THESIS

EFFECTIVENESS OF BACK- FLUSHING FOR CLEANING POROUS

PAVEMENTS

Fall 2006

By- Nilesh Shirke

Outline

• Introduction• Problem Statement• Research Question• Methodology• Construction of a Model• Detailed Procedure of Experiments • Experiments and Results • Analysis of Data• Result and Conclusion• Future Research

Committee Members

• Dr. Scott Shuler (Adviser/Chair)

• Dr. Angela Guggemos

• Dr. Charles Smith• Dr. Ramchand Oad (Outside Committee member)

Introduction

•Increased runoff

•Drainage

•Alternative pavement

•Void content

•Direct infiltration of rain water

•Replenish ground water

•Sustainable construction

Bean, Hunt, Bidelspach, & Smith, 2004; Leopold, Wolman, & Miller, 1964James, W., & Langsdorff, H., 2003; Bachtle, 1974; Caltrans, 2004; Georgia concrete and products association, 2005, p. 2; Surface System Drainage Design, 2005

Layers of Porous pavement

1. Porous Concrete Layer

2. Top Filter Layer

3. Reservoir Layer

4. Bottom Filter Layer

Georgia Stormwater Management Manual, 2002

Typical Cross-section of Porous Pavements

The Urban Land Institute, 1992, p 6.

Advantages of porous pavements

• Percolation of rainwater into the soil

• Aquifer recharge

• Ambient air temperature

• Snow and ice

• Soil erosion

• Decreases need of storm drains

Adams, 2003; Bachtle, 1974; Field, 1982; Ferguson 1994; Magnus, 2000; Pratt 1997; The Pervious Company, 2005; Georgia Concrete and Products Association, 2005; Miller, 2005

Disadvantage of Porous Pavements

• Susceptibility to clogging

• Reduces infiltration levels

• Groundwater contamination

• High failure rate

Field, 1982; UNI-Group U.S.A., 1998; United States Environmental Protection Agency, 1999.

• Maintaining infiltration capacity

• Clogging at the bottom

• Periodic maintenance

• Traffic levels and type of usage

• Severe clogging

Problem Statement

James & Langsdorff, 2003; The Urban Land Institute, 1981; United States Environmental Protection Agency, 1999; Siew-Ann et al., 2003; Georgia Stormwater Management Manual, 2002

Periodic Maintenance

Georgia Stormwater Management Manual, 2002, p 37

Research Hypothesis

When water is flushed through the pavement from bottom to the top with enough pressure, it removes the debris particles trapped in the pores of porous concrete layer.

• When water is pumped into the stone reservoir of the pavement, it will try to come out through the clogged porous concrete layer. While coming out from bottom to the top of the pavement, water should remove the particles and debris trapped in the pores of the pavement. The result of this flushing should make the pavement permeable again.

Research Question

Concept of Back Flush Method

Diagram of a Model Constructed for the Analysis of Back-Flush

Methodology

• Fabrication of steel frame • Construction of a porous concrete layer • Installation of model on a steel frame • Construction of various layers• Sieve analysis for clogging materials• Calculation of initial permeability• Clogging

• Back-flushing

Methodology

• Measurement of permeability cleaned concrete layer

• Back flush it for the second time.• Measurement permeability after 2nd

back-flush• Repetition of the procedure • Data collection• Analysis of the results• Conclusion

Photograph Showing Various Sections a Model

A Photograph Showing Full View of a Model

Section 1

• A two feet long and 8” diameter pipe for the construction of porous concrete layer

• Material Weight Proportions

- Cement-600 lbs, Aggregates 3/8”-2900 lbs, Water-242 lbs

• Sampling - ASTM C 702-98 splitting method

• Sieve Analysis - for 3/8” aggregates as per ASTM C 136-01

• Curing of concrete - ASTM 192 & C511 Storage tank in hydrated lime

Analysis of 3/8” aggregates as per ASTM C 136-01

Sieve Analysis for 3/8" Aggregates

0.00

20.00

40.00

60.00

80.00

100.00

120.00

3/8" No. 4 (4.75 mm) No. 8 (2.36 mm)

Sieve Size

% P

assi

ng

Section 2

A three feet long and 8” diameter pipe for construction of filter layers, stone layer of the pavement in it.

Section 3, 4 & 5

• Section 3: A ten feet long and 8” diameter pipe to store water to create head difference

• Section 4: A 1½” diameter pipe connected to tap water with water flow control valve in between.

• Section 5: A 1½” diameter pipe connected to section 1 and which is used to drain the water out after back-flushing.

