# Cleaner Design and Production of Lightweight Aggregates (LWAs) to Use in Agronomic Application
###### Abstract  
This research focused on the obtainment of sustainable lightweight aggregates (LWAs) for agronomic application. The cleaner production is based on saving matter through the valorization of waste available in industry as a substitute of clays into the formulation of the lightweight aggregates (LWAs). Three different types of clays (white, black, and red) and alternative raw materials were blended. Cattle bone flour ash (CBA) and a fertilizer glass (FG) were used to introduce K and P into the mixture in amounts suitable for fertilizer application, and a sewage sludge from a brewery wastewater treatment plant was used as pore forming agent. For the production of the LWAs, we mixed different percentage of waste in two different clay mixtures, which were thermally treated at 1000 \({}^{\circ}\)C for 1 h. Technological parameters such as loose bulk and oven dry density, total porosity, water absorption capacity, pH, and electrical conductivity were determined to evaluate the potential use of LWAs as a growing media. Moreover, scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) techniques were used, and leaching tests were performed to complete the samples' characterization. The results indicated the potential for manufacturing high-quality LWAs for the agronomic field by using energy-saving and matter-processing involving low temperatures with respect to the conventional process. lightweight aggregates; agro-waste; growing substrate; fertilizers +
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demonstrating the great interest in this field; however, some topics are still open, such as the application lightweight aggregates (LWAs) in the agronomic field. LWAs are characterized by a granular and porous structure with a loose bulk density no higher than 1.20 g/cm\({}^{3}\)[29]. These characteristics are promoted by high-temperature heating treatment (1200-1400 \({}^{\circ}\)C), where clay pellets receive a thermal shock that causes the formation of a hard vitrified layer surface, preventing the run out of gases deriving from the combustion of different clay compounds. This behavior forces the material to swell. The vitreous phase plays a key role in bloating and in microstructural and physical properties of LWAs [25; 28]. LWAs are generally composed of two types of materials that can produce glass phases and gases. To improve the inorganic oxide content in raw materials and control the viscosity of the glass phase, clay is still needed to produce satisfactory LWAs [25]. In this research, a sludge from a brewery wastewater treatment plant (BS) was incorporated as a pore forming agent in a clay formulation to reduce the sintering temperature using the exothermic reaction produced by the oxidation of organic matter within the clay matrix. The use of an energy-saving process (less than 200-300 \({}^{\circ}\)C) meant the possibility of obtaining materials with less environmental impact, boosting the local economy by offering innovative and sustainable materials. LWAs are commonly used as hydroponic growth medium [30] or are mixed with other growth media such as soil and peat to improve drainage systems; moreover, they are also used as growing media/drainage layer for green roofing. The LWAs suitable for agricultural use would have specific physicochemical characteristics such as bulk density between 0.75 and 1.20 g/cm\({}^{3}\), pH value in the range of 6.5-7.5, and electrical conductivity (EC) <2 mS/cm, as growing substrate conditions [31; 32]. Therefore, this study was conducted to evaluate the feasibility of using different types of clays mixed with the above-mentioned BS as pore-forming agent, as well as cattle bone flour ash (CBA) and a fertilizer glass (FG) tailored by the authors bringing K and P to the mixture for the production of sustainable LWAs for sustainable construction.