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"Cómo el concreto y los pavimentos permeables ayudan a reducir la acumulación de agua superficial"


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Dean Frank , Director en Dean Frank Associates

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"Cómo el concreto y los pavimentos permeables ayudan a reducir la acumulación de agua superficial"

  1. 1. How Pervious Concrete and Permeable Pavements Help Reduce Water Runoff Dean Frank, P.E., LEED Green Associate
  2. 2. What is Pervious Concrete? • Considered an open graded system. • Consists of: • Cement, • Coarse aggregate, • Little or no fine aggregates, • Water, • Admixtures. • No slump (or zero slump). • Point-to-point aggregate contact. • Aggregate adhered together with paste bridge.
  3. 3. Why Do We Need Pervious Pavement? • Recharging groundwater. • Reducing stormwater runoff: • Relieve stress on poor/underdesigned infrastructure. • Clean stormwater through filtration. • Meet U.S. EPA stormwater regulations: • Pervious concrete is among the Best Management Practices (BMPs) recommended by the EPA for the management of stormwater runoff. • Increase land use/efficiency for development. • Contributes to sustainability goals.
  4. 4. Streets and Roads Parking Lots
  5. 5. Sidewalks Paths Alleys Pervious concrete is generally NOT used in heavily loaded pavement applications (e.g. highways, delivery lanes, truck stops, etc.), but can be if designed and placed correctly
  6. 6. Pervious Pavement Profile: A System For Water Management Pervious Concrete 6” – 10” Choker Course (optional) 1” – 2” Open-Graded Base 6” – 24”+ Filter Fabric (optional) Subgrade
  7. 7. Pervious Concrete Pavement – Storm Water Cleansing Reduce: -Total Suspended Solids -Metals (eg. Cu, Zn, Pb) -Nutrients Pervious Concrete Aggregate Subbase Subgrade Water Table
  8. 8. Decorative Pervious Concrete Pavement Edgewater Park Minneapolis, MN Source: Cemstone Source: Bunyan Industries Sidewalk in China
  9. 9. Benefits of Pervious Concrete • Eliminates costly storm water management practices. • Provides for more efficient land development.
  10. 10. Pervious Concrete Pavement - Environmental Considerations • Percolation recharges groundwater. • Water resources are conserved. • Less need for irrigation. • Adjacent vegetation receives more rainwater. • Runoff reduced. • Cooler surface has less impact on air temperature.
  11. 11. Benefits of Pervious Concrete – Efficient Land Use • Closed existing detention pond. • Paved with Pervious Concrete. • Water storage for retention or on- site use. Prime Retail Outlets Williamsburg, VA
  12. 12. Converting a detention pond to usable parking space
  13. 13. Soil Considerations With Pervious Concrete • Top of subgrade should be above wet season water table by at least 2 feet. • Permeable soils desirable (Perm. > ~0.2 in/hr): • Increase subbase depth for lower permeability soils. • Consider special design details on expansive clay soils. • Compact subgrade to 92% - 95% of std. proctor. • Keep heavy axle loads off subgrade during construction.
  14. 14. Clay Soils • Increase Storage Capacity of Pervious Layers. • Increase Infiltration Rate of Soil (if possible). • Use Integrated Best Management Practices. • Impervious Liner Over Expansive Clays: • Use In Areas With Potential Drought Periods and Low Water Tables (i.e. Drying/Wetting Cycles), • Not Necessary In Areas With Semi-Saturated Clay.
  15. 15. Peak Water Table Considerations Pervious Concrete Aggregate Open-Graded Base Subgrade Wet Season Water Table Two (2) Foot Minimum
  16. 16. Properties of Pervious Concrete Air Void Content: • 15-35% typical - Field studies show 20-25% average. • Size of aggregate influences. • Void content lower than 15% does not provide sufficient interconnectivity for rapid percolation. Higher void content Higher Percolation Lower Compressive Strength Typical Unit Weights: • 100 to 120 lbs/ft3
  17. 17. Properties of Pervious Concrete 28-day Compressive Strength1: Typically 500 to 3,000 psi • 2,000 psi is typical and applicable for most applications. • Mixture proportioning and compaction affect strength: • Small amounts of fine aggregate can increase strength (careful not to fill voids). • Thickness of paste layer surrounding aggregates impact strength (relates aggregate size, cement content and w/c). • Compressive strength typically NOT used as acceptance criteria • Air void structure (~15 – 25%) and unit weight are used. • Flexural Strength: MR = 2.3f’c 2/3 = 366 psi (~2,000 psi compressive). Note 1: High variability associated with strength tests of pervious concrete.
