Mechanical properties and microstructure of autoclaved green UHPC blended with granite stone powders

Granite stone powder is a common type of stone-product industrial waste spreading over Fujian Province and other areas of China, causing serious environmental problems. This paper investigates the possibility of using granite stone powder to completely or partially replace quartz powder for preparing “Green” or “Eco” ultra-high performance concrete under autoclave curing regimes. The mechanical properties and microstructure of autoclaved ultra-high-performance concrete (UHPC) mixed with different replacement ratios of granite stone powders were tested. It was found that its mechanical properties still satisfied the original requirements even after total replacement of quartz powders by granite stone powders. Despite of a slight decrease in flowability after total replacement, flexural and compressive strength did not change significantly. The hydration product of flaky tobermorite crystal was found in both granite stone powder blended UHPC and in quartz powder blended UHPC, while the Ca/Si ratio varied slightly. Furthermore, the pore structure of unadulterated UHPC improved due to a larger population of harmless and less-harmful pores after quartz powder were replaced by granite stone powder.