Development of a Rapid Method to Evaluate Asphalt Deterioration

1. Introduction
  Asphalt used for paving gradually deteriorates due to the action of ultraviolet rays, heat, oxygen, and other factors after it comes into service. Excessive deterioration of the asphalt may cause loss of flexibility and eventual pavement damage. If the extent of asphalt deterioration can easily be identified, damage may be predicted. However, as shown in the upper part of Figure 1, the conventional method is complicated as it requires removing a sample of the road surface and analysis is highly labor-intensive. A more sophisticated maintenance management system may be possible if the analytical method does not damage the pavement and requires less effort. This study was therefore aimed to develop a method that allows rapid assessment of the degree of asphalt deterioration involving very few samples by using infrared spectroscopy.

Figure 1 Visual representation of the rapid evaluation of asphalt deterioration

2. Rapid Method of Assessing Asphalt Deterioration Using Infrared Spectroscopy
　Infrared spectroscopy is an analytical method that utilizes the absorption of infrared light at specific wavelengths depending on the chemical structure of the substance irradiated by infrared light, and is used for structural analysis and quantification of samples. In this study, as shown in the lower part of Figure 1, we devised a method to rapidly assess the degree of asphalt deterioration causing as little damage to the pavement as possible by using infrared spectroscopy, which can analyze a small amount of sample.

3. Removal of Analytical Inhibitors
  Asphalt paving is prepared by mixing aggregate (crushed stone), sand, and stone powder (calcium carbonate) with asphalt. When trying to analyze the asphalt in the pavement, other components than asphalt interfere with the analysis. Therefore, to improve the accuracy of the analysis, we explored a simpler method to remove inhibitors.
  As shown in Figure 2, when a small portion of asphalt pavement was dissolved in an organic solvent (toluene), and then filtered through a commonly available filter (particle retention capacity of 0.2 to 7 μm), and toluene was evaporated from the filtrate, infrared spectroscopy indicated asphalt deterioration more clearly as shown in Figure 3. As a result, the process of assessing asphalt deterioration, which used to take two days, can now be performed in one to two hours.

4. Future Initiative
  The method of assessing asphalt deterioration discussed in this report can also be used to determine the presence or absence of additives for high performance (commonly referred to as polymer modifiers) in the asphalt.
  Currently, most asphalt pavements in Japan are recycled. More advanced recycling will be possible if it is possible to determine the presence or absence of additives in the asphalt. Handheld-type analyzers (Figure 4) have been developed and can be easily used for such determination.
  We will also study the possibility of achieving more efficient recycling at asphalt recycling plants by applying these methods.

(Contact  :  Innovative Materials and Resources Research Center)

Study of Farmland Subsidence on Peatland

  The national government is currently promoting the consolidation of farmland into large-scale farming fields to strengthen agricultural competitiveness to ensure future continuity. The government is also promoting the rotational cultivation of the upland crop in paddy fields to improve profitability in these farmlands. These consolidation and rotational cultivation in paddy are also promoted in the Ishikari River basin, which is covered in vast paddy fields in Hokkaido, the largest food supply base in Japan.
  Meanwhile, peatland is distributed across this river basin. Farmland in peat districts tends to sink due to a drop in the groundwater level. If a certain area within a field, or one field among the several neighboring fields, sinks (uneven subsidence), for example in the case of paddy fields, uneven irrigation water depth within the field, deterioration of the function of underground drainage pipes and surrounding irrigation and drainage canals, and other problems may occur (Fig. 1). Accordingly, there is demand for methods to reduce farmland subsidence on peatland.

Fig. 1 Uneven subsidence on peat soil (paddy field)

  This study aimed to verify how differences in peat type, cultivation type (paddy fields or crop fields), and winter groundwater level impact the subsidence of rotational paddy field. This study was conducted in rotational paddy fields in two types of peatland with soil dressing, low-moor peat with poor porosity and high-moor peat with high porosity were prepared. Some field were used as a paddy field and others were used as a crop field. As well as cultivation type, in some fields, a high groundwater level was maintained, while not in the other fields during winter.

