Let's see the principle of concrete placement a little in detail.

If vibration is given to the soft concrete immediately after kneading, since a motion of aggregate (sand etc. is called thin aggregate and a gravel is called rough aggregate) is proportional to the given vibration acceleration and it is in inverse proportion to the weight, big aggregate has few motions and smaller aggregate moves mostly.

That is, in the propagation process of the vibration to soft concrete from vibrator, amplitude reduces its force by the distance while vibration frequency hardly changing its force. In this way, focusing on the point where vibration is give, cement paste and thin aggregate liquefy, fill the crevice between rough aggregate, and fill space, such as an air bubble, or push up it upwards and become to be stabilized.

That is, concrete liquefies by horizontal vibration of an internal vibrator, and is consolidated by gravity. In this way, if it continues applying suitable time and vibration, it will be transmitted further even far away. The part where close to vibration becomes denser and the vibration is transmitted to a long way through the dense part, but amplitude is absorbed in the dense part and limit of the vibration effect is caused. This limit is changed depending on conditions of concrete and vibrator.

It is as follows roughly

It is necessary to take the three above-mentioned elements into consideration.

On the other hand, the textbook is warned, "Too much vibration produces aggregate separation."　By our experience, fault caused by too much vibration was hardly experienced in the construction site, only by seeing such aggregate separation in a concrete secondary product factory and an intentional experiment rarely. It can be told that most of the placing failure in the site is related with shortage of vibration time.

From our experience: