Use of asphalt milling material in construction of the roadway

A pilot study on asphalt milling materials as green construction materials to replace virgin aggregates in the roadbase layer for a temporary diversion road at Pan Borneo Highway was conducted by WCT Berhad. Asphalt milling material was milled from the existing road, and various tests were conducted to determine the material characteristics. Based on the laboratory test results obtained, the asphalt milling materials has been used as subgrade for permanent road, the subbase and roadbase for temporary construction access and also the roadbase for temporary diversion road. This paper will discuss on the application of asphalt milling materials in roadbase of temporary diversion road. A 200m Trial section was constructed to obtain performance of milling asphalt materials. The result showed that the temporary road remained in good condition after 30 days of road traffic.


Introduction
Road construction and upgrading work demand consumption of a significant amount of non-renewable virgin materials. The fast depleting, declining quality of aggregate sources, and escalating price of bitumen have motivated the construction industry to seek green solutions to reduce production cost and use of virgin materials. There are many publications on the used recycled asphalt materials, however it is still not common in the Malaysia construction industry. The main issues are not only lacking of the facilities to produce the asphalt materials using recycled asphalt pavement materials but also lack of experience to ascertain the quality of mass production of recycled asphalt pavement materials and its performance. For this study, the use of asphalt milling material in the subgrade, subbase, and roadbase layers of a road is proposed.
Recycled asphalt obtained from the milling of existing bituminous surfacing in pavement construction are routinely used in many countries to conserve natural resources. Recycled asphalt pavement often contains high-quality, well-graded aggregates that are coated with bitumen. Economy, ecology, and energy conservation are all served when bitumen and aggregate-the two most frequently used pavement construction materials are reused to provide a strengthened and improved pavement. The major advantages of the use of recycled asphalt pavement are (a) lower cost, (b) reduction in the use of natural resources, (c) reduction of damage to other roads from the transportation of materials from a quarry site, (d) no increase in pavement thickness.
Hoppe et al. [1] recommended that the Virginia Department of Transportation (VDOT) to allow the use of recycled asphalt pavement in a roadbase material on highway construction projects. The study further recommended that the allowable percentage of recycled asphalt pavement in a blend be phased in gradually to allow VDOT to gain familiarity with the materials and processes involved. Federal Highway Administration [2] allows the use of recycled asphalt pavement in granular base or subbase aggregate. However, recycled asphalt pavement must be crushed, screened, and blended with conventional granular aggregate [5] The A2/M2 Cobham widening in Kent was the first full-scale use of asphalt arisings as a Type 4 sub-base in the UK [3]. The total length of the scheme was 17km, and work commenced in November 1999. The project encompassed the construction of a new London-bound carriageway and the reconstruction of existing carriageways to form a new coast-bound carriageway. The coast-bound works initially involved the removal of redundant sections of the A2/M2 carriageway. Planing operations produced site-won asphalt arisings, which were used in construction phases as Class 6F3 capping and Type 4 sub-base. A CSM Type 4 subbase site trafficking trial was undertaken at the site in November 2001.
For a road widening project, the construction of temporary road diversion is necessary before widening the road. The process will remove part of the surface of a paved area of the existing road. The asphalt milling material can be reused at the adjacent localized area if it is well planned. Hence, the intention to perform a Pilot Study on the usage of asphalt milling material as a subbase for Pan Borneo is proposed. Lebuhraya Borneo Utara Sdn Bhd supported the idea for conducting the pilot study and the associated research works and the usage of the asphalt milling material as permanent works shall be decided from the findings of the Pilot Study research. An industrial collobration program (ICP) between Monash University Malaysia and WCT Berhad has been initiated to conduct the pilot study on asphalt milling materials. The pilot study project explored three applications of asphalt milling materials: i.
Subgrade for the permanent road at Pan Borneo Highway was conducted at the WPC09, Bintulu to Tatau, Pan Borneo, Sarawak, Malaysia job site. ii.
Subbase and roadbase for temporary construction access; iii.
Roadbase for temporary diversion road; This paper presents the lab testing results, design and construction of temporary diversion road using asphalt milling materials. The 200m long temporary road is constructed from CH18+175 to CH18+375 of Pan Borneo Highway, as shown in    Table 1. The sample of the milling materials comply with the JKR specification for Atterberg limit, aggregate crushing value and compaction test except that the grading of the milling material did not comply with the grading of the subbase. The test results for roadbase are tabulated in Table 2. The test results showed a range for medium to fine gradation and it did not comply with the gradation limits for roadbase material as shown in Fig. 3. The CBR of asphalt milling materials was less than 80% of CBR, thus failed to comply to the CBR requirement of BS1377.   If the test results of the material failed the meet the soaked CBR values, it will be used for the following works: i. Milling material to be used as haunching layer for culvert installation. ii. Milling material to be used as backfilling for culvert installation. iii. Milling material to be used as patching pot holes on road surface.
Another main challenge of this study was that the asphalt milling materials collected from milling off the existing road to be reuse for temporary diversion road for the same project is insufficient for continuing construction due to the degradation of the materials. The milled off the material itself becomes fine. There were many occasions the recycle materials were insufficient and the timing was not right for road diversion construction. The materials were then used as granular filled for drainage work.

