Guidance for Usage of Permeable Pavement at Airports (2017)

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45 5.1 Overview Proper pavement design and materials selection are crucial to the durability and life-cycle per- formance of permeable pavements because they provide proactive defense against potential risks related to poor drainage, nondurable permeable pavement (such as due to raveling), and so on. For instance, if properly designed and constructed, pervious concrete pavements can remain in use for collector streets and most residential streets for 20 to 30 years while exhibiting structural performance similar to traditional pavements (Goede and Haselbach 2012). This chapter provides an overview of important considerations to be made during the materials selection stage. The discussion applies to all permeable pavements in general, but primarily focuses on porous asphalt and pervious concrete pavements because these are the pavement types most likely to be used for aircraft-area applications. However, it is acknowledged that much of the experience and technical basis for these guidelines are derived from roadway or parking lot applications of permeable pavements (instead of airport applications). 5.2 Subgrade The saturated hydraulic conductivity (Ks) of the subgrade is an important factor that needs to be considered in the design of permeable pavement systems. For full-infiltration (or retention) systems, a minimum Ks value of approximately 0.5 in./h is recommended to ensure effective per- meability (ASCE 2015). ASTM D3385, Test Method for Infiltration Rate of Soils in Field Using a Double-Ring Infiltrometer, is generally the recommended test for subgrade infiltration (or, for soils with an expected infiltration rate of 1.4 × 10-2 in./h to 1.4 × 10-5 in./h, ASTM D5093, Test Method for Field Measurement of Infiltration Rate Using a Double-Ring Infiltrometer with a Sealed Inner Ring). Subgrade support also needs to be determined for use in structural design. CBR testing using ASTM D1883, Bearing Ratio of Laboratory-Compacted Soils, which includes soaking the soil samples for 96 h to reach saturation, is generally recommended. A minimum CBR of 3 is rec- ommended in FAA design guidance (FAA 2016); the recommended input for PICP design is a minimum CBR of 5 (Smith 2015). With full-infiltration systems, the subgrade is not typically compacted, so the permeability is not compromised. However, not compacting the subgrade can increase the risk of rutting or settlement under heavier aircraft loading. For partial-infiltration (or no-infiltration) systems, the subgrade permeability is not as significant an issue. In this case, the subgrade can be compacted to meet FAA specifications, as required in Item P-152, Excavation, Subgrade, and Embankment (FAA 2014a). C h a p t e r 5 Materials Considerations

46 Guidance for Usage of permeable pavement at airports 5.3 Base/Subbase Reservoir Aggregate The base/subbase reservoir layer serves to retain stormwater and to support the permeable surface layer in accommodating traffic loads. Aggregates should be clean and uniformly graded. The minimum void space recommendation varies slightly between industry segments. For per- vious concrete, the recommended minimum void space is 20% to 40% (ACPA 2009), while the recommendation for porous asphalt pavement is a minimum of 40% (Hansen 2008). Void space in percent for the reservoir aggregate is determined using ASTM C29, Standard Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate. Furthermore, the amount of fine material in the aggregate passing sieve No. 100 should be between 0% and 2% in order to avoid clogging of the base (Hansen 2008). The reservoir aggregate gradation is typically ASTM No. 2 or No. 3, with ASTM No. 57 some- times used under pervious concrete (ASCE 2015). This layer, depending on hydrology and traffic applications, ranges from 8 to 36 in. thick for porous asphalt and 8 to 18 in. thick for pervious concrete. However, a thicker base/subbase reservoir layer may be needed in cold climates with freeze–thaw cycling. The final thickness is dependent on considerations of hydrology, soil per- meability, retention or detention system needs, frost depths, locations of underdrains, and so on. The case study projects (see Appendix B) investigated for this project typically used state materials specifications (such as summarized in Table 8), but the gradations of the base/subbase reservoir aggregates generally provide an open-graded material consistent with ASTM gradations. Both of the case study systems are partial-infiltration designs. Recycled construction materials, including crushed brick, recycled concrete aggregate, and reclaimed asphalt pavement, have been demonstrated to be suitable as base/subbase reservoir material for permeable pavement (Rahman et al. 2015). 