Enhanced tensile ductility and sustainability of high-strength strain-hardening cementitious composites using waste cement kiln dust and oxidized polyethylene fibers

To improve the tensile performance and sustainability of high-strength strain-hardening cementitious composites (SHCC), waste cement kiln dust (CKD) was used, replacing 30% of ordinary Portland cement (PC), and polyethylene (PE) fibers were modified through chromic acid and plasma treatments. The chemical structure and morphology of the PE fiber surface were modified by exposure to chromic acid and plasma treatment with two gas types, argon (Ar) and oxygen (O2), at various power levels and frequencies. The effect of surface treatment method on enhancing the tensile performance of SHCC was investigated. The surface oxidation and increased roughness of the fibers were verified through X-ray photoelectron spectroscopy and atomic force microscopy analyses. The oxygen/carbon atomic ratio and surface roughness of the PE fibers increased by up to 5.3 and 2.4 times, respectively, by the O2 gas plasma treatment. With 30% of PC replaced by CKD, 12% higher energy absorption capacity prior to tension softening could be obtained. The tensile ductility and energy absorption capacity of SHCC were significantly enhanced by using PE fibers treated with chromic acid for 10 min, approximately 145% and 64%, respectively, although its tensile strength decreased. The Ar-gas plasma effectively improved the compressive strength and tensile performance of the SHCC relative to the O2-gas plasma given an identical power level and frequency. The SHCC containing O2-plasma-treated fibers under 300 W and 40 kHz exhibited the best tensile performance and absorbed the highest energy of 310 kJ/m3, approximately two to five times greater than those of ordinary SHCC materials.