Question

Which of the following statement is correct while compacting concrete with vibrators?

(a) The vibrator should be inserted horizontally

(b) The vibrator should not be immersed through a full depth of freshly laid concrete

(c) The vibrator should not touch the form surface

(d) The vibrator should touch the form surface

I have been asked this question in an online interview.

The question is from Curing of Hardened Concrete in portion Testing of Concrete of Concrete Technology

Answer 1

Right answer is (c) The vibrator should not touch the form surface

Easy explanation: If there is a considerable amount of time lapse between the placements of subsequent lifts, it may be necessary to re vibrate the previous lift prior to placing additional concrete to minimize the potential for pour lines and cold joints.