ENVIRONMENTAL EXPOSURE CONDITIONS OF STRUCTURES
Sl. No.
| Environment
| Exposure Conditions
|
i | Mild | Concrete surfaces protected against weather or aggressive conditions, except those situated in coastal areas |
ii | Moderate | Concrete surface sheltered from severe rain or freezing whilst wet; concrete exposed to condensation and rain, concrete continuously under water; concrete in contact or buried under non-aggressive soil/ground water; concrete surfaces sheltered from saturated salt air in coastal area |
iii | Severe | Concrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing whilst wet or severe condensation; concrete completely immersed in sea water; concrete exposed to coastal environment |
iv | Very Severe | Concrete surfaces exposed to sea water spray, corrosive fumes or severe freezing conditions whilst wet; concrete in contact with or buried under aggressive sub-soil/ground water |
v | Extreme | Surfaces of members in tidal zone; members in direct contact with liquid/solid aggressive chemicals |
Source: Table 3 of IS: 456 – 2000
Minimum cement contents, maximum water-cement ratio and minimum grade of concrete for different exposures with normal weight aggregates of 20 mm nominal maximum size
Exposure Conditions
| Plain Concrete
| Reinforced Concrete
| ||||
Minimum cement content kg/cum
| Maximum free water-cement ratio
| Minimum grade of concrete
| Minimum cement content kg/cum
| Maximum free water-cement ratio
| Minimum grade of concrete
| |
Mild | 220 | 0.60 | - | 300 | 0.55 | M 20 |
Moderate | 240 | 0.60 | M 15 | 300 | 0.50 | M 25 |
Severe | 250 | 0.50 | M 20 | 320 | 0.45 | M 30 |
Very Severe | 260 | 0.45 | M 20 | 340 | 0.45 | M 35 |
Extreme | 280 | 0.40 | M 25 | 360 | 0.40 | M 40 |
Source: Table 5 of IS: 456 – 2000
Note:
1) Cement content prescribed in this table is irrespective of the grades of cement and it is inclusive of additions mentioned in clause 5.2 of IS: 456. The additions such as flyash or ground granulated blast furnace slag may be taken into account in the concrete composition with respect to the cement content and w-c ratio if the suitability is established as long as the maximum amounts taken into account do not exceed the limit of pozzolana and slag specified in the IS: 1489 (Part I) and IS: 455, respectively.
2) Minimum grade for plain concrete under mild exposure condition is not specified.
Adjustment to minimum cement for aggregates other than 20 mm nominal maximum size
Sl. No. | Nominal maximum aggregates size, mm in table above (kg/cum) | Adjustment to minimum cement contents |
(i) | 10 | +40 |
(ii) | 20 | 0 |
(iii) | 40 | -30 |
Source: Table 6 of IS: 456 – 2000