Adding Recycled Asphalt Pavements in Gravel Roads to Control Traffic Generated Dust

Abstract

As many of the developing countries Ethiopian`s road network is mostly gravel. It comprises 82.7% of the road network[g1] . Road users and residences around these roads highly exposed to the dust generated due to traffic. In the past years so many techniques of dust reduction has been applied, starting from application of water to using chemical adhesives. In this work an alternative option for dust reduction is presented. Subbase materials from Gelan-Insilale-Legedadi DS6[g2] road section and tear off asphalt pavement from Kality- Akaki road were bagged, tagged & transferred to laboratory. In laboratory in order to determine the engineering property ASTM¹ & AASHTO² standards were used. Precipitation Data from Ethiopian National Meteorology Agency, traffic count, vehicle classification of federal highway administration and laboratory test results of silt content & particle size multiplier K-value were used for adopting EPA³ dust quantification model & fugitive dust handbook equation. MINI-TAB17& Excel analyses were used to analyze the data. The result shows blending the 70% sub base with 30% RAP⁴ the dust emission was reduced by 17%. The method was also found to be both Ecological & Economical.

Key words: dust in Ethiopia, recycled asphalt pavement, dust quantification, gravel in Ethiopia

1. Introduction

According to ERA[g3] the total road network increased from 18,081 km in 1992 G. C increased to 52,896 km in 2011 G.C. from these roads 82.7% of all the roads are gravel roads, which is Design Standard 6 (DS6)⁵ and Rural Road 50 (RR50)⁶ roads (Organizational background of ERA⁷ docR.pdf). This paper reports is a part of a research project that aims to determine the effect of adding reclaimed asphalt pavement in gravel roads in order to reduce fugitive dust generated due to traffic.

The top problems associated with gravel roads is escapee of dust & loss of fine particles. The Ethiopian roads also suffer from these problems.

The main adverse impacts of traffic-generated dust from gravel roads are:

- Damage to the health of road users and nearby residents
- Reduced production from agriculture
- Increased risk of accidents for road users
- Increase in environmental damage through pollution
- Deterioration in road condition
- Increase in vehicle operating costs (Tony Greening, 2010).[g4]

The addition of recycled asphalt pavement to surfacing gravel does improve the performance of the surfacing gravel. It appears that fibers[g5] in ground pavement help to bind the materials that pass the 100 sieve in a sieve analysis in the gravel. This binding effect helps it to limit corrugation caused by acceleration and deceleration of vehicles. The Asphalt recycled shingle material is easy to handle. It can be blended uniformly with a loader or motor grader (Ksaibati, 2010).

The use of these materials is not very common however their application to treat unpaved roads is increasing during the last 10 years (Thomas J. Wood, 2014) .

Several open dust emission factors have been found to be correlated with the silt content (< 200 mesh[g6] ) of the material being disturbed. Dust emissions from unpaved roads have been found to vary directly with the fraction of silt (particles smaller than 75 micrometers [µm] in diameter) in the road surface materials (Handbook).[g7]

Conservative estimates of the dust generated on unsealed roads have been made using the United States Environmental Protection Agency (EPA) AP-422 dust prediction model (Equation1) (Jones, 2011).

Abbildung in dieser Leseprobe nicht enthalten

Where,

E = emission factor in kg/vehicle km

k = particle size multiplier (Jones, 2011)

s = silt content (<0.075 mm) of surface material (%)

S = average vehicle speed (km/h)

W = average vehicle weight (tones)

w = average number of wheels

p = mean annual days with rainfall greater than 0.25 mm (Jones, 2011) .

The Dust D generated per annum is calculated using the following equation:

Abbildung in dieser Leseprobe nicht enthalten

Where,

D= dust generated in Kg per annum

E= emission factor in Kg/vehicle Km

Vpd =vehicle per day of the given road section (Handbook) .

For the daily basis, Equation one becomes: (EPA, 2006)

Abbildung in dieser Leseprobe nicht enthalten

Where,

Where k, s and W, are as defined in Equation one and

Eext = annual or other long-term average emission factor in the same units as k [g8] ,

P = number of "wet" days with at least 0.254 mm (0.01 in) of precipitation during the averaging period,

N=number of days in the averaging period (e.g., 365 for annual, 91 for seasonal, 30

For monthly) (EPA, 2006)

For the hourly basis, equation one becomes: (EPA, 2006)

Where,

K, s and W a re as defined in Equation 1 and

E ext = annual or other long-term average emission factor in the same units as k [g9] ,

P = number of hours with at least 0.254 mm (0.01 in) of precipitation during the

Averaging period, and

N = number of hours in the averaging period (e.g., 8760 for annual, 2124 for season 720 for month)

Table1- 1 particle size multiplier (Cowherd, 2006)

Abbildung in dieser Leseprobe nicht enthalten

The oral data collected from different ERA regional directorates show that the Authority generated 306,252.28 cubic meters tear off asphalt pavement within the last five year which was removed and replaced with new Asphalt Concrete during upgrading projects (Officers, 2015).

