Remaining service life prediction using road structure performance data with pavement condition index (PCI) and Benkelman beam (BB) methods

. The design life of a road is the amount of time a road can take from the time the road is used until the road requires major repairs. The inability of a pavement to reach its design life can be caused by several factors. These factors cause the uncertainty of the service life of the road, so that the remaining service life of the pavement becomes difficult to predict. This study will discuss the condition of the road pavement and predict the remaining service life on the Losari - Pejagan road, Demak ring road, and Rembang - Bulu road sections using the PCI (Pavement Condition Index) and Benkelman Beam (BB) methods. Based on the analysis of road condition assessment, the average PCI value for the Losari - Pejagan road section is 45.76 (poor), for the Demak Ring road section is 74.63 (satisfactory), and for the Rembang - Bulu road section is 50.41 (poor). The results of the analysis of the remaining service life using the PCI method found that 67.2% of all segments on the three road had a remaining service life of less than a year and 32.8% of all segments had a remaining service life of more than 1 year. Using the BB method, it was found that the remaining service life of 93.7% segments on the three road are less than a year and 6.7% segments are more than 1 year.


Introduction
The design life of a road is the amount of time a road can take from the time the road is used until the road requires major repairs.In designing road pavement structure in Indonesia, the design life of a road is based Manual Desain Perkerasan Jalan, revisi 2017 (MDPJ 2017) Nomor 04/SE/Db/2017 [1].The design life of a road is often not reached.The inability of a road pavement to reach its design life can be caused by several factors [2].One of these factors is the incorrect assumption of the value of overloading, in planning the design life of the road.If the vehicle load continues to increase, it will have an impact on decreasing the strength of the pavement structure which is faster than the design life of a road.
Other factors that cause the planned life of the road not to be reached are poor drainage, unstable subgrade, substandard quality of pavement and construction materials [2].
Road performance is good if the road functional conditions and road structural conditions are in good condition.The functional condition of the road is related to the impact felt by road users including roughness, rutting and skid resistance [3].While the structural condition of the road functions to determine the ability of the pavement to support repeated vehicle traffic loads during the design life of a road.A decrease in the value of road structural conditions is indicated by pavement *Corresponding author: fajarhani@ft.uns.ac.id damage such as cracking, potholes, deformation and corrugation [3].
One way to maintain road conditions so that it remain at a good quality of road service is to evaluate the condition of the road pavement using the right method.
The Federal Highway Administration (FDWA) revealed that a number of major cities in America use the Pavement Condition Index (PCI) as the main method for assessing the functional condition of roads.Meanwhile, the International Roughness Index (IRI) is a popular pavement functional performance indicator in North America [4].The results of previous research study show that the relationship between PCI and IRI can vary significantly based on factors such as location, functional class, and slope of the road [5].
Several countries including the Indian Road Congress (IRC) recommend the use of tools such as the Falling Weight Deflectometer (FWD) for high-volume roads.While the Benkelman Beam tool is the first method developed to measure pavement deflection.The Benkelman Beam method is economical and easy to obtain [6].The Benkelman Beam was carried out to measure the surface layer deflection using a known static load [7].Based on Sanjay's research [8] there is a correlation between the structural conditions of the flexible pavement from the BB and FWD methods.The most common method for describing the nature of the response in a pavement structure is through the Boussinesq foundation [9].
Pavement damage indicates that the structural and functional performance of the road is unable to provide optimal service to road users.This study will discuss the condition of the road pavement and predict the remaining service life using the Pavement Condition Index (PCI) and Benkelman Beam (BB) methods.This study produces predictions of the remaining service life and functional condition of the road.Prediction of the remaining service life and functional condition of the road is used as a basis for consideration to determine the time and appropriate repairs to maintain a road pavement.

Pavement condition index (PCI) method
The Pavement Condition Index (PCI) method is a method for assessing road functional performance.In PCI there are values ranging from 0 to 100, where a value of 0 represents a very damaged pavement, while a value of 100 represents a very good pavement [10].The range of PCI rating values as contained in the Guidelines and Procedures for Maintenance of Airport Pavement (1982), as shown in Fig. 1.The Pavement Condition Index (PCI) values are measured using the Hawkeye 2000.Hawkeye is a smart vehicle for surveying road conditions with an integrated operating system with several specific sensor equipment in obtaining data on the characteristics and condition of road elements.This technology was launched to measure asset data and road conditions accurately, effectively and efficiently.
To evaluate road pavement, it is first divided into segments.The segment unit is an area that can be identified from the pavement section [4].The overall PCI value is calculated by Equation 1.
Maintenance and rehabilitation measures must be based on actual pavement damage, so that the PCI method can be used [2].Ontario Good Roads Association, 2009 divides the PCI value range as a PCI decision matrix that can be used for analysis of the remaining service life of the road with repair time classification of each PCI value for each road segment [11].Table 1 describes the time to improvement for toll, arterial, collector and local roads based on the PCI value of these roads.

