Design, Construction and Performance of Porous Asphalt Pavement in India for Rainwater Harvesting

7/22/2019 Design, Construction and Performance of Porous Asphalt Pavement in India for Rainwater Harvesting

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Design, Construction and Performance of Porous Asphalt Pavement

for Rainwater HarvestingBy

Prof. Prithvi Singh Kandhal and Sapan Mishra*

[Published in the Indian Roads Congress Journal, Indian Highways, Vol. 42 No. 3,

March 2014]

ABSTRACT

Multi-storied commercial and residential buildings, which significantly increase the

demand for water supply, are increasingly being constructed in urban India. In many

states of India such as Bihar, Delhi, Gujarat, Haryana, Punjab, Rajasthan and

Tamilnadu, the ground water is plunging at an alarming rate. Responsible town

planners, architects and civil engineers must be proactive and integrate rainwater

harvesting techniques in the design of all types of buildings, parking lots and low-

trafficked roads/streets. For example, Public Works Department (Buildings and

Roads) engineers can integrate government buildings with porous asphalt parking lot.

This would recharge the ground water in over-exploited/critical areas of India. The

revolutionary technology presented in this paper addresses that very need.

The porous asphalt pavement which can be used for parking lot or low-trafficked

roads/streets works like this. The top 75 mm asphalt layer is specially designed to

make it porous. Rainwater goes through it rapidly without any ponding. The water is

then stored in an underlying open-graded stone bed, which is about 225 mm thick.From there, water percolates slowly into the underlying soil. The porous parking lot

or street can be integrated with a roof rainwater harvesting system in the buildings

adjacent to it by diverting the roof water to the stone bed. Recently, the Jaipur

Development Authority has constructed the first ever porous asphalt parking lot in

India. This paper gives the details of its design, construction and performance.

1. INTRODUCTIONMulti-storied commercial and residential buildings, which significantly increase the

demand for water supply, are increasingly being constructed in urban India. However,additional water supply is hardly available. The Central Ground Water Board

(CGWB) has identified about 800 regions in India in which ground water level is

plunging at an alarming rate. These regions are located in Rajasthan, Madhya

Pradesh, Punjab, Haryana, Gujarat, Bihar, Delhi and Tamilnadu.

According to the 2004 data of CGWB, for every 125 units of ground water being

taken out in Jaipur, only 100 units are replenished by rain. It is estimated that the

ground water level in Jaipur is falling at the rate of about one meter every year.

* Respectively, Associate Director Emeritus, US National Center for Asphalt

Technology, Auburn University, Alabama, USA ([email protected]) and

Executive Engineer, Jaipur Development Authority ([email protected])


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According to the CGWB, all underground water will be depleted in Jaipur in about 10

years time1. There is some water in rocks below 100 meters but that water contains

harmful elements in it and may not be safe for drinking.

There is an urgent need to act now to recharge the ground water in over-exploited/critical areas of India. The Ground Water Advisory Council on Artificial

Recharge of the Ministry of Water Resources has suggested that there is a need to

develop separate technologies for recharge specifically for urban areas. This paper

addresses that very need.

The ground water problem was also felt in the US in urban areas, where rainwater

simply runs off without charging ground water. The Franklin Institute of Philadelphia,

Pennsylvania was tasked in early 1970s to develop technologies to address the

problem of plunging water table in urban areas. The first author had the privilege of

brainstorming with the Franklin Institute researchers in developing the concept of

porous asphalt parking lot for urban areas2. This concept was tried in some pilotprojects and was very successful. The concept was later fully developed in the 1980s.

It was also successfully tried on a road in Chandler, Arizona. At the present time it is

being used in many states of the US primarily for storm water management3. The

State of California has built over 150 projects since 1980. About 95% of rainwater

falling on a porous asphalt parking lot goes to recharge ground water. Even in case of

open ground with vegetation in rural areas, only about 33% of rainwater goes to

recharge ground water primarily due to evapo-transpiration losses. This percentage is

believed to be significantly lower in hot climate of Rajasthan.

This proven concept of building porous asphalt pavements was declared Outstanding

Engineering Project in 2000 by the American Society of Civil Engineers.

Responsible town planners, architects and civil engineers must be proactive and

integrate rainwater harvesting techniques in the design of all types of buildings,

parking lots and low-trafficked roads/streets. For example, Public Works Department

(Buildings and Roads) engineers can integrate government buildings with porous

asphalt parking lot4,5

. This would recharge the ground water in over-exploited/critical

areas of India. The revolutionary technology presented in this paper addresses that

very need.

2. CONCEPT OF POROUS ASPHALT PAVEMENT TECHNOLOGYThis technology is based on building porous asphalt pavements which can be used for

parking lots, recreational areas, or low-trafficked streets and roads. The porous asphalt

pavement works like this (Fig. 1). The top 50-100 mm thick asphalt layer is specially

designed to make it porous. Rainwater goes through it rapidly without any ponding at

the surface. The water is then stored in an underlying open-graded stone bed also

called stone reservoir. From there, water percolates slowly into the underlying natural

soil (subgrade). There is hardly any evaporation loss. Porous parking lots or streets

can be integrated with roof rainwater harvesting systems in the buildings adjacent to itas explained later. There is no need to bore deep wells or construct deep pits.


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A typical cross-section of the porous asphalt pavement system is shown in Figure 2.