5.4 Choke Stone, Filter Layer, and Bedding Layer The base/subbase reservoir aggregate can leave a rough surface. Open-graded aggregates can also be unstable under construction equipment loading. A choker stone course is sometimes used between the permeable surface layer and the reservoir course to provide an even and more stable platform for surface paving. Choke stone is typically a clean, uniform-sized, crushed aggregate. ASTM No. 57 stone is generally used for this layer (ASCE 2015). Although not a common component, a filter layer may be included in the design. This layer is used to assist in pollutant removal from stormwater. The thickness of this layer can range from 8 to 12 in., and the material composing it is generally poor-graded or coarse sand (Virginia Department of Environmental Quality 2011). To prevent the migration of sand particles into the reservoir layer, the filter layer should be underlain by a thin (3-in.) choker course. Table 8. Example gradations of base/ subbase reservoir aggregate. Sieve Size Culpeper (Virginia DOT No. 1) Paine Field (Washington State DOT Permeable Ballast) Percent Passing 4 in. 100 – 3½ in. 90 to 100 – 2½ in. 26 to 60 99 to 100 2 in. – 65 to 100 1½ in. 0 to 15 – ¾ in. 0 to 5 40 to 80 No. 4 – 5 max No. 100 – 0 to 2 Source: Campbell and Paris (2014a), CH2M (2013a).

Materials Considerations 47 PICP also incorporates a bedding layer for uniform placement of the units. This material is typically of an ASTM No. 8 gradation (Smith 2015) and is 1½ to 2 in. thick. It is the same material that is used for filling the paver joints. 5.5 Stabilized Permeable Base For roadway applications, the permeable surface layer is typically placed directly on the choke- stone layer (except for PICP having a bedding layer). However, the wheel loads of aircraft can be much greater than those of passenger vehicles. The FAA’s current design policy requires a stabilized base for aircraft traffic mixes with aircraft weights of more than 100,000 lbs. In air- field applications, a stabilized permeable base is beneficial because of the higher loads. Both the Culpeper apron and Richmond taxiway shoulder projects used a CTPB layer under the porous asphalt surface. Stabilized permeable bases are primarily CTPB and ATPB. The Innovative Pavement Research Foundation (IPRF) sponsored a study that evaluated the use of stabilized bases at airports, including providing guidance on CTPB and ATPB layers. The recommendation from that study was that CTPB and ATPB should have a permeability of not less than 250 in./h or more than 750 in./h (Hall et al. 2005). The permeability should be tested in the laboratory in accordance with ASTM D 2434, Constant Head Permeability Test (Hall et al. 2005). Further guidance in the IPRF document indicates that CTPB mix proportioning should have approximately 250 lbs/yd3 of cementitious material, and the job-mix formula for ATPB should have a minimum asphalt binder content of 2.0% to 3.5% to provide stability during construction and durability of the mix (Hall et al. 2005). Aggregate gradations range from ¾ in. to 1½ in. maximum aggregate size, and fines are limited to 0% to 6% passing the No. 8 sieve (Hall et al. 2005). An example gradation of CTPB (referred to as cement-stabilized open-graded mix) for the Culpeper apron project is provided in Table 9. 5.6 Permeable Surface Materials 5.6.1 Porous Asphalt Materials As described in Chapter 2, porous asphalt typically consists of conventional HMA or WMA with significantly reduced fines resulting in an open-graded mixture that allows water to pass through an interconnected void space. Porous asphalt typically has a higher binder content (6% to 6.5%) and can have additives to assist with durability and to reduce draindown. 5.6.1.1 Aggregate As with conventional HMA or WMA, aggregates need to be sound and durable. Requirements for conventional HMA aggregates, such as for wear, soundness, and deleterious content, also apply to the aggregates used for porous asphalt. Sieve Size Culpeper (Virginia DOT No. 57) Percent Passing 1½ in. 100 1 in. 95 to 100 ½ in. 25 to 60 No. 4 0 to 10 No. 8 0 to 5 Source: Campbell and Paris (2014b). Table 9. Stabilized open-graded mix gradation.

