## 1 Introduction  
A road-base binder is a powder, made of a mix of different components, which is the basis for constructing hydraulically bound base mixtures for the treatment of materials for bases, sub-bases and capping layers, and earthworks in airports, roads, railways, and other infrastructures [1]. Portland cement, bituminous materials, lime, and industrial wastes such as slag, furnace dust, coal fly ash, and others (up to 10% by mass) are the most common materials used in road binders [2]. Although there is potential for the use of waste materials and the reduced consumption of high-value components such as cement [1], there are few investigations related to the incorporation of waste in road binders [2], especially the environmental (heavy metals and radioisotopes) assessment of the waste incorporated. Mainly, the incorporation of waste in hydraulic road binders has focused on wood ash [3], cellulose ash [2], and steel slag [4]. Therefore, at present, the technical and environmental feasibility of incorporating other wastes composed mainly of limestone, such as seashells and eggshells, is unknown. No previous studies have been extended to other types of ash, such as olive pomace ash. European standards EN 13282-2 [5] on additives to road-base binders indicate the characteristics that certain wastes must have to be used in this kind of application. One of them is that the waste cannot emit radiation or contain hazardous materials. Even so,the standards do not always specify the tests that must be performed or the maximum limits that cannot be exceeded, and that is what this study attempts to investigate in depth. Globally, population growth has caused an increase in the demand for manufactured food and, therefore, an increase in waste generation [6]. On the other hand, worldwide, construction demands more natural resources than any other sector [7]. To improve the environmental sustainability of construction and other sectors, different wastes, some of a biological nature, have been evaluated as substitutes for materials traditionally used in construction (cement, mortar, and concrete) [8]. For example, the global aquaculture industry produces between six and eight million tons per year of seashells from different sources (scallops, oysters, mussels, cockles, etc.) [9]. Approximately 60% of total production becomes waste [10] and only 25% of this is reused [11]. Furthermore, the disposal of seashell waste generates unpleasant odors and requires a large area of land for dumping [12]. The same environmental problems occur in the poultry industry, which generates more than 250,000 tons of eggshell waste per year [13]. Other biological wastes are generated in the agricultural sector, such as olive pomace. It is estimated that a ton of processed olives produces approximately 27% olive oil and 73% waste. In Andalusia (Spain) alone, three million tons/year of pomace are generated [14]. The improper management of olive pomace can cause major environmental problems due to its high phenol content [15]. Eggshells are useful in various construction materials, such as cement [16], mortar, concretes, alkali-activated binders, and bricks [17] (due to their high calcium carbonate content. Eggshell powder has shown good strength parameters when mixed with concrete, from previous studies shown below [18]. There are previous studies on the use of seashell waste in cement production [19], as a fine/coarse aggregate in concrete [20; 21; 22], and as fireproof materials [11]. Due to its high energy content and low fuel cost, olive pomace is used as biomass; approximately 30% is used to produce electric energy. However, the combustion of olive pomace produces more than 50,000 tons/year of ash [14]. These ashes have been used in cement manufacturing [23], bricks [24], fireproof materials [25], geopolymers [14; 26], and mortar [27]. In this study, three different wastes of biological origins (eggshells, seashells from scallops, and ashes from biomass combustion (olive oil pomace)), have been used as raw materials in road binder.