The pavement consists of the following components from top downwards:

Open-graded, porous asphalt course 50-100 mm (typically 75 mm) thick 12.5 mm nominal size aggregate choking layer 25-50 mm thick (this is placed

over the stone bed so as to stabilize it and facilitate asphalt paving over it)

Clean, uniformly graded 40-75 mm size crushed aggregate compacted layer toact as a water reservoir (typically it is 225 mm thick and contains more than

40% voids to accommodate rainwater)

Non-woven geotextile to separate the soil subgrade and water reservoir courseso that soil particles do not migrate from the subgrade into the stone water

reservoir course thus choking it. Alternately, a 75 mm thick stone filter course

consisting of 10-25 mm size aggregate can be provided if good aggregate

gradation control can be maintained.

Uncompacted natural soil subgrade (bed)

Fig. 1. Schematic of porous asphalt pavement (Courtesy NAPA)


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Fig. 2. Typical cross-section of porous asphalt pavement (Courtesy NAPA)

As mentioned earlier, rooftop rainwater harvesting systems of the buildings adjacent

to porous parking lots or streets can be integrated into the porous asphalt pavement. A

typical rooftop rainwater harvesting system for buildings consists of the following

elements:

1. Vertical down pipes for carrying the water from the roof to ground level and ahorizontal pipe system for connecting all down pipes.

2. A silting pit fitted with a steel screen3. A soaking well with cement ring and shaft filled with filter media consisting

of large stone, medium size stone and coarse sand.

If the rooftop rainwater harvesting is integrated with the porous asphalt pavement,

item 3 above is not required. The water from the rooftop is carried directly to the

stone water reservoir and dispersed there through a series of perforated water pipes.

(Fig. 3). This way, the stone reservoir does not experience any localized flooding.

This system also means no soaking well or bore hole which involves considerablecost. In case of streets, water from the roof top of the buildings on the street can all be

diverted to the stone water reservoir course. Another major advantage of this

technology is that the water recharging the underground water is pure and free of

contaminants.

Fig. 3. Roof rainwater harvesting integrated with porous asphalt pavement

(Courtesy NAPA)

It should also be mentioned that porous cement concrete can also be used in lieu of

porous asphalt but this paper is limited to the use of the latter.


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3. DESIGN, CONSTRUCTION AND MAINTENANCE GUIDELINES FORPOROUS ASPHALT PAVEMENTS

Detailed guidelines for constructing porous asphalt pavement for parking lots and low

trafficked roads or streets for rainwater harvesting are given in Appendix.Some briefhighlights are given below.

It is recommended that the in-situ soil permeability infiltration rate is 12.5 mm per

hour. However, 2.5 mm per hour is acceptable by suitably increasing the thickness of

the stone reservoir course. In Jaipur, the infiltration rate of the local soil is

significantly higher than 12.5 mm per hour. Soil investigations should be carried out

by boring and/or test pit to test for permeability, determining the depth of high water

table, and determining depth to bedrock. Porous asphalt pavement is not suitable if (a)

local soil is clayey; (b) bedrock is close to pavement; and (c) location has high water

table. Also, porous asphalt pavement should not be constructed at a location subjected

to blowing sand. That is, the adjacent ground should either be paved or covered withgrass.

Compacted stone reservoir layer should be placed directly on natural soil subgrade

(bed) because fill is not recommended. Although a flat soil bed is preferred, slope of

natural soil bed should be limited to 5 percent. This would ensure that water at the

bottom of stone reservoir layer does not flow; rather it percolates downwards. If the

slope is steeper, a terraced parking lot can be considered.

The thickness of compacted stone course (containing about 40% voids) should be

designed to accommodate intensity and amount of rainfall prevailing in the region.

Typical designs are made for 6 months/24-hour rain storms. Conservative designs are

based on 20-year/24 hour rain storms, which can range from 35 mm to 400 mm in 24

hours. Typically, stone reservoir is about 225 mm (9 inches) thick, which can store

40% of 225 mm = 90 mm (3.7 inches) of rainfall temporarily. Obviously, the

thickness is increased if additional water (from rooftop or adjacent dense road

surface) needs to be accommodated.

The structural design of the pavement including the compacted stone reservoir course

and porous asphalt wearing course should be based on traffic using the facility.

Normally, porous asphalt pavements are recommended for parking lots, recreational

areas, and low-trafficked roads (with limited truck use). Both the porous asphaltcourse and the stone bed are structurally strong to withstand car and occasional truck

traffic. This is because both derive their strength from stone-on-stone contact6.

Work site should be protected from heavy equipment so that the natural soil subgrade

(bed) is not compacted otherwise its permeability may be reduced. Before placing the

stone reservoir layer, place a filter fabric over the soil bed so that soil particles do not

migrate upwards and clog the stone reservoir layer. As an alternate, a stone filter

course consisting of 12.5 mm stone particles has been found quite suitable. Place the

porous asphalt course last on the entire project so that it is protected from construction

debris. It should also be protected from soil laden runoff.


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Before placing the 50-100 mm thick porous asphalt course, place 25 to 50 mm thick

layer of 12.5 mm size stone to stabilize the surface of the stone reservoir course and

facilitate paving operation.