48 Guidance for Usage of permeable pavement at airports Porous asphalt maximum aggregate size for the surface courses is typically ½ to ¾ in. Although they are no longer included in FAA’s construction standards, for comparative purposes, FAA Item P-402, Porous Friction Course, provides aggregate gradations for ½ and ¾ in. maximum, shown in Table 10 along with the NAPA Information Series (IS) 115 gradation (FAA 2011b, Kandhal 2002). 5.6.1.2 Asphalt Cement Binder Based on case study interviews and literature review results, binder selection and content are significant factors in the performance of porous asphalt projects at airports. Improper binder selection or content has led to early raveling of the porous asphalt for some projects. Binder content is commonly between 6% and 6.5%, per AASHTO T 164 (ASCE 2015). The binder content will vary depending on the aggregate top size, with larger top-size aggregate requiring less binder (Hansen 2008). Performance-graded (PG) binders are recommended. State standards generally provide local climate-based grade requirements. The performance grade may be bumped depending on the aircraft weights or tire pressures. A grade bump is increasing the high-temperature rating to the next PG grade. The FAA Item P-401 specification (included in FAA 2014a) provides guid- ance on grade bumps for pavements receiving aircraft loadings (see Table 11). These should be considered in binder selection. The use of additives should be considered for porous asphalt pavements to prevent binder draindown into the lower layers and pavement degradation (ASCE 2015). Synthetic rubber is one additive that can be used. The Culpeper design required a minimum of 2% synthetic rubber. Table 10. Comparison of aggregate gradations for porous asphalt surfaces. Sieve Size Percent Passing Item P-402 IS 115 ¾ in. ½ in. ¾ in. 100 – 100 ½ in. 70 to 90 100 85 to 100 40 to 65 85 to 95 55 to 75 No. 4 15 to 25 30 to 45 10 to 25 No. 8 8 to 15 20 to 30 5 to 10 No. 30 5 to 9 9 to 17 – No. 200 1 to 5 2 to 7 2 to 4 in.83 Aircraft Gross Weight High-Temperature Adjustment to Binder Grade All Pavement Types 12,500 lbs – <100,000 lbs 1 grade 2 grade Typically, rutting is not a problem on airport pavements. However, at airports with a history of aircraft stacking at runway ends and taxiway areas, rutting has occurred due to the slow speed of loading on the pavement. If there has been rutting related to the project or it is anticipated that stacking may occur during the design life of the project, then the following grade bumping should be applied for the top 5 in. (125 mm) of paving in the end of runway and taxiway areas: for aircraft tire pressure of between 100 and 200 psi (0.7 and 1.4 MPa), increase the high temperature one grade; for aircraft tire pressure greater than 200 psi (1.4 MPa), increase the high temperature two grades. The low-temperature grade should remain the same. 100,000 lbs Source: FAA (2014a). Table 11. FAA-required grade bump.

Materials Considerations 49 Cellulose or mineral fibers are additional possible additives, which are generally added at 0.3% to 0.4% content, respectively, by total mass of mix (ASCE 2015). 5.6.1.3 Mixture Design A primary objective of porous asphalt mix design is to provide a mixture that is permeable yet durable. Raveling of the porous asphalt surface was one of the most common concerns expressed in the responses to this study’s survey. Two methods of porous asphalt mix design are discussed in NAPA publication IS 115, Design, Construction, and Maintenance of Open-Graded Asphalt Friction Courses (Kandhal 2002) and ASTM D7064, Standard Practice for Open-Graded Friction Course (OGFC) Mix Design. AI’s MS-2 Asphalt Mix Design Methods (AI 2015) may also be used, or states may have devel- oped their own mix design process. These methods are generally for pavements supporting vehicular loadings, so the process will need to take into consideration potentially heavier load applications. For instance, roadway porous asphalt may be designed using 50 gyrations in the Superpave method. The FAA’s Item P-401 requires 75 gyrations for aircraft weights greater than 60,000 lbs (FAA 2014a). The porous asphalt surface void content typically ranges from 18% to 22%, and surface per- meability ranges from 170 to 500 in./h (ASCE 2015). Testing voids of porous asphalt should measure the volume by dimension, using ASTM D3203, Standard Test Method for Percent Air Voids in Compacted Dense and Open Bituminous Paving Mixtures, or ASTM D6857, Standard Test Method for Maximum Specific Gravity and Density of Bituminous Paving Mixtures Using Automatic Vacuum