At three in the afternoon, the late spring sunlight was particularly glaring, with three tower cranes extending their long arms in coordinated motion. Workers moved back and forth, sweat beads rolling down their dark, sun-baked faces. River breeze carried the earthy scent of cement and sand, while summer cicadas were drowned out by the vibrations of concrete tamping. This is the construction site of the Fujiang River Sanshan Ship Lock Project undertaken by CCCC Second Harbor Engineering Company Ltd (hereinafter referred to as "CCCC Second Harbor Engineering"). The project is situated at the junction of Heye Township in Pengxi County, Suining City, Sichuan Province, and Mixin Town, Tongnan District, Chongqing, spanning across Pengxi, Chuanshan, and Chongqing's Tongnan regions. As a core project of the Chongqing-Sichuan joint initiative to build a shipping hub on the upper Yangtze River and the top-priority project under the "Unblock the Fujiang River" action plan, the project targets the long-standing navigation bottleneck left by the Sanshan Power Station, aiming to break through channel constraints, restore waterway connectivity, and chart a new course for the full resumption of navigation along the Fujiang River.
The ship lock main structure measures 255 meters in length—not particularly long—yet it is composed of 310,000 cubic meters of concrete, poured across 283 segments. The current phase involves the upper lock head, with the largest single pour reaching approximately 2,200 cubic meters of concrete. During mass concrete placement, hydration heat is released intensively; if temperature control goes awry and the temperature differential between interior and exterior becomes unbalanced, cracks can form within the concrete, leaving the lock with "internal injuries." These injuries erode the structural framework and undermine the lock's foundational stability.
"These 'internal injuries' can only be prevented—we cannot wait until problems surface to address them," explained Yi Xue, the project's technical manager. "Before large-scale construction, we conducted temperature calculations and found that the core temperature of the concrete reaches approximately 55°C, while the surface temperature matches ambient conditions, creating a differential of about 20°C." The interior of the concrete runs hot and expands, while the exterior remains cool and contracts—this push-and-pull inevitably causes internal damage. To effectively ward off such injuries, the project team has deployed four lines of defense.
The first line of defense starts with raw materials.
Cement is the primary source of heat generation in concrete. The originally planned low-heat cement had scarce supply and procurement difficulties within Sichuan Province, yet the project had to capitalize on the dry-season construction window—time being the lifeline of construction. However, ordinary cement produces higher hydration heat and fails to meet temperature control standards. After extensive deliberation among project leadership and technical staff, the decision was made to "switch to ordinary cement and have the on-site laboratory independently optimize the concrete mix design." Tasked with this assignment, testing technician Xia Xianyi led his team through months of repeated experimentation—reducing cement, fly ash, and admixture dosages while extending concrete curing age—thereby not only lowering hydration heat at the source while meeting construction standards but also significantly cutting construction costs.
The second line of defense involves pre-cooling raw materials.
Once raw materials are prepared, they require pre-cooling. The concrete mixing process itself continuously generates heat. "It's like freshly cooked porridge being too hot to eat—concrete mixed without any cooling measures makes temperature control even harder," said Liu Yifeng, the project's deputy chief engineer. Raw material pre-cooling employs two primary methods: cooling the mixing water and implementing a fly ash silo cooling spray system. The batching plant is equipped with two sets of chillers that continuously cool the mixing water in the storage tank, strictly controlling the concrete discharge temperature to no higher than 28°C. Since fly ash leaves the factory at elevated temperatures and would raise concrete temperature if used directly, a cooling spray system has been installed around the fly ash silo to douse the tank and cool the material within. Both strategies lower the overall temperature baseline of raw materials before pouring begins.
The third line of defense: installing an "air conditioner."
The third defense line involves installing an "air conditioner" for the poured concrete. "Since the internal temperature runs high, let's bring it down—just like opening an air conditioner when a room gets too hot," Liu Yifeng noted. This "air conditioner" is called the "cooling water pipe circulation system." At every 1.5-meter height of each concrete pour, 2.4mm-thick HDPE pipes are laid in a U-shape pattern, allowing cold water to pass through the concrete interior, carrying away heat. The warmed water then circulates to a cooling tower where it is chilled before returning to the cold-water tank, achieving water resource recycling. Once concrete curing is complete, the cooling pipes are grouted and sealed. "This system can simultaneously support temperature reduction and curing for 50 lock segments at once, greatly improving resource utilization efficiency," Liu added.
The fourth line of defense: round-the-clock monitoring and curing.
The fourth defense line stems from the project team's 24-hour continuous temperature monitoring and curing. To enable non-stop temperature tracking, technicians embed temperature-sensing elements within the concrete during rebar tying, monitoring temperature differentials in real time through three interior points and three surface points. Workers adjust surface watering and curing based on ambient temperature changes, maintaining surface moisture and temperature stability to prevent rapid moisture evaporation that could exacerbate shrinkage cracking.
These four lines of defense progress layer by layer, interlocking like four solid barriers that firmly keep the temperature differential between concrete interior and exterior within code requirements, eliminating structural "internal injuries" at their very source. On the surging Fujiang River, the ship lock rises steadily, building momentum for the full resumption of navigation along the entire waterway—breathing new life into this one-time "golden waterway" of central Sichuan.