Procedure of experiment

Calculation of permeability:

k = QL / AthWhere,• k = permeability, in/s• Q = quantity of flow, cu. inch• L = length of specimen, inch• A = cross-sectional area of specimen, sq. inch• t = interval of time over which flow Q occurs, s• h = difference in hydraulic head across the

specimen, in

Procedure of experiment

• Unclamp Section 1• Check permeability • Clogging• Measurement of permeability• Placement of section 1 over

section 2 • Attach section 5 to the section 1• Choose the head and fill section 3• Back-flush• Close the valve after back-flush• Detach section 5 from section 1

Procedure of experiment

• Unclamp section 1• Check permeability after

back-flush• Attach Section 1 for 2nd back-

flush• Attach section 5 to section 1• Back-flush for the 2nd time• Check permeability• Repeat the procedure• Efficiency of back-flush = k (back-flush)- k (clogged) / k

(Initial) – k (clogged)

Experiments and Results

• Average Strength of porous concreteHigh Porous Concrete - 895.59 psi

Low Porous Concrete - 1164 psi

Classification of clogging materials • Classification and gradation of soils by ASTM D

2487-00

Cu = D60/D10 &

Cc = (D30*D30) / (D60*D10)

Where, • Cu = Coefficient of Uniformity

• Cc = Coefficient of Curvature

• D10, D60 and D30 = Particle size diameters corresponding to 10, 60 and 30 % respectively, passing on cumulative particle-size distribution

Classification of Sand 1 & Sand 2Sand 1:• A Graph gives the value for D10 = 0.15, D60 = 1.15 and

D30 = 0.4Hence, • Cu = 8.33, Cc = 1.05• Cu>6 and 3>Cc>1 • Hence, it is a Well Graded Sand (SW).

Sand 2:• A Graph gives the value for D10 = 0.45, D60 = 1.8 and D30 = 0.8 Hence, • Cu = 4, Cc = 0.79• Cu<6 and 1>Cc. • Hence, it is a Poorly Graded Sand (SP).

Percentage Removal of Clogged Particles After Back-Flush

Average Permeability Recorded on High Porous Concrete Sample

A Chart for Average Permeability Recorded on High Porous Concrete Sample

Average Permeability Recorded on Less Porous Concrete Sample

A Chart for Average Permeability Recorded on Less Porous Concrete Sample

Analysis of Data

• ANOVA

• Four variables

• Class Levels Values

• Pressure 4 H L M VL

• Porosity 2 High Low

• Clogging 2 Sand 1 Sand 2

• Flush 2 Q1 Q2

SAS Output

• Source DF Type III SS Mean Square F Value Pr > F

• Pressure 3 3325.215458 1108.405153 5.58 0.0018• Porosity 1 6.211837 6.211837 0.03 0.8602• Clogging 1 79.570417 79.570417 0.40 0.5291• Flush 1 93.102204 93.102204 0.47 0.4962• Pressure*Porosity 3 652.060537 217.353512 1.09 0.3583• Pressure*Clogging 3 668.936625 222.978875 1.12 0.3468• Pressure*Flush 3 71.115388 23.705129 0.12 0.9485• Porosity*Clogging 1 265.268504 265.268504 1.33 0.2523• Porosity*Flush 1 121.770150 121.770150 0.61 0.4366• Clogging*Flush 1 674.690104 674.690104 3.39 0.0700• Pressu*Porosi*Cloggi 3 71.967954 23.989318 0.12 0.9476• Pressu*Porosit*Flush 3 54.522292 18.174097 0.09 0.9645• Porosi*Cloggin*Flush 1 198.030150 198.030150 1.00 0.3219• Pressu*Cloggin*Flush 3 22.284204 7.428068 0.04 0.9902• Pres*Poro*Clog*Flush 3 278.594508 92.864836 0.47 0.7061

Student-Newman-Keuls Test

Alpha = 0.05 Error Degrees of Freedom 64 Error Mean Square 198.7347

Number of Means 2 3 4 Critical Range 8.1301265 9.7646019 10.734814

***Means with the same letter are not significantly different.

SNK Grouping Mean N Pressure• A 79.953 24 H• A• B A 72.753 24 M• B• B 66.196 24 VL• B• B 65.321 24 L

Analysis

• No fixed pattern in particle removal

• Pressure- significant variable

• No significance of number of flushes

• Less water requirement

• Low pressure efficiency

Results and Conclusion

• Simplified Maintenance

• Monthly or quarterly back-flushing

• Increased use of porous pavements

• Low pressure works good

• Possible to create in the field

FUTURE RESEARCH

• More research work

• Laboratory study and Field study

• A very low pressure of water (0.5 psi)

• Drainage pipes in the porous pavement

• Division of porous pavement

• Storage of drained water

Thank You !!!