Analysis of Causes and Solutions for Bubbles on UHPC Component Surfaces

In the field of architectural decoration, UHPC (Ultra-High Performance Concrete) has become the material of choice for high-end projects such as grand theaters, commercial complexes, and landmark buildings, thanks to its outstanding mechanical properties and design expressiveness. However, during the production of UHPC components, surface air bubble issues not only affect aesthetics but may also compromise structural durability. As an industry leader with 28 years of full-chain experience in UHPC/GRC/GRG/GRP materials, Qinglong Group combines deepened design, manufacturing, and installation practices to thoroughly analyze the causes of air bubbles and propose systematic solutions, providing professional technical support for designers and owners.

I. Analysis of the Core Causes of Air Bubble Formation in UHPC Components

The unique characteristics of UHPC material make its bubble control more challenging than that of ordinary concrete. From material mix proportions to process steps, bubble formation often involves multiple factors:

1. Imbalanced material system: The high density of UHPC relies on the tight packing of ultra-fine powders. If the proportions of components such as cement, silica fume, and ultra-fine aggregates are improper, or if the selection and dosage of admixtures (such as water reducers and defoamers) are unbalanced, the slurry viscosity may become too high and air expulsion hindered. For example, excessive polycarboxylate water reducers may introduce unstable bubbles, while insufficient defoamer fails to effectively eliminate micro-bubbles generated during mixing.

2. Mixing and casting process defects: Excessively fast mixing speed or insufficient mixing time increases entrapped air that is difficult to release; excessive drop height during casting, lack of layered vibration, or improper control of vibration frequency and duration can all lead to bubble retention. Qinglong's practice at its Nanning production base found that for complex curved UHPC components (such as double-curved facade panels), traditional vibration methods tend to form bubble concentration zones, requiring optimization combined with vacuum-assisted forming technology.

3. Influence of mold and curing environment: Insufficient mold surface smoothness and uneven application of release agent hinder the smooth rise of bubbles; improper temperature and humidity control during curing, such as too rapid early heating, may prevent bubbles from escaping before the slurry hardens. In addition, differences in the air permeability of GRP (glass-reinforced thermosetting plastic) molds may also affect bubble escape efficiency.

II. Full-Chain Bubble Control Solutions: Qinglong's Practice from Design to Construction

To address bubble issues, Qinglong has built a standardized control system based on its full-chain advantages of "deepened design – manufacturing – installation":

1. Material formulation optimization: The optimal powder gradation is determined through orthogonal tests, and "dual-admixture technology" (silica fume + ultra-fine mineral powder) is adopted to reduce slurry viscosity; customized defoamers are selected, combined with a dynamic defoaming monitoring system to ensure precise admixture dosage. For example, in the Century Plaza translucent concrete project on Nanjing East Road, Qinglong reduced the bubble defect rate by more than 60% by adjusting the synergy between defoamers and water reducers.

2. Intelligent production process upgrade: Planetary mixers and vacuum mixing technology are introduced to reduce air entrapment; a combined process of robotic casting and high-frequency vibrating tables is adopted, and "low-amplitude, high-frequency" vibration parameters have been developed to suit the characteristics of lightweight materials such as GRG (glass fiber reinforced gypsum moldings). Meanwhile, BIM technology is used to simulate the component casting process, predicting bubble-prone areas and optimizing casting paths.

3. Refined mold and curing management: Mirror-grade stainless steel molds and water-based release agents are used to ensure surface flatness; during curing, a "three-stage temperature control" (pre-curing at 25°C → heating to 40°C → constant temperature curing) is implemented, combined with steam curing to accelerate bubble escape. In the Dongguan Women and Children's Activity Center GRC project, Qinglong controlled surface bubble diameters within 0.5mm through mold preheating and gradient curing.

4. Quality traceability and after-sales maintenance: A "one item, one code" quality traceability system is established to record the material mix proportions, production parameters, and bubble inspection data of each batch of components; for installed components, regular inspections and surface repair services are provided, using specialized repair materials (such as UHPC micro-repair mortar) to ensure long-term aesthetics.

III. Industry Insights: The Technical Logic Behind Bubble Control

Solving the air bubble problem in UHPC components is essentially a synergy of materials science, process technology, and engineering management. As a national high-tech enterprise and a participating unit in drafting the industry standard "General Technical Conditions for Non-Load-Bearing Components of Ultra-High Performance Concrete (UHPC)," Qinglong believes that designers need to fully consider the impact of component shapes on bubble control at the design stage and avoid overly complex cavity designs, while owners should pay attention to suppliers' full-chain service capabilities rather than a single production step when selecting suppliers. In the future, with the development of technologies such as 3D printing and self-healing materials, UHPC bubble control will advance toward intelligence and precision.

Qinglong Group has always been committed to the mission of "creating beautiful architecture." Through 28 years of technical accumulation and continuous innovation, it has integrated process defect control of UHPC/GRC/GRG/GRP materials into every project. From material R&D to project delivery, Qinglong is dedicated to providing customers with "zero-defect" decorative components, helping to create architectural works that combine aesthetic value with structural safety.