Pervious Concrete: Getting Down to the Details

Pervious Concrete Getting Down to the Details Sean Van Delist Cement Council of Texas

Permeable Pavements Pervious Concrete: What & Why? Pervious Concrete: How? Design & Construction Pervious Concrete: Other Considerations Questions & Answers Outline

Permeable Pavements: Applying the Technology

Porous Pavements Bruce K. Ferguson

Permeable Pavements are pavements that allow the passage of stormwater through the surface course layer. Permeable Pavements can provide the following benefits: Reduce Stormwater Runoff (Quantity) Clean Stormwater (Quality) Cool Stormwater Replenish the water table/ aquifers Allow for Rain water Harvesting Reduce Urban Sprawl Protect Trees Reduce Urban Heat Island Effect Eliminates Ponding Water What Are Permeable Pavements?

The Problem to be Fixed Pervious Surfaces Absorbs Stores Water Reduces or eliminates run-off Removes and destroys pollutants Infiltrates into natural soil Recharges ground water Sustains local ecosystem Maintains stream base flow Rainfall Impervious Surfaces Deflects Flushes pollutants into streams Aggravates flooding Erodes channels Ground water declines Streams go dry in summer Aquatic ecosystems die Water supplies insecure Rainfall and Run-off

Pervious Concrete- 5 basic permitted uses: Stormwater runoff reduction (quantity) Stormwater treatment (quality) Tree protection Wetlands protection Zoning credits

Filtration of TSS Oxidation Soil Filtration & Capture Bioremediation Stormwater Quality

Austin 0% credit for vehicular applications 100% credit for pedestrian applications LCRA Highland Lakes 90% credit for all applications San Antonio Required for exceeding maximum parking limits TCEQ- Edward’s Aquifer Not currently allowed over recharge w/o special consideration ZoningCredits

Pervious Pavement- It’s a System. Properly designed and constructed Permeable Pavement Systems provide a Structural and Hydraulic solution for sitework pavement loading conditions, stormwater detention and quality improvement requirements.

Permeable Pavements are pavements that allow the passage of stormwater through the surface course layer. Depending on the permeability of site soils, local hydrological conditions, and stormwater management objectives, the water is then managed in one of three ways: Full Exfiltration No Exfiltration Partial Exfiltration Permeable Pavements

Full Exfiltration Permeable Surface Course Gravel/Stone 40% voids Filter Fabric Curb

No Exfiltration Permeable Surface Course Gravel/Stone 40% voids Liner Curb

Partial Exfiltration Permeable Surface Course Gravel/Stone 40% voids Filter Fabric Curb

Objectives Three positions influence the decisions. Producer & Installer Hydrology Structure

Surface Course Types: Choosing the Proper Material for the Specific Application

Dubai Initiative “ It is a very good initiative as long as it does not consume too much water, and does not need much maintenance,

Considerations All systems function hydrologically All systems require some type of maintenance Match surface course for site conditions: Climate Type of Traffic Quantity of Traffic

Commonly called Decomposed Granite (DG) Crushed Granite

Filled with gravel, crushed stone or soil for grass to grow thru Plastic paving cells

Also known as Permeable Friction Course (PFC) Permeable Asphalt

Epoxy, polyurethanes, or other polymers used to bind aggregate or rubber chips together Polymer cement concretes

Grid/ Turf Pavers & Grasscrete

Main Differences to Consider Subgrade Must accommodate water flow Design for intentionally weakened subgrade Separation Layer Use with all soils except sand Subbase gap-graded Storage layer Subbase Subgrade

Layout/Grade/Slope Part of System Supports traffic Allows water to pass Water should flow vertically Minimize horizontal flow Storage in gravel base Can use pavement and ponding zone Flat system offers the maximum storage

Hydrology- Considerations Rainfall Characteristics Soil Permeability Stormwater Management Objectives

Soil Permeability ASTM D3385 -09 Standard Test Method for Infiltration Rate of Soils in Field Using Double-Ring Infiltrometer ASTM D5093 -02(2008) Standard Test Method for Field Measurement of Infiltration Rate Using Double-Ring Infiltrometer with Sealed-Inner Ring

Subgrade Compaction Of some debate Compact to 92 - 95% of modified proctor Compaction of the subgrade is inversely proportional to its permeability. Uniformity is more important than compaction percentage

Subgrade-Pumping The forceful displacement of soil and water from beneath the pavement through joints and cracks. Conditions for pumping: 1. Subgrade soils that will go into suspension 2. Free water between slab and subgrade 3. Frequent heavy wheel loads insert photo from winpump.ppt

Geotextiles Highly recommended Different types for different applications Overlap based on soil strength May add strength to subgrade- compensates for reduced compaction

