Frequently Asked Questions

A bridge maintenance contractor working for the UP PWD is rehabilitating a 35-year-old Yamuna expressway flyover where 18 bridge pier columns show extensive spalling and section loss from chloride-induced corrosion, with average repair depth of 70 mm and an average repair area of 4 square metres per column face — the specification requires EN 1504-3 structural repair — what is the complete large-scale repair workflow for 18 columns using MC-RocTec HB including preparation, reinforcement treatment, mortar application, and daily output targets for a specialist repair crew?

A 18-column bridge pier repair programme on a Yamuna expressway flyover is a major infrastructure rehabilitation contract representing approximately 18 x 4 x 2 faces = 144 square metres of repair area at 70 mm average depth = approximately 10 cubic metres of repair mortar (approximately 20,000 kg at 2.1 kg per litre — approximately 800 bags of MC-RocTec HB). This scale of repair requires a systematic production approach to achieve programme efficiency and consistent quality. Complete large-scale repair workflow: Phase 1 — mobilisation and preparation equipment setup (Days 1 to 3): set up scaffolding to all 18 columns (typically proprietary tube-and-fit bridge repair scaffolding with access platforms at each repair zone elevation); set up pneumatic chiselling equipment (2 to 3 heavy-duty percussion hammers, 7 to 9 kg class); set up high-pressure water jetting (500 to 1,000 bar) for pre-cleaning and final surface preparation; set up forced-action drum mixer (minimum 200-litre) or twin-shaft pan mixer for mortar batching at a central location with barrow distribution; set up rebar treatment station. Phase 2 — column preparation (approximately 1 to 1.5 columns per day per preparation crew): concrete removal — use 9 kg pneumatic percussion hammer to break out all visibly delaminated concrete plus 20 mm behind the last rebar on each face (to fully expose all corroded steel and ensure MC-RocTec HB encases bars on all sides). Confirm removal is sufficient by phenolphthalein spray test on the exposed surface — the background must turn pink (pH above 9) to confirm removal of all carbonated concrete. Minimum surface profile after preparation: CSP 5 (angular fractured coarse aggregate visible, surface undulation 2 to 5 mm) achieved by pneumatic chiselling — confirm with ICRI surface comparator. Saw-cut perimeter of repair area (90-degree saw cut, 10 to 15 mm deep) to form a clean, sharp repair boundary and eliminate feather edges. Rebar treatment — wire-brush all exposed reinforcement bars to bright metal (Sa 2.5 per ISO 8501-1) and immediately apply rebar protection coating (MC-Bauchemie zinc-rich or cementitious corrosion inhibitor primer) — do not allow cleaned bars to flash-rust before coating. Surface pre-wetting — pre-wet the concrete substrate to SSD condition and maintain until MC-RocTec HB application (do not allow to dry in hot sun between preparation and repair — shade the column face if required). Phase 3 — mortar application (approximately 1.5 to 2 columns per day per application crew of 4): application method selection by repair geometry: (a) hand-placed trowel application — for areas where access is clear and repair depth is uniform at 50 to 80 mm — mix MC-RocTec HB at 3.7 litres per 25 kg bag for a stiff-plastic consistency. Apply in layers of 40 to 50 mm per lift, compact firmly against the substrate with the trowel heel, ensure no voids around reinforcement bars. Allow each lift to reach initial set (3 to 5 hours) before applying the next lift on the same column face to avoid overloading fresh mortar before it has gained strength. (b) Form-and-pour application — for column faces with complex geometry, heavily congested reinforcement, or deep voids (80 to 120 mm depth) — mix MC-RocTec HB at 4.0 to 4.2 litres per 25 kg bag for a semi-flowable consistency. Erect polypropylene or steel formwork to the repair boundary with inspection ports at the top. Pour MC-RocTec HB from the top of the form — do not use an internal vibrator directly on the mortar (the polymer and fine particles can segregate under strong vibration); use gentle external form tapping with a rubber mallet for consolidation. Daily output target: a crew of 4 (1 mixer operator, 2 applicators, 1 material handler) can realistically apply: hand-placed method — 6 to 8 square metres of repair area per day at 70 mm average depth (approximately 0.5 to 0.56 cubic metres of mortar = 22 to 23 bags per working day); form-and-pour method — 8 to 10 square metres per day (more area but slower form setting up and stripping) — approximately 800 litres of mortar per day. For 144 square metres total at 6 to 8 square metres per day per crew: 18 to 24 working days for the application phase with a single crew — plan 20 working days of application followed by 7 days curing and inspection before handover. Phase 4 — curing (critical at bridge pier location — exposed to wind and sun): apply wet hessian wrapping to all repaired faces immediately after surface finishing — secure with polyethylene sheet outer wrap to prevent wind drying. Maintain wet curing for minimum 5 days per face. Phase 5 — finishing and protective coating: after 7 days from repair completion, apply MC-Dur 100 fine skim coat to fill any surface voids or minor imperfections on the repaired faces; after MC-Dur 100 has cured (7 days), apply MC-Color 2K anti-carbonation coating two-coat system to all pier column faces as specified (re-establishing the anti-carbonation barrier over the complete column face including repair and surrounding original concrete). Quality control documentation: maintain a repair log recording for each column — date of preparation, chiselling depth and area map, reinforcement condition and treatment, mortar batch numbers and mixing records, application date and temperature, curing dates. Photograph each stage for the contract QA record. Space Arc Engineering supplies MC-RocTec HB, MC-Dur 100, MC-Color 2K, rebar protection primer, and complete technical support for large-scale bridge pier repair programmes for UP PWD, NHAI, and DMRC contracts in Ghaziabad, Delhi NCR, and across Uttar Pradesh.