Available at: http://digitalcommons.calpoly.edu/theses/234
Date of Award
MS in Engineering - Materials Engineering
Rice straw is a global and proliferate agricultural waste whose production grossly outstrips viable uses. Current disposal methods are not sustainable, and more convenient methods – such as incineration – exude poor environmental stewardship. Although the direct use of straw bales in building construction presents a practical and sustainable alternative, engineering challenges associated with using it prevent its wide adoption. The Stak Block – a composite formed from compressed rice straw and a heat-cured adhesive – may overcome challenges associated with straw bale building. However, the times and temperatures needed to cure the binder with straw are not well understood. Therefore, the goal of this thesis was to study straw cubes (in lieu of the full-scale Stak Block) to discern a time-temperature relationship.
A finite element (FE) model of the Stak Block was created to simulate the heating process. The results of this study indicated that the adhesive may actually cure at temperatures less than 100°C. This data influenced the times and temperatures that binder-treated straw cubes were baked at for the first of several iterations. A chemical dye was used to discern if cubes had cured or not. In addition, mechanical testing was used to inspect cubes for curing and to support the results obtained from using a chemical dye. Results from cubes inspected with the chemical dye method were then used to develop an inverse relationship between time and temperature needed to cure the cubes – with the lowest observed cure temperature to be 65°C for 2 hours and the fastest cure time of 30 minutes at 150 and 125°C. Following the iterative experiments, an FE model of the cube was created and fitted to the results of the iterative experiments. Values for thermal conductivity (k = 0.1 W/m-K)and specific heat (Cp = 2000 J/kg-K) used to fit the FE cube model were applied appropriately to the Stak Block FE model in order to estimate curing times at different temperatures.