Research on Compatibility of Wheat Straw and Portland Cement

Abstract

 Straw burning has become a serious risk for environment and security. It is very urgent to develop and research materials to utilize straws. The compatibility between straw and portland cement is a problem to be resolved for application of straw fiber in cement-based materials. In the experiment, samples of cement-based composites with untreated straw fiber and pretreated straw fiber were prepared and mechanical properties of specimens were tested. The compatibility between straw fiber and portland cement can be improved through pretreatment process that consists of dipping straw fiber in 4% NaOH solution for 12 hours, then rinsing and drying. In this process, substances in fiber harmful to cement hydration are leached furthest. The negative influences of straw fiber on setting and hardening of cement paste are eliminated. The pretreatment can optimize the mechanical properties of the composite. The strength of composite is not linearly relative to cement-to-water ratio, instead, there exists an optimal water-to-cement ratio, i.e. 0.60. The strength of cement-based straw fiber composite prepared in this ratio reaches maximum.

Characterization of composite formed by cement and wheat straw treated with sodium hydroxide

“…Basta et al (2011) verified an improvement in the compressive strength and an increase of the density in composites with rice straw fibers pre-treated with linseed oil. Although Cai et al (2017) affirm that high values of compressive strength of straw-cement composites cannot be reached, because straw decompose into sugars in an alkaline environment, the results shown in Table 2 suggest that alkaline treatment did not affect the particles.…”

“…Wheat straw particles absorbed water during the mixing process with cement, forming particle agglomerations inside the composite. Cai et al (2017) described that straw fibers easily absorb water as well, resulting in straw fiber agglomeration, thus reducing the mechanical properties of the composite material.…”

“…The straw particles/cement ratio used in the production of the composites was 0.15, as specified by Cai et al (2017) as the optimal amount of wheat in cement composites. The water-to-cement ratio used was 0.80, unlike Cai et al (2017), for which the optimal value was 0.60 for wheat fibers, due to a higher water absorption observed on the particles.…”

“…The main goal of straw pretreatments is to improve its surface compatibility with the cement matrix, which happens by the dissolution of low-molecular-weight impurities and the roughening of the surfaces (Cai et al 2017;Yu et al 2017).…”

“…Alkaline pretreatment also causes several changes in the wheat straw, such as increasing the surface area, modifying the lignin structure, and swelling the cellulose (Elbashiry et al 2017). After pretreatment the wax layer of straw fiber is eroded, and the surface of the straw fiber becomes coarse with a large number of irregular holes, enhancing the fibers roughness and increasing the friction between cement paste and the straw fiber (Cai et al 2017). Most studies present pretreatments applied to the straw fibers instead of straw particles (Basta et al 2011;Khorami and Ganjian 2011;Qiao et al 2016;Elbashiry et al 2017;Naik and Kiran 2018).…”