Product Overview

Centrament Air is the specialist air-entraining admixture in the MC-Bauchemie Centrament admixture range for concrete requiring protection against freeze-thaw cycles in cold-region North Indian infrastructure. The fundamental mechanism of air entrainment in concrete is well understood but frequently misapplied in Indian practice: the purpose of entrained air is not to create void space for workability (that is the undesirable effect) but to create a network of uniformly distributed, discrete, microscopic air bubbles at 50 to 200 micron diameter and 0.2 to 0.4 mm average spacing (the spacing factor) within the concrete paste matrix — this air void system acts as a pressure relief network that absorbs the hydraulic pressure generated when water in the concrete capillary pores expands by approximately 9 percent on freezing; without this pressure relief, the hydraulic pressure (theoretically up to 50,000 psi at a freezing front) exceeds the tensile strength of the concrete paste and causes progressive spalling and scaling damage over repeated freeze-thaw cycles. Centrament Air, based on a vinsol resin or synthetic surfactant chemistry, entrains the required air content (typically 4 to 8 percent total air for maximum freeze-thaw protection in concrete exposed to de-icing salts; 3 to 6 percent for moderate freeze-thaw without de-icing salt) at a very low dosage (0.02 to 0.10 percent by weight of cement) that does not significantly affect setting time or the chemical concrete composition. In the North Indian infrastructure context, the primary users of Centrament Air are highway contractors building bridges and pavement concrete on national highways in Himachal Pradesh (Manali-Leh NH3), Uttarakhand (Rishikesh-Badrinath NH58 and NH7), and Jammu and Kashmir mountain roads where concrete is exposed to 50 to 150 freeze-thaw cycles annually and where de-icing salt treatment of road surfaces multiplies the freeze-thaw damage by the chloride scaling mechanism. Space Arc Engineering supplies Centrament Air for mountain highway, cold storage, and high-altitude infrastructure projects from Ghaziabad, Noida, and Delhi.

Applications

• Mountain highway bridges and concrete pavement on national highways in Himachal Pradesh, Uttarakhand, and Jammu and Kashmir — production of freeze-thaw resistant concrete for bridge deck slabs, pier caps, abutments, and concrete pavement on high-altitude national highways in North India where concrete is exposed to 50 to 150 annual freeze-thaw cycles (temperature range from -15 to -25 degrees Celsius in winter to +15 to +25 degrees Celsius in spring thaw); the combination of freeze-thaw cycling and de-icing salt application (chloride scaling) is the most severe durability exposure for concrete in the Indian context and requires the dual protection of air entrainment (for freeze-thaw cycles) and very low w/c (maximum 0.40, for chloride resistance); Centrament Air with Centrament Flow 300 or Centrament Flow 400 superplasticiser allows the production of well-proportioned concrete at w/c 0.38 to 0.42 with 5 to 7 percent entrained air and adequate workability for bridge deck construction
• Cold storage and refrigerated warehouse concrete for temperatures below zero degrees Celsius — production of concrete for floors, walls, and roofs of cold storage facilities, blast freezer chambers, and refrigerated warehouses in Delhi NCR, Greater Noida, and Uttar Pradesh food logistics corridor where the concrete is permanently maintained below zero degrees Celsius (typically -18 to -25 degrees Celsius for blast freezer), subjecting the concrete to continuous freeze condition and cyclic thermal stress when the facility is defrosted for cleaning; air-entrained concrete with Centrament Air provides the freeze-thaw resistance required for concrete in permanent freezing service without the spalling and scaling damage to concrete floors and walls that reduces the hygienic and structural integrity of cold storage facilities over 10 to 15 years
• Concrete exposed to de-icing salts on urban flyovers, toll plazas, and bridge decks — protection of concrete bridge deck slabs, kerb units, drainage channels, and approach slab pavement on urban flyovers, expressway bridges, and toll plazas in Delhi NCR and North India where sodium chloride or calcium chloride de-icing treatment is applied in winter; de-icing salts in combination with freeze-thaw cycles cause a surface scaling mechanism in concrete that is more severe than either de-icing salt or freeze-thaw alone — the chloride salt depresses the freezing point of the water at the concrete surface so the outermost 5 to 15 mm of concrete experiences more frequent freeze-thaw cycles than the bulk concrete interior, combined with the osmotic pressure effect of the concentrated salt solution extracting moisture from the concrete pores; air-entrained concrete with Centrament Air is the standard concrete specification for bridge deck slabs exposed to de-icing salt treatment in cold climates

Key Advantages

• IS 9103 Type AE compliance with stable, uniform entrained air void system for reliable freeze-thaw protection — Centrament Air is formulated and tested to IS 9103 Type AE specification and produces a stable, uniformly distributed entrained air void system in the concrete with the correct bubble size (50 to 200 microns) and spacing factor (below 0.200 mm for effective freeze-thaw protection per Powers freeze-thaw protection model); the stability of the entrained air through mixing, transit, pumping, and placement is critical — coarser air bubbles (above 500 microns) or non-uniformly distributed air pockets do not provide freeze-thaw protection, and air that collapses during transit or pumping provides no protection at all; Centrament Air is formulated to maintain entrained air stability through the mechanical shear of RMC transit (30 to 45 minutes), concrete pump transit (10 to 15 metres of 100 mm diameter pump line), and normal construction vibration
• Compatibility with the full range of Centrament plasticisers and superplasticisers for air-entrained high-performance concrete — air-entrained concrete for cold-region high-performance applications (mountain highway bridges at C35 to C45) requires the simultaneous use of an air-entraining admixture and a water-reducing superplasticiser (because the target air content of 4 to 7 percent and low w/c 0.38 to 0.42 cannot be achieved simultaneously without superplasticiser assistance); the compatibility of Centrament Air with the full Centrament plasticiser family (Centrament Plast, Centrament Flow 100 SNF, Centrament Flow 200, Centrament Flow 300 PCE) has been characterised by MC-Bauchemie to ensure predictable combined performance; some superplasticisers (particularly naphthalene-based SNF types) can destabilise air-entrained systems by competing for the cement particle surface with the air-entraining agent — the compatibility of the selected Centrament superplasticiser with Centrament Air should always be verified by trial mix before production