Synergistic Effect of Yak Dung Fiber and Yak Dung Ash on the Mechanical and Shrinkage Properties of Cement Mortar

The high value use of agricultural and livestock waste resources in the context of a low carbon economy is a challenge that currently plagues many countries. Yak dung, as a waste resource from livestock farming in the plateau, is considered to be a misplaced treasure. In this work, yak dung was processed into yak dung fiber (YDF) and yak dung ash (YDA), respectively, and the microscopic morphology of the YDF and YDA was assessed using scanning electron microscopy (SEM). The elements in the YDA were analyzed by energy dispersive X-ray spectroscopy (EDX). Moreover, cementitious composites were prepared with YDF at 0%, 0.3%, 0.5% and 0.7% and by replacing cement with YDA at 5%, 10% and 15% to assess the workability, mechanical properties and shrinkage properties of cementitious composites containing different YDF types (alkali treated and untreated), contents and different YDA contents. The results showed that alkali-treated YDF and YDA contain a large number of honeycomb structure pores, and the strength of cementitious materials with alkali-treated YDF was higher. The addition of YDF had a negative effect on the fluidity and compressive strength of the cementitious material, but the 0.3% YDF was beneficial in increasing its flexural strength. The compressive strength and flexural strength first increased and then decreased with the increase of YDA content. Both YDF and YDA inhibited the shrinkage of the cement paste, and the shrinkage strain of the cement matrix composites containing 0.3% YDF and 10% YDA was reduced by 51.1% compared to the control group. This work is expected to promote the application of yak dung waste in cementitious materials.