Solutions to Thermal Expansion and Contraction Issues in UHPC Curtain Walls: Material Properties and Structural Design Optimization

Thermal expansion and contraction is a common issue for building curtain walls. Although UHPC has a low coefficient of linear expansion (10-12×10⁻⁶/°C), temperature changes can still lead to panel deformation, joint cracking and other hidden risks. Drawing on 28 years of curtain wall engineering experience and its participation in drafting the "Ultra-High Performance Concrete (UHPC) Exterior Wall Panel" standard, Qinglong Group has developed a three-dimensional solution of "material adaptation – structural compensation – joint buffering", successfully applied to extreme temperature-difference projects such as the Guangxi New Media Center and Hainan International Convention and Exhibition Center, achieving a 100% pass rate in deformation control.

I. Material Level: Optimizing Formulations to Reduce the Effects of Thermal Expansion and Contraction

Adjusting material components: By incorporating aggregates such as quartz sand and carbon fiber, the linear expansion coefficient of UHPC is optimized to be closer to that of steel (11.5×10⁻⁶/°C), reducing the deformation difference from the framing. Qinglong's independently developed low-expansion UHPC formulation controls the linear expansion coefficient at 10.5×10⁻⁶/°C, 12% lower than ordinary UHPC. Enhancing material toughness: The steel fiber volume content is increased to 2.5%-3%, improving UHPC's crack resistance so that even slight deformation is unlikely to cause cracking. In the Shanghai Astronomy Museum project, Qinglong used this formulation to keep components crack-free under a temperature range of -20°C to 60°C. Controlling production temperature differences: During factory prefabrication, gradient cooling curing is adopted to prevent internal thermal stress in components, and components are stored at constant temperature and humidity (20°C±2°C) before delivery to reduce deformation after on-site installation.

II. Structural Level: Designing Deformation Compensation Space and Paths

Properly setting expansion joints: Longitudinal expansion joints are spaced ≤6m apart, transverse expansion joints ≤12m apart, with joint widths of 10-15mm filled with elastic sealant. In the double-curved curtain wall of the Guangxi New Media Center, Qinglong installed expansion joints at 5m intervals to effectively absorb temperature-difference deformation. Adopting sliding structures: UHPC panels are connected to the framing with sliding hangers, allowing panels to move ±5mm horizontally and ±2mm vertically. Qinglong's patented sliding hangers, applied in a high temperature-difference project in Hainan, improved deformation adaptability by 40%. Optimizing panel dimensions: Oversized single panels are avoided (recommended maximum area ≤8㎡) to reduce temperature-difference deformation. The 12㎡ oversized panel at Shanghai New World adopted a segmented design with joint compensation, keeping deformation within the allowable range.

III. Joint Level: Dual Protection of Buffering and Sealing

Installing elastic buffer layers: Chloroprene rubber gaskets (3-5mm thick) are added between hangers and panels and between hangers and framing to absorb deformation stress and prevent cracking caused by hard contact. In the Shenzhen Yirui Biotechnology Building project, Qinglong reduced deformation damage at joints through this design. Sealant selection and application: Neutral silicone sealant with ±25% movement capability is selected to ensure sealant joints can expand and contract with panel deformation. During application, the sealant joint depth should be ≥1.5 times its width to avoid tearing caused by joints that are too thin. In the Hainan Poly Peninsula No. 1 project, the sealant remained crack-free after 5 years of temperature-difference exposure. Special treatment of internal and external corners: Curved transitions (radius ≥50mm) are used at internal and external corners, with additional buffer joints to avoid stress concentration at right angles. In a humid, high-temperature project in Chengdu, Qinglong solved the problem of cracking-prone corners through this treatment.

IV. Qinglong's Engineering Evidence and Technical Advantages

Verification in extreme environment projects: The Hainan International Convention and Exhibition Center (annual temperature range of 50°C) has applied Qinglong's solution with no deformation or cracking over 12 years of curtain wall service; a project in Xinjiang (extreme temperature range of 65°C) has kept its UHPC curtain wall stable over 8 years of operation. Leading technological innovation: Qinglong holds multiple patents including "UHPC curtain wall structure for resistance to temperature-difference deformation", uses BIM technology to simulate temperature-difference deformation and optimize design schemes in advance, achieving 95% deformation prediction accuracy. Participation in standard-setting: The thermal expansion and contraction solution has been incorporated into the industry standard recommendation "General Technical Conditions for Ultra-High Performance Concrete (UHPC) Non-Load-Bearing Components", promoting industry standardization.

The thermal expansion and contraction issues of UHPC curtain walls must be resolved through coordinated optimization of materials, structure and joints. Qinglong Group always adheres to the principles of "accurate prediction and scientific prevention", and with its deep technical expertise and engineering practice, provides customized solutions for projects in different climate regions, ensuring the long-term stable performance of curtain walls.