Benefit-cost analysis and application of intelligent compaction for transportation

Accepted Manuscript Benefit-Cost Analysis and Application of Intelligent Compaction for Transportation Christopher M. Savan, Kam W. Ng, Khaled Ksaibati PII: DOI: Reference:

S2214-3912(16)30036-8 http://dx.doi.org/10.1016/j.trgeo.2016.07.001 TRGEO 90

To appear in:

Transportation Geotechnics

Received Date: Revised Date: Accepted Date:

17 March 2016 27 April 2016 6 July 2016

Please cite this article as: C.M. Savan, K.W. Ng, K. Ksaibati, Benefit-Cost Analysis and Application of Intelligent Compaction for Transportation, Transportation Geotechnics (2016), doi: http://dx.doi.org/10.1016/j.trgeo. 2016.07.001

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Benefit-Cost Analysis and Application of Intelligent Compaction for Transportation Christopher M. Savan EIT, M.S.; Project Engineer, GDA Engineers; 502 33rd Street, Cody, WY, 82414, USA. Ph: (949) 292-7126; [email protected]

Dr. Kam W. Ng (Corresponding Author) Assistant Professor, Corresponding Author, Department of Civil and Architectural Engineering, University of Wyoming, Dept. 3295, 1000 E. University Ave, Laramie, WY 82071, USA. Ph: (307) 766-4388; [email protected]

Dr. Khaled Ksaibati Professor, Department of Civil and Architectural Engineering, University of Wyoming, Dept. 3295, 1000 E. University Ave, Laramie, WY 82071, USA. Ph: (307) 766-6230; [email protected]

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ABSTRACT Conventional test methods for roadway compaction cover less than one percent of roadway; whereas, intelligent compaction (IC) offers a method to measure 100 percent of a roadway. IC offers the ability to increase compaction uniformity of soils and asphalt pavements, which leads to decreased maintenance costs and an extended service life. This paper examines IC technology, how IC quality control and assurance specifications can encourage IC adoption, knowledge and use of IC through survey responses, and benefits and costs of IC. The surveys reveal that a majority of respondents from state departments of transportation have conducted IC demonstration projects, but questions about cost and willingness of policymakers to adopt IC remain a barrier to implementation. The benefit-cost analysis demonstrates that use of IC reduces compaction costs by as much as 54 percent and results in a US$15,385 annual savings per 1.6 kilometer throughout the roadway’s life. The framework of the benefit-cost analysis can be readily adopted by transportation agencies to facilitate the implementation of intelligent compaction in future roadway construction.

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Keywords: Intelligent Compaction Benefit-Cost Roadway Construction Application

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1. Introduction Intelligent compaction (IC) has become a growing method for measuring soil and pavement compaction for roadways in the United States over the past decade. The integration of an accelerometer, global positioning system (GPS), and on-board computer to an IC roller has allowed for 100 percent compaction measurement of a roadway versus less than one percent using conventional compaction measurement devices (Mooney et al. 2010). Many industry professionals and organizations, including the United States Federal Highway Administration (FHWA), have noted the benefits of intelligent compaction in academic papers and industryoriented magazine articles (Federal Highway Administration 2013; Beainy et al. 2012). However, a literature review of the benefits and costs of IC by Savan (2014) revealed that there is little quantifiable evidence to support the claim of increased long-term or short-term cost savings by using IC. While it is generally accepted that the improvement of compaction quality using IC would enhance long-term roadway quality, there are no investigations that examine the financial return of improved compaction quality. This paper examines the construction-related costs and roadway lifecycle costs from use of IC. A brief discussion of survey results of professionals in the State of Wyoming and other state Departments of Transportation (DOTs) regarding IC are also included. A background of IC is provided in the first section of this paper with information about the implementation of IC by state DOTs. Surveys of Wyoming professionals and DOTs were conducted to provide information about the knowledge that professionals have about IC, perceived barriers to implementation of IC, and how IC is being implemented. A benefit-cost analysis is presented indicating the short-term (construction-based) and long-term (pavement lifecycle) benefits and costs when performing compaction with IC. 4

2. Background Intelligent compaction (IC) rollers provide a method to gather compaction data for 100 percent of the roadway area by measuring soil and pavement stiffness. IC rollers, also known as “intelligent soil compaction systems,” are defined by the National Cooperative Highway Research Program (NCHRP), Report 676 as having three characteristics (Mooney et al. 2010): 1. Continuous assessment of mechanistic soil properties (e.g. stiffness) through roller vibration monitoring, 2. On-the-fly modification of vibration amplitude and frequency, and 3. Integrated GPS to provide a complete geographic information system-based record of the site. Rollers that integrate items one and three from the above definition are also considered IC rollers by several roller manufacturers, but are referred to as “roller-integrated continuous compaction control” in the NCHRP report (Mooney et al. 2010). These types of rollers will be referred to as IC rollers throughout this paper. FHWA has been promoting IC via its Every Day Counts initiative. The initiative supports local workshops, demonstration projects, development of standard IC specifications, and additional technical assistance for state and local governments to implement IC. State and local transportation agencies are seen as the catalyst to adoption of IC because they provide contractors with Quality Control/Quality Assurance (QC/QA) specifications for compaction of roadways. Quality control is referred to as the method for testing compaction parameters, such as density and moisture content, by construction crews to verify the quality of the roadway; whereas, quality assurance is referred to as the validation of quality control methods and data through additional compaction testing. 5