The porous asphalt course should be designed as per established guidelines contained

in the US Manual on Design, Construction and Maintenance of Open Graded AsphaltFriction Course (OGFC)

6. Incidentally, OGFC is used in the US as a wearing course

on interstate highways, ranging in thickness from 20 to 25 mm. The objective of

laying OGFC on dense graded asphalt course is to provide a skid resistant pavement

during rains. Rainwater quickly penetrates the OGFC surface, flows at its bottom and

emerges from its edge on to shoulders. Not only the OGFC prevents hydroplaning of

motor vehicles during rains, it also provides a quieter pavement throughout the

year6,7,8

.

Normally, the asphalt mix would have 6 percent bitumen by weight of mix. It is

recommended to use polymer-modified bitumen so that there no drain down of binder

in the trucks transporting the porous mix from plant to paving site. Traffic should berestricted for 24 hours after construction of the porous asphalt wearing course.

The dramatic performance of porous asphalt pavements in the US is clearly visible in

Figures 4, 5, and 6. Figure 4 shows a parking lot which is porous where the cars are

parked whereas the driveway between the parked cars is dense asphalt. During rain,

water is standing on the driveway but has percolated into the porous parking area.

Figure 5 shows two parking lots just after rain. The one in the background is

conventional dense asphalt parking lot whereas the one in the foreground is a porous

asphalt parking lot. Their relative appearance after rain is so very clear.

Figure 6 shows view of a highway in Chandler, Arizona during rain. The left lanes

were constructed with porous asphalt and the right lanes were constructed with

conventional dense asphalt. After 20 years in service, the porous asphalt on this

highway is still functional. This highway is in semi arid region of Arizona with very

low rainfall similar to Rajasthan.

It is absolutely clear that the porous asphalt technology works. Ninety-five percent of

the rainwater falling on porous asphalt pavement goes to recharge the ground water.

Therefore, its effectiveness in capturing rainwater is very close to paved catchment

areas.


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Fig. 4. View during rain: driveway is dense asphalt with water ponding on it;

parking area on the right is porous asphalt with no water (Courtesy NAPA)

Fig. 5. View just after rain: parking lot in the background is dense asphalt with

water still ponding on it; parking lot in the foreground is porous asphalt

(Courtesy NAPA)


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Fig. 6. Highway in Chandler, Arizona during rain; left lanes are porous asphalt

and right lanes are conventional dense asphalt (Courtesy NAPA)

4. DESIGN, CONSTRUCTION AND PERFORMANCE OF POROUSASPHALT PARKING LOT IN JAIPUR

The Jaipur Development Authority (JDA) had planned to construct a conventional

dense graded asphalt parking lot at the Gandhi Nagar Railway Station in Jaipur. It was

decided to include an experimental porous asphalt area (about 85 m by 4 m) as part of

the large parking lot. It is believed to be the first ever porous asphalt pavement

constructed in India for rainwater harvesting.

The land where parking was developed by the JDA was initially a garbage dumping

yard. It was cleared and reclaimed to construct the parking lot to serve public at large.

Figure 7 shows the cross section of the porous asphalt parking lot on the left and thatof the conventional dense graded asphalt parking lot on the right. The two types of

parking lot pavements were divided by constructing a cement concrete partition wall

as shown in the figure.


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Figure 7. Cross sections of porous asphalt parking lot (left) and dense asphalt

parking lot (right) partitioned by a concrete wall

The porous asphalt parking lot for rainwater harvesting was designed and constructed

as follows.

Subgrade

The existing subgrade was tested for its average water infiltration capacity, which was

determined to be 46.5 mm/hour (1.83 inches/hour) which is well above the minimum

reasonable water infiltration rate of 12.5 mm/hour (0.5 inch/hour).

After removing the garbage, excess soil was excavated to the required level and grade

keeping about 150 mm (6 inches) soil to be excavated last. This was done to keep the

final subgrade relatively uncompacted from the construction equipment.

Stone filter course

It was necessary to provide a stone filter course between the finished subgrade and the

stone reservoir course so that fines from subgrade do not migrate upwards into the

stone reservoir course thereby reducing its storage capacity.

The thickness of the stone filter course was 75 mm (3 inches). The gradation of the

aggregate actually used in this course is given in Table 1; it met the AASHTO 57

gradation. The filter course was compacted lightly with a 2-ton steel wheel roller to

maintain its integrity and avoid compacting the natural subgrade.

Table 1. Gradation of Stone Filter Course

Sieve size, mm Recommended % Passing

(AASHTO 57)

Actual %

Passing

37.5 100 100

25 95-100 9512.5 25-60 36


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4.75 0-10 4

2.36 0-5 2

Stone reservoir course

The function of the stone reservoir course is to temporarily store rainwater which

percolates slowly into the natural subgrade below. The actual gradation of the cleanstone used in constructing this course is given in Table 2; it met the recommended

AASHTO 2 gradation.

Table 2. Gradation of Stone Reservoir Course

Sieve size,

mm

Recommended Percent Passing

(AASHTO No. 2)

Actual Percent

Passing

75 100 100

63.5 90-100 92

50 35-70 48

38 0-15 8

19 0-5 2

0.150 0-2 1.5

The total thickness of the stone reservoir course was 365 mm (14.4 inches). Being the

first ever porous asphalt parking lot in India, it was designed very much on the safe

side. It was laid and compacted in two lifts with an 8-ton steel wheel roller. Four

roller passes were applied in static mode and there were no roller marks. Rolled stone

reservoir course was tested for effectiveness by poring water over it from a bucket;

water disappeared from the surface instantly.

