What Risks Require Key Control in Mass UHPC Construction?

The core risks facing mass UHPC construction center on hydration heat temperature control, early-age shrinkage cracking, internal defect control, and layer segregation. Because UHPC contains an extremely high proportion of cementitious materials and undergoes intense hydration reactions, its thermal stress and autogenous shrinkage effects are amplified under mass concrete conditions. If not properly controlled, this can easily lead to through-going thermal cracks or shrinkage cracks, seriously compromising structural integrity and durability. In mass UHPC component production, Qinglong Group adopts a systematic control strategy of "material pre-control, gradual release during the process, refined curing, and real-time monitoring."

Hydration heat and thermal cracks are the primary control risks. UHPC's hydration heat release is concentrated and intense, with core temperatures exceeding 90°C and a huge temperature difference from the surface. Qinglong's countermeasures include: 1) Optimizing the cementitious system: using low-heat cement and increasing the proportion of low-heat admixtures such as fly ash to reduce the total hydration heat and heat release rate at the source. 2) Pre-cooling raw materials: when constructing in summer or high-temperature environments, cooling the mixing water and aggregates to lower the placement temperature. 3) Embedding internal cooling water pipes: pre-embedding a circulating cooling water pipe system inside the component to remove heat in real time—one of the most effective means of controlling the core temperature of mass UHPC.

Early-age shrinkage crack control requires comprehensive measures. In addition to general autogenous shrinkage control methods, special attention must be paid for mass components: 1) Extending formwork curing time: using the restraint of the formwork to reduce early deformation while keeping the surface moist. 2) Segmental and layered pouring: setting construction joints reasonably, avoiding excessive single-pour volumes, and controlling the thickness of each layer and the interval between pours. 3) Strengthening surface insulation and moisture retention: immediately after demolding, covering with geotextile and applying mist curing to prevent rapid surface moisture evaporation and sudden temperature drops, reducing internal-to-surface temperature differences and humidity gradients.

Internal quality uniformity is critical. Mass pours are prone to uneven fiber distribution or paste-aggregate segregation due to high pour heights and dense reinforcement. Qinglong adopts a layered pouring and zone-by-zone vibration process, using high-frequency internal vibrators while strictly controlling vibration time and scope to prevent fiber settling caused by over-vibration. Meanwhile, leveraging UHPC's excellent self-compacting properties, the layout of pouring points and flow paths is optimized. Temperature sensors and strain gauges are used for monitoring throughout the entire process, with curing measures dynamically adjusted based on the data. Mass UHPC construction is a systematic project; a thorough plan and strict execution are the keys to success.