"It's incredible! The demolition waste that used to pile up like mountains can actually become high-quality, economical, and practical concrete!" In the testing laboratory of Jiehang Inspection Company, a subsidiary of The Sixth Engineering (Xiamen) Co., Ltd. of CCCC Third Harbor Engineering Co., Ltd., a representative from a visiting concrete manufacturer marveled while feeling the solid and uniform sample of recycled aggregate.

Driven by the national strategy to strengthen the maritime sector, major waterborne construction projects like ports and harbors are steadily progressing in coastal regions such as Fujian. These projects have exceptionally strict requirements for concrete aggregates: they must not only withstand the pressures from frequent loading and unloading but also resist the high-salt, high-humidity, and highly corrosive marine environment. Both high strength and durability are essential.

However, traditional recycled aggregates often fall short – lacking sufficient strength, having high water absorption rates, and exhibiting unstable performance. They repeatedly failed in simulated marine environment tests, making them unsuitable for building a solid foundation for seaport construction. To balance environmental protection with practicality, the research team at Jiehang Inspection Company embarked on a path of independent research and development. "Disposing of waste concrete is very costly. We wanted to optimize the modification process to turn this waste into a valuable resource," explained Zhang Kai, Chief Engineer of Jiehang Inspection Company.

In August 2024, the research team started by analyzing the "genetic profile" of typical waste concrete. They collected samples of waste concrete from different construction sites and of different ages, meticulously disassembling and analyzing each one in the lab. Under advanced testing equipment, the "complex composition" of the construction waste was revealed: a mixture of concrete blocks, bricks, metal, and other materials, making it difficult to separate them completely during processing into recycled aggregate – the first major hurdle.

The team first tried using physical shaping methods, adjusting mechanical grinding parameters to remove the cement mortar from the aggregate surface, thereby improving the performance of the recycled aggregate. However, the test results were unsatisfactory; the prepared recycled aggregate had an average strength 10-20 MPa lower than natural aggregate, posing safety concerns. "Is using recycled aggregate in marine structures really just a pipe dream?" Zhang Kai pondered, gazing at the piles of samples in the lab.

With the physical approach proving unfeasible, the team quickly adjusted their strategy, turning to the field of materials chemistry. The members consulted vast amounts of literature, referenced domestic and international research findings, proposed dozens of hypotheses, and conducted hundreds of formula screenings and verifications. The lab lights often burned through the night, and 5 tons of trial concrete were consumed in the numerous attempts. In December 2024, the team finally achieved a breakthrough with a special surface activator they developed independently. It functioned like an industrial-grade "powerful cleaner," capable of removing residual calcium hydroxide and fine powders from the recycled aggregate, restoring a clean surface that could tightly "interlock" with the cement paste, significantly enhancing the bond strength. When the new, enhanced recycled aggregate passed all performance tests for marine engineering, the lab erupted in cheers.

But the joy was soon tempered by cost pressures. The special chemical materials and complex operational processes drove up the price of the recycled aggregate, making it less competitive in the market. Economic viability became the final barrier to commercial application. The research team rallied again, collaborating with industry material experts and equipment manufacturers to tackle the challenge. Through process optimization and equipment upgrades, they developed a full-chain production process of "precision processing – surface treatment – waste recycling," successfully reducing the overall cost by nearly 30%.

In May 2025, the final tests were conducted. The ultimate monitoring data showed that the crushed index of the recycled aggregate was controlled below 10%, the mud content was below 0.5%, and the gradation was excellent. Concrete prepared with this aggregate achieved a maximum 28-day strength of 70 MPa, an impermeability grade of P12, and its resistance to chloride ion diffusion met marine engineering requirements.

"For every ton of recycled aggregate used, we save one cubic meter of quarried stone and reduce carbon dioxide emissions by 3.7 kilograms. This is immensely significant for a province like Fujian, with its long coastline and large construction volume," Zhang Kai said with palpable pride. "More importantly, we have found a path that balances performance and cost. This will become a green key to solving the twin problems of construction waste and resource shortages, allowing construction waste to truly 'take root' on construction sites!"

The sea breeze swept across the test bench. The former concrete waste had now transformed into qualified building material, ready to contribute to seaport construction. This green solution, born in the laboratory, is steadily taking shape along the coast of eastern Fujian. (Content provided by: Zhuo Zhen)