The
capping material should not be weaker
than the concrete in the specimen.
However, if the cap is too strong,
there will be apparent increase in strength
of concrete due to large lateral restraint produced by strong cap.
The
influence
of capping material on strength is more
for medium
(strength >20MPa) & high strength concrete
(strength > 45MPa). For example, high strength capping
of 37M Pa
strength leads to 7-11% higher strength than low strength capping
in
compression tests carried out on 48 MPa concrete. For 69 MPa this
difference
is as high as 17%.
It
should be noted
that differences are smaller when
thickness of the cap is very small.