A literature review on current state DOT’s draft IC specifications indicates that state and local transportation agencies continue to require conventional compaction testing methods even if IC guidance is provided for roadway soil and pavement compaction. For example, California Department of Transportation (Caltrans) uses a combination of nuclear gauge readings and core sampling for pavement QC/QA; however, their draft IC specifications are not used system-wide. Similarly, Minnesota DOT (2016) has created special provisions for IC and has conducted several field demonstrations over the past decade; however, permanent specifications have not been integrated into their standard specifications manual. Texas, Michigan, and Iowa have developed special provisions for soils, but do not include QC/QA parameters for acceptance. Currently, 18 states, as shown in Fig. 1, have begun adopting IC QC/QA draft specifications and special provisions that may be reviewed for adoption into their standard specification manuals. More states are expected to begin drafting QC/QA specifications as more workshop and field demonstrations are scheduled. Fig. 1 displays the types of QC/QA specifications drafted by states. These draft specifications range from special provisions to comprehensive specifications for statewide roadway construction for soils/aggregates and pavements (The Transtec Group, Inc. 2014). The specifications detailed requirements for GPS data, documentation, test sections, and construction QC/QA. The two types of outcomes for the specifications involved reporting compaction value results for QC/QA or providing documentation of IC data for demonstration purposes. For soils, specifications used for QC/QA involved acceptance based on percent difference in measurement values (MVs) between roller passes and/or correlation of IC MVs with in-situ point measurements to establish IC target values. Georgia, Indiana, North Carolina and Vermont required correlations from test trips between in-situ point measurements and MVs. 6

Georgia also required an optimal pass number established when there was a less than five percent change in MVs. The remaining states’ IC specifications did not provide more detailed QC/QA specifications for soils (The Transtec Group, Inc. 2014). For pavements, most states have QC/QA specifications that establish a target number of roller passes by percent difference in MVs followed by establishing target values for MVs based on correlations of nuclear gauge or core samples on a test section. The exceptions to these specifications are Iowa, Nevada, Utah, and Rhode Island, which do not detail a method or requirements for compaction values (The Transtec Group, Inc. 2014). Despite having field demonstrations, pilot projects, technical training and workshops, and development of specifications and special provisions for IC, results of interviews with industry professions by Kimmel et al. (2016) revealed that these institutional incentives for IC were not the primary drivers for adoption. They examined the assessment and adoption of IC through the application of Kingdon’s theory of policy agenda setting. They concluded that the roadblocks to IC and its adoption were related to the conservative culture of individuals whose personal character, ideological affiliations and perception of social obligation inhibit changes. The positive outcomes of the benefit-cost analysis presented in this paper will hope to increase the risk tolerance and perseverance of these professionals who are willing to provide an opportunity for IC adoption and implementation. 3. Surveys Surveys of Wyoming professionals and DOTs were developed by the authors to understand the current knowledge of IC among professionals, perceived barriers to implementation of IC, and how IC is being implemented. The Wyoming survey was conducted in March, 2014 for public and private officials attending the Intelligent Compaction Data Management workshop 7

sponsored by the FHWA in conjunction with the Wyoming Department of Transportation (WYDOT) and the Wyoming Local Technical Assistant Program (WY LTAP). Fig. 2 is a photo of the workshop. The workshop included an overview of IC technology, types of IC QC/QA programs, and how to use VEDA software with QC/QA data. VEDA is a map-based tool originally developed for the Minnesota DOT by the Transtec Group, Inc. for viewing and analyzing geospatial data collected from various IC machines. VEDA has been recently updated to Veta 3 which can be downloaded from the IC website managed by The Transtec Group, Inc. (http://www.IntelligentCompaction.com/veta)

or

Minnesota

DOT

website

for

Veta

(http://www.dot.state.mn.us/materials/amt/veta.html). The Wyoming survey had 79 total respondents, of which 69 were employed by WYDOT, seven by private firms, and three by local governments. The DOT survey was conducted online from September through November 2014 and sent to representatives of all state DOTs in the United States. There were 32 respondents from the states shaded in gray in Fig. 3. The Wyoming survey results revealed that respondents were receptive to the idea of intelligent compaction but had a limited knowledge of and concerns about IC. Fifty-one percent of respondents said that they had heard of IC prior to the workshop. Among many concerns with IC, Table 1 indicates that the most notable concern was cost. Concerns about costs could be related to the limited amount of independent research conducted between the costs of IC compared to conventional compaction. Despite the concerns listed in Table 1, 70 percent of respondents thought that IC should be adopted in Wyoming while 26 percent were not sure and 4 percent did not respond. The DOT survey revealed information about how IC is applied in each state and what DOTs know about the associated benefits and costs with IC. DOTs indicated that they primarily use 8

nuclear gauge, proctor tests, and sand cone tests for soils and aggregates for QC/QA. Also, they primarily use nuclear gauge and core sampling for pavements. However, states are starting to integrate IC into their QC/QA programs. Table 2 lists DOTs’ statuses with IC QC/QA which chose to respond to the question. While several DOTs are in the process of implementing or considering IC, the amount of data on costs is very limited. Ten respondents indicated that they observed increases in construction related costs when using IC; however, this increase can be associated with the increased costs associated with training roller operators and not being able to take advantage of economies of scale, especially when only one or a few demonstration projects are conducted. Long-term benefit and cost data were less available with only three respondents (from Alaska, Texas, and Utah) indicating that they had information. Of these respondents, the respondent from Texas, who noted that Texas DOT had conducted eight IC projects in the past six years, indicated with a qualitative response that IC projects had “higher benefits than costs.” The next section provides an analysis of the benefit and costs associated with IC. 4. Benefit-Cost Analysis The FHWA has cited reduced construction and maintenance costs as a feature of IC rollers (Federal Highway Administration 2013); however, limited benefit-cost data is available to validate this claim. This is echoed by Wyoming professionals, whom indicated that the cost of IC was their largest concern and state DOTs, whom responded that cost was a concern. To address the prominent concern of cost, a framework for a benefit-cost analysis was developed based on costs for construction of a roadway and savings from improved compaction uniformity over the pavement lifecycle. The framework is illustrated using two case studies: a thick (five to ten-cm) asphalt overlay, and a new roadway section that includes soil and pavement layer compaction. 9

