How to Mitigate UHPC Autogenous Shrinkage Through Material Design

The autogenous shrinkage of UHPC is a technical challenge that cannot be overlooked behind its high performance, mainly arising from chemical shrinkage and the self-desiccation effect caused by the intense hydration of cementitious materials at an extremely low water-binder ratio. As the Qinglong Group with 28 years of UHPC R&D experience, we have successfully reduced the autogenous shrinkage of standard UHPC from 1000-1200μɛ to 400-600μɛ through a four-dimensional coordinated strategy of "mix proportion optimization, expansive component compensation, internal curing technology, and curing regime control". In the roof project of the Hainan International Convention and Exhibition Center, by incorporating a calcium-magnesium compound expansive agent and a saturated lightweight aggregate internal curing agent, combined with precise wet curing, shrinkage cracking of the 120,000-square-meter double-curved roof panels was effectively controlled, ensuring an outstanding record of ten years without cracking.

Cementitious System Optimization Is the Source of Shrinkage Control

Qinglong UHPC adopts a composite cementitious system of low-heat cement with silica fume and slag powder. By reducing the cement content (controlled at no more than 700kg/m³) and optimizing the silica fume dosage (20%-25%), the total hydration heat and shrinkage driving force are reduced. Meanwhile, quartz powder with a rational particle size distribution (D50=5-10μm) is introduced as an inert filler to partially replace active components, effectively improving the volume stability of the paste without significantly affecting strength. Experiments show that this system can reduce 7-day autogenous shrinkage by approximately 15%.

Coordinated Compensation with Expansive Components and Internal Curing Agents

To address chemical shrinkage, the Qinglong technical team adopts ettringite-based and magnesium oxide-based compound expansive agents, which generate moderate expansion stress in the early and middle stages respectively to compensate for shrinkage. More crucially, pre-saturated porous internal curing materials (such as ceramic sand with a particle size of 0.1-0.3mm) are introduced; these slowly release moisture during cement hydration, effectively mitigating the self-desiccation effect. In the Shenzhen Yirui Biotechnology Building project, this technology kept the 28-day autogenous shrinkage of UHPC components stable within 550μɛ.

A Scientific Curing Regime Is the Guarantee for Low Shrinkage

Material design must match the curing process. Qinglong emphasizes the importance of early wet curing, covering components with moisture-retaining film immediately after demolding to prevent rapid moisture evaporation. For critical components, a standard wet curing period of no less than 7 days is applied. Although steam curing can greatly enhance early strength, it exacerbates self-desiccation; therefore, we strictly control the heating rate (≤15°C/h) and the constant temperature (60±5°C) to strike a balance between strength development and shrinkage control.

Through the above systematic material design, Qinglong UHPC achieves ultra-high strength while its volume stability also meets the demanding requirements of engineering applications, clearing the technical obstacles for applications involving extra-large areas and extra-long components.