Why Is It Difficult for UHPC Elastic Modulus to Break Through 55GPa? Material Constitutive Relations and Qinglong Group's Modulus Enhancement Technology

The main limitation preventing UHPC's elastic modulus from exceeding 55GPa lies in the intrinsic properties of cement-based materials: the modulus ceiling is determined by the combined effect of cement paste (20-30GPa) and aggregates (70-80GPa), with a theoretical maximum of approximately 60GPa. Through 28 years of research and practice, Qinglong Group has stabilized UHPC's elastic modulus within the 45-55GPa range, achieving a measured modulus of 52GPa in the Wuhan Hanxiu Theater project. Although adding steel fibers and increasing aggregate content can moderately raise the modulus, an excessively high modulus sacrifices material toughness, requiring a balance between stiffness and deformation capacity.

Material composition determines the modulus foundation. Cement paste has a modulus of about 25GPa and quartz sand 70GPa; through maximum-density packing, the composite modulus can reach around 50GPa. We have tried incorporating high-modulus materials such as steel particles (modulus 200GPa), which can raise the modulus to 55GPa, but workability decreases noticeably. The addition of fibers has a limited effect on modulus, mainly enhancing toughness.

Production processes influence modulus development. The steam curing regime is crucial: our curing kilns precisely control temperature (60±2℃), promoting densification of C-S-H gel and increasing the modulus by 10-15%. However, excessively high curing temperatures cause microcracks, which actually reduce the modulus. Qinglong Group has found the optimal balance point by optimizing the curing curve.

The demand for modulus in applications should be viewed rationally. A modulus of 55GPa already far exceeds that of ordinary concrete (30GPa) and satisfies the vast majority of structural requirements. An excessively high modulus increases brittleness and is unfavorable for seismic resistance. We recommend selecting an appropriate modulus level based on specific project requirements.