The methodology to obtain cost data includes two specific cost cycles: construction and roadway life. The summation of the cycle costs are to be compared between two compaction methods: conventional compaction and testing versus IC compaction. Sensitivity analysis is also provided for each case study in order to further analyze costs where there are few data points for inputs. 4.1 Methodology The methodology used for analysis takes into account construction costs and roadway lifecycle costs as two separate time periods. Definitions for the time periods and compaction types are presented first. The framework for analyzing the differences between the conventional and intelligent compaction types is then presented for each time period. 4.1.1 Definitions The definitions below provide an outline for types of costs that would be defined within each time period and type of compaction. Construction Cycle Cost: The construction cycle includes the time period that begins with the preparations for conducting roadway compaction. This encompasses the costs for rollers, labor to operate the rollers, and conducting QC/QA testing. Roadway Lifecycle Cost: The roadway lifecycle means the expected service life of the roadway. The costs per year for conventional compaction and IC are calculated based on the capital cost of the roadway improvement divided by the service life of the roadway in years. Pavement maintenance costs are not considered in this study because the type of maintenance is highly dependent on the transportation agency and roadway characteristics. Also, the maintenance schedule and its associated cost will expect to alter if not prolong the service life of a pavement. This inclusion will complicate the direct comparison between conventional compaction and IC. For these reasons, the authors chose a conservative approach to estimate the roadway lifecycle 10

cost. If a transportation agency would like more detailed data for a specific roadway, they may opt to add their projected maintenance schedule with related costs to this analysis in order to project specific lifecycle costs. Conventional Compaction and Testing: Conventional compaction means any method of compaction used by contractors to perform roadway compaction and subsequent QC/QA methods that does not use a roller equipped with on-board stiffness or density measuring devices. QC/QA data is obtained by in-situ field tests. IC Compaction: IC compaction means the compaction of a roadway section by use of a device, such as one defined in the FHWA QC/QA sample specifications for IC, attached to a roller that allows for the measurement of soil stiffness. Generally, this includes the use of an accelerometer, GPS unit, and on-board computer to aid roller operators in compaction efforts. QC/QA data is obtained from the roller and is analyzed by a QC/QA technician or engineer (Federal Highway Administration 2014). 4.1.2 Framework The comparison between the two compaction methods is comprised of a summation of the costs from the two cost cycles over similar construction lengths and roadway lifecycles. The summed costs for each time period are compared to each other independently. In order to illustrate the framework, a project type and size must be chosen. The first case study is a project with a thick, 1.6 lane-kilometer (i.e., one lane-mile) asphalt overlay. The second case study is a new construction of a 1.6 lane-kilometer (one lane-mile) section, which includes subgrade compaction. This framework not only can be applied to new road construction but also can be applied to different types of roadway improvements, including reconstructions, so long as the data for each type of improvement is gathered and used accordingly. 11

Construction Cycle: Construction costs regarding roller equipment and labor for conventional compaction are gathered using pricing data from contractors. The costs are set as an hourly rate so that they can be used for different types of projects if necessary. A rate of compaction for construction crews can also be obtained from the contractors. The rate should yield an area per unit time period, for example 557 square meter per hour (6,000 square feet per hour). This allows for calculation of the amount of time that it would take a construction crew to complete the type of work that is being analyzed. This amount of time is then multiplied by the roller equipment and labor costs for each type of compaction as illustrated by Equation 1. Construction Cost = (Compaction Time in Hours) × [(Roller Cost per Hour) + (Roller Operator (1) Cost per Hour) + (GPS Cost per Hour)] + [(QC/QA Cost per Area) × (Area)]

Construction costs for IC were calculated based on a reduced amount of time to perform roller operations and the cost of an IC roller. The IC roller cost may be available from contractors, but if it is not, it should be obtained from IC roller manufacturers. The roller manufacturer chosen for a specific analysis should be based on similarities to the conventional roller used, such as setup (drum roller number and type), weight, and vibratory characteristics. In order to calculate the number of hours for compaction using IC, a 30 percent reduction in the number of hours it would take a conventional roller is applied, which is given by Equation 2. The reduction was based on the number of roller passes from IC rollers compared to conventional rollers to perform similar compaction work as observed by Briaud and Seo (2003). The test section area, used for QC/QA purposes, must be added into the amount of time needed for compaction using the IC roller. The total time required for compaction of the test area and the 12

roadway section is then multiplied by the hourly rates for labor and equipment to obtain the cost as demonstrated in Equation 3. IC Hours = (Conventional Compaction Hours for Roadway Section + Conventional Compaction (2) Hours for Test Section) × (100% – IC Efficiency %)

Cost per Line Item = (Hourly Rate of Line Item Cost) × (Hours)

(3)

The QC/QA program costs are also part of the total construction cost. The information for conventional compaction and testing can be obtained by surveying contractors on their costs related to QC/QA. Contractors may provide this information with equipment and labor costs separated or combined. The costs will be in either an hourly or unit area rate, such as square meters. In order to calculate the QC/QA program costs from hours, the rate of QC/QA performance must be converted using a time per unit volume or area as given by Equation 4. QC/QA Cost = (Hours to perform QC/QA) × (Area of QC/QA per hour) × (Cost of QC/QA per (4) area)

The calculated unit volume or unit area can then be converted into a total cost based on the size of the roadway being analyzed. The cost for the QC/QA program for intelligent compaction is then multiplied by the test section area divided by the total project area. QC/QA is provided on the test section area in order to correlate MVs with conventional testing methods, such as nuclear gauge or core sampling. The area used can vary depending on the project but is often between 91.5 to 183 m (300 to 600 feet) (Mooney et al. 2010) and several DOT IC specifications (The Transtec Group, Inc. 2014). Fig. 4 is a flow chart for calculating the cost of each type of compaction based on the equations and description of calculations. 13