Sealing Method (Hansen 2008). Because water easily flows through the layer, moisture issues are normally not present (Hansen 2008). However, NAPA recommends that porous asphalt be tested in the same manner as dense- graded HMA. The testing is performed using the porous asphalt materials in a “surrogate” mix. A minimum tensile strength ratio of 80% is recommended (Hansen 2008). Abrasion resistance is not generally considered in the current P-401 specification. With porous asphalt, abrasion resistance needs to be assessed. Cantabro abrasion testing (ASTM D7064) on unaged samples and samples aged 7 days is recommended, with results of the testing needing to be less than or equal to 20 and greater than or equal to 30, respectively (ASCE 2015). Higher binder content can yield a decrease in abrasion loss; however, too high a binder content may compromise the permeability of the pavement (ASCE 2015). Draindown is another porous asphalt property not generally included in conventional HMA design. Draindown should be less than or equal to 0.3% by testing in accordance with ASTM D6390 (Hansen 2008). 5.6.1.4 Common Porous Asphalt Testing Requirements The following are some of the testing requirements for porous asphalt: • ASTM D3203, Standard Test Method for Percent Air Voids in Compacted Dense and Open Bituminous Paving Mixtures: This test method is used to determine the percent air voids in compacted dense- and open-graded asphalt paving mixtures. • ASTM D3625, Standard Practice for Effect of Water on Bituminous-Coated Aggregate Using Boiling Water: This practice covers a rapid procedure for visually observing the loss of adhe- sion in uncompacted bituminous-coated aggregate mixtures due to the action of boiling water. • ASTM D4867, Standard Test Method for Effect of Moisture on Asphalt Concrete Paving Mixtures: This test method is to determine the potential of asphalt binder stripping from aggregate. The test determines the tensile strength ratio of the composite mixture. • ASTM D6390, Standard Test Method for Determination of Draindown Characteristics in Uncompacted Asphalt Mixtures: This test method is used to determine the amount of

50 Guidance for Usage of permeable pavement at airports draindown in an uncompacted asphalt mixture sample when the sample is held at elevated temperatures comparable to those encountered during the production, storage, transport, and placement of the mixture. The test is particularly applicable to mixtures such as porous asphalt and stone matrix asphalt. • ASTM D6752, Standard Test Method for Bulk Specific Gravity and Density of Compacted Bituminous Mixtures Using Automatic Vacuum Sealing Method: This test method covers the determination of bulk specific gravity of compacted bituminous mixtures by the vacuum sealing method. • ASTM D6857, Standard Test Method for Maximum Specific Gravity and Density of Bitumi- nous Paving Mixtures Using Automatic Vacuum Sealing Method: This test method covers the determination of maximum specific gravity and density of uncompacted bituminous paving mixtures at 77°F. • ASTM D7064, Standard Practice for Open-Graded Friction Course (OGFC) Mix Design: This practice covers the mix design of OGFC using the Superpave gyratory compactor or other suitable forms of compaction. The OGFC mix design is based on the volumetric properties of the mix in terms of air voids, as well as the presence of stone-on-stone contact. • ASTM WK44391, New Practice for Construction of Porous Asphalt Pavements with Stone Reservoirs: A committee is working on a specification for the design and construction of porous asphalt pavement. 5.6.2 Pervious Concrete Materials Pervious concrete features an open network of pores formed by using an open-graded aggre- gate to allow infiltration of stormwater through the pavement. As with porous asphalt, raveling of the surface was a common concern found in this study’s survey and interviews. Freeze–thaw durability was also identified as a concern in the industry survey and interviews. 