# Potential of Waste Oyster Shells as a Novel Biofiller for Hot-Mix Asphalt
###### Abstract  
This paper reports the use of waste oyster shells as a novel biofilm for hot-mix asphalt (HMA) pavement applications. The effects of different fractions (e.g., 0, 5, 10, 15 wt %) of oyster shell powder (OSP) on the bitumen performance were investigated. The chemical properties of unfilled and OSP-filled asphalts were characterized by means of thin layer chromatography-ionization detection (TLC-FID), Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Thermal characteristics were examined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Physical and rheological properties were assessed through penetration, softening point, ductility, and dynamic shear rheometer (DSR) tests. Results showed that OSP addition increased the resins content, as well as the stiffness of blends. No obvious reactions have occurred between the filler and the asphalt. A higher dose of OSP altered the morphology of the binder, whereas lower and intermediate doses improved its thermal stability and enhanced its low-temperature, rutting, and fatigue performances with respect to the plain asphalt. Overall, the waste oyster shells could be used as filler substitute, not only to improve the quality of road pavements but also to reduce the cost of their construction and solve the waste disposal problems. o +
Footnote †: journal: Applied Sciences  
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showing, and rutting of the pavement [3]. Mineral fillers play a dual role in paving mixtures. First, they are part of the mineral aggregate, i.e., they fill the interstices and provide contact points between larger aggregate particles and, thereby, strengthen the mixture. Second, when mixed with asphalt, mineral fillers form a high-consistency binder or matrix that cements larger aggregate particles together. This resulting filler-asphalt mastic is capable of affecting the physical and mechanical properties of the mixture to a large extent [4]. Various studies have shown that there are three primary mechanisms by which fillers reinforce asphalt binder [5; 6; 7]: volume filling, particle struturalization, and physicochemical interactions. Volume filling and particle struturalization are both means of mechanical reinforcement. Volume filling increases asphalt mastic stiffness simply as a result of the replacement of asphalt binder volume with rigid particles. Filler particles start to form an interconnected network at a filler volumetric concentration of roughly 40%, leading to a rapid increase in the rate of stiffening with increasing volume fraction [6; 8; 9]. At lower filler concentrations, particle contact is not established, and the mastic will behave as a dilute suspension, with volume filling constituting the dominant mechanical reinforcement mechanism. The third type of reinforcement, physico-chemical interaction, involves the adsorption of polar fractions (e.g., resins and asphaltenes) of the asphalt binder onto the surface of filler particles through electrostatic, dipole-dipole, or van der Waals forces [7; 10; 11]. Physiochemical interaction leads to the formation of an interphase adsorbed layer of the polar fractions of asphalt on the surface of filler particles. In addition, loss of certain components of the asphalt to adsorption modifies the chemistry and morphology of the non-adsorbed, \"effective\" binder matrix [12]. Different types of filler including limestone dust, Portland cement, crushed stone, granite powder, and fine sand are usually used in the asphalt mixtures [3]. Society's ever-growing concern for protecting the environment has resulted in concentrated attention on the possible reuse of waste materials in road construction [13; 14; 15; 16; 17]. Numerous efforts have been made to use waste materials of various origins to partially or fully replace conventional filler in the production of HMA.