  18. 18. Mixture Design Cement • 450 – 550 lbs. Portland Cement is typical (and desireable). • Type I or II, typical (ASTM C150 Standard Specification for Portland Cement). • ASTM C595 Standard Specification for Blended Hydraulic Cements and ASTM C1157 Standard Performance Specification for Hydraulic Cement may be used. • Fly Ash / Slag cement substitute acceptable (~10-15% cement replacement).
  19. 19. Mixture Design Water • w/cm ratio: 0.30 – 0.36 typical: • Need sufficient water to display a wet, metallic sheen on the aggregate. • Too much water in mix will lead to drainage of paste (clogging of pores). • Water may be added to truck on site. • Recycled water requirements – ASTM C94 Standard Specification for Ready- Mixed Concrete (or AASHTO M-157). Dry OK Wet
  20. 20. Mixture Design Coarse Aggregate • Texture and Porosity Affected by: • Aggregate Size • Aggregate Grading • Aggregate Angularity • Paving Equipment • Grading between ⅜ and ¾ inch • Aggregate Moisture Content: • Should be in saturated surface – dry (SSD) condition
  21. 21. Mixture Design Admixtures • Water-reducing admixtures (High- and Mid-Range): • Used depending on w/c ratio. • Retarding admixtures for cement hydration control: • May act as lubricants for discharge, and • Used in hot weather placements. • Accelerating admixtures extend working time for a mix: • Used in cold weather placements. • Super Absorbent Polymers (SAPs) • increases workability and speed of installation • holds significant water which allows for full hydration (i.e. improves curing) • Air-entraining admixtures: • Not commonly used, but • Used successfully in areas susceptible to freeze/thaw.
  22. 22. Mixture Design Fibers • Improves ability of mixture to hold together. • Increases permeability. • Comply with ASTM C1116 Standard Specification for Fiber-Reinforced Concrete.
  23. 23. Mixture Design • Target void content of 15% to 25% as measured by ASTM C1688 - Standard Test Method for Density and Void Content of Freshly Mixed Pervious Concrete. • During production and placement, produced density of fresh pervious concrete shall be within ±5 lbs. of the specified density based upon the approved mix design.
  24. 24. Fresh Concrete Surface Example with Rounded Aggregates
  25. 25. Hardened Concrete Surface Example with Angular Aggregates
  26. 26. Hardened Concrete Surface Example with Sealed Surface From Excessive Surface Paste (Due to Mixture Design & Improper Compaction)
  27. 27. Designing Cross- Sectional Thickness Design for: • Traffic Loading Conditions • Soil Conditions (Strength, Permeability) • Hydrologic Conditions Source: Charger Enterprises, Inc. Source: Pervious Concrete California Source:
  28. 28. Designing Cross- Sectional Thickness Two-Step Design Procedure: • Structural Design: For Traffic Loading Conditions • Hydrologic Design: For Environmental Conditions • Select the greater required thickness Source: Charger Enterprises, Inc.
  29. 29. Designing Cross-Sectional Thickness: Structural Design • Can be designed similar to conventional concrete pavement, but with lower flexural strength. • Calculated pervious concrete thickness is generally: • 6” for a typical parking lot (autos and occasional truck) or • 7 to 10” if more trucks are present or if poor soils are present. • Heavy truck and/or heavy turning areas may be a candidate for conventional concrete pavements.
  30. 30. Cross-Section Design – Goals: Hydrologic Design • Hydrologically functional landscape that mimics the natural hydrologic regime. • Mimic the predevelopment site hydrology by using pervious concrete pavement system that stores and allows infiltration of stormwater.
  31. 31. Cross-Section Design: Hydrological Considerations • Rainfall Intensity. • Rainfall Duration. • Soil Permeability: • Underdrain may be used for soil infiltration rates of less than 0.2” per hour. • Release Rate.