5.6.2.1 Aggregate As in conventional concrete, aggregates used in pervious concrete need to be sound and durable. Requirements for conventional concrete aggregates, such as reactivity, wear, soundness, and deleterious content, apply to the aggregates used for pervious concrete. Coarse aggregate should comply with ASTM C33. Permeability of pervious concrete is attained by the coarse aggregate gradation being limited to a single size or close to a uniform gradation (open graded). Although smaller aggregate has been effectively used for certain applications, aggregate grading is typically between ¾ and 3⁄8 in. maximum size, and using aggregate larger than 1 in. is not recommended for any application (ACI 2013). Gradations used for pervious concrete include ASTM C33 No. 67 (¾ in. to No. 4), No. 8 (3⁄8 in. to No. 16), and No. 89 (3⁄8 in. to No. 50). Very little to no fine aggregate (sand) is included in the mixture. A lower sand content con- tributes to higher void content and a permeable matrix. While the addition of even a small amount of fines in the mixture increases compressive strength and density, at the same time it reduces the infiltration rate (FHWA 2016). One study found that the connected porosity of permeable concrete mixtures was influ- enced more by the aggregate type (dolomite or steel slag) than the size of the aggregates (3⁄8 in. to No. 4 or ¾ in. to 3⁄8 in. aggregate fractions) (C´osic´ et al. 2015). 5.6.2.2 Cement/Cementitious Materials Cement should comply with ASTM C150; Types I or II are commonly used for pervious con- crete, and occasionally Type V (low alkali) is used, if needed. Secondary supplementary cementi- tious materials can be used. Fly ash conforming to ASTM C618 can be used in the mixture at 20% maximum weight replacement. Slag cement meeting ASTM C989, Grade 100 or Grade 120,

Materials Considerations 51 can also be used. Total cementitious material content commonly ranges from 450 to 550 lbs/yd3 (NRMCA [National Ready Mixed Concrete Association], n.d.). Alkali-silica reactivity-based requirements (maximum cement alkali content, maximum fly ash calcium oxide content, and so on) for conventional PCC should be followed. These are usually a part of state specifications and are also included in FAA Item P-501, Portland Cement Concrete Pavement. 5.6.2.3 Mix Design Pervious concrete is a highly permeable concrete that contains a high content of macroscopic pockets of air ranging from 15% to 25% and has flow rates in the range of 192 to 1,724 in./h (ACI 2010). A variety of mix proportions can produce a wide range of properties in pervious concrete, and various admixtures are available to enhance its overall performance. In general, it is difficult to simultaneously optimize the mechanical and durability properties and infiltration perfor- mance of pervious concrete. The current mix design and fabrication practices are documented by ACI Committee 522 (ACI 2010) and the ASCE Permeable Pavements Task Committee (ASCE 2015). The goal of pervious concrete mix proportioning is to produce a permeable, smooth, and durable pavement surface, typically achieved at around 20% voids. In the United States, the typical mix design of permeable concrete features a water/cement (w/c) ratio of between 0.27 and 0.34 (FHWA 2012). With a lower w/c ratio than conventional PCC, pervious concrete has lower slump and less workability. Higher w/c ratios may provide greater workability, but can result in the cement paste draining off the aggregate during place- ment. As with conventional PCC, the use of water reducers can improve workability. Water- reducing admixtures should meet the requirements of ASTM C494, Type A, B, or D. Further, hydration stabilizers are commonly used to increase workability over a longer duration and delay the initial set of the cement (FHWA 2016). Hydration stabilizers should conform to ASTM C494, Type B or D. Typical values of 28-day compressive strength for pervious concrete range from 400 to 4,000 psi (Tennis et al. 2004). Relatively high values of the compressive strength of pervious concrete can be achieved, but this occurs with a reduction of void content and compromised permeability (ACI 2010). ASCE’s Permeable Pavements manual points out that, for pervious concrete, strength and permeability are inversely related (ASCE 2015). The freeze–thaw durability of pervious concrete can be improved using many different methods, including using a small amount of fine aggregate, adding polypropylene fibers, using a slightly higher w/c ratio, increasing consolidation (lower porosity), introducing entrained air, increasing paste volume, replacing some Portland cement with fly ash or silica fume, and using a latex admixture (Schaefer et al. 2006, Kevern et al. 2008, Wu et al. 2010). A few studies have shown that the addition of air entraining admixtures complying with ASTM C260 is help- ful in maintaining the durability of the mixture in cold regions, but this is not confirmed (NRMCA, n.d.). However, there is no current method to measure the air content in the paste of pervious concrete; air content can only be measured in the hardened pervious concrete. The use of polyethylene or cellulose fibers can also improve freeze–thaw resistance, as well as increase abrasion resistance and tensile strength (Amde and Rogge 2013). Partial replacement of coarse aggregate with fines in mass dosages ranging from 4% to 6% tends to improve the freeze–thaw durability of pervious concrete (ASCE 2015). There are also admixtures that can be employed to improve abrasion resistance. These include styrene butadiene rubber polymer latex (Wu et al. 2010) or a small amount of nano-silica (2.5% by the weight of cement) (Longhi et al. 2015). Permeable concrete, relative to its impermeable counterpart, requires strict quality control of mixture proportioning during fabrication. The paste content is particularly critical to ensure