Separation Layer- Geotextiles Seperation Prevents intermixing of drain rock & subgrade Confinement Helps interlock drainrock Reinforcement Carrys some tensile load Protection Protects permeab ility of subgrade Filtration Allows passage of water

Geotextiles TenCate Mirifi 140N most recommended Non- woven polypropylene “ filter” fabric 6 heavier grades 500X may be more useful in clay soils Woven polypropylene “ stabilizer” fabric 100X & 600X also available

Rainwater Harvesting- Finley Stadium Chattanooga, Tennessee

Gradation Angularity Hardness Selection of Drain Rock (base) is important

Base Thickness Typically 6 inches Greater than 6 inches to increase storage Greater than 6 inches for freeze-thaw Not required in some cases Minimize root damage Native soils highly permeable

Storage Capacity Storage capacity typically governs design Depends on porosity of pavement, subbase, & subgrade. 1” of pavement with 20% porosity can store 0.20” 1” of #57 stone base with 40% porosity can store 0.40” 6” pavement on 6” subbase can store 3.6” of rain Curbs can be used for additional storage (ponding) (20%) 6 in. + (40%) 6 in. = 3.6 in. (20%) 6 in. + (40%) 6 in. + (100%) 6 in. = 9.6 in.

Pervious Concrete: What & Why?

Pervious Concrete…What is it? Constituents Cement Water Coarse Aggregates Admixtures Point-to-Point Aggregate Contact Adhered with Past Bridge Random Structure

Mixture Proportions 2400-2600 lbs.- #89 stone 100-400 lbs.- silica sand (<#16- >#200) 400-650 lbs.- portland cement 0.27-0.32 w/c ratio admixtures

Aggregate Texture and Porosity Affected by Aggregate Size Aggregate Grading Aggregate Angularity Paving Equipment Volume of aggregate per cubic yard of concrete is about 27 cubic feet

Surface Texture Comparison 3/8” rock or gravel is most common size due to smoothness and appearance

Cementitious Quantity Maintain the void structure Maintain point to point aggregate contact Maintain the paste thickness Adjust the cementitious content to coat the aggregate with .015 inch thickness.

Water Content Water/ Cement Ratio: 0.27-0.32 Contractor Controls Water Content to Match: Equipment Weather Water may be added at the jobsite

Water and Plasticity Recognize an unstable paste Recognize a wet, metallic sheen Recognize a flat, dull appearance The cement paste is delicate. If water content or plasticity is too high, the paste falls off the aggregate and sinks to the lower parts of the slab. If it is too low, the paste will dry rather than hydrate.

Admixtures Set Controlling Retarders Hydration Stabilizers Viscosity Modifying Admixtures (VMA) Integral Color Proprietary Additives- Acrylic/ Latex Polymers

Proprietary Systems Acrylic/ Latex Polymers Ecocreto, Stoneycrete, Magna-Crete, Enviro-Crete, Percocrete, Filtercrete, Leakcrete… Almost any liquid latex or acrylic will work Increases strength, color steadfastness and COST!

An Unnatural Act Making concrete that includes voids. Intentionally reducing concrete density. Knowingly reducing concrete strength.

Void content= 10 – 25% Drainage rate = 3 to 8 gal/min/ft 2 Equivalent of 275” to 725” of rain per hour! Pervious Concrete Properties

110 to 130 lbs/ft 3 unit weight Corresponds to void content 1000 to 4000 psi strength Introduction of small amount of fine aggregate and/ or polymers help can increase strength. Pervious Concrete Properties

Properties Testing- Quality Control Conventional concrete testing methods do NOT apply No/ Low slump concrete Compressive/ Flexural strength testing of lab & field samples has high variability and less accuracy Density & Void Content and Field Permeability are only tests for acceptance other ASTM Standards & Testing Methods are currently under development

ASTM C09.49 Standards & Work Groups Fresh density and void content- C1688 Field Permeability- C1701 Compressive Strength/ Flexural Strength Hardened Density and Voids Surface Durability

Designation: C 1688/ C 1688M – 08 0.25 cubic ft. bowl & standard proctor hammer 20 blows per 2 layers D ensity= M ass/ V olume Void content ( U )= T heoretical- D ensity T heoretical Standard Test Method for Density and Void Content of Freshly Mixed Pervious Concrete

Designation: C 1701/C 1701M – 09 Standard Test Method for Infiltration Rate of In Place Pervious Concrete

High variability with standard procedures Partially due to inconsistent modification of test Partially due to nature of materials Will always be difficult to match placement conditions Current Proposal 4X8 cylinders- 2 layers- 5 drops of proctor hammer Strength Testing

Falling Head Permeability Test

Evaluating the Surface Durability Potential of a Pervious Concrete Mixture

Pressure Washer Testing? 3000 psi 1 gpm 3-inch separation-nozzle to concrete

Unit Weight – At the Plant The unit weight is simply the weight of one cubic foot Critical in quality control Unit Weight should be +/- 5 pcf of design Should be performed at the plant ASTM C 138

Pulling Cores Larger projects might require cores Measure thickness No < ¼” No > ½” Measure Dry Density + or - 5 pcf ASTM C 42

Pervious Concrete: How? Design & Construction

How? Relatively new technology (in Texas) Few established standards and methods Little collected data on properties Design and construct conservatively!

