Very good point Tom! I've seen people blow out forms from over
vibrating! Too much vibrating will drop the aggregate to the bottom and
that is BAD!
At 01:54 PM 5/29/03 -0500, you wrote:
>Most of these comments are good however.
>A vibrator in the hands of an overzealous HAM may actually be bad.
>(All inuendo aside) Over vibrating concrete causes the heavy materials
>(ROCK) to settle and the light material (AIR) to rise.
>Air in the concrete is not a bad thing, in fact many times air is
>intentionally introduced using admixtures. Rock on the other hand is
>important in the strength of the mix. Rock provides the largest surface area
>for Portand Cement (the GLUE in concrete) to adhere to. If all the rock is
>at the bottom the strength of the top area of the pad will be relatively
>The cost of 3500 pound or even 4000 Pound mix is not significant in the
>large scheme (guessing $1 / yd). The pour is a relatively small and the
>price will be proportionately small. We pour 4000 pound concrete almost
>exclusively. YES it is overkill! However, the tradeoff is in workability.
>Stronger concrete has more of the expensive stuff.. the glue.. the Portland
>Cement and that is what makes the mixure "creamy" and easy to work. Too much
>water can "appear" to give these properties but good concrete is good
>concrete. Add water and increase slump (good description below). but good
>concrete (4000 pound mix) will have a good slump (lower number) because it
>has more GLUE.