Developing Sustainable Ultra High Strength Concrete Mixtures Using Spent Foundry Sand
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This study presents the development of ultra high strength concrete (UHSC) that has been made more sustainable by using both local materials from central Texas and spent foundry sand (FS) from the metal casting industry, which has also been obtained locally. This study first describes various trial mixtures tested as well as the specimen preparation techniques investigated that led to the final UHSC-FS mixtures. The developed mixtures were proportioned with local constituents to increase the sustainable impact of the material by reducing emissions due to shipping as well as making UHSC more affordable to a wider variety of applications. The final mixture design constituents were: river sand, locally available type I/II cement, silica fume, and spent FS, which was obtained from a local steel casting company. Multiple variables were investigated, such as the aggregate type and size, concrete age (7, 14, and 28-days), the curing regimen, and the water-to-cement ratio (w/cm) to optimize a UHSC mixture that used local materials and FS. This systematic development revealed that heat curing the specimens in a water bath at 50ºC (122ºF) after demolding and then dry curing at 200ºC (392ºF) two days before testing with a w/cm of 0.20 at 28-days produced the highest compressive strengths. Once an optimum UHSC mixture was identified a partial replacement of the fine aggregate with FS was completed at 10%, 20%, and 30%. The results showed an increase of compressive strength performance at 10% replacement, followed by no change at 20%, and finally a slight decrease at 30%. Developing this innovative material with local materials and FS ultimately produces a novel sustainable construction material, reduces the costs, and produces mechanical performance similar to prepackaged, commercially, available construction building materials.