Roadway Lifecycle: One of the largest benefits provided by IC is that it provides a more uniform compaction. Uniformity translates into an extended pavement life. The effects of compaction uniformity on pavement performance based on the Bomag IC were studied by Xu et al. (2012). Three-dimensional finite element model was built to simulate pavement responses using heterogeneous hot mix asphalt moduli obtained from a field IC measurement. These responses were input into the mechanistic-empirical pavement design guide (MEPDG) model to estimate pavement performances in terms of rutting and fatigue life. Results of the case study from the Indiana IC project revealed that the mean value of fatigue lives for the heterogeneous pavement model is 38.2% of those for the uniform pavement model. In other words, a uniform pavement achieved using IC will have a longer fatigue life than that of a conventionally compacted pavement by a factor of 2.6 (i.e., a reciprocal of the 38.2% = 100%/38.2%). When the pavement performance is described by its fatigue life, it is reasonable to claim that the service life of the uniform pavement through IC will be similarly increased by a factor of 2.6. In order to calculate the benefit from using IC, the cost per 1.6 lane-kilometer (one lane-mile) for asphalt overlay was calculated by multiplying the asphalt overlay thickness to asphalt construction cost per unit area for the total 1.6 lane-kilometer. The cost of roadway for asphalt overlay was divided by the remaining service life improvement to the roadway as given in Equation 5. The average cost per 1.6 lane-kilometer (one lane-mile) and remaining service life improvement should be obtained from a DOT or local municipality. Otherwise, the increase in remaining service life from IC can be similarly assumed at 2.6 times (260 percent) the conventional compaction method as suggested in this study. Understanding this suggested increase in service life was obtained from one study (Xu et al., 2012), a sensitivity analysis was presented in Section 4.2.4 to illustrate the effect of different service lives on associated lifecycle cost savings. 14

Cost per 1.6 lane-kilometer per year =


     .          

(5)

4.2 Case Study No. 1: Pavement Analysis The cost comparison between the two compaction methods is comprised of a summation of the costs from the two cost cycles over similar construction lengths and roadway lifecycles. To illustrate the application of proposed benefit-cost analysis framework, a case study of a thick, 1.6 lane-kilometer (one lane-mile) overlay asphalt pavement was presented. Table 3 contains the data inputs used for the analysis, which are discussed in more details in the subsections. 4.2.1 Construction Cycle Data The construction cycle costs for conventional compaction were gathered from a survey of contractors performing compaction services in Wyoming. The data used was the cost of a roller, roller operator, and GPS system per hour. These data were obtained from roller manufacturers, a phone survey of Wyoming contractors, and GPS system providers (Jones 2014; Bastian 2014; Newman 2014; Trimble Navigation Limited 2014). Also, QC/QA data were based on local contractor information (Bastian 2014). The summation of these data was used to create a cost per 1.6 lane-kilometer (one lane-mile) for the construction of a five to ten-centimeter (two to fourinch) thick asphalt overlay as given in Equation 1. Where data was given in ranges, a value within the range was assumed in order to create comparable data between the two compaction types. Also, the hourly rate for the roller operator was assumed to be the same for each type of roller. The cost of intelligent compaction was then calculated using a 30 percent reduction in the number of hours it would take a conventional roller. The reduction was based on the number of roller passes from IC rollers compared to conventional rollers as observed by Briaud and Seo (2003). It is important to note that the 30 15

percent was suggested based on one study. A sensitivity analysis presented in Section 4.2.4 shall be similarly performed to investigate the impact of different compaction efficiency on the construction cost estimation for IC. The time to compact the 152-meter by 3.7-meter (500-feet by 12-feet) test section area for establishing MV correlational to conventional compaction testing was added. QC/QA costs for IC were reduced to the area of the test section required to calibrate conventional testing methods with the IC’s measurement values. The cost of QC/QA testing was then multiplied by lineal meter of the test section, 152 meter, divided by the lineal meter in 1.6 kilometers which resulted in a multiplier of 0.095. Equation 6 is the cost of QC/QA for IC based on the conventional compaction QC/QA cost. This can also be described as the test section being 0.095 times the lineal length of 1.6 kilometer (one mile). VEDA software allows for instantaneous determination whether data complies with QC/QA standards. An initial expense to program QC/QA compliance into the software and train QC/QA engineers to use the software are required; however, it would not be a significant contributor to cost to a single project when averaged over several compaction projects. 3       45

QC⁄QA Costfor IC = QC/QA Cost of Conventional Compaction ×  45     

(6)

4.2.2 Roadway Lifecycle Data The benefit from increased uniformity was calculated for the thick asphalt overlay using the increased fatigue life multiplier. The average cost per 1.6 lane-kilometer (one lane-mile) for thick asphalt overlay is approximated to be US$250,000 based on estimates from WYDOT and other jurisdictions (WYDOT 2011; Caltrans 2011; City of Woodland 2007). Also, the average remaining service life improvement of a thick asphalt overlay is assumed to be 10 years under 16

conventional compaction methods. Under greater uniformity from IC, a thick asphalt overlay has been calculated to have a service life of 2.6 times greater or 26 years due to the increased fatigue life (Xu et al., 2012). 4.2.3 Results of Pavement Case Study The results for the construction cycle and the roadway lifecycle are presented separately in the following subsections. Calculations for the cost per unit and number of units are described in each subsection. Construction Cycle The unit costs for the roller, operator, and QC/QA for conventional compaction are listed in Table 3. The unit cost for the IC roller was based on the cost per month of the roller (i.e., US$7,500) divided by 176 work hours in a month. This was calculated using the assumption of 40 hours per work week, or eight hours per work day, and 22 work days per month. This yielded an hourly rate of US$42.61 for the IC roller. The same method was used to calculate the hourly cost of the GPS unit at US$0.89 per hour, which had a yearly rate of US$1,800. The conversion from monthly rates to hourly rates is given by Equation 7. Line Item Hourly Rate = (Line Item Cost / month) × (One month / 176 working hours)

(7)

The number of units in hours or per square meter was calculated using a combination of the rate of construction and the areas of the road section and test section. The rate of construction is ten hours per 1.6 lane-kilometer (one lane-mile) for conventional compaction as noted in Table 3. The distance of the test section was added to the 1.6-kilometer (one lane-mile) distance of the road section and then divided by the rate of construction. This result was then reduced by 30

