Alkali-Activated Inorganic Based Brake Pads: Realization and Performances of Alternative Friction Materials for a Concrete Industrial Application

Organic brake pads for automotive can be defined as brake linings with bonding matrix constituted of high-temperature thermosetting resins. Bonded together inside the polymeric binder are a mix of components (e.g. abrasives, lubricants, reinforcements, fillers, modifiers…), each playing a distinctive role in determining the tribology and friction activity of the final friction material. The herein reported work presents inorganic “alkali-activated”-based materials suitable for the production of alternative brake linings (i.e. brake pads), by means of an unconventional low-temperature wet process. Exploiting the hydraulic activity of specific components when exposed to an alkaline environment, such peculiar inorganic materials are capable of coming to a complete hardening without the need of traditional high-temperature energivorous procedures. The main advantages of these materials resides in: the decreased embodied energy of the employed raw materials, the reduction of process costs, a potential drop of the emitted pollutants coming from the high-temperature degradation of organic resins. In the present work the results of our investigation in the field are illustrated, our prototype inorganic material is indeed compared to the original resin-based OE and to another traditional phenolic alternative. Brake pads were tested on a full-scale automotive brake dynamometer, following SAE J2522 (AK Master) procedure. In order to prove the excellent performance of such inorganic materials even under high-demanding conditions, brake pads were also tested by means of an internal fading procedure. The results obtained so far are promising and pave the way to further developments toward a concrete industrialization of these unconventional class of friction materials.