Stone choking course

The stone choking layer is placed on the stone reservoir course so as to fill and level

its open large surface voids and to make it stable and smooth for asphalt paver. It was

placed in 50 mm (2 inches) thick layer and compacted well with an 8-ton steel wheel

roller in static mode only until a smooth surface was obtained for paving above it. The

gradation of this course was same as that of the stone filter course as given in Table 1.

The finished, rolled surface was tested by pouring water over it; water disappeared

instantly from its surface.


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Figure 8. Stone reservoir course being spread over stone filter course

Figure 9. Choking stone layer in place (left) ready for laying porous asphalt;

dense asphalt completed on right side

Porous asphalt wearing course

Different blending proportions of the three aggregates available at the asphalt batch

plant were tried so that the combined aggregate met the desired range of gradation for

porous asphalt. The following proportions met the requirement: 15 mm aggregate

(60%); 10 mm aggregate (32%); and stone dust (8%).


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A trial batch of 1200 kg was made at the batch plant with 6 percent bitumen using 720

kg 15 mm aggregate; 384 kg of 10 mm aggregate; and 96 kg of stone dust. The mix

temperature was 120 C (248 F).

The sampled bituminous mix was analyzed for bitumen content and gradation by

conducting extraction test. Both dry and washed gradations were determined. Testresults are given in Table 3.

Table 3. Gradation of porous asphalt mix produced

Sieve size,

mm

Required

percentage passing

as per NAPA IS-115

Percentage

passing actual,

dry gradation

Percentage

passing actual,

wash gradation

19.00 100 100 100

12.5 85-100 82 96

9.5 55-75 60 86

4.75 10-25 18 25

2.36 5-10 9 10

0.075 2-4 1.3 3.2

Type of bitumen: Although VG-30 paving bitumen meeting IS 73 is used in

conventional paving, stiffer bitumen is needed for porous asphalt parking lot so that

(a) there is no drain down of the asphalt binder within truck when this open-graded

mix with high bitumen content is transported from the plant to the paving site, and (b)

there is no scuffing when wheels of a parked vehicle are moved with power steering.

Therefore, polymer modified bitumen (PMB) Grade 40 complying with IS: 15462was used on this project. Table 4 gives the test properties of the bitumen used.

Table 4. Properties of PMB 40 used on project

Properties Specification Measured value

Penetration at 250C, 0.1 mm 30-50 45

Softening Point,0C, min 60 60.3

Elastic Recovery of half thread ofductilometer at 25

0C, % , min

75 66.5

Flash point,0C, min 220 285

Separation , difference in softening

point,0C, max

3 1.7


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Test of residue

Increase in softening

point, C, max

Reduction of penetration at 25 C,

max.

Elastic recovery of half thread in

ductilometer at 25 C , percent, min

5

35

50

1.5

33

57

Viscosity at 1500C, Poise, min 3.9 5.4

The design bitumen content was 6.0 percent by weight of the mix. High bitumen

content is used in this open graded mix so that thicker film of bitumen is obtained to

avoid premature oxidation of bitumen. One percent liquid anti stripping agent by

weight of bitumen was used to minimize stripping. This dosage was confirmed by

conducting 24-hour static immersion test in distilled water in accordance with IS:

6241.

Three mix samples were compacted in Marshall moulds with 50 blows on each side.

The moulds containing compacted specimens were placed under water tap for testingrelative water infiltration rate. Table 5 gives the test results for information, which are

reasonable based on visual observation.

Table 5. Relative water infiltration rates for compacted porous mix

Mix sample No. Mould number Time taken for 25 mm deep

water to drain, seconds

I 1 7.60

I 2 6.45

I 3 6.25

II 1 6.27

II 2 7.45

II 3 5.90

Schellenberg binder drainage test was conducted (see guidelines for procedure) on

two different trial mix samples. Drain down of 0.12 and 0.14 percent were obtained,

which were well below the acceptable maximum limit of 0.3 percent.


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Figure 10. Schellenberg binder drainage test

Compacted Marshall specimens were tested for average bulk specific gravity (Gmb)

which was determined to be 2.070. Maximum specific gravity of the loose mix

(Gmm) was determined by ASTM D 2041 and was found to be 2.471. Air voids were

calculated from Gmb and Gmm values. Average air void content in compacted

Marshall Specimens was determined to be 16.2 percent, which met the minimum 16

percent requirement to ensure adequate permeability of the porous asphalt mix.

Although there is no requirement for Marshall Stability and flow, these tests were

conducted for information only. The average Marshall stability was determined to be

323 kg and the average Marshall flow was determined to be 4.85.

On the day of scheduled laying of porous asphalt, there was some traffic problem in

the city of Jaipur. It was not certain as to how much time the truck will take to reach

paving site within the city some 25 km away from the hot mix plant outside the city.

Considering this unforeseen problem and high temperature of the mix (120 C) it was

arbitrarily decided to lower the bitumen content from 6.0 to 5.5 percent so that there is

no bitumen drain down problem in the truck during transit. When the truck arrived at

the paving site and emptied the mix on to paver, it was observed that there was nobitumen drainage at the bottom of the truck

The porous asphalt was laid in one lift to obtain compacted thickness of 75 mm. It

was compacted with 8-ton steel wheel roller in static mode. Only four passes were

made and there were no roller marks.

Stone reservoir was provided with an overflow outlet by extending this course beyond

the porous asphalt course (Figure 14). This was done so that water does not exert any

pressure underneath the porous asphalt course in case stone reservoir course gets

choked and its storage capacity is reduced from unforeseen circumstances.