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percent to account for the reduction in time using an IC roller as given by Equation 2 (Briaud and Seo 2003). The result of the reduction yielded an equivalent of 7.7 hours to perform IC. The number of units for QC/QA was calculated as the unit cost of US$0.04784 per square meter to perform QC/QA from Table 3 multiplied by the number of square meters that QC/QA was performed on. For conventional compaction, the QC/QA was performed on the area of the road section, which is 1,609 meters (5,280 feet) multiplied by 3.66 meters (12 feet). The area of the test section is 152 meters (500 feet) by 3.66 meters (12 feet) for QC/QA for IC. The remaining QC/QA is performed based on readings from the IC roller. The data can be downloaded from the roller and inputted into the VEDA software in a limited amount of time to check for compliance on the road section. The costs were yielded by summing the cost of each line item as shown in Table 4. Conventional compaction yields a cost of US$940.52 per 1.6 lane-kilometer and IC yields a cost of US$592.63 per 1.6 lane-kilometer, which is a 37-percent reduction compared to conventional compaction. The 37-percent reduction was mainly a result of the 30-percent reduction in compaction time and also the reduction in QC/QA costs. The increase in cost from the GPS system was marginal. The GPS cost was calculated by using the annual rental cost and dividing it by the ratio of hours that it was used during compaction. The number of hours to complete compaction of a roadway was 23 percent less using IC. This was calculated using the 30 percent reduction in compaction time using IC and increased by the additional 152 meter (500 feet) long by 3.66 meter (12 feet) wide area for the test section. Line-itemed calculations are contained in Table 4.

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Roadway Lifecycle The total cost of performing a thick, 1.6 lane-kilometer asphalt overlay was divided by the service life increase from the improvement. The service life improvement using conventional compaction was noted as ten years in Table 3. The total cost per 1.6 lane-kilometer of US$250,000 was divided by ten years to yield the annual cost for conventional compaction. The total cost was then divided by 26 years for IC, reflecting the 2.6 times of improved service life (Xu et al. 2012). The annual costs were then multiplied by 26 years for each the conventional compaction and IC to demonstrate comparable costs during the lifecycle of a 1.6 lane-kilometer road section using IC. Table 5 contains the data used for each of the compaction types. Conventional compaction yielded 16 years less service life compared to IC. The cost savings for IC compared to conventional compaction is US$15,385 per year or US$400,000 when spread over the lifetime of an IC road section. The cost savings using IC resulted from increased material uniformity. 4.2.4 Sensitivity Analysis for Pavement Case Study The results from the prior section demonstrate a cost savings by using IC in both the construction cycle and the roadway lifecycle. These results were based on the inputs from Table 3. A sensitivity analysis was performed on the pavement section analyzed in the prior sections in order to understand the effect of variations in input values on the outcome of the economic analysis. Variations may be anticipated because of the limited data that has been provided for inputs as well as different agencies in different regions. The inputs included in this sensitivity analysis include a range of values for compaction efficiency, roller cost, and the IC service life multiplier.

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Compaction Efficiency The compaction efficiency improvement for IC was provided at a rate of 30 percent based on work by Briaud and Seo (2003). Beyond these authors’ work, very little work has been done to summarize the efficiency savings of IC. The sensitivity analysis for this section includes compaction efficiency for IC ranging from negative 15 percent to 45 percent. The IC efficiency is plotted against the percent cost difference of conventional compaction to IC in Fig. 5. The remaining inputs were held constant at the values provided in Table 3. The results of the sensitivity analysis apply only to the construction cycle. For example, at the previously selected IC efficiency of 30 percent, the percent cost difference is 37.1 percent, which is the difference in total costs of US$941.60 for conventional and US$592.63 for IC as indicated in Table 5.2 and expressed in percentage. The relationship between the IC efficiency to the cost difference between conventional compaction and IC is linear. As discovered in the previous section, 30-percent efficiency results in a 37.1 percent decrease in costs for IC relative to conventional compaction. The break-even point (i.e., cost for conventional equals IC) is when the IC efficiency is negative 13.7 percent. The IC efficiency can be negative but still yield a cost savings due to the decrease in QC/QA costs associated with using IC. Comparatively, an IC efficiency of 45 percent yields a 50.2 percent cost savings. More research is needed to understand the range of IC efficiencies for different types of compaction projects; however, the savings from on QC/QA when using IC demonstrates that IC would still be viable even if the relative IC efficiency is below zero percent. Roller Cost A range of conventional roller costs was used to demonstrate the differing costs that exist in the roller compactor market. Pricing for a conventional roller can depend on the age, type, and 20

region of use. Also, companies or government agencies may own conventional rollers that have outperformed their anticipated service life and have a substantially lower cost relative to a newer roller model. A range of hourly costs of a conventional roller between US$0 and US$42.61 is provided. The upper value is the hourly cost of the IC roller. Fig. 6 contains the hourly cost of a conventional roller plotted against the cost per 1.6 lane-kilometer for compaction of a thick overlay. The cost per 1.6 lane-kilometer of IC is plotted based on the hourly rate of a conventional compactor. The IC cost is the cost to perform IC at the prevailing hourly rate of IC equipment given in Table 4. Fig. 7 shows the cost difference in terms of a percentage. The resulting break-even point is when the hourly cost of a conventional roller is US$1.10. This would require the roller to be greatly discounted from a typical price of US$36 per hour (Table 3), the value used for the analysis in the previous section. A conventional roller costing the same amount as the IC roller would have a cost US$415.07 greater per 1.6 lane-kilometer, which is 41.2 percent more than IC. This sensitivity analysis reveals that IC provides cost savings for a wide range of conventional roller costs, and savings for conventional compaction is only available at greatly depreciated conventional roller values. Service Life Improvement from Using IC Improved pavement quality from compaction uniformity using IC was assumed to result in 2.6 times the service life of a conventionally compacted pavement section based on Xu et al. (2012). Fig. 8 shows the lifecycle cost savings based on a variety of service life multipliers from using IC. This sensitivity analysis was performed due to the limited amount of research on increased service life from using IC. The multiplier of 2.6 times the service life of a conventionally compacted pavement results in an annual cost savings of US$15,385 per 1.6 lane-kilometer as demonstrated earlier in this 21

