# Characterization of Asphalt Binders Modified with Bio-Binder from Swine Manure
## 1 Introduction  
Bitumen is an essential component in asphalt mixtures manufacturing that is in high demand. The production of one metric ton of asphalt mixture requires an energy consumption between 21 and 28 kgce [1]. This high energy consumption, in addition to the current price of energy and the dependence on petroleum-derived products, results in the road construction sector having high costs that limit its competitiveness. The environmental cost in terms of carbon footprint, energy consumption, and raw-material consumption must be considered. Thus, the carbon footprint due to the production of one ton of asphalt mixture ranges from 70 to 95 kg CO\({}_{2}\) eq. [2]. An approach to reduce the environmental and economic costs in asphalt pavement manufacturing is to decrease the consumption of petroleum-based asphalt binders [3]. This could be carried out by using greener binders, called bio-binders, which allow the total or partial substitution of petroleum-based asphalt binders. To produce this green binder, so-called bio-materials are used, which come from recycled materials, co-products, or waste [4], such as organic matter. Thus, recent research shows that the properties of the produced bio-binders are similar to those of petroleum-based binders and, therefore, could be used in the field of asphalt mixtures [5, 6, 7, 8, 9]. Livestock manure is the excrement and waste materials excreted by livestock, or the mix of bedding with residual materials, which acquire different names depending on their origin and dry-matter content (pouldry manure or swine manure) [10]. Traditionally,livestock manure has been used as an organic fertilizer in crop soils, acting as an instrument for their maintenance thanks to the increase in the content of organic matter and nutrient elements. However, the intensification of livestock farming experienced in recent decades has led to the generation of livestock manure exceeding the assimilation capacity that land can tolerate to maintain the balance of the nutrient cycle, causing pollution of the soil itself and the groundwater due to an excess of nitrates. All the aforementioned data highlight the need for good management of livestock manure. The easiest way is to manage it at the source, attempting to reduce these excesses through good management of the volume of water and feed consumed by the animals [11]. However, due to the productive characteristics of the livestock sector and the economic impact they have in industrially underdeveloped areas, it is necessary to find alternative solutions to those proposed to date by different administrative institutions, which allow for the valorization of the product outside the agricultural sector. An innovative method for waste recycling, specifically converting biomass into bio-oil, is the use of the so-called conversion technologies [12]. Technological advances in the area of conversion technologies, both thermochemical and biochemical, allow for new ways to reduce the current problem of pollution caused by livestock manure, while obtaining valuable chemical and energy resources of ecological origin [13]. There are different thermochemical conversion technologies, such as pyrolysis, hydrothermal liquefaction, gasification, or direct combustion [14]. Due to the presence of moisture in livestock manure, and with the purpose of reducing the previous thermal treatments to the conversion process, the hydrothermal liquefaction process emerges as the technology with the greatest potential in swine manure conversion [15]. Recent studies have highlighted the convenience of incorporating oils or bio-oils in the production of bituminous mixtures in order to improve their mechanical properties [16; 17; 18; 19; 20]. [PERSON] et al. [21] demonstrated the potential of using a bio-binder obtained from microalgae waste in the manufacture of bituminous mixtures. Likewise, [PERSON] et al.