52 Guidance for Usage of permeable pavement at airports that the paste fully coats and adheres to the aggregates and allows the open structure to be con- nected with adequate strength and permeability. The aggregate moisture level must be carefully monitored since the water absorbed by the aggregate and excess moisture accompanied with the aggregate largely affects the final performance of the permeable concrete. Generally, the unit weight test is a better test than the slump test for quality control. In comparison to conventional concrete, the mixing time requirements with the same equipment are increased, and the deliv- ery and installation times must be largely shortened. In addition, the freeze–thaw durability, strength, and permeability of permeable concrete are also largely determined by the compaction energy (Kevern 2010, Kevern et al. 2010). 5.6.2.4 Common Pervious Concrete Testing Requirements The following are some of the common testing requirements used for pervious concrete: • ASTM C1688, Standard Test Method for Density and Void Content of Freshly Mixed Pervious Concrete: This test method is used to determine the density of freshly mixed pervious concrete under standardized conditions and gives formulas for calculating the void content of pervious concrete. • ASTM C1701, Standard Test Method for Infiltration Rate of In Place Pervious Concrete: This test method covers the determination of the field water infiltration rate of in-place pervious concrete. • ASTM C1747, Standard Test Method for Determining Potential Resistance to Degradation of Pervious Concrete by Impact and Abrasion: This test method is used to determine the poten- tial resistance to degradation of pervious concrete by measuring the mass loss of specimens subjected to the combined action of impact and abrasion in a rotating steel drum. • ASTM C1754, Standard Test Method for Density and Void Content of Hardened Pervious Concrete: This test method provides a procedure for determining the density and void con- tent of hardened pervious concrete specimens. • ASTM WK29213, Test Method for Compressive Strength of Pervious Concrete: This is a pro- posed test method for verifying pervious concrete material strength on a project. • ISO 17785-1:2016, Testing Methods for Pervious Concrete, Part I Infiltration Rate: Specifies the procedure for testing the infiltration rate of hardened pervious concrete specimens in the laboratory. It is not a method for measuring the permeability of pervious concrete. 5.6.3 PICP One advantage of concrete pavers is that they are manufactured in a controlled environment and can be tested prior to placement. Concrete pavers should be manufactured in accordance with ASTM C936. Concrete pavers are typically 23⁄8 in. thick for vehicular applications and typi- cally 31⁄8 in. thick for aircraft applications (McQueen et al. 2003). Concrete pavers 31⁄8 in. thick can achieve compressive strengths of 8,000 to 10,000 psi at 28 days (McQueen et al. 2003). Freeze-thaw–resistant pavers can be achieved for local conditions and can be tested for durability. Concrete paver shape should be uniform, and spacer bars should be uniform in size. 5.6.3.1 Common PICP Testing Requirements • ASTM C67, Standard Test Methods for Sampling and Testing Brick and Structural Clay Tile: Provides test methods for the sampling and testing of brick and structural clay tile. • ASTM C140, Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units: Provides general testing requirements for application to concrete products. • ASTM C144, Standard Specification for Aggregate for Masonry Mortar: Specification provides aggregate characteristic requirements for use in masonry mortar. • ASTM C936, Standard Specification for Solid Concrete Interlocking Paving Units: Specifica- tion for interlocking concrete pavers used in the construction of paved surfaces and manufac- tured from cementitious materials, aggregates, chemical admixtures, and other constituents.

