Developing a Structural Design Method for Pervious Concrete Pavement Norb Delatte, P.E., Ph.D. Cleveland State University
CSU Pervious Pavement Demonstration – August 24, 2005
CSU Pervious Pavement Demonstration – August 24, 2005
Pervious Pavement Design
Hydraulic design Structural design Select greater required thickness
Engineering Design – Delatte’s Simplified Definition Anticipate everything that can possibly go wrong Make sure it doesn’t happen But remember… engineering is the art of doing for $ 1 what any idiot could do for $ 2
Structural Design Procedures ACI 522 draft chapter 6 – AASHTO AASHTO or PCA if strength falls within limits (usually doesn ’t) Bruce K. Ferguson “Porous Pavements” – p. 420, “Six inches probably minimum thickness…” and “Heavier traffic loads require thicker slabs.” ACI 325.12R and 330.1R tables require minimum flexural strength of 500 psi
Structural Design Procedures PCA Pervious Concrete Pavements (EB302, p. 15) suggests AASHTO, WinPas, PCAPAV, ACI 325.9R (??), or ACI 330R, or using flexible pavement structural numbers We need a proper engineering procedure
Erie Street project – Kent, Ohio
Erie Street Water currently runs over street straight into Cuyahoga River Pavement redesign for traffic, parking, bike path Bars, restaurants, small businesses – need to design for delivery trucks
Structural Design Inputs Properties of pavement material (pervious concrete) Modulus of subgrade reaction (k) Traffic – number of vehicles, axle loads
Structural Design Outputs Minimum pavement thickness Maximum joint spacing (based on curling and warping) Joint design (aggregate interlock or doweled) – at present only aggregate interlock joints are used for pervious concrete
Overkill? How much permeability do you need?
Pervious Concrete Grades Low Strength
High Strength
High Permeability
Low Permeability
STRENGTH
PERMEABILITY
Hydraulic Grade
Normal Grade
Structural Grade
Material Testing
Purpose – sort pervious concrete into proper grade Strength testing – field samples taken to laboratory Research – determine expected material properties (density, strength, modulus of elasticity, permeability) for each grade
Pervious Concrete Properties Strength and durability depend on Quality of the material delivered Construction procedures Placement Rolling/compaction Curing
Analogy to RCC – material + compaction
RCC Sample Compaction 180 170 Unit Weight
c p 160 , t h g i e 150 w t i n 140 U
Theoretical Maximum
130 120 0
50 Number of Gyrations
100
RCC Density versus Compressive Strength – Cores 9000 8000 i s 7000 p , h t 6000 g n e r t 5000 S e v 4000 i s s e r 3000 p m o C2000
50-day field specimens 28 day mix B Linear (50-day field specimens)
1000 0 148
150
152
154 Density, pcf
156
158
160
RCC Density versus Splitting Tensile Strength – Cores 900 800 i s p , 700 h t g n 600 e r t S500 e l i s n 400 e T g 300 n i t t i l p 200 S
51-day field speci 28 day mix B Linear (51-day fiel specimens)
100 0 144
146
148
150
152 Density, pcf
154
156
158
160
RCC Splitting Tensile Strength 650 w/c = 0.40 625
w/c = 0.45
w/c = 0.40
w/c = 0.50
2
R = 0.8719
600 ) i s 575 p ( e l i s n e T 550 g n i t t i l p 525 S
w/c = 0.45 2
R = 0.5512
2
R = 0.6487
w/c = 0.50
500
475
450 159.0
159.5
160.0
160.5
161.0
Unit Weight (pcf)
161.5
162.0
162.5
StreetPave Software
Developed by ACPA, based on PCA 1984 procedure Handles range of material properties for pervious concrete – flexural strength, E Provides for doweled or aggregate interlock joints, with or without edge support
Traffic Determination
Material properties – pavement and base
Thickness and joint spacing
Design Example Reliability – 85 % for 20 year design life Traffic – 4 lane minor arterial with 500 ADTT and 2 % growth Drainable base with k = 100 pci Conventional concrete pavement for comparison = 550 psi flexural strength, dowels, edge support Pervious concrete pavement = 350 psi flexural strength, no dowels, no edge support
Comparison of Results
Conventional concrete – requires 7.5 inch pavement thickness with 1.25 inch dowels, 15 foot joint spacing recommended Pervious concrete – requires 11.5 inch pavement thickness, 15 foot joint spacing Increase pervious concrete strength to 400 psi – reduce thickness to 10.5 inch
Is the Design Valid?
Long term performance depends on Fatigue performance Aggregate interlock joint performance Durability (e.g., freeze-thaw) Clogging
Still a lot of questions…
Residential Design Example Reliability – 85 % for 20 year design life Traffic – 2 lane residential with 3 ADTT and 2 % growth Drainable base with k = 100 pci Conventional concrete pavement for comparison = 550 psi flexural strength, no dowels, no edge support Pervious concrete pavement = 350 psi flexural strength, no dowels, no edge support
Comparison of Results
Conventional concrete – requires 6 inch pavement thickness, 12 foot joint spacing recommended Pervious concrete – requires 8 inch pavement thickness, 15 foot joint spacing Increase pervious concrete strength to 400 psi – reduce thickness to 7.5 inch
FHWA Drip 2.0 Software – Roadway Geometry
Library of drainable base materials
Base layer design by time-to-drain or depth-offlow methods
Results
Based on predicted infiltration, from hydrologic analysis Select properties of base material, e.g. AASHTO # 57 Determines minimum thickness of base material Can also design geotextile separators and edge drains
Application to Kent Project
Estimate pervious concrete material properties Samples from CSU demo Other lab work
Estimate subgrade support – soil testing, hydraulic requirements for base Prepare a range of designs, sensitivity analyses
Further Research – 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
Internal curing – use of saturated fine lightweight aggregate to supply internal water
Conclusions StreetPave seems like a reasonable design tool – so far Need to know what the actual in -place flexural strength of pervious concrete is Does pervious concrete obey the same fatigue relationships as pervious concrete? Will pervious concrete maintain aggregate interlock at joints over time, under traffic?