The proposed pavement structure for temporary diversion road using asphalt milling material
It is noted that most of milling material fails to comply with the CBR requirement of Roadbase. Therefore, a full test section for the application of roadbase is conducted to verify the performance. The proposed test section for pavement structure for the temporary diversion road was shown in Fig.4. The text section consists of a subbase of 300mm crusher run subbase, 250mm milling material of roadbase and 160mm ACBC for this pilot study. This test section will be tested based on daily usage of the temporary road & vehicles category as shown in Table 3. The traffic consists of 40% are heavy size vehicles, 30% are medium size vehicles, and 30% light size vehicles. Table below shows the category of the vehicles. The test results for all compaction passes showed that the relative compaction (%) was more than the specification requirement of 95%. Based on the above mentioned, the minimum relative compaction achieved after 8 passes was 98.3%. Therefore, it is 8 passes shall be implemented for the test section during the road construction.
The construction of the temporary road started with subgrade. Each layer of fill shall be spread and levelled by bulldozer followed by compaction of the roller compactor. The thickness of the compacted subgrade is 300mm thick. For subbase, each layer of subbase shall not exceed 300mm thick compacted thickness shall be laid and compacted to the lines, levels, grades, dimensions and cross-sections. Compaction using a vibratory roller was carried out for each layer to achieve CBR value of 30 or more when compacted to 95% of the maximum dry density determined in the B.S 1377 compaction test (4.5kg Rammer Method). Roadbase layer began after the subbase was completed. 250mm thick of milling recycled asphalt material shall be laid, level and well compacted. 125mm thick each layer. The 160mm asphaltic concrete base course was laid by pavers machine after the roadbase layer is completed. After the laying of the first layer, tack coat application was made prior to laying of the 2nd layer of 80mm thick ACBC.  Table 1 shows the comparison of the cost-saving derived from the reuse of asphalt milling materials of this pilot study. For a temporary diversion road, the cost of laying of 300mm thick subbase and 350mm thick roadbase is estimated at RM69,280.00. Based on the use of asphalt pavement milling materials, the construction cost is estimated at RM59,840.00. Therefore, there is a cost-saving of RM 9,440.00, and as shown in Table. 4. It is approximately of 14% of cost saving.

Conclusion
The constructed temporary diversion road with recycled asphalt milling materials was open for traffic. Based on the 30 days of road monitoring, the road is able to perform to standard even though the grading or particle size of the asphalt milling materials and CBR value did not meet the grading specification. However, the durability has yet to be examined. A further study is required to look into the grading and the combination of pavement structure design. The use of asphalt milling materials for temporary diversion road construction resulted in a cost-saving of material. In summary, this pilot study has demonstrated that the use of recycled asphalt milling pavement in construction is economically feasible. The data collected from this pilot study will be an essential reference for future studies.