weight of water, page-3

Imagine you are lying in a tub of water, hot, cold whatever takes your fancy. You feel "weightless" because the water is actually pushing you up. Of course you are not really weightless, you weigh exactly the same as when you got in and started sipping that cold beer (just enough to offset any losses from sweat and respiration and let's not be antisocial in this tub).

The same goes for the rod. Friction and upthrust forces balance it's weight. If the test is a penetrometer type where the rod is dropped from a defined height then the work done by the upward, slowing forces will equal the change in gravitational potential energy of the dropped rod if my memory of university applied maths is still functioning.

As it stands alone in its bath of wet roadbase, the rod weighs the same as it did before the test.

However a true sceptic might ask, "...but is it EXACTLY the same?..."

Little scratches etc will be wearing the test rod very slowly away so that after a bit of use it would need to be reweighed to ensure it still meets the test criteria.