Flame-retardant mechanism and mechanical property of flame-retardant corn straw brick (FRCSB)

In this paper, the pyrolysis characteristics of flame-retardant corn straw brick (FRCSB) and the changes in weights, dimensions, colors, mechanical properties, and micromorphology after high temperature treatment were studied. The results indicate that FRCSB demonstrates excellent flame retardancy. The evaporation process of water in FRCSB is delayed, completing only at a heat treatment temperature of 300 degrees C, whereas the evaporation processes for Ca(OH)2 and corn straw fiber are completed at 200 degrees C and 100 degrees C, respectively. The decomposition process of corn straw fiber and Ca(OH)2 in FRCSB is also delayed and slowed compared to their individual decomposition rates. This delay occurs because the calcium carbonate (CaCO3) formed from the reaction between Ca(OH)2 and CO2 creates a barrier on the surface of FRCSB, preventing heat exchange. The observed changes in color and weight of FRCSB during heat treatment support these findings. Furthermore, a specific range of heat treatment reduces the moisture content of FRCSB and increases its compressive strength up to 18.86 MPa at 200 degrees C. However, the compressive strength decreases rapidly due to the decomposition of corn straw fiber within FRCSB. Therefore, the key to enhancing the mechanical properties of FRCSB at high temperatures lies in preventing the decomposition of corn straw fiber in the brick. The strongly alkaline environment provided by Ca(OH)2 allows corn straw fiber to retain its properties during heat treatment, thereby improving the performance of FRCSB by serving as a support and connector.