Nobuyuki Yoshida
Research Center for Urban Safety and Security, Kobe University, Kobe, Hyogo, Japan
Recycling Law (existing), Electric Household Appliance Recycling Law (existing), Construction Material Recycling Act (newly enacted), Food Recycling Law (newly enacted) and Law on Promoting Green Purchasing (newly enacted). Construction Material Recycling Act and Law on Promoting Green Purchasing have a significant influence on construction industry, and procurement of processed or recycled products is being increased in public works year by year.
Moreover, laws promoting use of recycled material would not necessarily ensure that all processed materials are approved in actual use without other considerations.
Constraints from environmental and also engineering aspects are imposed. Most environmental concerns are designated in Water Pollution Control Law (revised in 2001a) and Soil Pollution Measures Law (enacted in 2002).
In the followings, the designing method of asphalt pavement adopted in Japan is first outlined together with the process of adopting by-products and new mater-ial in pavement construction.
Recent movement towards performance-specified construction is also briefly described, and engineering and environmental requirements are presented in rela-tion to some of presently used processed materials.
2 DESIGNING METHOD OF ASPHALT PAVEMENT IN JAPAN
In Japan, pavement design has been carried out based upon a subgrade CBR value and an equivalency conversion thickness (TA), so-called CBR-TAmethod, since 1967. A multi-layered elasticity based designing method was also conceptually introduced in 1992 but it is not presently used in practice and the CBR-TAmethod is a dominant method. Figure 1 shows the CBR-TAdesign flow used in Japan (Japan Road Association, 1992).
TAis an equivalency conversion thickness, representing the pavement thickness required if the total pavement depth was to be constructed with hot asphalt mix-tures used for binder and surface courses. It is estimated by
(1)
where N is the total number of 49 kN-equivalent wheel load applications (wheels per one direction) in a specific design period, say 10 years, and CBR is a design subgrade CBR.
A pavement section is designed so as for TA to be greater than TAabove. TA is computed as
TA a1T1 a2T2 … anTn (2)
T N
A 3 84. CBR0 16.0 3
.
188 DESIGN ANDCONSTRUCTION OFPAVEMENTS ANDRAILTRACKS
where TA is the equivalency conversion thickness of the designed pavement section, aiis an equivalency conversion coefficient for each pavement material used, and Tiis the thickness of each layer. From this, it is seen that, in principle, designing a pavement section requires equivalency conversion coefficients for all the mater-ial used. Equivalency conversion coefficients for currently used standard pave-ment material are summarized in Table 1 (Japan Road Association, 1992).
In the case that non-standard material is attempted to be used in pavement con-struction, there are two ways to follow: one is to derive an equivalency conversion coefficient for the material and the other is to verify that it possesses the quality equivalent to or better than standard pavement material. Determination of an UTILIZATION OFPROCESSEDMATERIAL INPAVEMENTSURFACE ANDBASE-COURSE 189
Prediction of design traffic volume
Determination of design traffic volume
Estimate of subgrade bearing capacity
Determination of design CBR Determination of target TA
Selection of materials for each layer Min. thickness of each layer
In-situ condition Determination of each layer thickness and calculation of TA' and H'
Replaced depth Z
Frost blanket thickness Z-H' Calculation of design CBR
Figure 1. Flow of structural design of asphalt pavement (Japan Road Association, 1992).
equivalency conversion coefficient for non-standard material is based upon per-formance of trial pavement on actual road in principle and is usually done in case of standardizing the material. It is very often time-consuming and costly.
Figures 2 and 3 show the process of adopting by-products and new material in pavement construction, respectively, referring to Japan Road Association (1992).
In the both cases, the environmental safety of the material of concerned is the utmost concern, and it is also important to ensure that it possesses the quality and performance equivalent to or better than standard pavement material. For this, trial construction is usually carried out. For instance, cracks, rut depth and longitudinal roughness observed are measured on trial pavement with non-standard material at a regular interval and used to compute variation of a present serviceability index with time. It is, then, compared with that of trial pavement with standard material or relevant past data, from which performance equivalency is to be evaluated.
Laboratory test based derivation may also be possible as such that an equiva-lency conversion coefficient is deduced through comparison of the elastic modulus or uniaxial compressive strength of non-standard material with those of standard one; however, this has been rare to author’s knowledge.
190 DESIGN ANDCONSTRUCTION OFPAVEMENTS ANDRAILTRACKS
Table 1. Equivalency conversion coefficient, ai(modified after Japan Road Association, 1992).
Location Material Quality spec. ai
Surface & binder course Hot asphalt mix Specified separately 1.00 Base-course Bituminous stabilization Hot-mixed: Marshall 0.85
stability 3.43 kN
Cold-mixed: Marshall 0.55 stability 2.45 kN
Cement stabilization Uniaxial Compressive strength 0.55 (7 days) 2.9 MPa
Lime stabilization Uniaxial Compressive strength 0.45 (10 days) 0.98 MPa
Mechanically-stabilized Modified CBR 80 0.35 crushed stone
Mechanically-stabilized Modified CBR 80 0.35 iron & steel slag
Hydraulic, Uniaxial Compressive strength 0.55 mechanically-stabilized (14days) 1.2 MPa and
iron & steel slag Modified CBR 80
Subbase-course Crusher-run, iron & steel Modified CBR 30 0.25 slag, sand, etc. 20 Modified CBR 30 0.20 Cement stabilization Uniaxial Compressive 0.25
strength (7 days) 0.98 MPa Lime stabilization Uniaxial Compressive 0.25
strength (10 days) 0.7 MPa
UTILIZATION OFPROCESSEDMATERIAL INPAVEMENTSURFACE ANDBASE-COURSE 191
Material to be evaluated as pavement material
Quality better than or equal to existing
material?
Figure 2. Process of adopting by-products in pavement construction (Japan Road Association, 1992).
In 2001, Manual for Asphalt Pavement was fully revised and renamed as Pavement Design and Construction Guide (Japan Road Association, 2001b), supplemented with Pavement Construction Manual (Japan Road Association, 2001c). A multi-layered elasticity based designing method was illustrated with some examples in a bit better way than in 1992: however, because of ambiguity in damage models, soft-ware, etc., little application has been reported so far except research purposes. On the other hand, implementation of performance-specification was probably the most important and influential matter in the revised manual.
3 PERFORMANCE-SPECIFICATION IN ASPHALT PAVEMENT CONSTRUCTION
3.1 Performance indices and examples
In response to the issue of “Technical standards regarding pavement structure” in 2001 by Ministry of Land, Infrastructure and Transport (Japan Road Association, 2001a), performance-specification was implemented in the Pavement Design and Construction Guide as mentioned earlier. The performance indices are specified in