REJUPAVE Technology for High RAP Recycling of Bituminous Pavement

Satish Pandey, Principal Scientist at CSIR-CRRI, New-Delhi, and Associate Professor, Academy of Scientific and Innovative Research, gives a brief overview of Hot Mix recycling process using bio-oil based rejuvenator REJUPAVE to facilitate high RAP utilization in recycled bituminous mixes, along with its application methodology and benefits.


India is having world’s second largest road network in terms of length. Bituminous roads constitute around 95% of this road network, which requires periodic maintenance to maintain the riding quality. This periodic maintenance is usually carried out using bituminous overlays. Application of bituminous overlays on distressed bituminous surfaces is a costly road maintenance measure which consume huge quantities of natural aggregates and bitumen. Recycling of bituminous layers using Hot-in-Plant recycling technique with maximum amount of reclaimed asphalt pavement material can significantly minimize the requirement of virgin natural aggregates and bitumen for road construction. Unfortunately, the present RAP utilization level in the country is largely limited to 30% in Hot-in Plant recycling process that too is not being carried out in majority of the road projects. Bituminous pavement recycling using REJUPAVE Technology can facilitate 50 to 80 % Reclaimed Asphalt Pavement (RAP) material utilization in recycled bituminous mixes which can lead to 25 to 40% net saving in the cost of road maintenance works besides reducing ever increasing reliance on natural materials for road construction works. This paper provides a brief overview of Hot mix recycling process using bio-oil based rejuvenator, REJUPAVE to facilitate high RAP utilization in recycled bituminous mixes with its application methodology and benefits.

Introduction

Bituminous pavement recycling of bituminous binder course and wearing course layers is necessary to save natural aggregates and virgin bitumen. The benefits of using reclaimed asphalt pavement (RAP) material in fresh bituminous mixes has multiple benefits which includes conservation of natural resources (aggregate, binder and fuel), reductions in energy consumption, decreases in GHG emissions (including greenhouse gases) and reduction in cost of maintenance. In contrast, the incorporation of elevated quantities of RAP in bituminous pavements presents several challenges, such as the variability of the RAP, design methodology, and adequate long-term performance. Bituminous mixes, used in road surfacing work, consists of aggregate and bitumen binder. As bituminous surfacing ages, the bitumen binder is oxidized and the bitumen loses its elastic properties. This oxidative hardening of the bitumen binder is manifested in the form of different types of surface distresses such as cracks, fatigue cracking, pot holes, ravelling of the surface, etc. The riding quality and the structural integrity of distressed bituminous surface can be restored through recycling of bituminous layers. Reclaimed Asphalt Pavement Material (RAP) are milled through the pavement surface and can be reused with virgin hot mix asphalt (HMA) in different proportion depending upon the extent of oxidative hardening of the residual binder in the RAP. REJUPAVE technology of Hot Mix Recycling is based on the bio-oil based rejuvenator REJUPAVE developed by CSIR-CRRI which replenishes the viscoelastic properties of oxidized binder thus facilitating the uses of reclaimed aged bitumen and aggregates retrieved from distressed bituminous layers in recycled bituminous mixes. REJUAPEV technology of the pavement recycling is based upon the bio oil based rejuvenator REJUPAVE and distinct bituminous mix design methodology including mixing and compaction temperature to facilitate high RAP utilization in recycled bituminous mixes through Hot-in Plant recycling technique. This paper proves a brief overview of REJUPAVE technology for road recycling and maintenance works along with their material composition, application methodologies and benefits.

Material and Mix Design for Hot Mix Recycling

For hot-in plant recycling of asphalt mixes major ingredients are Reclaimed Asphalt Pavement Material (RAP), Rejuvenator, virgin aggregates and virgin bitumen binder. Following sub sections provides the characteristics of different ingredients along with mix design methodology:

Rejuapave Rejuveanator

REJUAPVE rejuvenator is an organic bio-oil based rejuvenator developed by CSIR-CRRI to restore the rheological and visco-elastic properties of oxidized bituminous binder of reclaimed asphalt pavement material. It also helps to lower down the laying and compaction temperature of recycled hot bituminous mixes produced through Hot-in plant recycling process. Physical properties of Rejupave rejuvenator is given in Table 2.1.

REJUPAVE can be added directly in the bitumen tank or can be added in to bitumen line through separate bin. In present work designed dosage of REJUPAVE was directly added in to bitumen tank.

Characterization of Reclaimed Asphalt Material (RAP)

Distressed bituminous material reclaimed through milling process from bituminous layers is called Reclaimed Asphalt Pavement (RAP) Material. RAP can be extracted through binder and wearing course of bituminous pavement. In India majority of bituminous pavements are having Dense Bituminous Macadam as binder course and Bituminous Concrete as wearing course layers. RAP is extracted from different bituminous layers through milling process and stored in separate bins for further classification and characterization. RAP material largely consists crushed aggregates coated with oxidized bituminous binder. Binder content in the RAP generally varies between 2 to 4% by weight of RAP. Photo 2.1 shows the distressed bituminous surface and extraction of RAP through milling machine.


