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rvoir base course and to <br />the surface, a two in. layer <br />. crushed stone aggregate <br />mended. Based on previ- <br />)erience, this stabilizer <br />s necessary because vehl* <br />ling asphalt hot mix across <br />rvoir course would create <br />t require constant grading <br />cd grade prior to hot mix <br />ion. <br />I Graded Asphalt Concrete <br />Course: Porous asphalt <br />of a wearing course of <br />aded asphalt concrete over <br />course of uniform sized <br />itc. It differs from conven- <br />isphalt concrete in that It <br />s very little dust or sand; its <br />lume typically is around 16 <br />t as compared with the two <br />e percent void volume of <br />tional asphalt concrete. <br />( Pavement Research <br />ts <br />Rochester, New York, two <br />3 lots were selected to dem* <br />:e the effectiveness of po- <br />avements to reduce the rate <br />nnwater runoff and to invests <br />le long-term structural integ- <br />such pavements under se- <br />environmental conditions, <br />f these sites was selected to <br />ite the structural integrity <br />>ermeability for the porous <br />nent under conditions of <br />truck traffic. <br />iults of the study indicated: <br />ak runoff rates were reduced <br />much i's 83 percent. (2) The <br />ment, subjected to 100 <br />[/thaw cycles, showed no ob- <br />ble structural degradation, <br />r drained through the pave- <br />without problems during the <br />r. (3) Through observations <br />►w monitoring, the structural <br />ty of porous pavement (in- <br />where heavy vehicles were <br />1) was not impaired. (4) Clog- <br />d result from runoff carrying <br />vy sediment load and was <br />[d through cleaning. (5) Cost <br />structing a porous pavement <br />jg lot using impermeable <br />rane and underdrains was <br />higher than a conventional- <br />ed lot with stormwater inlets <br />. A^O URBAN R0AC6/JULY. 1965 ^ <br />"iVI <br />• i! <br />m <br />.y <br />A. <br />f. <br />J-y. <br />VVi <br />and subsurface piping. <br />In Austin, Texas, the overall ob ­ <br />jective for this research was to <br />demonstrate, evaluate and deter­ <br />mine the feasibility of using various <br />porous pavement. The resulting in­ <br />formation will be used to develop <br />design criteria for potential porous <br />pavement construction. <br />The first phase of this project <br />has been completed and published <br />in an EPA research report entitled, <br />‘‘Phase 1—Design and Operational <br />Criteria.” Phase 11 of this project — <br />Figure 1. Concrete porous pavement. <br />Figure 2. Typical section of porous asphalt paving. <br />50 RURAL AT4) UFCAN ROADS/XZ.Y. 1903 <br />still onging—compares the runoff <br />and wear quality characteristics of <br />porous asphalt pavement and con ­ <br />crete lattice blocks to other kinds <br />of conventional parking areas. <br />Advantages <br />The primary objective of porous <br />asphalt pavements for this pro ­ <br />gram is to control runoff and asso <br />ciated water quality degradation <br />Important benefits from porous as <br />phalt pavements include: (1) Atten <br />uation of the runoff rate and vol <br />ume; (2) Improved erosion control; <br />(3) Enhancement of water quality <br />in areas where runoff from imper­ <br />vious areas has potential for be­ <br />coming contaminated; (4) A reduc­ <br />tion or abatement in the need for <br />curbs and storm sewer installation <br />or expansion; (5) Maintenance of <br />natural vegetation and drainage <br />patterns; (6) Reduction or elimina ­ <br />tion in the nuisance factor to pedes­ <br />trian and motorist from standing <br />puddles and temporary storage in <br />lots and streets; (7) Increase in the <br />amount of groundwater recharge <br />to local aquifers in water defficient <br />areas; and (8) Improved road safe ­ <br />ty due to a higher friction coeffi­ <br />cient, reduced hydroplaning and <br />improved visibility. <br />Disadvantages <br />The greatest coi.cern using po ­ <br />rous pavement is its susceptibility <br />to clogging. Based on past experi­ <br />ence, this problem should not oc­ <br />cur if proper care and maintenance <br />are taken. <br />Porous pavement effectiveness <br />must be evaluated during the melt­ <br />ing of ice and snow accumulated on <br />its surface or if rain occurs when <br />the subsurface is frozen. The test <br />site in Rochester showed that this <br />was not a problem. <br />Another disadvantage in the use <br />of porous pavement is that some <br />existing building codes are not in­ <br />tended for this new technology. For <br />example, if conventional draining <br />structures (curbs, gutters inlets, <br />etc.) are arbitrarily required in all <br />parking areas, then the construc ­ <br />tion costs of porous pavement in <br />stallation becomes less economi <br />cally attractive. □