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Properties Of Concrete

Heat island phenomenon rises the temperature of cities, increases the energy demand for cooling and deteriorates comfort conditions in the urban environment. To counterbalance the impact of the phenomenon, important mitigation techniques have been proposed and developed. Pavements present a very high fraction of the urban areas and contribute highly to the development of heat island in cities. The use of cool pavements presenting substantially lower surface temperature and reduced sensible heat flux to the atmosphere, appears to be one of the most important proposed mitigation solutions. The present paper investigates and describes the actual state of the art on the field of cool pavements. The main thermal and optical parameters defining the thermal performance of pavements are analyzed. Almost all of the developed technologies, where data and results are available, are considered while emphasis is given on the presentation of reflective and permeable/water retentive pavements. The main technological achievements on both fields are reviewed while existing applications are described and performance data are given when available. The existing results clearly show that the mitigation and cooling potential of cool pavements is very significant and can highly contribute to decrease temperature on the urban environment.

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Using cool pavements as a mitigation strategy to fight urban heat island—A review of the actual developments

Conventional impervious pavements have dark surface and large thermal inertia. During summertime they tend to absorb and store solar radiation but negate the evaporative cooling, contributing to the development of urban heat island (UHI). The idea of using cool pavements to mitigate the UHI has gained momentum recently. This review synthesizes the existing definition, physical mechanism, and typical cooling techniques of cool pavements, presenting the influence of cool pavements on the urban thermal environment. Benefits, penalties, costs and policies for the applications of cool pavements are presented with special emphasis on reflective pavements and evaporative pavements. The review suggests that the definition of cool pavements remain incomplete; that the influence of cool pavements on the air temperature in the urban canopy layer is unknown; and that the impact of cool pavements on the thermal conditions of adjacent buildings and pedestrians remains unknown. Many speculations of using cool pavements to battle the UHI effect need refinements and validations. Heat-harvesting pavements seem interesting because they not only stay cool but harness renewable energy. However, the results from the heat-harvesting pavement prototype require scrutiny on the power output, durability, and lifetime of the pavement system. Future studies are expected to understanding the impacts of cool pavements on pedestrian thermal stress, on adjacent building’s energy loads, and on the air temperature in the urban canopy layer.

A review on the development of cool pavements to mitigate urban heat island effect

This chapter describes the methodology used in EPA’s Waste Reduction Model (WARM) to estimate streamlined life-cycle greenhouse gas (GHG) emission factors for concrete beginning at the point of waste generation. The WARM GHG emission factors are used to compare the net emissions associated with concrete in the following two waste management alternatives: recycling and landfilling. Exhibit 1 shows the general outline of materials management pathways for concrete in WARM. For background information on the general purpose and function of WARM emission factors, see the Introduction & Overview chapter. For more information on Recycling and Landfilling, see the chapters devoted to these processes. WARM also allows users to calculate results in terms of energy, rather than GHGs. The energy results are calculated using the same methodology described here but with slight adjustments, as explained in the Energy Impacts chapter.

나의 Concrete 연구실

More than 2.5 billion people on the globe rely on groundwater for drinking and providing high-quality drinking water has become one of the major challenges of human society. Although groundwater is considered as safe, high concentrations of heavy metals like arsenic (As) can pose potential human health concerns and hazards. In this paper, we present an overview of the current scenario of arsenic contamination of groundwater in various countries across the globe with an emphasis on the Indian Peninsula. With several newly affected regions reported during the last decade, a significant increase has been observed in the global scenario of arsenic contamination. It is estimated that nearly 108 countries are affected by arsenic contamination in groundwater (with concentration beyond maximum permissible limit of 10 ppb recommended by the World Health Organization. The highest among these are from Asia (32) and Europe (31), followed by regions like Africa (20), North America (11), South America (9) and Australia (4). More than 230 million people worldwide, which include 180 million from Asia, are at risk of arsenic poisoning. Southeast Asian countries, Bangladesh, India, Pakistan, China, Nepal, Vietnam, Burma, Thailand and Cambodia, are the most affected. In India, 20 states and 4 Union Territories have so far been affected by arsenic contamination in groundwater. An attempt to evaluate the correlation between arsenic poisoning and aquifer type shows that the groundwater extracted from unconsolidated sedimentary aquifers, particularly those which are located within the younger orogenic belts of the world, are the worst affected. More than 90% of arsenic pollution is inferred to be geogenic. We infer that alluvial sediments are the major source for arsenic contamination in groundwater and we postulate a strong relation with plate tectonic processes, mountain building, erosion and sedimentation. Prolonged consumption of arsenic-contaminated groundwater results in severe health issues like skin, lung, kidney and bladder cancer; coronary heart disease; bronchiectasis; hyperkeratosis and arsenicosis. Since the major source of arsenic in groundwater is of geogenic origin, the extend of pollution is complexly linked with aquifer geometry and aquifer properties of a region. Therefore, remedial measures are to be designed based on the source mineral, climatological and hydrogeological scenario of the affected region. The corrective measures available include removing arsenic from groundwater using filters, exploring deeper or alternative aquifers, treatment of the aquifer itself, dilution method by artificial recharge to groundwater, conjunctive use, and installation of nano-filter, among other procedures. The vast majority of people affected by arsenic contamination in the Asian countries are the poor who live in rural areas and are not aware of the arsenic poisoning and treatment protocols. Therefore, creating awareness and providing proper medical care to these people remain as a great challenge. Very few policy actions have been taken at international level over the past decade to reduce arsenic contamination in drinking water, with the goal of preventing toxic impacts on human health. We recommend that that United Nations Environment Programme (UNEP) and WHO should take stock of the global arsenic poisoning situation and launch a global drive to create awareness among people/medical professionals/health workers/administrators on this global concern.

