Differences in Mold Requirements Between UHPC Single-Curved and Double-Curved Panels and Cause Analysis

Molds are the “skeleton” of UHPC panel forming. The difference between single-curved and double-curved panels is not merely a divide in geometric form, but a comprehensive contest of material properties, process precision, and engineering costs.

Today, as building envelopes increasingly pursue dynamic aesthetics, UHPC (Ultra-High Performance Concrete) has become the “star material” of landmark buildings thanks to its ultra-high strength, excellent durability, and outstanding shaping capability. As an industry leader with 28 years of deep expertise in UHPC/GRC/GRG/GRP materials, Qinglong Group has found in design development and production practice that the difference in mold requirements between single-curved and double-curved panels directly affects project implementation efficiency and final results. This article analyzes the core differences and technical logic of the two from three aspects: mold design, material selection, and process control.

I. Mold Design: A Precision Leap from “Planar Geometry” to “Spatial Curved Surfaces”

Single-curved UHPC panel molds feature regular single curvature (such as cylindrical and conical surfaces), and their mold design can achieve standardized production through parametric modeling. Taking Qinglong Group’s Nanning production base as an example, single-curved molds typically use modular steel molds: by combining arc-shaped frames of fixed radii with flat formwork, together with adjustable support structures, batch production needs can be met. The advantage of this design lies in high mold reusability, with a one-time investment cost of roughly 1/3 to 1/2 that of double-curved molds.

Double-curved UHPC panels face the “double curvature” challenge, having to handle composite surface changes along both the X and Y axes. Their mold design must rely on 3D scanning and reverse engineering technology: first, a precise digital model is built with Rhino/Grasshopper, then CNC machining is used to produce foam or resin master molds, and finally fiberglass (GRP) molds are cast from them. In the Century Plaza renovation project on Nanjing East Road, to realize a translucent concrete double-curved envelope, the digital modeling and machining cycle for a single mold set took as long as 15 days—more than three times that of a single-curved mold.

II. Material Selection: The Art of Balancing Load-Bearing Capacity and Flexibility

Single-curved molds place greater emphasis on structural stability. Qinglong typically uses Q235 steel plates (8-12mm thick) as the base material, combined with structural steel frames to enhance overall rigidity, capable of withstanding lateral pressure of about 50kN/m² during UHPC pouring. Double-curved molds, on the other hand, involve complex surface geometry that is difficult to machine in steel and prone to stress concentration, so fiberglass reinforced plastic (GRP) composite molds are preferred. This material offers 0.2% elastic deformation capability, conforms precisely to double-curved surfaces, and weighs only 1/5 of a steel mold of the same volume, making on-site installation and adjustment easier.

Notably, double-curved molds require additional consideration of the material’s coefficient of thermal expansion. In the Dongguan Women and Children’s Activity Center project, Qinglong embedded a carbon fiber thermally conductive layer inside the GRP mold, controlling thermal deformation during pouring to within 0.3mm/m and ensuring the dimensional accuracy of double-curved components.

III. Process Control: Full-Process Management from “Standardization” to “Customization”

Single-curved panel molds allow assembly-line production. Qinglong adopts a “one mold, multiple uses” strategy: panel dimensions can be adjusted simply by replacing the side baffles, with production efficiency reaching 100-150㎡/day. Double-curved molds, however, require a “one mold, one plan” approach—from digital model review and master mold precision inspection to mold assembly calibration, every step requires full tracking by the technical team. Taking a 1000㎡ double-curved UHPC curtain wall as an example, the mold preparation cycle is about 45 days, twice that of a single-curved project, with a scrap rate as high as 15%-20%.

In demolding, single-curved panels can use conventional hydraulic ejection devices, while double-curved panels, due to their tight surface fit, require a special release agent (containing polytetrafluoroethylene) sprayed on the mold surface, combined with vacuum suction cups to assist demolding—a process that extends the demolding time for a single panel to over 30 minutes.

In essence, the mold differences between UHPC single-curved and double-curved panels reflect the eternal proposition of “function and aesthetics” in architectural decorative materials. As a national “Specialized, Refined, Distinctive and Innovative” enterprise, Qinglong Group, through 28 years of full-chain experience, has developed complete solutions spanning parametric design, mold development, and intelligent manufacturing. From the single-curved UHPC shading system for a commercial complex in Guangzhou to the double-curved GRP-UHPC composite envelope for a landmark project in Saudi Arabia, Qinglong has always upheld its mission of “creating aesthetically beautiful architecture,” providing designers and owners with material solutions that combine technical feasibility and artistic expression. In the future, as 3D-printed mold technology matures, the cost bottleneck of double-curved UHPC is expected to be further overcome, injecting more possibilities into building envelope innovation.