Frequently Asked Questions

A building owner in Delhi is planning a preventive maintenance programme for an 8-year-old multi-storey reinforced concrete industrial building where carbonation depth measurements on cores show that carbonation has reached 10 to 15 mm on unprotected column faces, and the reinforcement cover depth is only 20 to 25 mm — is MC-Color 2K anti-carbonation coating sufficient to prevent reinforcement corrosion from starting, or does the building also require concrete repair at this stage, and what is the complete 10-year maintenance plan?

At 8 years old with carbonation depths of 10 to 15 mm and cover depths of only 20 to 25 mm, this building is approaching the critical threshold where active reinforcement corrosion is expected to commence within 2 to 8 years without intervention — the residual cover depth of 5 to 15 mm remaining ahead of the carbonation front represents a very short remaining initiation period in the Delhi NCR urban atmosphere. The assessment and 10-year maintenance plan are as follows. Current condition interpretation: the half-cell potential survey (ASTM C876) is essential to determine whether reinforcement corrosion has already started — half-cell potentials more negative than minus 350 mV (versus CSE) indicate greater than 90 percent probability of active corrosion. If the building shows: (a) half-cell potential more negative than minus 350 mV in any column zone — active corrosion has started and concrete repair (chipping back to bright bar, MC-Dur mortar repair) is required NOW before applying anti-carbonation coating; (b) half-cell potential between minus 200 and minus 350 mV — corrosion is possible but not confirmed — apply anti-carbonation coating as preventive intervention; (c) half-cell potential less negative than minus 200 mV — corrosion unlikely — apply anti-carbonation coating as planned maintenance. For the typical case of a mixed result (some columns showing possible corrosion, most in the uncertain zone) — repair all columns with half-cell potential more negative than minus 350 mV and apply MC-Color 2K anti-carbonation coating to all columns as Phase 1 of the maintenance programme. Is MC-Color 2K sufficient alone, or is concrete repair also required? MC-Color 2K applied now to columns with 10 to 15 mm carbonation depth and 20 to 25 mm cover can extend the time before carbonation reaches the reinforcement by a significant factor: unprotected concrete at current Delhi NCR CO2 concentration (approximately 450 ppm) and typical humidity: remaining carbonation front travel time from 15 mm to 22 mm depth (assuming 22 mm effective cover after concrete preparation) = approximately 3 to 6 years. With MC-Color 2K (sd value 100 m): the coating reduces the effective CO2 concentration at the concrete surface by approximately 1,000-fold — the remaining carbonation front travel is extended by this factor relative to the CO2 concentration gradient — in practice, this typically extends the remaining carbonation propagation time by 5 to 15 years. The combination of 3 to 6 year remaining carbonation front travel plus 5 to 15 year extension from MC-Color 2K provides a total predicted remaining initiation period of 8 to 21 years from now — bringing the building to a total age of 16 to 29 years before corrosion initiation, versus 11 to 14 years without treatment. This justifies the immediate application of MC-Color 2K as a cost-effective intervention. However, any active corrosion zones identified by half-cell survey must be repaired — the anti-carbonation coating cannot stop corrosion that has already started. Complete 10-year maintenance plan: Year 1 — condition survey (half-cell potential survey, carbonation depth measurement, covermeter survey, visual inspection); repair all actively corroding zones (chip back, MC-Dur 600 mortar repair, MC-Dur 200 rebar primer); apply MC-Color 2K two-coat system to all column and beam faces at sd value minimum 100 m specification; document treated areas and coating batch numbers. Year 3 to 4 — inspection: visual check of coating integrity (cracking, delamination, chalking, mechanical damage); re-coat any damaged areas with one coat MC-Color 2K. Year 5 — mid-cycle maintenance: drill one core per representative elevation, phenolphthalein check on core, measure remaining unprotected zone; re-apply one coat MC-Color 2K to all faces as planned maintenance re-coat (sd value refreshed). Year 8 — major survey: half-cell potential re-survey of all columns; full re-coat of MC-Color 2K two-coat system over sound existing coating (confirm inter-coat adhesion first); repair any new repair zones identified. Year 10 — assessment for next cycle planning. Total material cost for the first 10-year cycle (MC-Color 2K application plus mid-cycle re-coat) for a typical 8-storey building of 40 columns at 200 square metres of column face area: approximately 400 m2 x 0.4 kg/m2 x 2 coats = 320 kg MC-Color 2K for the initial application — a relatively modest cost compared to the structural repair cost that would be incurred if corrosion is allowed to progress to the spalling stage (typically 8 to 15 times the preventive coating cost per square metre). Space Arc Engineering supplies MC-Color 2K, MC-Dur mortar repair products, and complete building concrete maintenance programme support for industrial and commercial building owners in Delhi, Ghaziabad, Noida, Greater Noida, and Uttar Pradesh.