Benkelman beam (BB) method
The structural performance of road pavements can be determined by non-destructive testing using a tool called the Benkelman Beam (BB).The test procedure using the Benkelman Beam (BB) tool is considered very effective because this test does not cause damage to the pavement construction.Based on the Guidelines for Testing Flexural Pavement Deflection with the Benkelman Beam SNI 2416: 2011 there are 3 types of measurements obtained including maximum rebound deflection, rebound deflection, and deflection bowl due to certain wheel loads.
The maximum rebound deflection is the amount of rebound deflection at the position at the point of contact of the Benkelman Beam after the load has moved 6 meters.The rebound deflection of the inflection point is the amount of rebound deflection at the position at the point of contact of the Benkelman Beam after the load has moved 0.4 meters.Deflection bowl is a curve that describes the shape of the deflection of a road segment [12].

Methods
This study will discuss the condition of the road pavement and predict the remaining service life on the Losari -Pejagan road, Demak ring road, and Rembang -Bulu road sections using the PCI (Pavement Condition Index) and Benkelman Beam (BB) methods.
The road section is divided into several segments with 1 segment being 1000 meters long.Then calculate the average PCI value for each segment and calculate the average PCI value for the entire road section.After that determine the condition and remaining service life of the road based on the PCI average value.

Result and discussion
Based on The Pavement Condition Index (PCI) Rating in Fig. 1, 5 segments were found in the very poor category, namely segments 1, 2, 3, 5, and 6, each segment having a PCI value in the range of 25-40.Furthermore, there are 3 segments that have poor criteria, namely segments 4, 7, and 8 with PCI values in the range of 40-55.Whereas segments 9 and 10 have satisfactory criteria with a PCI value of 80.26% in segment 9 and 75.55% in segment 10.So that the average PCI value is 45.76% included in the condition poor.The PCI value for each segment can be seen in Table 2.When the adequate decision is converted that the remaining service life is 11-20 years, 20 years is taken from the design life on flexible pavement, while 11 years is taken from the upper limit of the next decision.Furthermore, in the now rehabilitate decision it is converted that the remaining service life is 0.5-0.9years, this is because at that age the road must receive rehabilitation.Then in the now reconstruct decision it is converted that the remaining service life is 0-0.4 years, because in that decision the road conditions are already damaged and reconstruction must be carried out.After knowing the PCI value of each segment on the Road section, it is then interpolated to obtain the remaining service life for each segment.Tables 2-4 shows the PCI values, the results of calculating the remaining service life and the improving time for each segment.
The prediction of remaining service life using the PCI method is affected by the PCI value per road segment.For example, segment 1 has a PCI value of 34.02%; then with Table 1 these values are interpolated with the results of the remaining life conversions that have been carried out and the remaining service life for segment 1 is 0.28 years.Then based on Table 1 the PCI value is 34.02% on arterial roads including the time of improvement for now reconstructing.Based on the analysis of road condition assessment, the average PCI value for the Losari -Pejagan road section is 45.76 (poor), for the Demak Ring road section is 74.63 (satisfactory), and for the Rembang -Bulu road section is 50.41 (poor).
Recapitulation of the calculation of the prediction of the remaining service life based on the Benkelman Beam deflection value can be seen in Tables 5-7.All segments have a very short remaining service life, less than 1 year.The low remaining period of service life can be caused by several factors such as overloading the vehicle load so that the deflection is very large.
The results of the remaining service life analysis using Pavement Condition Index (PCI) values are then correlated to the results of the remaining service life analysis using Benkelman Beam (BB) deflection data.The results of these two methods are compared to find out whether the functional condition of the road as represented by the Pavement Condition Index (PCI) data and the structural condition of the road as represented by the Benkelman Beam (BB) deflection data have differences.Comparison of the remaining service life using the PCI method and the BB method for each road pavement segment can be seen in Fig. 2-4.There are two segments that have a very large difference between the predicted remaining service life using the PCI method and the BB method, the two segments are segment 9 and 10.In these two segments, the prediction of service life using the PCI method has a higher remaining life than using BB method.This may be due to the fact that in this segment the functional conditions have been repaired and rehabilitated, but there has been no improvement in the structural conditions.

Conclusion
The results of the analysis of the remaining service life using the PCI method found that 67.2% of all segments on the three road had a remaining service life of less than a year and 32.8% of all segments had a remaining service life of more than one year.Using the BB method, it was found that the remaining service life of 93.7% segments on the three road are less than a year and 6.7% segments are more than one year.

Table 1 .
The PCI decision matrix.

Table 2 .
The PCI values, the remaining service life and the improving time (Losari-Pejagan road).

Table 3 .
The PCI values, the remaining service life and the improving time (Rembang-Bulu road).

Table 4 .
The PCI values, the remaining service life and the improving time (Demak ring road).

Table 5 .
Remaining service life based on the Benkelman Beam method (Demak ring road).

Table 6 .
Remaining service life based on the Benkelman Beam method (Rembang-Bulu road).

Table 7 .
Remaining service life based on the Benkelman Beam method (Losari-Pejagan road).