The effect of quarry dust on the flexural strength of concrete has been experimentally studied and reported in this paper. Concrete used was prepared by replacing 25% and 100% of sand by weight with ...quarry dust. Also, conventional sand concrete was prepared as reference concrete for comparison. 100mm cube and 100×100×500mm plain beam specimens were prepared using concrete strengths ranging from 25N/mm2 to 47N/mm2 for the three replacement levels of 0%, 25% and 100% to obtain the compressive and flexural strengths respectively at 28days. From the results, it was observed that the flexural strength of concrete with 25% and 100% quarry dust were respectively 2% and 4.3% higher compared with concrete with no quarry dust. By carrying out regression analysis, empirical formulas in the form y=axb were obtained for concrete with quarry dust. The equations were compared with formulas proposed by ACI, BS, IS codes of practice for estimating the flexural strength using the compressive strength of concrete. It was found that incorporating quarry dust in concrete improves its flexural strength.
The paper presents results of study on concrete using quarry dust to replace sand at levels of 0%, 25%, and 100% by weight. Design mixes were prepared to achieve concrete grades C25, C30, C35, C40 ...and C45 for each of the three replacement levels. Prismatic specimens were prepared to study the stress-strain behaviour of the concrete. It was observed that the stress-strain curves were similar for all sand replacement levels and that concrete with 100% quarry dust had the maximum strain values. The results of the study showed that for all concrete grades, 25% sand replacement level gave higher (7.9%) modulus of elasticity (MoE) while 100% sand replacement level gave lower (8.6%) MoE relative to 0% sand replacement level. The estimated MoE was compared with values obtained from the formulas proposed by the BS, ACI and IS for estimating the MoE using the compressive strength of concrete. It was found that blending sand and quarry dust produces concrete of enhanced mechanical properties.
Descriptive analysis of meningitis outbreak in Jaman North districts of Brong Ahafo Region.
Descriptive secondary data analysis.
records of meningitis cases were extracted from case-based forms and ...line list.
The source and pattern of outbreak.
A total of 367 suspected cases with 44 confirmed were recorded from Jaman North during the period of January to March 2016. The mean age of those affected was 58 ± 13 years. The case fatality rate was 0.82% and the proportion of males to females was 1:1.3 (160/207). The age group most affected was 15-29 years (54.7%) and the least was 45-49 years (3.0%).
formed 77.3% of confirmed cases whilst
was 20.5%. Cases with
came from a border town in La Cote d'Ivoire.
A protracted propagated meningitis outbreak occurred; and the predominant bacteria strain among confirmed cases was
Cases were mainly females and the most vulnerable group were people aged 15-29 years.
This work was funded by the authors. Author BKD was sponsored under CDC (Frontline FETP)-CDC CoAg 6NU2GGH001876.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We investigated the effects of selective logging disturbances on tree diversity and soil characteristics in the Bia Conservation Area in southwest Ghana. The study was conducted in unlogged, 29-35 ...years post-logged and swamp forests using ten 25 m× 25 m plots. In total, we identified 310 individual trees belonging to 87 species. Mean Shannon-Weiner index was highest in the post-logged forest but there were no significant differences in tree density, dominance, or DBH size class distributions between these forests. Soil physical properties such as pH and bulk density up to 30 cm depth were similar in the two of forests In terms of soil nutrient status, available P, exchangeable K and total N contents were all similar in the unlogged and post-logged forests. Our findings suggest that the effects of logging on tree diversity are compara-tively long-term, in contrast to its short-term effects on some top soil physical and chemical characteristics.
AbstractBridge agencies seek to apply appropriate rehabilitation or maintenance treatments at the right time. For a specific treatment, improper timing can have significant adverse consequences: ...Premature application could mean wasteful spending by the agency even if road users and the community enjoy the benefits of a superior bridge condition, and deferred or delayed application can result in higher user or community disbenefits caused by poor condition and consequent reduced asset longevity in the long-term. For short-term decisions regarding the identification of the most cost-effective paint action at a specific time (do nothing, spot paint, overcoat, or recoat), the paper presents a methodology for developing a painting decision tree. For long-term decisions regarding the identification of the most cost-effective schedule over the superstructure lifetime, the paper demonstrates a methodology for developing a long-term schedule of painting activities. An analysis of the state of paint scheduling at a specific highway agency revealed that the current practice of complete recoating every 25 years may not be optimal. Instead, a painting schedule that includes the application of lower-level treatments (spot repairing and overcoating) can yield as much as a 19% reduction in the lifecycle cost and a 31.97% higher cost-effectiveness compared to the current practice.
The present study conducted an empirical highway segment crash frequency analysis on the basis of fixed-parameters negative binomial and random-parameters negative binomial models. Using a 4-year ...data from a total of 158 highway segments, with a total of 11,168 crashes, the results from both models were presented, discussed, and compared. About 58% of the selected variables produced normally distributed parameters across highway segments, while the remaining produced fixed parameters. The presence of a noise barrier along a highway segment would increase mean annual crash frequency by 0.492 for 88.21% of the highway segments, and would decrease crash frequency for 11.79% of the remaining highway segments. Besides, the number of vertical curves per mile along a segment would increase mean annual crash frequency by 0.006 for 84.13% of the highway segments, and would decrease crash frequency for 15.87% of the remaining highway segments. Thus, constraining the parameters to be fixed across all highway segments would lead to an inaccurate conclusion. Although, the estimated parameters from both models showed consistency in direction, the magnitudes were significantly different. Out of the two models, the random-parameters negative binomial model was found to be statistically superior in evaluating highway segment crashes compared with the fixed-parameters negative binomial model. On average, the marginal effects from the fixed-parameters negative binomial model were observed to be significantly overestimated compared with those from the random-parameters negative binomial model.