This report consists of five chapters structured in such a way that a detailed clarification of the thesis based on the outlined methodology. In the first chapter a general introduction is presented with the description of recycled asphalt shingle, objective and scope of the study. The second chapter presents a literature review of related works. In Chapter three the methodology & materials of the study are presented. The results & discussion of the study are presented. The last chapter presents conclusion and recommendation for future works.[g11]

1.1 Problem statement

As the volume of traffic on unpaved roads in Ethiopia increases with increased economic development, dust loss and surface distresses will continue to rise. It would make sense to pave some of these roads, but due to the current economic issue it is not easy to afford for these expensive operations, especially when the future volume of these roads are unknown. An alternative option needs to be explored that will reduce dust loss.

1.2 Research objective

The objective of this thesis is to determine the effect of employing reclaimed asphalt pavement to gravel roads for dust reduction.

1.3 Research question

- How can we apply this stabilization mechanism in our country?
- How can we quantify the dust generated due to traffic on this road?
- What is the effect of adding recycled asphalt pavement to the surfacing material of gravel roads?[g12]

1.4 Scope

A laboratory test was conducted to establish the engineering properties of the sub base materials, blends at 30% RAP⁸ blend&50 % RAP blend. The gradation &binder content of the Re-claimed asphalt pavement is also determined. EPA model& Fugitive dust hand book emission formulas was employed for dust quantification purpose. For result analysis & computations Excel &MINI-TAB analysis employed.

1.5 Limitation of the study

- The EPA model & fugitive dust hand book emission equation, developed by United States Environmental Protection Agency was adopted directly without any calibration.
- The rheological properties of the Reclaimed asphalt pavement sample was not established[g13]

2. Materials and Methodology

2.1 Materials

The objective of the thesis was to explore the application of recycled asphalt pavement in gravel roads to reduce dust loss from gravel roads. To accomplish this objective, field data collected &laboratory experiments were conducted in TCD⁹. The reused asphalt pavement was obtained from Maseltegna area, Kality –Akakiy road which was tear-off waste during road maintenance. Gelan-Inslale-Legedadi road is DS6 gravel road, which is located around the capital city (Addis Ababa) and constructed by Oromia roads construction Enterprise, the supervision was under the consultancy service of Oromia Water Works Design and Supervision office under the Regional State of Oromia. Traffic count done on this road for Seven days starting from 4th of May to 10th of May 2015 from 1:00 pm to 2:00pm, of the road shows that, the major deterioration factor for this road as most of the gravel roads is the traffic volume on the road, which is the main reason for the dust generate on the road. The road was constructed to provide access for the newly constructed factories &a new sewage plant constructed around Lege-tafo, for the city of Addis. Hence it is vulnerable to heavy trucks, which is the main cause of dust emission on this road. The sub-base[g14] material was taken from Gelan–Insilale-Legedadi DS6 (Design standard 6) gravel road construction project.

Reused asphalt pavement from Maseltegna area (top asphalt surface is removed from existing road to resurface) is taken and tested in the laboratory in order to establish they`re Engineering properties. From the traffic count we can understand that the pavement along this section is vulnerable to repeated loads &the traffic is congested, hence the causes of this pavement failure might be rutting. Therefore, the tear off pavement that is bagged and transported to laboratory might be less stiff. However, for the purpose of this paper only extraction of the sample is desired. After determining the engineering properties of these materials, two samples of blend prepared. The first blend was 50: 50 mix ratio of sub base [g15] and reused asphalt pavement, the quarry site.

Tear off asphalt pavement from Maseltegna area (top asphalt surface is removed from existing road to resurface) is taken and tested in the laboratory in order to establish their Engineering properties.

From the traffic count we can understand that the pavement along this section is vulnerable to repeated loads & the traffic is congested, hence the causes of this pavement failure might be rutting. Therefore, the tear off pavement that is bagged and transported to laboratory might be less stiff, however for the purpose of this paper only extraction of the sample is desired.

After determining the engineering properties of these materials, two samples of blend prepared. The first blend was 50: 50 mix ratio of sub base and reused asphalt pavement, the second blend was 70% sub base and 30% reused asphalt pavement. After the extraction test performed the reused asphalt pavement was crushed in to pieces using miller in laboratory.