section. A multiplier of three results in an annual cost savings of US$16,667. A more conservative estimate for improved service life would be an improvement of 1.5 times the service life of a conventionally compacted section. A 1.5-times improvement results in an annual savings of US$8,333, and annual cost savings decreases more rapidly as the multiplier approaches one. Table 6 contains the data for a roadway section that has a service life improvement of 1.5 times using IC. 4.3 Case Study No. 2: New Roadway Construction This case study examines the cost difference between compaction of a roadway section for both soil and pavement layers for 1.6 lane-kilometer (one lane-mile) using conventional compaction and IC. The methodology used is similar to the methodology outlined in the prior section; however, there are two differences. The cost of rollers for soil materials were used for corresponding soil layers and the calculation of hours to complete the compaction was based on the speed of rollers. Speeds of 4.8 and 12.9 kilometers per hour (3 to 8 miles per hour) were used to demonstrate the difference in cost based on varying speeds, which were used in case studies (Mooney et al. 2010). Table 7 lists the inputs used to calculate costs. Table 8 contains the cost calculation per 1.6 lane-kilometer of roadway based on the inputs and using the more conservative speed of 4.8 kilometers per hour (3 miles per hour). In order to calculate the amount of time to compact the soil and the pavement, the lane width divided by the roller width of 2.13 meters (7 feet) was rounded up to the nearest whole number and multiplied by the number of passes and the length and finally divided by the speed as given in Equation 8. The number of hours to perform compaction was then multiplied to the corresponding hourly rate for the soil and pavement compactors. The operator, GPS, and QC/QA costs were calculated similarly to the pavement case study. 22

Compaction Hours = 8ROUNDUP TO INTEGER B

×

Lane Width GH × Number Passes Roller Width

(8)

Roadway Length Roller Speed

Compaction of the soil and pavement lanes for 1.6 lane-kilometer at an average roller speed of 4.8 kilometers per hour (3 miles per hour) results in a US$1,470.33 savings using IC, which is 54.4% decrease compared to conventional compaction. A sensitivity analysis was performed to demonstrate the cost savings at average roller speeds of 4.8 and 12.9 kilometers per hour (3 to 8 miles per hour). These values were plotted with the percent of in-situ QC/QA performed on the roadway section versus the percentage of cost savings. Fig. 9 depicts the results from the sensitivity analysis. The analysis reveals that using IC is more cost effective for each speed and percent of in-situ QC/QA performed except when 100 percent in-situ QC/QA is performed with a roller speed of 12.9 kilometers per hour (8 miles per hour). 5. Conclusions The performance of a roadway is related to the quality of the roadway’s compaction. Conventional compaction and testing methods are insufficient for evaluating the compaction quality of a roadway section due to a lack of QC/QA testing coverage. IC provides a method to increase QC/QA testing coverage to 100 percent while providing more uniform compaction. Eighteen states, with support from the FHWA, have already begun drafting IC QC/QA specification, and at least 36 states have initiated the process of implementing IC by starting with workshops and field demonstrations. Surveys of Wyoming professionals and state DOTs indicate that there is support for the implementation to IC; however, cost information remains a concern and data are limited. While 23

several publications, academic and industry-oriented, have indicated substantial benefits when using IC, there has not been a substantial benefit-cost analysis performed on the short-term and long-term costs of IC. A frame work for benefit-cost analysis was proposed to systematically evaluate the economic benefits of IC. This framework was developed based on costs for construction of a roadway and savings from improved compaction uniformity over the pavement lifecycle. The methodology to obtain cost data includes two specific cost cycles: construction and roadway life. The framework is illustrated using a case study of a hypothetical, thick (five to ten-centimeter) asphalt overlay. The benefit-cost analysis in this paper demonstrated a 37-percent decrease in construction costs for a thick asphalt overlay and 54-percent decrease for new roadway construction when using IC. The increased service life from using IC was determined based on increased compaction uniformity, which resulted in a US$15,385 savings per year per 1.6 lane-kilometer.

The framework of the benefit-cost analysis can be readily adopted by

transportation agencies to facilitate the implementation of intelligent compaction in future roadway construction.

Acknowledgements The authors would like to thank the Mountain Plains Consortium for funding this research. Also, special thanks to Wyoming Department of Transportation for the contributions to the Wyoming survey and state Departments of Transportation contributed to the nationwide survey.

References Bastian S. Simon Constractors: Phone Interview [Interview]; 26 March 2014. 24

Beainy F, Commuri S, Zaman M. Quality assurance of hot mix asphalt pavements using the intelligent asphalt compaction analyzer. Journal of Construction Engineering and Management, 2012; 138(2). ASCE; 2012 [p. 178-187]. Briaud J-L, Seo J. Intelligent compaction: overview and research needs. Texas A&M University, College Station, TX; 2003. (http://www.intelligentcompaction.com/downloads/PapersReports/Texas_Briaud_IC%20 Report_200409.pdf) Caltrans. 2011 State of the pavement report-based on the 2011 pavement condition survey. California Department of Transportation Division of Maintenance Pavement Program; 2011. (http://www.dot.ca.gov/hq/maint/Pavement/Pavement_Program/PDF/2011_SOP.pdf) City of Woodland. Appendix C- repair, maintenance and rehabilitation techniques; 2007. (http://www.cityofwoodland.org/civicax/filebank/blobdload.aspx?blobid=3813) Dynapac. Dynapac - Rollers - Compaction control systems - Compaction meter. Atlas Copcp Group; 2013. (http://www.dynapac.com/en/Products/?cat=36&product=662) Facas NW, Mooney MA. Position reporting of data from intelligent compaction rollers. Journal of Testing and Evaluation 2010; 38(1). ASTM; 2010 [p. 1-6]. Federal Highway Administration. Intelligent compaction. Techbrief, Summer, U.S. Department of Transportation, Washington D.C.; 2013. (http://www.fhwa.dot.gov/construction/pubs/hif13051.pdf) Federal Highway Administration. Intelligent compaction technology for soils applications. U.S. Department of Transportation, Washington D.C.; 2014. (https://www.fhwa.dot.gov/construction/ictssc/ic_specs_soils.pdf) Jones D. Sakai America: Email Correspondence [Interview]; 9 April 2014.

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Kimmel SC, Toohey NM, Delborne JA. Roadblocks to responsible innovation: exploration technology assessment and adoption in U.S. public highway construction. Technology in Society 2016; 44. Elsevier; 2016 [p. 66-77]. Kröber W, Floss R, Wallrath W. Dynamic soil stiffness as quality criterion for soil compaction. Geotechnics for Roads, Rail Tracks and Earth Structures. A.A.Balkema Publishers, Lisse /Abingdon/Exton (Pa)/Tokyo; 2001 [p. 189-199]. Miller JS, Bellinger WY. Distress identification manual for the long-term pavement performance program. FHWA-RD-03-031, Federal Highway Administration, U.S. Department of Transportation, Washington D.C.; 2003. (https://www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/reports/03 031/03031.pdf) Minnesota Department of Transportation. Quality management special-intelligent comaction (IC) method. Special provisions for intelligent compaction (IC) method, Advanced Materials & Technology (AMT), Minnesota Department of Transportation, St. Paul; 2016. (http://www.dot.state.mn.us/materials/amt/icdocs/2016%20Quality%20IC%20Method%2 0SP2016-60%2003.01.16%20version.pdf) Mooney MA, Adam D. Vibratory roller integrated measurement of earthwork compaction: an overview. Proceedings of Seventh International Symposium on Field Measurements in Geomechanics, September 24-27, Boston, Massachusetts; 2007 [p. 1-12]. Mooney MA, Facas NW. Extraction of layer properties from intelligent compaction data. Final Report for Highway IDEA Project 145, Transportation Research Board, Washington, D.C; 2013. Mooney MA, Rinehart RV, Facas NW, Musimbi OM, White DJ, Vennapusa PKR. Intelligent soil compaction systems. National Cooperative Highway Research Program, Report 676, Transportation Research Board, Washington D.C.; 2010. 26

Newman N. High Country Construction: Phone Interview [Interview]; 21 July 2014. Savan C. Intelligent compaction for roadway soils and pavement. Master Thesis, University of Wyoming, Laramie; 2014. Scherocman J, Rakowski S, Uchiyama K. Intelligent compaction, does it exist? Proceedings of the 52 Annual Conference of the Canadian Technical Asphalt Association. Polyscience Publications Inc.; 2007 [p. 373-398]. The Transtec Group, Inc. Intelligent Compaction, Equipment, Soil IC Rollers; 2013. (http://www.intelligentcompaction.com/index.php?q=node/10) The Transtec Group, Inc. Intelligent Compaction, Projects, IC Specifications; 2014. (http://www.intelligentcompaction.com/projects/specifications/) The Transtec Group, Inc. Intelligent compaction data management workshop. Laramie, WY; 2014. Trimble Navigation Limited. Trimble Positioning Services - Trimble VRS Now; 2014. (http://www.trimble.com/positioning-services/vrs-now.aspx) Wyoming Department of Transportation. State transportation improvement plan (STIP); 2011. (http://www.dot.state.wy.us/files/live/sites/wydot/files/shared/District_3/STIP-LINC.pdf) Wyoming Department of Transportation. 2013 weighted average bid prices; 2013. (http://www.dot.state.wy.us/home/business_with_wydot/contractors/contractor_bids/weig hted_bid_price.html) Xu Q, Chang GK, Gallivan VL, Horan RD. Influences of intelligent compaction uniformity on pavement performances of hot mix asphalt. Construction and Building Materials 2012; 30(1). Elsevier; 2012 [p. 746-752].

27

Fig. 1. IC QC/QA Draft Specifications by States (Savan 2014)

Fig. 2. IC Data Management Workshop in Laramie, WY.

28

Fig. 3. Map of State DOT Respondents Shaded in Gray (Savan 2014)

29

Conventional Compaction Number of Hours of Conventional Compaction

Multiply (Eqn. 5.3)

Intelligent Compaction + Hours to Compact Test Section) × (100% – IC Efficiency %) (Eqn. 5.2)

Line Item Cost Per Hour Roller Operator

Number of Hours of Intelligent Compaction Multiply (Eqn. 5.3)

Line Item Cost Per Hour Roller Operator GPS

Add

Add

QC/QA Cost based on roadway area (Eqn. 5.4)

QC/QA Cost based on test section area (Eqn. 5.4)

Cost of Conventional Compaction

Cost of Intelligent Compaction

Fig. 4. Flow Chart for Calculating Compaction Cost

30

45.0% 35.0% 25.0% 15.0% 5.0% -5.0% -15%

-5%

5%

15% IC Efficiency

25%

35%

45%

Fig. 5. Cost Difference with Varying IC Efficiency

$1,200 Cost per Lane Mile

Cost Difference Conventional to IC

55.0%

$1,000 $800 $600 $400 $200 Conventional Compaction

IC

$$-

$10

$20 $30 $40 Cost of Conventional Roller

$50

Fig. 6. Cost Difference (US$) Based on Hourly Cost of Conventional Roller

31

45% Cost per Lane Mile Conventional to IC

40% 35% 30% 25% 20% 15% 10% 5% 0% -5% $-

$10 $20 $30 $40 Cost of Conventional Roller (US$)

$50

Annual Cost Difference Per Lane Mile (US$)

Fig. 7. Percent Cost Difference Based on Hourly Cost of Conventional Roller

$18,000 $16,000 $14,000 $12,000 $10,000 $8,000 $6,000 $4,000 $2,000 $1

1.2

1.4 1.6 1.8 2 2.2 2.4 Service Life Increase Multiplier Using IC

2.6

Fig. 8. Lifecycle Cost Saving Based on Service Life Improvement from IC

32

2.8

Cost Savings IC to Conventional

80% Roller Speed 4.8 km/hr

70%

Roller Speed 12.9 km/h

60% 50% 40% 30% 20% 10% 0% -10% 0%

25% 50% 75% Percent of QC/QA on Road Section Using IC Fig. 9. Cost Saving by Amount of QC/QA performed