Pervious Concrete Truths • You have to select, design, and build it right • You can design it to fail • You can design it to succeed • It requires your knowledge & care Pervious concrete is distinct and different • Every installation is site-specific

Pervious Concrete-Technical Resources

Administered by Texas Aggregates & Concrete Assoc. Several classes offered annually across the state Private training classes available upon request

National Network Portland Cement Association National Ready Mixed Concrete Association American Society of Concrete Contractors American Concrete Institute American Society for Testing and Materials

Structural Design Procedures ACI 522 Chapter 6 – AASHTO or PCA if strength falls within limits (usually doesn’t) PCA Pervious Concrete Pavements suggests AASHTO, WinPas, PCAPAV, ACI 325, or ACI 330R, or using flexible pavement structural numbers ACI 325.12R and 330.1R tables require minimum flexural strength of 500 psi Bruce K. Ferguson “Porous Pavements” – p. 420, “Six inches probably minimum thickness…” and “Heavier traffic loads require thicker slabs.” We need a proper engineering procedure

Further Research Needed– Design and Performance Field performance studies under heavy traffic Fatigue relationship for pervious concrete Performance of aggregate interlock joints over time (faulting progression) Feasibility of using dowels – diameter, bearing stress

Further Research – Materials Structural grades Different aggregate gradations Small amount of fine aggregate Tradeoff between strength and permeability

In the Interim… Increase Attention to Detail Increase Emphasis on Construction Quality Reduce Emphasis on Strength Design Conservatively

Pavement Thickness Minimums 4-5” Sidewalks& Trails 5-6” Residential Driveways 5-7” Parking lots 7-9” Commercial Driveways Consider Conventional Concrete & PICP Heavy truck traffic High volume traffic Areas with a lot of turning pervious conventional

Traffic: Type Quantity Subgrade & Subbase Properties Surface Course Properties Thickness Strength General Pavement Section Thickness Determination

Strength vs. Thickness Section strength – proportionate to: Square of the thickness Material Strength So, if you want a stronger pavement, you can Use a LOT stronger concrete Use a little more concrete If the concrete has to be weaker (and in this case, it does) You can make the section as strong by making it thicker A Little thicker…

Thickness vs. Modulus of Rupture

Thickness… Turns out to be the answer to a number of questions Poor Subgrade? Increases Thickness More traffic? Increase Thickness Heavier Loads? Increase Thickness Lower Flexural Strength? Increases Thickness

What does this say about strength? If you can’t have strength Make it thicker A little thicker If you can’t affirm strength Make it thicker A little thicker If you need strength Make it thicker Don’t make the materials stronger Unless you don’t need pervious.

Finishing: The Typical Process Spreading Strike-off Compacting Jointing Curing 1 2 3 4 5

“ Each builder has a style; a favorite way to assemble his method, his setup, and his crew. Some will perform their flatwork as though they were building pianos. Others will slap it down, any way that gets them paid. Such is the difference between craftsmen and henchmen. There seems to be room for everyone…” Ken Bunyan (Dave Mitchell) inventor of the Bunyan hydraulic roller screed.

Finishing Qualifications Require a Contractor who has successfully completed the NRMCA Pervious Concrete Contractor Certification Course is required. Specified # of Technicians, Installers, & Craftsmen In addition to this requirement, the placing contractor shall furnish: A minimum of 2 completed projects with addresses Unit weight acceptance data In-situ pavement test results including void content and unit weight Sample of product Proposed equipment to be used

Various Placing Equipment Types

Concrete Compaction More Compaction = Less Porosity Strength Increases  Porosity Decreases  More Compaction 

Ensuring a Durable Surface- Preventing Raveling Sufficient Compaction Match Placement Method with Mix Design Proper Mixing Water (w/c) Preventing Evaporation Rapid Placement Proper Curing Limit Traffic and Turning tire sheer can loosen the aggregate One potential solution is to grind down the pavement surface about half an inch.

