Dr. Ambika Behl, Principal Scientist, CSIR-CRRI and Chakarpani Shekhawat, Product Manager, Wirtgen India

Rapid growth in industrial development and economy in last two decades has demanded upgradation of the existing road network in the country. Though there is a huge road network in the country, it is still inadequate to meet accessibility and mobility requirements. The conventional method of providing bituminous surfacing on flexible pavements requires significant amounts of materials and energy, so to reduce consumption of fuel and aggregates, pavement recycling technology can be adopted.

Pavement recycling can be performed in three ways: by cold mix recycling, hot mix recycling, and full depth reclamation process. If pavement failure is restricted to the upper layer only and the pavement is in a suitable bearing condition, hot recycling can be a good solution. If the pavement has structural flaws and is severely damaged, such as fatigue along the wheel path, rutting, and reflected cracking, full-depth reclamation (FDR) method is suggested. If the situation falls somewhere in between, then cold recycling can be the answer.

FDR and its Benefits
Full-depth reclamation of asphalt pavement is a pavement restoration technology that involves recovering an existing asphalt pavement as well as the underlying foundation into a new base layer. The depth of reclamation is affected by the current pavement’s thickness and condition, soil properties, and on traffic condition. In general, reclamation depth varies in between 100 to 300 mm. Full-depth reclamation reduces the pavement construction cost by 25–40 percent when compared with conventional pavement cost.

There are numerous advantages of full-depth reclamation, including increased bearing capacity, increased durability, structural strength, and stability of pavement. In comparison to approaches that require aggregates to be transported to the site, full-depth reclamation process reuses the in-place aggregates and hence less amount of virgin aggregates is required.

The reclamation process is defined in five phases including in-place pulverization and mixing of present asphalt layer with base and subgrade material. Several additives and water are blended with obtained pulverised pavement on which required gradation and compaction is performed to achieve a desired level. This process is followed by application of the surface course.

The use of cement in FDR provides a number of technological, economic, and environmental benefits. It results in pavements that are more durable, less erosive, and water-resistant, and can withstand stress due to high traffic loads. The slab-like characteristics of cement stabilized base layer mitigates the subgrade failure, pothole formation, and road roughness of pavement. This also leads to reduced design pavement thickness. It is important to calculate optimum stabilizer content of cement on the basis of strength and durability of treated slab in a laboratory to avoid formation of shrinkage cracks.

Upgradation of a PMGSY Road in Nagaland using FDR Technology
Upgradation of PMGSY Road Using Full Depth Reclamation Process in the State of NagalandPhoto 1: Project Road
Work for the PMGSY road in the state of Nagaland was executed under the PWD (R&B) Dimapur Division. Design for stabilized base using full depth reclamation was provided by CSIR-CRRI.

Preliminary visit of the site was done by CRRI officials, and it was found that the roadbed had a lot of big boulders that had to be removed before stabilization work could be started. The excavated material from site was transported to a CRRI lab along with the required aggregate, cement and chemical additives for carrying out the design work. The design traffic was given as 1 MSA.

When the samples received from site were analyzed and evaluated; it was found that they had single size aggregate and did not meet the gradation requirement. PI of the soil samples was also found to be on the higher side. All the soil samples were tested and PI was found to be in the range of 12-19. The additional aggregates were required as per gradation requirement of stabilized layer to achieve the desired strength. The CTB mix design work was carried out in CRRI by adding additional aggregates as per the gradation requirement. The design mix was targeted as per the gradation given in Table 400-4 (section 400) of MoRTH Specifications (5th revision)

Requirements of mix design for Stabilized Base Layer
Mix design for stabilization of selected base/sub-base course materials aims to provide adequate resistance against damage under traffic and environmental load stresses as they are important in maximizing the life of a pavement. Cement stabilized pavements are a unique category of materials which possess elastic modulus greater than granular materials but less than conventional cement concrete. The stabilized pavement layers are typically roller-compacted and thus require sufficient water content to achieve compaction but at the same time also requires water sufficient for cement hydration and workability with a grader.

Materials used in Cement stabilized aggregate base and Cement stabilized sub-base comprise three components basically: aggregates, cement and water. The proportioning of these elements is crucial in order to provide a matching supplement for structural design. The factors to be considered in the design of mix are gradation, density, index properties, and strength. Of these, gradation is the most important factor. The particle size distribution that gives maximum density is generally aimed at:

Fuller’s formula may be used to obtain the theoretical gradation for maximum density and is given by: P = 100 (d/D)0.5

Where, P = per cent finer than diameter, d (mm) in the material.
D = diameter of the largest particle, mm

Granular materials stabilized with cement may be allowed for use as capping layer over weak subgrade, as sub-base and base layer of pavement. For use in a base /sub-base course, the material shall be sufficiently well graded to ensure a well closed surface finish and have a grading within the range given in Table 400-4.

