Influence of pretreatment of rice straw on hydration of straw fiber filled cement based composites

Abstract The morphological and structural characteristics of four different fibers, the pristine rice straw (RF1) and three fibrous materials (RF2, RF3 and RF4) during the components separating process from rice straw, were investigated. The results indicated the pretreatment of rice straw could eliminate amorphous hemicellulose and lignin, increase the crystallinity and improve the thermal stability of rice straw fiber. Additionally, the effect of four kinds of straw fibers on hydration of the straw fiber filled cement based composites were studied using isothermal calorimetry, X-ray diffraction (XRD) and thermogravimetry (TGA) techniques. For this purpose, the composites containing 10 wt.% of the pristine and the pretreated rice straw fiber were prepared. As a result, the presence of both the pristine and the pretreated rice straw fiber delays and inhibits the hydration of cement. The composites containing RF1 showed the lowest rate of heat of hydration (almost 0 mW) and sustained the cumulative heat (7.9 J) compared to the composites containing RF2, RF3 and RF4 (240.1, 318.2 and 317.1 J, respectively) in the first 7 days. However, the cumulative heat of the composites with the pretreated rice straw fibers was still lower than the control cement paste (334.2 J). The XRD and TGA results revealed that the amount of calcium hydroxide is lower in the composites containing rice straw than in neat cement. This study recommends that the pretreated rice straw fibers had less influence on the hydration of cement.