  The results are shown in Fig. 2.

Fig-2 Relationship between groundwater level and cumulative changes in subsidence

  This figure shows the cumulative changes in elevation (negative figures mean subsidence) of a subsidence board installed at a depth of 80 cm from the ground surface. Legends represent paddy field where a high winter groundwater level was maintained (①), a crop field where a high winter groundwater level was maintained (②), and a crop field where the winter groundwater level was not controlled (③) both in low-moor peat (Site A) and high-moor peat (Site B).
  Comparison of low-moor peat and high-moor peat showed no subsidence in paddy field ① in either area, but subsidence was observed both in crop field ② and ③ and subsidence tended to be more expressed in high-moor peat. Comparison between high-moor peat crop field ② and ③ indicates that subsidence was less expressed in crop field ② where a high winter groundwater level was maintained.
  The study accordingly showed that peat subsidence varies depending on the peat type, cultivation type, and winter groundwater level, suggesting that subsidence may be mitigated by maintaining a high groundwater level during winter.

(Contact  :  Rural Resource Conservation Research Team, CERI)

Study of Redesigning Road Spaces
−To propose plans and designs of viewpoint parking−

  Since FY 2022, the Scenic Landscape Research Team has been studying planning and designing techniques to redesign (rebuild) road spaces in suburban areas to comprehensively improve the landscape, safety and usability in response to social and environmental changes and various needs such as tourism use and cycle tourism (Fig. 1).

  Based on the research, this paper is a report of case studies and analytical results concerning viewpoint parking, one way of using roadside open spaces. In foreign countries, viewpoint parking (hereinafter referred to as VPP) is also called viewpoint car parks, and is regarded as parking spaces with a commanding or scenic view. Such spaces are constructed to provide comfortable, high-quality rest areas and photo spots.
  During the current fiscal year, we have classified VPP¹⁾²⁾ in Japan, as in foreign countries, according to the viewing place and view type using Google Earth and other resources (Fig. 2), and then conducted on-site surveys at scenic spots in national parks (Fig. 3).
  As a result, we found that VPP at viewing places away from roadside parking areas (Type II) were generally excellent in terms of comfort and a sense of openness. However, it is often difficult to construct Type II VPP due to on-site limitations.
  With this study,accordingly, we focus on redesigning roadside Type I VPP with the objective of applying the design concept of Type II VPP to that of Type I VPP, and review findings concerning whether the following aspects can be adopted as basic policies.

  ・Viewing places: Planning and designing by imagining situations where visitors are actually using them³⁾ in terms of, for example, the use of local resources and materials (wood and stone) and the installation of decks as photo spots and road signposts immediately before reaching the viewing places.　

　

  ・Views: Planning and designing that take the proper elevation angle/depression angle, reduction of utility poles and other roadside equipment and an appropriate combination of scenic components into consideration 　

  In a future study, on-site survey locations will be expanded to clarify the direction of VPP redesigning and we will start preparing a trial design.

　


Fig. 3 Examples of VPP on-site survey results　

References

1) Hokkaido Regional Development Bureau, the Ministry of Land, Infrastructure, Transport and Tourism: Website of Road Planning Division. Viewpoint Parking (Hokkaido).

2) Timothy Davis, Todd A. Croteau, and Christopher H. Marston: America's National Park Roads and Parkways Drawings from the Historic American Engineering Record, Johns Hopkins University Press, pp.52-245, 2004. 2) Timothy Davis, Todd A. Croteau, and Christopher H. Marston:America's National Park Roads and Parkways Drawings from the Historic American Engineering Record, Johns Hopkins University Press, pp.52-245,2004. 　　

3) Civil Engineering Research Institute for Cold Region. How Landscape Considerations Should be Handled – Procedure and Method for Landscape Predication and Assessment, pp.16-28, 2022.　

(Contact  :  Scenic Landscape Research Team, CERI)