  32. 32. Cross-Section Design: Hydrologic Design • Permeability of Pervious Concrete: • 3.5 gal/ft2/hr is typical • Accommodates rainfall events of 340 in/hr! • Permeability far exceeds significant storm events. • Storage - Four potential areas: • Infiltration into subgrade. • In the subbase. • In the pervious pavement. • On top of the pavement (ponding to top of curb).
  33. 33. Cross-Section Design: Site Layout/Planning - (Warm Climates) Filter Fabric T0 T1 T2 Pervious Concrete ~20% Voids Aggregate Base ~ 40% Voids Subgrade Stormwater Curb Water may be stored above or below the top of the pervious layer during a storm event.
  34. 34. Cross-Section Design: Site Layout/Planning - (Cold Climates) Filter Fabric T1 T2 Pervious Concrete Aggregate Base ~40 % Voids Subgrade Curb
  35. 35. Other Design Considerations: Curbs Allow Run-Off Hold Run-Off
  36. 36. Prevent Debris From Clogging Slab
  37. 37. SWALE Other Design Considerations: Slopes Water
  38. 38. Other Design Considerations: No Adjacent Dirt Parking Dirt Tracking On To Pervious Concrete Pavement
  39. 39. Top of Pavement Elevation Higher Than Grass/Landscaping Other Design Considerations: Grading
  40. 40. Other Design Considerations: Islands
  41. 41. Impervious Asphalt Pervious Concrete Concrete Transition Strip Other Design Considerations: Transitions
  42. 42. Stormwater Storage Options: Additional Storage
  43. 43. Freeze-Thaw Resistance – Mix Design • Pervious concrete can perform well in F-T environments. • In hard-freeze areas where subgrade stays frozen, aggregate base should be used as storage (24+ inches thick in some cases). • Other freeze environments where subgrade is not continually frozen, typical aggregate thicknesses may apply.
  44. 44. Freeze-Thaw Resistance – Mix Design • Smaller aggregate provides greater resistance to F-T. • Small addition of sand (7%) may also increase resistance. • However, it also reduces voids and permeability slightly. • Adding fibers improves durability slightly. Ref: Pervious Concrete Mixture Proportions for Improved Freeze-Thaw Durability, Kevern, et al.
  45. 45. Site Preparation - Compaction Don’t over compact, subgrade must remain permeable.
  46. 46. Construction – Place Filter Fabric (If Specified) Geotextile fabric is sometimes specified.
  47. 47. Construction – Place/Compact Open Graded Base
  48. 48. Construction - Setting Forms Use string lines to set form elevation. Wood or steel forms can be used.
  49. 49. Construction – Surface Texture • Important to keep the voids open. • Do NOT use trowels unless mix is designed appropriately. • Do NOT seal the surface. • Avoid roller marks.
  50. 50. Construction – Mixer Discharge • Pervious concrete flows down chutes at slower rate. • Minimize number of chutes. • Will restrict the discharge radius. • Place in successive semi- circular arcs. • Squared-off at end of each truck’s discharge.
  51. 51. Construction – Strike-Off Methods Motorized Roller Screed (1-step placement method) Vibratory Truss Screed (2-step placement method)
  52. 52. Construction – Jointing: Why Joint Slab? • Concrete shrinks as it sets, hardens and dries out. • Result in cracks. • Joints control location of cracks. • Shrinkage not as great as in conventional concrete. • Panels should be made as square as possible. • Cut in perpendicular to the curb. • Length to width ratio should not exceed 1.5. • Maximum joint spacing 20 feet. • Joint depth = ¼ to ⅓ pavement thickness.
  53. 53. Construction – Jointing: Types of Joints Control Joint Isolation Joint Construction Joint
  54. 54. Construction – Jointing: Tooled Joints Joint Roller Tooled Joint
  55. 55. Construction – Jointing: Saw Cut Joints • Discouraged for the inexperienced. • Can damage both edges. • Dust can clog voids. • However, joint sawing has been done successfully: • Vacuum dust or wet slurry. • Care must be taken to keep pavement from drying out during the saw cutting.
  56. 56. Construction – Curing Process • Maintain adequate moisture and temperature. • Continue strength and durability. • Water will evaporate from concrete unless moisture is maintained. • Curing uninterrupted for 7 days.
