Table 1. Virgin Aggregate Gradation for DBM Grade II
Reclaimed Asphalt Pavement (RAP) is a popular recycled material used in the construction of pavements. In contrast, incorporating RAP into asphalt mixtures is a complex process that involves a thorough understanding of all aspects of the mix design. The purpose of this review paper is to provide a comprehensive analysis of asphalt mixtures containing RAP. Based on this study and previous research papers, it is possible to conclude that using RAP is advantageous because RAP mixes can produce results that are equal to or even better than virgin mixes. The specifications and mix design followed the MORTH 5th revision for dense bituminous macadam grade II mix. The Marshall properties were obtained, which includes bulk density, flow stability, voids in mineral aggregates, and an air void filled with bitumen. RAP mixes have a positive effect on a number of parameters including Marshall Stability, Indirect tensile strength and rutting. This study provides information about RAP technology to the designers, engineers and researchers.
Large amounts of reclaimed asphalt pavement (RAP) materials are produced during highway maintenance and construction. A portion of this can be used in new hot mix asphalt concrete, while the remainder can be used for other purposes. The environmental impact, waste stream, and transportation costs associated with road maintenance and construction activities would be reduced if these materials could be re-used in road base and sub-base. Blending aggregates and adding chemical stabilizers can improve the properties of RAP materials. Construction and demolition of wastes have gradually increased in recent years (Gottumukkala et al., 2018). The lack of available landfills has resulted in waste disposal problem. The greatest solution may be to reuse these materials after properly recycling them. By recycling these road aggregates produced at the same location, the cost will be reduced by approximately 25% to 30% (Guo et al., 2016).
Before using such materials, the mechanical properties must be tested, and if necessary, appropriate blending must be performed. Reclaimed asphalt pavement (RAP) materials and recycled concrete aggregate (RCA) are the most commonly used recycled materials. RAP and RCA production yields a high-quality grading aggregate. The asphalt coating applied to RAP aggregates reduces water absorption in aggregates (Xu et al., 2013).
Recycled asphalt pavement (RAP) is another increasingly popular energy-saving and environmental friendly alternative to the asphalt industry. The reuse of aggregates and bitumen results in significant savings when recycling the existing bituminous mixes (Huang et al., 2005). By using recycled materials, it is estimated that about 14 to 34% of cost will be reduced while considering only the material and construction costs (Sulyman et al., 2014).
According to studies, incorporating RAP in various proportions in bituminous mixes increased the mechanical properties of the mix (Kristjansdottir et al., 2007). It is possible to use 100% recycled asphalt without affecting the performance of asphalt mixes (McDaniel & Anderson, 2001). The use of recycled aggregate had no effect on the tensile strength, moisture susceptibility, or mechanical response of the mixes. The rutting resistance of recycled asphalt mixes has been found to be comparable to that of virgin mix (Vargas-Nordcbeck & Timm, 2012). Replacement of HMA mix with 0 and 40% of RAP induces low moisture damage susceptibility, when compared to conventional HMA mix (Copeland, 2011). As compared to 10 and 20% RAP, mixture properties changed significantly at 30% RAP content (Hoyos et al., 2011).
Previous research studies show that emissions from the production of WMA are lower than those from the production of conventional HMA (Barthel et al., 2004; De Groot et al., 2001). Under various conditions, emissions ranging from 30 to 98% of that of HMA were observed (Hasan et al., 2019).
The materials used in this study are conventional aggregates, bitumen, RAP and cement. All of the material properties meet the requirements of the MORTH 5th revision specification and their respective IS codes.
Bitumen grade 60/70 has been used in this study. The obtained RAP also has 60/70 grade. Basic tests like penetration, softening point, flash and fire test were performed and the results have been obtained.
In accordance with Bureau of Indian Standards, physical properties were tested in laboratory and fairly strong, tough, hard and desirable right shaped aggregates were used (Bureau of Indian Standard, 1963a, 1963b, 1963c). As per Table 500-10 of MoRTH (5th revision) dense bituminous macadam grade II (Bureau of Indian Standard, 1970; Indian Roads Congress, 2013) has been chosen as shown in Table 1.
Table 1. Virgin Aggregate Gradation for DBM Grade II
RAP physical characteristics include bitumen content, particle gradation, and moisture condition, according to a literature review and conventional practice. These various characteristics vary depending on the RAP source, including the characteristics of the asphalt pavement from which the RAP has been produced. RAP can be obtained by various process like milling and full depth reclamation. Milling or full-depth removal/reclamation of asphalt pavement is the most common methods of removal. Milling is the process of removing the pavement surface with a milling machine that can remove up to 50 mm (2 inch) of thickness in a single pass. Ripping and breaking the pavement with a bulldozer rhino horn and/or pneumatic pavement breakers is required for full-depth removal.
