Testing a Novel Geopolymer Binder as a Refractory Material for Rocket Plume Environments at SSC

The project focuses on the development of a new alumina-silicate based cementitious binder (geopolymer) capable of acting as a high performance refractory material with low ablation rate and high early mechanical strength. Such a binder would represent a significant contribution to NASA's efforts to develop a new generation of refractory 'hot face' liners for rocket plume environments created by thrusters powered by either Liquid Oxygen (LOX)/Liquid Natural Gas (LNG) propellants or solid phase rocket fuel. The results of the controlled and full scale tests at NASA SSC E-Complex, a multi-use propulsion test bed, revealed the newly developed geopolymer products exhibited comparable or superior performance compared to commercial refractories currently used by NASA. Erosion rates for the geopolymer samples versus the commercial refractories tested were lower for the majority of the cases, and total erosion was also lower or equal for similar test durations. Geopolymer binders proved to be good candidates for the repair of existing structures due to their excellent adhesion to parent surfaces, as demonstrated by the tests conducted on repaired tested panels. Additionally, the post-test characterization results conducted at Louisiana Tech's Institute for Micromanufacturing showed an increase in compressive strength following testing, when mullite-based aggregate was used. One sample that was fired more than once, exhibited a 50% increase in compressive strength, suggesting that geopolymer concrete may even improve its properties after repeated firing. The project involved the development and testing of a new alumina-silicate based multi-purpose, cost-effective, 'green' cementitious binder (geopolymer) capable of acting as a high performance refractory material with both a low ablation rate and a high early mechanical strength. This work was built upon previous research undertaken by the research team in the areas of geopolymer binders. Full scale and laboratory controlled tests were performed to compare geopolymer performance to currently available commercial products (e.g. Sentinel, Greencast). Geopolymer's thermal shock resistance properties were tested on eleven different fly ash stockpiles specimens from around the world. The geopolymer specimens were subjected to ASTM C-1100 (Standard Test Method for Ribbon Thermal Shock Testing of Refractory Materials). Samples were subjected to incremental 5-5-5-15-30 second flame exposure durations and to a 15 or 30 accumulated exposure, depending on the sample performance (e.g., if the plume became detached). Field test durations were limited to prevent excessive erosion of the test panels and subsequent plume detachment. Laboratory testing also demonstrated that geopolymer could withstand thermal shock and exposure to flame. Additionally, a computational model was created to determine the optimal chemical ratios for geopolymer to be exposed to elevated temperatures. Additionally, due to their excellent adhesion to pre-existing surfaces geopolymer binders were proven to be good candidates for use in repair of existing structures upon which they were applied and retrofitted; this was demonstrated and observed via tests conducted on repaired tested panels. Overall, the demonstration testing program revealed that the geopolymer products had equal or superior performance compared to commercial refractories currently used by NASA. More »