Porosity of Permeable Friction

Courses (PFC)Brandon Klenzendorf

April 28, 2009CE 397 – Statistics in Water Resources

Layer of porous asphalt 1 to 2 inches thick over impervious roadway surface

Water enters pore space and provides benefits:◦ Reduced splash/spray◦ Improved traction◦ Reduced hydroplaning◦ Improved water quality

Pores become clogged with sediment over time resulting in a loss of porosity

Can we predict the extent of clogging over time?

PFC Introduction

Conventional Asphalt

PFC Overlay

PFC cores are extracted from three roadways for the past three years:◦ Loop 360◦ FM 1431◦ FM 620◦ March 2007◦ February 2008◦ February 2009

PFC Cores

PFC layer

33 total porosity measurements

Porosity Data

10

12

14

16

18

20

22

24

2006 2007 2008 2009 2010

Poro

sity

(%)

Year

Loop 360

FM 1431

FM 620

10

12

14

16

18

20

22

24

2006 2007 2008 2009 2010

Poro

sity

(%)

Year

Loop 360

FM 1431

FM 620

Kruskall-Wallis Test◦ H0: all groups have identical distributions

◦ Reject H0 if K ≥ Kα (from tables)

Mann-Whitney Test (Rank Sum Test)◦ H0: the means of two groups are identical

◦ Reject H0 if T ≤ Tα/2 (from tables)

Statistical Tests

3

1

2

2

1

1

12

jjj

NRn

NNK

jn

iij

jj Rn

R1

1

n

iiRT

1

Kruskal-Wallis Test

Test Results

Grouped by

Kcalc K0.05 Decision Comment

2007 5.42 5.60Do Not Reject

H0

All locations had the same porosity in 2007

2008 9.35 5.62 Reject H0

At least one location had a different

porosity

2009 7.46 5.62 Reject H0

At least one location had a different

porosity

Loop 360 6.23 5.63 Reject H0At least one year had a different porosity

FM 1431 5.60 5.60 Reject H0At least one year had a different porosity

FM 620 5.96 5.60 Reject H0At least one year had a different porosity

Compare two years of Loop 360 porosity◦ Mann-Whitney Test

Extend this analysis to the other roadways Extend this analysis to individual years

Test Results

Grouped by

Statistic

Critical

Decision Comment

‘07 & ‘08 T=16 7.0Do Not

Reject H0

2007 and 2008 had the same porosity

‘08 & ’09 T=26 27.0 Reject H02008 and 2009 had different porosities

‘07 & ‘09 T=23 23.0 Reject H02007 and 2009 had different porosities

Multiple variables can influence PFC porosity◦ Life of pavement◦ Traffic volume◦ Precipitation◦ Roadway geometry (slope, width, etc.)◦ Nearby construction sites, etc.

Only consider first four variables

Trends in Porosity

Estimate annual average daily traffic (AADT)

Linear regression from 16 years of data

Traffic Volume

LCRA Hydromet data for Loop 360 and FM 1431 Need to find precipitation data for FM 620

Precipitation

Complete multiple variable trend analysis Write final report Extend this analysis to hydraulic

conductivity data (data set not complete) Determine correlation between porosity and

hydraulic conductivity How can these measurements be used to

predict PFC benefits (water quality)?

Future Work

Questions or Comments?

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PFC Introduction Porosity Data Statistical Tests

◦ Kruskall-Wallis Test◦ Mann-Whitney Test

Test Results Trend Analysis Future Work

Outline

Compare porosity in travel lane to shoulder on Loop 360◦ Both Kruskal-Wallis test and Mann-Whitney test

Test Results

Grouped by

Statistic

Critical

Decision Comment

Travel Lane K=4.27 5.60Do Not

Reject H0

All years had the same porosity in the travel

lane

Shoulder T=7 6.0Do Not

Reject H0

All years had the same porosity in the shoulder

Comparison T=49 32.0

Do Not Reject H0

No difference between travel lane and shoulder

Porosity

Remove impervious base materialVacuum sealed core

Submerged specific weight device