An Initial Study of Ultra High Performance Concrete as Reusable Mold Material for Aluminum Casting

The initial investigation evaluates the feasibility of ultra high performance concrete (UHPC) as a material for reusable molds in aluminum casting. Two specific UHPC formulations were investigated: one based on ordinary Portland cement (OPC) and another utilizing alkali-activated materials (AAM). The study focused on investigating the surface through roughness measurements and the thermal durability through repeated casting cycles. The thermal stability of the molds was investigated by thermogravimetric analysis, mercury intrusion porosimetry, crack segmentation, optical microscopy, and electron microscopy. Results indicate that molds fabricated from AAM-UHPC exhibit relatively better performance in terms of maintaining structural integrity and surface quality over repeated uses. AAM-UHPC molds were able to withstand up to ten casting cycles with acceptable surface degradation and no significant failure, while OPC-UHPC molds exhibited a faster degradation under similar conditions. Microstructural changes and the interaction of UHPC materials with molten aluminum were investigated, highlighting the low adhesion and defect formation. Additionally, the molds demonstrated sound casting quality, with a grain size comparable to that achieved using traditional steel molds (~ 90 µm), underscoring the potential of UHPC materials for enhancing casting quality and efficiency. The study concludes that UHPC, particularly with alkali-activated formulations, shows promise for low-pressure casting environments.