For present work RAP is obtained from Varanasi Ring Road project site of GR Infra pvt. Ltd. As more than 30% RAP is required to be utilized using Hot-in Plant recycling process the extracted RAP was further segregated in COARSE and FINE RAP by segregating it through deck sieves. Coarse RAP primary comprises the fraction of RAP passing from 19 mm sieve while the fine RAP consists, fraction of RAP passing from 9.5 mm sieve. Coarse and Fine RAP were further subjected to sieve analysis to determine their gradation and residual binder content. Residual binder content is determined through binder extraction test by carrying out quantitative separation of aggregate and bitumen. Washed aggregates are further tested for various physical properties to ensure their compliance with Table 500-8 “Physical requirements for Coarse Aggregate for Dense Bituminous Macadam” of MoRTH specifications for Road and Bridge works. Photo 2.2 shows the coarse and fine RAP samples while table 2.2 provide the gradation and characteristics of RAP samples.


Virgin natural aggregates, belonging from basaltic rock groups were obtained from the project site and used to meet out the gradation requirement with variable RAP content. Table 2.1 gives the gradation of coarse and fine RAP along with the residual binder content and moisture content.

Mix Design of Recycled Bituminous Mix

Target viscosity of virgin bituminous binder VG 40, for variable RAP content i.e 40,50 and 60% RAP content is determined through the viscosity vs. RAP% graph as shown in figure 2.1. This graph is developed as per the procedure prescribed in ASTM D 4887. Equation 2.1 of ASTM D 4887 is utilized to determine the target viscosity of virgin bituminous binder (VG 40) at variable RAP contents:


Where,

Vv= Viscosity of Virgin Binder or Soften Virgin Binder (Poise),

Vb= Viscosity of Blend (Poise),

Vr= Viscosity of RAP Binder (Poise),

% RAP= Percentage of RAP in Recycled Mix

For 50% RAP content target absolute viscosity of virgin bituminous binder comes out to be 1850 poise. A trial mix blends with 50% RAP content was developed by mixing the coarse and fine RAP with virgin aggregates and stone dust in such a manner that the resultant blend shall satisfy the stipulated gradation requirements for DBM grade II mix as per MoRTH specifications for Road and Bridge works, Vth revision. Table 2.3 and Fig. 2.3 shows the recycled mix blends with 50% RAP content.


Job mix for 50% RAP content is developed using Marshall method of mix design as stipulated in Asphalt Institute manual MS 20 for Hot Mix Recycling. Job mix is prepared to carry out Hot-in-Plant Recycling using Marini batch type hot mix plant having hot/coarse and cold/fine RAP feeding capacity. Hot and Cold RAP are utilized in equal quantity to achieve 50% RAP content in the recycled mix. Total binder content in the recycled hot mix for 50% RAP content is kept 4.75% by weight of mix. Table 2.4 provides the job mix composition for 50% RAP content along with the Marshall properties of recycled mix.

Preparation of Recycled Mix and Laying Protocol

Recycled bituminous DBM II mix at 50% RAP content is prepared using MARINI Hot mix recycling plant with Cold and Hot RAP feeding facility as shown in photo 2.3.


REJUPAVE rejuvenator was added into the bitumen tank with virgin binder. Bituminous mixes are produced at 130⁰C in Hot Mix plant. Recycled Dense Bituminous Macadam Mix-II layer with 50% RAP content is laid on the project site in 50 mm compacted thickness. Addition of COLD RAP in pug mill of HMA plant lower down the mix temperature of recycled bituminous mix. Photo 2.4 shows the compaction of Dense bituminous Macadam layer with 50% RAP content along with measurement of rolling temperature and laying thickness. Photo 2.5 shows the road section built with 50% RAP content in DBM-II Layer in Feb. 2021 at Varanasi ring road project site. Post construction bituminous cores were extracted to assess various mechanical and physical properties. From the laboratory and field test results it is found that the recycled Dense Bituminous Macadam mix (DBM-2) with 50% RAP, and REJUPAVE rejuvenator is satisfying various mechanical properties such as Marshall Stability, ITS, Resilient Modulus and Field density as per mix design requirement. Marshal specimens casted through plant mix were also found to satisfying the various mechanical properties requirements stipulated in MoRTH specification 5th revision for Road and Bridge Work clause 505 for Dense Bituminous Macadam.

Conclusion

Bituminous pavement recycling using REJUPAVE technology provides a cost-effective green alternative to maximise RAP utilization in bituminous layer construction. High RAP recycling also reduces the cost of conventional bituminous overlays and minimizes the requirement of virgin aggregates and virgin bituminous binder for bituminous road construction and maintenance works. Based upon the laboratory and field trials findings, following conclusions are drawn:

1. REJUPAVE rejuvenator restore the viscoelastic properties of oxidized binder of the RAP thus reduces the requirement of virgin binder for recycling of bituminous pavement
2. Combination of Hot and Cold RAP feeding can be effectively utilized to maximize the RAP content in the recycled mix
3. REJUPAVE rejuvenator is found to facilitating desired compaction of bituminous layer at lower laying and temperature ranges as well
4. Dense Bituminous Macadam mix prepared with 50% RAP content is found to satisfying various mechanical properties stipulated in MoRTH specification for DBM -II layer.

Acknowledgement

This field work would not have been possible without the exceptional support of M/s G.R.Infraprojects Limited and Verma Industries. The generosity and expertise of one and all have improved this study in innumerable ways. CSIR-CRRI placed on record its deep gratitude to M/s G.R.Infraprojects Limited and Verma Industries for their invaluable support during the field work.

References:

1. MoRTH specifications 5th revision for Road and Bridge Works
2. IRC:120:2015: Guidelines for Recycling of Bituminous Pavement
3. ASTM D 4887 M-11 Standard Practice for Preparation of Viscosity Blends for Hot Recycled Asphalt Materials
4. IRC:SP:101:2019 Guidelines for Warm Mix Asphalt