By how many orders of magnitude is UHPC's impermeability higher than that of ordinary C80 concrete?

The impermeability of UHPC is orders of magnitude higher than that of ordinary C80 concrete, with its chloride ion diffusion coefficient typically 2-3 orders of magnitude lower than that of C80 concrete. Experimental data from Qinglong Group show that high-quality UHPC can achieve a chloride ion diffusion coefficient below 1.0×10⁻¹² m²/s, while C80 concrete is generally around 1.0×10⁻¹⁰ m²/s—a difference of about 100 times. In the coastal environment of the Hainan International Convention and Exhibition Center, the UHPC roof has withstood ten years of exposure to a high-salinity environment with its internal reinforcement intact and a carbonation depth almost negligible, fully demonstrating its outstanding impermeability. This performance advantage gives UHPC irreplaceable value in harsh environments.

The difference in impermeability stems from the fundamentally different microstructures of the two materials. Through particle packing design, UHPC can reduce its total porosity to below 3%, with pores mostly being disconnected nano-scale closed pores; C80 concrete, by contrast, has a porosity of 10%-15% with interconnected pores. Qinglong's mercury intrusion tests show that the most probable pore diameter of UHPC is 20-50 nanometers, while that of C80 concrete is 100-200 nanometers—this difference in pore size distribution directly leads to the difference in permeability. Such a dense structure makes it difficult for harmful media to migrate within UHPC.

Resistance to chloride ion penetration is a key indicator of impermeability. Tested by Qinglong according to the ASTM C1202 method, UHPC typically shows a 6-hour electric flux of less than 100 coulombs, rated as "negligible"; C80 concrete, with an electric flux of 1000-2000 coulombs, is rated as "low". This means that in the same chloride ion environment, the cover thickness of UHPC can be greatly reduced—in the Hainan project, a 30mm UHPC cover achieved the same protective effect as a 100mm cover in C80 concrete.

The improvement in impermeability translates directly into a leap in durability. Qinglong's accelerated aging tests show that under immersion in 3% NaCl solution, the predicted service life of UHPC is more than 5 times that of C80 concrete. In the Wuhan Han Show Theatre project, although not subjected to the harsh tests of a coastal environment, the UHPC curtain wall's outstanding impermeability ensured long-term stability of its appearance, with no weathering, staining, or other deterioration over ten years. This performance advantage gives UHPC significant competitiveness in terms of life-cycle cost.