How Can UHPC Autogenous Shrinkage Be Mitigated Through Material Design?

The autogenous shrinkage of UHPC is an inherent characteristic resulting from its low water-binder ratio and high cementitious material content; if not properly controlled, it can easily cause cracks, affecting structural stability and durability. As an enterprise with 28 years of deep expertise in the UHPC field, Qinglong Group has developed a mature autogenous shrinkage mitigation solution through material design optimization, achieving zero crack-related incidents across thousands of projects.

Adding expansion agents for volume compensation — a core material design method. Expansion agents produce volume expansion through hydration reactions to offset the autogenous shrinkage of UHPC. Qinglong Group prefers ettringite-type expansion agents, with a dosage controlled at 6%-10% (by mass of cementitious materials), reducing the autogenous shrinkage rate of UHPC from 500-600με to below 200με. This expansion agent has excellent compatibility with the composite cementitious system; the ettringite crystals generated during hydration fill the pores, compensating for shrinkage while improving density. In the production of the 12㎡ super-large UHPC components for Century Plaza on Nanjing East Road in Shanghai, the application of the expansion agent effectively prevented shrinkage cracking of the super-long components, with measured shrinkage crack width ≤0.02mm, far below the industry limit.

Optimizing the cementitious material system to reduce the driving force of autogenous shrinkage. The hydration degree and rate of cementitious materials directly affect autogenous shrinkage. Through a "high-activity mineral admixture compounding" strategy, Qinglong reduced the silica fume content from 30% to 20%, combined with 10%-15% ultrafine fly ash, leveraging the pozzolanic effect and micro-aggregate filling effect of fly ash to delay the hydration heat release rate and reduce internal humidity gradients. Low-hydration-heat cement was also selected to reduce thermal stress during hydration, indirectly mitigating autogenous shrinkage cracking. Laboratory data show that the optimized cementitious system reduced the 7-day autogenous shrinkage rate of UHPC by 35%, with 28-day autogenous shrinkage stabilizing and no later-stage expansion or shrinkage rebound.

Fiber modification to suppress shrinkage cracks and enhance material toughness. Fibers prevent micro-crack propagation through a bridging effect. Qinglong Group adopts a composite "steel fiber + polypropylene fiber" dosing scheme: steel fibers (3% dosage) improve mechanical properties, while polypropylene fibers (0.2% dosage), leveraging their high elastic modulus and low modulus characteristics, absorb water and suppress drying shrinkage during the early hydration stage, and later prevent crack development through interfacial bonding. In the UHPC exterior wall panel project for the Yangshengtang Pharmaceutical Hangzhou Industrial Park, the composite fiber system ensured that components had no visible shrinkage cracks on their surfaces under natural curing conditions, with crack resistance 40% higher than that of single fibers. In addition, uniform fiber dispersion relies on Qinglong's automated mixing equipment, ensuring the fiber distribution deviation per cubic meter of UHPC is ≤±3%.

Precise admixture regulation to optimize workability and shrinkage characteristics. Qinglong uses polycarboxylate-based retarding superplasticizers to control the water-binder ratio at 0.18-0.20 while ensuring a spread of 200-250mm, avoiding drying shrinkage caused by excess water. Water-retaining agents are also compounded at a dosage of 0.3%-0.5% to lock in internal moisture, extend the hydration reaction time, and reduce self-desiccation shrinkage. In the perforated panel project for the Ouargla Hotel in Algeria, precise admixture regulation enabled UHPC to maintain good workability at a low water-binder ratio, with autogenous shrinkage controlled at 180με and no cracks in complex components with perforation rates exceeding 50%.

Mitigating UHPC autogenous shrinkage is the result of the coordinated action of multiple materials. Through a comprehensive solution combining expansion agent compensation, cementitious system optimization, composite fiber modification, and admixture regulation, Qinglong Group minimizes autogenous shrinkage risk. These material design insights stem from practical experience accumulated over thousands of projects, ensuring both the high performance of UHPC and improved construction adaptability. Customers facing autogenous shrinkage control needs are advised to prioritize manufacturers with material R&D capabilities and project experience, solving shrinkage cracking at its root through scientific material design rather than relying solely on curing measures.