Surface-Finishing and Cast-Iron Corrosion-Screening Performance of a Rapeseed-Oil-Based Waterborne Concrete Release Agent

Surface voids and formwork corrosion affect the appearance and maintenance of fair-faced concrete. This study evaluated an integrated waterborne release agent containing a rapeseed-oil oil-in-water emulsion, a poly (N-isopropylacrylamide-co-acrylic acid) [P(NIPAM-co-AA)] modifier, and triethanolamine borate. Emulsifier blends were screened by 24 h phase stability, followed by a 16-run, five-factor, four-level emulsification screen. The selected formulation was S80:OP-10 = 9:1 at 6 wt% total emulsion, processed at 60 °C for 70 min. On steel formwork vibrated for 120 s, three technical repeats gave a lower surface-void area fraction for the integrated formulation than for a commercial product (0.90 ± 0.10% versus 2.20 ± 0.18%; 59.1% relative reduction). The void-area share for equivalent diameters ≤1 mm increased from 73.8 ± 2.5% to 88.2 ± 2.0%. In a controlled-humidity cast-iron rust-spot test, 2.5% triethanolamine borate gave a longer time to first rust than diethanolamine borate (1920 ± 95 versus 1440 ± 80 min). A field comparison showed lower surface-void fractions on the treated pier (0.037 ± 0.008%) than on the untreated reference (0.242 ± 0.035%). These results identify a candidate formulation for surface finishing and cast-iron corrosion screening and support subsequent independent-batch, release-force, and steel-formwork validation.