A brief introduction of asphalt mixtures for DBM grade II with different percentages of RAP mixed with warm mixes and hot mixes without sacrificing performance are mentioned. Figure 1 depicts the methodology that has been used for this study.
Figure 1. Layout of Methodology
Studies have been reported to indicate the effect of RAP on the performance of hot mixes and warm mixes. In case of warm mix asphalt two predominant additives that have been used are Zeolite and Sasobit and the analysis have been reported on the same.
Data regarding Marshall, indirect tensile strength and rutting for both hot mix and warm mix were collected from different journals (ASTM International, 2006, 2011). And the collected raw data has been segregated on the basis of different RAP content which varies from 20, 30, 40 and 50%. Indirect tensile strength of warm asphalt mix with RAP content and different additives were analyzed. Regression analysis has been performed on the data to get best fit line for the data with an equation of the form y = mx+c, and R2 which varies from 0 to 1.
The basic physical properties tests of reclaimed aggregates and binder were conducted and the obtained values were presented in Table 2.
Table 2. Properties of Recovered Binder
The results of the Marshall test with different proportions of RAP content (0, 10, 20, 30, 40, 50 and 60%) has been represented in Figure 2. Figures 2 (a), (b), (c), (d) and (e) illustrates the relationship between Marshall parameters like VMA, VFB, flow, air voids and stability respectively with various RAP proportions.
Figure 2. Relation between Marshall Parameters with RAP for (a) Voids in Mineral Aggregate, (b) Voids Filled with Bitumen, (c) Flow, (d) Air Voids, (e) Stability
Figure 3 (a), (b), (c), (d) and (e) indicates variation of Marshall parameters with various RAP proportions and binder content for both hot asphalt mix and warm asphalt mix. Proportion of RAP varies from 20% to 50% and the binder content varies from 5% to 6.5%.
Figure 3. Relation between Marshall Parameters with Binder Content and RAP Proportion for (a) Voids in Mineral Aggregate, (b) Voids Filled with Bitumen, (c) Flow, (d) Air Voids, (e) Stability
Figure 4 (a), (b), (c), (d) and (e) indicates variation of Marshall parameters with various RAP proportions for both hot mix and warm mix. y=mx+c represents expression of a straight line, where y-axis indicates linearly dependent and x-axis indicates linearly independent, m is the slope of the line and c indicates intercept of a linear line. Square of correlation is represented as R2, where R2 varies from 0 to 1.
Figure 4. Variation of Marshall Parameters with RAP Content for Both Hot and Warm Mixes for (a) Voids in Mineral Aggregate, (b) Voids Filled with Bitumen, (c) Flow, (d) Air Voids, (e) Stability
Rut depth analysis for HMA mixes with RAP proportions of 0, 30 and 50% were analysed. Figure 5 shows variation of rut depth in mm with various RAP proportions. There is linear variation of rut depth with respect to RAP content, as the RAP content increases the rut depth decreases.
Figure 5. Variation of Rut Depth (mm) with Various RAP Proportions
Figure 6 (a), (b) and (c) indicates variation of unsoaked, soaked and TSR with various RAP proportions for warm Asphalt mix with and without additives. Additives like Zeolite and Sasobit are used.
Figure 6. Variation of Indirect Tensile Strength Parameters with Various RAP Proportion and Additives (Zeolite and Sasobit)
In this study DBM II grade as per MORTH is adopted to check the suitability of various proportions of RAP mixtures. Based on Marshall tests results, it has been concluded that 35% of RAP has been found to be optimum. The regression equations to relate the bitumen content with Marshall properties such as VMA, VFB, flow, air voids and stability for various percentages of RAP has been presented. According to Marshall parameters it has been concluded that hot mix asphalt (HMA) showed better performance compared to warm mix asphalt (WMA). An increasing trend is observed in the indirect tensile strength due to the use of different additives. Sasobit additive gave better results than Zeolite in comparison with the virgin material. Better strength results were obtained for WMA mixes with different proportion of RAP content by adoption of Sasobit additive. For 40% RAP content, TSR ratio of WMA mix with Sasobit additive has achieved 2.25% more strength compared to conventional mix. In the same way, Zeolite additive has achieved 1.69% more strength compared to conventional WMA mix. The rut depth in the HMA mixes has been improved by 33.3% when compared to virgin aggregates and 30% RAP content. Increase in RAP content to about 50% comparatively gave a better result in terms of rut depth for HMA mixes. From the results obtained it is concluded that incorporation of 50% RAP content improved the rut depth to about 66% when compared to virgin aggregates.