Frequently Asked Questions

Is air-entrained concrete with Centrament Air 430 necessary for road and bridge concrete in Ghaziabad and Delhi NCR given that the region rarely sees sustained temperatures below freezing, and under what conditions would a structural engineer specify it?

The specification of air-entrained concrete for road and bridge construction in Delhi NCR is a nuanced engineering judgement that depends on the freeze-thaw exposure class of the specific structure, the number of annual freeze-thaw cycles, and the saturation condition of the concrete during freezing. In European and North American concrete standards (EN 206, ACI 318), the freeze-thaw exposure class for a given structure is determined by the number of freeze-thaw cycles per year and the degree of water saturation of the concrete during freezing. Delhi NCR falls into a mild freeze-thaw exposure class by international standards: the average number of days per year when the minimum temperature falls below 0 degrees C in Delhi is approximately 10 to 20 days (typically January), compared to 60 to 100 days in central Europe and 120 to 150 days in northern Canada. This limited freeze-thaw exposure means that non-air-entrained concrete of adequate quality (water-cement ratio below 0.45, minimum cement content 350 kg per cubic metre) will generally provide acceptable freeze-thaw durability for most structures in Delhi NCR, provided the concrete is well compacted, well cured, and has achieved adequate strength before first frost exposure. Under these conditions — standard M30 or above concrete for highway bridges and road slabs in Ghaziabad — the marginal freeze-thaw benefit of Centrament Air 430 is outweighed by the approximately 3 to 5 percent compressive strength reduction caused by air entrainment (each 1 percent of entrained air reduces compressive strength by approximately 4 to 6 percent), and air-entrained concrete is generally not specified for Delhi NCR road and bridge concrete by NHAI, UPEIDA, or PWD specifications. However, air-entrained concrete with Centrament Air 430 should be specified for the following situations in Delhi NCR and Uttar Pradesh. Structures in elevated freeze-thaw exposure zones: highway bridges and tunnels at elevations above 1,000 m in the Shivalik Hills and lower Himalayan foothills of Uttarakhand and Himachal Pradesh (served by Delhi NCR contractors), where freeze-thaw cycling is more frequent and severe. Concrete pavement and slabs exposed to deicing salts: road slabs at toll plazas, airport aprons, and expressway entry ramps where rock salt or calcium chloride deicers may be used — the combined effect of deicing salts and freeze-thaw is substantially more damaging than freeze-thaw alone, requiring entrained air for protection. Water-retaining structures subject to repeated wetting and freezing: irrigation canal linings, culverts, and retaining walls in areas prone to frost in December and January that remain saturated with water through the winter (saturated concrete is many times more susceptible to freeze-thaw damage than partially dry concrete). Where IS 456 Table 3 or IS 2911 classify the aggressive environment as XF1 or above (freeze-thaw exposure class): these classifications may apply in hill state projects or for structures with specific frost exposure assessments. For the mainstream road and building concrete specification in Ghaziabad and Delhi NCR, Centrament Air 430 is not routinely required but is available from Space Arc Engineering for projects serving hill regions or structures with documented freeze-thaw exposure requirements. Space Arc Engineering provides guidance on exposure class assessment and admixture specification for specific projects across North India.