1,720,988 research outputs found
Granulometric and Pore-Based Index Properties of Porous Asphalt Mixes
No full textWhen properly designed for urban source areas such as roadways, porous asphalt functions to
provide hydrologic restoration while functioning as a filtration interface. This study
examined the role of aggregate granulometry on the pore-based indices of porous asphalt,
specifically permeability (hydraulic conductivity), void ratio and porosity. Three different
groups of porous asphalt gradations comprised of 12 series of samples and separated based on
gradation size indices have been examined. Two groups represent common mix designs in
Italy while the third group represents micro-draining mixes which are less common. For all
samples the vertical (kv) and horizontal (kh) permeability were measured with the
commensurate total void contents (e) and total porosity (n). Marshall tests were performed in
order to control the stability of the mixes. The directional permeability values were strongly
correlated with kh as approximately 60% of kv across the range of permeability tested. There
was a strong relationship between the permeability and the void content, and as the void
content increases, the permeability also increases linearly. For a given aggregate gradation,
each increment of asphalt content increase caused a decrement in permeability and porosity.
Results indicated that in addition to the coefficient of uniformity (U) and the total void
content, a size-based granulometric index (P5·P2·Dmax) provided a relationship with vertical
permeability and the total void content that were very consistent for the entire range of porous
asphalt mixes. Results of this study allow the role of mix design on the permeability to be
examined. These mix design results are a necessary precursor to examination of in-situ
permeability after placement, and degradation of such permeability as a function of time and
rainfall-runoff hydraulic and particulate loadings
Relationships among gradation curve, clogging resistance, and pore-based indices of porous asphalt mixes
No full textWhen properly designed, porous asphalt functions both to make safer the driving in wet condition, and to provide hydrologic restoration while functioning as a filtration interface. This study examined the role of aggregate ranulometry both on the pore-based indices of porous asphalt and on the clogging resistance. Three groups of porous asphalt gradations comprised of 12 series of samples and separated based on gradation size indices have been examined. For all samples the vertical (kv) and horizontal (kh) permeability were measured with the commensurate total void contents (e) and total porosity (n). Also clogging resistance was evaluated by measuring hydraulic conductivity before and after 1 year of exposure of the samples to dust intrusion. Marshall tests were also performed in order to control the stability of the mixes. There was a strong relationship between the permeability and the void content. For a given aggregate gradation, each increment of asphalt content increase caused a decrement in permeability and porosity. As for the clogging resistance potential, it seems to be more related to the initial permeability than to the other pore-based parameters. Results indicated that in addition to the coefficient of uniformity (U) and the total void content, a size-based granulometric index (P5·P2·Dmax) provided a relationship with vertical permeability and the total void content that were very consistent for the entire range of porous asphalt mixes. Results of this study allow the role of mix design on the permeability to be examined. These mix design results are a necessary precursor to examination of in-situ
permeability after placement, and degradation of such permeability as a function of time and rainfall-runoff hydraulic and particulate loading
Partitioning of zinc, copper and lead in urban drainage from paved source area catchments
No full textRepresentation of metal partitioning in urban drainage is required when determining loadings, treatment, maintenance and regulatory compliance. This study examined partitioning and transport of metals from urban paved surfaces: highway; parking lot (landside) and apron terminal (airside) within aviation site; terminals within port area. Equilibrium concentrations of metals and particulate matter (PM) using a non-parametric analysis for a series of six paved surface area catchments were compared. In particular, two American highway sites and four Italian sites located in the Liguria Region (two port terminal and two aviation sites) are examined and compared with event-based concentrations collected from catchments with similar land uses. The highway sites are more heavily loaded with PM (up to averagely 470 mg/l of PM as total suspended solids) while the terminal port ones reveal the most significant mass delivery of metals, as high as 1 mg/l. Transport of metal phases on an event basis, thus relating hydrology and PM mass delivery impacting metal partitioning, are examined. At all catchment sites, copper and lead reveal the greatest affinity for the particulate-bound fraction while zinc shows significantly different partitioning behaviour that may be partially depending on the specific site characteristics and the chemistry of zinc. Partitioning, indexed through a partitioning coefficient, Kd, accounts for hydrologic transport, PM transport and interactions with and between metals. Kd can vary by orders of magnitude across a runoff event for the source area catchments of this study. A Kd condition in the range of 104–105 l/kg appears to be approached for all metals as elapsed runoff time increases. Based on the variability of partitioning, whether intra- or inter-event, results indicate that paved source area treatment requires a combination of sedimentation, filtration and adsorption mechanisms for in-situ unit operations and processes
Simulation of Particulate Matter Fate and Head Loss in a Passive Urban Drainage Radial Filter
No full textDifferentiation of Mass and Flow Limited Rainfall-Runoff Events for Overland Flow from Small Urban Catchments
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ON THE KINETICS OF POLLUTANTS IN STORMWATER RUNOFF
No full textTransport, bioavailability and fate of metals in storm water runoff are investigated by analyzing data collected at three commercial land-use sites in the town of Genoa (Italy): a landside site within the airport area and a tourism and a dry-bulk terminal sites within the port area. The monitoring campaign, carried out from November 2005 to December 2006, provided hydrologic and water chemistry data. Results clearly indicate the difference between airport and port terminal sites in terms of total suspended solids concentration values ranging from 30 mg/l at the airport-landside site to 1 g/l at the dry-bulk terminal site. Findings of metals partitioning investigation indicate that particulate lead seems to dominate the dissolved fraction irrespective of the water quality characteristics such as TSS and pH, while copper and zinc confirm the tendency for a predominant dissolved fraction and such trend seems strongly related to the TSS mass delivery. Metals speciation was simulated using the thermodynamic equilibrium model MINTEQ. Results of this metal complexation model indicate that zinc speciation is strongly dominated by the ionic form, while copper and lead exhibit a higher tendency to form complexes, thus their behavior is related to the ligands concentration associated with the specific land us
Stormwater Phosphorus Adsorption on Oxide Coated Media
No full textAs a minimum, mass transfer of phosphorus (P) species to and from filter media in stormwater systems requires a quantitative description of the equilibrium, kinetics and breakthrough phenomena. However such behavior can be extremely variable depending on the properties of media. Obtaining physically representative adsorption equilibria (as opposed to single-point isotherms or non-singular P-index guides) is crucial since the isotherms so derived generally are utilized as the basis for further adsorption design and engineering application. This study examined the favorable adsorption properties of aluminum oxide coated media (AOCM) and the unfavorable adsorption behavior of media such as perlite and sand for phosphorus. The adsorption of phosphate on AOCM has been found to be dependent on pH and maximum removal efficiencies have been obtained at slightly acidic conditions. Phosphorus adsorption was shown to increase with decreasing AOCM adsorbent size. Low desorption, which likely resulted from strong bonding between P and AOCM, was also obtained. Good adsorption capacities were obtained for the typical conditions of urban rainfall runoff. It is also found Freundlich isotherm could successfully represent data of P adsorption on AOCM. Upon treatments by AOCM, phosphorus concentrations could be reduced to a suitable level for discharge into natural surface waters, which suggests the promising application of AOCM. In comparison, perlite and sand had negligible capacity and phosphorus was easily desorbed from these media. AOCM was studied for breakthrough curve (BTC) characteristics and feasibility as a subsequent adsorptive filtration process after primary sedimentation of stormwater. This study provides insights on conditions pertinent to the design of engineered in-situ P treatment, such as how adsorption equilibrium and kinetics, bulk and intraparticle mass transfer, solution pH, P loading concentration, hydraulic retention time and surface loading affect the transport and BTC on porous AOCM. Smaller AOCM size leads to better BTC due to higher contacting area. Good BTC results favor low P concentration and low surface loading. The maximum adsorption capacities calculated from BTC are generally smaller than values from adsorption isotherm, indicating the presence of mass-transfer limitations and limited contact time in the flow through systems. Results of BTC of P adsorption on AOCM column indicate that AOCM are capable of efficient and effective treatment for urban rainfall runoff, while perlite and sand are wholly ineffective. BTC models, especially mechanistic models, provide valuable and cost effective information in guiding design and operation of stormwater treatment systems for P
Examination of Pervious Pavement Pore Parameters with X-Ray Tomography
No full textPervious pavement (PP) is an infrastructure material that can alter rainfall-runoff relationships, filter particulate matter (PM), and
sequester runoff constituents. Beyond a measure of total porosity ( φt), less-commonly measured pore parameters and relationships thereof
influence these phenomena. In this study, cementitious PP (CPP), used as a permeable surface for an exfiltration system loaded by runoff, was examined. X-ray tomography (XRT) was utilized to examine pore size and frequency, generate a total-to-effective porosity (φt − φe) relation- ship, quantify pore tortuosity (Le=L), and relationships for specific surface area (SSA), pore-size distributions ðPSDÞpore, and φt. Gravimetric analyses were used for SSA based on mass ðSSAÞs as well as validation of XRT porosity. Results indicate that φt ranged from 10 to 30% while φe ranged from 4 to 27%. Relationships for (φt − φe), SSA, φt, and median pore diameter (d50n) were represented with a power law model (PLM). Using φt the ðSSAÞpt of pores ranged from 11,000 to 19,000 m2=m3 while for φe, ðSSAÞpe ranged from 12,000 to 21,000 m2=m3. XRT results show that the ðPSDÞpore is hetero-disperse. (Le=L) ranged from 2.9 to 5.9, compared to 1.4 for a monodisperse and uniform distribution of pore sizes. The ðLe=LÞ-φt relationship and probability density function (pdf) of (Le=L) were Gaussian. Beyond the common index of φt, these parameters are building blocks for infiltration, filtration, evaporation, storage, and reaction components of models such as the storm water management model (SWMM) and computationalfluid Dynamics (CFD
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