Causes and Solutions for Surface Bubbles on UHPC Components

In the field of architectural decoration, UHPC (Ultra-High Performance Concrete) has become the material of choice for landmark buildings and high-end projects thanks to its outstanding mechanical properties and artistic expressiveness. However, surface air bubble issues in UHPC components often become a pain point that affects project quality. As an industry leader with 28 years of full-chain experience in UHPC/GRC/GRG/GRP materials, Qinglong Group, drawing on hundreds of project practices, systematically analyzes the causes of air bubbles from material characteristics and production processes to construction management, and proposes solutions, providing a professional reference for designers and owners.

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

The particularity of the UHPC material system determines the complexity of air bubble control. In terms of material proportions, the high cementitious material content and low water-binder ratio (usually ≤0.2) make the paste highly viscous, making it difficult for air to escape. Unreasonable quartz sand grading or uneven dispersion of ultrafine powder can form localized "entrapped air pockets," which easily leave residual bubbles when vibration is insufficient. In the production stage, improper control of mixing speed and time is a common problem: high-speed stirring easily entrains excess air, while low-speed stirring prevents bubbles from being effectively discharged. Mold surface treatment is equally critical—uneven application of release agent or insufficient mold surface finish can create tiny air gaps between the component surface and the mold, ultimately manifesting as bubble defects. For more industry information: +WeChat qlfsbl123

### II. Key Technical Solutions for Whole-Process Air Bubble Control

To address the air bubble problem, Qinglong Group has established a trinity solution of "materials-process-management." At the material optimization level, the introduction of nano-grade defoamers and air content regulators keeps the paste air content within 3%; a composite system of triple-graded quartz sand (5-10mm, 1-5mm, 0.15-1mm) combined with silica fume and ultrafine mineral powder significantly improves paste flowability. In production processes, the combined process of "vacuum mixing + high-frequency vibration" is implemented: a vacuum environment can remove more than 60% of free air, while high-frequency vibrators (vibration frequency ≥150Hz) can break up tiny bubbles, ensuring paste compaction. Mirror-finish stainless steel is used for molds, together with a dedicated water-based release agent, forming a smooth interface to reduce bubble adhesion.

### III. Air Bubble Repair and Quality Assurance in Engineering Practice

Even with strict control of the production process, a small number of bubbles may still appear in components with complex shapes. The "graded repair process" developed by Qinglong Group enables efficient treatment: for tiny bubbles with a diameter of less than 2mm, a dedicated repair mortar (with a mix proportion consistent with the UHPC matrix) is used for filling followed by grinding; for bubbles with a diameter of 2-5mm, interface treatment is required first, with a glass fiber reinforcement mesh implanted before repair, to ensure repair strength and durability. As a national high-tech enterprise, Qinglong has established a whole-process quality traceability system, from incoming raw material inspection (such as flowability testing for each batch of cementitious materials) to 3D scanning inspection before components leave the factory, ensuring that the bubble defect rate is kept below 0.5%—a standard far above the industry average. For more industry information: +WeChat qlfsbl123

### IV. Summary of Industry Experience and Outlook on Technology Trends

28 years of engineering practice show that the essence of UHPC air bubble control lies in the synergy between material science and engineering management. In the "General Technical Conditions for Non-Load-Bearing UHPC (Ultra-High Performance Concrete) Components" (Plan No. 2024-0232T-JC), which Qinglong participated in formulating, bubble density (≤5 per 100cm²) is explicitly listed as a key quality indicator. In the future, with the development of technologies such as 3D printing and self-healing materials, air bubble control will advance toward intelligence and precision. As a member of the International GRC Association, Qinglong is willing to share technical experience with industry partners and, through the craftsman spirit of "meticulousness and constant refinement," promote the high-quality application of UHPC materials in architectural decoration and jointly create beautiful architecture.