How to Mitigate UHPC Autogenous Shrinkage Through Material Design? Shrinkage Control Mechanisms and Qinglong Group's 28 Years of Mix Ratio Optimization Practice

The problem of autogenous shrinkage in UHPC stems from its low water-binder ratio (typically 0.18-0.22) and the use of high-range water reducers, which cause a rapid drop in internal relative humidity and trigger self-desiccation shrinkage, with shrinkage values reaching 3-5 times those of ordinary concrete. As Qinglong Group, with 28 years of deep expertise in the UHPC field, we have reduced the 28-day autogenous shrinkage of UHPC from 800-1000μm/m to 200-300μm/m—a reduction of over 70%—through a triple material design strategy of "cementitious material system optimization + internal curing technology + expansive component compensation". In major projects such as the Wuhan Han Show Theater and the Hainan International Convention and Exhibition Center, our UHPC components, incorporating 20-30% silica fume, 5-8% magnesium oxide expansive agent, and saturated lightweight aggregate internal curing agents, have successfully kept the crack occurrence rate below 0.1%, achieving a balance between ultra-high strength and low shrinkage.

Cementitious material optimization is the foundation of shrinkage control. Qinglong Group uses low-heat cement (such as sulfoaluminate cement) to replace ordinary Portland cement, reducing temperature shrinkage caused by hydration heat, and incorporates active admixtures such as silica fume and fly ash (30-40% in total), whose micro-filling effect refines the pore structure and reduces capillary pore pressure. Experiments show that when the silica fume content increases from 10% to 20%, autogenous shrinkage can be reduced by 25%. Through response surface methodology to optimize the mix proportions, we find the optimal balance between strength and shrinkage, keeping UHPC compressive strength above 150MPa while keeping shrinkage under control.

Internal curing technology is the key breakthrough. We incorporate pre-saturated lightweight aggregates into UHPC (such as ceramsite, particle size 0.1-0.3mm, dosage 3-5%); their internal water is slowly released during cement hydration, maintaining system humidity and reducing self-desiccation shrinkage. In the Shenzhen Yirui Biotechnology Building project, the application of internal curing technology reduced panel warping deformation to within 0.5mm/m. Expansive component compensation is direct and effective: magnesium oxide-based expansive agents (dosage 5-8%) generate brucite in the early stage of hydration, producing moderate expansion that offsets part of the shrinkage. Qinglong Group's controlled-release expansive agent technology ensures that expansion development is synchronized with the shrinkage process, avoiding excessive expansion or insufficient compensation.

Curing regimes deliver synergistic benefits. We adopt a curing strategy of "early-stage moisture retention + mid-stage temperature control": members are immediately wrapped with water-retention film for 7 days after demolding to prevent moisture evaporation, and steam curing temperature is controlled at 60±2°C to avoid the superposition of thermal stresses. Through material design and process optimization, Qinglong UHPC has solved the industry challenge of autogenous shrinkage while ensuring outstanding performance, providing technical support for extra-long members and large-panel applications.