What Causes Air Bubbles on the Surface of UHPC Components?

Surface air bubbles on UHPC components are a common quality defect that affects both aesthetics and durability; their formation stems from multiple factors including materials, process, and environment. Based on extensive production practice, Qinglong Group believes that bubble control must be achieved through mix ratio optimization, process improvement, and strict management, reducing the bubble rate to below 0.5% to ensure component quality.

Material factors are the basis of bubble formation. An excessively high water-binder ratio (>0.25) increases air content, while an overdose of superplasticizer (>1.5%) introduces bubbles. Through optimized mix proportions, Qinglong Group controls the water-binder ratio at 0.20-0.22 and the superplasticizer dosage at 1%-1.2%, reducing bubble sources. High mud content in aggregates (>1%) or fiber agglomeration also causes bubbles. Every batch of raw materials is tested to ensure compliance with standards.

Process control is key. Insufficient or excessive mixing time leads to uneven bubble distribution. Qinglong Group adopts vacuum dewatering technology (vacuum degree -0.08MPa) to remove large bubbles. Inadequate compaction or over-vibration introduces new bubbles. Robotic spraying parameters are optimized, with pressure at 0.4-0.6MPa and uniform movement speed. The curing regime is also important, as too rapid a temperature rise causes bubbles to expand. Through whole-process monitoring, bubble problems are kept under control.

Environmental factors such as high temperature and low humidity accelerate water evaporation and form bubbles. Qinglong Group controls the temperature and humidity of its production workshops (20±5°C, humidity ≥70%) to reduce environmental impact. With scientific management, UHPC surfaces are smooth and flawless.