Case Analysis from Nevada Section of Transportation's Perspective
Nowadays increasing variety of firms and companies have began to alter to the rules of sustainability in performing business and activities. These concepts also make good business sense once we try to enhance the environmental, cultural and financial value of something. The travel industry is not a different and many Departments of Travel (DOT's) have previously shifted to this by adding "Life Cycle Research" of pavements. Life circuit analysis of pavements is a thorough approach where financial costs of different alternatives during the life of a pavement are examined and the best an example may be chosen to be carried out. It really is a complicated process and varies from one DOT to some other but usually there are a few recommendations laid down by the Federal Highway Administration that are implemented.
For our research study, we have determined the Nevada Section of Transportation, also known as NDOT. This record presents a brief overview of the many components and strategies found in pavement analysis, maintenance and rehabilitation are discussed at length. NDOT has a precise Pavement Management System to gather data and the application of LCA for building of pavements was already started. The many parameters considered in LCA as well as the restrictions are reviewed in this record.
Keywords: Pavement, Life Pattern Evaluation, NDOT, Maintenance, Rehabilitation
Pavements, like any other thing, have an absolute life cycle. They may be designed by keeping a certain period of utility in mind. The constant use of roadways often brings about their degradation in their serviceability. The rate of the deterioration is dependent on many factors both environmental and weight related. Using appropriate maintenance and treatment techniques at the right time can also impact the life of an pavement drastically. The life routine of pavements can be quite broadly defined as
Stage 1: New Pavement
Newly designed pavements fall under this category. They require almost no auto repairs while used.
Stage 2: Slight Repairs
After some first time, the electricity of the highways begins to diminish. Some maintenance work is favored.
Stage 3: Major Repairs
After very long time operating the roads become lacking structurally and ongoing use of highways in this condition is not recommended.
Stage 4: Complete Reconstruction
Roads in this status of disarray aren't be used except under extreme circumstances and require a complete overhaul and development of new pavements.
However, some firms have been lagging in their work to properly preserve their roadways. It has led to one third of the highways in USA being in poor or poor condition. Annually an estimated of 70 billion dollars to keep the highway network in USA. This appreciable total has led visitors to try and take care of pavements better. Constant analysis of pavements has been followed by many express DOT's to try and limit pavement deterioration once it is in use.
There are two major categories for maintenance of pavements generally terms are
Maintenance is the procedure of repair of roads is done on a little size as the pavements contain only minimal faults and are set relatively easily. Some common maintenance techniques include fog seals and split sealing and mainly slow down the deterioration rate of the pavements .
Rehabilitation is the procedure where existing servings of destroyed pavements are completely redone as the damage is of relevance. Rehabilitation techniques include in-place recycling and overlays and reset the complete procedure for deterioration .
The cost of either maintenance or rehabilitation of pavement is substantive and ongoing to rise right now. This has lead highway firms to work with tools that will help combine economics and procedures research to attain pavements that are both affordable without compromising their long-term properties. The most frequent method in use is the life span Cycle Cost Evaluation or the LCCA . It is a process where in fact the value of the total project is calculated using the initial cost and discounted future costs over the life span of the pavement. The the different parts of LCCA is described by different DOT's individually. For this survey the situation of Nevada DOT is chosen and LCCA used by NDOT will be discussed later.
The Nevada DOT was founded in 1917 and has since built and taken care of almost 5, 400 a long way of street. There can be an additional greater than 46, 000 kilometers of public highway mostly maintained by local businesses. The roads looked after by NDOT consideration limited to 20% of highways in Nevada but these roads take into account 52% of most traffic and 82% of heavy pickup truck traffic of the state of hawaii . In the fiscal years of 2013 and 2014, NDOT spend around 270 million us dollars on maintenance treatment repair works. As you can infer from the information the procedure of keeping the roadways is costly and for that reason NDOT uses various tools that will help to reduce this cost in the long run. Some of these tools are talked about in this report.
Connecting the empirical data accumulated from the field and theoretical data calculated by an engineer in the laboratory has been one of the very most difficult task in pavement executive. Long term pavement performance has gained importance as it is a significant element of any cost analyses that is conducted on the pavements. Therefore, predicting permanent performance of pavements with good correctness can offer valuable data for pavement modeling.
Field data gathered from various sites can even be used to validate if the materials has required attributes or the look was sufficient. This may in their change help in changing future pavement designs to raised perform in the field. This has led to the creation of any Pavement Management System by pavement engineers. Data accumulated from various sites in the field is collected in the PMS and stored for further analysis by technical engineers. This collected data can be employed to build up and confirm pavement performance models
The PMS employed by NDOT was set up in 1980 which is compliance with ISTEA rules. It monitors various pavement characteristics as time passes over a mile-by-mile basis for the whole NDOT system. The data collected includes cracking, rut depth, patching, surface condition, and ride with data on traffic and damages are collected for informational purposes only.