Compaction of pervious concrete material during placement

Edge Thickness & Compaction is Critical

Stresses are Greatest at Edges & Corners

Edging ? Some debate May prevent raveling May promote raveling Must be done quickly Must be done correctly

Evaporation Control Sub base Saturation Fogging Evaporation Retarders Confilm The Bean Curing- Plastic Sheeting

Understand Potential for Evaporation Recognize surface area exposure Recognize air humidity Recognize windy conditions

Cement Hydration Recognize low water traits Recognize early hydration process Recognize evaporation Water / Cement ratio is about ½ the water of conventional concrete. The low water cement ratio causes hydration to flash. Normal pervious materials require more mixing. Batch water and add water must be more closely controlled. Mixer discharge is slower and may batter the inside of the drum.

Cement Hydration Launch The first fifteen minutes Tricalcium Aluminate The first two hours Tricalcium Silicate The rich cement content and low water content is prone to flash. the hydration, starting during the first fifteen minutes. The clock begins ticking when the ingredients are combined. Load 80% of the water and all the admixtures before introducing the cement and aggregate.

Recognize Different Evaporation & Set Characteristics Drum Mixer Volumetric Mixer

Prepare the Poly Unpacked, Unfolded, Rolled Quick installation Follow closely behind the placement Full supply, roll on PVC pipe Full length = slab + 3 feet Full width = slab + 3 feet

Shrinkage Restraint (friction from the foundation) Temperature changes Ambient (expansion/contraction) Gradient (may cause curling) Changes in moisture content Surface drying (may cause curling) Service loads Factors That Influence Slab Cracking (Pavement Stresses)

Rebar, even epoxy coated, rusts away over time Low-slump, high-void material forms poorly around fiberglass rebar Don’t need reinforcement even with conventional concrete for most pavement applications anyway – prepare the subgrade properly and joint it properly to take care of crack and curl control Remember that an extra inch of concrete can do much more for you than rebar anyway Reinforcement? Dowels?

Load Transfer Edge and corner stresses are greatest Use Thickened Edges Use curbs to control stresses

Jointing Best Practices Control (contraction) Construction Isolation Understand limitations of material & construction methods Use Common Sense

Control Joints 15’ typical-20’ max. 1:1.5 maximum aspect ratio 1/4D Align with joints in plain concrete No need to seal?

Effects of Joint Spacing 10.0 ft 3.0 ft 3.0 ft 3.0 ft Ultra-thin Slabs Deflect Concrete in Compression Standard Slabs Bend Concrete in Tension

Control Joints- Tooled Pizza Cutter Thin blade, small radius Don’t use traditional jointers

Control Joints- Saw cut Too early= raveling Too late= ineffective May hinder hydration Cut at 7 days???

Sealing Joints? Joints don’t need to be sealed, but sealant can reduce or eliminate raveling at joints

Construction joints Use thickened section or thickened edges for load transfer issues If additional load transfer is needed, use traditional pavement

Isolation Joints Not expansion joints Some debate over use Proper installation critical to good performance

“ Natural” Construction/ Isolation Joints?

Where Pervious Concrete Abuts Conventional Pavement or Structures

Important Points for Design & Construction of Pervious Concrete Get a soils report Determine thickness design based on usage, ADTT and soil type. Determine base thickness based on design storm, soil type and flow concentration Pay close attention to detail in methods and materials. Use a contractor with NRMCA certified pervious concrete technicians. Utilize industry resources – they are free!!

Pervious Concrete: Other Considerations

Pervious Concrete- LEED 3.0 Considerations May Contribute to: SS Credit 6.1 Stormwater Design—Quantity Control (1) SS Credit 6.2 Stormwater Design—Quality Control (1) WE Credit 1 Water Efficient Landscaping (1-4) MR Credit 4 Recycled Content (1-2) MR Credit 5 Regional Materials (1-2) Regional Priority Credits for SS 6.1 & 6.2 (1-2) May Detract from: SS Credit 7.1 Heat Island Effect—Nonroof

Pervious Concrete Maintenance Design the installation with minimal exposure to sediment from other areas Minimize the level of flow concentration Sweep routinely as you would a parking lot of any other paving material Set up periodic testing for infiltration capacity if a maintenance agreement is required by the approving agency

Prevent Debris from Washing Onto Slab

Slope Grade Away from Pavement SWALE

Routine Maintenance- Litter Removal Leaf blowers work well if done on a regular basis Vacuum trucks effective at removing fresh deposited large debris Sweeping not very effective

Routine Maintenance- Litter Removal

Removing Sediments Low pressure, high volume water High pressure water usually not needed

Questions? For additional information or assistance, Please call or email: Sean Van Delist 210-883-8060 [email_address]

Pervious Concrete: Getting Down to the Details

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