Which Risks Require Key Control in Mass UHPC Construction? Core Technical Solutions for Risk Prevention and Control

Mass UHPC construction involves large component volume, concentrated hydration heat, and high shrinkage stress, which can easily lead to risks such as temperature cracks, shrinkage cracks, and insufficient compactness, severely affecting component performance and service life. Accurately identifying and controlling core risks is the key to successful mass UHPC construction. Based on 28 years of large-scale project construction experience, Qinglong has summarized core technical solutions for risk prevention and control.

1. Temperature Crack Risk Control

The internal-external temperature difference caused by concentrated hydration heat is the main cause of temperature cracks in mass UHPC, requiring coordinated control through “cooling + thermal insulation.” Pre-cooling of raw materials is the foundation: cement and aggregates are stored in a cool environment after arriving on site, and ice water is used for mixing to lower the initial pouring temperature. Qinglong controls the pouring temperature below 25°C. During pouring, a layered pouring process is adopted, with each layer 30-50cm thick and intervals of ≥2 hours to avoid superimposed hydration heat. In a mass UHPC base project in Shanghai, Qinglong used layered pouring to keep the maximum internal temperature below 65°C. During the curing stage, thermal insulation and moisture retention measures are adopted: covering with geotextile and plastic film, and laying electric heating blankets when necessary, keeping the internal-external temperature difference at ≤25°C. Slow cooling reduces thermal stress, while regular temperature monitoring allows real-time adjustment of curing measures to avoid cracks caused by sudden temperature changes.

2. Shrinkage Crack Risk Control

Mass UHPC has large shrinkage and is prone to cracking when shrinkage stress exceeds the material's tensile strength; prevention and control must address both materials and processes. In material design, expansion agents and water-retaining agents are added: the expansion agent dosage is 5%-8% of the cementitious material mass to compensate for drying shrinkage, while the water-retaining agent improves moisture retention capacity to reduce autogenous shrinkage. Qinglong tests show that adding expansion agents can reduce the shrinkage rate by 40%. Fiber composite reinforcement is key: steel fibers are combined with polypropylene fibers, and the bridging effect of the fibers inhibits crack propagation, with total fiber content controlled at 2%-3%. During construction, the vibration process is optimized by using high-frequency vibrators to ensure compaction and prevent void defects from aggravating shrinkage cracks. After pouring, covering for curing is carried out promptly, extending the moisture-retention curing time to more than 14 days. In the mass UHPC component construction of the Yangshengtang Pharmaceutical Hangzhou Industrial Park, Qinglong used this solution to effectively control shrinkage crack width below 0.1mm.

3. Insufficient Compactness Risk Control

Mass UHPC has large cross-sections that are difficult to vibrate, making insufficient internal compactness likely, which affects strength and durability. Optimizing the vibration process is the core: insert-type high-frequency vibrators are combined with surface vibrators, with vibration time controlled at 20-30 seconds per point to ensure thorough vibration without segregation. Qinglong is equipped with automated vibrating equipment to improve vibration uniformity. During pouring, vent holes are set to discharge internal air and reduce bubble defects; especially in component corners and rebar-dense areas, the density of vent holes is increased. In terms of mix ratio optimization, paste fluidity is appropriately improved: high-efficiency water reducers are selected to lower the water-binder ratio while ensuring workability. Qinglong adjusts the admixture dosage to achieve a paste spread of over 600mm, facilitating the filling of cross-section corners. In the finished product stage, ultrasonic testing instruments are used for compactness testing, and non-conforming areas are promptly treated with pressure grouting to ensure overall compactness.

4. Construction Organization and Quality Control Risk Control

Improper construction organization can easily lead to schedule delays and quality fluctuations, requiring well-planned and detailed construction schemes. The construction process should be reasonably planned, with clear time nodes and responsible persons for each stage of pouring, vibrating, and curing. Qinglong uses BIM technology to simulate the entire construction process and avoid construction conflicts in advance. Raw materials are strictly measured with automated metering equipment, with errors controlled within ±0.5% to ensure accurate mix ratios. Process testing is strengthened: test blocks are made for each batch of pouring to monitor strength development, while component surfaces are inspected for flatness and cracks, with surface defects promptly addressed. For overseas projects such as the mass UHPC construction of the Ouargla Hotel in Algeria, Qinglong adjusted construction schedules based on local climate conditions to avoid high-temperature periods, ensuring stable construction quality. Through refined whole-process management and control, various construction risks are effectively reduced.