Effect of liquid crystal display glass powder to blast furnace slag ratio on the microstructure and mechanical properties of ultra-high-performance alkali-activated concrete

This study investigated the microstructure and mechanical properties of ultra-high-performance alkali-activated concrete (UHP-AAC) with five different ratios of liquid crystal display glass powder (LCDGP) and blast furnace slag (BFS) and four different steel fiber types. The main reaction product was C-(N-)A-S-H gels when solely using BFS, reduced and partially changed to N-A-S-H gels by increasing the LCDGP amount. X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analyses confirmed these microstructural changes. Scanning electron microscopy (SEM) showed enhanced fiber-matrix bonding at the optimal LCDGP content, and thermogravimetric analysis (TGA) indicated increased formation of a bonded gel. The highest compressive strength (164.5 MPa) was obtained at an LCDGP/BFS ratio of 8 %. LCDGP/BFS ratios of 8-16 % effectively enhanced the tensile performance; however, beyond this range, tensile performance began to decline. The straight fiber in UHP-AAC enhanced its tensile strength better than the hooked fiber, given the identical aspect ratio of 65; however, the hooked fiber enhanced its strain capacity and g-value better than the straight fiber. In conclusion, LCDGP/BFS ratios of 8-16 % and the use of long straight steel fibers provide the best tensile performance for UHP-AAC.