  57. 57. Construction – Curing Additional Precautions • Exposure time of pervious concrete should be minimized. • Should not exceed 20 minutes. • For high temperature, windy conditions or low humidity (also in cold weather), exposure time should be reduced further. • Or other precautions like fog sprays should be used to protect the surface from drying.
  58. 58. Construction – Moist Cure 1. Cure with 6 mil plastic (minimum), 2. Secure edges of plastic, 3. Cover within 20 minutes or less, 4. Continue curing, uninterrupted, for at least 7 days.
  59. 59. Maintenance for Long-Term Performance
  60. 60. Maintenance • Maintenance different than other pavements. • Goal: Keep permeability close to design. May not restore all voids. • Owner’s responsibility. • Ensures longevity of system. • Prevent clogging during construction. • Limit debris from construction. Clogging From Construction
  61. 61. Maintenance • Pervious concrete pavement can function well with no cleaning. Is not mandatory. • Will work better if sand, dirt, leaves and other debris are removed.
  62. 62. Maintenance Frequency of Cleanings: • Depends on amount of sediment deposited. • Inspect pavement periodically: • Recommended annually for most conditions. • Observe drainage during a significant storm event. • Trash, leaves or paper may degrade into small particles that may migrate into the voids and appears to have removed debris from surface.
  63. 63. Maintenance Methods
  64. 64. Maintenance Methods – Power Washing
  65. 65. Maintenance Methods – Vacuuming
  66. 66. Maintenance – Miscellaneous Considerations • Sweeping pervious may be ineffective. • Small sediment gets trapped in coarse surface. • Do not sweep from impervious onto pervious areas. • Do not flush impervious areas onto pervious areas. • Chemicals to clean pervious not recommended. • Owner should establish a maintenance plan. • Periodic evaluation of permeability. • Contractor should assist the owner with developing this maintenance plan. • Use methods that do not damage (ravel) the surface.
  67. 67. References - ACI 522R-10 • Provides technical information on pervious concrete’s: • application, • properties, and • construction methods.
  68. 68. References - ACI 522.1-13 • Materials and Construction Specification for Pervious Concrete Pavement
  69. 69. References - ACI 522.1 - 13: Specification for Pervious Concrete Pavements • Performance Specification. • Provides Guidelines for: • Quality Assurance: • Materials • Testing and Acceptance • Placement Methods • Does not provide recipe for pervious concrete mix design.
  70. 70. References – National Pervious Concrete Pavement Association (NPCPA)
  71. 71. References – NRMCA Concrete Answers Series Link
  72. 72. Summary • Pervious concrete pavement can: • Reduce stormwater runoff • Recall: It is a recommended BMP by EPA! • Recharge groundwater. • Clean stormwater through filtration. • Increase land use/efficiency for development. • Pervious concrete may be used: • over both permeable and impermeable soils, and • in areas with freeze potential.
  73. 73. Summary Streets and Roads Sidewalks Paths Alleys Parking Lots
  74. 74. Acknowledgment Special Thank You to the National Ready Mixed Concrete Association (NRMCA)
  76. 76. WORLD OF CONCRETE LAS VEGAS “ ”Show Floor • WOC General • Precast • Masonry • Concrete Repair • Demolition • Precast 700,000 square feet of indoor and outdoor exhibit space and 60,000 attendees • Technology for Construction • Material Handling • Concrete and Decorative • Outdoor Exhibits Education • Hands-On Training • Interactive Workshops • Live Demonstrations • Luncheons and Forums • Certification Exams • Editorial Tours
  77. 77. WORLD OF CONCRETE Who Attends WOC? • Commercial Contractors • Concrete Contractors • Concrete Pumpers • Engineers • Masonry Contractors • Dealers/Distributors • Architects • General Building Contractors • Public Works Contractors • Precast Producers • Ready Mix Producers • Highway/Paving & Bridge Contractors Who Exhibits at WOC? Original equipment manufacturers from around the world and exclusive U.S. distributors of equipment, tools, products and services for the commercial construction, concrete and masonry industries. WOC delivers approximately 1,500 leading suppliers, including more than 320 international suppliers.