under strength concrete

huangyhg

under strength concrete
i have some piles that were to be placed with a fc' value of 27.5 mpa. the actual concrete breaks came in at 19.0 mpa.
the axial loads are 262 kn bearing on a 760 x 760 plate, so crushing is not an issue.  the anchor bolts are 1000mm long.  are there any other concerns that i have to be aware of with the reduced concrete stength?
is the low strength due to reduced cement content?
this may affect the sulphate resistance of the pile and the ability of the rebar to resist corrosion.
the ability of teh pile to resist horizontal shear and bending forces will be reduced.
9/27/02--to nicholi from mapestru--re weak concrete
1.   agree with "jeg".
2.   would add: concern for affect of weak bond between a.bs and concrete, ( unless ab's configuration negates need for good bond;)
3.   would add: concern for weak side bearing between top regions of abs and concrete, which could result in gradual loss of shear continuity between concrete pile and plate, above, and gradual deterioration of structural integrety of top of pile;
4.   if piles are already in place: in view of the approx. 1/3 loss of specified concrete strength,---i would think in terms of developing some form of special reinforcement of the top regions of the piles, and/or the pile-superstructure interface regions,( possibly encasement in some form of epoxy bound fiber-reinforced structural plastic wrapping ?).
5.   if the piles are not yet driven in place: i would think it not unreasonable to require new, --- properly fabricated piles to be provided by the contractor.
6.  remember: piles are part of the foundation, and if they do deteriorate fast, they will be almost unreachable for repair, after all construction is finished.
7.   good luck.