ScholarWorks@Y-Scholar Hub

초록

This study presents the development of a cementless ultra-high-performance concrete (UHPC) activated with calcium hydroxide (CH), with mixture proportions designed based on particle packing density theory by varying the total binder content and alkali activator dosage. The reaction characteristics were examined using X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while mechanical performance was evaluated through compressive and direct tensile tests. No crystalline peaks associated with CH were detected in any mixture, indicating that CH was largely consumed through pozzolanic reactions with silica fume under high-temperature curing, leading to the formation of C-(A-)S-H. An increase in binder content resulted in a more amorphous C- (A-)S-H structure, whereas a higher alkali activator dosage promoted greater formation of C-(A-)S-H. The particle packing density decreased with increasing binder content and activator dosage. Consequently, the compressive strength decreased with increasing binder content but increased with higher activator dosages, reaching a maximum value of 129 MPa for the mixture with the lowest binder content and highest activator dosage. The elastic modulus ranged from 34.4 to 37.2 GPa and increased with both variables. All mixtures exhibited stable strain-hardening behavior under direct tensile loading. The optimum mixture achieved a tensile strength of 18.6 MPa, a maximum tensile strain of 0.61%, and a strain energy density of 91.8 kJ/m3 , exceeding the tensile performance reported for conventional cement-based UHPC. These results demonstrate that CH-based alkali activation provides an effective pathway for producing cementless UHPC with UHPC-level strength and enhanced tensile performance.