Development of Multi-scale Self-healing High-volume Fly Ash UHPC
Dr. Xianming Shi, Washington State University
Despite its higher initial cost than conventional concrete, ultra-high performance concrete (UHPC) is gaining popularity in applications such as prefabricated connections, bridge decks, beams, girders, pile foundations, thin-wall shell structures, encasement of corroded steel girders, and encasement of substandard or corroded columns. The durability of UHPC is challenged once cracks are generated in the UHPC structural members. The high materials cost of UHPC also limits its wide application in pavement and other civil infrastructures. In this context, the overarching goal of this project is to design a cost-effective UHPC featuring the use of high volume fly ash (HVFA) binder and ability to heal the cracks when and where needed. The multiscale self-healing ability of the HVFA UHPC will be achieved through the combined use of microcapsules and light-weight aggregate (LWA), so as to maintain the superior durability of the UHPC. To this end, this exploratory laboratory investigation aims to:
1) design healing agents and multi-dimensional microcapsules and LWAs to heal cracks with different widths
2) identify cost-effective mix designs for UHPC with the use of HVFA binder
3) evaluate the self-healing effectiveness of dog-bone shape HVFA UHPC specimens, using the direct tensile test and digital image correlation technique.
The specific design of this novel UHPC is as follows. Different sizes of polymeric microcapsules (with inorganic healant) are obtained through a water-in-oil suspension polymerization technique and LWAs are encapsulated with a modified polymer coating. The healing agents incorporating a novel nano-material, graphene oxide (GO), are synthesized to improve the healing efficiency of cracked UHPC. More crystals are expected to form inside the cracks and provide comparable strength as the intact part, so that the tensile properties of cracked UHPC can be greatly recovered after self-healing.
Dr. Xianming Shi