Upgradation of PMGSY Road Using Full Depth Reclamation Process in the State of Nagaland

The mix design shall be done to achieve a specified strength (compressive strength/unconfined compressive strength as specified) when tested on a specimens compacted to the density at optimum moisture content, tested in accordance with IS:2720(Part 8, as specified in the contract) after 7 days moist curing. The thickness of different stabilized layers, selection/choice for adoption of a particular grading and strength requirements of these layers are decided on the basis of pavement design.

Test Requirements
The unconfined compressive strength test: This test is carried out on cylindrical or cube specimens prepared by mixing the aggregate at a pre-determined moisture content and stabilizer (cement) content and compacting the mixed material into a mould at either a pre-determined density or at a given compactive effort. The choice of specimen size and shape depends on the grading of the soil; it is clearly desirable to keep as small as possible the ratio of the maximum particles size to the smallest dimension of the mould.

Mix Design of CCS Treated Base (CTB) Course for Thekurama Road Nagaland
In the present case, CTB mix was designed for 1 MSA, 7-day laboratory unconfined compressive strength (UCS) more than 3 MPa is required (as per IRC SP 72:2015- for low volume road) for use in base course. Samples of existing WMM, fresh aggregates from site were sent to CRRI. In this project work use of Roadcem additive was used. The laboratory trials were done at CSIR-CRRI for design of Cement treated base layer by using soil aggregate mix, fresh aggregate with different sizes (40mm,20mm,10mm) and 5% cement (OPC-43).

Compaction Characteristics
1. Maximum Dry Density (MDD)=2200 Kg/Cum (Modified Procter density as per IS 2720 Part:VIII).

2. Optimum Moisture content (OMC): 7.0 %

Upgradation of PMGSY Road Using Full Depth Reclamation Process in the State of NagalandPhoto2: Showing 15 cm Casted Cube mould for UCS Test

Upgradation of PMGSY Road Using Full Depth Reclamation Process in the State of NagalandPhoto 3: Showing UCS Test in progress

Unconfined Compressive Strength (UCS)
15 cm cube casted with existing soil and aggregate mix with 5% cement (OPC43)

UCS found at 7 days = 3.84 MPa.

At 5 percent cement addition, the compressive strength of 7 days cured specimen was found as per the requirement.

Upgradation of PMGSY Road Using Full Depth Reclamation Process in the State of Nagaland

Upgradation of PMGSY Road Using Full Depth Reclamation Process in the State of Nagaland

Field Implimentation
To prepare the road surface for full depth recycling, big boulders were removed (pic 5). Fresh aggregate, cement and additive were spread over the existing road surface as per the design mix requirement. (Pic 6 shows the aggregates and stabilizer additives spread on the surface). WR 200 Recycling machine was used with water tanker for pulverizing the existing pavement surface and in-situ mixing of stabilizing additive, cement and water was carried out to create a homogeneous mix. Top 210 mm was pulverized. (pic 7). Preliminary compaction is done with the help of padfoot roller (photo 8a) and final compaction is done with steel drum compactor (pic 8c). The compaction was then followed with curing process prior to overlaying with bituminous surface. Curing is to be done for minimum 7 days with water spraying 2-3 times a day. Aggregate interlayer is also provided as crack relief layer.

Upgradation of PMGSY Road Using Full Depth Reclamation Process in the State of NagalandPhoto 7: In situ FDR Stabilization in progress

Upgradation of PMGSY Road Using Full Depth Reclamation Process in the State of Nagaland

Photo 9 shows the finished CTB surface. The FDR process with stabilization resulted in construction time saving, minimal use of virgin aggregates, less transportation of materials and several other environmental benefits.