•The study developed the Modified Equivalent Vehicle (MEV) methodology.•Overweight bridge damage cost is influenced by the attributes of the truck and bridge.•Marginal cost of bridge damage is from ...$0.01 to $36.35 per ft. length per pass of bridge per vehicle.
Civil infrastructure managers have a profound interest in knowing the costs of infrastructure degradation caused by user operations that exceed statutory limits; that way, they are better informed to establish or revise policies related to permit fee structures for such extra-legal operations. In the specific context of vehicle weight permitting for highway bridges, past determinations have typically relied largely on bridge damage simulation using theoretical relationships between the loading and failure modes. Unlike the theory-based simulations, empirical data analysis uses observed field data and therefore are expected to yield more intuitive insights about the actual relationship between in-service loading patterns and their damage (and the cost of repair thereof). A few past studies have used such empirical approaches with some success but have generally been stymied by practical considerations including the lack of adequate translational relationships between the vehicles operating on the road and the vehicle classes typically considered in load analysis. Also, the overweight (OW) cost differences across different bridges attributes (material type, design type, functional class, and age) remain to be investigated. In a bid to overcome these limitations, this paper uses observed in-service data for vehicle loads and the life-cycle costs associated with bridge deterioration repair. The proposed methodology includes a technique that correlates AASHTO design vehicles to FHWA vehicle classes, estimates the total life-cycle cost of bridge upkeep, and allocates this cost to each user group (vehicle class) based on the axle configuration and usage frequency (vehicle-miles travelled) of that class. For each vehicle class, the marginal cost of bridge damage is determined on the basis of the incremental cost responsibility (as a result of adding that vehicle class to the traffic stream) and the typical traffic volume of that vehicle class, and were found to range from $0.01 to as much as $36.35per ft. length per pass of bridge, depending on OW class, and bridge functional class, material type, and age. The paper quantifies the extent to which bridge damage cost due to an overweight truck is influenced by the attributes of the truck and the bridge. The results can be of help to agencies seeking to formulate, update, or evaluate current or future OW permitting policies from the perspective of highway bridge damage among other impacts. This effort is considered timely in the current era when several highway agencies are considering relaxation of their OW permitting policies as a part of efforts to project a business-friendly image in a bid to spur economic development in their states.
The time has come for renewed emphasis on the life cycle management of the physical aspects of transportation infrastructure. The urgency for this new direction is underscored by the fact that the ...physical transportation network at most countries constitutes the most valuable publicly owned infrastructure and efforts must be made to keep it resilient to possible threats of man-made or natural disasters over its service life so that the movement of people and goods can continue uninterrupted to serve the economy and maintain the quality of life. The concept of transportation asset management (TAM) is a systematic process based on multiple disciplines (engineering, finance, operations research and economics), to make cost-effective repair and replacement decisions geared towards a sustained state of good repair over the infrastructure life cycle. This paper first argues for the continued application of asset management principles for transportation infrastructure in the new millennium. The paper then discusses the development cycle of transportation infrastructure as a prelude to a discussion of the key functions of an asset management system. The paper proceeds to identify the components (asset types) and elements of asset management (that is, the tasks that are carried out by an asset manager in an agency). The challenges and opportunities of asset management in the new millennium are then discussed. These include, among others, the specter of climate change, infrastructure resilience, sustainable development of transportations assets, the emerging era of autonomous vehicles and smart cities, and the consideration of transportation assets as a holistic system-of-systems. These issues are addressed in the context of the availability of big data and advances in analytical techniques and computing power.
This work aims at the compensation of beam hardening artifacts by the means of an extended three-dimensional polychromatic statistical reconstruction to be applied for flat panel cone-beam CT.
We ...implemented this reconstruction technique as being introduced by Elbakri et al. (2002) 1 for a multi-GPU system, assuming the underlying object consists of several well-defined materials. Furthermore, we assume one voxel can only contain an overlap of at most two materials, depending on its density value. Given the X-ray spectrum, the procedure enables to reconstruct the energy-dependent attenuation values of the volume.
We evaluated the method by using flat-panel cone-beam CT measurements of structures containing small metal objects and clinical head scan data. In comparison with the water-corrected filtered backprojection, as well as a maximum likelihood reconstruction with a consistency-based beam hardening correction, our method features clearly reduced beam hardening artifacts and a more accurate shape of metal objects.
Our multi-GPU implementation of the polychromatic reconstruction, which does not require any image pre-segmentation, clearly outperforms the standard reconstructions of objects, with respect to beam hardening even in the presence of metal objects inside the volume. However, remaining artifacts, caused mainly by the limited dynamic range of the detector, may have to be addressed in future work.
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