2.2 Methods

The samples of the materials were bagged, tagged and transferred to TCD (Transport Construction &Design Share Company) materials testing laboratory to be properly tested. Lab technicians performed extraction test on the sample of tear off asphalt pavement. From this test the gradation and binder content and specific gravity are determined. The data collected for this study include traffic count, vehicle weight from Federal Highway Administration (FHWA)¹⁰ of the United States vehicle class classification, and meteorological data from National Meteorology Agency for the project location site the average number of wheels for each type. The Average vehicle speed was calculated by taking 0.5km of the road section &stop watch, based on SI unit formula Speed= distance/time. The silt content (s) &the particle size multiplier K-value is taken from laboratory result. The S value of sub grade material 12% the 50:50 blend8% and 70:30 blend 10%. The precipitation data from National Meteorology Agency for the project location site for the past10 years were taken to determine the average number of days in which the P value is greater than or equal to 0.25mm. From the data the average number of days in which the P-value>=0.25 mm was calculated to be 16.55 days, for the year 2014/2015. The average was calculated from September 2014 to –August 2015. The AADT of Gelan –Insilale- Legedadi road was found to be 197. This value will be applied for dust quantification of Gelan-Insilale road section based on EPA model.

The Average vehicle speed was calculated by taking 0.5km of the road section & stop watch, based on SI unit formula Speed= distance/time.

The average number of wheels also calculated based on observational study, for the four vehicle classes.

The silt content (s) & the particle size multiplier K-value is taken from laboratory result. The s value of sub grade material 12% the 50:50 blend 8% and 70:30 blend 10%. The reduction of the silt content implies the reduction of fugitive dust due to traffic.

Table 2- 1 Average Number of wheels on each day of traffic count on Gelan-Insilalae-Legedadi road[g16]

Abbildung in dieser Leseprobe nicht enthalten

The K-value of the sub base material was determined to be 0.014, the 50% sub base and 50% RAP blend was found to be 0.013 and that of 70% RAP blend was found to be 0.014.

Abbildung in dieser Leseprobe nicht enthalten

Figure 3- 1 Laboratory pavement crushing miller[g17]

Various tests were performed on the sub-base material to determine the desired characteristics of a given material: gradation, Atterberg limits, shrinkage limit, MDD ¹¹ (Maximum Dry Density), CBR¹² (California bearing ratio), OMC¹³ (Optimum Moisture Content) along with the percentage of particle size distribution.

The strength of the sub base material is the main factor that determines the thickness of the flexible pavements for roads and airfields. The strength is expressed in terms of California Bearing Ratio test. For this thesis three point method CBR is employed according to AASHTOT-180& 99 procedures.

Three cylindrical metal moulds, i.e. CBR moulds, having a nominal internal diameter of 152mm and height 127mm. The moulds fitted with a detachable base plate & removable extension. The internal face is smooth, cleaned & dried before the materials were compacted with rammer of 2.5kg & 4.5kg.

The consistency of the materials is determined using Atterberg`s limit. The liquid limit is determined using Casagrande`s liquid limit device & plastic limits using porcelain evaporating dish with other lab equipment for the test.

The plasticity index (PI) is numeric difference of liquid limit & plastic limit: PI= LL-PL, is then determined based on AASHTO T-89& 90 Procedures.

Hydrometer method combined with wet sieve enable a continuous particle size distribution curve of a soil to be plotted from the size of coarsest particle down to the clay sizes.

This method covers the quantitative determination of the particle size distribution in a soil from the coarse sand to the clay size by means of sedimentation. The test is based on AASHTO T-88 procedures. Based on the laboratory test the specific gravity becomes 2.53 for the sub base material, it increase to 2.63 when 30% RAP is employed & increase to 2.65 when 50% RAP is employed.

Solvent extraction was applied for extraction test. Sodium hexa met phosphate was applied to separate the binder (Bitumen) from the aggregate according to AASHTO T-164.

3. Result & Discussion

Following the data collection described in the previous chapter the analysis & discussion is based on, descriptive analysis, MINITAB 17, Excel & (EPA) AP-42[2] equation 1.

Abbildung in dieser Leseprobe nicht enthalten

Based on this data the result (output) then used to compare the dust generated (D), per annum for sub base only and the blends based on the formula developed by fugitive dust hand book presented as follows:

Where,

D= dust generated in Kg per annum

E= emission factor in Kg/vehicle Km

Vpd =vehicle per day of the given road section (Handbook) .

Vpd is calculated for the whole road section i.e. 38 km, therefore Vpd =AADT¹⁴ *38 km

Finally cost comparison between sub base surfacing material and blends will be discussed.

[...]

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¹ American Society for Testing &Materials

² American Association of state highway & transportation officials

³ Environmental Protection of Agency of the United States

⁴ Recycled Asphalt Pavement

⁵ Design Standard 6

⁶ Rural Road 50

⁷ Ethiopian Roads Authority

⁸ Recycled Asphalt Pavement

⁹ Transport Construction Design share Company

¹⁰ Federal Highway Administration

¹¹ Maximum Dry Density

¹² California Bearing Ratio

¹³ Optimum Moisture Content

¹⁴ Annual Average Daily Traffic