The right-leg tower pedestal of the west cable tower of the Shiziyang Channel was successfully poured and completed.

On June 24, the right-leg tower pedestal and T1 segment tower column of the west cable tower of the Shiziyang Channel, constructed by CCCC Second Harbor Engineering Co., Ltd. (a central enterprise based in Chongqing), were successfully poured and completed.

Notably, C80 concrete was successfully applied in this pouring, and the optimal mix proportion for C80 concrete was determined, verifying the applicability of the newly developed pouring technology, complete sets of equipment, and temperature control measures, laying a solid foundation for subsequent C80 concrete pouring of the cable tower.

As a mega project in the Guangdong-Hong Kong-Macao Greater Bay Area, the Shiziyang Channel is the first double-deck river-crossing passage at the Pearl River Estuary. The controlling project, the Shiziyang Bridge, adopts a double-deck steel truss suspension bridge scheme with a main span of 2,180 meters that crosses the river in a single span, making it the world's largest-span double-deck suspension bridge. Once completed, it will set five world-leading records: main span length, number of lanes, main tower height, anchorage foundation, and main cable scale.

Among these, the cable tower of the Shiziyang Bridge adopts a steel-shell concrete composite bridge tower with a height of 342 meters, also the world's tallest bridge tower of its type. A single bridge tower consists of 62 segments and 6 steel cross beams.

However, adopting a steel-shell concrete composite bridge tower means the Shiziyang Bridge cable tower must ensure the mechanical performance of the ultra-high steel plate concrete composite bridge tower, with the steel shell walls filled with C80 special concrete featuring high strength, high elasticity, high robustness, and low shrinkage.

Previously, there was no practical experience to draw on regarding the structural characteristics of C80 concrete's first application in steel-concrete cable towers and the technical challenges faced during construction.

The mega project Shiziyang Bridge.

To this end, the Tao Jianfei Innovation Studio team of the CCCC Second Harbor Engineering Test Center embarked on a research and development journey. First, the project team strictly controlled the performance indicators of raw materials and drafted an initial concrete mix proportion.

"In previous concrete mix proportions, the cement proportion was high, cement hydration heat release was large, and the adiabatic temperature rise of concrete was relatively high, posing a greater cracking risk when applied to solid structures. After several tests, the concrete temperature peak still exceeded requirements, and the tests were unsuccessful," said Wu Yang, director of the project laboratory.

Through the accumulation and analysis of multiple test data, the project department optimized the theoretical mix proportion, appropriately reducing the proportions of cement and fly ash while adding a certain proportion of anti-cracking agent and flow modifier. After multiple adjustments, the concrete performance and indicators all met design requirements. While ensuring concrete strength, the chloride ion diffusion coefficient was improved and the self-cementitiousness was enhanced, producing concrete with good workability, low hydration heat, and higher density.

On June 22, a day that all team members both anticipated and felt nervous about—the right-leg tower pedestal and T1 segment tower column of the west cable tower of the Shiziyang Channel officially began pouring.

"Attention all groups, during pouring, go slow and steady..." The tower pedestal and T1 segment of the tower column were poured together as a whole, with a total of 1,676.2 cubic meters of C80 concrete poured. The pouring sequence followed the principle of "outside first, then inside; from the perimeter to the center; layered and alternating pouring" until the concrete reached the design elevation.

The summer weather was unusually muggy, and the sun in the blue sky blazed like fire, making everyone drip with sweat. But no one bothered to wipe their sweat, concentrating fully on completing the established procedures they had rehearsed countless times before.

After 30 hours of shift work, the final batch of concrete was poured. Only then did the entire team breathe a sigh of relief, and their anxious hearts finally settled.

The T1 segment tower column of the Shiziyang Bridge.

Every project has unpredictable technical difficulties; every technical difficulty is a tough "hard bone" to crack.

Late that night, the small meeting room on the second floor of the Shiziyang Bridge project department was still brightly lit, and the sound of whiteboard markers was particularly loud. Project chief engineer Zeng Wei was leading the technical research team in a summary after the C80 concrete pouring: "After this pouring was completed, 13 indicators including the slump flow, segregation rate, temperature changes, and mechanical properties of the C80 concrete were tested, all meeting design specification requirements."

The successful pouring and completion of the right-leg tower pedestal and T1 segment tower column of the Shiziyang Channel cable tower not only verified the applicability of the C80 concrete preparation technology and complete sets of pouring equipment, but also pioneered a new path for construction of similar bridges, providing valuable practical experience.