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Figure 11. Porous asphalt paving in progress over stone choking layer

Figure 12. Porous asphalt lay down and compaction


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Figure 13. Completed parking lot: porous asphalt on left and dense asphalt on

right

Figure 14. Extension of stone reservoir course at the edge of parking lot for

overflow


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Figure 15. Close up of porous asphalt pavement surface

Figure 16. Water from tanker hose readily penetrating porous asphalt surface


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Figure 17. Water from tanker hose simply flowing on dense asphalt surface

Figure 18. Relative performance of porous asphalt (right) and dense asphalt

(left) during monsoon rain in June 2013


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After the compacted porous asphalt mat cooled to ambient temperature, its general

permeability was tested by pouring water on it from a bucket. Water disappeared

almost instantly.

The parking lot was completed in October 2012. In absence of rain at that time, a

water tanker was brought in to check the relative permeability of the porous asphaltand the conventional dense graded asphalt pavements. As expected, water from the

hose pipe was rapidly penetrating the porous asphalt surface and was just flowing on

the dense asphalt surface. The comparison can be seen in Figures 16 and 17.

Later, the porous asphalt parking lot was observed during the first two heavy rains of

the monsoon season on 11 and 27 June 2013. Rainwater was almost disappearing on

the porous asphalt surface and was flowing on the conventional dense asphalt. This

relative stark difference can be seen in Figures 18 and 19. Therefore, it has been

verified in the field that porous asphalt is performing really well as expected.

Figure 19. General view of porous asphalt (right) and dense asphalt during

monsoon rain in June 2013


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It is estimated that this porous asphalt test section measuring only 85 m by 4 m would

recharge the groundwater by over 2 lakhs liters per year considering average annual

rainfall of 640 mm in Jaipur. If the whole JDA parking lot (3,545 sq m area) was built

with porous surface it would have recharged the groundwater by over 22 lakhs liters

per year9.

It is hoped public and private agencies in India would construct porous asphalt

parking lots/low-trafficked streets and roads, in areas where the groundwater level is

depleting.

5. CONCLUSIONS AND RECOMMENDATIONS

Porous asphalt pavement is one of the responses to plunging ground water table in

Jaipur and elsewhere in India. It can be integrated with the roof rainwater harvesting

system effectively and economically. According to experience in the US, properlydesigned and constructed porous asphalt pavement can last more than 20 years. Such

a pavement can be used for parking lots, recreational areas, and low-volume roads and

streets.

The first ever porous asphalt pavement in India for rainwater harvesting has been

constructed successfully by the Jaipur Development Authority in October 2012. Its

design, construction and performance have been described in the paper.

Government should encourage (and mandate in critical areas) construction of porous

asphalt pavements in urban areas. Town planners, architects and civil engineers

should be proactive by incorporating this unique rainwater harvesting system while

designing government buildings, residential buildings, commercial buildings, parking

lots and roads in new townships.

5. ACKNOWLEDGEMENTFigures 1 through 6 are courtesy of US National Asphalt Pavement Association

(NAPA). Permission given by Mr. Kuldeep Ranka, Commissioner, Jaipur

Development Authority for constructing this first ever porous asphalt parking lot in

India is appreciated.

6. REFERENCES1. Mathur, R. P. Regional Director, Central Underground Water Board. Presentation

made at the Water Resources Workshop held in Raj Bhawan of Jaipur on 4 November

2009.

2. Thelen, E. and L. F. Howe. Porous Pavement. The Franklin Institute Reserch

Laboratories, 1978.


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3. Jackson, N. Design, Construction and Maintenance Guide for Porous Parking Lots.

National Asphalt Pavement Association, Information Series IS-131, October 2003.

4. Kandhal, P. S. Presentation made at the Water Resources Workshop held in Raj

Bhawan of Jaipur on 4 November 2009 presided by H. E. Governor S. K. Singh.

5. Kandhal, P.S. A Revolutionary Technique of Rainwater Harvesting Integrated into

the Design of Buildings and Parking Lots. Water Digest Magazine, March-April

2011, New Delhi, India.

6. Kandhal, P. S. Design, Construction and Performance of Open-Graded Asphalt

Friction Courses. National Asphalt Pavement Association, Information Series IS-115,

May 2002.

7. Kandhal, P.S. and R.B. Mallick. Open-Graded Friction Course: State of the

Practice. Transportation Research Board, Transportation Research Circular Number

E-C005, December 1998.

8. Roberts, F.L., P.S. Kandhal, E.R. Brown, D.Y. Lee, and T.W. Kennedy. Hot Mix

Asphalt Materials, Mixture Design and Construction. NAPA Education Foundation,

Lanham, Maryland, Second Edition, 1996.

9. Kandhal, P.S. Role of Permeable Pavement in Groundwater Recharge. Presentation

at the Rajasthan State Workshop on Water Conservation: Issues and Challenges. Held

in Jaipur by the Centre for Science and Environment (CSE), 7 February 2013.

APPENDIX

GUIDELINES FOR CONSTRUCTING POROUS ASPHALT PAVEMENT

FOR PARKING LOTS AND LOW TRAFFICKED ROADS OR STREETS

FOR RAINWATER HARVESTING

1. Introduction

These guidelines deal with the basic outline for the design, construction and controls

needed for constructing porous asphalt pavement for parking lots and low-traffickedroads or streets for rainwater harvesting. The porous asphalt pavement shall be

constructed as per project drawings under the guidance of the Engineer.

