Utilization of reclaimed asphalt pavement aggregates containing waste from Sugarcane Mill for production of concrete mixes

Highlights

• Use of RAP and BGA in concrete can be a sustainable approach.

• Coarse RAP has more potential than Fine RAP for concrete pavements.

• BGA can replace 10% cement in RAP inclusive concrete.

• RAP blended with BGA would be economically and environmentally friendly.

Abstract

The present study investigates the potential of waste originating from road sector (RAP) and agricultural industry (Sugarcane Bagasse Ash) for production of concrete mixes. 5 mixes were prepared by partial replacing natural aggregates by coarse RAP (CRAP) and fine RAP (FRAP) in the proportions of 50% and 100%. 3 subsequent mixes were prepared by incorporating 100% RAP aggregates blended with 10% and 15% Bagasse Ash (BGA) as part replacement of cement. It was noted that incorporations of FRAP aggregates decreased the fresh, mechanical and durability properties of concrete significantly compared to CRAP aggregates. Incorporation of 10% BGA was found to enhance the mechanical and durability properties of 100% RAP concrete significantly. Economic analysis of the considered mixes showed that incorporations of RAP aggregates blended with BGA can reduce the total cost of 1 m³ concrete by more than 40% as compared to conventional concrete. From the present study, it is recommended to replace 10% of cement by BGA in RAP concrete as this would not only strengthen the pavement but provides with environmental and economic benefits.

Introduction

Concrete is considered to be utmost consumable resources next to water (Mukharjee and Barai, 2014). Besides its durability, zero maintenance if well-constructed is another property which gains the attention of the system towards making concrete pavements as the new life line of the nation (Singh et al., 2017a). But scarcity of Natural Aggregates (NA) and high initial cost remains the cause for building flexible pavements despite knowing the superiority of concrete over flexible pavements. On the other hand, production of concrete components such as aggregates and cement accelerates the global warming by producing enormous amount of CO₂ (Cao et al., 2016). Production of 1 ton of cement produces equal amount of CO₂ (Noor-ul-Amin et al., 2015) which is approximately equal to 7% of total gas produced all over the globe (Rerkpiboon et al., 2015).

More than 90% of Indian highways are of flexible pavements in which majority have attained its service life. Demolition of the same generates large quantity of inert waste that are either hauled off to the disposal site or stockpiled along the generation point (Wang, 2016). Besides high transportation cost, it also requires huge land for disposal. This increases the burden on landfill facilities and results in being dumped at nearby farms (Afonso et al., 2016). Hindrance to existing facilities and unaesthetically view further deteriorates the situation. On the other hand, ban on queering activities and unparalleled availability of trustworthy recycled aggregates compels the construction authorities to search for an economical alternative for the construction of pavements. Studies pertaining to use of RAP in base, subbase, embankments and as a fill material has been conducted widely by different authors (Avirneni et al., 2016, Ebrahim Abu El-Maaty Behiry, 2013, Montepara et al., 2012, Stolle et al., 2014, Thakur et al., 2012) whereas utilization in wearing course of concrete pavements remains scanty. Out of which feasibility of FRAP has not been investigated in detail due to gap graded nature of FRAP aggregates. But in developing and under developed countries like India, Bangladesh, Sri Lanka extraction of RAP materials is carried out by demolition of the pavement using bulldozer or backhoe which can provide well graded fine RAP aggregates due to involvement of significant dust particles from underlying layers of the flexible pavements. The asphalt coating around RAP aggregates becomes very stiff owing to long term ageing during service life (Huang et al., 2011). Moreover, stockpiling of RAP in open atmosphere results in further oxidation of asphalt layer. Re-use of RAP with stiffened asphalt layer in bituminous mixtures was found to increase the performance by reducing the stress concentration (Huang et al., 2005a), however, limited studies are available on effect of RAP on performance of concrete pavements.

Studies pertaining to use of RAP aggregates in concrete reveals that asphalt layer sticking around the RAP aggregates plays an important role in reducing the fresh and mechanical properties of concrete significantly (Modarres and Hosseini, 2014, Settari et al., 2015, Al-Oraimi et al., 2009, Berry et al., 2015, Brand et al., 2012, Brand and Roesler, 2015, Hossiney and Tia, 2010, Mahmoud et al., 2013, Huang et al., 2005b, Huang et al., 2006, Mathias et al., 2009, Delwar et al., 1997, Okafor, 2010, Singh et al., 2017b). Reductions in compressive, splitting tensile and flexural strength compared to control mix were observed in all the studies due to formation of bond between asphalt layer and cementitious matrix rather than between aggregate surface and cement mortar. Tendency of asphalt to repel to water was noted to increase the initial slump of fresh concrete mix whereas in some cases high viscosity of the same even decreased the workability. Coarser grading of FRAP aggregates results in poor cement mortar paste which eventually produces concrete of very low strength. Due to above mentioned points a maximum limit of 50% on coarse RAP (CRAP) and 0% FRAP were recommended by almost all the authors to be used for productions of Portland Cement Concrete (PCC).