Using the data gathered from the field seven performance signals are calculated to classify pavements into four repair categories. The performance indicators calculated are
- Rut Depth
- Present Serviceability Index (PSI)
The PSI employed by NDOT is computed by the following formula
PSI = 5*e-0. 0041*IRI - 1. 38RD2 - 0. 01(C+P)0. 5
Where IRI = International Roughness Index (in/mile)
RD = Rut Depth (in)
C = Breaking Area (feet2/1000 ft2)
P = Patching Area (ft2/1000 foot2)
For the considered pavement points are given for the severe nature and extent of each of the distress indicators. The total summation of the factors is used to assign the pavement into one of four repair categories which are
- Do Nothing
For details make reference to "Development of Pavement Performance, Analyses and Strategies" .
The PSI of pavements is held in check by performing routine maintenance and rehabilitation activities. As described maintenance as an activity only decreases the rate of deterioration while on the other hand treatment will show an initial change in PSI and may also change the rate of deterioration of pavement. Generally, one observes that the cost of maintenance of pavement is commonly lower than the expense of treatment. Therefore, if one should be cost effective there needs to be a balance between the maintenance and treatment of pavements. That's only using one kind of repair work will be more economically inefficient. NDOT has chosen specific repair activities to catalog in the condition of Nevada predicated on availability of earlier data. If a technique was chosen without sufficient performance data, then the model would be of limited use only.
The techniques thus utilized by NDOT include
Maintenance Techniques: - Rehabilitation Techniques: -
Sand Seals, Chips Seals. Flexible Overlays, Roadbed Adjustment, Mill and Overlays
Sand seal is the use of an asphalt emulsion being sprayed on with a level of clean sand or fine aggregate being embedded in the emulsion either by distributing immediately or using a pneumatic wheel roller. After program of the tire-roller extra particles are removed from the pavement. The sand seals are of help for improving the top properties of pavements and can also assist in filling any fine splits of pavement surface. Furthermore, the fine sand can also enhance the skid repellent properties of the street while reducing the chances of raveling. .
Chip seals have become one of the most used surface treatment technique for streets with less traffic. Similar to a sand seal, a chip seal is the process of spraying asphalt and applying a part of aggregate over it. The asphalt applied could be in form of hot asphalt cement, cutback or emulsified asphalt. After the application of any of the listed types of asphalt aggregate part is administers onto the top, prior to the asphalt either cools down or the emulsion breaks to be able to take full advantage of adhesion. The aggregates in the asphalt matrix are further seated and reoriented using a pneumatic roller. Afterwards the surplus aggregates are taken off the surface by use of brooming. Chip seals are being used as a coverage from further raveling as well as seal any small splits that are in the pavement. Sometimes use of light and portable aggregates is justified in chip seals where heavier aggregates might become a cause for windshield breaking. LWA are produced mainly from light vitamins like shale, slate or clay and are usually more expensive and less durable than normal aggregates but they are much lighter in weight. This light-weight stops these aggregates from being able to crack windshields in the event they become projectiles. The breaking of windshields can even be prevented by use of polymer customized emulsion .
Flexible overlay is a way of treatment wherein on top of the old structure a new intermediate part is constructed. The major purpose of this new covering is to both add an additional composition to the pavement also to prevent the proliferation of reflective breaks from the composition underneath. The old composition can still provide a uniform support. The look and planning of the overlay should be achieved keeping into consideration the expected traffic launching that the pavement will be under. As a result this system usually causes a rise in the highway account. Care also must be taken to prevent water from getting between the overlay and old framework. To prevent this the materials uses in the overlay should be analyzed for both moisture susceptibility and sturdiness .
Asphalt highways are also reclaimed using roadbed modification. This system is usually put on pavements where in fact the PSI has dropped way below desired level. Pulverization of existing pavement is performed to a depth depending after the framework of the old pavement. The pulverization process sometimes also contains bottom materials sometimes if the depth of pulverization is higher than the bituminous part. On the other hand, if the depth is lower than that of existing framework then use of cold milling can be beneficial as this will lead to nominal disturbance to the materials underneath. The materials pulverized is then blended with cement and drinking water, where it works quite simply as aggregates. This concrete is disseminate and compacted in line with the design meant. Pavements with very fragile or uneven foundations can benefit from this technique .
Mill and Overlays
The mill and overlay method is a way of rehabilitation where the top surface of the damaged pavement is removed, usually up to 2 ins. This removal is performed through a milling machine competent to perform the task. Removing the top covering comprises of the milling portion of the method and usually takes around a few days. Afterwards a fresh covering of bituminous layer is constructed on top of the structure, instead of the removed surface. The top of milled pavement is covered with liquid asphalt that serves as a tack cover between the old structure and the new bituminous coating. The structure of the overlay can take around one or two days depending upon the width of pavement and the traffic. The asphalt overlay to be put on pavement is usually embedded to a depth of 1Ѕ" using a paver .
When producing NDOT's pavement performance model three types of data were considered - Structural, Environmental and PMS. A list of factors from these categories was made that may impact pavement performance was compiled into standard data collection form. Analyzing all the standardized data the next data models were finally used when growing the model-
- Materials data of activity being modeled: These data are the types and percentages of asphalt binder and aggregates used in the maintenance or treatment activity for which the performance model is being developed.