The porous asphalt pavement consists of the following starting from the bottom

upwards: subgrade; stone filter course; stone reservoir course; stone choking layer;

and porous asphalt course. Guidelines for constructing these different courses or

layers are given below in that order.

2. Subgrade

Subgrade should be allowed to remain natural and uncompacted to maintain its

permeability. No excessive construction traffic should be permitted on the subgrade.It is advised to excavate for the desired subgrade level (at least the last 150 mm or 6


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inches) when all preparations have been made for laying the stone filter course and

the stone reservoir course.

If there are any depressions in the subgrade which need to be filled and levelled, use

permeable sand and compact it lightly.

The slope of the finished subgrade should not exceed 5 percent. In case of steeper

slope, terraced parking lots need to be considered. Subgrade soil should be such that it

can drain water within 48 to 72 hours. Infiltration capacity of subgrade soils used in

the past in the US has ranged from 2.5 mm/hour to 76 mm/hour (0.1 inch/hour to 3

inches/hour). A rate of 0.5 inch/hour is considered very reasonable. Subgrade with

clayey soils is not desirable.

3. Stone Filter Course

The stone filter course is provided between the subgrade and the stone reservoir

course so that fines from the subgrade do not migrate upwards into the stone reservoir

thereby reducing its storage capacity. It also provides some platform for laying thestone reservoir course.

Note:Although nonwoven geotextile fabric has been used between the subgrade and

the stone reservoir for this purpose, some clogging of the geotextile material has been

reported from the fines washed down on its surface.

Typically, the stone filter course is 75 mm (3 inches) thick and the following

AASHTO 57 gradation given in Table 1 is used.

Table 1. Gradation of Stone Filter Course (AASHTO 57)

Sieve size, mm Percent Passing

37.5 mm (1.5) 100

25 mm (1) 95-100

12.5 mm (1/2) 25-60

4.75 mm 0-10

2.36 mm 0-5

After spreading the stone filter course aggregate on the prepared subgrade, only light

rolling should be done with a 2-3 ton roller.

4. Stone Reservoir Course

The function of the stone reservoir course is to temporarily store rainwater which

percolates slowly into the natural subgrade below. Its AASHTO Gradation 2 consists

of large uniformly graded aggregate particles 40 mm to 65 mm (1.5 to 2.5 inches) in

size with about 40% voids to accommodate rainwater. The stone should be clean.

Desired gradation is given in Table 2.

Table 2. Gradation of Stone Reservoir Course (AASHTO No. 2)


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75 mm (3) 100

63.5 mm (2.5) 90-100

50 mm (2) 35-70

38 mm (1.5) 0-1519 mm (0.75) 0-5

0.150 mm 0-2

The thickness of this course is designed to hold rainwater during a 25-year, 24-hour

rain storm. Its minimum thickness is 230 mm (9 inches). It should empty within 72

hours. Its thickness is designed based on expected rainfall and desired structural

strength.

Stone reservoir course should be laid and compacted in 150 mm to 180 mm (6 to 8

inches) lifts and rolled in static mode only with a light roller (about 5 ton) until noroller marks are visible and it is true to the desired grade. Test the rolled stone

reservoir course by pouring water over it, water should disappear instantly from its

surface.

Note:The stone reservoir course should be provided with an overflow outlet so that in

extreme cases such as choking, water does not exert any pressure underneath the

porous asphalt course thus damaging it. Overflow can be provided by extending the

stone reservoir course like an apron by about 0.45 to 0.6 m (1.5 to 2 feet) beyond the

overlying porous asphalt pavement course. In case of kerbed parking lot, a suitable

outlet control structure with internal weir and an outlet channel or pipe should be

provided.

5. Stone Choking Layer

The stone choking layer is placed on the stone reservoir course so as to fill and level

its open large surface voids and makes it stable and smooth for asphalt paver.

Normally, it is placed in 50 mm (2 inches) thick layer and compacted well with a light

(about 5 ton) roller in static mode only until a smooth surface is obtained for paving

above it. Test the finished, rolled surface by pouring water over it, water should

disappear instantly from its surface.

The stone choking layer consists of either a clean, single size aggregate (12.5 mm) asgiven in Table 3 or AASHTO 57 gradation given in Table 4.

Table 3. Gradation of Stone Choking Layer (Alternate 1- Single Size)


12.5 mm (1/2) 100

9.5 mm (3/8) 0-5


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Table 4. Gradation of Stone Choking Layer (Alternate 2- AASHTO 57)


37.5 mm (1.5) 100

25 mm (1) 95-100

12.5 mm (1/2) 25-604.75 mm 0-10

2.36 mm 0-5

6. Porous Asphalt Course

Do notapply any tack coat before placing the porous asphalt course; it is likely to

reduce its permeability. The porous asphalt course is usually placed in 75 mm (3

inches) thickness in one lift. After compaction in the field it must have at least 16%

air voids to provide the desired porosity and permeability.

Specifications for Dense Graded Bituminous Mixes IRC: 111-2009 shall generally befollowed to produce and lay porous asphalt with the additional/special requirements

noted herein.

6.1 Gradation: It is important that the gradation given in Table 5 is strictly adhered to

obtain the desired porosity and permeability.

