Material Design Mitigation Strategies for UHPC Autogenous Shrinkage

The autogenous shrinkage of UHPC is a key issue affecting its early-age performance stability and long-term durability. As a group with 28 years of dedicated experience in the UHPC field, Qinglong Group believes that scientific material design can effectively mitigate autogenous shrinkage. Autogenous shrinkage mainly originates from chemical shrinkage and the self-desiccation effect during cement hydration at low water-binder ratios; the autogenous shrinkage value of high-quality UHPC should be controlled within 500-800μm/m. Based on the practice of projects such as the Shenzhen Yirui Biotechnology Building, Qinglong Group has summarized a three-dimensional mitigation strategy of optimizing the cementitious material system, incorporating shrinkage compensation components, and improving the curing regime.

Optimizing cementitious materials is the foundation for mitigating autogenous shrinkage. Reducing cement content and incorporating active supplementary cementitious materials such as silica fume (15%-20%) and slag powder (20%-30%) can reduce chemical shrinkage. In its mix proportion design, Qinglong Group controls the total cementitious material content at 400-500kg/m³, with cement accounting for no more than 70%. In the roofing works of the Hainan International Convention and Exhibition Center, incorporating ultra-fine fly ash (particle size ≤10μm) reduced early autogenous shrinkage by 25%. Meanwhile, the C3A content is kept below 8%, and medium heat-of-hydration cement is selected to avoid excessive temperature rise that would aggravate autogenous shrinkage.

Shrinkage compensation components are the key measure. Internal curing materials such as saturated lightweight aggregates (pre-wetted ceramsite, particle size 1-3mm) can continuously supply water internally to compensate for the water demand of hydration. Qinglong Group incorporates 2%-3% internal curing agent into the mix, reducing the autogenous shrinkage development rate by 30%. Expansive agents (UEA type, dosage 6%-8%) can produce moderate expansion at an early age to offset part of the shrinkage. In the Wuhan Hanxiu Theater project, by combining internal curing and expansion techniques, the 14-day autogenous shrinkage value was controlled within 600μm/m.

Coordinated optimization of the curing regime. Although the focus is on material design, curing is indispensable. Qinglong Group uses sprayed curing agents (film-forming type, applied at 150g/m²) combined with plastic film covering to keep early-age humidity above 95%. Under standard curing conditions, combined with material optimization, the early-age cracking risk of UHPC is significantly reduced. Through systematic material design, Qinglong UHPC has achieved effective control of autogenous shrinkage in multiple major projects.