How to Mitigate UHPC Autogenous Shrinkage Through Material Design?

The autogenous shrinkage of UHPC is an inherent challenge caused by its low water-binder ratio (typically 0.18-0.22) and high cementitious material content. It mainly manifests as early plastic shrinkage and long-term self-desiccation shrinkage; if left uncontrolled, it can easily induce microcracks and compromise durability. As an industry leader with 28 years of deep expertise in the UHPC field, Qinglong Group has drawn on hands-on experience from national-level landmark projects such as the Wuhan Hanxiu Theater and Hainan International Convention and Exhibition Center to develop a systematic approach to mitigating autogenous shrinkage through material design: optimizing the cementitious system (adding 20-30% silica fume to replace part of the cement), introducing internal curing agents (such as saturated lightweight aggregates), using shrinkage-compensating materials (magnesia-based expansive agents), and controlling fiber content (2-3% to avoid localized stress concentration). In the UHPC curtain wall project for the Shenzhen Yirui Biotech Building, we combined silica fume with a dedicated expansive agent to reduce the 28-day autogenous shrinkage of UHPC from a baseline of 800-1000με to 500-600με, effectively preventing early cracking. Material design is the first line of defense against autogenous shrinkage and must start at the microstructure level.

Optimizing the Cementitious Material Composition Is the Fundamental Solution

Reducing cement content and adding active supplementary materials such as silica fume and slag powder can reduce hydration heat and self-desiccation effects. Qinglong Group commonly replaces 20-25% of the cement with silica fume in its formulations; its extremely fine particles (specific surface area ≥20000m²/kg) optimize the pore structure and reduce shrinkage caused by water loss from capillary pores. Meanwhile, a low-heat cement system is adopted to reduce thermal-rise shrinkage risk at the source.

Introducing Internal Curing and Expansive Components Is the Key Measure

Adding internal curing agents (such as pre-saturated lightweight aggregates) provides a continuous internal water supply that delays self-desiccation. In major projects, Qinglong Group adds 5-8% saturated ceramsite to keep internal humidity above 90% for up to 7 days, reducing shrinkage by 30%. Magnesia-based expansive agents form brucite during mid-stage hydration, producing moderate expansion that compensates for shrinkage, but the dosage must be precisely controlled (typically 4-6%) to prevent excessive expansion.

Coordinated Control of Fibers and Aggregates

Fibers (steel or synthetic) can suppress plastic shrinkage cracks, but excessive amounts introduce restraint and aggravate stress. Qinglong Group determines the optimal fiber volume content (2-2.5%) through testing to ensure uniform fiber distribution. Aggregates use continuous grading with a maximum particle size ≤0.6mm, improving packing density and reducing paste volume, thereby lowering the source of shrinkage.

Through full-process material design, Qinglong Group keeps autogenous shrinkage within a safe range, and combined with steam curing (e.g., 80℃×24h), further promotes early strength development, releases shrinkage stress, and ensures the long-term integrity of UHPC components.