Table 5. Gradation of Porous Asphalt Pavement Mix


19 mm 100

12.5 mm 85-100

9.5 mm 55-75

4.75 mm 10-25

2.36 mm 5-10

0.075 mm 2-4

6.2 Type of Paving Bitumen:Although VG-30 paving bitumen meeting IS 73 is

used in conventional paving, stiffer bitumen is needed for porous asphalt parking lotso that (a) there is no drain down of the asphalt binder within truck when this open-

graded mix with high bitumen content is transported from the plant to the paving site,

and (b) there is no scuffing when wheels of a parked vehicle are moved with power

steering. Therefore a polymer modified bitumen (PMB) Grade 40 complying with IS:

15462 should be used.

6.3 Bitumen Content:Bitumen content by weight of mix should be 6 percent.

Thicker films of bitumen are necessary in the porous asphalt pavement with over 16%

air void content so that bitumen does not get oxidized prematurely in service.

6.4 Anti Stripping Agent: A suitable anti stripping agent should be mixed in theproposed bitumen. It is necessary because water will pass through the porous asphalt


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pavement. The effectiveness of the anti stripping agent should be tested with the 24-

hour static immersion test in distilled water as per IS: 6241 or 10-minute boiling test

given in Annexure A.

6.5 Mix temperature: Since the open graded porous asphalt mix contains relatively

higher bitumen content, the bitumen can drain down to the truck bed if the mixtemperature is too high. That would result in either fatty or too lean mix spots during

paving. It is recommended to make the mix in 95-120 C (200-250 F) temperature

range to minimize bitumen drain down during transportation. Establish the mix

temperature so that drain down does not exceed 0.3 percent if determined by the drain

down test given in Annexure B or C. If the drain down exceeds 0.3 percent even at

relatively low mix temperatures, increase the amount of material passing 0.075 mm

sieve but not to exceed 4 percent. Examine the truck bed after unloading the mix into

paver to confirm there is no actual drain down problem.

6.6 Mix Design: Compact the mix using aggregate gradation given in Table 5 and 6.0

percent bitumen binder by weight of mix in Marshall mould with 50 blows on eachside. Make three specimens. Allow the mix to cool completely in the moulds (in a

refrigerator if needed) before extracting the specimens without any damage.

Determine the bulk specific gravity of the compacted specimens by geometrical

measurements. Determine the maximum specific gravity of the loose porous asphalt

mix as per ASTM D 2041. Calculate the percent air voids in compacted specimens

using bulk specific gravity and the maximum specific gravity. Air voids should be at

least 16 percent to ensure reasonable porosity and permeability.

Before extracting the specimens from the moulds, conduct an approximate water

permeability check. Hold the mould containing specimen under a water tap. Water

should readily pass through the compacted porous asphalt. If not, revise the gradation

of the aggregate.

6.7 Paving and compaction: Trucks carrying the porous asphalt should be covered

with tarpaulin because the mix has tendency to cool at a faster rate. The 75 mm thick

porous asphalt should be paved in single lift and compacted promptly with an 8-10

ton roller in static mode only. Only 2-3 passes are needed to compact the porous

asphalt course. Do not use pneumatic tired roller. Too much compaction would reduce

its porosity and permeability.

Examine the truck bed after the mix has been emptied on to paver to see if there is anybinder drain down. If so, the paved surface would have either fatty spots or lean spots.

Decrease the mix temperature immediately to prevent any further drain down.

After the porous asphalt is compacted, make a permeability check by pouring water

on its surface, the water should disappear immediately. If not, there is something

wrong in terms of mix composition (bitumen content and gradation) and/or

compaction. Until this test is successful, paving work shall not proceed any further.

Do not allow any traffic on the paved surface at least for 24 hours.

7. Maintenance of Porous Asphalt Parking Lot


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Place a sign board at the porous asphalt parking lot so that its surface is not sealed by

any means in future. If needed, the parking lot can be patched lightly; not more than

10 percent of the surface area.

The parking lot should be reasonably protected from excessive wind blown soil or

sand; mud tracking from adjacent areas; and construction debris to maintain itspermeability.

Overflow outlet from the stone reservoir course should be checked periodically to

ensure it is functional.

If the permeability of porous asphalt is reduced drastically for some unforeseen

reason, it can be reclaimed , recycled and relaid,

ANNEXURE A of APPENDIX

Boiling Water Test for Detecting Presence of Anti Stripping Agent in

Bituminous Mixes (After ASTM D 3625)

This boiling water test shall be conducted at least twice at random on each day of

bituminous mix production to detect if an anti stripping agent (such as hydrated lime

or liquid anti strip) has been used in the mix in required dosage to prevent stripping of

the bituminous mix. Mix samples should also be taken at the paving site and test

conducted everyday right at the paving site.

Follow the procedure as given below.

1. Boil distilled water in a glass beaker of 1000-2000 ml capacity filled abouthalf.

2. Place about 250 grams of fresh bituminous mix into the boiling water.3. After the water resumes boiling, continue boiling for 10 minutes.4. Cool water to room temperature, decant (drain off) water, and spread the

bituminous mix on a white paper towel.

5. Examine the mix for bituminous coating. At least 95% of aggregate surfaceshould retain bituminous coating. Any thin, brownish, translucent areas are

considered coated.

6.

Reject the mix if bitumen coating is found to be less than 95 percent.