Materials Considerations 53 This specification provides guidelines for physical requirements, sampling and testing, visual inspection, and rejection of specimens. • ASTM C979, Specification for Pigments for Integrally Colored Concrete: Specification covers the requirements for colored and white pigments in powder form to be used as admixtures for producing integrally colored concrete. • ASTM C1645, Test Method for Freeze–Thaw and De-icing Salt Durability of Solid Concrete Interlocking Paving Units: Evaluates the freezing and thawing resistance of solid interlocking concrete paving units conforming to the requirements of ASTM C936. • ASTM C1781, Standard Test Method for Surface Infiltration Rate of Permeable Unit Pavement Systems: Determines the field surface infiltration rate of in-place permeable unit pavement systems. • CSA-A231.2, Precast Concrete Pavers: Specifies requirements for concrete pavers manufac- tured from hydraulic cement concrete to be used in the construction of pedestrian and vehicu- lar traffic areas. 5.7 Other Materials 5.7.1 Fabric/Liner The base/subbase reservoir layer is typically separated from the subgrade by a layer of filter fabric. The use of a filter fabric reduces the migration of fines into the base/subbase reservoir, which would ultimately reduce the storage capacity of the reservoir. For no-infiltration systems, an impervious liner (e.g., geotextile, clay barrier) between the base/subbase reservoir course and subgrade is used to prevent infiltration of stormwater into the subgrade (ASCE 2015). Generally, woven or non-woven geotextiles fabrics can be used for separation, reinforcement, or drainage between pavement layers or neighboring soils; AASHTO M 288 is a common ref- erence for selection criteria (ASCE 2015). Specifically, a filter fabric or an impervious liner in compliance with ASTM D6767-02 is placed between the subgrade layer and the base/subbase course (NRMCA, n.d.). Non-woven geotextile fabrics can prevent the migration of fines from the subgrade and contamination of a base layer (Hansen 2008). While requirements can vary from state to state, Table 12 provides an example of required properties of the filter fabric. Filter fabrics are not recommended for use underneath the permeable surface layer since they can collect fines and reduce permeability (ASCE 2015). In addition to protecting weak subgrades, liners are incorporated into some design features. As an example, an impervious liner was used in the Paine Field pervious concrete project to pro- tect the berms (or check dams) between infiltration beds in the stepped design. Liner properties used for Paine Field are summarized in Table 13. Table 12. Example filter fabric requirements. Property Unit ASTM Test Method Requirement Grab tensile lb D4632 180 Elongation percent D4632 50 Puncture lb D4833 80 Burst psi D3786 290 Trapezoid tear lb D4533 50 UV resistance percent D4355 70 Water flow rate gpm/ft2 D4491 130 Permeability cm/s D4491 33 Apparent opening size sieve size D4751 70 Elongation percent D4632 50 Source: Campbell and Paris (2014a).

54 Guidance for Usage of permeable pavement at airports 5.8 Specifications 5.8.1 Industry Groups Two ACI publications, ACI Standard 522.1-13 (Specification for Pervious Concrete Pavement) and ACI Report 522R-10 (Report on Pervious Concrete), provide useful specifications related to the construction of pervious pavements. The former covers materials, preparation, forming, plac- ing, finishing, jointing, curing, and quality control of pervious concrete pavement. It includes provisions for testing, evaluation, and acceptance of pervious concrete pavement, which can be referenced as a supplement to project specifications, as appropriate. The latter provides technical information on pervious concrete’s application, design methods, materials, properties, mixture proportioning, construction methods, testing, and inspection. It is not intended as a reference to project specifications but rather as a basis for developing mandatory language within the project specifications. Among the various applications cited for pervious concrete are (a) parking lots; (b) base course for streets, roads, driveways, and airports; and (c) pavements, walls, and floors where better acoustic absorption characteristics are desired. NAPA IS 131 (Porous Asphalt Pavements for Stormwater Management: Design, Construction, and Maintenance Guide) provides detailed guidance on the structural and hydrological design of porous asphalt pavements as well as the materials used and construction and maintenance practices (Hansen 2008). While detailed guidance is provided for materials and construction, specifications are not included with the document. Although