulation, after accounting for psychosocial risk, was supported for the eyes-closed but not the eyes-open condition. The hypothesis that individual differences in parenting skill change in PCIT group would be associated with children’s post-treatment theta/beta ratio was not supported. Taken together, this study fills a valuable gap in understanding whether parenting intervention, namely PCIT, can modify children’s neural markers of attention regulation after accounting for early adversity exposure
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