ANNEXURE B of APPENDIX

Outline of ASTM D 6390, Determination of Drain Down Characteristics in

Uncompacted Asphalt mixtures

A. Scope and Summary of TestThis method determines the amount of drain down in an uncompacted asphalt mixture

sample when the sample is held at elevated temperatures, which are encounteredduring the production, transportation, and placement of the mixture. This test is


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especially applicable to open-graded asphalt mixtures (such as open-graded friction

course and porous asphalt) and gap-graded mixtures such as stone matrix asphalt

(SMA).

A fresh sample of the asphalt mixture (either made in the laboratory or from an

asphalt plant) is placed in a wire basket. The wire basket is hung in a forced draftoven for one hour at a pre-selected temperature. A catch plate of known mass is

placed below the basket to collect material drained from the sample. The mass of the

drained material is determined to calculate the amount of drain down as a percentage

of the mass of the total asphalt mix sample.

B. Testing Equipment1. Forced draft oven, capable of maintaining temperatures in a range of

120 to 175 C with +/- 2 C of the set temperature.

2. Plates to collect the drained material3. Standard wire basket meeting the dimensions shown in Figure 1. A

standard 6.3 mm sieve cloth shall be used to make the basket. The

dimensions shown in the figure can vary by +/- 10 percent.

4. Balance readable to 0.1 gramC. Testing Procedure

1. For each mixture to be tested, the drain down characteristics shall bedetermined at two temperatures: at the anticipated plant production

temperature and at a temperature 10 C higher than the anticipated

production temperature. Duplicate samples shall be tested at each

temperature. Therefore, a minimum of 4 samples shall be tested.

2. Weigh the empty wire basket (Mass A).3. Place in the wire basket 1200 +/- 200 grams of fresh, hot asphalt

mixture (either prepared in the laboratory or from an asphalt plant) as

soon as possible without losing its temperature. Place the mix loosely

in the basket without consolidating it. Determine the mass of the wire

basket plus sample to the nearest 0.1 gram (Mass B).

4. Determine the mass of the empty plate to be placed under the basket tonearest 0.1 gram (Mass C).

5. Hang the basket with the mix in the oven preheated to a selectedtemperature. Place the catch plate beneath the wire basket. Keep thebasket in the oven for 1 hour +/- 5 minutes.

6. Remove the basket and catch plate from the oven. Let cool to ambienttemperature. Determine the mass of the catch plate plus the drained

material to the nearest 0.1 gram (Mass D).

7. Calculate the percentage of mixture which drained to the nearest 0.1 %as follows:

Drain down (percent) = (D-C)/(B-A) multiplied by 100

Where,

A = mass of the empty wire basket, gB = mass of the wire basket plus sample, g


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C = mass of the empty catch plate, g

D = mass of the catch plate plus drained material, g

8. Average the two drain down results at each temperature and report theaverage to nearest 0.1 percent.

Figure 1. Wire basket assembly for drain down test

ANNEXURE C of APPENDIX

The Schellenberg Binder Drainage Test

1. Determine the mass (A) of an empty 850-ml glass beaker, approximately 98mm diameter by 136 mm high, to the nearest 0.1 gram.

2. Pour approximately 1 kg of the mix immediately into the glass beaker aftermixing at the anticipated field mixing temperature. Re-weigh the beaker

together with mix (B) to the nearest 0.1 gram.

3. Place the glass beaker with a glass or tin cover in an oven maintained at 170 C+ 1 C for 1 hour + 1 minute.

4. At the end of 1-hour period, immediately remove the glass beaker from theoven and empty the beaker without the use of any shaking or vibration. Re-

weigh the beaker (C) to the nearest 0.1 gram.

5. Calculate the percentage of binder drain down (defined as the percentage ofmass of the mix deposited in the beaker) as follows:


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Binder Drain down (percent) = (C-A) / (B-A) multiplied by 100

LIST OF FIGURES AND TITLES

Figure 1. Schematic of porous asphalt pavement

Figure 2. Typical cross-section of porous asphalt pavement system

Figure 3. Roof rainwater harvesting integrated with porous asphalt pavement

Figure 4. View during rain: driveway is dense asphalt with water ponding on it;

parking area on the right is porous asphalt with no water on surface

Figure 5. View just after rain: parking lot in the background is dense asphalt with

water still ponding on it; parking lot in the foreground is porous asphalt

Figure 6. Highway in Chandler, Arizona during rain; left lanes are porous asphalt andright lanes are conventional dense asphalt

Figure 7. Cross sections of porous asphalt parking lot (left) and dense asphalt parking

lot (right) partitioned by a concrete wall

Figure 8. Stone reservoir course being spread over stone filter course

Figure 9. Choking stone layer in place (left) ready for laying porous asphalt; dense

asphalt completed on right side

Figure 10. Schellenberg binder drainage test

Figure 11. Porous asphalt paving in progress over stone choking layer

Figure 12. Porous asphalt lay down and compaction

Figure 13. Completed parking lot: porous asphalt on left and dense asphalt on right

Figure 14. Extension of stone reservoir course at the edge of parking lot for overflow

Figure 15. Close up of porous asphalt pavement surface

Figure 16. Water from tanker hose readily penetrating porous asphalt surface

Figure 17. Water from tanker hose simply flowing on dense asphalt surface

Figure 18. Relative performance of porous asphalt (right) and dense asphalt (left)

during monsoon rain in June 2013

Figure 19. General view of porous asphalt (right) and dense asphalt during monsoon

rain in June 2013

Design, Construction and Performance of Porous Asphalt Pavement in India for Rainwater Harvesting

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