Arsenic contamination of groundwater: A global synopsis with focus on the Indian Peninsula

Portland cement pervious concrete (PCPC) is increasingly used in the United States in sidewalks and parking lots due to its benefits in reducing the quantity of runoff water and improving water quality. In the United States, PCPC typically has high porosity and low strength, which has resulted in limited use of pervious concrete in hard wet freeze environment (i.e., Midwest and North East). The purpose of this research is to develop a PCPC mix that not only has sufficient porosity for stormwater infiltration but also desirable strength and freeze-thaw durability. In this research, concrete mixes were designed with various sizes and types of aggregates, water-to-binder ratios, binder contents, and amounts of admixtures. Porosity, permeability, strength, and freeze-thaw durability of these mixes were evaluated. Preliminary research results indicated that the use of single sized aggregate could provide concrete with high porosity but not adequate strength. Above a certain level, increasing cement content resulted in a reduced concrete porosity with insignificant influence on concrete strength. Using sand and latex significantly improved the workability of PCPC and resulted in higher strength, appropriate permeability and freeze-thaw resistant at 180 cycles up to date.

Mix Design Development for Pervious Concrete In Cold Weather Climates Authors

Portland cement pervious concrete (PCPC) is increasingly being used in the United States in sidewalks and parking lots due to its benefits in reducing the amount of runoff water and improving water quality. In the United States, PCPC typically has high porosity and low strength, which has resulted in limited use of pervious concrete in hard wet freeze environments (i.e., the Midwest and Northeast). The purpose of this research is to develop a PCPC mix that not only has sufficient porosity for stormwater infiltration, but also desirable strength and freeze-thaw durability. In this research, concrete mixes were designed with various sizes and types of aggregates, water-to-binder ratios, binder contents, and amounts of admixtures. Porosity, permeability, strength, and freeze-thaw durability of these mixes were evaluated. Preliminary research results indicated that the use of single-sized aggregate could provide concrete with high porosity but not adequate strength. Above a certain level, increasing cement content resulted in a reduced concrete porosity with insignificant influence on concrete strength. Using sand and latex significantly improved the workability of PCPC and resulted in higher strength, appropriate permeability, and freeze-thaw resistance at 180 cycles to date.

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Mix Design Development for Pervious Concrete in Cold Weather Climates

Recent stormwater management regulations from the Environmental Protection Agency (EPA) and greater emphasis on sustainable development has increased interest in pervious pavement as a method for reducing stormwater runoff and improving stormwater quality. Pervious concrete is one of several pervious pavement systems that can be used to reduce stormwater runoff and treat stormwater on site. Pervious concrete systems have been used and are being proposed for all parts of the United States, including northern climates where severe freezing and thawing can occur. The purpose of the research is to develop pervious concrete mixtures that have sufficient porosity for stormwater infiltration along with desirable porosity, strength, and freeze-thaw durability. In this research, concrete mixtures were developed with single-sized river gravel aggregate (4.75 mm) and constant binder contents, together with high range water reducer. River sand was used as a replacement for up to 7 % coarse aggregate. Two different types of polypropylene fibers (a shorter fibrillated variable-length and a longer fibrillated single-length) were incorporated at several addition rates from 0 to 0.1 % by volume of concrete. The engineering properties of the aggregate were evaluated along with the porosity, permeability, strength, and freeze-thaw durability of selected concrete mixtures. The results indicate that the use of sand and fibers provided beneficial effects on pervious concrete properties, including increased strength, maintained or improved permeability, and enhanced freeze-thaw resistance.

Pervious Concrete Mixture Proportions for Improved Freeze-Thaw Durability

As the world becomes more urbanized, concerns over the urban heat island (UHI) are more pronounced. Increased urban temperatures have a negative affect on the natural and human environment by producing increased energy usage and smog formation. Pervious concrete pavement is one technology that may help mitigate increased urban temperatures. Temperature data from an instrumented site in Iowa and heat storage phenomena for various weather patterns are presented. The site contains both pervious concrete pavement with a solar reflectance index (SRI) of 14 and traditional concrete pavement with an SRI of 37. Leadership in Energy and Environmental Design (LEED) accepted a high SRI (>29) as one method to characterize a cool surface. Heat capacities of both systems were studied along with a sensitivity analysis of the inputs. The research supports the conclusion that even though pervious concrete may have a much lower SRI than traditional concrete made with similar materials, it can be considered a cool pavement ...

Cyclic Heat Island Impacts on Traditional Versus Pervious Concrete Pavement Systems

Pervious concrete is becoming more common as a storm-water management tool in freeze-thaw climates. One of the main concerns or obstacles preventing a more widespread application is the aspect of freeze-thaw durability, whether perceived or actual. This paper describes a series of tests designed to determine the specific role coarse aggregate has on the freeze-thaw durability of pervious concrete using the ASTM C666A procedure. 17 different coarse aggregate samples were obtained from locations across the United States and Canada. Pervious concrete mixtures were placed using a mixture proportion previously determined as freeze-thaw durable. The range of durable aggregate gradations clearly defined a gradation specification and suggestions are made for optimizing the gradation with a small portion of sand. Mixtures with excellent freeze-thaw performance contained either granite or highly durable river gravel. The impact of aggregate angularity on mixture proportions and ultimate yield is also discussed.

John T. Kevern

Papers

Mix Design Development for Pervious Concrete In Cold Weather Climates Authors

Mix Design Development for Pervious Concrete in Cold Weather Climates

Pervious Concrete Mixture Proportions for Improved Freeze-Thaw Durability

Cyclic Heat Island Impacts on Traditional Versus Pervious Concrete Pavement Systems

Effect of Coarse Aggregate on the Freeze-Thaw Durability of Pervious Concrete