- Materials data of existing pavement levels: These data are the types and percentages of asphalt binder and aggregates used in the levels underlaying the maintenance or rehabilitation activity for which the performance model is being developed.
- Structural data: These data include the thickness of the many tiers in the pavement framework including the width of the maintenance or rehabilitation activity that has been modeled. The structural amount (SN) as described by the AASHTO design guide was used to normalize the structural data among every one of the pavement section. Research 3 describes the technique used to convert the level thicknesses into SN ideals.
- Pavement performance data: These data include the PSI, percent breaking, and average rut depth values as from the NDOT PMS data platform.
- Traffic data: The equivalent single axle insert (ESAL) was used as the traffic component. The average daily ESAL information were from the PMS data foundation and used to obtain the cumulative ESALs over the life span of the maintenance or treatment activity.
- Environmental data: These data include maximum and least temperatures, quantity of freeze/thaw cycles, number of wet times, and total annual precipitation.
LCCA is an instrument that can be used by NDOT to judge the economic analysis of pavements when contemplating the entirety of its useful life. It requires into consideration the original costs as well as maintenance and repair cost that the pavement will probably experience in its life. This tool can be utilized by pavement technicians to boost their budget to enhance the overall useful life of the pavement. Different alternatives for repairs are believed and the main one with the most energy or least cost is chosen to be put forward for consideration. LCCA is made from the following steps-
- All original treatment alternatives must be identified
- For each option, their analysis period as well as treatment system should be determined
- The price of gross annual and each alternatives maintenance should be computed
- The economic diagnosis calculated for every option should be compared
- The choice with the best financial analysis should be selected predicated on LCCA
When executing LCCA, NDOT uses the AASHTO approved Present Well worth method. This method is highly recommended and frequently used by state highway companies. In this method, any future expenditure is converted to present value of the buck. Today's value of future expenditures is the amount of money which will need to be invested at a particular compound interest rate for the total sum to be equal to the value into the future expense. The method used in calculation is
PW = F(1/(1+i) n)
Where F = The future expense after n years
i = Discount rate
n = Quantity of years
Since the expenses of production makes on changing with time due to inflation and other monetary factors, a discount rate is chosen to compare the price across all schedules.
LCCA is conducted on the pavement for a specific analyses period. The distance of the analyses period has been computed for various types of highways keeping important factors into consideration.
Highway Class Analysis Period (Years)
High Level Urban 30 - 50
High Size Rural 20 - 50
Low Amount Paved 15 - 25
Low Volume level Aggregate Surface 10 - 20
For newly created flexible pavements NDOT advises an analysis amount of 25-40 years while for rehabilitation they recommended a period of 20 years. This data is derived from two major conditions, (a) It represents an authentic life of asphalt mixtures and (b) a couple of rehabilitation durations are contained in the period.
Pavements have a precise life pattern. Regular repair work must be done through the useful life of the pavement to maintain it to a serviceable level. NDOT uses PSI as an sign to look for the serviceability level of pavement. PSI can range between 0 to 5. 0 and repair is done over a pavement when the PSI drops below an unacceptable level. NDOT uses 2. 5 as the terminal level of PSI with streets having average daily traffic of more than 750.
NDOT also offers placed some actuality checks in place for calculating the pavement performance period. They are not considered in when in performance models because they can become an empirical check to the prices obtained from theoretical models. These bank checks include data such as traffic accidents, high maintenance costs, specific site failures, etc.
LCAA also include cost factors that encompass all the expenditure that is incurred by the pavement from the design phase till the finish of its useful life cycle. These costs have to be properly compared for different alternatives in LCCA to reach at the most monetary pavement. These costs can include
- First Costs: These include both the costs for the initial development of the pavement and the price for the functions that occurred to facilitate the structure like studies, designs and analyses.
- Annual Maintenance Costs: Included in these are the expenses that is use to keep up an most effective PSI degree of the pavement so as to provide a simple drive to the individuals.
- Road Consumer Costs: These are the expenses that are associated with driving on the road and include things such as increase in travel time, crashes, change in gasoline intake by vehicle etc.
- Salvage Value: This is the value of the street by the end of its life circuit. These casts can be either positive or negative depending on the condition of the street.
1. Pavement Interactive
2. Evaluation of pavement life circuit cost evaluation: Review and analysis
3. Point out Highway Preservation Report
4. Development of Pavement Performance, Analyses and Procedures
5. https://www. fs. fed. us/eng/pubs/html/99771201/99771201. htm
6. http://onlinemanuals. txdot. gov/txdotmanuals/pdm/flexible_base_overlay_and_flexible_base_thickening. htm
7. https://www. nevadadot. com/uploadedFiles/NDOT/About_NDOT/NDOT_Divisions/Operations/Construction/CM%20Section%206%20-%20300. pdf
8. https://www. stpaul. gov/departments/public-works/street-maintenance/mill-overlay
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