Like that of RAP materials, agricultural waste such as sugarcane waste is being dumped at backyards of the generation point creating disposal problems (Bajwa et al., 2016) and also adding to air, land, and ground water pollution. But unlike other waste, this is considered to be hazardous solid waste (Moisés et al., 2013) and can create health issues. India is the second largest producer of the sugarcane after Brazil (Pongpat et al., 2017, Pryor et al., 2017). With production of such magnitude of sugarcane it also generates enormous amount of waste known as Sugarcane Bagasse. Burning of bagasse in boilers for production of electricity produces byproduct ash known as Sugarcane Bagasse Ash (BGA) (Cordeiro et al., 2009a). This ash consists of abundant content of silica which can be used as pozzolana for partial replacement of ordinary Portland cement (OPC) (Bahurudeen et al., 2014, Ganesan et al., 2007). The pozzolanic activity of BGA can be increased by decreasing the size of particles (80% passing through 60 μm) and by increasing the surface area by more than 300 m²/kg (Cordeiro et al., 2009b). Almost all the studies reported enhancement in mechanical properties of concrete up to 10% replacement of OPC by BGA (Singh et al., 2000, Bahurudeen et al., 2015, Setayesh et al., 2017) whereas few researchers found enhancement in splitting tensile strength at 15% replacement level also (Modani and Vyawahare, 2013, Loh et al., 2013). Taking cognizance of literature, the authors decided to part replace OPC by 10% and 15% BGA in order to decide the optimum replacement level of OPC by BGA in RAP inclusive concrete.

Utilization of RAP in combinations with BGA seems to be a sustainable approach and may provide following benefits;

• Would conserve precious natural aggregates and cement for future generations.

• On spot utilization of RAP, would curtail transportation cost. This would be too beneficial for the sites situated far from markets (high altitude regions). Similarly, utilization of BGA in part replacement of cement would be highly cost effective.

• Reducing the burden such as hauling waste to landfill, suitable space for disposal and other landfill facilities.

• Reduction in carbon footprints, therefore environmental friendly approach.

• Aesthetical (removing wastes from roadside farms).

Utilization of RAP aggregates for production of concrete mixes has not been investigated vastly whereas studies related to properties of FRAP inclusive concrete remains scanty due to gap graded nature of the same. Moreover, the use of BGA for RAP inclusive concrete has never been studied at all. Therefore, the present study is first of its kind wherein the properties of 100% RAP concrete blended with different proportions (literature reported optimum replacement level) of BGA is studied in detail.

Crushed natural aggregates having 16 mm nominal maximum size and natural river sand were used as coarse and fine aggregates for the present investigation. The specific gravity & water absorption as determined by IS:2386 (1997) of coarse and fine aggregates were found to be 2.64 & 0.91% and 2.61 & 0.81% respectively. The bulk density of coarse and fine natural aggregates was found to be 1423 kg/m³ and 1649 kg/m³ respectively. 43 grade Ordinary Portland Cement (OPC) having consistency of 32% with initial and final setting time of 54 min and 311 min, respectively, was used for present study. The specific gravity of cement was found to be 3.15.

A local constructing firm dismantled the 20 years old flexible pavement up to base course using backhoe and the extracted RAP material was stockpiled along the road side in an empty farm (Fig. 1 a) for over 6 months. The RAP material was mixture of bituminous concrete, premix carpet and bituminous macadam courses. Due to stockpiling for such long duration the top part of farm lost its organic benefits. Near about 40 tons of RAP material was brought to the laboratory and screened through 4.75 mm sieve (Fig. 1b) to separate coarse (Fig. 1c) and fine RAP (Fig. 1d) aggregates from the waste mixture. The remaining part remained stockpiled at the farm which continues to create hurdles to the farmers, local transport and becoming more unaesthetic. A large quantity of dust was observed to be present in RAP aggregate which might incurred from water bound macadam layer during extraction. Also, stockpiling in open farm for such long duration might had increased the dust content in RAP material. Interestingly, FRAP aggregates, as can be seen in Fig. 2, are well graded in nature which is contrary to the literature reported results. This is attributed to the presence of abundant amount of dust in FRAP aggregates which filled the gaps of the grading making it relatively well graded. However, FRAP aggregates are found to be coarser than natural fine aggregates and this may be attributed to the conglomerations of fine particles in presence of asphalt. The physical properties of CRAP and FRAP aggregates are illustrated in Table 1. As illustrated in Table 1, specific gravity and bulk density of CRAP and FRAP aggregates were noted to be lesser than natural coarse and fine aggregates respectively, whereas water absorption of the same were noted to be higher than natural aggregates. CRAP aggregates were found to have 2.17% asphalt content whereas 5.2% asphalt was found in FRAP aggregates as determined by ASTM 2172 (2011).

Sugarcane Bagasse Ash (BGA) was collected from a local Sugarcane Mill (Uttam Sugar Mill) located in the state of Uttarakhand, India. In the sugar mill, raw bagasse (waste after extraction of juice) is usually burnt in boilers at varying temperature between 600 °C and 800 °C. The Ash after burning is usually sprinkled with water to avoid soaring in air and dumped at backyards in open farms (Fig. 3 a). After preliminary investigation which included Loss on Ignition (LOI) of samples of different sizes it was decided to utilize fraction passing 45 μm (Fig. 3b) sieve (to increase the pozzolana activity) to part replace cement. The physical properties of cement as well as of BGA is presented in Table 2 which conforms with the specifications of ASTM C618 (2015a).