33

100%

Table 1 Wyoming Survey: Do You Have Any Concerns with Intelligent Compaction? Responses

Percent of Respondents

Cost Reliability of data Not a specified quality control/assurance method Lack of operator ability and/or time and cost to train operators Unfamiliar with technology Reliability and durability of technology There are no concerns

33.3% 26.4% 22.2% 22.2% 20.8% 19.4% 19.4%

Table 2 DOT Survey: DOT Status with QC/QA Specifications for IC. Responses

Response Count

Yes, quality assurance standards for intelligent compaction have been adopted Yes, draft standards have been completed and are awaiting adoption Yes, we are in the process of drafting standards No, but we plan on drafting standards No, and we do not plan on drafting standards at the current time

34

3 4 5 1 8

Table 3 Input Data for Benefit-Cost Analysis. Item

QC/QA per square meter

Unit Cost (US$) / Source Quantity Construction Costs $ 0.04784 Simon Contractors, WY (Bastian 2014)

IC Reduction in compaction cost

30%

Briaud and Seo (2003)

Lane width, meters

3.7

Assumption

IC to conventional QC/QA cost

10%

Conventional roller cost per hour

$ 36

IC pavement roller cost per month

$ 7,500

Roller operator per hour

$ 30

NCHRP 676 (Mooney et al. 2010) High Country Construction, WY (Newman 2014) Sakai America (Jones 2014) High Country Construction, WY (Newman 2014) High Country Construction, WY (Newman 2014) Simon Contractors, WY (Newman 2014)

Conventional compaction hours/1.6 lanekm Compaction cost per square yard

$ 0.20

GPS System rental per year

$ 1,800

Test Section Length, meters Work hours per week Increased service life with IC, multiplier

10

Trimble Navigation Limited (2014) NCHRP 676 (Mooney et al. 2010), DOT IC 152 Specs (The Transtec Group, Inc. 2014) 40 Assumption Lifecycle Costs 2.6 Xu et al. (2012)

Average asphalt life, years

10

Cost per 1.6 lane-kilometer

$ 250,000

35

Average overlay service life WYDOT (2011), Caltrans (2011), City of Woodland (2007)

Table 4 Cost of Construction Cycle per 1.6 Lane-Kilometer. Conventional Compaction

Intelligent Compaction

Unit

Number of Units

Total Cost (US$)

Cost (US$) per Unit

Unit

Number of Units

Total Cost (US$)

$ 36.00

hour

10

$ 360.00

$ 42.61

hour

7.7

$ 328.10

Operator

$ 30.00

hour

10

$ 300.00

$ 30.00

hour

7.7

$ 231.00

GPS

n/a

n/a

n/a

n/a

$ 0.89

hour

7.7

$ 6.85

QC/QA

$ 0.04784

m2

5886.3

$ 281.60

$ 0.04784

m2

557.7

$ 26.68

Total

-

-

-

$ 941.60

-

-

-

$ 592.63

Item

Cost (US$) per Unit

Roller

n/a - Data is not applicable

Table 5 Roadway Lifecycle Costs per 1.6 Lane-Kilometer for One Year and 26 Years. Compaction Type

Service Life (years)

Cost Per Year

Cost Over 26 Years

Conventional

10

$ 25,000

$ 375,000

Intelligent

26

$ 9,615

$ 250,000

Difference

-16

$ 15,385

$ 400,000

Table 6 Roadway Lifecycle Costs per 1.6 Lane-Kilometer for One Year and 15 Years. Compaction Type

Service Life (years)

Cost Per Year (US$)

Cost Over 15 Years (US$)

Conventional

10

$ 25,000

$ 375,000

Intelligent

15

$ 16,667

$ 250,000

Difference

-5

$ 8,333

$ 125,000

36

Table 7 Inputs for Soil/Pavement Case Study. Item

Construction Cycle Cost (US$) / Quantity

Source

QC / QA per square meter per layer

$ 0.04784

Simon Contractors, WY

IC Reduction in Compaction Cost

30%

Briaud & Seo, 2003

Lane Width, meter

3.66

Assumption

IC to Conventional QC/QA cost

10%

Conventional Soil Roller Cost per hour Conventional Pavement Roller Cost per hour

$ 34.03 $ 36.00

NCHRP 676 based on test section size Wagner Rents, Fort Collins, CO High Country Construction, WY

IC Soil Roller Cost per month

$ 7,000

Sakai America

IC Pavement Roller Cost per month

$ 7,500

Sakai America

Operator Cost per hour

$ 30.00

High Country Construction, WY

Number of passes per layer

6

Assumption

Average Roller Speed (km/h)

4.8 and 12.9

Assumption

Layer Thickness, cm (Subgrade/ subbase/ base/ binder/ surface)

20.3/ 20.3 / 20.3 / 10.2 / 5.1

Assumption

GPS System, per year

$ 1,800.00

Trimble

TABLE 8 Cost of Construction Cycle Per 1.6 Lane-Kilometer. Conventional Compaction Item

Cost (US$) per Unit Soil Roller $ 34.03 Pav. Roller $ 36.00 Operator $ 30.00 GPS QC/QA $ 0.24 Total

Unit hour hour hour sq. m

Intelligent Compaction

Number Total Cost Cost per of Units (US$) Unit (US$) 12.0 8.0 20.0 5866

$ 408.41 $ 288.00 $ 600.00 $$ 1,408.00 $ 2,704.41

37

$ 39.77 $ 42.61 $ 30.00 $ 0.89 $ 0.24

Unit hour hour hour hour sq. m

Number Total Cost of Units (US$) 9.2 $ 365.83 6.1 $ 261.31 15.3 $ 459.90 15.3 $ 13.64 556 $ 133.40 $ 1,234.08