Upgradation of PMGSY Road Using Full Depth Reclamation Process in the State of NagalandPhoto 9: Finished CTB Surface

References
  1. Ghanizadeh, A.R., Rahrovan, M. and Bafghi, K.B., 2018. The effect of cement and reclaimed asphalt pavement on the mechanical properties of stabilized base via full-depth reclamation. Construction and Building Materials, 161, pp.165-174.
  2. Dai, S., Skok, E., Westover, T., Labuz, J. and Lukanen, E., 2008. Pavement rehabilitation selection.
  3. Stroup-Gardiner, M., 2011. Recycling and reclamation of asphalt pavements using in-place methods (No. Project 20-05 (Topic 40-13)).
  4. Reeder, G.D., Harrington, D.S., Ayers, M.E. and Adaska, W., 2017. Guide to Full-Depth Reclamation (FDR) with Cement (No. SR1006P).
  5. Morian, D.A., Solaimanian, M., Scheetz, B. and Jahangirnejad, S., 2012. Developing standards and specifications for full depth pavement reclamation (No. FHWA-PA-2012-004-090107). Pennsylvania. Dept. of Transportation.
  6. Smith, S. and Braham, A., 2018. Comparing layer types for the use of PavementME for asphalt emulsion Full Depth Reclamation design. Construction and Building Materials, 158, pp.481-489.
  7. Stroup-Gardiner, M., 2011. Recycling and reclamation of asphalt pavements using in-place methods (No. Project 20-05 (Topic 40-13)).
  8. Bang, S., Lein, W., Comes, B., Nehl, L., Anderson, J., Kraft, P., deStigter, M., Leibrock, C., Roberts, L., Sebaaly, P.E. and Johnston, D., 2011. Quality Base Material Produced Using Full Depth Reclamation on Existing Asphalt Pavement Structure–Task 4: Development of FDR Mix Design Guide (No. FHWA-HIF-12-015). United States. Federal Highway
  9. Godenzoni, C., Graziani, A., Bocci, E. and Bocci, M., 2018. The evolution of the mechanical behaviour of cold recycled mixtures stabilised with cement and bitumen: field and laboratory study. Road Materials and Pavement Design, 19(4), pp.856-877.
  10. Gonzalo-Orden, H., Linares-Unamunzaga, A., Pérez-Acebo, H. and Díaz-Minguela, J., 2019. Advances in the study of the behavior of Full-Depth Reclamation (FDR) with cement. Applied Sciences, 9(15), p.3055.
  11. Guthrie, W.S., Brown, A.V. and Eggett, D.L., 2007. Cement stabilization of aggregate base material blended with reclaimed asphalt pavement. Transportation Research Record, 2026(1), pp.47-53.
  12. Pappas, J., 2012. Environmental considerations of in-place recycling. In Virginia Pavement Recycling Conference. Virginia: Virginia tech transportation institute.
  13. Luhr, D.R., Adaska, W.S. and Halsted, G.E., 2007. Guide to full-depth reclamation (FDR) with cement.
  14. Mallick, R.B., Bonner, D.S., Bradbury, R.L., Andrews, J.O., Kandhal, P.S. and Kearney, E.J., 2002. Evaluation of performance of full-depth reclamation mixes. Transportation Research Record, 1809(1), pp.199-208.
  15. Puppala, A.J., Hoyos, L.R. and Potturi, A.K., 2011. Resilient moduli response of moderately cement-treated reclaimed asphalt pavement aggregates. Journal of Materials in Civil Engineering, 23(7), pp.990-998.
  16. Kearney, E.J. and Huffman, J.E., 1999. Full-depth reclamation process. Transportation Research Record, 1684(1), pp.203-209.
  17. Maccarrone, S., Holleran, G., Leonard, D.J. and Hey, S., 1994. Pavement recycling using foamed bitumen. In 17TH ARRB CONFERENCE, GOLD COAST, QUEENSLAND, 15-19 AUGUST 1994; PROCEEDINGS; VOLUME 17, PART 3.
  18. Jones, D., Louw, S. and Wu, R., 2016. Full-Depth Reclamation: Cost-Effective Rehabilitation Strategy for Low-Volume Roads. Transportation Research Record, 2591(1), pp.1-10.
  19. Bang, S., Lein, W., Comes, B., Nehl, L., Anderson, J., Kraft, P., deStigter, M., Leibrock, C., Roberts, L., Sebaaly, P.E. and Johnston, D., 2011. Quality Base Material Produced Using Full Depth Reclamation on Existing Asphalt Pavement Structure–Task 4: Development of FDR Mix Design Guide (No. FHWA-HIF-12-015). United States. Federal Highway Administration. Office of Pavement Technology.
  20. Batioja, D.D., 2011. Evaluation of cement stabilization of a road base material in conjunction with full-depth reclamation in Huaquillas, Ecuador. Brigham Young University.
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