How to Compact Concrete in Junction between Fresh Concrete and Existing Hardened Concrete?

In the previous posts we have discussed about stages of manufacturing concrete. We have learned many aspects of compaction stage of concreting process. In our recent we have discussed about insertion spacing of vibrator head in concrete. Here we will learn about method of compaction of fresh concrete in junction with fresh hardened concrete.

In many practical purposes we have to cast concrete in junction with existing old or recently hardened concrete in case of construction joints. It is observed that when fresh concrete is placed above or beside the existing concrete, there have some defects. This is due to insufficient vibrating of concrete layer near hardened layer. In many instances the flexible shaft becomes inactive when it gets contact with hard surface. In this situation the following procedure can be adopted.

The surface of hardened concrete is prepared by removing greasy or loose particles, removing laitance and roughening it. Then the clean surface is wetted with sufficient water. A grout of cement-sand having 1:1 proportion with creamy consistency is applied over the cleaned wet surface of existing old concrete and then fresh concrete is poured with subsequent vibration. This procedure produces a better solution for concreting in conjunction with hardened concrete.