the guide does not specifically cite airport airside facilities as feasible locations for porous asphalt pavement systems, it does provide design details for applications involving roads, streets, and parking lots that are often part of an airport’s landside facilities. The ICPI’s Permeable Interlocking Concrete Pavements (Smith 2015) provides specifications for PICP in Section 4. The publication provides for materials requirements and includes a construction checklist to assist with inspection. It also provides an example of a maintenance agreement. Although not specifically for PICP, paver materials requirements for aircraft load- ings are provided in Airfield Pavement Design with Concrete Pavers (McQueen et al. 2003). Property Unit Test Method Requirement Thickness mils ASTM D1593 40 ± 2% Specific gravity N/A ASTM D792 1.20, min Elongation at break percent ASTM D882, Method A 430, min Tensile strength lb/in. width ASTM D882, Method A 97, min Tear resistance, each direction lbs ASTM D1004, Die C 10, min 100% modulus lbs/in. ASTM D882, Method A 40 Water extraction, as compared to blanks of same nominal thickness percent loss ASTM D1239 0.2% loss, max Volatility percent loss ASTM D1203, Method A 0.5, max Low temperature, pass ºF ASTM D1790 minus 29 Dimensional stability (designated MD and TD in the specification), each direction percent change ASTM D1204 3, max Source: CH2M (2013b). Table 13. Example liner requirements.

Materials Considerations 55 These industry references focus on vehicular applications. The IPRF report, Stabilized and Drainable Base for Rigid Pavement (Hall et al. 2005), provides example specifications for stabilized permeable base layers for pavements supporting aircraft loads. This report also provides guidance on construction. 5.8.2 State Specifications Most state standards contain permeable pavement materials specifications, and these stan- dards typically vary by state. Each state’s standards are based on local conditions and experi- ence. The FAA’s AC 150/5100-13A provides a procedure for approval of state standards that is permitted under U.S. Code 47105(c). However, as discussed in Chapter 4, there are additional requirements for using state standards for pavements carrying aircraft loadings. The AAPTP report, Guidelines for Use of Highway Specifications for HMA Airport Pavements (Buncher and Boyer 2009), provides some guidance on the use of state standards. One of the primary require- ments identified in that report is to have acceptance and quality control levels equivalent to the requirements in the FAA’s materials specifications. 5.8.3 Federal Specifications 5.8.3.1 FAA Specifications The FAA’s materials specifications are contained in AC 150/5370-10 (version “G” at the time of this study), Standards for Specifying Construction of Airports. The current FAA construc- tion specifications do not contain permeable pavement materials. An MOS would be needed for permeable pavements under its construction guidelines. The specifications can provide a base- line document that can be modified to the properties required for permeable pavement—for example, modifying P-209, Crushed Aggregate Base Course, to meet the requirements of base/ subbase reservoir aggregate. In any airside construction project, it is important to ensure that appropriate levels of acceptance and quality control are maintained. The Culpeper apron and Richmond taxiway shoulder projects used the FAA’s Item P-402, Porous Friction Course, specification (included in FAA 2014a) for their porous asphalt surfaces. The project specifications required a synthetic-rubber–modified asphalt cement. However, since those projects were designed, P-402 has been removed from the current version of the AC. 5.8.3.2 Unified Facilities Guide Specifications The UFGS provides construction specifications for the military branches. UFGS does contain sections for permeable pavement materials; however, permeable pavement materials are identi- fied as being for roadways and parking lots. The following specifications are included in the UFGS: • Section 32 10 00 – [Pervious] Bituminous Concrete Pavement. • Section 32 11 10 – Drainage Layer (includes both aggregate and stabilized layers). • Section 32 11 16.16 – [Base Course for Rigid] [and Subbase Course for Flexible] [Subbase Course for Pervious] Paving. • Section 32 11 24 – Graded Crushed Aggregate Base Course for [Pervious][Flexible] Pavement. • Section 32 13 43 – Pervious Concrete Paving. • Section 32 12 43.16 – Porous Friction Course for Airfields and Roads (U.S. Department of Defense 2016). ICPI has also developed a federal specification for PICP: Section 32 14 13.19 – Permeable Interlocking Concrete Pavement (ICPI 2016).