Pile Design and Construction Practice, Fifth edition

24 Types of pile

To comply with the requirements of BS8110 precast piles of either ordinary or prestressed
concrete should have nominal cover to the reinforcement as shown in the following table:

Exposure conditions Nominal cover (mm) for concrete grade of
50 and
25 30 40 over

Buried concrete and concrete continuously under water 40 30 25 20
Alternate wetting and drying and freezing 50 40 30 25
Exposed to sea water and moorland water with abrasion 60 50

Using covers larger than required may lead to spalling of the concrete during driving.
In EC2-1-1 Clause 4.4 nominal cover to reinforcement is defined as cnomcmincdev
where cminis dependent on bond requirements or environmental conditions as summarized
in the Code.cdevallows for deviations, usually set at 10 mm but reduced where strict
QA/QC procedures are in force. BS8500 provides tabulated classifications for cover, char-
acteristic concrete strength, cement content and type of cement combination depending on
exposure conditions and type of steel corrosion; for example, for an intended life of 50 years
and 20 mm maximum aggregate:

Corrosion Exposure Cement Cover (mm) with concrete class and cement content (kg/m^3 )

due to conditionsa typesb 20 c25c30c35c40c45c

Carbonation Moderate All except C40/50 C32/40 C28/35 C25/30

humidity pfa36% 340 300 280 260

(XC3 and 4)

Chlorides from Tidal, splash Group 5

sea water and spray and 6 C35/45 C32/40

zones (XS3) 380 360

Group 4 C45/55

380

Notes

a Degrees of exposure as defined in BS8500 and EC2-1-1.

b Cement types ‘CEM I to V’ and combinations are defined in Table 1 of BSEN 197-1 and in Groups in Table A.17

of BS8500. pfa (fly ash) as BS EN 450.

Neither BSEN 12794 nor BSEN 13369 comments on minimum cover for precast piles,
other than advising that cover may be modified in accordance with BSEN 13369. For example,
the cover may be reduced by 5 mm when using concrete class C40/50 or above, but requires
an increase of 5 mm where achievement of dimensional tolerances may be a factor.
BS8500 also specifies cement combinations and class of concrete to be used to resist
attack on the concrete itself, again depending on exposure conditions. In addition, reference
should be made to BRE Special Digest 1 and Section 10.3.