Posted by Engin Seyhan - 14 October, 2019
Surface applied corrosion inhibitors (SACI) are widely used for mitigating the corrosion of steel reinforcement in concrete. As explained in Part 1 of this article, SACIs, the type of corrosion inhibitors usually applied to hardened concrete, penetrate towards the steel reinforcement, providing passive protection, which can be broken down under some circumstances. Concrete is highly susceptible to cracking over time. When cracks appear, water and chlorides can easily reach the rebars, accelerating the corrosion reactions. Based on the existing challenges in corrosion mitigation in reinforced concrete, a new approach has been followed by BASF scientists. Several different technologies have been studied for years to overcome the negative impact of the cracking and achieve efficient corrosion protection even in post-cracked concrete. The result of these studies is MasterProtect 8500 CI: a dual-function, silane-based, surface-applied corrosion inhibitor which enhance the service life of any steel-reinforced concrete structure, new or existing. This product has also been proved to be effective in the case of post-application cracks.
MasterProtect 8500 CI: proven performance
Independent testing of MasterProtect 8500CI has shown it to be very effective in reducing active corrosion in steel-reinforced concrete. Modified ASTM G109 testing was carried out. The concrete specimens were treated with MasterProtect 8500 CI. The specimens were cracked before the SACI was applied and additional specimens were treated with MasterProtect 8500 CI before cracking. As it can be seen below from Figure1, the specimen treated with MasterProtect 8500CI before cracking shows only slight corrosion. In the case of the specimen cracked after coating, corrosion started but then stopped, increasing over nine months of ponding.
Figure 1. ASTM G109 specimens coated with MasterProtect 8500CI before and after cracking, and an untreated control specimen. Crack widths: ~0.3 mm
In another ASTM G109 test series, different commercial SACI treatments were applied to the specimens - including a water-based amino alcohol, a conventional silane SACI, and MasterProtect 8500 CI - to study the impact of cracking on treated samples. Three of the untreated blocks along with the treated blocks were cracked perpendicular to the top reinforcing bar before ponding with 3% NaCl solution. After each cycle of drying and ponding, corrosion measurements using ASTM C876 half-cell testing were taken prior to the dry cycle. An appendix 2 ASTM C876 provides guidance on the interpretation of the readings. The results in Figure 2 clearly shows the low corrosion potential with both MasterProtect 8000 CI and MasterProtect 8500 CI compared with other specimens, which show development of corrosion potential.